JP5934538B2 - Three-phase rectifier - Google Patents

Description

  Embodiments described herein relate generally to a three-phase rectifier that rectifies a voltage of a three-phase AC power source and converts the voltage into a DC voltage.

  A rectifier circuit that rectifies the voltage of a general three-phase AC power source and converts it into a DC voltage has three series circuits formed by connecting a pair of diodes in series, and the interconnection point of each diode of these series circuits is Connected to each phase of the three-phase AC power supply. A smoothing capacitor is connected to the output terminal of the rectifier circuit, and a load is connected to the smoothing capacitor.

  The three-phase AC voltage is composed of three phase voltages whose phases are different from each other by 120 °. With these phase voltages, a current flows through the positive diode of each series circuit to the smoothing capacitor, and each of the series circuits is supplied from the smoothing capacitor. Current flows through the negative diode.

  In addition, in order to improve the power factor in such a rectifier circuit and to suppress the harmonic current contained in the input current, a reactor is provided on the input side and a plurality of switches for forming a short circuit for these reactors are connected. In addition, a three-phase active filter is employed in which the input current waveform follows a sine wave by high-frequency switching of these switches.

JP 2010-233292 A

  In order to reduce a current flowing through one rectifier circuit and supply a large current by a rectifier circuit having a small current capacity, it is conceivable to connect a plurality of rectifier circuits in parallel to a three-phase AC power supply. In the case of a three-phase rectifier in which a plurality of rectifier circuits are connected in parallel to such a three-phase AC power supply and a three-phase active filter is provided in these rectifier circuits, high-frequency switching for harmonic suppression is performed for each rectifier circuit. Therefore, as a whole three-phase rectifier, there is a problem that propagation noise accompanying high-frequency switching becomes large, and circuit elements such as filters for reducing this noise increase.

  An object of an embodiment of the present invention is to provide a three-phase rectifier capable of improving power factor and suppressing harmonics while reducing high-frequency switching noise.

A three-phase rectifier according to claim 1, wherein a positive side diode and a negative side diode are connected in series, and an interconnection point between the two diodes is connected to the R phase of a three-phase AC power source, a positive side diode, S-phase series circuit in which negative diodes are connected in series and the connection point of both diodes is connected to the S phase of the three-phase AC power supply, positive diodes and negative diodes are connected in series, and the two diodes are interconnected A plurality of rectifier circuits each having a T-phase series circuit connected to the T-phase of the three-phase AC power source and converting the voltage of the three-phase AC power source into a DC voltage; and parallel to each diode A plurality of connected switching elements, a plurality of reactors provided between the respective phases of the three-phase AC power supply and the series circuits, and a control unit. The control means is a half cycle period in which the input voltage from the three-phase AC power source is a positive level from the zero crossing point to the next zero crossing point among the switching elements. next together with the turning on intermittently at different timings among the rectifier circuits in the front edge and the rear edge side, from said input voltage zero cross point of the switching elements connected in parallel with each of the positive side diodes from the three-phase AC power supply The rectifier circuits are intermittently turned on at different timings on the leading edge side and the trailing edge side of the half cycle period in which the negative level is reached up to the zero cross point . The leading edge side is a period excluding an initial predetermined period. The trailing edge side is a period excluding the last predetermined period .

The block diagram which shows the structure of one Embodiment. The figure which shows the switching period of one Embodiment. The figure which shows the waveform of the input voltage and input current in one Embodiment. The figure which expands and shows a part of input current waveform in FIG. 3 with the ON / OFF pattern of the switching element. The figure which shows the magnitude | size of the harmonic current in one Embodiment for every order. The figure which shows the switching period of the modification of one Embodiment. The figure which shows the waveform of the input current in the modification of one Embodiment with the ON / OFF pattern of a switching element. The figure which shows the waveform of the ripple current which flows into the smoothing capacitor in the modification of one Embodiment. The figure which shows the waveform of the conventional ripple current as a reference. FIG. 6 is a waveform diagram of an R-phase input voltage, an input current, and respective R-phase input currents of the rectifier circuits 20 and 60 showing a state in which the waveforms of the input voltage and the input current are out of phase.

