Power Conversion Equipment

Abstract

To suppress size increase of a capacitor of each cell converter accompanying single-phase power pulsation.SOLUTION: A power conversion device comprises: a plurality of clusters; and a control unit which controls the plurality of clusters, in which each of the plurality of clusters comprises: a pair of DC terminals; a pair of AC terminals; and one or more cell converters, each cell converter comprises: a DC-DC converter connected between the pair of DC cell terminals and the capacitor; and a DC-AC converter connected between the pair of AC cell terminals and the capacitor, each pair of DC cell terminals of the cell converter is connected in parallel with the pair of DC terminals, each pair of AC cell terminals of the cell converter is connected in series between the pair of AC terminals, and the control unit pulsates DC power on the side of the pair of DC terminals with the same frequency as that of pulsation of AC power on the side of the pair of AC terminals to reduce voltage ripples of the capacitor in each of the plurality of clusters.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] Conventionally, a multi-cell power conversion device has been known that includes a plurality of cells connected in series for each phase, and each of the plurality of cells includes a DC / DC converter, an inverter, and a capacitor connected between the DC / DC converter and the inverter. This multi-cell power conversion device can handle high voltages by connecting the output terminals of the inverters in series (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-64436 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the cells of each phase function as a single-phase power converter, single-phase power pulsation occurs in the capacitor of each cell. If the capacitance of the capacitor of each cell is relatively small, the voltage ripple of the capacitor becomes large due to the single-phase power pulsation occurring in each cell. If this voltage ripple becomes excessive, there is a risk that the distortion of the AC current flowing through the AC side of each cell will become large. If the capacitance of the capacitor of each cell is increased in order to reduce the voltage ripple of the capacitor, the capacitor of each cell will become large, which will ultimately lead to an increase in the size of the power conversion device.

[0005] The present disclosure provides a power conversion device capable of suppressing an increase in the size of the capacitor of each cell converter due to single-phase power pulsation. [Means for solving the problem]

[0006] The present disclosure relates to A plurality of interconnected clusters; A control unit that controls the plurality of clusters, Each of the plurality of clusters includes: A power generating device comprising a pair of DC terminals, a pair of AC terminals, and one or more cell converters; Each of the cell converters comprises: a capacitor, a pair of DC cell terminals, a pair of AC cell terminals, a DC-DC converter connected between the pair of DC cell terminals and the capacitor, and a DC-AC converter connected between the pair of AC cell terminals and the capacitor; the pair of DC cell terminals of each of the cell converters are connected in parallel to the pair of DC terminals; the pair of AC cell terminals of each of the cell converters are connected in series between the pair of AC terminals; The control unit provides a power conversion device in which, in each of the multiple clusters, the DC power on the pair of DC terminals is pulsated at the same frequency as the pulsation of the AC power on the pair of AC terminals, thereby reducing voltage ripple of the capacitor. Effect of the Invention

[0007] According to the technique of the present disclosure, it is possible to suppress an increase in the size of the capacitor of each cell converter that is caused by single-phase power pulsation. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a configuration example of a power conversion device according to an embodiment; [Diagram 2] 4 is a timing chart showing an example of a relationship between input / output power and a capacitor voltage of a power conversion device. [Diagram 3] 1 is a diagram for explaining the relationship between input and output power in a capacitor between a DC-DC converter (converter side) and a DC-AC converter (inverter side). FIG. [Figure 4] 3 is a block diagram showing an example of the configuration of a control unit according to the first embodiment. FIG. [Diagram 5]3 is a block diagram specifically illustrating an example of the configuration of a control unit according to the first embodiment. FIG. [Figure 6] 4 is a timing chart showing an example of an operation by a control unit according to the first embodiment. [Figure 7] 4 is a timing chart showing an overall example of an operation by a control unit according to the first embodiment. [Figure 8] FIG. 11 is a block diagram showing an example of the configuration of a control unit according to a second embodiment. [Figure 9] 4 is a block diagram showing an example of the configuration of a positive phase / reverse phase separation unit; FIG. [Figure 10] FIG. 11 is a block diagram specifically illustrating a first configuration example of a control unit according to the second embodiment. [Figure 11] FIG. 11 is a block diagram specifically illustrating a second configuration example of a control unit according to the second embodiment. [Figure 12] FIG. 11 is a block diagram showing an example of the configuration of a control unit according to a third embodiment. [Figure 13] FIG. 13 is a block diagram specifically illustrating an example of the configuration of a control unit according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The following describes the embodiments.

