JP2020078210A - Power conversion apparatus - Google Patents

Abstract

To provide a power conversion apparatus capable of desired power conversion.SOLUTION: A power conversion apparatus comprises first and second DC capacitors C1, C2, a first leg L1 connected in parallel with the first capacitor C1, a second leg L2 connected in parallel with the second capacitor C2, a positive side arm A1 including multiple unit converters C connected in series between the output terminal of the first leg L1 and an AC terminal for connection with an AC load, a negative side arm A2 including multiple unit converters C connected in series between the output terminal of the second leg L2 and the AC terminal, and a control circuit CNT calculating the sum of a first operation amount current value for making the voltage average value of a cell capacitor CA of the unit converter C a prescribed value, and a second operation amount current value for making the voltage average value of the first and second DC capacitors C1, C2 prescribed values, and then calculating an AC current component Iac from the detection values of current Ip and current In, and generating a gate signal so that the AC current component Iac follows a command value including the sum.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a power conversion device.

  Conventionally, a three-phase two-level converter has been applied to a power conversion device that converts AC power into DC power or DC power into AC power. The three-phase / two-level converter can be configured by the minimum required six semiconductor switching elements in configuring a power conversion device that converts DC power into three-phase AC power and outputs the power. It is possible to realize downsizing and cost reduction.

  On the other hand, the output voltage waveform is obtained by performing PWM (pulse width modulation) for binary switching of + Vdc / 2 and −Vdc / 2 for each phase when the input DC voltage is Vdc, for example. , It has a pseudo-generated AC waveform, and probably contains harmonic voltage caused by switching. Therefore, measures are taken to reduce harmonics due to switching by inserting a filter composed of a reactor and a capacitor in the output path of the three-phase AC power of the power converter.

  However, when connecting the power system and the power converter, in order to reduce the harmonic components flowing out to the power system to a level at which other devices are not adversely affected, the filter capacity for reducing the harmonics is increased. Therefore, the cost and the weight of the power conversion device are increased.

  By increasing the switching frequency, it is possible to downsize the filter for reducing harmonics, but by increasing the switching frequency, the loss accompanying switching increases and not only the power loss increases. Therefore, it becomes necessary to improve the cooling performance of the power converter. It may be difficult to install a cooling fan in a power conversion device used outdoors or the like. In that case, it is difficult to reduce the size of the entire power conversion device because the cooling unit is increased in size.

On the other hand, it is a power converter having a configuration in which unit converters having capacitors and semiconductor switches are connected in multiple stages, and is a modular multilevel conversion capable of converting a high voltage equivalent to a power system voltage or a distribution system voltage. Research and development of a container (MMC: Modular Multilevel Converter) is in progress.
When this power converter is put into practical use, the output voltage waveform and the output current waveform become closer to a sine wave waveform due to the multi-leveling, so that there is an advantage that a harmonic filter is unnecessary. Furthermore, by shifting the switching timings of the plurality of unit converters from each other, it is possible to obtain the same output waveform as in the conventional case at a low switching frequency, and thus it is possible to reduce switching loss.

  As a circuit for reducing the number of MMC unit converters, for example, a neutral point clamped modular multilevel converter (hereinafter referred to as NPC-MMC (Neutral Point Clamped Modular Multilevel Converter)) has been proposed. The NPC-MMC is equipped with a high-voltage chopper that divides the voltage on the DC side with two capacitors and that includes a leg composed of a semiconductor switch connected in parallel with each capacitor, and has a multi-stage unit converter at the AC terminal of the high-voltage chopper. Connected and configured. With this configuration, the number of unit converters can be reduced to about half as compared with the conventional MMC.

JP, 2005-146692, A

Makoto Hagiwara, Yasufumi Akagi, “PWM Control Method and Operation Verification of Modular Multilevel Converter (MMC)”, IEEJ Transactions, Volume 128, No. 7, 2008

  As described above, the NPC-MMC has two DC capacitors on the DC side. The DC capacitor needs to maintain the voltage of the two DC capacitors because it is discharged when the power is supplied to the DC side or due to leakage current of the capacitor itself.

  Further, in the NPC-MMC, when the DC side is connected to the voltage source, the electric power discharged from the DC capacitor is supplied from the voltage source. However, when a current source or load, or a control voltage source controlled to operate the current source is connected to the DC side, the voltage supplied to the DC side decreases as the DC capacitor discharges, and the desired power conversion There was a possibility that it could not operate.

  Furthermore, in order to obtain output power with few harmonics, the cell capacitor included in the unit converter must also maintain the voltage. That is, it is required to maintain the voltage of the DC capacitor and the cell capacitor at the same time.

  It is an object of the embodiments of the present invention to provide a power conversion device capable of suppressing harmonics and loss due to switching and capable of performing desired power conversion.

  The power converter according to the embodiment includes a first DC capacitor, a second DC capacitor connected in series with the first DC capacitor, a first switching leg connected in parallel with the first DC capacitor, and the second DC capacitor. A second switching leg connected in parallel with the capacitor; a positive arm including a plurality of unit converters connected in series between an output terminal of the first switching leg and an AC terminal connected to an AC load; A negative side arm including a plurality of unit converters connected in series between the output terminals of the two switching legs and the AC terminal, and an average value of voltages of cell capacitors included in the unit converters are set to predetermined values. The sum of a first feedback manipulated variable current value and a second feedback manipulated variable current value having an average value of the voltages of the first DC capacitor and the second DC capacitor as a predetermined value is calculated, and the positive arm From the detected value of the current flowing in the negative side arm and the current flowing in the negative side arm, the AC current component flowing in the AC terminal is calculated, and the first switching leg so that the AC current component follows the command value including the sum. And a control circuit that generates a gate signal for the second switching leg and the plurality of unit converters.

