V-connected inverter

Abstract

To provide a V-connected inverter with which it is possible to suppress the voltage distortion of a fundamental wave and the higher harmonic of a specific frequency.SOLUTION: There is provided a V-connected inverter comprising a main circuit unit and a control unit 100. The control unit 100 includes: a voltage command value output unit 110 for outputting a dq-axis voltage command value; a voltage value / frequency output unit 120 for outputting a first three-phase voltage value and a specific frequency; an average command value output unit 130 for outputting a single-phase average command value; a first voltage correction unit 140 for outputting a second three-phase voltage value; a second voltage correction unit 150 for outputting a third three-phase voltage value; a dq-axis voltage value output unit 160 for performing three-phase / dq conversion on the added value of the second and the third phase-phase voltage values; a dq-axis command value output unit 170 for outputting a dq-axis command value; a three-phase command value output unit 220 for performing dq / three-phase conversion and outputting a three-phase command value; and a switch control unit 230 for controlling a switching element on the basis of the three-phase command value.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a V-connected inverter.

Background Art

[0002] Among the three-phase inverters of power conditioners that connect a photovoltaic power generation device to a three-phase AC power supply, there are those with an isolation transformer method and those with a transformerless method. The transformerless inverter has a configuration in which one of the three-phase (U-phase, V-phase, W-phase or R-phase, S-phase, T-phase) outputs is connected to the neutral point of the DC power supply, and generally the V-phase (or S-phase) is grounded to the neutral point and used, so it is called a V-connected (or V-phase grounded, S-phase grounded, four-arm method three-phase) inverter.

[0003] While the three-phase inverter with an isolation transformer method controls three line voltages with three legs, the V-connected inverter controls two line voltages (the line voltage between the U and V phases and the line voltage between the V and W phases) with two legs without using an isolation transformer. Therefore, the V-connected inverter has a configuration with one less leg (two arms) than a three-phase inverter, so it has the advantage of reducing the number of components.

[0004] On the other hand, the V-connected inverter has a problem that output voltage distortion is likely to occur (output voltage imbalance is likely to occur). Since the V-connected inverter does not directly control the line voltage between the W and U phases, if voltage distortion occurs between other phases, the line voltage between the W and U phases will be distorted under its influence. That is, due to the output voltage error factor, not only harmonics are generated, but also errors occur in the amplitude and phase of the fundamental wave, resulting in output voltage imbalance. For example, if the amplitudes of the fundamental waves of the line voltage between the U and V phases and the line voltage between the V and W phases are different, the amplitude and phase of the fundamental wave of the line voltage between the W and U phases will change, and a three-phase unbalanced voltage will be output from the V-connected inverter. Although the V-connected inverter has the above problems, due to the advantages of reducing the number of components and eliminating the need for an isolation transformer, it is used in power conditioners for photovoltaic power generation systems assuming grid connection.

[0005] In the case of an inverter of a distributed power system that performs not only grid-connected operation but also independent operation, since a single-phase load is connected during independent operation, it is necessary to consider the voltage distortion (voltage error) of the fundamental wave due to the unbalanced load between phases.

[0006] Patent Document 1 describes a V-phase grounded inverter that outputs three-phase AC power during grid-connected operation and outputs single-phase AC power during independent operation. The V-phase grounded inverter described in Patent Document 1 enables power supply to a single-phase load during independent operation. However, when a single-phase load is connected to a V-connected inverter, there are problems that voltage distortion of the fundamental wave and harmonics of a specific frequency occur, resulting in imbalance in the output voltage.

[0007] Patent Document 2 describes a control method using a harmonic compensation device that compensates for harmonics of three-phase AC current, and a control method for an inverter that outputs an AC output current according to a d-axis output command value and a q-axis output command value. However, Patent Document 2 does not describe the overall control (voltage-current control) of a V-connected inverter that supplies three-phase AC voltage to an unbalanced load. Also, the control method described in Patent Document 2 can be expected to have a suppression effect on the second harmonics of a V-connected inverter. However, since it includes I (integral) control, when this control method is applied to the voltage distortion of the fundamental wave, there is a problem of overcontrol when the target value changes. Furthermore, this control method also has a problem that it cannot handle harmonics of specific frequencies other than the second harmonics.

[0008] Patent Document 3 describes a control method for an inverter that controls three legs to perform three-phase output. According to the control method described in Patent Document 3, even when an unbalanced load is connected to the three-phase output of the inverter, a balanced three-phase output voltage can be maintained without affecting the current control, and harmonic components can be suppressed even when a non-linear load is connected. However, since the control method described in Patent Document 3 is a control method for an inverter that controls three legs to perform three-phase output as described above, it cannot be applied to a V-connected inverter that controls two line voltages with two legs. That is, the control method described in Patent Document 3 has a problem that it cannot cope with voltage distortion of the fundamental wave and harmonics of a specific frequency in a V-connected inverter.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a V-connected inverter capable of suppressing voltage distortion of the fundamental wave and harmonics of a specific frequency.

