JP7230633B2 - power converter - Google Patents

Description

The present invention relates to a power converter, and more particularly to a power converter that generates various DC voltages from high-voltage AC voltage.

In general, on the consumer side such as factories and buildings, a power supply system that converts AC voltage supplied from a power system to DC voltage and supplies it to various electrical equipment includes a transformer, an AC / DC converter, and a DC / DC Various power conversion devices such as converters are used to step down high-voltage AC voltage received from transmission lines or the like, and to generate various DC voltages from the stepped-down AC voltage (see Patent Document 1).

JP 2015-165732 A

However, as described above, conventional power supply systems on the consumer side generate various DC voltages from high-voltage AC voltages using a plurality of power converters such as transformers and AC/DC converters. , there is a problem that the power conversion efficiency is low.

In addition, when the power supply system is a high-voltage interconnection system having a power generation facility with a power generation capacity of 50 kW or more, such as an industrial solar power generation facility, more transformers, AC/DC converters, etc. are required. Therefore, there is a problem that the system becomes larger.

SUMMARY OF THE INVENTION The present invention has been made in view of the problems described above, and an object of the present invention is to realize a compact and highly efficient power supply system.

A power conversion device according to a representative embodiment of the present invention includes a plurality of conversion units that are connectable to electric wires corresponding to respective phases of a three-phase alternating current and that are star-connected or delta-connected to each other; the conversion unit having a plurality of bridge cells connected in series, the bridge cells having a first input/output terminal and a second input terminal for inputting and outputting an AC voltage; an output terminal, a capacitor, an inverter circuit that switches connections between the first input/output terminal and the second input/output terminal, and the capacitor in response to a control signal from the control unit; a connected first output terminal; and a second output terminal connected to the other end of the capacitor.

According to the power converter according to the present invention, it is possible to realize a compact and highly efficient power supply system.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of the power converter device which concerns on Embodiment 1 of this invention. 4 is a diagram for explaining the operation of bridge cells in the power conversion device according to Embodiment 1; FIG. 4 is a diagram for explaining the operation of bridge cells in the power conversion device according to Embodiment 1; FIG. 4 is a diagram for explaining the operation of bridge cells in the power conversion device according to Embodiment 1; FIG. 4 is a diagram for explaining the operation of bridge cells in the power conversion device according to Embodiment 1; FIG. 4 is a timing chart of voltages output between input and output terminals of bridge cells in the power converter according to Embodiment 1. FIG. 4 is a diagram for explaining the principle of multi-level voltage generation by the conversion unit of the power converter according to the first embodiment; FIG. 3 is a diagram showing an equivalent circuit of a conversion unit of the power conversion device according to Embodiment 1; FIG. It is a figure which shows the structure of the power converter device which concerns on Embodiment 2 of this invention. FIG. 9 is a diagram for explaining the operation of bridge cells in the power conversion device according to Embodiment 2; FIG. 9 is a diagram for explaining the operation of bridge cells in the power conversion device according to Embodiment 2; 9 is a timing chart showing voltages output between input and output terminals of bridge cells in the power conversion device according to Embodiment 2. FIG. It is a figure which shows the structure of the power converter device which concerns on Embodiment 3 of this invention. It is a figure which shows the structure of the power converter device which concerns on Embodiment 4 of this invention.

1. Outline of Embodiment First, an outline of a representative embodiment of the invention disclosed in the present application will be described. In the following description, as an example, reference numerals on the drawings corresponding to constituent elements of the invention are described with parentheses.

[1] A power conversion device according to a representative embodiment of the present invention is connectable to electric wires (20a to 20c) corresponding to each phase (a to b) of a three-phase alternating current, and is connected to each other in a star connection or A plurality of delta-connected converters (1a to 1c) and controllers (2, 2C) for controlling the converters, wherein the converters comprise a plurality of series-connected bridge cells (10_1 to 10_n , 10A_1 to 10A_n,), and the bridge cell includes a first input/output terminal (P1) and a second input/output terminal (P2) for inputting and outputting an alternating voltage, a capacitor (C), and the control an inverter circuit (11) for switching the connection between the first input/output terminal and the second input/output terminal and the capacitor according to control signals (Sa to Sc) from the unit; and an inverter circuit (11) connected to one end of the capacitor. and a second output terminal (P4) connected to the other end of the capacitor.

[2] In the above power conversion device, the capacitors of the bridge cells in the conversion units may have different capacitances.

[3] In the above power converter, the inverter circuit includes a first transistor (T1), a second transistor (T2), and a third transistor (T3) each having a first main electrode, a second main electrode, and a control electrode. , and a fourth transistor (T4), wherein the first main electrode of the first transistor and the second main electrode of the third transistor are connected to the first input/output terminal, and the second main electrode of the first transistor is connected to the first input/output terminal. A main electrode and a second main electrode of the second transistor are connected to the first output terminal, and a first main electrode of the second transistor and a second main electrode of the fourth transistor are connected to the second input/output terminal. A first main electrode of the third transistor and a first main electrode of the fourth transistor are connected to the second output terminal, and control electrodes of the first to fourth transistors are connected to the control electrodes. A signal may be input.

[4] In the above power converter, the inverter circuit includes a first transistor (T1) and a second transistor (T2) each having a first main electrode, a second main electrode, and a control electrode, and the first transistor and the second main electrode of the second transistor are connected to the first input/output terminal, the second main electrode of the first transistor is connected to the first output terminal, and the Even if the first main electrode of the second transistor is connected to the second input/output terminal and the second output terminal, and the control signals are input to the control electrodes of the first and second transistors, respectively. good.

