Power conversion device

Abstract

A power conversion device (100) includes: an inverter (2) that receives an input voltage and generates an inverter voltage; a filter (3) that receives the inverter voltage and outputs an output voltage; a detection unit (4) that detects a DC component of the output voltage; a feedback control unit (5) that receives an AC voltage command and the DC component and determines an inverter voltage command so that the DC component becomes equal to a target value; and a PWM control unit (6) that receives the inverter voltage command and performs pulse width modulation control of the inverter (2). The target value is zero or a value in accordance with the offset error of the detection unit (4). The feedback control unit (5) calculates a compensation amount for compensating the DC component and determines, as the inverter voltage command, the AC voltage command on which the product of the absolute value of sine waves synchronized with the period of the AC voltage command and the compensation amount is superimposed.

Description

Technical Field

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

Background Art

[0002] Conventionally, a power conversion device including an inverter that converts a DC voltage into an AC voltage has been known. Various loads are connected to such a power conversion device, and a DC component corresponding to the load conditions may be generated in the output voltage. Japanese Patent Application Laid-Open No. 6-098559 (Patent Document 1) discloses a circuit for suppressing such a DC component. The circuit disclosed in Patent Document 1 includes a pulse signal modulation unit that changes a pulse signal for operating the switch element of the inverter circuit every half cycle according to the magnitude of the DC component so as to cancel the DC component in the AC output of the inverter circuit.

[0003] In a power conversion device that generates a voltage simulating a power system independently of the power system, a system connection device may be connected as a load. When the power system enters an island operation state where the power system has disappeared, the system connection device takes anti-island operation measures defined by the system connection regulations (JEAC9701) from the viewpoints of the safety of personnel and equipment and system restoration. The anti-island operation measures include an island operation detection function and a function of disconnecting the system connection device via a protection relay or the like when the island operation is determined by the island operation detection function.

[0004] As the island operation detection function, there are a passive island operation detection function such as detecting changes in the phase, distortion, and frequency of the system voltage, and an active island operation detection function that promotes the change from the change in the frequency of the system voltage. The active island operation detection function injects reactive power so as to promote the change from the change in the frequency of the AC voltage to be measured.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When a load and a grid connection device are connected to a power conversion device, a DC component corresponding to the load condition is generated in the output voltage of the power conversion device, and when a frequency change occurs, reactive power can be injected by the active mode single operation detection function of the grid connection device. The frequency change corresponds to the variation of the zero-crossing interval obtained from the positive half-cycle period and the negative half-cycle period. When reactive power is injected, the frequency change of the output voltage of the power conversion device is promoted. Therefore, finally, the grid connection device is disconnected by single operation detection, and the grid connection device cannot be used. In the technology disclosed in Patent Document 1, the pulse signal changes according to the magnitude of the DC component every half cycle. Therefore, it takes time to suppress the DC component and the frequency change generated in the output voltage of the power conversion device. In particular, when the DC component fluctuates transiently, such as when the load is connected or disconnected, the DC component and the frequency change cannot be suppressed early.

[0007] The present disclosure has been made to solve the above problems, and an object thereof is to provide a power conversion device capable of suppressing a DC component and a frequency change generated in an output voltage early.

Means for Solving the Problems

[0008] A power conversion device according to an aspect of the present disclosure includes at least one circuit that receives a DC input voltage and performs power conversion. Each of the at least one circuit includes an inverter that receives the input voltage and generates an inverter voltage, a filter that receives the inverter voltage and outputs an output voltage, a detection unit that detects a DC component of the output voltage, a feedback control unit that receives an AC voltage command and the DC component and determines an inverter voltage command so that the DC component becomes a target value, and a PWM control unit that receives the inverter voltage command and performs pulse width modulation control on the inverter. The target value is zero or a value corresponding to an offset error of the detection unit. The feedback control unit calculates a compensation amount for compensating the DC component, and determines an AC voltage command in which the product of the absolute value of a sine wave synchronized with the period of the AC voltage command and the compensation amount is superimposed as the inverter voltage command.

Advantages of the Invention

[0009] According to the power conversion device according to an aspect of the present disclosure, the feedback control unit constantly detects the DC component, and determines a voltage command to the inverter so that the DC component becomes zero or a value corresponding to the offset error. Thereby, the DC component of the output voltage from the filter can be suppressed at an early stage. Furthermore, by determining the inverter voltage command by superimposing the product of the absolute value of a sine wave synchronized with the period of the AC voltage command and the compensation amount on the AC voltage command, the frequency change of the output voltage from the filter is suppressed at an early stage. In this way, the DC component and the frequency change generated in the output voltage are suppressed at an early stage.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Hereinafter, a plurality of embodiments will be described, but it has been planned from the beginning of the application to appropriately combine the configurations described in each embodiment. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions will not be repeated. Furthermore, the forms of the constituent elements shown throughout the specification are merely examples and are not limited to these descriptions.