FIG. 1 is a diagram schematically showing a configuration example of the power conversion device according to the first embodiment. FIG. 2 is a diagram schematically showing a configuration example of a unit converter of the power conversion device shown in FIG. FIG. 3 is a diagram for explaining an example of the operation of the power conversion device according to the first embodiment. FIG. 4 is a diagram schematically illustrating a configuration example of the control circuit of the power conversion device according to the first embodiment. FIG. 5: is a figure which shows schematically one structural example of the control circuit of the power converter device of 2nd Embodiment. FIG. 6 is a diagram schematically showing a configuration example of a control circuit of the power conversion device according to the third embodiment. FIG. 7: is a figure which shows schematically one structural example of the control circuit of the power converter device of 4th Embodiment.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing a configuration example of the power conversion device according to the first embodiment.
The power conversion device 20 of the present embodiment includes a positive side DC terminal TA, a negative side DC terminal TB, and three-phase AC terminals TU, TV, TW, and an AC load 10 and a DC load (not shown). Can be connected between. The DC load is, for example, a solar power generation system, a DC power supply such as a UPS (Uninterruptible Power Supply), a battery, or another power conversion device.

  The power conversion device 20 includes a first DC capacitor C1, a second DC capacitor C2, first switching legs L1U, L1V, L1W, second switching legs L2U, L2V, L2W, and positive arms A1U, A1V, A1W. And first buffer reactors LAU, LAV, LAW, negative side arms A2U, A2V, A2W, second buffer reactors LBU, LBV, LBW, instrument transformer 22, and control device CNT. ..

  The first DC capacitor C1 and the second DC capacitor C2 are connected in series between the positive side DC terminal TA and the negative side DC terminal TB. There is a neutral potential between the first DC capacitor C1 and the second DC capacitor.

  The first switching legs L1U, L1V, L1W are connected in parallel with the first DC capacitor C1. The second switching legs L2U, L2V, L2W are connected in parallel with the second DC capacitor C2.

  In the power conversion device 20 of the present embodiment, the first DC capacitor C1 and the second DC capacitor C2 are shared by three phases, but two DC capacitors may be connected in parallel for each of the three phases. Good.

Each of the first switching legs L1U, L1V, L1W includes a first switching element S1U, S1V, S1W and a second switching element S2U, S2V, S2W.
Each of the second switching legs L2U, L2V, L2W includes a third switching element S3U, S3V, S3W and a fourth switching element S4U, S4V, S4W.

  The first switching elements S1U, S1V, S1W and the second switching elements S2U, S2V, S2W are connected in series between the positive side DC terminal TA and the neutral point potential. That is, the first switching elements S1U, S1V, S1W and the second switching elements S2U, S2V, S2W are connected in parallel with the first DC capacitor C1.

  The third switching elements S3U, S3V, S3W and the fourth switching elements S4U, S4V, S4W are connected in series between the negative side DC terminal TB and the neutral point potential. That is, the third switching elements S3U, S3V, S3W and the fourth switching elements S4U, S4V, S4W are connected in parallel with the second DC capacitor C2.

  The first switching elements S1U, S1V, S1W, the second switching elements S2U, S2V, S2W, the third switching elements S3U, S3V, S3W, and the fourth switching elements S4U, S4V, S4W are, for example, IGBTs (insulated). It is a self-extinguishing element such as a gate bipolar transistor) or a MOSFET (metal-oxide-semiconductor field-effect transistor).

Each of the positive side arms A1U, A1V, A1W and the negative side arms A2U, A2V, A2W includes a plurality of unit converters C connected in series.
The positive side arms A1U, A1V, A1W and the negative side arms A2U, A2V, A2W are the first output terminals O1U between the first switching elements S1U, S1V, S1W and the second switching elements S2U, S2V, S2W. First buffer reactors LAU, LAV between O1V, O1W and second output terminals O2U, O2V, O2W between third switching elements S3U, S3V, S3W and fourth switching elements S4U, S4V, S4W. , LAW, and second buffer reactors LBU, LBV, LBW are connected in series.

  In the example of the power conversion device 20 shown in FIG. 1, the positive arms A1U, A1V, A1W and the negative arms A2U, A2V, A2W are the first buffer reactors LAU, LAV, LAW, and the second buffer reactor LBU. , LBV, LBW, but may be connected, for example, via a coupling reactor or a transformer, or may be directly connected.

  Positive side arms A1U, A1V, A1W and negative side arms A2U, A2V, A2W are AC loads at AC terminals TU, TV, TW between buffer reactors LAU, LAV, LAW and buffer reactors LBU, LBV, LBW. It is electrically connected to 10.

The instrument transformer 22 converts the AC voltage of the AC line connecting the AC load 10 and the power conversion device 20 into a voltage that can be used by the control circuit CNT, and outputs the voltage to the control circuit CNT.
The control circuit CNT controls the first switching elements S1U, S1V, S1W and the second switching elements S2U, S2V so that the output power of the power conversion device 20 becomes a predetermined value according to a command value supplied from the outside. S2W, third switching elements S3U, S3V, S3W, fourth switching elements S4U, S4V, S4W, positive side arms A1U, A1V, A1W, and negative side arms A2U, A2V, A2W are controlled. ..