[5] In the above power converter, between the first output terminal and the second output terminal of one bridge cell among the plurality of bridge cells, the above-mentioned output terminal of another bridge cell different from the one bridge cell It may further comprise a DC/DC converter (4) for supplying a DC voltage generated based on the voltage between the first output terminal and said second output terminal.

[6] In the above power conversion device, the DC/DC converter includes a primary coil (L1) having one end connected to the first output terminal of the other bridge cell and the a transformer (TR) having a secondary coil (L2) connected to a second output terminal; a first main electrode connected to the second output terminal of the other bridge cell; A switching transistor (Ts) having a second main electrode connected to the other end and a control electrode to which a signal is input from the control unit (Ts), one end connected to the other end of the secondary coil, and the other end Between a rectifying element (DR) connected to the first output terminal of the one bridge cell and allowing a current to flow from the one end to the other end, and between the other end of the rectifying element and one end of the secondary coil and a connected output capacitor (Cout).

[7] In the above power converter, between the first output terminal of the other bridge cell and the other end of the rectifying element, or between the second output terminal of the other bridge cell and one end of the secondary coil and an output changeover switch (SW) connected to the bridge cell, wherein the control unit detects when the voltage between the first output terminal and the second output terminal of the other bridge cell is within a predetermined range. and turning on the output selector switch, and turning off the output selector switch when the voltage between the first output terminal and the second output terminal of the other bridge cell is outside a predetermined range. , a signal may be applied to a control electrode of the switching transistor to switch the switching transistor.

2. Specific Examples of Embodiments Specific examples of embodiments of the present invention will be described below with reference to the drawings. In the following description, constituent elements common to each embodiment are denoted by the same reference numerals, and repeated descriptions are omitted.

FIG. 1 is a diagram showing the configuration of a power converter according to Embodiment 1 of the present invention.
A power converter 100 shown in FIG. 1 is a device that generates a plurality of DC voltages from an AC voltage. The power converter 100 generates a low DC voltage such as 12V or 48V from a high AC voltage such as 6.6 kV.

The power conversion device 100 receives AC power output from an AC power supply 5 via electric wires 20a to 20c. The AC power supply 5 is power transmission equipment that supplies AC power in a three-phase, three-wire system, and is, for example, a transformer at a substation or a pole transformer. The electric wires 20a to 20c are electric wires for transmitting three-phase (a-phase, b-phase, and c-phase) AC voltages.

The power conversion device 100 includes a plurality of conversion units 1a to 1c. The conversion units 1a to 1c are functional units provided corresponding to each phase of the three-phase AC, and dividing the AC voltage of one corresponding phase into a plurality of voltages.

The converters 1a to 1c are connectable to corresponding electric wires 20a to 20c, respectively, and are star-connected to each other. Specifically, one end of the conversion unit 1a is connected to a wire 20a supplied with an a-phase AC voltage, and one end of the conversion unit 1b is connected to a wire 20b supplied with a b-phase AC voltage. One end of 1c is connected to an electric wire 20c supplied with a c-phase AC voltage. The other ends of the converters 1a to 1c are commonly connected.

In the following description, when the converters 1a to 1c are not distinguished, they may simply be referred to as "converter 1".

As shown in FIG. 1, the power conversion device 100 constitutes a single-type multilevel conversion circuit in which three conversion units (clusters) 1a to 1c are connected in a star shape, that is, a single star MMC (Modular Multilevel Converter). ing.

The power conversion device 100 operates as a reactive power compensation circuit for the three-phase AC power propagating on the electric wires 20a to 20c, and converts AC voltage into DC voltage by the bridge cells 10 of each conversion unit 1a to 1c described later. It also functions as a DC converter.

In general, a single-type multilevel converter circuit as a conventional reactive power compensator is not configured to output a voltage from both ends of the capacitor C of each bridge cell 10, but the power converter according to the present embodiment By providing output terminals P3 and P4 at both ends of the capacitor C of each bridge cell 10, 100 is configured so that the DC voltage of the capacitor C can be output.

Further, in the conventional single-type multi-level converter circuit as a reactive power compensator, the electrostatic capacitances of the capacitors C of the bridge cells 10 are all set to the same value. The device 100 can generate various DC voltages by making the capacitances of the capacitors C of the bridge cells 10 different from each other.
Hereinafter, the conversion unit 1 configuring the power conversion device 100 will be described in detail.

The converter 1 has a plurality of bridge cells 10 connected in series. Specifically, the converter 1a has n (n is an integer equal to or greater than 2) bridge cells 10_1 to 10_n connected in series between the electric wire 20a and the neutral point N. As shown in FIG. Conversion unit 1b has n bridge cells 10_1 to 10_n connected in series between electric wire 20b and neutral point N. As shown in FIG. The converter 1c has n bridge cells 10_1 to 10_n connected in series between the electric wire 20c and the neutral point N. As shown in FIG.

Further, as shown in FIG. 1, a coil L (buffer reactor) may be connected in series to each of the converters 1a to 1c in order to control current and suppress short-circuit current.