[0012] Embodiment 1. (Configuration of Power Conversion Device) FIG. 1 is a diagram showing the configuration of a power conversion device according to Embodiment 1. As shown in FIG. 1, the power conversion device 100 includes an inverter 2, a filter 3, and an inverter control circuit 9.

[0013] The inverter 2 receives the DC input voltage from the DC power supply 1 and generates an AC voltage (hereinafter referred to as the "inverter voltage") Vinv. The inverter 2 is a full-bridge inverter and includes semiconductor switching elements 2a to 2d. That is, the inverter 2 includes a circuit in which two legs, each having a configuration in which two upper arms (semiconductor switching elements 2a and 2c) and two lower arms (semiconductor switching elements 2b and 2d) are connected in series, are connected in parallel. Among the semiconductor switching elements 2a to 2d, the semiconductor switching elements located diagonally operate at the same timing. Specifically, the semiconductor switching element 2a, which is the upper arm of the left leg, and the semiconductor switching element 2d, which is the lower arm of the right leg, perform a switching operation at the same timing. Also, the semiconductor switching element 2b, which is the lower arm of the left leg, and right the semiconductor switching element 2c, which is the upper arm of the leg, perform a switching operation at the same timing.

[0014] The filter 3 receives the inverter voltage Vinv and outputs an AC output voltage Vc. The filter 3 illustrated in FIG. 1 is an LC filter including an inductor L and a capacitor C.

[0015] The inverter control circuit 9 controls the inverter 2. As shown in FIG. 1, the inverter control circuit 9 includes a detection unit 4, a feedback control unit 5, and a PWM (Pulse Width Modulation) control unit 6.

[0016] The detection unit 4 detects the DC component DCVc of the output voltage Vc. For example, the detection unit 4 is composed of a voltage detector 4a that detects the voltage of the capacitor C and a low-pass filter 4b. The detection unit 4 constantly detects the DC component DCVc of the output voltage Vc by smoothing the AC component of the output voltage Vc.

[0017] The feedback control unit 5 receives the AC voltage command, the DC component DCVc detected by the detection unit 4, and the target value DCVc*, and determines the inverter voltage command Vinv* so that the DC component DCVc becomes the target value DCVc*.

[0018] The AC voltage command is represented by the product of its amplitude (maximum value) V* and a sine wave sinθ synchronized with its period, and corresponds to the target value of the output voltage Vc.

[0019] The target value DCVc* is the target value of the DC component DCVc and is set according to the offset error in the detection unit 4. The offset error is a detection error caused by variations in component constants, temperature changes, etc. in the path from the input terminal of the voltage detector 4a to the output terminal of the low-pass filter 4b. When there is no offset error, zero is set as the target value DCVc*. Note that when there is no offset error, it also includes cases where the offset error is small enough to be negligible. When there is an offset error, a value corresponding to the offset error (the offset error itself in the example shown in FIG. 1) is set as the target value DCVc*.

[0020] The inverter voltage command Vinv* corresponds to the target value of the inverter voltage Vinv output from the inverter 2.

[0021] The feedback control unit 5 calculates a compensation amount for compensating the DC component DCVc, and determines an AC voltage command in which the product of the absolute value of the sine wave sinθ synchronized with the period of the AC voltage command and the compensation amount is superimposed as the inverter voltage command Vinv*.

[0022] As shown in FIG. 1, the feedback control unit 5 includes a subtractor 51, a calculator 52, a multiplier 53, an absolute value circuit 54, a multiplier 55, and an adder 56.

[0023] The subtractor 51 subtracts the DC component DCVc from the target value DCVc*. That is, the subtractor 51 calculates the deviation between the target value DCVc* and the DC component DCVc.

[0024] The arithmetic unit 52 receives the output of the subtractor 51 and calculates a compensation amount for compensating the DC component DCVc. For example, the arithmetic unit 52 calculates the compensation amount by PI (Proportional-Integral) calculation using the deviation between the target value DCVc* and the DC component DCVc.

[0025] The multiplier 53 multiplies the amplitude V* of the AC voltage command and the sine wave sinθ synchronized with the period of the AC voltage command.

[0026] The absolute value circuit 54 receives the sine wave sinθ synchronized with the period of the AC voltage command and outputs the absolute value of the sine wave sinθ.

[0027] The multiplier 55 multiplies the absolute value of the sine wave sinθ output from the absolute value circuit 54 and the compensation amount output from the arithmetic unit 52.

[0028] The adder 56 adds the output of the multiplier 53 and the output of the multiplier 55. The inverter voltage command Vinv* is output from the adder 56. The output of the multiplier 53 is the AC voltage command. Therefore, the output of the multiplier 55 corresponds to the correction component superimposed on the AC voltage command. The adder 56 generates the inverter voltage command Vinv* by superimposing the output (correction component) of the multiplier 55 on the AC voltage command.