[0010] Fig. 1 is a diagram showing an example of the configuration of a power conversion device according to one embodiment. A power conversion device 10 shown in Fig. 1 converts input DC power into three-phase AC power and outputs the power to a three-phase power system 14. The power conversion device 10 includes a plurality of clusters 11 (11U, 11V, 11W), a plurality of reactors 40 (40U, 40V, 40W), and a control unit 30.

[0011] The multiple clusters 11 are connected to each other, and in the example shown in Fig. 1, are star-connected. Each of the multiple clusters 11 has a pair of DC terminals a, b, a pair of AC terminals c, d, and one or more cell converters 20. In the example shown in Fig. 1, each of the multiple clusters 11 has three cell converters 20 of the same configuration, and is connected to the power system 14 via multiple reactors 40. The connection to the power system 14 may be via a transformer (not shown).

[0012] A pair of DC terminals a, b of each of the multiple clusters 11 are connected in parallel to a common DC path. The AC terminal c of the U-phase cluster 11U is connected to the U-phase power line of the power system 14 via a reactor 40U. The AC terminal c of the V-phase cluster 11V is connected to the V-phase power line of the power system 14 via a reactor 40V. The AC terminal c of the W-phase cluster 11W is connected to the W-phase power line of the power system 14 via a reactor 40W. The AC terminals d of the clusters 11 of each phase are connected to each other at the neutral point.

[0013] The multiple cell converters 20 for each phase convert DC power input from a common DC path into AC power and output it. Each of the multiple cell converters 20 for each phase has a capacitor 15, a pair of DC cell terminals e, f, a pair of AC cell terminals g, h, a DC-DC converter 12, and a DC-AC converter 13. The multiple cell converters 20 for each phase are connected in series via the pair of AC cell terminals g, h.

[0014] A pair of DC cell terminals e, f of each of the multiple cell converters 20 is connected in parallel to a pair of DC terminals a, b of the cluster 11 to which it belongs. A pair of AC cell terminals g, h of each of the multiple cell converters 20 is connected in series between a pair of AC terminals c, d of the cluster 11 to which it belongs.

[0015] The DC-DC converter 12 is connected between a pair of DC cell terminals e, f and a capacitor 15. The DC-DC converter 12 converts DC power input from the pair of DC cell terminals e, f into DC power of a predetermined voltage and outputs it to the capacitor 15. The DC-DC converter 12 is, for example, an insulated DC / DC converter. The DC-DC converter 12 has, for example, an inverter circuit 16 that converts DC power into high-frequency AC power, a high-frequency transformer 17 that transforms the AC power into a predetermined AC voltage, and a converter circuit 18 that converts the transformed AC power into DC power of a predetermined voltage. FIG. 1 illustrates a case where the DC-DC converter 12 is a DAB (Dual Active Bridge) converter.

[0016] Capacitor 15 is a capacitive element that smoothes the voltage of the DC link between DC-DC converter 12 and DC-AC converter 13, and more specifically, smoothes the voltage output from converter circuit 18 of DC-DC converter 12.

[0017] The DC-AC converter 13 is connected between a pair of AC cell terminals g, h and the capacitor 15. The DC-AC converter 13 is a single-phase inverter that converts DC power input from the capacitor 15 into AC power of a predetermined voltage and frequency and outputs it from the pair of AC cell terminals g, h. The DC-AC converter 13 has an inverter circuit 19 that converts DC power into AC power.

