JP6692801B2 - Multilevel inverter and method for providing multilevel output voltage by utilizing multilevel inverter - Google Patents

Description

  The present invention relates to inverters, and more particularly to multilevel inverters and methods for providing multilevel output voltages with multilevel inverters.

  A gradient magnetic field coil is used in magnetic resonance imaging (MRI). Gradient coil currents must achieve tens of ppm accuracy for hundreds of amps due to imaging requirements. For example, as shown in the current profile 100 in FIG. 1, the gradient coil current Icoil needs to change from −180 A to +180 A within a short time (ms range).

  In order to precisely control the current of the gradient coil, a gradient amplifier is required to supply an accurate voltage to the gradient coil, and the gradient amplifier requires that the current Icoil of the gradient coil be changed from one level to another level. It is necessary to supply a high voltage during a current transient that changes to a low voltage and a low voltage during a current steady state in which the gradient coil current Icoil remains at a certain level. For example, as shown in FIG. 1, a state in which the current Icoil of the gradient coil changes from -180A to 180A or 180A to -180A is a current transient state, and the gradient coil current Icoil is either -180A or 180A. The state that remains in the crab is the steady state of current.

  However, conventional gradient amplifiers typically generate high frequency harmonics. Therefore, as shown in FIG. 2A, an electromagnetic interference (EMI) filter 220 is required between the gradient amplifier 210 and the gradient coil 230 to remove the high frequency harmonics generated by the gradient amplifier 210. .. As shown in FIG. 2B, a conventional EMI filter 220 typically includes two inductors L1 and L2, two damping resistors R1 and three capacitors C1, C2 and C3.

  Heretofore, different topologies have been proposed for gradient amplifiers, among which gradient amplifiers of cascaded H-bridge (CHB) topology are widely used in the industry. The existing gradient amplifier 210 with CHB topology consists of one conventional two-level inverter or more cascaded conventional two-level inverters. FIG. 3 shows a schematic diagram of a conventional two-level inverter 300. As shown in FIG. 3, a conventional two-level inverter 300 includes a first half-bridge leg 310 formed by switches QAH and QAL coupled in series and a switch QBH and QBL coupled in series. And a second half-bridge leg 320, and the first half-bridge leg 310 and the second half-bridge leg 320 are connected in parallel to a DC power supply 330 having a voltage Vbus. The conventional two-level inverter 300 comprises a voltage VA output by the first half bridge leg 310 at node A located between switches QAH and QAL and a second half voltage at node B located between switches QBH and QBL. It provides an output voltage VAB which is the difference from the voltage VB output by the bridge leg 320.

  However, a conventional gradient amplifier 210 consisting of a two-level inverter typically produces many high frequency harmonics. Therefore, in order to attenuate many high frequency harmonics generated by the gradient amplifier 210, a large inductance value for the inductors L1 and L2 included in the EMI filter 220 and a large resistance value for the damping resistor R1 included in the EMI filter 220 are provided. A value and a large capacitance value for capacitors C1, C2, C3 included in EMI filter 220 are required. However, when the resistance value of the damping resistor R1 is large, the filter efficiency is deteriorated, and when the inductance values of the inductors L1 and L2 are large and the capacitance values of the capacitors C1, C2, and C3 are large, the entire system control bandwidth is increased. affect.

  Further, returning to FIG. 2A, the gradient coil 230 needs to be connected to ground 240 for safety and EMI shielding requirements, and thus between the gradient coil 230 and ground 240. Has a large overlap area, which results in a large stray capacitance Cstray. Since the gradient amplifier 210 has a large change in output voltage during operation, a large common mode current Istray flows through the stray capacitance Cstray. The common mode current Istray is sensed by the high precision current sensor 250 disposed between the gradient coil 230 and the EMI filter 220 and acts as a high frequency disturbance that leads to instability during operation of the MRI system.

  In addition, the current in the gradient coil 230 fluctuates with a large amplitude, because the gradient amplifier 210 has a large change in the output voltage, which leads to a high current ripple in the gradient coil 230.

  Therefore, in view of the above-mentioned drawbacks of conventional gradient amplifiers consisting of two-level inverters, there is a need for new gradient amplifiers with improved performance.

  To this end, the inventors of the present invention have conducted numerous experiments and found that the defect in the conventional gradient amplifier 210 is due to the two-level inverter utilized in the amplifier, which causes a large change in the output voltage. However, it was then found that the conventional gradient amplifier 210 leads to the generation of many high frequency harmonics.

  Accordingly, the present invention provides a multi-level inverter and a method for providing a multi-level output voltage with a multi-level inverter to address the aforementioned problems.

  According to a first aspect of the present invention, this aspect proposes a multi-level inverter comprising at least one cascaded H-bridge multi-level module, each H-bridge multi-level module comprising a first H-bridge multi-level module. A first H-bridge multi-level leg having a plurality of output levels at the output terminals of the legs, and a second H-bridge multi-level leg having a plurality of output levels at the output terminals of the second H-bridge multi-level legs , The first and second H-bridge multi-level legs are connected in parallel, and the multi-level output of the H-bridge multi-level module is output between the output terminals of the first and second H-bridge multi-level legs, Each of the first and second H-bridge multi-level legs is connected in parallel via a coupling inductor. An inverter leg and a second inverter leg, the first inverter leg being coupled to the primary winding of the coupled inductor to provide a first input voltage having a plurality of voltage levels; Coupled to a secondary winding of the coupled inductor to provide a second input voltage having a plurality of voltage levels, the primary and secondary windings of the coupled inductor coupled in series, and coupled in series The junction nodes of the primary and secondary windings form the output terminals of the H-bridge multilevel leg, the first input voltage having a predetermined phase shift with respect to the second input voltage.

  In this way, each of the first H-bridge multi-level legs and the second H-bridge multi-level legs of each H-bridge multi-level module outputs a multi-level output voltage, so that the multi-level inverter can It can have small changes, thus eliminating the problems caused by large changes in output voltage.

  In one embodiment of the present invention, each of the first and second inverter legs comprises a half bridge leg in which a high side (upper) switch and a low side (lower) switch are coupled in series, the first H bridge. The drive signals of the high-side switches of the first and second inverter legs of the multilevel leg have a predetermined phase shift with respect to each other, and the first and second inverter legs of the second H-bridge multilevel leg. The drive signals of the low-side switches have a predetermined phase shift with respect to each other. In this way, the first input voltage provided by the first inverter leg can have a predetermined phase shift with respect to the second input voltage provided by the second inverter leg. In one embodiment of the present invention, M H-bridge multi-level modules are cascaded, and the output of each H-bridge multi-level module has a 360 ° / M phase shift with respect to an adjacent H-bridge multi-level module. However, here, M is an integer of 2 or more.

  In this way, the multi-level inverter can increase the even switching frequency, thus resulting in reduced current ripple.

  According to a second aspect of the present invention, this aspect proposes a method for providing a multi-level output voltage by means of a multi-level inverter, which multi-level inverter comprises at least one cascaded H-bridge multi-level module. Each H-bridge multi-level module comprises a first H-bridge multi-level leg and a second H-bridge multi-level leg connected in parallel, and the output voltage of the H-bridge multi-level module is: Output between the output terminals of the second H-bridge multi-level legs, each of the first and second H-bridge multi-level legs being coupled in parallel via a coupling inductor to a first inverter leg and a second inverter leg. An inverter leg, the first inverter leg coupled to the primary winding of the coupled inductor, and the second inverter leg Are coupled to the secondary winding of the coupled inductor, the primary and secondary windings of the coupled inductor are coupled in series, and the junction nodes of the primary and secondary windings coupled in series are H-bridge multilevel legs. And forming a first voltage having a plurality of levels by the first inverter leg of the first H-bridge multi-level leg of each H-bridge multi-level module, the method comprising: Generating a second voltage having a plurality of levels having a predetermined phase shift with respect to the first voltage by the second inverter leg of the first H-bridge multi-level leg of the H-bridge multi-level module; Having multiple levels based on the first and second voltages generated by the first H-bridge multi-level leg of each H-bridge multi-level module Generating a voltage of 3; generating a fourth voltage having a plurality of levels by the first inverter leg of the second H-bridge multi-level leg of each H-bridge multi-level module; Second H-bridge of the multi-level module: generating a fifth voltage having multiple levels with a predetermined phase shift with respect to a fourth voltage by the second inverter leg of the multi-level leg; Generating a sixth voltage having multiple levels based on the generated fourth and fifth voltages by the second H-bridge multi-level leg of the multi-level module, and each H-bridge multi-level module, Generating a multi-level output voltage based on the generated third and sixth voltages; Providing the multi-level output voltage of the multi-level inverter based on the multi-level output voltage output by the level module.