[0029] The PWM control unit 6 receives the inverter voltage command Vinv* and performs pulse width modulation control on the inverter 2. Specifically, the PWM control unit 6 controls the on / off of each of the semiconductor switching elements 2a to 2d included in the inverter 2.

[0030] A DC power supply 1 is connected to the input terminal of the power conversion device 100. For example, a load 7 and a system connection device 8 are connected to the output terminal of the power conversion device 100. Only one of the load 7 and the system connection device 8 may be connected to the output terminal of the power conversion device 100. The type of the load 7 is not particularly limited. The load 7 illustrated in FIG. 1 includes, for example, a transformer and a half-wave rectifier circuit. Note that the load 7 (or a part of the load 7) may be detachable from the power conversion device 100.

[0031] (Operation example) Referring to FIG. 2, an operation example of the power conversion device 100 will be described. FIG. 2 is a diagram showing an operation example of the power conversion device according to Embodiment 1. In FIG. 2, before and after the connection of the load 7 including the half-wave rectifier circuit, the output voltage Vc, the average value Vcavg per basic period of the output voltage Vc, the current output from the inverter 2 (hereinafter referred to as "inverter current IL"), and the difference between the positive half-cycle period T1 and the negative half-cycle period T2 of the output voltage Vc are shown.

[0032] As shown in FIG. 2, due to the connection of the load 7 including the half-wave rectifier circuit, the inverter current IL becomes zero in one of the polarities (negative polarity in the figure) of the positive and negative polarities of the output voltage Vc. The waveform of the output voltage Vc decreases by the amount of the reactor voltage drop in the one-sided polarity (positive polarity in the figure) where current is generated from a waveform with symmetric positive and negative polarities. Due to the decrease in the voltage of the one-sided polarity, the average value Vcavg per basic period of the output voltage Vc decreases from zero. The average value Vcavg corresponds to the DC component DCVc of the output voltage Vc. Although the average value Vcavg decreases from zero, the positive half-cycle period T1 and the negative half-cycle period T2 of the output voltage Vc do not change significantly immediately after the connection of the load 7.

[0033] Due to the decrease in the voltage of the one-sided polarity, a DC component DCVc of the output voltage Vc is generated. When the DC component DCVc is generated, a compensation amount for compensating the DC component DCVc is calculated, and an AC voltage command in which the product of the absolute value of the sine wave sinθ synchronized with the period of the AC voltage command and the compensation amount is superimposed is determined as the inverter voltage command Vinv*.

[0034] In the example shown in FIG. 2, since the voltage of the positive polarity is decreasing, a negative DC component DCVc is generated. Therefore, when zero is set as the target value DCVc*, a positive deviation is output from the subtracter 51 shown in FIG. 1. The arithmetic unit 52 calculates a positive compensation amount in order to compensate for the negative DC component DCVc. Then, the feedback control unit 5 determines an AC voltage command in which the product of the absolute value of the sine wave sinθ and the positive compensation amount is superimposed as the inverter voltage command Vinv*. As a result, the DC component DCVc of the output voltage Vc is adjusted to zero.

[0035] Also, in order to determine the inverter voltage command Vinv* as an AC voltage command in which the product of the absolute value of the sine wave sinθ synchronized with the period of the AC voltage command and the compensation amount is superimposed, the voltage fluctuation near the zero cross by the feedback control is small. Therefore, changes in the positive half-wave period T1 and the negative half-wave period T2 of the output voltage Vc can be suppressed.

[0036] (Comparison with the reference form) FIG. 3 is a diagram showing the configuration of a power conversion device according to the reference form. The power conversion device 900 shown in FIG. 3 includes an inverter control circuit 909 instead of the inverter control circuit 9 as compared with the power conversion device 100 shown in FIG. 1. The inverter control circuit 909 is different in that it includes a feedback control unit 905 instead of the feedback control unit 5 as compared with the inverter control circuit 9 shown in FIG. 1. The feedback control unit 905 is different in that it does not include the absolute value circuit 54 and the multiplier 55, and includes an adder 956 instead of the adder 56 as compared with the feedback control unit 5 shown in FIG. 1.

[0037] The adder 956 adds the output of the multiplier 53 and the output (compensation amount) of the arithmetic unit 52. The inverter voltage command Vinv* is output from the adder 956. That is, the feedback control unit 905 determines an AC voltage command in which the compensation amount itself is superimposed as the inverter voltage command Vinv*.

[0038] FIG. 4 is a diagram showing an operation example of the power conversion device according to the reference embodiment. In FIG. 4, as in FIG. 2, before and after the load 7 including the half-wave rectifier circuit is turned on, the output voltage Vc, the average value Vcavg per basic period of the output voltage Vc, the inverter current IL, and the difference between the positive half-wave period T1 and the negative half-wave period T2 of the output voltage Vc are shown.