The bridge cell 10 is a circuit that generates a predetermined DC voltage from an AC voltage that is input. As shown in FIG. 1, the bridge cell 10_1 includes input/output terminals P1 and P2, output terminals P3 and P4, an inverter circuit 11, and a capacitor C. As shown in FIG. The circuit configurations of the bridge cells 10_1 to 10_n are the same, and FIG. 1 shows the internal configuration of the bridge cell 10_1 as an example.

The input/output terminals P1 and P2 are terminals for inputting and outputting AC power. That is, the input/output terminals P1 and P2 input AC voltages from the electric wires 20a to 20c and output multi-level voltages generated by the plurality of bridge cells 10 to the electric wires 20a to 20c.

The output terminals P3 and P4 are terminals for outputting a DC voltage. A load 3 driven by a DC voltage can be connected to the output terminals P3 and P4.

The capacitor C is an element that stores electric power supplied from the electric wires 20a to 20c through the inverter circuit 11. FIG. One end of the capacitor C is connected to the output terminal P3, and the other end of the capacitor C is connected to the output terminal P4.

The inverter circuit 11 is a circuit that switches connections between the input/output terminals P1 and P2 and the capacitor C according to control signals Sa to Sc from the control section 2 . The inverter circuit 11 includes at least two transistors. Specifically, the inverter circuit 11 includes transistors T1 to T4 forming a full bridge circuit and diodes D1 to D4.

The transistors T1 to T4 are transistors having a current interrupting function, such as IGBTs (Insulated Gate Bipolar Transistors) and GCTs (Gate Commutated Turn-off Thyristors).

The transistors T1 and T3 are connected in series between the output terminals P3 and P4. That is, the emitter electrode as the first main electrode of the transistor T1 is connected to the input/output terminal P1 and the anode electrode of the diode D1. A collector electrode as a second main electrode of the transistor T1 is connected to the output terminal P3 and the cathode electrode of the diode D1. The emitter electrode as the first main electrode of transistor T3 is connected to output terminal P4 and the anode electrode of diode D3. A collector electrode as a second main electrode of the transistor T3 is connected to the input/output terminal P1 and the cathode electrode of the diode D3.

Transistor T2 and transistor T4 are connected in series between output terminals P3 and P4. That is, the emitter electrode as the first main electrode of the transistor T2 is connected to the input/output terminal P2 and the anode electrode of the diode D2. A collector electrode as a second main electrode of the transistor T2 is connected to the output terminal P3 and the cathode electrode of the diode D2. An emitter electrode as a first main electrode of the transistor T4 is connected to the output terminal P4 and the anode electrode of the diode D4. A collector electrode as a second main electrode of the transistor T4 is connected to the input/output terminal P2 and the cathode electrode of the diode D4.

The transistors T1-T4 of the bridge cells 10_1-10_n are controlled to be on/off by control signals Sa-Sc from the controller 2. FIG.

In FIG. 1, reference symbols Sa to Sc represent bundles of control signals for driving the respective transistors T1 to T4 constituting the respective bridge cells 10_1 to 10_n. That is, the reference symbol Sa represents a bundle of control signals (gate drive signals) for driving gate electrodes as control electrodes of the transistors T1 to T4 in the conversion unit 1a. Reference symbol Sb represents a bundle of control signals (gate drive signals) for driving gate electrodes as control electrodes of the transistors T1 to T4 in the conversion unit 1b. Reference symbol Sc represents a bundle of control signals (gate drive signals) for driving gate electrodes as control electrodes of the transistors T1 to T4 in the conversion unit 1c.

2A to 2D are diagrams for explaining the operation of the bridge cell 10 in the power converter according to Embodiment 1. FIG. FIG. 3 is a timing chart of voltages output between the input/output terminals P1 and P2 of the bridge cell 10 in the power converter according to the first embodiment.

By switching the switching patterns of the transistors T1 to T4, the bridge cell 10 charges the capacitor C with AC power input from the electric wires 20a to 20c via the input/output terminals P1 and P2, and reduces the voltage Vc of the capacitor C. Output from the input/output terminals P1 and P2 to the electric wires 20a to 20c.

As switching patterns of the transistors T1 to T4, there are four patterns shown in FIGS. 2A to 2D.

That is, the first switching pattern shown in FIG. 2A is a state in which the transistors T1 and T4 are turned on and the transistors T2 and T3 are turned off. In this case, the input/output terminal P1 is connected to one end of the capacitor C via the transistor T1, and the input/output terminal P2 is connected to the other end of the capacitor C via the transistor T4. As a result, as shown in FIG. 3, the voltage Vo between the input/output terminals P1 and P2 (the voltage at the input/output terminal P1 with respect to the input/output terminal P2) becomes "+Vc".

A second switching pattern shown in FIG. 2B is a state in which the transistors T1 and T2 are turned on and the transistors T3 and T4 are turned off. In this case, the input/output terminal P1 and the input/output terminal P2 are short-circuited through the transistors T1 and T2. As a result, the voltage Vo between the input/output terminals P1 and P2 becomes "0" as shown in FIG.

A third switching pattern shown in FIG. 2C is a state in which the transistors T1 and T2 are turned off and the transistors T3 and T4 are turned on. In this case, the input/output terminal P1 and the input/output terminal P2 are short-circuited through the transistors T3 and T4. As a result, the voltage Vo between the input/output terminals P1 and P2 becomes "0" as shown in FIG.