  As described above, the method for supplying the multi-level output voltage by the multi-level inverter according to the present invention can reduce the change of the output voltage supplied by the multi-level inverter, and thus the output voltage is large. Problems caused by changes can be eliminated.

  According to a third aspect of the invention, this aspect comprises a multi-leg with n H-bridge multi-level legs and a coupled inductor having n windings coupled together at a junction node of the n windings. A level inverter is proposed, where each of the n H-bridge multi-level legs has at least one cascaded H-bridge inverter, n is an integer greater than 1, and the n H-bridge multi-level legs are , Coupled in parallel through a coupling inductor, each of the n H-bridge multilevel legs being coupled to one of the n windings to provide an input voltage having a plurality of voltage levels, And the junction node forms the output terminal of the multi-level inverter to supply the multi-level output level, and the input voltage supplied by the n H-bridge multi-level legs. Has a phase shift relative to each other.

  In this way, the multi-level inverter can have smaller changes in the output voltage, while at the same time reducing cost and making it smaller because the multi-level inverter uses only one coupled inductor. it can.

  In one embodiment of the invention, the at least one cascaded H-bridge inverter comprises at least one powered H-bridge inverter and at least one floating H-bridge inverter. In this way, multi-level inverters may require less power.

  According to a fourth aspect of the present invention, this aspect proposes a method for providing a multi-level output voltage by a multi-level inverter, the multi-level inverter comprising n H-bridge multi-level legs and a coupled inductor. , N is an integer greater than 1 and each of the n H-bridge multi-level legs has at least one cascaded H-bridge inverter and the coupled inductors are connected to each other at a junction node of n windings. With n windings coupled, the n H-bridge multi-level legs are coupled in parallel via a coupling inductor, each of the n H-bridge multi-level legs being of n windings. The junction node, coupled to one of the two, forms the output terminal of a multi-level inverter, the method comprising n H-bridge multi-level legs each. Is a step of generating n voltages having a plurality of voltage levels, the n voltages having a phase shift with respect to each other, and a multilevel inverter based on the generated n voltages. Providing a multilevel output voltage to be output.

  In this way, the multi-level inverter can have smaller changes in the output voltage, while at the same time reducing the cost and making it smaller as only one coupled inductor is required by the multi-level inverter. You can

  According to a fifth aspect of the present invention, this aspect includes a multiplicity of n H-bridge multi-level legs and a split set of coupled inductors symmetrically coupled on opposite sides of the n H-bridge multi-level legs. A level inverter is proposed, each of the n H-bridge multi-level legs having at least one cascaded H-bridge inverter, n being an integer greater than 1, and each of the coupled inductor sets being n Having n windings coupled to each other at a junction node of the windings, each of the n H-bridge multi-level legs having a coupled inductor set for supplying an input voltage having a plurality of voltage levels. Between one of the n windings of one of the coupled inductors and one of the n windings of another coupled inductor of the coupled inductor set The junction nodes in the combined and coupled inductor sets form the output terminals of a multilevel inverter to provide multilevel output levels, and the input voltages provided by the n H-bridge multilevel legs are relative to each other. Have a phase shift.

  In this way, the multi-level inverter can have a smaller change in output voltage, while at the same time using a split set of coupled inductors, which results in galvanic isolation requirements and electromagnetic compatibility (EMC). Can meet.

  In one embodiment of the invention, the at least one cascaded H-bridge inverter comprises at least one powered H-bridge inverter and at least one floating H-bridge inverter. In this way, multi-level inverters may require less power.

  According to a sixth aspect of the invention, this aspect proposes a method for providing a multi-level output voltage by means of a multi-level inverter, wherein the multi-level inverter comprises a partition of n H-bridge multi-level legs and a coupled inductor. Set, n is an integer greater than 1, and each of the n H-bridge multi-level legs has at least one cascaded H-bridge inverter, and the split set of coupled inductors is n H-bridges. Symmetrically coupled on both sides of the bridge multi-level leg, each of the coupled inductor sets has n windings coupled together at a junction node of the n windings, and n H-bridge multi-level legs. Each of one of the n windings of one coupled inductor of the coupled inductor set and another of the coupled inductor set of Coupled to one of the n windings of the combined inductor, the junction node in the coupled inductor set forms the output terminal of the multi-level inverter, and the method comprises n H-bridge multi-level legs. To generate n voltages each having a plurality of voltage levels, the n voltages having a phase shift with respect to each other, and a multi-step based on the generated n voltages. Providing a multi-level output voltage output by the level inverter.

  In this way, the multi-level inverter can have smaller changes in the output voltage, while at the same time using galvanic isolation requirements and electromagnetic compatibility (EMC) because it uses a split set of coupled inductors. it can.

Various embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings.
Figure 3 shows a schematic of a typical current profile of a gradient coil. 3 shows a schematic diagram of the connection relationship between a gradient amplifier, an EMI filter, and a gradient coil. The schematic circuit diagram of an EMI filter is shown. 1 shows a schematic diagram of a conventional two-level inverter. The waveforms of the voltages VA and VB output by the two half bridge legs of the conventional two-level inverter and the waveform of the voltage VAB output by the conventional two-level inverter in the steady current state are shown. 5 shows the waveform of voltage VAB output by a conventional two-level inverter in a current transient state. Figure 3 shows a schematic diagram of an H-bridge multi-level module according to the first embodiment of the invention. Figure 3 shows a schematic view of a coupled inductor according to the first embodiment of the invention. 1 shows a schematic diagram of a multi-level inverter according to the first embodiment of the invention. 3 shows a flow chart of a method for supplying a multi-level output voltage with a multi-level inverter according to the first embodiment of the present invention. 5 shows waveforms of voltages VA1, VA2, and VA according to the first embodiment of the present invention. 5 shows waveforms of voltages VB1, VB2, and VB according to the first embodiment of the present invention. 5 shows a waveform of the output voltage VAB in a current steady state generated by the multilevel inverter according to the first embodiment of the present invention. 5 shows a waveform of the output voltage VAB in a current transient state generated by a multi-level inverter according to the first embodiment of the present invention. Figure 3 shows a schematic diagram of a multi-level inverter consisting of three cascaded H-bridge multi-level modules according to a variant of the first embodiment. 12 shows waveforms of output voltages VAB1, VAB2, and VAB3 in a current transient state produced by three H-bridge multi-level modules of the multi-level inverter shown in FIG. 11 according to the first embodiment of the present invention. Figure 6 shows a schematic view of an H-bridge multi-level leg with 5 output levels according to a variant of the first embodiment of the invention. FIG. 7 shows a schematic view of an H-bridge multi-level leg with 9 output levels, according to a variant of the first embodiment of the invention. 6 shows a schematic diagram of a multi-level inverter according to a second embodiment of the invention. 6 shows a flow chart of a method for supplying a multi-level output voltage with a multi-level inverter according to a second embodiment of the invention. FIG. 6 shows a schematic diagram of a first H-bridge multi-level leg of a multi-level inverter and the voltage generated by the H-bridge inverter according to a second embodiment of the invention. FIG. 6 shows a schematic diagram of a second H-bridge multi-level leg of a multi-level inverter and the voltage generated by the H-bridge inverter according to a second embodiment of the invention. FIG. 6 shows a schematic diagram of the output voltage generated by a multi-level inverter according to the second embodiment of the present invention. Figure 6 shows a schematic diagram of a multi-level inverter according to a third embodiment of the invention. Figure 6 shows a schematic diagram of a multi-level inverter according to the fourth embodiment of the invention. Figure 6 shows a schematic diagram of a multi-level inverter according to the fifth embodiment of the invention. FIG. 6 shows a schematic diagram of the connection relationship between k windings of a coupled inductor and k H-bridge multilevel legs of a multilevel inverter according to variants of the second and third embodiments of the invention. .

  The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

  As mentioned above, the inventors of the present invention have conducted numerous experiments and found that the defect in the conventional gradient amplifier 210 is due to the two-level inverter utilized in the amplifier, which causes a large change in the output voltage. In turn, it was found that the conventional gradient amplifier 210 leads to the generation of many high frequency harmonics.

  Specifically, FIG. 4A shows the voltages VA and VB output by the two half-bridge legs of the conventional two-level inverter 300 and the voltage output by the conventional two-level inverter 300 in the steady current state. Figure 5 shows a schematic of VAB, where Vbus is chosen to be 450v as an example. As shown in FIG. 4A, each of the voltages VA and VB (represented by 401 and 402, respectively) output by the first and second half-bridge legs 310, 320 of the conventional two-level inverter 300 in steady state current. Has two output levels 0v and Vbus, and the voltage VAB output by conventional two-level inverter 300 in current steady state, which is represented by 403, also has two output levels 0v and Vbus. However, it includes two voltage pulses in each period.