[0039] As shown in FIG. 4, due to the decrease in the voltage of one-sided polarity, the average value Vcavg per basic period of the output voltage Vc decreases from zero. As a result, the DC component DCVc of the output voltage Vc is generated. When the DC component DCVc is generated, the feedback control unit 905 calculates a compensation amount for compensating the DC component DCVc, and determines an AC voltage command with the compensation amount superimposed as the inverter voltage command Vinv*. Thereby, the DC component DCVc of the output voltage Vc is adjusted to zero. That is, the average value Vcavg per basic period of the output voltage Vc is adjusted to zero.

[0040] However, when adjusting the average value Vcavg to zero, since the compensation amount itself is superimposed on the output voltage Vc, as shown in FIG. 4, the positive half-wave period T1 and the negative half-wave period T2 of the output voltage Vc change greatly.

[0041] When the positive half-wave period T1 and the negative half-wave period T2 of the output voltage Vc change greatly, it gives a large fluctuation to the frequency change detected by the grid-connected device 8. As a result, the grid-connected device 8 injects reactive power by the active mode single operation detection function.

[0042] FIG. 5 is a diagram showing an example of a method for determining the injection power of reactive power by the grid-connected device. In FIG. 5, a graph showing the relationship between the frequency change amount dF detected by the grid-connected device 8 and the reactive power injection force Q* is shown. The frequency change amount dF is detected based on the positive half-wave period T1 and the negative half-wave period T2 of the voltage at the AC connection terminal in the grid-connected device 8. The grid-connected device 8 determines the reactive power injection force Q* corresponding to the detected frequency change amount dF according to the graph shown in FIG. 5.

[0043] As shown in FIG. 5, the system connection device 8 determines the reactive power injection power Q* according to the gain G1 when the frequency change amount dF is within the range of -dF0 to dF0, and determines the reactive power injection power Q* according to the gain G2 outside the range. dF0 is a predetermined threshold value.

[0044] The larger the injected reactive power, the greater the voltage fluctuation of the current path impedance caused by the reactive power, so the frequency change amount dF increases. The increase in the frequency change amount dF ultimately leads to the disconnection of the system connection device 8 by single operation detection. As shown in FIG. 5, generally, the gain G1 is set smaller than the gain G2. Therefore, it is expected that the power conversion device suppresses the frequency change amount dF from fluctuating outside the range of -dF0 to dF0.

[0045] In the configuration of the power conversion device 900 shown in FIG. 3, as shown in FIG. 4, the positive half-wave period T1 and the negative half-wave period T2 of the output voltage Vc change greatly. Therefore, the disconnection of the system connection device 8 caused by the injection of reactive power by the active mode single operation detection function cannot be suppressed.

[0046] On the other hand, in the configuration of the power conversion device 100 shown in FIG. 1, as shown in FIG. 2, the fluctuations of the positive half-wave period T1 and the negative half-wave period T2 of the output voltage Vc are suppressed. Therefore, the disconnection of the system connection device 8 caused by the injection of reactive power by the active mode single operation detection function can be suppressed.

[0047] (Comparison with Patent Document 1 when the DC component of the output voltage fluctuates transiently) Next, with reference to FIGS. 6 to 8, an operation example in the case where the DC component DCVc of the output voltage Vc fluctuates transiently immediately after the load 7 is connected will be described.

[0048] FIG. 6 is a diagram showing an example of the output voltage Vc when the DC component DCVc transiently varies. FIG. 7 is a diagram schematically showing a correction component superimposed on the AC voltage command when the technique described in Patent Document 1 is used. FIG. 8 is a diagram schematically showing a correction component superimposed on the AC voltage command in Embodiment 1. FIGS. 7 and 8 show the correction components generated for the output voltage Vc shown in FIG. 6. Note that the correction component shown in FIG. 8 is the output of the multiplier 55 shown in FIG. 1.

[0049] As shown in FIG. 6, the DC component DCVc is zero at time t0 when the load 7 is turned on, but is increasing monotonically.

[0050] In the technique described in Patent Document 1, the pulse signal for operating the switch element of the inverter circuit changes according to the magnitude of the DC component every half cycle. Therefore, as shown in FIG. 7, since the DC component DCVc is zero at time t0, the correction component superimposed on the AC voltage command is zero in the half cycle starting from time t0. As a result, in that half cycle, the inverter is not adjusted so that the DC component DCVc becomes zero.

[0051] At time t1 when a half cycle has elapsed from time t0, a pulse signal corresponding to the DC component DCVc is generated. Therefore, in the half cycle starting from time t1, a correction component for making the DC component DCVc at time t1 zero is superimposed on the AC voltage command. However, as shown in FIG. 6, the DC component DCVc continues to increase gradually even after time t1. Therefore, in the half cycle starting from time t1, the DC component DCVc is once adjusted to near zero immediately after time t1, but then gradually increases.