A fourth switching pattern shown in FIG. 2D is a state in which the transistors T1 and T4 are turned off and the transistors T2 and T3 are turned on. In this case, the input/output terminal P1 is connected to the other end of the capacitor C via the transistor T3, and the input/output terminal P2 is connected to one end of the capacitor C via the transistor T2. As a result, the voltage Vo between the input/output terminals P1 and P2 becomes "-Vc" as shown in FIG.

The control unit 2 switches the switching patterns of the transistors T1 to T4 of the conversion units 1a to 1c according to the control signals Sa to Sc to generate multi-level voltages, which are supplied to the electric wires 20a to 20a through the input/output terminals P1 and P2. 20c side.

FIG. 4 is a diagram for explaining the principle of multi-level voltage generation by the conversion unit 1 of the power converter according to the first embodiment.
For ease of understanding, FIG. 4 shows the waveform of the multi-level voltage Vo generated by the conversion unit 1 when the number of bridge cells 10 included in the conversion unit 1 is two (n=2), Correspondence with the switching pattern of the bridge cell 10 is shown.

In FIG. 4, of the two bridge cells 10, the bridge cell 10 connected to the electric wires 20a to 20c side is called "upper bridge cell 10H", and the bridge cell 10 connected to the neutral point N side is called "lower bridge cell 10L”. Also, the voltage of the input/output terminal P1 of the upper bridge cell 10H with respect to the input/output terminal P2 of the lower bridge cell 10L is expressed as "Vo". Here, the case where the neutral point N is connected to the ground potential is shown as an example.

In FIG. 4, the capacitance of the capacitor C of the upper bridge cell 10H is "3c/4", the capacitance of the capacitor C of the lower bridge cell 10L is "c/4", and the upper bridge cell 10H is held at "Vdc/4", and the voltage of the capacitor C of the lower bridge cell 10L is held at "3Vdc/4".

As shown in FIG. 4, during period t1, the transistors T1 and T4 of the upper bridge cell 10H are turned on and T2 and T3 are turned off, while the transistors T1 and T4 of the lower bridge cell 10L are turned on and T2 and T3 are turned on. turn off. As a result, the voltage Vo becomes "Vdc".

During period t2, the transistors T1 and T4 of the upper bridge cell 10H are turned on and T2 and T4 are turned off, while the transistors T1 and T2 of the lower bridge cell 10L are turned on and T4 and T3 are turned off. As a result, the voltage Vo becomes "Vdc/4".

In period t3, the transistors T1 and T2 of the upper bridge cell 10H are turned on and T3 and T4 are turned off, while the transistors T1 and T2 of the lower bridge cell 10L are turned on and T3 and T4 are turned off. As a result, the voltage Vo becomes "0".

In period t4, the transistors T2 and T3 of the upper bridge cell 10H are turned on and T1 and T4 are turned off, while the transistors T1 and T2 of the lower bridge cell 10L are turned on and T3 and T4 are turned off. As a result, the voltage Vo becomes "-Vdc/4".

In period t5, the transistors T2 and T3 of the upper bridge cell 10H are turned on and T1 and T4 are turned off, while the transistors T2 and T3 of the lower bridge cell 10L are turned on and T1 and T4 are turned off. As a result, the voltage Vo becomes "-Vdc".

As shown in FIG. 4, by combining three switching patterns of the upper bridge cell 10H and the lower bridge cell 10L, the two upper bridge cells 10H and the lower bridge cell 10L generate "5" types (levels) of voltages. Vo can be generated.

A multi-level voltage Vo can also be generated based on the same principle when there are n bridge cells. That is, when the conversion unit 1 is composed of n bridge cells 10, (2n+1) kinds of voltages can be generated.

The converters 1a to 1c supply the above-described multi-level voltage Vo to the corresponding electric wires 20a to 20c via the input/output terminals P1 and P2. At that time, a predetermined DC voltage is generated across the capacitors C of the bridge cells 10 of the converters 1a to 1c. For example, in the case of FIG. 4, a DC voltage of "Vdc/4" is generated across the capacitor C (=3c/4) of the upper bridge cell 10H, and the capacitor C (=c/4) of the lower bridge cell 10L is generated. ), a DC voltage of “3Vdc/4” is generated across the terminals.

Therefore, in the power conversion device 100 according to Embodiment 1, by providing the output terminals P3 and P4 at both ends of the capacitor C of each bridge cell 10, it becomes possible to take out the DC voltage from the output terminals P3 and P4. .

Here, as shown in FIG. 4, the capacitances of the capacitors C of the bridge cells 10 in one conversion unit 1a to 1c may be different from each other. According to this, the DC voltage generated across the capacitor C of each bridge cell 10 (between the output terminals P3 and P4) can be made different from each other, and a plurality of DC voltages can be generated in one converter 1a to 1c. It becomes possible to

For example, when DC voltages of 12V, 48V, and 72V are generated by the conversion unit 1a having three bridge cells 10, the capacitor C1 of the bridge cell 10 that generates 12V is set to "c", and the capacitor C1 of the bridge cell 10 that generates 48V is set to "c". The capacitor C2 should be "4c" and the capacitor C3 of the bridge cell 10 generating 72V should be "6c".

Thus, by appropriately setting the capacitance of the capacitor C of each bridge cell 10, a desired DC voltage can be obtained.
On the other hand, in order to prevent the three-phase AC power from being adversely affected by the electric wires 20a to 20c, the voltages Vo output via the input/output terminals P1 and P2 of the converters 1a to 1c must be equal to each other. This point will be described in detail with reference to FIG.