[0018] Each of the inverter circuit 16, the converter circuit 18, and the inverter circuit 19 includes a power conversion circuit having a plurality of switching elements, and a drive circuit (not shown) that operates the power conversion circuit. The switching elements include, for example, a transistor and a diode connected in anti-parallel to the transistor. Specific examples of the transistor include an IGBT (Insulated Gate Bipolar Transistor) and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0019] The control unit 30 is a control device that controls the multiple clusters 11, and includes, for example, a memory and a processor. The functions of the control unit 30 are realized by a processor such as a CPU (Central Processing Unit) operating according to a program stored in the memory. The functions of the control unit 30 may be realized by a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC).

[0020] The power conversion device 10 can output a multilevel voltage waveform having a voltage equal to or greater than the withstand voltage of the switching elements and with reduced harmonics by the control unit 30 causing each of the multiple cell converters 20 to output voltage waveforms with different phases from each other.

[0021] The power conversion device 10 is applicable to, for example, a power conditioning system (PCS) of a solar power generation device, a static var compensator (STATCOM), a high voltage direct current (HVDC) system, and the like.

[0022] Next, a description will be given of the voltage ripple of the capacitor 15. For ease of understanding, the description will be given assuming that the number of cell converters in each phase is one.

[0023] Fig. 2 is a timing chart showing an example of the relationship between the input / output power of the power conversion device and the capacitor voltage when the system voltage and system current of the power system 14 are sinusoidal waves. Fig. 3 is a diagram for explaining the relationship between the input / output power of the capacitor 15 between the DC-DC converter 12 (converter side) and the DC-AC converter 13 (inverter side). Figs. 2 and 3 show a relationship diagram of the U-phase input power, the U-phase output power, and the differential power (= the power entering and leaving the capacitor 15) when power is supplied to a symmetrical three-phase load.

[0024] When the input power factor is 1, the instantaneous input power P U teeth,

[0025]

number

[0026] The change in electrostatic energy ΔE of the capacitor 15 is

[0027]

number

[0028] From equations (2) and (3), the capacitor voltage ripple D is

[0029]

number

[0030] In the present embodiment shown in FIG. 1, the control unit 30 pulsates the DC power on the pair of DC terminals a, b at the same frequency as the pulsation of the AC power on the pair of AC terminals c, d in each of the multiple clusters 11, thereby reducing the voltage ripple of the capacitor 15. More specifically, the control unit 30 pulsates the DC power on the pair of DC terminals a, b of the U-phase cluster 11U at the same frequency as the pulsation of the AC power on the pair of AC terminals c, d of the U-phase cluster 11U, thereby reducing the voltage ripple of the capacitor 15 of the U-phase cluster 11U. The control unit 30 pulsates the DC power on the pair of DC terminals a, b of the V-phase cluster 11V at the same frequency as the pulsation of the AC power on the pair of AC terminals c, d of the V-phase cluster 11V, thereby reducing the voltage ripple of the capacitor 15 of the V-phase cluster 11V. The control unit 30 pulsates the DC power on the pair of DC terminals a, b of the W-phase cluster 11W at the same frequency as the pulsation of the AC power on the pair of AC terminals c, d of the W-phase cluster 11W, thereby reducing the voltage ripple of the capacitor 15 of the W-phase cluster 11W. By the control unit 30 performing such control, the power conversion device 10 according to the present embodiment can suppress distortion of the AC current flowing through the pair of AC terminals c, d in each of the multiple clusters 11, and can suppress distortion occurring in the system current of the power system 14. Since the voltage ripple of each capacitor 15 of the multiple clusters 11 is reduced, an increase in the capacity of each capacitor 15 can be suppressed. As a result, an increase in the size of each capacitor 15 can be suppressed, and thus an increase in the size of the power conversion device 10 can be suppressed.