[0052] As shown in Fig. 7, when the DC component DCVc of the output voltage Vc transiently fluctuates, in the technique described in Patent Document 1, the DC component DCVc cannot be adjusted to zero early. Since the DC component DCVc is not adjusted to zero, the positive half-cycle period and the negative half-cycle period may also change. Therefore, the disconnection of the system connection device 8 caused by the injection of reactive power by the active mode single operation detection function cannot be sufficiently suppressed.

[0053] In the power conversion device 100 according to Embodiment 1, the feedback control unit 5 constantly detects the DC component DCVc, and determines the inverter voltage command Vinv* so that the DC component DCVc becomes the target value DCVc*. As a result, as shown in Fig. 8, the DC component DCVc is suppressed early.

[0054] Furthermore, since the product of the sine wave sinθ synchronized with the period of the AC voltage command and the compensation amount (correction component) is superimposed on the AC voltage command, the voltage fluctuation near the zero crossing is small. Therefore, the changes in the positive half-cycle period T1 and the negative half-cycle period T2 of the output voltage Vc are suppressed. As a result, the disconnection of the system connection device 8 caused by the injection of reactive power by the active mode single operation detection function can be suppressed.

[0055] Embodiment 2. Fig. 9 is a diagram showing the configuration of the power conversion device according to Embodiment 2. The power conversion device 200 shown in Fig. 9 is different from the power conversion device 100 shown in Fig. 1 in that it includes an inverter control circuit 209 instead of the inverter control circuit 9. The inverter control circuit 209 is different from the inverter control circuit 9 shown in Fig. 1 in that it includes a feedback control unit 205 instead of the feedback control unit 5.

[0056] Similar to the feedback control unit 5, the feedback control unit 205 calculates a compensation amount for compensating the DC component DCVc, and determines the AC voltage command with the product of the absolute value of the sine wave sinθ synchronized with the period of the AC voltage command and the compensation amount superimposed thereon as the inverter voltage command Vinv*.

[0057] The feedback control unit 205 includes a subtractor 51, a calculator 52, a divider 251, an adder 252, a subtractor 253, filters 254 and 255, multipliers 256 and 257, an adder 258, and a multiplier 259.

[0058] The divider 251 divides the compensation amount output from the calculator 52 by the amplitude V* of the AC voltage command.

[0059] The adder 252 adds 1 to the output of the divider 251 (i.e., the value obtained by dividing the compensation amount by the amplitude V* of the AC voltage command). That is, (1 + compensation amount / V*) is output from the adder 252. The subtractor 253 subtracts the output of the divider 251 from 1. That is, (1 - compensation amount / V*) is output from the subtractor 253.

[0060] The filter 254 allows the portion of the sine wave sinθ that is zero or greater and synchronized with the period of the AC voltage command to pass through. The filter 255 allows the portion of the sine wave sinθ that is zero or less and synchronized with the period of the AC voltage command to pass through.

[0061] The multiplier 256 multiplies the output of the adder 252 and the output of the filter 254. That is, the multiplier 256 outputs the product of the portion of the sine wave sinθ that is zero or greater (positive polarity portion) and (1 + compensation amount / V*).

[0062] The multiplier 257 multiplies the output of the subtractor 253 and the output of the filter 255. That is, the multiplier 256 outputs the product of the portion of the sine wave sinθ that is zero or less (negative polarity portion) and (1 - compensation amount / V*).

[0063] The adder 258 adds the output of the multiplier 256 and the output of the multiplier 257. When the sine wave sinθ is positive, the output of the filter 255 becomes zero, so the output of the multiplier 257 also becomes zero. Therefore, the output of the adder 258 coincides with the output of the multiplier 256. That is, the product of sinθ and (1 + compensation amount / V*) is output. On the other hand, when the sine wave sinθ is negative, the output of the filter 254 becomes zero, so the output of the multiplier 256 also becomes zero. Therefore, the output of the adder 258 coincides with the output of the multiplier 257. That is, the product of sinθ and (1 - compensation amount / V*) is output.

[0064] The multiplier 259 multiplies the amplitude V* of the AC voltage command and the output of the adder 258. The inverter voltage command Vinv* is output from the multiplier 259.

[0065] When the sine wave sinθ is positive, the product of sinθ and (1 + compensation amount / V*) is output from the adder 258. Therefore, from the multiplier 259, a command in which the product of sinθ and the compensation amount is superimposed on the AC voltage command (that is, the product of V* and sinθ) is output as the inverter voltage command Vinv*. Since sinθ is positive, sinθ is equal to the absolute value of sinθ. Therefore, from the multiplier 259, a command in which the product of the absolute value of sinθ and the compensation amount is superimposed on the AC voltage command is output as the inverter voltage command Vinv*.