  Further, FIG. 4B shows a schematic diagram of the voltage VAB output by a conventional two-level inverter 300 during a current transient, where Vbus is chosen to be 450v by way of example. As shown in FIG. 4B, the voltage VAB (which is represented by 404) output by a conventional two-level inverter 300 during a current transient has two output levels 0v and Vbus, and within each period. It includes two voltage pulses.

  As can be seen from FIGS. 4A and 4B, the voltage VAB output by the conventional two-level inverter 300 switches from 0v to Vbus or vice versa at each transition, ie, is output by the conventional two-level inverter 300. The voltage VAB changes the amount of Vbus each time, and thus the conventional two-level inverter 300 has a large amount of change in the output voltage (450v-0v = 450v in this example). Therefore, the gradient amplifier 210 formed by the conventional two-level inverter 300 also has a large change in the output voltage, and many high frequency harmonics are generated by the gradient amplifier 210.

  Therefore, in light of the inventor's insight, the present invention provides a multi-level inverter, which has more than one output level and is therefore formed by a conventional two-level inverter. The change in output voltage is smaller than that of the existing gradient amplifier, and thus the problem caused by the large change in output voltage in the existing gradient amplifier can be solved.

  In the following, various embodiments of the invention will be described in detail in conjunction with the drawings.

First Embodiment FIG. 5 shows a schematic diagram of an H-bridge multi-level module 50 according to a first embodiment of the present invention. As shown in FIG. 5, the H-bridge multi-level module 50 includes an H-bridge multi-level leg A510 and an H-bridge multi-level leg B540, and the H-bridge multi-level leg A510 and the H-bridge multi-level leg B540 are direct currents having a voltage Vbus. It is connected in parallel to the power supply 580. In the first embodiment, Vbus is selected to be 450v as an example. However, one of ordinary skill in the art will readily appreciate that Vbus may have other values as desired.

  The H-bridge multi-level leg A510 includes a first inverter leg 512, a second inverter leg 514, and a coupled inductor 516. As will be appreciated by those in the art, any inductor or transformer with multiple windings is called a coupled inductor.

  The first inverter leg 512 and the second inverter leg 514 are connected in parallel to the DC power supply 580. The first inverter leg 512 is a half-bridge leg formed by the high side switch QAH1_A1 and the low side switch QAL1_A1, and the switches QAH1_A1 and QAL1_A1 are coupled in series.

  The second inverter leg 514 is a half bridge leg formed by the high side switch QAH1_A2 and the low side switch QAL1_A2, and the switches QAH1_A2 and QAL1_A2 are coupled in series.

  As shown in FIG. 6, the coupled inductor 516 includes a primary winding p and a secondary winding s wound around a magnetic core. The primary winding p and the secondary winding s are coupled in series and have a junction node A. The current icm flowing through the junction node A is the sum of the current icm1 flowing through the primary winding p of the coupled inductor 516 and the current icm2 flowing through the secondary winding s of the coupled inductor 516. Since the primary winding p and the secondary winding s of the coupled inductor 516 are coupled in series, the magnetic flux generated by the current icm1 and the current icm2 cancel each other out when the current icm1 is the same as the current icm2. Therefore, the coupled inductor 516 acts as a resistor.

  Returning to FIG. 5, the node A1 between the high-side switch QAH1_A1 and the low-side switch QAL1_A1 of the first inverter leg 512 is connected to the primary winding p of the coupled inductor 516, and the high voltage of the second inverter leg 514 is high. A node A2 located between the side switch QAH1_A2 and the low side switch QAL1_A2 is connected to the secondary winding s of the coupled inductor 516. Junction node A of coupled inductor 516 forms the output terminal of H-bridge multilevel leg A510.

  Similarly, H-bridge multi-level leg B540 includes a first inverter leg 542, a second inverter leg 544, and a coupled inductor 546.

  The first inverter leg 542 and the second inverter leg 544 are connected in parallel to the DC power supply 580. The first inverter leg 542 is a half-bridge leg formed by the high side switch QBH1_B1 and the low side switch QBL1_B1, and the switches QBH1_B1 and QBL1_B1 are coupled in series.

  The second inverter leg 544 is a half bridge leg formed by the high side switch QBH1_B2 and the low side switch QBL1_B2, and the switches QBH1_B2 and QBL1_B2 are coupled in series.

  Coupling inductor 546 is the same as coupling inductor 516, includes primary and secondary windings coupled in series, and may have a junction node B of the primary and secondary windings. The node B1 located between the switches QBH1_B1 and QBL1_B1 of the first inverter leg 542 is connected to the primary winding of the coupling inductor 546 and the node B2 located between the switches QBH1_B2 and QBL1_B2 of the second inverter leg 544 is coupled. It is connected to the secondary winding of inductor 546. Junction node B may form the output terminal of H-bridge multi-level leg B540.

  The output terminals of H-bridge multi-level leg A 510 and H-bridge multi-level leg B 540 form the output terminals of H-bridge multi-level module 50. Each of the switches QAH1_A1, QAL1_A1, QAH1_A2, QAL1_A2, QBH1_B1, QBL1_B1, QBH1_B2, QBL1_B2 is a power transistor (for example, insulated gate bipolar transistor (IGBT), metal oxide semiconductor field effect transistor (MOSFET: metal). The switches QAH1_A1, QAL1_A1, QAH1_A2, QAL1_A2, QBH1_B1, QBL1_B1, QBH1_B2, QBL1_B2 may have the same voltage rating and current rating.

  FIG. 7 shows a schematic diagram of a multi-level inverter 70 according to the first embodiment of the present invention. As shown in FIG. 7, the multi-level inverter 70 includes the one H-bridge multi-level module 50 described above, and the H-bridge multi-level module 50 is connected to the DC power supply 78 having the voltage Vbus. As shown in FIG. 7, the multi-level inverter 70 is connected to the gradient magnetic field coil 230 via the EMI filter 220.

  In the following, the principle of the H-bridge multi-level module 50, that is, the method for supplying the multi-level output voltage by utilizing the multi-level inverter will be explained in conjunction with FIG. 8, which shows the first embodiment of the present invention. 6 shows a flowchart of a method 800 for providing a multi-level output voltage with a multi-level inverter 70 according to an embodiment.

  As shown in FIG. 8, in step S802, the first inverter leg 512 of the H-bridge multi-level module 50 in the multi-level inverter 70 outputs the drive signals for the high-side switch QAH1_A1 and the low-side switch QAL1_A1 of the first inverter leg 512. , The voltage VA1 is generated at the node A1 of the first inverter leg 512 under the condition that these drive signals of these two switches are modulated to be complementary. The voltage VA1 is input to the primary winding of the coupled inductor 516 of the H-bridge multilevel module 50 of the multilevel inverter 70. As shown in FIG. 9A, the voltage VA1 represented by 901 has two output levels 0v and Vbus, and as described above, Vbus is 450v as an example.

  In step S804, the drive signals of the high-side switch QAH1_A2 and the low-side switch QAL1_A2 of the second inverter leg 514 are modulated so that the drive signals of these two switches are complementary, and the drive signal of the high-side switch QAH1_A2 is modulated. Has a duty cycle that is the same as the duty cycle of the drive signal of the high side switch QAH1_A1 and the drive signal of the high side switch QAH1_A2 has a θ phase shift with respect to the drive signal of the high side switch QAH1_A1. The leg 514 generates the voltage VA2 at the node A2 of the second inverter leg 514. The voltage VA2 is input to the secondary winding of the coupled inductor 516 of the H-bridge multilevel module 50 of the multilevel inverter 70. As shown in FIG. 9A, the voltage VA2, represented by 902, has two output levels, 0v and Vbus. Since the drive signal of the high side switch QAH1_A2 has a θ phase shift with respect to the drive signal of the high side switch QAH1_A1, the voltage VA2 has a θ phase shift with respect to the voltage VA1.

In step S806, the H-bridge multi-level leg A510 of the H-bridge multi-level module 50 in the multi-level inverter 70 generates the voltage VA at the node A based on the voltages VA1 and VA2. In this embodiment, the turns ratio between the primary and secondary windings of the coupled inductor 516 is 1: 1 and thus the voltage VA is calculated according to equation 1.
VA = (VA1 + VA2) / 2 (Formula 1)
Since voltage VA2 has a θ phase shift with respect to voltage VA1, voltage VA represented by 903 has three levels 0v, 1 / 2Vbus, and Vbus, as shown in FIG. 9A.