FIG. 5 is a diagram showing an equivalent circuit of the converters 1a to 1c.
As shown in the figure, each conversion unit 1a to 1c can be regarded as a circuit in which a plurality of capacitors and coils L are connected in series.

As described above, the output voltages of the converters 1a to 1c, that is, the voltage Van between the terminal a and the terminal N, the voltage Vbn between the terminal b and the terminal N, and the voltage Vbn between the terminal c and the terminal N must be equal to each other. Therefore, the capacitors of the bridge cells 10 in the conversion units 1a to 1c must satisfy the following formula (1).

As a result, the converters 1a to 1c can generate various DC voltages while suppressing adverse effects on the three-phase AC power on the electric wires 20a to 20c.

In practice, the capacitor C of each bridge cell 10 is charged and discharged when energized, and if the capacitor C is left as it is, the non-uniformity of the capacitor voltage will increase and the waveform of the voltage Vo will be distorted. Therefore, balance control is required to keep the capacitor voltage of each bridge cell 10 constant and uniform. Specifically, power is exchanged between the converters 1a to 1c of each phase so that the arithmetic mean of the capacitor voltage of the capacitor C is balanced.

For example, when the converters 1a to 1c are star-connected, the balance between the converters 1a to 1c is maintained by superimposing the zero-phase voltage v0 on the voltage command values of the converters 1a to 1c. Since the AC voltage and the AC current of each of the converters 1a to 1c are normally orthogonal, no active power is generated between the converters 1a to 1c. In this state, when the zero-phase voltage v0 is superimposed on the voltage command values of the converters 1a to 1c, the phase relationship between the AC voltage and the AC current changes, and active power is exchanged between the converters 1a to 1c. . By using this, it is possible to balance the arithmetic mean of the capacitor voltage of the capacitor C among the converters 1a to 1c of each phase.

As described above, the power conversion device 100 according to Embodiment 1 constitutes a single-type multilevel conversion circuit including a plurality of bridge cells 10, and the output terminals P3 and P4 are connected to both ends of the capacitor C of each bridge cell 10. is provided.
According to this, by appropriately switching the transistors T1 to T4 as switches constituting each bridge cell 10, the conversion unit 1 operates as a static var compensator (STATCOM) and responds to the input AC voltage. Therefore, it can operate as an AC/DC converter that charges the capacitor C of each bridge cell 10 and outputs the DC voltage across the capacitor C from the output terminals P3 and P4.

In the power conversion device 100 according to Embodiment 1, by making the capacitances of the capacitors C of the bridge cells 10 different, the voltage generated in each capacitor C can be made different. Thereby, the power converter 100 can generate a plurality of different DC voltages from one AC voltage.

Thus, according to the power conversion device 100 according to Embodiment 1, instead of using a plurality of AC/DC conversion circuits and DC/DC converters as in the conventional power supply system, Since it is possible to generate multiple DC voltages, it is possible to suppress the decline in power conversion efficiency compared to conventional power supply systems, and to suppress the increase in the scale of the system. becomes.

Therefore, according to the power conversion device 100 according to Embodiment 1, it is possible to realize a smaller and more efficient power conversion system. In addition, since the power conversion device 100 generates a plurality of DC voltages by each bridge cell 10 that constitutes a single-type multilevel conversion circuit, generation of harmonics can be suppressed as compared with the conventional power supply system. This makes it possible to suppress noise generated from the power conversion device 100 and prevent malfunction of other external devices due to noise.

<<Embodiment 2>>
FIG. 6 is a diagram showing the configuration of a power converter according to Embodiment 2 of the present invention.
A power conversion device 100A according to Embodiment 2 differs from the power conversion device according to Embodiment 1 in that the bridge cells are half-bridge circuits, and in other respects, the power conversion device 100A according to Embodiment 1 is different. Similar to 100.

As shown in FIG. 6, the inverter circuit 11A of the bridge cells 10A_1 to 10A_n forming the conversion units 1Aa to 1Ac in the power converter 100A includes transistors T1 and T2 forming a half bridge circuit and diodes D1 and D2. contains.

Transistor T1 and transistor T2 are connected in series between output terminals P3 and P4. That is, the emitter electrode as the first main electrode of the transistor T1 is connected to the input/output terminal P1 and the anode electrode of the diode D1. A collector electrode as a second main electrode of the transistor T1 is connected to the output terminal P3 and the cathode electrode of the diode D1. An emitter electrode as a first main electrode of the transistor T2 is connected to the input/output terminal P2, the output terminal P4 and the anode electrode of the diode D2. A collector electrode as a second main electrode of the transistor T2 is connected to the input/output terminal P1 and the cathode electrode of the diode D2.

The transistors T1 and T2 of the bridge cells 10A_1 to 10A_n are controlled to be on/off by control signals Sa to Sc from the control unit 2, like the bridge cell 10 according to the first embodiment.

7A and 7B are diagrams for explaining the operation of the bridge cell 10A in the power conversion device 100A according to Embodiment 2. FIG. FIG. 8 is a timing chart showing voltages output between the input/output terminals P1 and P2 of the bridge cell 10A in the power converter 100A according to the second embodiment.

By switching the switching patterns of the transistors T1 and T2, the bridge cell 10A charges the capacitor C with AC power input from the wires 20a to 20c via the input/output terminals P1 and P2, and reduces the voltage Vc of the capacitor C. Output from the input/output terminals P1 and P2 to the electric wires 20a to 20c.