  The control circuit CNT includes, for example, at least one processor such as a CPU (central processing unit) and an MPU (micro processing unit), and a memory in which a program executed by the processor is recorded, and is operated by software. May be configured as. The configuration of the control circuit CNT will be described later in detail with reference to the drawings.

FIG. 2 is a diagram schematically showing a configuration example of a unit converter of the power conversion device shown in FIG.
The unit converter C includes a first cell switching element SA, a second cell switching element SB, a cell capacitor CA, and a capacitor voltage detection circuit VS.

  The first cell switching element SA and the second cell switching element SB are connected in series. The first cell switching element SA and the second cell switching element SB are, for example, self-extinguishing elements such as IGBT (insulated gate bipolar transistor) and MOSFET (metal-oxide-semiconductor field-effect transistor).

The cell capacitor CA is connected in parallel with the first cell switching element SA and the second cell switching element SB.
The unit converter C is the source of the second cell switching element SB of the unit converter C connected to the high potential side between the first cell switching element SA and the second cell switching element SB (first terminal T1). (Second terminal T2) is electrically connected. The first terminal T1 of the unit converter C on the highest potential side is electrically connected to the first output terminals O1U, O1V, O1W. The second terminal T2 of the unit converter C on the lowest potential side is electrically connected to the second output terminals O2U, O2V, O2W.

The capacitor voltage detection circuit VS detects the voltage of the cell capacitor CA and outputs the voltage value (or voltage equivalent value) to the control circuit CNT.
When the voltage of the cell capacitor CA is Vc, when the first cell switching element SA is turned on and the second cell switching element SB is turned off, the output of the unit converter C becomes Vc [V], and the first cell switching element SA Is turned off and the second cell switching element SB is turned on, the output of the unit converter C becomes 0 [V].

  The configuration of the unit converter C is not limited to that shown in FIG. 2, and any other configuration may be used as long as it has a switching element and a cell capacitor and can switch the output voltage in the switch state. .. For example, the unit converter C may be a full bridge circuit including four switching elements and a cell capacitor.

Next, an example of the operation of the power conversion device 20 of this embodiment will be described.
FIG. 3 is a diagram for explaining an example of the operation of the power conversion device according to the first embodiment.
Here, the AC phase voltage Vac output by the power conversion device 20, the output voltage Vp of the first switching legs L1U, L1V, L1W, the output voltage Vn of the second switching legs L2U, L2V, L2W, the positive arms A1U, A1V, The output voltage Varmp of A1W, the output voltage Varmn of the negative arms A2U, A2V, A2W, the current Ip of the positive arms A1U, A1V, A1W, and the current In of the negative arms A2U, A2V, A2W are chronologically arranged. Shows an example of the change.

  In addition, Iac is a current (or an alternating current component) of the AC terminals TU, TV, TW, and Vdc is a DC voltage (a voltage between the positive DC terminal TA and the negative DC terminal TB). , Idc are currents on the DC side.

  The first switching elements S1U, S1V, S1W and the third switching elements S3U, S3V, S3W are turned on in a 1/2 cycle (0 <ωt <π) in which the output AC voltage Vac of the power conversion device 20 is positive, It turns off in a 1/2 cycle (π <ωt <2π) in which the output AC voltage Vac is negative.

  As a result, the output voltage Vp of the first switching legs L1U, L1V, L1W becomes equal to the voltage of the first DC capacitor C1 and the output AC voltage Vac becomes negative in the 1/2 cycle when the output AC voltage Vac becomes positive. It becomes zero in 1/2 cycle.

  The second switching elements S2U, S2V, S2W and the fourth switching elements S4U, S4V, S4W are turned on in a 1/2 cycle when the output AC voltage Vac of the power conversion device 20 is negative, and the output AC voltage Vac is positive. It turns off in a certain 1/2 cycle.

  As a result, the output voltage Vn of the second switching legs L2U, L2V, L2W becomes zero in the 1/2 cycle in which the output AC voltage Vac becomes positive, and becomes the second DC in the 1/2 cycle in which the output AC voltage Vac becomes negative. It becomes equal to the voltage of the capacitor C2.

  Between the first output terminals O1U, O1V, and O1W and the second output terminals O2U, O2V, and O2W, the voltage of the first DC capacitor C1 is output in the negative 1/2 cycle when the AC voltage is positive. In the / 2 cycle, the voltage of the second DC capacitor C2 is output.

Since the voltage of the first DC capacitor C1 and the voltage of the second DC capacitor C2 are approximately half the DC voltage Vdc between the positive side DC terminal TA and the negative side DC terminal TB, the first output The voltage between the terminals O1U, O1V, O1W and the second output terminals O2U, O2V, O2W is approximately 1/2 of the DC voltage Vdc.
That is, the output voltage Vp of the first switching legs L1U, L1V, L1W can be expressed by the following formula.
Vp = Vdc / 2 (0 <wt <π)
= 0 (π <wt <2π)

The output voltage Vn of the second switching legs L2U, L2V, L2W can be expressed by the following formula.
Vn = 0 (0 <wt <π)
= -Vdc / 2 (π <wt <2π)

  On the other hand, the positive-side arm and the negative-side arm composed of the unit converter C have an appropriate on / off time ratio (duty) of the unit converter C so that desired voltages Varmp and Varmn as shown in FIG. 3 can be output. Adjusted. For example, the control circuit CNT uses the PWM (Pulse Width Modulation) technique of comparing the output command value of the unit converter C and the triangular wave, and thereby the first cell switching element SA and the second cell switching element of the unit converter C are used. A gate signal with SB can be generated. At this time, by appropriately shifting the phase of the triangular wave carrier of each unit converter C, it is possible to output a voltage with few harmonics.