  In step S808, the drive signals of the high-side switch QBH1_B1 and the low-side switch QBL1_B1 of the first inverter leg 542 of the H-bridge multi-level module 50 in the multi-level inverter 70 are set so that the drive signals of these two switches are complementary. It is modulated, the drive signal of the low-side switch QBL1_B1 has the same duty cycle as the duty cycle of the drive signal of the high-side switch QAH1_A1, and the drive signal of the low-side switch QBL1_B1 is 180 ° out of phase with the drive signal of the high-side switch QAH1_A1. Under shift conditions, first inverter leg 542 develops voltage VB1 at node B1 of first inverter leg 542. The voltage VB1 is input to the primary winding of the coupled inductor 546 of the H-bridge multilevel module 50 in the multilevel inverter 70. As shown in FIG. 9B, the voltage VB1 represented by 904 has two levels 0v and Vbus, and as described above, Vbus is 450v as an example.

  In step S810, the drive signals of the high-side switch QBH1_B2 and the low-side switch QBL1_B2 of the second inverter leg 544 of the H-bridge multi-level module 50 of the multi-level inverter 70 are set so that the drive signals of these two switches are complementary. Being modulated, the drive signal of the low-side switch QBH1_B2 has the same duty cycle as the duty cycle of the drive signal of the low-side switch QBH1_B1, and the drive signal of the low-side switch QBH1_B2 has a θ phase shift with respect to the drive signal of the low-side switch QBH1_B1. Under state, second inverter leg 544 develops voltage VB2 at node B2 of second inverter leg 544. The voltage VB2 is input to the secondary winding of the coupled inductor 546 of the H-bridge multilevel module 50 of the multilevel inverter 70. As shown in FIG. 9B, the voltage VB2 represented by 905 has two output levels 0v and Vbus. Since the drive signal of the high side switch QBH1_B2 has a θ phase shift with respect to the drive signal of the high side switch QBH1_B1, the voltage VB2 has a θ phase shift with respect to the voltage VB1.

In step S812, the H-bridge multi-level leg B540 of the H-bridge multi-level module 50 in the multi-level inverter 70 generates the voltage VB at the node B by using the voltages VB1 and VB2. In this embodiment, the turns ratio between the primary and secondary windings of coupled inductor 546 is 1: 1 and thus voltage VB is calculated according to equation 2.
VB = (VB1 + VB2) / 2 (Formula 2)
Since voltage VB2 has a θ phase shift with respect to voltage VB1, voltage VB represented by 906 has three output levels 0v, 1 / 2Vbus, and Vbus, as shown in FIG. 9B.

  In step S814, the H-bridge multi-level module 50 of the multi-level inverter 70 outputs the difference between the voltages VA and VB generated by the H-bridge multi-level leg A510 and the H-bridge multi-level leg B540 of the H-bridge multi-level module 50. A voltage VAB is generated.

  In this embodiment, the duty cycle of the drive signal of the high side switch QAH1_A1 selected for the steady current state is different from the duty cycle of the drive signal of the high side switch QAH1_A1 selected for the current transient state. As a result, as shown in FIG. 10A, the current steady state output voltage VAB (denoted by 1001) produced by the H-bridge multi-level module 50 has two output levels, 0v and 1 / 2Vbus. , Four voltage pulses within each period, while the output voltage VAB (which is represented by 1002) in the current transient state generated by the H-bridge multilevel module 50 is 3 as shown in FIG. 10B. It has one output level 0 v, 1/2 Vbus, and Vbus, and contains two voltage pulses in each period.

  Since the multi-level inverter 70 includes one H-bridge multi-level module 50 in this embodiment, the output voltage VAB generated by the H-bridge multi-level module 50 of the multi-level inverter 70 becomes the output voltage VAB of the multi-level inverter 70. Become.

  As can be seen from the above description, the θ phase shift between the voltages VA1 and VA2 and between the voltages VB1 and VB2 has three output levels 0v, 1 / 2Vbus, and Vbus for each of the voltages VA and VB in the first embodiment. The voltages VA and VB having three output levels 0 v, 1/2 Vbus, and Vbus are connected to the output voltage VAB output by the multi-level inverter 70 in the current steady state, as shown in FIG. 10A. The output voltage VAB switched between 0v and 1 / 2Vbus at each transition and output by the multilevel inverter 70 in the current transient state is between 0v and 1 / 2Vbus at each transition, as shown in FIG. 10B. It leads to switching between 1/2 Vbus and Vbus.

  Therefore, the output voltage VAB output by the multi-level inverter 70 changes the amount of 1/2 Vbus at each transition, thus making the change in output voltage smaller than existing gradient amplifiers. Since the output voltage VAB output by the multi-level inverter 70 has a smaller change in the output voltage, less high-frequency harmonics are generated by the multi-level inverter 70, and thus the high-frequency harmonics generated by the multi-level inverter 70 are attenuated. The EMI filter 220 for achieving this can use a damping resistor having a smaller resistance value, a capacitor having a smaller capacitance value, and an inductor having a smaller inductance value, thereby improving the filter efficiency of the EMI filter 220. It does not affect the overall control bandwidth of the system. Further, if the change in the output voltage of the multi-level inverter 70 is smaller, the common mode current caused by the stray capacitance Cstray is much smaller, and the stabilization is greatly facilitated. Further, when the change in the output voltage of the multi-level inverter 70 is smaller, the current ripple of the gradient magnetic field coil 230 is also reduced.

  In addition, the output voltage VAB generated by the multi-level inverter 70 in the current steady state includes four voltage pulses in each period, and the output voltage VAB output by each two-level inverter of the existing gradient amplifier is shown in FIG. 4B. Since, as shown, there are two voltage pulses in each period, the equivalent switching frequency of the multi-level inverter 70 at current steady state is twice the equivalent switching frequency of each two-level inverter of the existing gradient amplifier, and thus , Multi-level inverter 70 further provides less current ripple at current steady state than existing gradient amplifiers.

  In the first embodiment, the multi-level inverter 70 includes only one H-bridge multi-level module 50, but the multi-level inverter 70 may optionally include multiple cascaded H-bridge multi-level modules 50. Should be understood to include. FIG. 11 shows a schematic diagram of a multi-level inverter 70 consisting of three cascaded H-bridge multi-level modules 50 according to a variant of the first embodiment.

  When the multi-level inverter 70 includes a plurality of cascaded H-bridge multi-level modules 50, the switches included in the multi-level inverter 70 are configured so that the voltage generated by each H-bridge multi-level module of the multi-level inverter 70 is multi-level. Modulated to have a 360 ° / n phase shift with respect to the voltage produced by adjacent H-bridge multi-level modules of level inverter 70, where n is a cascaded H-bridge included in multi-level inverter 70. Number of multi-level modules 50). FIG. 12 shows a schematic diagram of the current steady state voltage produced by the three cascaded H-bridge multi-level modules 50 of the multi-level inverter 70 shown in FIG. 11, 1201, 1202 and 1203 respectively. The voltages VAB1, VAB2, VAB3 generated by three cascaded H-bridge multi-level modules 50 are represented.

  The 360 ° / n phase shift between any two adjacent H-bridge multi-level modules 50 of the multi-level inverter 70 means that the voltage pulses generated by the plurality of H-bridge multi-level modules 50 of the multi-level inverter 70 are multi-level. This leads to being evenly distributed in the output voltage VAB generated by the inverter 70. Therefore, the output voltage VAB produced by the multi-level inverter 70 will contain more voltage pulses in each period, which will result in the multi-level inverter 70 providing a greater equivalent switching frequency and thus a ramp. The current ripple of the magnetic field coil 230 can be reduced.

In the first embodiment, the turns ratio between the primary winding and the secondary winding of each of the coupled inductors 516 and 546 is 1: 1. It should be understood that the turns ratio to the wire is n1: n2, where n1 and n2 are different integers. In this case, the voltages VA and VB are calculated according to the following formulas.
VA = (VA1 * n1 + VA2 * n2) / (n1 + n2), and VB = (VB1 * n1 + VB2 * n2) / (n1 + n2)

In the first embodiment, each of the H-bridge multi-level leg A 510 and the H-bridge multi-level leg B 540 of the H-bridge multi-level module 50 has an H-bridge multi-level having three output levels (0 v, 1/2 Vbus, and Vbus). As the level legs, each of the H-bridge multi-level leg A510 and the H-bridge multi-level leg B540 of the H-bridge multi-level module 50 has 2 ^m +1 output levels to make the change of the output voltage smaller. It is to be understood that it is a H-bridge multi-level leg, where m is an integer greater than one.