[0031] The control unit 30 superimposes the compensation power, which changes according to the pulsation of the AC power on the pair of AC terminals c, d, on the DC power on the pair of DC terminals a, b, in each of the multiple clusters 11. The control unit 30 superimposes the compensation power of each phase on the DC power of the corresponding phase and adjusts the distribution of the DC power input from the common DC path among the three phases, thereby reducing the capacitor voltage ripple D in the single-phase power pulsation. By the control unit 30 performing such control, the power conversion device 10 according to the present embodiment can suppress the distortion of the AC current flowing through the pair of AC terminals c, d in each of the multiple clusters 11, and can suppress the distortion occurring in the system current of the power system 14. The control unit 30 adjusts the distribution of the input power among the clusters and evenly distributes the power input to the converter cells belonging to the same cluster, thereby further reducing the capacitor voltage ripple D of each phase.

[0032] Even if the control unit 30 pulsates the DC power input to a pair of DC terminals a, b of each phase in response to the pulsation of the AC power on the side of the pair of AC terminals c, d, there is almost no effect on the DC bus side connected to the pair of DC terminals a, b of each phase, because the circuit shown in FIG. 1 is a three-phase circuit.

[0033] For example, the steady-state component of the DC power at the pair of DC terminals a, b of each phase and the steady-state component of the AC power at the pair of AC terminals c, d of each phase are all 200 kW. The pulsating components of the AC power at the pair of AC terminals c, d of each phase of the U phase, V phase, and W phase are 200 sin2ωt, 200 sin(2ωt-4π / 3), and 200 sin(2ωt-2π / 3), respectively (all in kW). In addition, α is a compensation coefficient smaller than 1. At this time, the control unit 30 superimposes a compensation power of 200αsin2ωt on the steady-state component of the DC power of the U phase, superimposes a compensation power of 200αsin(2ωt-4π / 3) on the steady-state component of the DC power of the V phase, and superimposes a compensation power of 200αsin(2ωt-2π / 3) on the steady-state component of the DC power of the W phase. As a result, there is almost no effect on the DC bus side connected to a pair of DC terminals a, b of each phase (200αsin2ωt+200αsin(2ωt-4π / 3)+200αsin(2ωt-2π / 3)=0).

[0034] The control unit 30 adjusts the magnitude of the compensation power superimposed on the DC power of each phase using the compensation coefficient α. If the capacitance of the capacitor 15 is made too small, there is a risk that disturbances in the voltage control (control stability) will deteriorate. However, by introducing the compensation coefficient α, the risk of such deterioration can be reduced.

[0035] FIG. 4 is a block diagram showing an example of the configuration of the control unit according to the first embodiment. The control unit 30A shown in FIG. 4 is an example of the control unit 30. The control unit 30A has a current command unit 31 and a compensation unit 32A. The current command unit 31 generates a current command for turning on or off a plurality of switching elements in the DC-DC converter 12 so that the voltage of the capacitor 15 becomes a predetermined target voltage. The current command unit 31 supplies a current command for the cluster 11 of each phase to the compensation unit 32A. The compensation unit 32A superimposes a compensation power that changes with the same frequency and phase as the pulsation of the AC power output from a pair of AC terminals c and d on the DC power input to a pair of DC terminals a and b in each of the plurality of clusters 11. The compensation unit 32A has a pulsation extraction unit 33, a compensation amount calculation unit 34, and an adder 35 (35u, 35v, 35w).

[0036] Fig. 5 is a block diagram specifically showing an example of the configuration of the control unit according to the first embodiment. Fig. 6 is a waveform diagram showing an example of the configuration of each unit. The compensation unit 32A extracts the pulsation of the AC power output from a pair of AC terminals c, d in each of the multiple clusters 11, and adjusts the compensation power to be superimposed on the DC power input to a pair of DC terminals a, b according to the extracted pulsation. The compensation unit 32A has a pulsation extraction unit 33, a compensation amount calculation unit 34, and an adder 35 (35u, 35v, 35w).