  Here, for the sake of explanation, assuming that the reference potential on the DC side is the neutral point potential of the positive DC terminal TA and the negative DC terminal TB, the output voltage Varmp of the positive arms A1U, A1V, A1W is given by the following formula. Can be represented.

Varmp = Vdc / 2-Vac (0 <wt <π)
= -Vac (π <wt <2π)
The output voltage Varmn of the negative arms A2U, A2V, A2W can be expressed by the following formula.

Varmn = Vac (0 <wt <π)
= Vdc / 2 + Vac (π <wt <2π)
By operating the first switching legs L1U, L1V, L1W, the second switching legs L2U, L2V, L2W, the positive side arms A1U, A1V, A1W, and the negative side arms A2U, A2V, A2W as described above, the electric power is increased. The AC phase voltage Vac of the converter 20 can be set to a desired value.

Next, the current Ip of the positive arms A1U, A1V, A1W and the current In of the negative arms A2U, A2V, A2W will be described.
The power conversion device 20 of the present embodiment includes, for example, a current detector that detects the current Ip of the positive arms A1U, A1V, A1W and the current In of the negative arms A2U, A2V, A2W.

The current Ip of the positive arms A1U, A1V, A1W and the current In of the negative arms A2U, A2V, A2W can be separated into an alternating current component Iac and a circulating current component Iz by the following variable conversion formula.
Iac = Ip-In
Iz = (Ip + In) / 2
The AC current component Iac is a component that goes out from the AC terminals TU, TV, TW. On the other hand, the circulating current component Iz is a component that does not go out from the AC terminals TU, TV, TW, and is a virtual current. In the present embodiment, the alternating current component Iac is positive in the direction from the outside toward the alternating current terminals TU, TV, TW, and the circulating current component Iz is the negative arm A2U, A2V, A2W to the positive arm A1U, A1V. , A1W is positive in the direction of flow.

The current Ip of the positive arms A1U, A1V, A1W and the current In of the negative arms A2U, A2V, A2W can be expressed by the following formulas using the alternating current component Iac and the circulating current component Iz.
Ip = Iac / 2 + Iz
In = -Iac / 2 + Iz

Next, a configuration example of the control circuit CNT of the power conversion device 20 of the present embodiment will be described.
FIG. 4 is a diagram schematically illustrating a configuration example of the control circuit of the power conversion device according to the first embodiment.
In the present embodiment, the control circuit CNT includes a cell capacitor voltage average value control unit 31, a DC capacitor voltage control unit 32, an AC current control unit 33, a circulating current control unit 34, a comparator COM, and a PWM control unit 35. , 36, switching devices SP and SN, a cell capacitor voltage balance control unit 37, a DC capacitor voltage balance control unit 38, adders AD1 to AD5, and multipliers M1 and M2.

The cell capacitor voltage average value control unit 31 includes a subtracter (first subtractor) S1 and a multiplier (first multiplier) G1.
The subtractor S1 outputs the difference obtained by subtracting the average value Vcave of the cell capacitor voltage Vc from the cell capacitor voltage command value input from the outside.

The average value Vcave of the cell capacitor voltage can be calculated by the control circuit CNT. For example, when the positive side arms A1U, A1V, A1W and the negative side arms A2U, A2V, A2W each include N unit converters C, the cell capacitor voltage average value Vcave is 6N unit converters in total. It is the average value of the voltage Vc of the cell capacitor CA of C, which can be expressed by the following equation.
Vcave = ((Vcup1 + ... VcupN) + (Vcun1 + ... VcunN) + ... + (Vcwn1 + ... VcwnN)) / (6N)

  The multiplier G1 outputs the product of the value output from the subtractor S1 and a predetermined gain. The output value of the multiplier G1 is the value of the feedback operation amount current (first feedback operation amount current) of the cell capacitor voltage. The gain multiplied by the multiplier G1 is set in consideration of responsiveness and stability.

  The cell capacitor voltage average value control unit 31 is, for example, a proportional control circuit or a proportional integration circuit that controls the difference between the cell capacitor voltage command value and the cell capacitor voltage average value to be zero.

The DC capacitor voltage control unit 32 includes a subtractor (second subtractor) S2 and a multiplier (second multiplier) G2.
The subtractor S2 outputs a difference obtained by subtracting the DC capacitor voltage average value from the DC capacitor voltage command value input from the outside. The average value of the DC capacitor voltage can be calculated by the control circuit CNT.

  The multiplier G2 outputs the product of the value output from the subtractor S2 and a predetermined gain. The output value of the multiplier G2 is the value of the feedback operation amount current (second feedback operation amount current) of the DC capacitor voltage. The gain multiplied by the multiplier G2 is set in consideration of responsiveness and stability.

  The DC capacitor voltage control unit 32 is, for example, a proportional control circuit or a proportional-integral control circuit that outputs a manipulated variable such that the difference between the DC capacitor voltage command value and the DC capacitor voltage average value becomes zero.

  The DC capacitor voltage balance control unit 38 outputs an operation amount for matching the voltage values of the first DC capacitor C1 and the second DC capacitor C2, that is, for balancing the voltage values. For example, the DC capacitor voltage balance control unit 38 outputs an operation amount that makes the difference between the voltage values of the first DC capacitor C1 and the second DC capacitor C2 zero.