Each of the H-bridge multilevel module 50 of the H-bridge multilevel legs A510 and H-bridge multilevel legs B540 ^is, when an H-bridge multilevel legs having ² m +1 single output ^level, the ² m +1 single output level The H-bridge multi-level legs with are constructed in the following manner: three H-bridge multi-level legs with three output levels are coupled in parallel via a coupling inductor similar to coupling inductor 516 to form three H-bridge multi-level legs. The H-bridge multi-level leg with output levels is first extended to an H-bridge multi-level leg with 5 output levels, and then two H-bridge multi-level legs with 5 output levels are combined in a similar manner to the coupling inductor 516. By connecting in parallel through an inductor, five output levels An H-bridge multi-level leg with a bell is extended to an H-bridge multi-level leg with 9 output levels, etc., and finally two H-bridge multi-level legs with 2 ^m-1 +1 output levels. the coupling by coupling in parallel via the same coupling inductor and the inductor 516, H-bridge multi-level H-bridge multilevel legs having 2 ^{m-1 +1} single output level has a 2 ^m +1 single output level Expanded to the legs. 13A and 13B show schematic diagrams of an H-bridge multi-level leg with five output levels and an H-bridge multi-level leg with nine output levels, respectively, 132 and 134 each having three output levels. , And each of 136 and 138 represents an H-bridge multi-level leg having five output levels.

Second Embodiment FIG. 14 shows a schematic diagram of a multi-level inverter 1400 according to a second embodiment of the present invention. As shown in FIG. 14, the multi-level inverter 1400 includes a coupled inductor 1320, a first H-bridge multi-level leg 1340, and a second H-bridge multi-level leg 1360. First H-bridge multi-level leg 1340 and second H-bridge multi-level leg 1360 are coupled in parallel via coupling inductor 1320.

  Coupling inductor 1320 is similar to coupling inductor 516 and includes primary and secondary windings coupled in series and may have a junction node A of the primary and secondary windings. The junction node A of the coupled inductor 1320 forms the output terminal of the multilevel inverter 1400 and supplies the multilevel output voltage Vm to the gradient coil 230. One side of the first H-bridge multi-level leg 1340 and one side of the second H-bridge multi-level leg 1360 are connected to the primary and secondary windings of the coupled inductor 1320, respectively. The junction node between the other side of H-bridge multi-level leg 1340 and the other side of second H-bridge multi-level leg 1360 forms the other output terminal of multi-level inverter 1400.

  The first H-bridge multi-level leg 1340 includes three cascaded H-bridge inverters 1342, 1344, 1346.

  The H-bridge inverter 1342 includes a first half-bridge leg F11 and a second half-bridge leg F12 that are connected in parallel to the DC power supply U1. The first half bridge leg F11 includes a high side switch QHA1 and a low side switch QLA1 coupled in series. The second half bridge leg F12 includes a high side switch QHB1 and a low side switch QLB1 coupled in series. The drive signals of these switches are such that the drive signal of the switch QHA1 and the drive signal of the switch QLA1 are complementary, the drive signal of the switch QHB1 and the drive signal of the switch QLB1 are complementary, and the drive signal of the switch QHA1 is It has the same duty cycle as the drive signal of switch QLB1 and the drive signal of switch QLB1 is modulated to have a 180 ° phase shift with respect to the drive signal of switch QHA1.

  Similarly, the H-bridge inverter 1344 includes a first half-bridge leg F21 including a high-side switch QHA2 and a low-side switch QLA2 coupled in series, and a second half-bridge switch FHB2 and a low-side switch QLB2 coupled in series. And half-bridge legs F22, and the legs F21 and F22 are connected in parallel to the DC power source U2. The drive signals of the switches QHA2, QLA2, QHB2, QLB2 are the drive signals of the switch QHA2 with respect to the drive signal of the switch QHA1. Similar to the drive signals for switches QHA1, QLA1, QHB1, QLB1 except that they have a Θ phase shift. The H-bridge inverter 1346 includes a first half-bridge leg F31 including a high-side switch QHA3 and a low-side switch QLA3 coupled in series, and a second half-bridge including a high-side switch QHB3 and a low-side switch QLB3 coupled in series. The legs F31 and F32 are connected in parallel to the DC power supply U3, and the drive signals of the switches QHA3, QLA3, QHB3, and QLB3 are the phase shifts of the drive signal of the switch QHA3 with respect to the drive signal of the switch QHA2. Are the same as the drive signals for the switches QHA2, QLA2, QHB2, QLB2, except that

  The second H-bridge multi-level leg 1360 includes three cascaded H-bridge inverters 1362, 1364, 1366.

  The H-bridge inverter 1362 includes a first half-bridge leg F41 including a high-side switch QHA4 and a low-side switch QLA4 connected in series, and a second half-bridge including a high-side switch QHB4 and a low-side switch QLB4 connected in series. The leg F42 and the legs F41 and F42 are connected in parallel to the DC power source U4, and the drive signals of the switches QHA4, QLA4, QHB4, QLB4 are the phase shift of the drive signal of the switch QHA4 with respect to the drive signal of the switch QHA1. Are the same as the drive signals for the switches QHA1, QLA1, QHB1, and QLB1 except that

  The H-bridge inverter 1364 includes a first half-bridge leg F51 including a high-side switch QHA5 and a low-side switch QLA5 coupled in series, and a second half-bridge including a high-side switch QHB5 and a low-side switch QLB5 coupled in series. The leg F52 and the leg F52 are connected in parallel to the DC power supply U5, and the drive signals of the switches QHA5, QLA5, QHB5, QLB5 are the phase shift of the drive signal of the switch QHA5 with respect to the drive signal of the switch QHA2. Are the same as the drive signals for the switches QHA2, QLA2, QHB2, QLB2, except that

  The H-bridge inverter 1366 includes a first half-bridge leg F61 composed of a high-side switch QHA6 and a low-side switch QLA6 coupled in series, and a second half-bridge composed of a high-side switch QHB6 and a low-side switch QLB6 coupled in series. The leg F62 and the leg F61 and F62 are connected in parallel to the DC power supply U6, and the drive signals of the switches QHA6, QLA6, QHB6, QLB6 are the phase shift of the drive signal of the switch QHA6 with respect to the drive signal of the switch QHA3. Are the same as the drive signals of the switches QHA3, QLA3, QHB3, and QLB3, except that

  The Θ phase shift and the Ψ phase shift between the drive signals are generated by the H bridge inverters 1362 and 1364, between the output voltages generated by the H bridge inverters 1342 and 1344, between the output voltages generated by the H bridge inverters 1344 and 1346. There is a Θ phase shift between the output voltages generated by the H-bridge inverters 1364 and 1366 and between the output voltages generated by the H-bridge inverters 1364 and 1366. Leading to the existence of a Ψ phase shift between the output voltages produced by the H-bridge inverters 1346, 1366. In other words, the modulation of the switches of H-bridge inverters 1342, 1344, and 1346 has a phase shift with respect to the modulation of the switches of H-bridge inverters 1362, 1364, and 1366. This phase shift results in a phase shift between the output voltages V1 and V2. With the output voltages V1 and V2 according to this modulation scheme being supplied to the coupled inductor 1320, the ripple frequency of the output signal Vm will be the number of stacked H-bridge inverters (eg three stacked in the embodiment of FIG. 14). H-bridge inverter) and this will be explained in more detail. Furthermore, since the levels of the output voltages V1 and V2 are related to the number of stacked H-bridge inverters, the number of switching levels of the output signal Vm is increased by a factor equal to the number of stacked H-bridge inverters. It will be appreciated by those skilled in the art.

  Furthermore, the DC power supplies U1, U2, U3, U4, U5 and U6 have the same voltage Vbus.

  Compared to the multi-level inverter 70 in the first embodiment which uses six coupled inductors, the multi-level inverter 1400 in the second embodiment uses only one coupled inductor. Therefore, the multi-level inverter 1400 of the second embodiment is lower in cost and smaller in size than the multi-level inverter 70 of the first embodiment.

  FIG. 15 shows a flowchart of a method for providing a multi-level output voltage by a multi-level inverter 1400 according to the second embodiment of the present invention. The method of FIG. 15 is described in detail in connection with FIG.