[0037] The pulsation extraction unit 33 multiplies the system current and system voltage of the power system 14 for each phase to calculate the AC power at the pair of AC terminals c, d of each phase (the system-side output power of each phase). The pulsation extraction unit 33 adds up the system-side output power of each phase and divides the sum by the number of phases (3 in this case). The pulsation extraction unit 33 subtracts the value obtained by this division from the system-side output power of each phase, thereby removing the steady-state component of the system-side output power of each phase and extracting the pulsation component of the system-side output power of each phase.

[0038] The compensation amount calculation unit 34 calculates the compensation power, which is the product of the extracted pulsation component of each phase and the compensation coefficient α. This allows the magnitude of the compensation power to be superimposed on the DC power input to each phase to be adjusted by the compensation coefficient α. The compensation amount calculation unit 34 calculates the compensation current (an example of the compensation amount) to be superimposed on the current command of each phase by dividing the compensation power of each phase by the measured value of the DC bus voltage. The DC bus voltage may be the voltage of a DC path connected to a pair of DC terminals a and b, or the voltage between a pair of DC terminals a and b.

[0039] The adder 35 (35u, 35v, 35w) generates a compensated current command for each phase by adding the compensation current for the corresponding phase to the current command for each phase.

[0040] The control unit 30A generates a control command for controlling the DC-DC converter 12 in the cluster 11 of each phase from the compensated current command of each phase. When the DC-DC converter 12 is a DAB converter, the control unit 30A generates the phase difference between the primary side and the secondary side as a control command. When the DC-DC converter 12 is an LLC converter, the control unit 30A generates the operating frequency of the LLC converter as a control command. The LLC converter is a converter that utilizes resonance caused by the leakage inductance and excitation inductance of a transformer and the capacitance of a capacitive element.

[0041] 6, compensation unit 32A reduces the difference between the power flowing in and out of capacitor 15, thereby reducing the amount of power stored in capacitor 15. Since the amount of power stored in capacitor 15 is reduced, the voltage ripple of capacitor 15 is reduced.

[0042] The compensation amount calculation unit 34 can effectively reduce the voltage ripple of the capacitor 15 by, for example, adjusting the compensation coefficient α according to the target value of the voltage ripple of the capacitor 15. The target value of the voltage ripple of the capacitor 15 is determined, for example, based on the above formula (4). Alternatively, the compensation coefficient α may be a predetermined fixed value, in which case the amount of calculation of the compensation power by the compensation amount calculation unit 34 can be reduced.

[0043] Fig. 7 is a timing chart showing an overall operation example of the control unit according to the first embodiment. As shown in Fig. 7, the control unit according to the first embodiment can reduce the voltage ripple of the capacitor of each phase.

[0044] FIG. 8 is a block diagram showing an example of the configuration of a control unit according to the second embodiment. In the second embodiment, the description of the configuration and effects similar to those of the first embodiment will be omitted or simplified by invoking the above description. A control unit 30B shown in FIG. 8 is an example of the control unit 30. The control unit 30B has a current command unit 31 and a compensation unit 32B. The current command unit 31 is the same as that of the first embodiment. The compensation unit 32B superimposes a compensation power that changes with the same frequency and phase as the pulsation of the AC power output from a pair of AC terminals c, d on the DC power input to a pair of DC terminals a, b in each of the multiple clusters 11. The compensation unit 32B has a positive phase / negative phase separation unit 36, a pulsation extraction unit 33, a compensation amount calculation unit 34, and an adder 35 (35u, 35v, 35w).

[0045] The compensation unit 32B determines the compensation power from the positive and negative sequence components of the system voltage and system current. This is because pulsation appears in the output power when the output power from each cluster is unbalanced. The positive and negative sequence separation unit 36 ​​calculates the positive sequence voltage, positive sequence current, negative sequence voltage, and negative sequence current shown in the following formulas from the measurement results of the system voltage and system current.