  The cell capacitor voltage balance control unit 37 outputs an operation amount for matching, that is, balancing the voltages Vc of all the cell capacitors CA. For example, the cell capacitor voltage balance control unit 37 outputs an operation amount that makes the difference between the cell capacitor CA of the unit converter C of the positive arm and the cell capacitor CA of the unit converter C of the negative arm zero.

  The adder AD1 is the sum of the values of the output of the DC capacitor voltage control unit 32 (DC capacitor voltage feedback operation amount current) and the output of the cell capacitor voltage average value control unit 31 (cell capacitor voltage feedback operation amount current). Is output to the AC current control unit 33.

  The DC capacitor voltage control unit 32 sets the feedback operation amount current of the voltage of the DC capacitors C1 and C2 to zero when a voltage source (or a circuit that operates the voltage source) is connected between the DC terminals TA and TB.

The alternating current control unit 33 calculates an alternating current component Iac (= Ip-In) calculated from the values of the detected positive side arm current Ip and negative side arm current In, and the alternating current component Iac is input. The voltage command value Vac is calculated so as to match the current command value (output value of the adder AD1).
The output value (voltage command value Vac) of the AC current control unit 33 is input to the comparator COM, the multiplier M2, the switch SN, and the adder AD3.

Adder AD5 adds the output value of DC capacitor voltage control unit 32 (feedback operation amount current of DC capacitor voltage) and the output value of adder AD4, and outputs the result to circulating current control unit 34.
The adder AD4 adds the output value of the cell capacitor voltage balance control unit 37 and the output value of the DC capacitor voltage balance control unit 38 and outputs the result.

  The circulating current controller 34 calculates a circulating current component Iz (= (Ip + In) / 2) from the detected values of the positive side arm current Ip and the negative side arm current In, and outputs a command value current input from the outside. The voltage command value Vdc is output so as to realize the circulating current component Iz to be satisfied.

  The comparator COM compares the voltage command value Vac with the reference potential and compares the first switching element S1U, S1V, S1W, the second switching element S2U, S2V, S2W, the third switching element S3U, S3V, S3W, It outputs a gate signal to the fourth switching elements S4U, S4V, S4W.

  That is, the comparator COM turns on the first switching elements S1U, S1V, S1W and the third switching elements S3U, S3V, S3W when the voltage command value Vac is positive (greater than the reference voltage), and the voltage command value Vac is negative ( When it is smaller than the reference voltage), a gate signal for turning off the first switching elements S1U, S1V, S1W and the third switching elements S3U, S3V, S3W is output.

  Further, the comparator COM turns on the second switching elements S2U, S2V, S2W and the fourth switching elements S4U, S4V, S4W when the voltage command value Vac is negative (smaller than the reference voltage), and the voltage command value Vac is positive ( A gate signal for turning off the second switching elements S2U, S2V, S2W and the fourth switching elements S4U, S4V, S4W is output when the voltage is higher than the reference voltage.

The multiplier M2 outputs a value obtained by multiplying the voltage command value Vac input from the AC current control unit 33 by -1, to the adder AD2 and the switch SP.
The multiplier M1 outputs a value obtained by multiplying the voltage command value Vdc input from the circulating current control unit 34 by 1/2 to the adders AD2 and AD3 and the switch SN.

The adder AD2 adds the value (-Vac) input from the multiplier M2 and the value (Vdc / 2) input from the multiplier M1 and outputs the result to the switch SP.
The adder AD3 adds the voltage command value Vac output from the AC current control unit 33 and the value (Vdc / 2) input from the multiplier M1 and outputs the result to the switch SN.

The switches SP and SN are configured to switch the output value in synchronization with the timing when the output value of the comparator COM switches.
For example, in the switch SP, when the voltage command value Vac is positive (greater than the reference voltage), the output value (command value of the positive arm voltage Varmp) is the output value of the adder AD2 (= Vdc / 2-Vac). When the voltage command value Vac is negative (smaller than the reference voltage), the output value (command value of the voltage Armp on the positive side arm) is switched to the output value (= -Vac) of the multiplier M2.

  Further, in the switch SN, when the voltage command value Vac is positive (greater than the reference voltage), the output value (command value of the negative arm voltage Varmn) becomes the output value (= Vac) of the AC current control unit 33, When the voltage command value Vac is negative (smaller than the reference voltage), the output value (command value of the negative side arm voltage Varmp) is switched to the output value of the adder AD3 (= Vdc / 2 + Vac).

  The PWM control unit 35 uses the value input from the switch SP as a voltage command value, compares the voltage command value with the carrier wave, and switches the switching element SA of the unit converter C of the positive arms A1U, A1V, and A1W. An SB gate signal is generated and output.

  The PWM control unit 36 uses the value input from the switch SN as a voltage command value, compares the voltage command value with the carrier wave, and switches the switching element SA of the unit converter C of the negative arms A2U, A2V, A2W. An SB gate signal is generated and output.

