Power conversion device

Abstract

Provided is a power conversion device including: a plurality of clusters that are wired to each other; and a control section that controls the plurality of clusters, wherein the plurality of clusters each have a pair of direct current terminals, a pair of alternating current terminals, and one or more unit converters, the unit converters each have a capacitor, a pair of direct current unit terminals, a pair of alternating current unit terminals, a direct current-direct current converter connected between the pair of direct current unit terminals and the capacitor, and a direct current-alternating current converter connected between the pair of alternating current unit terminals and the capacitor, the pair of direct current unit terminals of each of the unit converters are connected in parallel to the pair of direct current terminals, the pair of alternating current unit terminals of each of the unit converters are connected in series between the pair of alternating current terminals, and the control section causes the direct current power on the pair of direct current terminal side to pulsate at the same frequency as the pulsation of the alternating current power on the pair of alternating current terminal side in each of the plurality of clusters, to reduce the voltage ripple of the capacitor.

Description

TECHNICAL FIELD

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

[0002] Conventionally, a multi-cell power conversion device is known, which is provided with a plurality of cells connected in series for each phase, and each of the plurality of cells has a DC / DC (direct current / direct current) converter, an inverter, and a capacitor connected between the DC / DC converter and the inverter. The multi-cell power conversion device deals with high voltage by connecting outputs of the inverters in series (see, for example, Patent Literature 1).

[0003] <Related Art Documents>

[0004] <Patent Literature>

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2016-64436 SUMMARY

[0006] <Problems to be Solved by the Invention>

[0007] 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. In a case where the capacitor capacity of each cell is small, the voltage ripple of the capacitor increases due to the single-phase power pulsation occurring in each cell. If the voltage ripple becomes too large, distortion of the alternating current flowing on the alternating current side of each cell can increase. If the capacity of the capacitor of each cell is increased in order to reduce the voltage ripple of the capacitor, the capacitor of each cell can be upsized, which in turn causes the power conversion device to be upsized.

[0008] The present disclosure provides a power conversion device that can suppress upsizing of the capacitor of each cell converter caused by single-phase power pulsation.

[0009] <Means for Solving the Problems>

[0010] The present disclosure provides a power conversion device including: a plurality of clusters that are wired to each other; and a control section that controls the plurality of clusters, wherein the plurality of clusters each have a pair of direct current terminals, a pair of alternating current terminals, and one or more unit converters each having a capacitor, a pair of direct current unit terminals, a pair of alternating current unit terminals, a direct current-direct current converter connected between the pair of direct current unit terminals and the capacitor, and a direct current-alternating current converter connected between the pair of alternating current unit terminals and the capacitor, the pair of direct current unit terminals of each of the unit converters are connected in parallel to the pair of direct current terminals, and the pair of alternating current unit terminals of each of the unit converters are connected in series between the pair of alternating current terminals, the control section causes the direct current power on the pair of direct current terminal side to pulsate at the same frequency as the pulsation of the alternating current power on the pair of alternating current terminal side in each of the plurality of clusters to reduce the voltage ripple of the capacitor.

[0011] <Effects of the Invention>

[0012] According to the technology of the present disclosure, it is possible to suppress the large-scale of the capacitor of each unit converter that is caused by the single-phase power pulsation. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a diagram illustrating a configuration example of a power conversion device according to one embodiment.

[0014] Figure 2 is a timing chart illustrating one example of the relationship between the input / output power and the capacitor voltage of a power conversion device.

[0015] Figure 3 is a diagram for explaining the relationship between the input / output power in the capacitor between the direct current-direct current converter (inverter side) and the direct current-alternating current converter (converter side).

[0016] Figure 4 is a block diagram illustrating a configuration example of a control section according to the first embodiment.

[0017] Figure 5 is a block diagram specifically illustrating a configuration example of a control section according to the first embodiment.