[0066] On the other hand, when the sine wave sinθ is negative, the product of sinθ and (1 - compensation amount / V*) is output from the adder 258. Therefore, from the multiplier 259, a command in which the product of the absolute value of sinθ and the compensation amount is superimposed on the AC voltage command (that is, the product of V* and sinθ) is output as the inverter voltage command Vinv*.

[0067] Thus, similar to the first embodiment, the feedback control unit 205 according to the second embodiment also determines the AC voltage command with the product of the absolute value of the sine wave sinθ and the compensation amount superimposed thereon, which is synchronized with the period of the AC voltage command, as the inverter voltage command Vinv*. As a result, the same effects as those of the first embodiment are obtained.

[0068] In the above description, the arithmetic unit 52 and the divider 251 are separate entities. However, the arithmetic unit 52 may perform operations including division by the divider 251 and output the above compensation amount / V*. In this case, the divider 251 is omitted.

[0069] Embodiment 3. FIG. 10 is a diagram showing the configuration of a power conversion device according to Embodiment 3. The power conversion device 300 shown in FIG. 10 is different from the power conversion device 100 shown in FIG. 1 in that it includes capacitors Cp and Cn and includes an inverter 302 instead of the inverter 2.

[0070] The capacitors Cp and Cn are connected in series between the input terminals connected to the DC power supply 1 and divide the input voltage. One end of the capacitor Cp is connected to the positive terminal of the input terminals connected to the DC power supply 1. One end of the capacitor Cn is connected to the negative terminal of the input terminals connected to the DC power supply 1. The other ends of the capacitors Cp and Cn are connected to each other.

[0071] The inverter 302 is a half-bridge inverter and includes one leg in which semiconductor switching elements 2e and 2f are connected in series. The semiconductor switching elements 2e and 2f are alternately turned on and off. As a result, an alternating inverter voltage Vinv is generated between the connection point of the capacitors Cp and Cn and the connection point of the semiconductor switching elements 2e and 2f.

[0072] Also in the power conversion device 300 according to Embodiment 3, the feedback control unit 5 determines an AC voltage command Vinv* in which the product of the absolute value of the sine wave sinθ synchronized with the period of the AC voltage command and the compensation amount is superimposed. Thereby, the same effect as in Embodiment 1 is obtained.

[0073] Embodiment 4. The power conversion devices according to the above Embodiments 1 to 3 supply single-phase AC power. In contrast, the power conversion device according to Embodiment 4 supplies three-phase AC power using a three-phase four-wire system.

[0074] FIG. 11 is a diagram showing the configuration of the power conversion device according to Embodiment 4. A system connection device 408 having, for example, a three-phase four-wire configuration is connected to the power conversion device 400 shown in FIG. 11.

[0075] As shown in FIG. 11, the power conversion device 400 includes capacitors Cp and Cn, three inverters 412, 422, and 432, three filters 413, 423, and 433, and three inverter control circuits 419, 429, and 439.

[0076] The inverter 412, the filter 413, and the inverter control circuit 419 receive the input voltage from the DC power supply 1 and perform power conversion to constitute a circuit that supplies AC power of the U phase. The inverter 422, the filter 423, and the inverter control circuit 429 receive the input voltage from the DC power supply 1 and perform power conversion to constitute a circuit that supplies AC power of the V phase. The inverter 432, the filter 433, and the inverter control circuit 439 receive the input voltage from the DC power supply 1 and perform power conversion to constitute a circuit that supplies AC power of the W phase.

[0077] The capacitors Cp and Cn are connected in series between the input terminals connected to the DC power supply 1 and divide the input voltage, similar to Embodiment 3. A neutral line is connected to the connection point between the capacitor Cp and the capacitor Cn.

[0078] Each of the inverters 412, 422, and 432 has the same configuration as the inverter 302 of Embodiment 3 and is a half-bridge inverter.

[0079] The filters 413, 423, and 433 have the same configuration as the filter 3 of Embodiment 1 and are LC filters each including inductors Lu, Lv, and Lw and capacitors Cu, Cv, and Cw.

[0080] Each of the inverter control circuits 419, 429, and 439 has the same configuration as the inverter control circuit 9 of Embodiment 1. That is, each of the inverter control circuits 419, 429, and 439 includes a detection unit 4, a feedback control unit 5, and a PWM control unit 6. However, AC voltage commands with a phase shift of 2π / 3 from each other are input to the feedback control unit 5 included in the inverter control circuits 419, 429, and 439. That is, the phases of the AC voltage commands received by the feedback control unit 5 of the inverter control circuits 429 and 439 are different from the phase of the AC voltage command received by the feedback control unit 5 of the inverter control circuit 419 by -2π / 3 and +2π / 3, respectively. Specifically, the sine waves synchronized with the period of the AC voltage command received by the feedback control unit 5 of the inverter control circuits 419, 429, and 439 are represented by sinθ, sin(θ - 2π / 3), and sin(θ + 2π / 3), respectively.