  As shown in FIG. 15, in step S1500, the first H-bridge multi-level leg 1340 of the multi-level inverter 1400 determines that the drive signal of the switch QHA1 and the drive signal of the switch QLA1 are complementary, and the drive signal of the switch QHB1 is complementary. And the drive signal of the switch QLB1 are complementary, the drive signal of the switch QHA1 has the same duty cycle as the drive signal of the switch QLB1, and the drive signal of the switch QLB1 is 180 ° phase-shifted with respect to the drive signal of the switch QHA1. The drive signal of the switch QHA2 and the drive signal of the switch QLA2 are complementary, the drive signal of the switch QHB2 and the drive signal of the switch QLB2 are complementary, and the drive signal of the switch QHA2 drives the switch QLB2. Has the same duty cycle as the signal , The drive signal of the switch QLB2 has a 180 ° phase shift with respect to the drive signal of the switch QHA2, the drive signal of the switch QHA3 and the drive signal of the switch QLA3 are complementary, and the drive signal of the switch QHB3 and the drive signal of the switch QLB3 are The drive signal is complementary, the drive signal of switch QHA3 has the same duty cycle as the drive signal of switch QLB3, the drive signal of switch QLB3 has a 180 ° phase shift with respect to the drive signal of switch QHA3, Under the condition that the switches included in the first H-bridge multi-level leg 1340 are modulated such that there is a Θ phase shift between the drive signals of the switches QHA1, QHA2 and between the drive signals of the switches QHA2, QHA3, A voltage V1 having a plurality of output levels is generated. The voltage V1 is input to the primary winding of the coupled inductor 1320. An example of the voltage generated by the first H-bridge multi-level leg 1340 and its H-bridge inverter is shown in FIG. 16A, where T represents one period, at 1601, 1602, 1603, and 1604, respectively. The voltages V1, V11, V12, V13 represented are output by the first H-bridge multi-level leg 1340 and H-bridge inverters 1342, 1344, 1346, respectively, and Vbus is assumed to be 450v.

  In step S1502, the second H-bridge multi-level leg 1360 of the multi-level inverter 1400 controls the Ψ phase between the drive signals of the switches QHA1 and QHA4, between the drive signals of the switches QHA2 and QHA5, and between the drive signals of the switches QHA3 and QHA6. There is a shift, the drive signal of the switch QHA4 and the drive signal of the switch QLA4 are complementary, the drive signal of the switch QHB4 and the drive signal of the switch QLB4 are complementary, and the drive signal of the switch QHA4 is the switch signal of the switch QLB4. Has the same duty cycle as the drive signal, the drive signal of switch QLB4 has a 180 ° phase shift with respect to the drive signal of switch QHA4, and the drive signal of switch QHA5 and the drive signal of switch QLA5 are complementary; Drive signal of switch QHB5 and switch The drive signal of switch QLB5 is complementary, the drive signal of switch QHA5 has the same duty cycle as the drive signal of switch QLB5, and the drive signal of switch QLB5 has a 180 ° phase shift with respect to the drive signal of switch QHA5. The drive signal of the switch QHA6 and the drive signal of the switch QLA6 are complementary, the drive signal of the switch QHB6 and the drive signal of the switch QLB6 are complementary, and the drive signal of the switch QHA6 is the drive signal of the switch QLB6. And the drive signal of switch QLB6 has a 180 ° phase shift with respect to the drive signal of switch QHA6, between the drive signals of switches QHA1 and QHA4, between the drive signals of switches QHA2 and QHA5, and Ψ phase shift between the drive signals of QHA3 and QHA6 So they present, in a state where switches included in the second H-bridge multilevel leg 1360 is modulated to generate a voltage V2 having a plurality of output levels. The voltage V2 is input to the secondary winding of the coupled inductor 1320. Since there is a Ψ phase shift between the drive signals of the switches QHA1 and QHA4, between the drive signals of the switches QHA2 and QHA5, and between the drive signals of the switches QHA3 and QHA6, the voltage V2 has a Ψ phase shift with respect to the voltage V1. ..

  An example of the voltage generated by the second H-bridge multi-level leg 1360 and its H-bridge inverter is shown in FIG. 16B, where T represents one period, at 1605, 1606, 1607, and 1608, respectively. The voltages V2, V21, V22, V23 represented are output by the second H-bridge multi-level leg 1360 and H-bridge inverters 1362, 1364, 1366, respectively, and Vbus is assumed to be 450v.

In step S1504, the multilevel inverter 1400 generates the output voltage Vm from the voltage V1 and the voltage V2. In the second embodiment, the turns ratio between the primary winding and the secondary winding of the coupled inductor 1320 is 1: 1. Therefore, the voltage Vm is calculated according to Equation 3.
Vm = (V1 + V2) / 2 (Formula 3)
An example of the output voltage Vm generated by the multi-level inverter 1400 is shown in FIG. 16C, where the voltage Vm is represented by 1609.

  As can be seen from FIG. 16C, the output voltage Vm generated by the multi-level inverter 1400 switches between 0v and 1/2 Vbus (225v) at each transition, thus the output voltage Vm generated by the multi-level inverter 1400. Changes 1/2 Vbus at each transition. Therefore, the multi-level inverter 1400 has a smaller change in output voltage than the existing gradient amplifier.

  Furthermore, as can be seen from the content disclosed in the second embodiment, it is generated by the three cascaded H-bridge inverters 1342, 1344, 1346 of the first H-bridge multi-level leg 1340 of the multi-level inverter 1400. Output voltages V11, V12, V13 and output voltages V21, V22, V23 generated by the three cascaded H-bridge inverters 1362, 1364, 1366 of the second H-bridge multi-level leg 1360 of the multi-level inverter 1400. Are connected by a coupled inductor 1320 and are modulated with Θ and Ψ phase shifts. Therefore, the combination of this modulation scheme and the coupled inductor 1320 allows the output voltage Vm generated by the multilevel inverter 1400 to include 12 voltage pulses within each period, as shown in FIG. 16C, while As shown in FIGS. 16A and 16B, each of the H-bridge inverters 1342, 1344, 1346, 1362, 1364, 1366 includes only two voltage pulses within each period, and thus the output voltage Vm of the multilevel inverter 1400. The ripple frequency is 6 times the ripple frequency of the output voltage generated by each H-bridge inverter, and the switching frequency of the multilevel inverter 1400 is 6 times the switching frequency of each H-bridge inverter. Since the multi-level inverter 1400 includes six cascaded H-bridge inverters, the ripple frequency of the output voltage of the multi-level inverter 1400 is changed by the combination of this modulation method and the coupling inductor 1320. It will be multiplied by the number of connected H-bridge inverters.

Third Embodiment FIG. 17 shows a schematic diagram of a multi-level inverter 1700 according to a third embodiment of the present invention. As shown in FIG. 17, in the multi-level inverter 1700 of the third embodiment, both H-bridge inverters 1342 and 1362 are connected to a single DC power source U1 (that is, the H-bridge inverters 1342 and 1362 are fed H-bridges). Inverters), the H-bridge inverters 1344, 1346 of the first H-bridge multi-level leg 1340, and the H-bridge inverters 1364, 1366 of the second H-bridge multi-level leg 1360 are floating H-bridge inverters. It is different from the multi-level inverter 1400 of the second embodiment. That is, the H-bridge inverter 1344 as a floating H-bridge inverter is connected to the capacitor Cdc1 instead of the DC power supply U2, and the H-bridge inverter 1346 as a floating H-bridge inverter is connected to the capacitor Cdc2 instead of the DC power supply U3. The H-bridge inverter 1364 as a floating H-bridge inverter is connected to the capacitor Cdc3 instead of the DC power supply U5, and the H-bridge inverter 1366 as a floating H-bridge inverter is connected to the capacitor Cdc4 instead of the DC power supply U6. The floating H-bridge inverter is described in detail in PCT application WO 2010 / 109399A1, the entire disclosure of which is incorporated herein by reference.

  Compared to the multi-level inverter 1400 of the second embodiment, the multi-level inverter 1700 of the third embodiment may require less DC power. Furthermore, the introduction of a floating H-bridge inverter in the multi-level inverter 1700 provides an additional degree of freedom in the modulation algorithm of the multi-level inverter 1700, which is the case when no current is flowing in the gradient coil 230. Even so, it can be used to charge the capacitors of the floating H-bridge inverter of multi-level inverter 1700 at startup.

  The method for supplying the multi-level output voltage by the multi-level inverter 1700 according to the third embodiment of the present invention is the same as the method according to the second embodiment of the present invention described above. Then, the description is omitted.

Fourth Embodiment FIG. 18 shows a schematic diagram of a multi-level inverter 1800 according to a fourth embodiment of the present invention. As shown in FIG. 18, the multi-level inverter 1800 of the fourth embodiment is similar to the multi-level inverter 1800 of the second embodiment in that the multi-level inverter 1800 includes a set of coupled inductors 1322, 1324 instead of the coupled inductor 1320. Different from the level inverter 1400. Each of the coupled inductors 1322, 1324 has half the impedance of the coupled inductor 1320 of the second embodiment, ie, the coupled inductor 1320 of the second embodiment is divided into a set of coupled inductors 1322, 1324.