As switching patterns of the transistors T1 and T2 of the bridge cell 10A, there are two patterns shown in FIGS. 7A and 7B.

That is, the first switching pattern shown in FIG. 7A is a state in which the transistor T1 is turned on and the transistor T2 is turned off. In this case, the input/output terminal P1 is connected to one end of the capacitor C, and the input/output terminal P2 is connected to the other end of the capacitor C. As a result, the voltage Vo between the input/output terminals P1 and P2 becomes "+Vc" as shown in FIG.

The second switching pattern shown in FIG. 7B is a state in which transistor T1 is turned off and transistor T2 is turned on. In this case, the input/output terminals P1 and P2 are short-circuited. As a result, the voltage Vo between the input/output terminals P1 and P2 becomes "0" as shown in FIG.

The power conversion device 100A switches the switching patterns of the transistors T1 and T2 of the conversion units 1Aa to 1Ac according to the control signals Sa to Sc, thereby generating a multi-level voltage according to the same principle as the power conversion device 100 according to the first embodiment. Generate Vo. The generated multi-level voltage Vo is output to the electric wires 20a to 20c through the input/output terminals P1 and P2. At this time, the DC voltage across the capacitor C of each bridge cell 10A is output from the output terminals P3 and P4.

Here, by making the capacitances of the capacitors C of the bridge cells 10A in one conversion unit 1Aa to 1Ac different from each other, it is possible to generate a plurality of DC voltages in one conversion unit 1Aa to 1Ac. Become.

As described above, according to the power conversion device 100A according to the second embodiment, as with the power conversion device 100 according to the first embodiment, it is possible to generate a plurality of DC voltages from one AC power. As compared with the power supply system of the above, it is possible to suppress a decrease in power conversion efficiency and to suppress an increase in the scale of the system.

<<Embodiment 3>>
FIG. 9 is a diagram showing the configuration of a power converter according to Embodiment 3 of the present invention.
A power conversion device 100B according to Embodiment 3 differs from the power conversion device according to Embodiment 1 in that conversion units 1a to 1c are connected to each other by delta connection. It is the same as the power conversion device 100 according to the first form.

As shown in FIG. 9, the converters 1a to 1c are connectable to corresponding electric wires 20a to 20c, respectively, and are delta-connected to each other. Specifically, one end of the conversion unit 1a is connected to a wire 20a supplied with an a-phase AC voltage, and the other end of the conversion unit 1a is connected to a wire 20b supplied with a b-phase AC voltage. . One end of the conversion portion 1b is connected to a wire 20b to which a b-phase AC voltage is supplied, and the other end of the conversion portion 1b is connected to a wire 20c to which a c-phase AC voltage is supplied. One end of the conversion portion 1c is connected to a wire 20c to which a c-phase AC voltage is supplied, and the other end of the conversion portion 1c is connected to a wire 20a to which a-phase AC voltage is supplied.

The power conversion device 100B constitutes a single-type multilevel conversion circuit in which three conversion units (clusters) 1a to 1c are connected in a delta configuration, that is, a single delta MMC. As with the power converter 100 according to Embodiment 1, the power converter 100B operates as a reactive power compensation circuit for the three-phase AC power propagating through the electric wires 20a to 20c, and the bridge cells of the converters 1a to 1c. 10 also functions as an AC/DC converter that converts AC voltage to DC voltage.

That is, the power conversion device 100B switches the switching patterns of the transistors T1 to T4 of the bridge cells 10 in the conversion units 1a to 1c according to the control signals Sa to Sc, thereby performing the same operation as the power conversion device 100 according to the first embodiment. generates a multi-level voltage Vo according to the principle of , and outputs it to the electric wires 20a to 20c via the input/output terminals P1 and P2, and outputs the DC voltage across the capacitor C of each bridge cell 10 to the output terminals P3 and P4. Output from

As described above, according to the power conversion device 100B according to the third embodiment, as with the power conversion device 100 according to the first embodiment, it is possible to generate a plurality of DC voltages from one AC power. As compared with the power supply system of the above, it is possible to suppress a decrease in power conversion efficiency and to suppress an increase in the scale of the system.

<<Embodiment 4>>
FIG. 10 is a diagram showing the configuration of a power converter according to Embodiment 4 of the present invention.
A power conversion device 100C according to Embodiment 4 differs from the power conversion device according to Embodiment 1 in that DC voltage can be supplied from a plurality of bridge cells to one load. , is the same as the power converter 100 according to the first embodiment.

As shown in FIG. 10, the power conversion device 100C includes a DC/DC converter 4 in addition to the converters 1a to 1c corresponding to the phases described above. Specifically, the power converter 10C can supply power from one bridge cell 10 and power from another bridge cell 10 via the DC/DC converter 4 to a predetermined load 3C. It's becoming

More specifically, the power converter 10C has a DC/DC converter 4 and an output switching switch SW.

The DC/DC converter 4 connects an output terminal P3 and an output terminal of another bridge cell different from the one bridge cell between the output terminal P3 and the output terminal P4 of one bridge cell among the plurality of bridge cells 10. A DC voltage generated based on the voltage across P4 is supplied.