[1] An embodiment of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, a three-phase rectifier 10 is connected to the R, S, and T phases of a three-phase AC power supply 1, and an output voltage of the three-phase rectifier 10 (voltage generated in a smoothing capacitor 90 described later) is loaded. 2 is supplied. The load 2 is, for example, an inverter device for driving a motor. In this embodiment, the three-phase rectifier 10 using the two rectifier circuits 20 and 60 will be described. However, the number of rectifier circuits is not limited to this as long as it is plural.

  The three-phase rectifier 10 includes a first rectifier circuit 20 connected to the three-phase AC power source 1, and harmonic reduction reactors 11 to 13 provided in a connection line between the first rectifier circuit 20 and the three-phase AC power source 1. The zero cross detection circuits 41 to 43 and the current sensors 51 to 53 provided on the connection line between the reactors 11 to 13 and the three-phase AC power source 1, and the voltage detection circuit 47 for detecting the output voltage of the first rectifier circuit 20. The second rectifier circuit 60 connected to the three-phase AC power source 1, the reactors 14 to 16 for reducing harmonics provided in the connection line between the second rectifier circuit 60 and the three-phase AC power source 1, and the reactors 14 to 16 Voltage detection circuit 48 for detecting the output voltage of the second rectifier circuit 60, the first and second detection circuits 44 to 46, the current sensors 54 to 56, and the second rectifier circuit 60 provided on the connection line between the power supply 1 and the three-phase AC power source 1. Rectifier circuit 20, 6 The smoothing capacitor 90 is connected to the output terminal, and a control unit 100.

  Zero-cross detection circuits 41 and 44 detect the zero-cross point of the R-phase input voltage from the three-phase AC power supply 1, and zero-cross detection circuits 42 and 45 detect the zero-cross point of the S-phase input voltage. Similarly, the zero cross detection circuits 43 and 46 detect the zero cross point of the T-phase input voltage. Current sensors 51 and 54 detect an R-phase input current from the three-phase AC power supply 1 to the first rectifier circuit 20, and current sensors 52 and 55 detect an S-phase from the three-phase AC power supply 1 to the first rectifier circuit 20. The input current is detected, and the current sensors 53 and 56 detect the T-phase input current from the three-phase AC power supply 1 to the first rectifier circuit 20.

  The first rectifier circuit 20 and the second rectifier circuit 60 are provided with the current sensors 51 to 53 and 54 to 56 for detecting the respective phase currents. However, in order to reduce the number of parts, the respective rectifier circuits 20 and 60 are provided. In FIG. 5, current sensors may be provided only for two specific phases, and the other one phase may be calculated.

  The first rectifier circuit 20 includes a positive-side diode 21 and a negative-side diode 22 connected in series, and an interconnection point between the two diodes is connected to the R-phase of the three-phase AC power supply 1. And a negative diode 24 are connected in series, and an S-phase series circuit in which the mutual connection point between the two diodes is connected to the S phase of the three-phase AC power source 1, a positive diode 25 and a negative diode 26 are connected in series. The diode interconnection point has a T-phase series circuit connected to the T-phase of the three-phase AC power source 1, converts the three-phase AC voltage of the three-phase AC power source 1 into a DC voltage, and outputs a positive output terminal (+ ) And the negative output terminal (-). Switching elements such as MOSFETs 31 to 36 are connected in parallel to the diodes 21 to 26 of the first rectifier circuit 20, respectively.

  Note that the MOSFETs 31 to 36 each have a parasitic diode therein, so that these parasitic diodes may be used as the diodes 21 to 26 as they are. Note that a transistor or an IGBT may be used as the switching element.