[0046]

number

[0047] FIG. 10 is a block diagram specifically showing a first configuration example of the control unit according to the second embodiment. The compensation unit 32Ba is an example of the compensation unit 32B. The compensation unit 32Ba extracts the pulsation of the AC power output from a pair of AC terminals c, d in each of the multiple clusters 11, and adjusts the compensation power to be superimposed on the DC power input to a pair of DC terminals a, b according to the extracted pulsation. The compensation unit 32Ba has a positive phase / negative phase separation unit 36, a pulsation extraction unit 33, a compensation amount calculation unit 34, and an adder 35 (35u, 35v, 35w).

[0048] The pulsation extraction unit 33 calculates the first power of each phase by multiplying the positive-phase current and the positive-phase voltage, which are the outputs of the positive-phase / negative-phase separation unit 36, for each phase, and calculates the second power of each phase by multiplying the negative-phase current and the negative-phase voltage, which are the outputs of the positive-phase / negative-phase separation unit 36, for each phase. The pulsation extraction unit 33 adds up the first power and the second power for each phase to calculate the positive-phase power of each phase (the sum of the first power and the second power), and divides the positive-phase power of each phase by the number of phases (3 in this case). The pulsation extraction unit 33 subtracts the value obtained by this division from the positive-phase power of each phase, thereby removing the steady-state component of the output power on the system side of each phase and extracting the pulsation component of the output power on the system side of each phase.

[0049] Fig. 11 is a block diagram specifically showing a second configuration example of the control unit according to the second embodiment. The compensation unit 32Bb is an example of the compensation unit 32B. The compensation unit 32Bb in Fig. 11 differs from the compensation unit 32Ba in Fig. 10 in that the configuration of the pulsation extraction unit 33 is different, but is functionally the same as the compensation unit 32Ba.

[0050] The pulsation extraction unit 33 in FIG. 11 calculates the first power of each phase by multiplying the positive-phase current and the positive-phase voltage, which are the outputs of the positive-phase and negative-phase separation unit 36, for each phase, and calculates the second power of each phase by multiplying the negative-phase current and the negative-phase voltage, which are the outputs of the positive-phase and negative-phase separation unit 36, for each phase. The pulsation extraction unit 33 divides the value obtained by adding up the first powers of each phase by the number of phases (3 in this case). The pulsation extraction unit 33 can remove the steady component of the first power on the system side of each phase by subtracting the value obtained by the division from the first power of each phase, and extracts the pulsation component of the first power on the system side of each phase. The pulsation extraction unit 33 can remove the steady component of the second power on the system side of each phase by subtracting the value obtained by the division from the second power of each phase, and extracts the pulsation component of the second power on the system side of each phase.

[0051] The pulsation extraction unit 33 sums up the pulsation component of the first power on the system side of each phase and the pulsation component of the second power on the system side of each phase, and outputs the summed pulsation components of each phase to the compensation amount calculation unit 34.

[0052] FIG. 12 is a block diagram showing a configuration example of a control unit according to the third embodiment. In the third embodiment, the description of the configuration and effects similar to those of the first and second embodiments will be omitted or simplified by invoking the above description. A control unit 30C shown in FIG. 12 is an example of the above control unit 30. A compensation unit 32C in FIG. 12 acquires the phase of the system voltage of each phase of the power system 14 connected to the multiple clusters 11, and pulsates the DC power according to the acquired phase of the system voltage of each phase. The compensation unit 32C has a phase detection unit 37, a reference signal generation unit 38, a compensation amount calculation unit 34, and an adder 35 (35u, 35v, 35w). FIG. 13 is a block diagram specifically showing a configuration example of a control unit according to the third embodiment.

[0053] The phase detector 37 acquires the phase of the system voltage of each phase of the power system 14. The reference signal generator 38 generates a reference signal for each phase using the phase θ of the system voltage of each phase detected by the phase detector 37. The reference signal generator 38 generates a U-phase reference signal sin2θ, a V-phase reference signal sin(2θ-4π / 3), and a W-phase reference signal sin(2θ-2π / 3).