In the present embodiment, an example will be described in which the one bridge cell 10 is defined as "the bridge cell 10_n of the conversion unit 1b" and the other bridge cell 10 is defined as the "bridge cell 10_n of the conversion unit 1a". Note that the one bridge cell 10 and the other bridge cell 10 are not limited to the above example, and may be any two bridge cells 10 that constitute the power conversion device 10C.

The DC/DC converter 4 is, for example, an insulated DC/DC converter. For example, the DC/DC converter 4 has a transformer TR, a switching transistor Ts, a rectifying element DR, and an output capacitor Cout for forming a flyback converter.

Transformer TR includes a primary coil L1 and a secondary coil L2.
The switching transistor Ts is, for example, a field effect transistor having a gate electrode as a control electrode, a source electrode as a first main electrode, and a drain electrode as a second main electrode. The switching transistor Ts performs a switching operation when a signal is input to the gate electrode from the control section 2C.
The rectifying element DR is an element that allows current to flow in one direction, such as a diode. Note that the rectifying element DR may be a rectifying transistor whose on/off is appropriately controlled.

One end of the primary coil L1 of the transformer TR is connected to the output terminal P3 of the bridge cell 10_n of the conversion unit 1a. The other end of the primary coil L1 of the transformer TR is connected to the drain electrode of the switching transistor Ts.

One end of the secondary coil L2 of the transformer TR is connected to the output terminal P4 of the bridge cell 10_n of the conversion unit 1b. The other end of the secondary coil L2 is connected to the anode electrode of the rectifier DR.

The rectifying element DR has one end (anode electrode) connected to the other end of the secondary coil L2, and the other end (cathode electrode) connected to the output terminal P3 of the bridge cell 10_n of the conversion unit 1b. Specifically, the cathode electrode of the rectifying element DR is connected to the bridge cell 10_n of the conversion unit 1b via the output changeover switch SW.

The output capacitor Cout is connected between the other end (cathode electrode) of the rectifier DR and one end of the secondary coil L2.

The output switching switch SW has a function of switching between power supply from the bridge cell 10_n of the conversion unit 1b and power supply from the bridge cell 10_n of the conversion unit 1a via the DC/DC converter 4 to the predetermined load 3C. Department.

For example, the output switching switch SW is connected between the output terminal P3 of the bridge cell 10_n of the conversion unit 1b and the cathode of the rectifying element DR. The output switching switch SW may be connected between the output terminal P4 of the bridge cell 10_n and one end of the secondary coil L2.

The power converter 100C according to the fourth embodiment normally supplies a DC voltage from the bridge cell 10_n of the conversion unit 1b to the load 3C. On the other hand, when the bridge cell 10_n of the conversion unit 1b fails for some reason and it becomes impossible to supply an appropriate DC voltage to the load 3C, the power conversion device 100C converts the bridge cell 10_n of the conversion unit 1a to the DC voltage. /DC converter 4 to supply a DC voltage to the load 3C.

For example, the control unit 2C monitors the voltage between the output terminals P3 and P4 of the bridge cell 10_n of the conversion unit 1b, determines whether the bridge cell 10_n is outputting an appropriate DC voltage, and to switch the power supply source to the load 3C.

That is, when the voltage Vox between the output terminal P3 and the output terminal P4 of the bridge cell 10_n of the conversion unit 1b is within a predetermined range, the control unit 2C turns on the output switch SW and switches the switching transistor Ts. turn off. As a result, when the bridge cell 10_n of the conversion unit 1b is operating normally, power is supplied to the load 3C by the bridge cell 10_n of the conversion unit 1b.

On the other hand, when the voltage Vox between the output terminal P3 and the output terminal P4 of the bridge cell 10_n of the conversion unit 1b is outside the predetermined range, the control unit 2C turns off the output switch SW and switches the switching transistor A signal is applied to the gate electrode of Ts to switch the switching transistor Ts. Specifically, the control unit 2C adjusts the voltage between the output terminals P3 and P4 of the bridge cell 10_n of the conversion unit 1b (the voltage across the load 3C) to a desired value with the switch SW turned off. , the transistor Ts is switched by a PWM (Pulse Width Modulation) signal with an appropriate duty ratio.
As a result, when the bridge cell 10_n of the conversion unit 1b is not operating normally, power is supplied from the bridge cell 10_n of the conversion unit 1a to the load 3C via the DC/DC converter 4 .

As described above, in the power conversion device 100C according to the fourth embodiment, at least one other bridge cell 10 is connected via the DC/DC converter 4 to the load 3C receiving a DC voltage supply from one bridge cell 10. connected.

According to this, even if one bridge cell 10 that normally supplies power to the load 3C fails, power is supplied from the other bridge cell 10 to the load 3C via the DC/DC converter 4. , the reliability of the power conversion device 100C can be improved.

Further, the DC/DC converter 4 is realized by an isolated flyback converter using a transformer TR, thereby electrically isolating the bridge cells 10 of the conversion unit 1a and the bridge cells 10 of the conversion unit 1b. Therefore, it is possible to further improve the reliability of the power converter 100C.

Further, in the power conversion device 100C according to the fourth embodiment, the control unit 2C determines whether or not the voltage Vox of the bridge cell 10_n of the conversion unit 1b to which power is normally supplied is within a predetermined range. , the output selector switch SW and the DC/DC converter 4 are controlled based on the determination result.
According to this, it is possible to appropriately determine whether or not the bridge cell 10_n operates normally with respect to the load 3C, and then appropriately switch the power supply source to the load 3C. It is possible to further improve the performance.