  The second rectifier circuit 60 has the same circuit configuration as the first rectifier circuit 20, and a positive side diode 61 and a negative side diode 62 are connected in series, and an interconnection point between the two diodes is the R phase of the three-phase AC power supply 1. An R-phase series circuit connected to the S-phase, a positive-side diode 63 and a negative-side diode 64 connected in series, and an interconnection point between the two diodes connected to the S-phase of the three-phase AC power source 1; The three-phase AC power supply 1 has a T-phase series circuit in which a side diode 65 and a negative-side diode 66 are connected in series, and an interconnection point between the two diodes is connected to the T-phase of the three-phase AC power supply 1. The voltage is converted into a DC voltage and output from the positive output terminal (+) and the negative output terminal (−). Switching elements such as MOSFETs 71 to 76 are connected in parallel to the diodes 61 to 66 of the second rectifier circuit 60, respectively.

The control unit 100 has the following means (1) and (2) as main functions.
(1) Based on the zero cross point detection result of each phase of the three-phase AC power supply 1 by the zero cross detection circuits 41 to 43, in parallel with the negative side diodes 22, 24, and 26 of the MOSFETs 31 to 36 of the first rectifier circuit 20. The connected MOSFETs 32, 34, and 36 are intermittently turned on at least at the leading edge side of the phase where the R-phase input voltage, S-phase input voltage, and T-phase input voltage from the three-phase AC power supply 1 are at the positive level, respectively, and the positive side The MOSFETs 31, 33, and 35 connected in parallel with the diodes 21, 23, and 25 are intermittently connected at least on the leading edge side of the phase where the R-phase input voltage, the S-phase input voltage, and the T-phase input voltage from the three-phase AC power supply 1 are negative levels. First control means to be turned on automatically.

  (2) Based on the detection results of the zero cross detection circuits 44 to 46, among the MOSFETs 71 to 76 of the second rectifier circuit 60, the MOSFETs 72, 74, and 76 connected in parallel with the negative diodes 62, 64, and 66 are three-phase AC power supplies. The R-phase input voltage, the S-phase input voltage, and the T-phase input voltage from 1 are intermittent at different timings at least on the leading edge side of the phase where the MOSFETs 32, 34, and 36 on the first rectifier circuit 20 side are turned on. And the MOSFETs 71, 73, 75 connected in parallel with the positive diodes 61, 63, 65 are connected to the negative phase levels of the R-phase input voltage, S-phase input voltage, and T-phase input voltage from the three-phase AC power source 1, respectively. At least at the leading edge of the phase, and intermittently at timings different from the ON of the MOSFETs 31, 33, 35 on the first rectifier circuit 20 side. Second control means for down.

  As shown in FIG. 2, the leading edge side of the phase at which the input voltage is at a positive level has an electrical angle of 0 from the zero crossing point to the next zero crossing point of the R-phase input voltage, S-phase input voltage, and T-phase input voltage. Among the half-cycle periods of ° to 180 °, the periods Rx1, Sx1, and Tx1 are the forward electrical angles of 0 ° to 60 °. The leading edge of the phase at which the input voltage is at a negative level is a half cycle of an electrical angle of 180 ° to 360 ° from the zero cross point to the next zero cross point of the R phase input voltage, S phase input voltage, and T phase input voltage. Among the periods, the periods Ry1, Sy1, and Ty1 have a forward electrical angle of 180 ° to 240 °. Further, intermittently turning on means repeating on and off at a predetermined interval. Further, when the MOSFET on the second rectifier circuit 60 side is intermittently turned on at a timing different from that of the MOSFET on the first rectifier circuit 20 side in the second control means, the timing is different for both on and off. In this case, both cases where only the ON timing is made different are included.

Next, the operation will be described.
In the phase where the R-phase input voltage is at a positive level, a current flows from the commercial AC power supply 1 through the reactor 11 and the positive diode 21 of the first rectifier circuit 20 to the smoothing capacitor 90, and the current passing through the smoothing capacitor 90 is First, it returns to the S phase of the commercial AC power supply 1 through the negative side diode 24 and the reactor 12 of the first rectifier circuit 20, and then as the phase of the R phase advances, the negative side diode 26 and the reactor 13 of the first rectifier circuit 20. A path that passes through the T phase of the commercial AC power supply 1 is formed. Similarly, in the second rectifier circuit 60, a current flows from the commercial AC power supply 1 through the reactor 14 and the positive diode 61 of the second rectifier circuit 60 to the smoothing capacitor 90 in a phase where the R-phase input voltage becomes a positive level. The current passing through the smoothing capacitor 90 first returns to the commercial AC power source 1 through the negative diode 64 and the reactor 15 of the second rectifier circuit 60, and then passes through the negative diode 66 and the reactor 16 of the second rectifier circuit 60. Thus, a path returning to the commercial AC power source 1 is formed.