[0081] Furthermore, in each of the inverter control circuits 419, 429, and 439, a target value DCVc* corresponding to the offset error of the detection unit 4 is input to the subtractor 51.

[0082] Also in the power conversion device 400 according to Embodiment 4, the feedback control unit 5 corresponding to each phase determines the AC voltage command with the product of the absolute value of the sine wave synchronized with the period of the AC voltage command and the compensation amount superimposed thereon as the inverter voltage command Vinv*. Thereby, the same effect as in Embodiment 1 is obtained.

[0083] The power conversion device 400 according to Embodiment 4 supplies three-phase AC power. Therefore, the power conversion device 400 can suppress the DC component DCVc generated according to the load 7 without significantly changing the positive half-cycle period and the negative half-cycle period in a configuration corresponding to a multi-phase AC output. Therefore, during self-operation, it can be effectively utilized without stopping the system connection device having an active mode single-operation function.

[0084] In addition, in FIG. 11, the load 7 is installed in a path parallel to the capacitor Cu. However, the load 7 may be installed in any of the paths of the capacitor Cv, the capacitor Cw, the series connection ends of the capacitor Cu and the capacitor Cv, the series connection ends of the capacitor Cv and the capacitor Cw, and the series connection ends of the capacitor Cu and the capacitor Cw. Furthermore, the load 7 is not limited to a single-phase configuration and may take either a three-phase three-wire load configuration or a three-phase four-wire load configuration. The system connection device 408 may have a three-phase three-wire configuration.

[0085] Embodiment 5. FIG. 12 is a diagram showing the configuration of a power conversion device according to Embodiment 5. The power conversion device 500 according to Embodiment 5 is a modification of the power conversion device 400 according to Embodiment 4 and has a V-phase installation type configuration. A system connection device 508 having, for example, a three-phase three-wire configuration is connected to the power conversion device 500 shown in FIG. 12.

[0086] As shown in FIG. 12, the power conversion device 500 includes capacitors Cp, Cn, two inverters 512, 522, two filters 513, 523, and two inverter control circuits 519, 529.

[0087] The capacitors Cp, Cn are connected in series between the input terminals connected to the DC power supply 1 in the same manner as in Embodiment 3 to divide the input voltage. A V-phase line is connected to the connection point between the capacitor Cp and the capacitor Cn.

[0088] The inverter 512, the filter 513, and the inverter control circuit 519 receive the input voltage from the DC power supply 1 and perform power conversion to constitute a circuit that supplies AC power of the U phase. The inverter 522, the filter 523, and the inverter control circuit 529 receive the input voltage from the DC power supply 1 and perform power conversion to constitute a circuit that supplies AC power of the W phase.

[0089] Each of the inverters 512, 522 has the same configuration as the inverter 302 of Embodiment 3 and is a half-bridge inverter.

[0090] The filters 513 and 523 have the same configuration as the filter 3 in the first embodiment, and are LC filters each including inductors Luv and Lwv and capacitors Cuv and Cwv.

[0091] Each of the inverter control circuits 519 and 529 has the same configuration as the inverter control circuit 9 in the first embodiment. That is, each of the inverter control circuits 519 and 529 includes a detection unit 4, a feedback control unit 5, and a PWM control unit 6. However, the phase of the AC voltage command received by the feedback control unit 5 included in the inverter control circuit 529 is different by π / 2 from the phase of the AC voltage command received by the feedback control unit 5 included in the inverter control circuit 519. That is, the sine waves synchronized with the period of the AC voltage command input to the feedback control units 5 of the inverter control circuits 519 and 529 are represented by sinθ and sin(θ + π / 2), respectively.

[0092] Furthermore, in each of the inverter control circuits 519 and 529, a target value DCVc* corresponding to the offset error of the detection unit 4 is input to the subtracter 51.

[0093] Also in the power conversion device 500 according to the fifth embodiment, the feedback control unit 5 corresponding to each phase determines the AC voltage command Vinv* in which the product of the absolute value of the sine wave synchronized with the period of the AC voltage command and the compensation amount is superimposed. Thereby, the same effect as in the fourth embodiment is obtained.

[0094] In FIG. 12, the load 7 is installed in a path parallel to the capacitor Cuv. However, the load 7 may be installed in any path of the capacitor Cwv and the series connection end of the capacitor Cuv and the capacitor Cwv. Furthermore, the load 7 is not limited to a single-phase configuration, and may have a three-phase three-wire load configuration.

[0095] Embodiment 6. FIG. 13 is a diagram showing the configuration of the power conversion device according to Embodiment 6. The power conversion device 600 according to Embodiment 6 is a modification of the power conversion device 400 according to Embodiment 4 and supplies three-phase three-wire type three-phase AC power. A system connection device 508 having, for example, a three-phase three-wire configuration is connected to the power conversion device 600 shown in FIG. 13.