[0054] The compensation amount calculation unit 34 calculates the compensation power, which is the product of the reference signal of each phase and the compensation coefficient α. This makes it possible to adjust the magnitude of the compensation power superimposed on the DC power input to each phase using the compensation coefficient α. The subsequent control contents are the same as those in the above embodiment.

[0055] Although the power conversion device has been described above by way of an embodiment, the present invention is not limited to the above embodiment. Various modifications and improvements, such as combinations or substitutions with part or all of other embodiments, are possible within the scope of the present invention.

[0056] For example, the isolated DC / DC converter is not limited to a configuration in which a full-bridge circuit is provided on each of the primary and secondary sides of a transformer, and the bridge circuit provided on at least one of the primary and secondary sides may be a half-bridge circuit. Also, the isolated DC / DC converter is not limited to a DAB converter, and may be a converter of a type other than a DAB converter (for example, an LLC converter, a flyback type, a feedforward type, etc.). [Explanation of symbols]

[0057] 10 Power conversion device 11U,11V,11W Cluster 12 DC-DC converter 13 DC-AC converter 14 Power system 15 Capacitor 16 Inverter circuit 17 High Frequency Transformer 18 Converter Circuit 19 Inverter circuit 20 Cell Converter 30,30A Control section 31 Current command section 32 Compensation Department 33 Pulsation extraction part 34 Compensation amount calculation section 35u, 35v, 35w adder 36 Positive and reversed phase separation section 37 Phase detection section 38 Reference signal generation section 40U, 40V, 40W Reactor a,b A pair of DC terminals c,d A pair of AC terminals e,f A pair of DC cell terminals g,h A pair of AC cell terminals

Claims

1. A plurality of interconnected clusters; A control unit that controls the plurality of clusters, Each of the plurality of clusters includes: A power generating device comprising a pair of DC terminals, a pair of AC terminals, and one or more cell converters; Each of the cell converters comprises: a capacitor, a pair of DC cell terminals, a pair of AC cell terminals, a DC-DC converter connected between the pair of DC cell terminals and the capacitor, and a DC-AC converter connected between the pair of AC cell terminals and the capacitor; the pair of DC cell terminals of each of the cell converters are connected in parallel to the pair of DC terminals; the pair of AC cell terminals of each of the cell converters are connected in series between the pair of AC terminals; The control unit converts the DC power on the pair of DC terminals into pulsating power at the same frequency as the pulsation of the AC power on the pair of AC terminals in each of the multiple clusters, and outputs the pulsating power by the DC-DC converter, thereby reducing voltage ripple of the capacitor.

2. The power conversion device according to claim 1 , wherein the control unit superimposes a compensation power that changes in accordance with pulsation of the AC power on the DC power.

3. The power conversion device according to claim 2 , wherein the control unit adjusts a magnitude of the compensation power in accordance with a compensation coefficient.

4. The power conversion device according to claim 3 , wherein the control unit adjusts the compensation coefficient in accordance with a target value of a voltage ripple of the capacitor.

5. The power conversion device according to claim 3 , wherein the compensation coefficient is a fixed value.

6. The power conversion device according to claim 2 , wherein the control unit extracts pulsation of the AC power and adjusts the compensation power in accordance with the extracted pulsation.

7. The power conversion device according to claim 6 , wherein the control unit measures a voltage and a current on the side of the pair of AC terminals, and extracts the pulsation of the AC power from the measured voltage and current.

8. 7. The power conversion device according to claim 6, wherein the control unit calculates a positive-sequence voltage, a positive-sequence current, a negative-sequence voltage, and a negative-sequence current from results of measuring the voltage and the current on the pair of AC terminals, and extracts the pulsation of the AC power from the calculated positive-sequence voltage, positive-sequence current, negative-sequence voltage, and negative-sequence current.

9. 5. The power conversion device according to claim 1, wherein the control unit acquires a phase of a system voltage of each phase of a power system to which the plurality of clusters are connected, and pulsates the DC power in accordance with the acquired phase of the system voltage of each phase.

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