  In addition to the above-described operation, the MOSFET 32 on the first rectifier circuit 20 side is intermittently turned on in the leading edge side period Rx1 of the phase where the R-phase input voltage becomes a positive level, and the second timing is different from the on-state. The MOSFET 72 on the rectifier circuit 20 side is intermittently turned on. In the present embodiment, the MOSFET 32 and the MOSFET 72 are alternately turned on so as not to be turned on simultaneously. As a result of the setting of the switching timing, the MOSFET on the first rectifier circuit 20 side and the MOSFET on the second rectifier circuit 60 side have different timings both on and off. Further, the ON (continuation) period of each MOSFET is set to be gradually shortened as the phase advances.

  When the MOSFET 32 is turned on, the interconnection point of the diodes 21 and 22 of the first rectifier circuit 20 is brought into conduction with the negative output terminal of the first rectifier circuit 20, and as shown by the arrow in FIG. Thus, a short circuit is formed through the reactor 11, the MOSFET 32, the negative diode 24, and the reactor 12. On the other hand, when the MOSFET 72 is turned on, the interconnection point between the diodes 61 and 62 of the second rectifier circuit 60 is electrically connected to the negative output terminal of the second rectifier circuit 60, and the reactor 14, MOSFET 72, negative A short circuit is formed through the side diode 64 and the reactor 15.

  In the phase where the S-phase input voltage is at a positive level, a current flows from the commercial AC power supply 1 through the reactor 12 and the positive diode 23 of the first rectifier circuit 20 to the smoothing capacitor 90, and the current passing through the smoothing capacitor 90 is First, there is a path that returns to the commercial AC power source 1 through the negative side diode 26 and the reactor 13 of the first rectifier circuit 20 and then returns to the commercial AC power source 1 through the negative side diode 22 and the reactor 11 of the first rectifier circuit 20. It is formed. At the same time, a current flows from the commercial AC power source 1 through the reactor 15 and the positive side diode 63 of the second rectifier circuit 60 to the smoothing capacitor 90, and the current passing through the smoothing capacitor 90 is first a negative side diode of the second rectifier circuit 60. 64 and the reactor 15 are returned to the commercial AC power source 1, and then a path is formed to return to the commercial AC power source 1 through the negative diode 66 and the reactor 16 of the second rectifier circuit 60.

  In addition to the above-described operation, the MOSFET 34 on the first rectifier circuit 20 side is intermittently turned on in the leading edge side period Sx1 of the phase in which the S-phase input voltage becomes a positive level, and the second timing is different from the on-state. The MOSFET 74 on the rectifier circuit 20 side is intermittently turned on. Specifically, the MOSFET 34 and the MOSFET 74 are turned on alternately. The ON period is gradually shortened as the phase advances.

  When the MOSFET 34 is turned on, the interconnection point between the diodes 23 and 24 of the first rectifier circuit 20 is electrically connected to the negative output terminal of the first rectifier circuit 20, and the reactor 12, MOSFET 34, and negative diode are connected to the commercial AC power supply 1. 26, a short circuit is formed through the reactor 13. On the other hand, when the MOSFET 74 is turned on, the interconnection point of the diodes 63 and 64 of the second rectifier circuit 60 is electrically connected to the negative output terminal of the second rectifier circuit 60, and the reactor 15, MOSFET 74, negative A short circuit is formed through the side diode 66 and the reactor 16.