[0018] Figure 6 is a timing chart illustrating an operation example of a control section according to the first embodiment.

[0019] Figure 7 is a timing chart illustrating an operation example of a control section according to the first embodiment as a whole.

[0020] Figure 8This is a block diagram showing an example of the configuration of the control unit according to the second embodiment.

[0021] Figure 9 This is a block diagram showing an example of the configuration of the phase separation section.

[0022] Figure 10 This is a block diagram specifically illustrating a first configuration example of the control unit according to the second embodiment.

[0023] Figure 11 This is a block diagram specifically illustrating a second configuration example of the control unit according to the second embodiment.

[0024] Figure 12 This is a block diagram showing an example of the configuration of the control unit according to the third embodiment.

[0025] Figure 13 This is a block diagram specifically illustrating an example of the configuration of the control unit according to the third embodiment.

[0026] Symbol Explanation

[0027] 10 Power conversion device

[0028] 11U, 11V, 11W Cluster

[0029] 12 DC-DC converters

[0030] 13 DC-AC converter

[0031] 14 Power System

[0032] 15 Capacitors

[0033] 16 Inverter Circuit

[0034] 17. High-frequency transformer

[0035] 18. Converter Circuit

[0036] 19 Inverter Circuit

[0037] 20-unit converter

[0038] 30, 30A Control Unit

[0039] 31 Current Command Section

[0040] 32 Compensation Department

[0041] 33 Pulsating Extraction Section

[0042] 34 Compensation Calculation Department

[0043] 35u, 35v, 35w adder

[0044] 36. Phase separation section

[0045] 37 Phase Detection Unit

[0046] 38. Reference Signal Generation Unit

[0047] 40U, 40V, 40W reactor

[0048] a and b, a pair of DC terminals

[0049] c and d are a pair of AC terminals.

[0050] e, f A pair of DC unit terminals

[0051] g, h A pair of AC unit terminals Detailed Implementation

[0052] The implementation method will be described below.

[0053] Figure 1 This is a diagram illustrating an example configuration of a power conversion device according to one embodiment. Figure 1 The power conversion device 10 shown converts the input DC power into three-phase AC power and outputs it to the three-phase power system 14. The power conversion device 10 includes multiple clusters 11 (11U, 11V, 11W), multiple reactors 40 (40U, 40V, 40W), and a control unit 30.

[0054] Multiple clusters 11 are interconnected, in Figure 1 In the example shown, it is star-connected. Each of the multiple clusters 11 has a pair of DC terminals a and b, a pair of AC terminals c and d, and one or more unit converters 20. Figure 1 In the example shown, multiple clusters 11 each have three identical unit converters 20 and are connected to the power system 14 via multiple reactors 40. The connection to the power system 14 may be via a transformer not shown.

[0055] Each of the multiple clusters 11 has a pair of DC terminals a and b 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 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 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 reactor 40W. The AC terminals d of each phase cluster 11 are interconnected at the neutral point.

[0056] Multiple unit converters 20 in each phase convert DC power input from a common DC path into AC power and output it. Each of the multiple unit converters 20 in each phase has a capacitor 15, a pair of DC unit terminals e and f, a pair of AC unit terminals g and h, a DC-DC converter 12, and a DC-AC converter 13. The multiple unit converters 20 in each phase are connected in series via a pair of AC unit terminals g and h.

[0057] Each of the multiple unit converters 20 has a pair of DC unit terminals e and f connected in parallel to a pair of DC terminals a and b of its respective cluster 11. Each of the multiple unit converters 20 has a pair of AC unit terminals g and h connected in series between a pair of AC terminals c and d of its respective cluster 11.