  Each of the set of coupled inductors 1322, 1324 is the same as coupled inductor 1320 and includes a primary winding and a secondary winding coupled in series and has a junction node A of the primary winding and the secondary winding. obtain.

  As shown in FIG. 18, split sets of coupled inductors 1322 and 1324 are symmetrically coupled to both sides of the first and second H-bridge multilevel legs 1340 and 1360. Specifically, the first H-bridge multi-level leg 1340 is coupled between the primary windings of the coupled inductors 1322, 1324, and the second H-bridge multi-level leg 1360 is coupled between the secondary windings of the coupled inductors 1322, 1324. Be combined with. The junction node A of the coupled inductors 1322, 1324 forms the two output terminals of the multilevel inverter 1800.

  The multi-level inverter 1800 is beneficial for galvanic isolation requirements and EMC compliance because the coupled inductors 1322, 1324 are symmetrically arranged within the multi-level inverter 1800. Furthermore, if two capacitors C1 and C2 are placed on two sides of the gradient coil 230, respectively, a set of coupled inductors 1322, 1324 is coupled with the two capacitors C1 and C2 to form a second order filter. Which can attenuate high frequency harmonics more effectively.

  The method for supplying the multi-level output voltage by the multi-level inverter 1800 according to the fourth embodiment of the present invention is the same as the method according to the second embodiment of the present invention described above. Then, the description is omitted.

Fifth Embodiment FIG. 19 shows a schematic diagram of a multi-level inverter 1900 according to a fifth embodiment of the present invention. As shown in FIG. 19, in the multi-level inverter 1900 of the fifth embodiment, the H-bridge inverters 1342 and 1362 are power feeding H-bridge inverters, and the H-bridge inverters 1344 and 1346 of the first H-bridge multi-level leg 1340, And the H-bridge inverters 1364, 1366 of the second H-bridge multi-level leg 1360 are floating H-bridge inverters, unlike the multi-level inverter 1800 of the fourth embodiment.

  The method for supplying the multi-level output voltage by the multi-level inverter 1900 according to the fifth embodiment of the present invention is the same as the method according to the second embodiment of the present invention described above. Then, the description is omitted.

Modifications In the second and fourth embodiments, the DC power supplies U1, U2, U3, U4, U5 and U6 have the same voltage Vbus, but the DC power supplies U1, U2, U3, U4, U5 and U6 are mutually connected. It should be appreciated by one of ordinary skill in the art that it is possible to have different voltages.

  It should be appreciated that the Θ phase shift and / or Ψ phase shift described in the second, third, fourth, and fifth embodiments may be constant or may change over time.

  In the second, third, fourth and fifth embodiments, the drive signals of the switches QHA1 and QHA2, the drive signals of the switches QHA2 and QHA3, the drive signals of the switches QHA4 and QHA5, and the drive of the switches QHA5 and QHA6 are driven. It should be appreciated that although the same Θ phase shift exists between the signals, these phase shifts can be different from each other.

  In the second, third, fourth and fifth embodiments, the same Ψ phase shift exists between the drive signals of the switches QHA1 and QHA4, between the drive signals of the switches QHA2 and QHA5, and between the drive signals of the switches QHA3 and QHA6. However, it should be understood that these phase shifts may differ from each other.

  In the second, third, fourth, and fifth embodiments, each of the first H-bridge multi-level leg 1340 and the second H-bridge multi-level leg 1360 includes three cascaded H-bridge inverters. However, it should be understood that the number of H-bridge inverters included in each of the first H-bridge multi-level leg 1340 and the second H-bridge multi-level leg 1360 can be less than or greater than three, as desired. ..

  In the second, third, fourth, and fifth embodiments, the number of H-bridge inverters included in the first H-bridge multi-level leg 1340 is equal to the number of H-bridge inverters included in the second H-bridge multi-level leg 1360. It is understood that the number of H-bridge inverters included in the first H-bridge multi-level leg 1340 may be different from the number of H-bridge inverters included in the second H-bridge multi-level leg 1360. I want to be done.

  Each of the first H-bridge multi-level leg 1340 and the second H-bridge multi-level leg 1360 in the third and fifth embodiments includes one feed H-bridge inverter and two floating H-bridge inverters. It should be appreciated that each of the one H-bridge multi-level leg 1340 and the second H-bridge multi-level leg 1360 includes at least one feed H-bridge inverter and at least one floating H-bridge inverter.

In the second, third, fourth, and fifth embodiments, the turns ratio between the primary winding and the secondary winding of the coupled inductor 1320 is 1: 1, but the primary winding and the secondary winding of the coupled inductor 1320 have the same winding ratio. It should be understood that the turns ratio with the secondary winding can be n3: n4, where n3 and n4 are different integers. In this case, the voltage Vm is calculated according to the following mathematical formula.
Vm = (V1 * n3 + V2 * n4) / (n3 + n4)

  In the second and third embodiments, the multi-level inverter comprises two H-bridge multi-level legs 1340, 1360, while the multi-level inverter comprises k H-bridge multi-level legs T1, T2, T3 ,. ． ． , Tk, where k is an integer greater than 2. The switch included in the multi-level inverter has a voltage generated by the k H-bridge multi-level legs having a phase shift with respect to each other, and is generated by an H-bridge inverter included in each of the k H-bridge multi-level legs. The applied voltages are modulated to have a phase shift with respect to each other. In this case, the coupled inductor 1320 has K windings m1, m2, m3 ,. ． ． , Mk, and has a junction node A of K windings. The k H-bridge multi-level legs T1, T2, T3 ,. ． ． , Tk, each of the k windings m1, m2, m3 ,. ． ． , Mk. FIG. 20 shows a schematic diagram of the connection between the k windings of the coupled inductor 1320 and the k H-bridge multi-level legs of the multi-level inverter, the H-bridge multi-level leg T1 being connected to the input voltage V1. The H-bridge multi-level leg T2 is coupled to the winding m1 of the coupled inductor 1320 to supply, and the H-bridge multi-level leg T2 is coupled to the winding m2 of the coupled inductor 1320 to supply the input voltage V2. The H-bridge multi-level leg Tk is coupled to the winding m3 of the coupled inductor 1320 to provide the input voltage V3, etc., and the H-bridge multi-level leg Tk is coupled to the winding mk of the coupled inductor 1320 to provide the input voltage Vk, The junction node A of the coupling inductor 1320 outputs the voltage Vm as the output voltage of the multilevel inverter. It is clear that the more H-bridge multi-level legs included in the multi-level inverter, the more voltage pulses are included in each cycle of the output voltage of the multi-level inverter, and as a result, the current ripple of the gradient coil 230 is increased. It leads to reduction.

  In the fourth and fifth embodiments, the multi-level inverter includes two H-bridge multi-level legs 1340, 1360, but it should be understood that the multi-level inverter includes k H-bridge multi-level legs. In this case, each of the coupled inductors 1322 and 1324 includes k windings connected together and has a junction node A of k windings. Each of the k H-bridge multilevel legs included in the multilevel inverter is connected between one of the k windings of coupled inductor 1322 and one of the k windings of coupled inductor 1324. To be done. The switch included in the multi-level inverter has a voltage generated by the k H-bridge multi-level legs having a phase shift with respect to each other, and is generated by an H-bridge inverter included in each of the k H-bridge multi-level legs. The applied voltages are modulated to have a phase shift with respect to each other.

  While the preferred embodiment has been described in detail by way of example, other embodiments and variations of the invention will be apparent to those skilled in the art in view of this specification and practice of the invention disclosed herein. Let's see The specification and the examples given should be regarded as illustrative only, and the appended claims are intended to cover any other embodiments or variations that fall within the true scope of the invention. It is intended to be included.

  It should be noted that the method steps presented in the present invention should not be limited to the steps described above. It will be apparent to those skilled in the art that various aspects of the claimed invention can be practiced in other examples that depart from these specific details.

  Furthermore, in a device claim enumerating several means, several of these means can be embodied by one and the same item of hardware, as will be readily appreciated by those skilled in the art. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

  It should be noted that the above described embodiments are illustrative rather than limiting of the present invention and that one of ordinary skill in the art could design alternative embodiments without departing from the scope of the appended claims. I want to be done. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim or herein. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. In the system claim enumerating several units, some of these units may be embodied by the same software item and / or hardware item. The use of words such as first, second, and third does not indicate any order. These words should be interpreted as names.