  In the phase where the T-phase input voltage is at a positive level, a current flows from the commercial AC power supply 1 through the reactor 13 and the positive diode 25 of the first rectifier circuit 20 to the smoothing capacitor 90, and the current passing through the smoothing capacitor 90 is First, there is a path that returns to the commercial AC power source 1 through the negative side diode 22 and the reactor 11 of the first rectifier circuit 20, and then returns to the commercial AC power source 1 through the negative side diode 24 and the reactor 12 of the first rectifier circuit 20. It is formed. At the same time, a current flows from the commercial AC power supply 1 through the reactor 16 and the positive diode 65 of the second rectifier circuit 60 to the smoothing capacitor 90, and the current passing through the smoothing capacitor 90 is firstly the negative diode of the second rectifier circuit 60. 62 and the reactor 14 are returned to the commercial AC power source 1, and then a path is formed to return to the commercial AC power source 1 through the negative diode 64 and the reactor 15 of the second rectifier circuit 60.

  In addition to the above operation, the MOSFET 36 on the first rectifier circuit 20 side is intermittently turned on in the leading edge side period Tx1 of the phase in which the T-phase input voltage is at a positive level, and the second timing is different from the on-state. The MOSFET 76 on the rectifier circuit 20 side is intermittently turned on. Specifically, the MOSFETs 36 and 76 are turned on alternately. The ON period is gradually shortened as the phase advances.

  When the MOSFET 36 is turned on, the interconnection point of the diodes 25 and 26 of the first rectifier circuit 20 is electrically connected to the negative output terminal of the first rectifier circuit 20, and the reactor 13, MOSFET 36, and negative diode are connected to the commercial AC power supply 1. 22, a short circuit is formed through the reactor 11. On the other hand, when the MOSFET 76 is turned on, the interconnection point of the diodes 65 and 66 of the second rectifier circuit 60 is electrically connected to the negative output terminal of the second rectifier circuit 60, and the reactor 16, MOSFET 76, negative A short circuit is formed through the side diode 62 and the reactor 14.

  In the leading edge side periods Ry1, Sy1, and Ty1 of the phase in which the R-phase input voltage, the S-phase input voltage, and the T-phase input voltage are negative levels, the MOSFET 31 that is connected in parallel with the positive-side diodes 21, 23, and 25 of the first rectifier circuit 20 33, 35 are intermittently turned on, and the MOSFETs 71, 73, 75 connected in parallel with the positive side diodes 61, 63, 65 of the second rectifier circuit 60 are intermittently turned on at an alternate timing. About the operation | movement accompanying these intermittent ON of MOSFET, it becomes the same operation pattern as a positive level period fundamentally only by the opposite of positive / negative. Therefore, the detailed description is abbreviate | omitted.

  Thus, the MOSFETs 32, 34, and 36 of the first rectifier circuit 20 and the second rectifier circuit in the leading edge side periods Rx1, Sx1, and Tx1 of the phase in which the R-phase input voltage, the S-phase input voltage, and the T-phase input voltage are positive levels. 60 MOSFETs 72, 74, 76 are intermittently turned on, and the first rectifier circuit 20 in the leading edge side periods Ry 1, Sy 1, Ty 1 of the phase in which the R-phase input voltage, the S-phase input voltage, and the T-phase input voltage become negative levels. By intermittently turning on the MOSFETs 31, 33, 35 and the MOSFETs 71, 73, 75 of the second rectifier circuit 60, as shown in FIG. 3, the input current to the three-phase rectifier 10 (= first rectifier circuit) 20) and the input current to the second rectifier circuit 60) can be approximated to a sine wave with good followability. Thereby, while a power factor improves, the harmonic current contained in the input current to the said three phase rectifier 10 can be suppressed.

  FIG. 4 is an enlarged view of the leading edge side periods Rx1, Sx1, and Tx1 of the input current waveform of FIG. 3 together with the on / off pattern of the MOSFET.

  In addition, since the MOSFET on the first rectifier circuit 20 side and the MOSFET on the second rectifier circuit 60 side are turned on alternately, the change in the input current of the commercial AC power supply 1 can be reduced.