[0058] A DC-DC converter 12 is connected between a pair of DC unit terminals e and f and a capacitor 15. The DC-DC converter 12 converts DC power input from the pair of DC unit terminals e and f into DC power of a predetermined voltage and outputs it to the capacitor 15. The DC-DC converter 12 is, for example, an isolated DC / DC converter. The DC-DC converter 12 may include, for example, an inverter circuit 16 that converts DC power into high-frequency AC power, a high-frequency transformer 17 that converts the AC power into a predetermined AC voltage, and a converter circuit 18 that converts the converted AC power into DC power of the predetermined voltage. Figure 1 An exemplary example is shown where the DC-DC converter 12 is a DAB (Dual Active Bridge) converter.

[0059] Capacitor 15 is a capacitor element that smooths the voltage of the DC link between DC-DC converter 12 and DC-AC converter 13. More specifically, it smooths the voltage output from converter circuit 18 of DC-DC converter 12.

[0060] A DC-AC converter 13 is connected between a pair of AC unit terminals g and h and a 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 unit terminals g and h. The DC-AC converter 13 has an inverter circuit 19 for converting DC power into AC power.

[0061] Inverter circuit 16, converter circuit 18, and inverter circuit 19 each include a power conversion circuit with multiple switching elements and a drive circuit section (not shown) that enables the power conversion circuit to operate. The switching elements include, for example, transistors and diodes connected in anti-parallel to the transistors. Specific examples of transistors include IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).

[0062] The control unit 30 is a control device for controlling multiple clusters 11, and includes, for example, a memory and a processor. The functions of the control unit 30 are implemented by using a program stored in the memory to make a processor such as a CPU (Central Processing Unit) work. The functions of the control unit 30 can be implemented using a FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0063] In the power conversion device 10, the control unit 30 outputs voltage waveforms with each of the multiple unit converters 20 having a different phase from each other, thereby enabling the output of a multi-stage voltage waveform with a voltage exceeding the withstand voltage of the switching elements and with reduced harmonics.

[0064] The power conversion device 10 can be applied, for example, to the PCS (Power Conditioning System) of photovoltaic power generation devices, the STATCOM (Statistical Power Compensation System), and the HVDC (Hypervoltage Direct Current) transmission system.

[0065] Next, the voltage ripple of capacitor 15 will be explained. It should be noted that, for ease of understanding, the explanation will be based on the example of one unit converter in each phase.

[0066] Figure 2 This is a timing diagram illustrating an example of the relationship between the input and output power of a power conversion device and the capacitor voltage when the system voltage and system current of power system 14 are sinusoidal. Figure 3 This diagram illustrates the relationship between the input and output power in the capacitor between the DC-DC converter 12 (converter side) and the DC-AC converter 13 (inverter side). Figure 2 and Figure 3The diagram shows the relationship between the input power of phase U, the output power of phase U, and its differential power (= the power entering and exiting capacitor 15) when power is supplied to a symmetrical three-phase load.

[0067] Under the condition that the input power factor is 1, the instantaneous input power P U This is represented as follows (e.g., U phase).

[0068] [Number 1]

[0069]

[0070] Among them, V U I is the maximum value of the system voltage of phase U. U Let ω be the maximum value of the system current in phase U, ω be the system angular frequency, and t be time. From formula (1), it is clear that the output power of phase U pulsates at a frequency twice the system angular frequency ω. At this time, the voltage across capacitor 15 (capacitor voltage E) is... DC The current pulsates (pulsation ΔE) by the current flowing into and out of capacitor 15 due to electrical pulsation. DC ).

[0071] The change in electrostatic energy ΔE of capacitor 15 is expressed as follows.

[0072] [Number 2]

[0073]

[0074]

[0075] According to formulas (2) and (3), the capacitor voltage ripple D is expressed as follows.

[0076] [Number 3]

[0077]

[0078] The maximum value of the system voltage of phase U, V U The maximum value of the system current in phase U, I U The system angular frequency ω and the capacitor voltage E DC The value is determined by the circuit specifications (fixed value). If the capacitor capacitance C is increased in order to reduce the capacitor voltage ripple D, the capacitor 15 will become larger, which in turn will lead to the power conversion device 10 becoming larger.