<<Expansion of Embodiment>>
Although the invention made by the inventors of the present invention has been specifically described above based on the embodiments, it goes without saying that the invention is not limited thereto, and that various modifications can be made without departing from the gist of the invention. stomach.

For example, in the third embodiment, the inverter circuit 11 forming the delta-connected converters 1a to 1c is a full bridge circuit, but the present invention is not limited to this. For example, like the power converter 100A according to the second embodiment, the inverter circuit 11 may be a half bridge circuit.

Further, in the above-described fourth embodiment, the case where the DC/DC converter is connected between the bridge cells 10 of the different conversion units 1a and 1b is illustrated, but the present invention is not limited to this. A DC converter may be connected. For example, in FIG. 10, the bridge cell 10_n of the conversion unit 1a may be connected via the insulated DC/DC converter 4 to the load 3 connected to the bridge cell 10_2 of the conversion unit 1a.

Further, in the above-described fourth embodiment, the case of adopting a redundant configuration including the DC/DC converter 4 in the power conversion device 100 according to the first embodiment was illustrated, but the present invention is not limited to this, and the power according to the second embodiment Similarly, a redundant configuration including the DC/DC converter 4 can be adopted for the converter 100A and the power converter 100B according to the third embodiment.

In the above embodiment, each of the conversion units 1a to 1c has n bridge cells 10_1 to 10_n, respectively. can be different.

1, 1a to 1c, 1Aa to 1Ac ... conversion section, 2, 2C ... control section, 3, 3C ... load, 4 ... DC/DC converter, 5 ... AC power supply, 10, 10_1 to 10_n, 10A, 10A_1 to 10A_n, 10C, 10H, 10L... Bridge cell, 11, 11A... Inverter circuit, 20a, 20b, 20c... Wire, 100, 100A to 100C... Power converter, C... Capacitor, Cout... Output capacitor, D1 to D4... Diode, DR Rectifying element L Coil L1 Primary coil L2 Secondary coil P1, P2 Input/output terminals P3, P4 Output terminals Sa to Sc Control signals T1 to T4 Transistors.

Claims (6)

A plurality of conversion units that are connectable to electric wires corresponding to each phase of a three-phase alternating current and are star-connected or delta-connected with each other, and a control unit that controls the conversion units,
The conversion unit
having multiple bridge cells connected in series,
The bridge cell is
a first input/output terminal and a second input/output terminal for inputting and outputting an alternating voltage;
a capacitor;
an inverter circuit that switches connection between the first input/output terminal and the second input/output terminal and the capacitor in response to a control signal from the control unit;
a first output terminal connected to one end of the capacitor;
a second output terminal connected to the other end of the capacitor ;
Between the first output terminal and the second output terminal of one bridge cell among the plurality of bridge cells, the first output terminal and the second output of another bridge cell different from the one bridge cell Further comprising a DC/DC converter for supplying a DC voltage generated based on the voltage across the terminals
Power converter. The power converter according to claim 1,
A power conversion device, wherein the capacitors of the bridge cells in the conversion units have different electrostatic capacities. In the power conversion device according to claim 1 or 2,
The inverter circuit is
a first transistor, a second transistor, a third transistor, and a fourth transistor having a first main electrode, a second main electrode, and a control electrode, respectively;
a first main electrode of the first transistor and a second main electrode of the third transistor are connected to the first input/output terminal;
a second main electrode of the first transistor and a second main electrode of the second transistor are connected to the first output terminal;
a first main electrode of the second transistor and a second main electrode of the fourth transistor are connected to the second input/output terminal;
a first main electrode of the third transistor and a first main electrode of the fourth transistor are connected to the second output terminal;
A power converter, wherein the control signal is input to each control electrode of the first to fourth transistors. In the power converter according to claim 1 or 2,
The inverter circuit is
a first transistor and a second transistor having a first main electrode, a second main electrode and a control electrode, respectively;
the first main electrode of the first transistor and the second main electrode of the second transistor are connected to the first input/output terminal;
the second main electrode of the first transistor is connected to the first output terminal;
the first main electrode of the second transistor is connected to the second input/output terminal and the second output terminal;
A power converter, wherein the control signals are input to the control electrodes of the first and second transistors, respectively. In the power converter according to claim 1 ,
The DC/DC converter is
a transformer having a primary coil having one end connected to the first output terminal of the other bridge cell and a secondary coil having one end connected to the second output terminal of the one bridge cell;
a first main electrode connected to the second output terminal of the other bridge cell; a second main electrode connected to the other end of the primary coil; and a control electrode to which a signal is input from the control section. a switching transistor having
a rectifying element having one end connected to the other end of the secondary coil, the other end connected to the first output terminal of the one bridge cell, and allowing a current to flow from the one end to the other end;
an output capacitor connected between the other end of the rectifying element and one end of the secondary coil;
A power converter comprising: In the power converter according to claim 5 ,
an output selector switch connected between the first output terminal of the other bridge cell and the other end of the rectifying element or between the second output terminal of the other bridge cell and one end of the secondary coil; have
When the voltage between the first output terminal and the second output terminal of the other bridge cell is within a predetermined range, the control unit turns on the output changeover switch to control the other bridge cell. When the voltage between the first output terminal and the second output terminal of is out of a predetermined range, the output changeover switch is turned off and a signal is supplied to the control electrode of the switching transistor to A power conversion device characterized by switching a switching transistor.

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