  If the MOSFET on the first rectifier circuit 20 side and the MOSFET on the second rectifier circuit 60 side are turned on synchronously, a short circuit is formed in both the first rectifier circuit 20 and the second rectifier circuit 60 when the MOSFET is turned on. The current change (increase) flowing through the commercial AC power supply 1 becomes large. As a result, the generation of harmonics is increased. On the other hand, if the MOSFET on the first rectifier circuit 20 side and the MOSFET on the second rectifier circuit 60 side are alternately turned on, that is, not turned on at the same time, the current of the commercial AC power supply 1 by forming a short circuit when the MOSFET is turned on. The change (increase) is only an increase in one rectifier circuit, and the current change can be reduced. As a result, the change in current flowing through the commercial AC power supply 1 is not so large, and the change in current can be reduced as compared with the case of synchronous on.

  Further, when the ripple of the input current to the three-phase rectifier 10 is reduced, the amount of heat generated by the smoothing capacitor 90 is reduced by the amount of the ripple of the current flowing through the smoothing capacitor 90. As a result, the life of the smoothing capacitor 90 is reduced. Will improve.

  The magnitude of the harmonic current included in the input current to the three-phase rectifier 10 is shown in FIG. The hatched bar graph indicates the harmonic current of the present embodiment, and the broken line indicates the power supply harmonic current limit value defined by IEC (International Electrical Standards Conference) 61000-3-2.

  Further, by turning on the MOSFET on the first rectifier circuit 20 side and turning on the MOSFET on the second rectifier circuit 60 side alternately, the on / off frequency (also referred to as a high frequency switching frequency) of the MOSFET is changed to the first rectifier circuit 20. It can be reduced to, for example, 2 kHz, which is half or less, for example, compared with 10 kHz, for example, when ON of the MOSFET on the side and ON of the MOSFET on the second rectifier circuit 60 are synchronized. As the on / off frequency is reduced, high-frequency switching noise conducted to the input side and other phases can be greatly reduced. Further, with the reduction of the high-frequency switching noise, the number and capacity of mounted components such as a noise filter can be reduced.

  Periods Rx1, Sx1, and Tx1 of the leading edge side where the MOSFET is intermittently turned on are 0 ° to 60 °, and the periods Rx1, Sx1, and Tx1 are less affected by the on / off control of one phase on the current waveforms of the other two phases. It hits the rise. Therefore, by selecting this period, a large harmonic current reduction effect can be obtained with a small number of switching operations. In addition, the number of times of switching can be greatly reduced and high-frequency switching noise can be reduced as compared with the case of switching at a high frequency in all phases as in the conventional three-phase active filter.

[2] Modification
(1) In the above-described embodiment, as the period in which the MOSFET is intermittently turned on, the period Rx1, Sx1, Tx1 of the leading edge side 0 ° to 60 ° of the phase in which the input voltage becomes positive level, and the input voltage becomes negative level The period Ry1, Sy1, Ty1 of the leading edge side 0 ° to 60 ° of the phase is set. In addition, as shown in FIG. 6, the period of 120 ° to 180 ° of the trailing edge side of the phase where the input voltage becomes a positive level. Rx2, Sx2, Tx2, and periods Ry2, Sy2, Ty2 of 120 ° to 180 ° of the trailing edge side of the phase where the input voltage becomes a negative level may be set.

  In the period Rx2, Sx2, Tx2, Ry2, Sy2, and Ty2 of the trailing edge side 120 ° to 180 °, the ON / OFF control of one phase has a relatively large influence on the current waveforms of the other two phases. If switching is performed during this period, the period during which the input current is 0 can be reduced without significantly increasing the number of switching operations, and the reactors 11, 12, and 13 can be made smaller.