[0079] exist Figure 1In the illustrated embodiment, the control unit 30 pulsates the DC power on the pair of DC terminals a and b at the same frequency as the pulsation of the AC power on the sides of the pair of AC terminals c and d in each of the plurality of 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 and b of the U-phase cluster 11U at the same frequency as the pulsation of the AC power on the sides of the pair of AC terminals c and 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 and b of the V-phase cluster 11V at the same frequency as the pulsation of the AC power on the sides of the pair of AC terminals c and 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 DC terminals a and b of the W-phase cluster 11W at the same frequency as the pulsation of the AC power on the AC terminals c and d sides of the W-phase cluster 11W, thereby reducing the voltage ripple of the capacitor 15 of the W-phase cluster 11W. By performing this control by the control unit 30, the power conversion device 10 according to this embodiment can suppress the distortion of the AC current flowing through the AC terminals c and d in each of the plurality of clusters 11, and can also suppress the distortion generated in the system current of the power system 14. Since the voltage ripple of the capacitor 15 of each of the plurality of clusters 11 is reduced, the increase in the capacitance of each capacitor 15 can be suppressed. Therefore, the enlargement of the capacitor 15 can be suppressed, and consequently, the enlargement of the power conversion device 10 can be suppressed.

[0080] In each of the plurality of clusters 11, the control unit 30 superimposes a compensation power that varies according to the pulsation of the AC power on the side of a pair of DC terminals a and b. By superimposing this compensation power of each phase onto the DC power of the corresponding phase and adjusting the distribution of DC power input from the common DC path among the three phases, the control unit 30 reduces the capacitor voltage ripple D caused by single-phase power pulsation. Through this control by the control unit 30, the power conversion device 10 according to this embodiment can suppress the distortion of the AC current flowing through the pair of AC terminals c and d in each of the plurality of clusters 11, and can also suppress the distortion generated in the system current of the power system 14. By adjusting the distribution of input power among the clusters and equally distributing the power input to the converter units belonging to the same cluster, the control unit 30 can further reduce the capacitor voltage ripple D of each phase.

[0081] Even if the control unit 30 pulsates the DC power input to the pair of DC terminals a and b of each phase based on the pulsation of the AC power on the AC terminals c and d, due to Figure 1The circuit shown is a three-phase circuit, so it has almost no effect on the DC bus side connected to the pair of DC terminals a and b of each phase.

[0082] For example, the constant portion of the DC power on the DC terminals a and b sides of each phase, and the constant portion of the AC power on the AC terminals c and d sides of each phase, are both set to 200kW. Furthermore, the pulsating portions of the AC power on the AC terminals c and d sides of each phase in U, V, and W are set to 200sin2ωt, 200sin(2ωt-4π / 3), and 200sin(2ωt-2π / 3) respectively (all in kW). Additionally, α is set as a compensation coefficient less than 1. At this time, the control unit 30 superimposes a compensation power of 200αsin2ωt on the constant portion of the DC power in phase U, 200αsin(2ωt-4π / 3) on the constant portion of the DC power in phase V, and 200αsin(2ωt-2π / 3) on the constant portion of the DC power in phase W. Therefore, there is almost no effect on the DC bus side of the pair of DC terminals a and b connected to each phase (200αsin2ωt+200αsin(2ωt-4π / 3)+200αsin(2ωt-2π / 3)=0).

[0083] The control unit 30 adjusts the magnitude of the compensation power superimposed on the DC power of each phase according to the compensation coefficient α. If the capacitance of the capacitor 15 is too small, it may lead to a deterioration of voltage control disturbances (control stability). However, by introducing the compensation coefficient α, the possibility of this deterioration can be reduced.