Claims (13)

N H-bridge multi-level legs, each having M cascaded H-bridge inverters, where n and M are integers greater than 1.
A coupled inductor having n windings wound around a core and coupled together at a junction node of the n windings, the n H-bridge multilevel legs comprising: Coupled in parallel via each of the n H-bridge multi-level legs to one of the n windings to provide an input voltage having a plurality of voltage levels, the junction The node forms the output terminal of a multi-level inverter for providing a multi-level output level, the input voltages provided by the n H-bridge multi-level legs having a phase shift with respect to each other,
A multi-level inverter, wherein the voltage generated by the M cascaded H-bridge inverters has a 360 ° / M phase shift with respect to adjacent H-bridge inverters. N H-bridge multi-level legs, each having M cascaded H-bridge inverters, where n and M are integers greater than 1.
And a split set of coupled inductors symmetrically coupled on opposite sides of the n H-bridge multilevel legs, each of the coupled inductor sets being wound around a core and joining n windings. Having n windings coupled together at a node, each of the n H-bridge multi-level legs of the set of coupled inductors for supplying an input voltage having a plurality of voltage levels. Of one of said n windings of one coupled inductor of said and one of said n windings of another coupled inductor of said set of coupled inductors, the junction node of the set of the inductor forms an output terminal of the multi-level inverter in order to supply the multi-level output level, the supply of the said n H-bridge multilevel legs That the input voltage has a phase shift relative to each other,
A multi-level inverter, wherein the voltage generated by the M cascaded H-bridge inverters has a 360 ° / M phase shift with respect to adjacent H-bridge inverters.   The number of the cascaded H-bridge inverters in each of the n H-bridge multi-level legs is the same as the number of the cascaded H-bridge inverters in each of the other H-bridge multi-level legs, Or the multilevel inverter of Claim 1 or 2 which is different.   The multi-level inverter according to claim 1 or 2, wherein the M cascaded H-bridge inverters comprise at least one fed H-bridge inverter and at least one floating H-bridge inverter. A multi-level inverter comprising M cascaded H-bridge multi-level modules, M being an integer greater than 1.
Each H-bridge multi-level module has a first H-bridge multi-level leg having a plurality of output levels at the output terminal of the first H-bridge multi-level leg and a plurality of output terminals of the second H-bridge multi-level leg. And a second H-bridge multi-level leg having an output level of, the first and second H-bridge multi-level legs being connected in parallel, the multi-level output of the H-bridge multi-level module being Output between the output terminals of the first and second H-bridge multi-level legs,
Each of the first and second H-bridge multi-level legs includes a first inverter leg and a first inverter leg coupled in parallel via a coupling inductor that includes a primary winding and a secondary winding wound around a core. Two inverter legs, the first inverter leg coupled to the primary winding of the coupled inductor to provide a first input voltage having a plurality of voltage levels, the second inverter leg Is coupled to the secondary winding of the coupled inductor to provide a second input voltage having a plurality of voltage levels, the primary and secondary windings of the coupled inductor are coupled in series, and in series A junction node of the coupled primary and secondary windings forms the output terminal of the H-bridge multi-level leg, the first input voltage being a predetermined phase shift with respect to the second input voltage. Have
A multi-level inverter, wherein the voltage generated by the M cascaded H-bridge multi-level modules has a 360 ° / M phase shift with respect to adjacent H-bridge multi-level modules.   The multi-level inverter of claim 5, wherein each of the first and second inverter legs comprises a half-bridge leg having a high side switch and a low side switch coupled in series.   The drive signals of the high-side switches in the first and second inverter legs of the first H-bridge multi-level leg have the predetermined phase shift with respect to each other and the second H-bridge multi-level leg 7. The multi-level inverter according to claim 6, wherein the drive signals of the low side switches in the first and second inverter legs of the have a predetermined phase shift with respect to each other. The first and second input voltages having 2 ^n-1 +1 voltage levels result in 2 ⁿ +1 output levels output from each of the first and second H-bridge multi-level legs, The multilevel inverter according to claim 5, wherein n is an integer of 1 or more. H-bridge multilevel legs having 2 k ⁺¹ single output level by two H-bridge multilevel legs having 2 k ⁺¹ single output level is connected in parallel via the coupled inductor, 2 k ^{+ 1 +1} or Extended to H-bridge multilevel legs with output levels of k, where k is 1 ,. ． ． , N, the multi-level inverter of claim 8. A method for providing a multi-level output voltage by a multi-level inverter, said multi-level inverter comprising M cascaded H-bridge multi-level modules, M being an integer greater than 1, each H being The bridge multi-level module includes a first H-bridge multi-level leg and a second H-bridge multi-level leg connected in parallel, and the output voltage of the H-bridge multi-level module is the first and second H-bridge multi-level legs. Output between the output terminals of the H-bridge multi-level legs, each of said first and second H-bridge multi-level legs via a coupled inductor including a primary winding and a secondary winding wound around a core. A first inverter leg and a second inverter leg coupled in parallel with each other, wherein the first inverter leg includes the coupling Coupled to the primary winding of the inductor, the second inverter leg is coupled to the secondary winding of the coupled inductor, the primary and secondary windings of the coupled inductor are coupled in series, and A junction node of the coupled primary and secondary windings forms the output terminal of the H-bridge multi-level leg, the method comprising:
Generating a first voltage having a plurality of levels by the first inverter leg of the first H-bridge multi-level leg of each H-bridge multi-level module;
The second inverter leg of the first H-bridge multi-level leg of each H-bridge multi-level module produces a second voltage having a plurality of levels having a predetermined phase shift with respect to the first voltage. Steps to
Generating a third voltage having a plurality of levels based on the generated first and second voltages by the first H-bridge multi-level leg of each H-bridge multi-level module;
Generating a fourth voltage having a plurality of levels by the first inverter leg of the second H-bridge multi-level leg of each H-bridge multi-level module;
The second inverter leg of the second H-bridge multi-level leg of each H-bridge multi-level module produces a fifth voltage having a plurality of levels having the predetermined phase shift with respect to the fourth voltage. The step of generating
Generating a sixth voltage having a plurality of levels based on the generated fourth and fifth voltages by the second H-bridge multi-level leg of each H-bridge multi-level module;
Generating, by each H-bridge multi-level module, a multi-level output voltage based on the generated third and sixth voltages;
Providing a multi-level output voltage of the multi-level inverter based on the multi-level output voltage output by each H-bridge multi-level module,
The method, wherein the output of each H-bridge multi-level module has a 360 ° / M phase shift with respect to an adjacent H-bridge multi-level module. Each of the first and second inverter legs comprises a half bridge leg having a high side switch and a low side switch coupled in series,
The drive signals of the high side switches in the first and second inverter legs of the first H-bridge multi-level leg have the predetermined phase shift with respect to each other, and the second H-bridge multi-level leg. 11. The method of claim 10, wherein the drive signals of the low side switches in the first and second inverter legs of the legs have the predetermined phase shift with respect to each other. A method for providing a multi-level output voltage by a multi-level inverter, said multi-level inverter comprising n H-bridge multi-level legs and n windings wound around a core. And n and M are integers greater than one, each of the n H-bridge multi-level legs has M cascaded H-bridge inverters, and the n windings are , Coupled to each other at a junction node, the n H-bridge multi-level legs are coupled in parallel through the coupling inductor, and each of the n H-bridge multi-level legs is coupled to the n windings. And the junction node forms an output terminal of the multi-level inverter, the method comprising:
Generating n voltages with the n H-bridge multi-level legs, each of the n voltages having a plurality of voltage levels, the n voltages being phase-shifted with respect to each other. With a step,
Supplying a multi-level output voltage output by the multi-level inverter based on the generated n voltages.
The method wherein the voltage generated by the M cascaded H-bridge inverters has a 360 ° / M phase shift with respect to adjacent H-bridge inverters. A method for providing a multi-level output voltage by a multi-level inverter, wherein the multi-level inverter comprises n H-bridge multi-level legs and a split set of coupled inductors, where n and M are integers greater than one. And each of the n H-bridge multi-level legs has M cascaded H-bridge inverters, and the split set of coupled inductors are on either side of the n H-bridge multi-level legs. Symmetrically coupled, each of the set of coupled inductors being n windings wound around a core and coupled together at a junction node of the n windings. has, each of said n H-bridge multilevel legs, among the n windings of one coupled inductor of the set of the coupled inductor One, the junction node of the coupled inductor of another coupled inductor of the set of the coupled between one of the n windings, and the set of the coupled inductor, the multilevel inverter Forming an output terminal of
Generating n voltages with the n H-bridge multi-level legs, each of the n voltages having a plurality of voltage levels, the n voltages being phase-shifted with respect to each other. With a step,
Supplying a multi-level output voltage output by the multi-level inverter based on the generated n voltages.
The method wherein the voltage generated by the M cascaded H-bridge inverters has a 360 ° / M phase shift with respect to adjacent H-bridge inverters.