Next, the effect of the power converter 20 of this embodiment is explained.
The voltage of the capacitor changes with the power flowing into the capacitor. For example, the inflow power Pcellp of the cell capacitor CA of the unit converter C of the positive side arms A1U, A1V, A1W can be expressed by the following formula.
Pcellp = -Varmp × Ip
=-(Vdc / 2-Vac) (Iac / 2 + Iz)
= (Vac-Vdc / 2) Iac / 2-Vdc * Iz / 2 + Vac * Iz
(0 <wt <π)
=-(Vac) (-Iac / 2 + Iz)
= Vac × Iac / 2-Vac × Iz (π <wt <2π)

Further, for example, the inflow power Pc1 of the first DC capacitor C1 can be expressed by the following formula.
Pc1 = Vp × Ip
= Vdc × Iac / 4 + Vdc × Iz / 2 (0 <wt <π)
= 0 (π <wt <2π)

If the average of the AC one cycle averages over both periods (0 <wt <π) and (π <wt <2π), the inflow power Pcellp of the cell capacitor CA can be expressed by the following formula.
Pcellp = (Vac−Vdc / 4) Iac / 2−Vdc × Iz / 4

In addition, if the average of both AC periods of (0 <wt <π) and (π <wt <2π) is taken, the inflow power Pc1 of the first DC capacitor C1 is expressed by the following formula. You can
Pc1 = Vdc × Iac / 8 + Vdc × Iz / 4

The same applies to the cell capacitor CA and the second DC capacitor C2 of the unit converter C of the negative arm A2U, A2V, A2W.
That is, for example, the inflow power Pcelln of the cell capacitor CA of the unit converter C of the negative side arms A2U, A2V, A2W can be expressed by the following formula.
Pcelln = -VarmnxIn
=-(Vac) (-Iac / 2 + Iz)
= Vac × Iac / 2-Vac × Iz (0 <wt <π)
= (Vdc / 2 + Vac) (Iac / 2 + Iz)
= (Vdc / 2 + Vac) Iac / 2 + Vdc × Iz / 2 + Vac × Iz
(Π <wt <2π)

Further, for example, the inflow power Pc2 of the second DC capacitor C2 can be expressed by the following formula.
Pc2 = Vn × In
= 0 (0 <wt <π)
= Vdc × Iac / 4−Vdc × Iz / 2 (π <wt <2π)

The inflow power Pcelln of the cell capacitor CA can be expressed by the following equation by taking the average of both periods of (0 <wt <π) and (π <wt <2π) as the AC one cycle average power.
Pcelln = (Vdc / 4 + Vac) Iac / 2 + Vdc × Iz / 4

In addition, if the average of both AC periods of (0 <wt <π) and (π <wt <2π) is taken, the inflow power Pc2 of the second DC capacitor C2 is expressed by the following formula. You can
Pc2 = Vdc × Iac / 8-Vdc × Iz / 4

  According to the first term of the equations of the inflow powers Pcellp, Pcelln, Pc1, and Pc2, the inflow powers Pcellp, Pcelln, Pc1, and Pc2 can be increased by increasing the alternating current component Iac, and the alternating current component Iac By reducing it, the inflow power Pcellp, Pcelln, Pc1, and Pc2 can be reduced. Therefore, by adjusting the alternating current component Iac, the cell capacitor CA of the unit converter C of the positive side arms A1U, A1V, A1W, the cell capacitor CA of the unit converter C of the negative side arms A2U, A2V, A2W, the first It is possible to adjust the voltages of the DC capacitor C1 and the second DC capacitor C2.

  That is, in the AC current control unit 33, the sum of the values of the feedback operation amount current of the DC capacitor voltage and the feedback operation amount current of the cell capacitor voltage is set as the command value of the AC current component Iac, so that the positive arm A1U. , The cell capacitors CA of the unit converters C of A1V and A1W, the cell capacitors CA of the unit converters C of the negative arms A2U, A2V, and A2W, and the voltages of the first DC capacitor C1 and the second DC capacitor C2. It becomes possible to do.

  That is, according to the power converter 20 of the present embodiment, in addition to the power supplied to the AC load 10, the switching capacitor and the leakage current generated in the capacitor and the switching element, the loss of the detection circuit, and the like cause the cell capacitor CA and the DC capacitor. It is possible to prevent the voltages of C1 and C2 from gradually decreasing.

  As described above, according to the present embodiment, it is possible to provide a power conversion device capable of suppressing harmonics and loss due to switching and performing desired power conversion.

Next, the power conversion device of the second embodiment will be described in detail with reference to the drawings.
In the following description, the same components as those of the power conversion device 20 according to the first embodiment described above will be designated by the same reference numerals and description thereof will be omitted.
The power converter 20 of this embodiment is different from the first embodiment in the configuration of the control circuit CNT.

FIG. 5: is a figure which shows schematically one structural example of the control circuit of the power converter device of 2nd Embodiment.
The power conversion device 20 of the present embodiment is a modification of the first embodiment, and further includes a first gain multiplier G3 and a second gain multiplier G4.

The first gain multiplier G3 outputs a product obtained by multiplying the feedback operation amount current value of the cell capacitor voltage output from the cell capacitor voltage average value control unit 31 by the gain K1 to the adder AD1.
The second gain multiplier G4 outputs a product obtained by multiplying the feedback operation amount current value of the DC capacitor voltage output from the DC capacitor voltage control unit 32 by the gain K2 to the adder AD1.

  As described above, it is expected that the controllability will be improved by multiplying each gain by different gain before calculating the sum of the feedback manipulated current of the DC capacitor voltage and the feedback manipulated current of the cell capacitor voltage. To be done.

  For example, referring to the equation of the inflow power of the capacitor described in the above-described first embodiment, when the coefficient related to the alternating current component Iac and the coefficient related to the circulating current component Iz are compared in the same expression and in different expressions. Are different. Therefore, in the present embodiment, before the sum of the feedback operation amount current of the DC capacitor voltage and the feedback operation amount current of the cell capacitor voltage is multiplied by different gains, the AC current component Iac and the circulating current component Iz are multiplied. Are also used to control the cell capacitor voltage average value Vcave and the DC voltage Vdc to improve the controllability.