[0084] Figure 4 This is a block diagram showing an example of the configuration of the control unit according to the first embodiment. Figure 4 The control unit 30A shown is an example of the control unit 30 described above. The control unit 30A includes a current command unit 31 and a compensation unit 32A. The current command unit 31 generates a current command to turn multiple switching elements within the DC-DC converter 12 on or off in a manner that causes the voltage of the capacitor 15 to become a predetermined target voltage. The current command unit 31 supplies the current commands for each phase cluster 11 to the compensation unit 32A. In each of the multiple clusters 11, the compensation unit 32A compensates for the DC power input to a pair of DC terminals a and b by superimposing a phase change at the same frequency as the pulsation of the AC power output from a pair of AC terminals c and d. The compensation unit 32A includes a pulsation extraction unit 33, a compensation amount calculation unit 34, and adders 35 (35u, 35v, 35w).

[0085] Figure 5 This is a block diagram specifically illustrating an example of the configuration of the control unit according to the first embodiment. Figure 6This is a waveform diagram illustrating an example of the configuration of each part. The compensation unit 32A extracts the pulsation of the AC power output from a pair of AC terminals c and d in each of the plurality of clusters 11, and adjusts the compensation power superimposed on the DC power input to a pair of DC terminals a and b based on the extracted pulsation. The compensation unit 32A includes a pulsation extraction unit 33, a compensation amount calculation unit 34, and adders 35 (35u, 35v, 35w).

[0086] The pulsation extraction unit 33 calculates the AC power (the output power of the system side of each phase) at a pair of AC terminals c and d of each phase by multiplying the system current and system voltage of the power system 14 for each phase. The pulsation extraction unit 33 adds up the output power of the system side of each phase and divides the sum by the number of phases (3 in this case). By subtracting the value calculated by this division from the output power of the system side of each phase, the pulsation extraction unit 33 can remove the constant portion of the output power of the system side of each phase, thereby extracting the output power of the system side of each phase.

[0087] The compensation calculation unit 34 calculates the compensation power as the product of the extracted pulsating portion of each phase and the compensation coefficient α. Therefore, the magnitude of the compensation power superimposed on the DC power input to each phase can be adjusted using the compensation coefficient α. The compensation calculation unit 34 calculates the compensation current superimposed on the current command of each phase (an example of the compensation amount) by dividing the compensation power of each phase by the measured value of the DC bus voltage. The DC bus voltage can be the voltage of the DC path connected to a pair of DC terminals a and b, or the voltage between a pair of DC terminals a and b.

[0088] Adder 35 (35u, 35v, 35w) generates compensated current commands for each phase by adding the corresponding phase compensation current to the current commands for each phase.

[0089] The control unit 30A generates control commands from the compensated current commands of each phase for controlling the DC-DC converters 12 within the cluster 11 of each phase. When the DC-DC converter 12 is a DAB converter, the control unit 30A generates the phase difference between the primary and secondary sides 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. An LLC converter is a converter that utilizes the resonance caused by the leakage inductance and magnetizing inductance of the transformer and the capacitance of the capacitor elements.

[0090] Through compensation section 32A, such as Figure 6As shown, because the difference in power between capacitor 15 and capacitor 15 decreases, the accumulated amount in capacitor 15 decreases. Because the accumulated amount in capacitor 15 decreases, the voltage ripple of capacitor 15 decreases.

[0091] The compensation calculation unit 34 can effectively reduce the voltage ripple of capacitor 15 by adjusting the compensation coefficient α according to the target value of the voltage ripple of capacitor 15. The target value of the voltage ripple of capacitor 15 is determined, for example, based on the formula (4) described above. Alternatively, the compensation coefficient α can be a predetermined fixed value, in which case the amount of compensation power calculation performed by the compensation calculation unit 34 can be reduced.

[0092] Figure 7 This is a timing diagram showing an overall example of the operation of the control unit according to the first embodiment. (As shown) Figure 7 As shown, the voltage ripple of the capacitors in each phase can be reduced by the control unit according to the first embodiment.