[0096] As shown in FIG. 13, the power conversion device 600 is different from the power conversion device 400 shown in FIG. 11 in that the capacitors Cp, Cn and the neutral line are omitted.

[0097] Also in the power conversion device 600 according to Embodiment 6, the feedback control unit 5 corresponding to each phase determines an AC voltage command Vinv* in which the product of the absolute value of a sine wave synchronized with the period of the AC voltage command and the compensation amount is superimposed. Thereby, the same effect as in Embodiment 4 is obtained.

[0098] In FIG. 13, the load 7 is installed in a path parallel to the series connection ends of the capacitor Cu and the capacitor Cw. However, the load 7 may be installed in either the series connection ends of the capacitor Cv and the capacitor Cw or the series connection ends of the capacitor Cu and the capacitor Cv. Further, the load 7 is not limited to a single-phase configuration and may have a three-phase three-wire load configuration.

[0099] The power conversion device 300 according to Embodiment 3 may include the feedback control unit 205 according to Embodiment 2 instead of the feedback control unit 5. Further, in the power conversion devices according to Embodiments 4 to 6, the inverter control circuits 419, 429, 439, 519, 529 may have the same configuration as the inverter control circuit 209 according to Embodiment 2.

[0100] It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present disclosure is shown not by the above description of the embodiments but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Description of Symbols

[0101] 1 DC power supply, 2,302,412,422,432,512,522 inverters, 2a~2f semiconductor switching elements, 3,254,255,413,423,433,513,523 filters, 4 detection unit, 4a voltage detector, 4b low-pass filter, 5,205,905 feedback control unit, 6 PWM control unit, 7 load, 8,408,508 system connection device, 9,209,419,429,439,519,529,909 inverter control circuit, 51,253 subtracter, 52 arithmetic unit, 53,55,256,257,259 multipliers, 54 absolute value circuit, 56,252,258,956 adders, 100,200,300,400,500,600,900 power conversion devices, 251 divider, C, Cn, Cp, Cu, Cuv, Cv, Cw, Cwv capacitors, L, Lu, Luv, Lv, Lw, Lwv inductors.

Claims

1. A power conversion device, comprising at least one circuit that receives a DC input voltage and performs power conversion, each of the at least one circuit includes an inverter that receives the input voltage and generates an inverter voltage, a filter that receives the inverter voltage and outputs an output voltage, a detection unit that detects a DC component of the output voltage, a feedback control unit that receives a first parameter representing the magnitude of an AC voltage command, a second parameter representing a sine wave synchronized with the period of the AC voltage command, and the DC component, and determines an inverter voltage command so that the DC component becomes a target value, and a PWM control unit that receives the inverter voltage command and performs pulse width modulation control on the inverter, wherein the target value is zero or a value corresponding to an offset error of the detection unit, the feedback control unit calculates a compensation amount for compensating the DC component, when the first parameter is V*, the second parameter representing the sine wave is sinθ, and the compensation amount is α, generates V*sinθ + α|sinθ| as the inverter voltage command, a power conversion device.

2. The feedback control unit includes a first multiplier that multiplies the first parameter and the sine wave, an absolute value circuit that outputs an absolute value of the sine wave, a second multiplier that multiplies the absolute value and the compensation amount, and an adder that adds the output of the first multiplier and the output of the second multiplier, wherein the inverter voltage command is output from the adder, the power conversion device according to Claim 1.

3. The feedback control unit includes a first filter unit that passes a sine wave greater than or equal to zero, a second filter unit that passes a sine wave less than or equal to zero, a first adder that adds 1 to a value obtained by dividing the compensation amount by the first parameter, a subtractor that subtracts a value obtained by dividing the compensation amount by the first parameter from 1, a first multiplier that multiplies the output of the first filter unit and the output of the first adder, a second multiplier that multiplies the output of the second filter unit and the output of the subtractor, a second adder that adds the output of the first multiplier and the output of the second multiplier, and a third multiplier that multiplies the first parameter and the output of the second adder, wherein the inverter voltage command is output from the third multiplier, the power conversion device according to Claim 1.

4. The power conversion device according to any one of claims 1 to 3, wherein the feedback control unit further includes an arithmetic unit that calculates the compensation amount by PI arithmetic using a deviation between the DC component and the target value.

5. The at least one circuit includes a first circuit, a second circuit, and a third circuit, The phases of the sine waves received by the feedback control units included in the second circuit and the third circuit are different from the phase of the sine wave received by the feedback control unit included in the first circuit by -2π / 3 and +2π / 3, respectively. The power conversion device according to any one of claims 1 to 4.

6. The at least one circuit includes a first circuit and a second circuit, The phase of the sine wave received by the feedback control unit included in the second circuit is different from the phase of the sine wave received by the feedback control unit included in the first circuit by π / 2. The power conversion device according to any one of claims 1 to 4.

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