  By setting the gains K1 and K2 to appropriate values, for example, even when disturbance occurs, the output voltage can more quickly follow the command value, and as a result, the desired power conversion operation is restored. It is possible to shorten the time.

  That is, according to the present embodiment, similarly to the above-described first embodiment, it is possible to provide a power conversion device capable of suppressing harmonics and loss due to switching and performing desired power conversion.

Next, the power converter of 3rd Embodiment is demonstrated in detail with reference to drawings.
FIG. 6 is a diagram schematically showing a configuration example of a control circuit of the power conversion device according to the third embodiment.
The power conversion device 20 of the present embodiment is a modification of the first embodiment and further includes a subtractor S3.
The subtractor S3 outputs the difference obtained by subtracting the output value of the cell capacitor voltage average value control unit 31 from the output value of the DC capacitor voltage control unit 32 to the adder AD5.

  Although the cell capacitor CA and the DC capacitors C1 and C2 of the unit converter C are controlled by the AC current component Iac in the above-described first embodiment, for example, one of the cell capacitor CA and the DC capacitors C1 and C2 is used. Only the battery continues to be charged or discharged, and the desired power conversion operation may become impossible.

  Therefore, in the power conversion device 20 of the present embodiment, the circulating current component Iz is used, and the difference between the feedback operation amount current of the DC capacitor voltage and the feedback operation amount current of the cell capacitor voltage is used as the command value of the circulating current component Iz. By doing so, the cell capacitor CA and the DC capacitors C1 and C2 can be controlled.

  That is, according to the mathematical expression of the inflow power of the capacitor described in the above-described first embodiment, as shown in the second term, for example, by flowing the positive circulating current component Iz, the cell capacitor CA is discharged. Then, the DC capacitors C1 and C2 are charged. That is, it is possible to adjust the voltage of the cell capacitor CA and the DC capacitors C1 and C2 by adjusting the value of the circulating current component Iz.

  That is, the circulating current control unit 34 sets the difference between the value of the feedback operation amount current of the DC capacitor voltage and the value of the feedback operation amount current of the cell capacitor voltage as the command value of the circulating current component Iz, so that the positive arm A1U. , The cell capacitors CA of the unit converters C of A1V and A1W, the cell capacitors CA of the unit converters C of the negative arms A2U, A2V, and A2W, the voltages of the first DC capacitor C1, and the second DC capacitor C2, It becomes possible to control independently and simultaneously.

  That is, according to the power converter 20 of the present embodiment, in addition to the power supplied to the AC load 10, the switching capacitor and the leakage current generated in the capacitor and the switching element, the loss of the detection circuit, and the like cause the cell capacitor CA and the DC capacitor. It is possible to prevent the voltages of C1 and C2 from gradually decreasing.

  As described above, according to the present embodiment, it is possible to provide a power conversion device capable of suppressing harmonics and loss due to switching and performing desired power conversion.

Next, a power conversion device according to the fourth embodiment will be described in detail with reference to the drawings.
FIG. 7: is a figure which shows schematically one structural example of the control circuit of the power converter device of 4th Embodiment.
The power converter of this embodiment is a modification of the third embodiment, and further includes a first gain multiplier G3, a second gain multiplier G4, a third gain multiplier G5, and a fourth gain multiplier G6. ing.

The first gain multiplier G3 outputs a product obtained by multiplying the feedback operation amount current value of the cell capacitor voltage output from the cell capacitor voltage average value control unit 31 by the gain K1 to the adder AD1.
The second gain multiplier G4 outputs a product obtained by multiplying the feedback operation amount current value of the DC capacitor voltage output from the DC capacitor voltage control unit 32 by the gain K2 to the adder AD1.

  The third gain multiplier G5 outputs a product obtained by multiplying the feedback operation amount current value of the cell capacitor voltage output from the cell capacitor voltage average value control unit 31 by the gain K3 to the subtractor S1.

  The fourth gain multiplier G6 outputs a product obtained by multiplying the feedback operation amount current value of the DC capacitor voltage output from the DC capacitor voltage control unit 32 by the gain K4 to the subtractor S1.

  As described above, by calculating the sum of the values of the feedback operation amount current of the DC capacitor voltage and the feedback operation amount current of the cell capacitor voltage (AC current command value), each of them is multiplied by a different gain to control. It is expected that the quality will improve.

  In addition, the controllability is improved by multiplying the difference between the feedback operation amount current of the DC capacitor voltage and the feedback operation amount current of the cell capacitor voltage (circulation current command value) by different gains. Is expected to become.

  That is, in the present embodiment, different gains are multiplied before summing the values of the feedback operation amount current of the DC capacitor voltage and the feedback operation amount current of the cell capacitor voltage and before subtracting the values. , The AC current component Iac and the circulating current component Iz are used similarly to control the cell capacitor voltage average value Vcave and the DC voltage Vdc to improve the controllability.

  By setting the gains K1, K2, K3, and K4 to appropriate values, the output voltage can be made to follow the command value more quickly even when disturbance occurs, and as a result, desired power conversion can be performed. It is possible to shorten the time required to return to the operation.

  That is, according to the present embodiment, similarly to the above-described first embodiment, it is possible to provide a power conversion device capable of suppressing harmonics and loss due to switching and performing desired power conversion.

  In the above-described first to fourth embodiments, the sum and difference of the values of the feedback operation amount current of the DC capacitor voltage and the feedback operation amount current of the cell capacitor voltage are used to calculate the cell capacitor CA and the DC capacitor C1, Although the voltage with C2 is controlled, the calculation method may change depending on which direction of the voltage and the current is positive and the gain setting.

  Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the scope equivalent thereto.

  In the first to fourth embodiments, the operation of the power conversion device has been described assuming that the voltage Vac and the current Iac have the same phase and active power is generated by the multiplication result (Vac · Iac). However, the power conversion device shown in FIG. 1 can change the phase of the current Iac as compared with the phase of the voltage Vac, and the phase of the current Iac is deviated from the phase of the voltage Vac by 90 degrees, for example. In this case, even if the alternating current component Iac is increased, the voltage between the DC capacitors C1 and C2 and the cell capacitor CA cannot be increased or decreased.

  Thus, in the above-described first to fourth embodiments, the AC current control unit 33 converts the three-phase AC from the fixed coordinate system into the d-axis component having the same phase as the AC and the q-axis component having a 90-degree phase shift. It may be configured to further include a coordinate conversion unit for performing the above. A conversion method called so-called dq conversion, which is a technique used in general power conversion devices.

  From the above, instead of the AC current component Iac, the feedback operation amount current of the voltage of the DC capacitors C1 and C2 (first feedback operation amount current) and the feedback operation amount current of the voltage of the cell capacitor CA (second feedback operation amount current). By calculating the command value of the d-axis current (active current) Id using the sum of and, and setting it as the command value of the AC current control unit 33, the phase of the AC current component Iac is not taken into consideration and the cell capacitor CA It becomes possible to control the voltages of both the DC capacitors C1 and C2. The d-axis current Id includes a current required for charging or discharging the cell capacitor CA and the DC capacitors C1 and C2, as well as a current required for a desired power conversion operation.

10 ... AC load, 20 ... Power converter, 31 ... Cell capacitor voltage average value control unit, 32 ... DC capacitor voltage control unit, 33 ... AC current control unit, 34 ... Circulating current control unit, 35, 36 ... PWM control unit , 37 ... Cell capacitor voltage balance control unit, 38 ... DC capacitor voltage balance control unit, AD1-AD5 ... Adder, A1U, A1V, A1W ... Positive arm, A2U, A2V, A2W ... Negative arm, C1 ... First DC capacitor, C2 ... Second DC capacitor, G1-G6, M1, M2 ... Multiplier, O1U-O1W, O2U-O2W ... Output terminal, SB1, SB2 ... Subtractor.

Claims (7)

A first DC capacitor,
A second DC capacitor connected in series with the first DC capacitor;
A first switching leg connected in parallel with the first DC capacitor;
A second switching leg connected in parallel with the second DC capacitor;
A positive arm including a plurality of unit converters connected in series between an AC terminal connected to an AC load and an output terminal of the first switching leg,
A negative arm including a plurality of unit converters connected in series between the AC terminal and the output terminal of the second switching leg;
A first feedback manipulated variable current value having an average value of the voltages of the cell capacitors included in each of the plurality of unit converters as a predetermined value, and an average value of the voltages of the first DC capacitor and the second DC capacitor. A second feedback operation amount current value which is a predetermined value and a sum are calculated, and an AC current component flowing through the AC terminal is calculated from detected values of the current flowing through the positive arm and the current flowing through the negative arm. A control circuit that calculates and generates a gate signal for the first switching leg, the second switching leg, and the plurality of unit converters so that the alternating current component follows a command value that includes the sum. An electric power conversion device comprising:   The control circuit calculates a difference obtained by subtracting the second feedback operation amount current value from the first feedback operation amount current value, and calculates a difference between a current flowing through the positive side arm and a current flowing through the negative side arm. 2. The power conversion according to claim 1, wherein the circulating current component that is not output from the AC terminal is calculated, and the gate signal is generated so that the circulating current component follows a command value including the difference. apparatus.   The control circuit includes a first gain multiplier that multiplies the first feedback operation amount current value by a gain, and a second gain multiplier that multiplies the second feedback operation amount current value by a gain, and the sum is the above. The power conversion device according to claim 1, wherein the power conversion device has a value obtained by adding an output value of the first gain multiplier and an output value of the second gain multiplier.   The control circuit includes a third gain multiplier that multiplies the first feedback operation amount current value by a gain, and a fourth gain multiplier that multiplies the second feedback operation amount current value by a gain, and the difference is the The power conversion device according to claim 2, wherein the power conversion device has a value obtained by subtracting the output value of the fourth gain multiplier from the output value of the third gain multiplier. The control circuit outputs a difference between a voltage command value of the cell capacitor input from the outside and an average value of voltages of the cell capacitors included in the plurality of unit converters, and a first subtractor; A first multiplier that multiplies the output value of the 1-subtractor by a gain and outputs the value as the first feedback manipulated variable current value;
A second subtractor that outputs a difference between a voltage command value of the first DC capacitor and the second DC capacitor input from the outside and an average value of voltages of the first DC capacitor and the second DC capacitor; , A second multiplier that multiplies the output value of the second subtractor by a gain and outputs the second feedback manipulated variable current value, and a DC capacitor voltage control section. The power conversion device according to any one of claims 1 to 4.   The control circuit sets the second feedback manipulated variable current value to zero when a circuit that operates as a voltage source is connected in parallel with the first DC capacitor and the second DC capacitor. The power conversion device according to any one of claims 1 to 5. The control circuit has a coordinate conversion unit that performs coordinate conversion of a three-phase alternating current into a d-axis component having the same phase as the alternating current and a q-axis component that is 90 degrees out of phase.
The power conversion device according to any one of claims 1 to 6, wherein the AC current component is a d-axis component.