[0093] Figure 8 This is a block diagram illustrating an example configuration of the control unit according to the second embodiment. In the second embodiment, the description of the same configuration and effects as in the first embodiment is based on the above description, with omissions or simplifications. Figure 8 The control unit 30B shown is an example of the control unit 30 described above. The control unit 30B has a current command unit 31 and a compensation unit 32B. The current command unit 31 is the same as in the first embodiment. The compensation unit 32B, in each of the plurality of clusters 11, superimposes a phase change on the DC power input to a pair of DC terminals a and b to compensate for the AC power output from a pair of AC terminals c and d at the same frequency as the pulsation. The compensation unit 32B has a forward / reverse phase separation unit 36, a pulsation extraction unit 33, a compensation amount calculation unit 34, and adders 35 (35u, 35v, 35w).

[0094] The compensation unit 32B determines the compensation power from the positive and negative components of the system voltage and system current, respectively. This is because, in the case of an imbalance in the output power from each cluster, pulsations will occur in the output power. The positive and negative phase separation unit 36 ​​calculates the positive phase voltage, positive phase current, negative phase voltage, and negative phase current, as shown in the following formula, from the measurement results of the system voltage and system current.

[0095] [Number 4]

[0096]

[0097]

[0098]

[0099]

[0100] Figure 9 This is a block diagram showing an example of the configuration of the forward and reverse phase separation section. The forward and reverse phase separation section performs dq-axis transformation from phase abc for the measured system voltage and system current, and separates them into forward and reverse parts to calculate the forward voltage, reverse voltage, forward current, and reverse current.

[0101] Figure 10 This is a block diagram specifically illustrating 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 described above. In each of the plurality of clusters 11, the compensation unit 32Ba extracts the pulsation of the AC power output from a pair of AC terminals c and d, and adjusts the compensation power superimposed on the DC power input to a pair of DC terminals a and b according to the extracted pulsation. The compensation unit 32Ba has a forward and reverse phase separation unit 36, a pulsation extraction unit 33, a compensation amount calculation unit 34, and adders 35 (35u, 35v, 35w).

[0102] The pulsation extraction unit 33 calculates the first power of each phase by multiplying the positive current and positive voltage output by the positive-phase separation unit 36 ​​for each phase, and calculates the second power of each phase by multiplying the negative current and negative voltage output by the positive-phase separation unit 36 ​​for each phase. The pulsation extraction unit 33 calculates the positive power of each phase (the sum of the first power and the second power) by adding the first power and the second power for each phase, and divides the positive power of each phase by the number of phases (3 in this case). The pulsation extraction unit 33 extracts the pulsating portion of the system-side output power of each phase by subtracting the value calculated by this division from the positive power of each phase.

[0103] Figure 11 This is a block diagram specifically illustrating 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 described above. Figure 11 The compensation part 32Bb and Figure 10 The difference between the compensation section 32Ba and the pulsation extraction section 33 is that the structure of the pulsation extraction section is different, but the function is the same as that of the compensation section 32Ba.

[0104] Figure 11The pulsation extraction unit 33 calculates the first power of each phase by multiplying the positive-phase current and positive-phase voltage output from the positive-phase separation unit 36 ​​for each phase, and calculates the second power of each phase by multiplying the negative-phase current and negative-phase voltage output from the positive-phase separation unit 36 ​​for each phase. The pulsation extraction unit 33 divides the value obtained by adding the first power of each phase by the number of phases (3 in this case). The pulsation extraction unit 33 extracts the pulsation portion of the first power on the system side of each phase by subtracting the value obtained by this division from the first power of each phase. The pulsation extraction unit 33 extracts the pulsation portion of the second power on the system side of each phase by subtracting the value obtained by this division from the second power of each phase.

[0105] The pulsation extraction unit 33 adds the pulsation portion of the first power on the system side of each phase and the pulsation portion of the second power on the system side of each phase, and outputs the added pulsation portion of each phase to the compensation calculation unit 34.