  (2) Set 0 ° to (40 ° ± 10 °) as the period Rx1, Sx1, Tx1, Ry1, Sy1, Ty1 on the leading edge side, and set the period Rx2, Sx2, Tx2, Ry2, Sy2, Ty2 on the trailing edge side ( 160 ° ± 10 °) to 180 ° may be set. For example, in the case where 0 ° to 30 ° is set as the periods Rx1, Sx1, Tx1, Ry1, Sy1, Ty1 on the leading edge side, 150 ° to a longer length as the periods Rx2, Sx2, Tx2, Ry2, Sy2, Ty2 on the trailing edge side A period of 180 ° is set. When a longer 0 ° to 50 ° is set as the period Rx1, Sx1, Tx1, Ry1, Sy1, Ty1 on the leading edge side, 170 ° to 180 ° as the periods Rx2, Sx2, Tx2, Ry2, Sy2, Ty2 on the trailing edge side Set the period. In short, the period of the leading edge side and the period of the trailing edge side may be distributed within an electric angle of 60 °.

  Switching between the leading edge side 0 ° to (40 ° ± 10 °) and the trailing edge side (160 ° ± 10 °) to 180 ° is performed during the leading edge side 0 ° to 60 ° and the trailing edge side 120 ° to 180 °. Compared with the case of switching, the MOSFETs 31 to 36 that are turned on throughout the entire period (0 ° to 180 °) are any one, and the effect of improving controllability and reducing switching noise can be obtained.

(3) In the first embodiment, the MOSFETs on the first rectifier circuit 20 side and the MOSFETs on the second rectifier circuit 60 side are turned on alternately and the period during which they are turned on at the same time is eliminated, but as shown in FIG. The MOSFETs on the first rectifier circuit 20 side and the MOSFETs on the second rectifier circuit 60 side may be turned on by shifting each other by a predetermined period t1 instead of alternately. As the predetermined period t1, for example, 50% of the ON period of the MOSFET is variably set sequentially.
In this case, the ripple current flowing through the smoothing capacitor 90 has the waveform shown in FIG. In FIG. 8 and FIG. 9, (charge) current flowing into the smoothing capacitor 90 is represented by “+”, and (discharge) current flowing out from the smoothing capacitor 90 is represented by “−”.

  FIG. 9 shows the ripple current waveform when the MOSFET on the first rectifier circuit 20 side and the MOSFET on the second rectifier circuit 60 side are synchronized. FIG. 9 shows the amount of ripple current compared to the case of FIG. Is increasing. This is because the current flowing from the first rectifier circuit 20 and the second rectifier circuit 60 to the load 2 decreases when the MOSFET on the first rectifier circuit 20 side and the MOSFET on the second rectifier circuit 60 side are turned on in synchronization. This is because the discharge current of the smoothing capacitor 90 increases to compensate for the decrease.

  The amount of ripple current flowing through the smoothing capacitor 90 can be reduced by shifting the timing at which the MOSFET on the first rectifier circuit 20 side is turned on and the timing at which the MOSFET on the second rectifier circuit 60 side is turned on for a predetermined period t1. In the data in FIG. 8, the amount of ripple current is about 14% less than in the case of FIG.

  As the amount of ripple current flowing through the smoothing capacitor 90 decreases, the amount of heat generated by the smoothing capacitor 90 decreases, and as a result, the life of the smoothing capacitor 90 is improved.

  (4) The detection results of the zero cross points by the zero cross detection circuits 41 to 46 may be inconsistent due to influences of component performance errors and arithmetic processing errors. Considering this point, as shown in FIG. 6, as the switching period for intermittently turning on the MOSFET, the first predetermined period t0 is excluded from the periods Rx1, Sx1, Tx1, Ry1, Sy1, Ty1 on the leading edge side. It is desirable to set a period excluding the last predetermined period t2 from the trailing edge side periods Rx2, Sx2, Tx2, Ry2, Sy2, Ty2.