[0106] Figure 12 This is a block diagram illustrating an example configuration of the control unit according to the third embodiment. In the third embodiment, the description of the same configuration and effects as in the first and second embodiments is based on the above description for omission or simplification. Figure 12 The control unit 30C shown is an example of the control unit 30 described above. Figure 12 The compensation unit 32C 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 includes a phase detection unit 37, a reference signal generation unit 38, a compensation amount calculation unit 34, and an adder 35 (35u, 35v, 35w). Figure 13 This is a block diagram specifically illustrating an example of the configuration of the control unit according to the third embodiment.

[0107] The phase detection unit 37 acquires the phase of the system voltage of each phase of the power system 14. The reference signal generation unit 38 uses the phase θ of the system voltage of each phase detected by the phase detection unit 37 to generate a reference signal for each phase. The reference signal generation unit 38 generates a reference signal sin2θ for phase U, a reference signal sin(2θ-4π / 3) for phase V, and a reference signal sin(2θ-2π / 3) for phase W.

[0108] The compensation calculation unit 34 calculates the compensation power, which is the product of the reference signal for each phase and the compensation coefficient α. Therefore, the magnitude of the compensation power superimposed on the DC power input to each phase can be adjusted using the compensation coefficient α. Subsequent control procedures are the same as in the implementation described above.

[0109] The power conversion device has been described above through embodiments, but the present invention is not limited to the above embodiments. Within the scope of the present invention, various modifications and improvements can be made, such as combinations or substitutions with some or all of the other embodiments.

[0110] For example, an isolated DC / DC converter is not limited to a configuration where full-bridge circuits are provided on both the primary and secondary sides of the transformer, but can also be a half-bridge circuit where a bridging circuit is provided on at least one of the primary and secondary sides. Furthermore, an isolated DC / DC converter is not limited to a DAB converter, but can also be a converter of other forms (such as LLC converters, flyback converters, feedforward converters, etc.).

Claims

1. A power conversion device, comprising: Multiple clusters are interconnected; as well as The control unit controls the multiple clusters. Each of the plurality of clusters has a pair of DC terminals, a pair of AC terminals, and one or more unit converters. Each of the unit converters includes a capacitor, a pair of DC unit terminals, a pair of AC unit terminals, a DC-DC converter connected between the pair of DC unit terminals and the capacitor, and a DC-AC converter connected between the pair of AC unit terminals and the capacitor. The pair of DC unit terminals of each of the unit converters are connected in parallel with the pair of DC terminals. The pair of AC unit terminals of each of the unit converters are connected in series between the pair of AC terminals. The control unit, in each of the plurality of clusters, converts the DC power on the pair of DC terminals into pulsating power via the DC-DC converter at the same frequency as the pulsation of the AC power on the pair of AC terminals and outputs it to reduce the voltage ripple of the capacitor.

2. The power conversion device according to claim 1, wherein, The control unit superimposes a compensation power that varies according to the pulsation of the AC power onto the DC power.

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

4. The power conversion device according to claim 3, wherein, The control unit adjusts the compensation coefficient according to the target value of the 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 any one of claims 2 to 4, wherein, The control unit extracts the pulsation of the AC power and adjusts the compensation power according to the extracted pulsation.

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

8. The power conversion device according to claim 6, wherein, The control unit calculates the positive phase voltage, positive phase current, reverse phase voltage, and reverse phase current from the results obtained by measuring the voltage and current on the pair of AC terminals, and extracts the pulsation of the AC power from the calculated positive phase voltage, positive phase current, reverse phase voltage, and reverse phase current.

9. The power conversion device according to any one of claims 1 to 4, wherein, The control unit obtains the phase of the system voltage of each phase of the power system that supplies the multiple clusters for connection, and pulsates the DC power according to the obtained phase of the system voltage of each phase.

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