  If the detection results of the zero cross points by the zero cross detection circuits 41 to 46 do not match, as shown in FIG. 10, the phase of the zero cross point of the input voltage and the phase of the zero cross point of the input current are shifted. Sometimes. In particular, in a situation where the zero cross point constantly fluctuates due to the PLL control, a large shift of 200 μs or more may occur between the phase of the zero cross point of the input voltage and the phase of the zero cross point of the input current. In such a situation, a so-called reverse phase period occurs in which the input current is at a negative level while the input voltage is at a positive level. When switching is performed in such a state, a large distortion occurs in the waveform of the input current near the zero cross point. FIG. 10 shows a state where switching is performed immediately after the zero cross point on the leading edge side and switching is performed until the trailing edge side reaches the next zero cross point. For this reason, in the period of t0 on the leading edge side, although the current is on the negative side, useless switching for short-circuiting the R phase and the S phase, that is, turning on the MOSFET 32 on the first rectifier circuit 20 side and the second rectifier circuit The 20-side MOSFET 72 is turned on. On the other hand, in the period of t2 at the trailing edge, the reverse effect occurs that the current phase is further delayed by turning on the MOSFET 32 that short-circuits the R phase and the T phase and turning on the MOSFET 72, and the waveform of the input current is destroyed. Yes.

  Therefore, a predetermined period t0 at the beginning (front edge side) and a predetermined period t2 at the end (rear edge side) from the detection of the zero cross point on the leading edge side, which is a predetermined period based on the detection result of the zero cross point, are set as the switching prohibition period. Thus, unnecessary switching is eliminated and the waveform of the input current to the three-phase rectifier 10 (= the sum of the input current to the first rectifier circuit 20 and the input current to the second rectifier circuit 60) is made close to a sine wave. Can do. Note that the predetermined times t0 and t2 are respectively times that are tested and set to appropriate values in advance, and in order to prevent the current phase from being greatly delayed, the predetermined period t0 on the leading edge side <the predetermined period on the trailing edge side It is preferable to set to t2.

  (5) Since the switching prohibition period is provided as in (4) above, the zero crossing of the input voltage and the input voltage can be made closer, so the zero crossing point of the input current is detected from the detection results of the current sensors 51-56. The switching period may be set based on the detection result. In this case, the zero cross detection circuits 41 to 46 can be omitted.

  (6) In addition, the said embodiment and modification are shown as an example, and are not intending limiting the range of invention. The novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the spirit of the invention. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply, 2 ... Load, 10 ... Three-phase rectifier, 11-16 ... Reactor, 20 ... 1st rectifier circuit, 21, 23, 25 ... Positive side diode, 22, 24, 26 ... Negative side diode Reference numerals 31 to 36, switching elements, 41 to 46, zero cross detection circuit, 60, second rectifier circuit, 61, 63, 65, positive diode, 62, 64, 66, negative diode, 71 to 76, switching element , 90: smoothing capacitor, 100: control unit

Claims (2)

An R-phase series circuit in which a positive diode and a negative diode are connected in series, and an interconnection point between the two diodes is connected to an R phase of a three-phase AC power supply, and a positive diode and a negative diode are connected in series. The S-phase series circuit is connected to the S-phase of the three-phase AC power source, and the positive-side diode and the negative-side diode are connected in series, and the interconnection point between the two diodes is the T-phase of the three-phase AC power source. A plurality of rectifier circuits for converting the voltage of the three-phase AC power source into a DC voltage and outputting the DC voltage.
A plurality of switching elements connected in parallel to each of the diodes;
A plurality of reactors provided between the respective phases of the three-phase AC power supply and the series circuits;
Among the switching elements, the switching elements connected in parallel with the negative diodes are connected to the leading edge of a half cycle period in which the input voltage from the three-phase AC power source is a positive level from the zero cross point to the next zero cross point, and intermittently while turned on at different timings among the respective rectifier circuits at the trailing edge side, the next zero cross point input voltage from the zero cross point of the switching elements connected in parallel with each of the positive side diodes from the three-phase AC power supply Control means for intermittently turning on at different timings between the rectifier circuits on the leading edge side and the trailing edge side of the half cycle period that is a negative level until
Bei to give a,
The leading edge side is a period excluding an initial predetermined period,
The trailing edge side is a period excluding the last predetermined period.
A three-phase rectifier characterized by that. The leading edge side is a period excluding the initial predetermined period t0 ,
The trailing edge side is a period excluding the last predetermined period t2 (> t0) .
The three-phase rectifier according to claim 1 .

Images