Means for Solving the Problems

[0011] In order to solve the above problems, the V-connected inverter according to the present invention includes a main circuit section and a control section, wherein the main circuit section A switch circuit having first and second legs connected in parallel, each leg having an upper arm and a lower arm including a switching element, the first leg outputting a first line voltage between a U-phase line and a V-phase line, and the second leg outputting a second line voltage between the V-phase line and a W-phase line, voltage detection means for detecting the first line voltage and the second line voltage, A V-connected inverter comprising: The control unit includes: a voltage command value output unit that outputs dq-axis voltage command values; a voltage value / frequency output unit that outputs a first three-phase voltage value, which is a voltage value of each line voltage of the U-phase line, the V-phase line, and the W-phase line, based on the detection value of the voltage detection means, and outputs a specific frequency that is a frequency component that is an integer multiple of the fundamental wave; an average command value output unit that outputs a single-phase average command value, which is an average value of the dq-axis voltage command values; a first voltage correction unit that outputs a second three-phase voltage value, which is a correction value for each line voltage of the fundamental wave, based on the first three-phase voltage value and the single-phase average command value; a second voltage correction unit that outputs a third three-phase voltage value, which is a correction value for each line voltage of the specific frequency, based on the first three-phase voltage value and the specific frequency; a dq-axis voltage value output unit that performs three-phase / dq conversion on the sum value of the second three-phase voltage value and the third three-phase voltage value to output a dq-axis voltage value; a dq-axis command value output unit that performs control to approximate the difference between the dq-axis voltage value and the dq-axis voltage command value to zero and outputs a dq-axis command value; a three-phase command value output unit that performs dq / three-phase conversion on the dq-axis command value to output a three-phase command value; a switch control unit that performs on / off control of the switching element based on the three-phase command value.

[0012] According to this configuration, the V-connected inverter according to the present invention can be used in a distributed power system or the like that performs not only grid-connected operation but also stand-alone operation. When a single-phase load, which is an unbalanced load, is connected and / or when a non-linear load is connected, it is possible to suppress the voltage distortion of the fundamental wave and the harmonics of a specific frequency included in the line-to-line voltages of the U-phase line, V-phase line, and W-phase line.

[0013] In the V-connected inverter, The first voltage correction unit a rectification unit that performs rectification processing on the first three-phase voltage values and outputs the result; a low-pass filter that obtains and outputs a DC component from the output of the rectification unit; a PI control unit that performs PI control on the difference between the output of the low-pass filter and the single-phase average command value; a deviation rate calculation unit that calculates the deviation rate between the output of the PI control unit and the single-phase average command value; a calculation unit that multiplies the output of the deviation rate calculation unit by the first three-phase voltage values to generate the second three-phase voltage values; and an inverse calculation unit that suppresses over-control of the integral element of the PI control unit by making the output of the deviation rate calculation unit match the output of the PI control unit.

[0014] In the V-connected inverter, The second voltage correction unit a first positive-sequence three-phase / dq conversion unit that performs positive-sequence three-phase / dq conversion on the first three-phase voltage values; a first low-pass filter that obtains and outputs a first DC component from the output of the first positive-sequence three-phase / dq conversion unit; a first PI control unit that performs PI control to bring the first DC component close to 0; a negative-sequence three-phase / dq conversion unit that performs negative-sequence three-phase / dq conversion on the first three-phase voltage values; a second low-pass filter that obtains and outputs a second DC component from the output of the negative-sequence three-phase / dq conversion unit; a second PI control unit that performs PI control to bring the second DC component close to 0; A reverse dq / 3-phase conversion unit that performs reverse-phase dq / 3-phase conversion on the output of the second PI control unit, A second direct-phase 3-phase / dq conversion unit that performs direct-phase 3-phase / dq conversion on the output of the reverse dq / 3-phase conversion unit, A direct-phase dq / 3-phase conversion unit that performs direct-phase dq / 3-phase conversion on the sum value of the output of the first PI control unit and the output of the second direct-phase 3-phase / dq conversion unit to generate the third three-phase voltage value, can be configured to include.

[0015] In the V-connected inverter, The second voltage correction unit A 3-phase / dq conversion unit that performs 3-phase / dq conversion on the first three-phase voltage value and outputs a d-axis value and a q-axis value, A first high-pass filter that obtains and outputs an AC component from the d-axis value, A first dq conversion unit that performs dq conversion on the output of the first high-pass filter, A first PI control unit that performs PI control to bring the output of the first dq conversion unit closer to zero, A first inverse dq conversion unit that performs inverse dq conversion on the output of the first PI control unit to generate a d-axis correction value, A second high-pass filter that obtains and outputs an AC component from the q-axis value, A second dq conversion unit that performs dq conversion on the output of the second high-pass filter, A second PI control unit that performs PI control to bring the output of the second dq conversion unit closer to zero, A second inverse dq conversion unit that performs inverse dq conversion on the output of the second PI control unit to generate a q-axis correction value, A dq / 3-phase conversion unit that performs dq / 3-phase conversion on the d-axis correction value and the q-axis correction value to generate the third three-phase voltage value, can be configured to include.

[0016] In the V-connected inverter, The second voltage correction unit A first 3-phase / dq conversion unit that performs 3-phase / dq conversion on the first three-phase voltage value using the specific frequency and outputs first dq-axis values, A first low-pass filter that obtains and outputs a first DC component from the first dq-axis value; A first PI control unit that performs PI control to bring the first DC component closer to 0; A second 3-phase / dq conversion unit that performs 3-phase / dq conversion on the first 3-phase voltage value using a frequency that is two times or more the specific frequency and outputs a second dq-axis value; A second low-pass filter that obtains and outputs a second DC component from the second dq-axis value; A second PI control unit that performs PI control to bring the second DC component closer to 0; A dq / 3-phase conversion unit that performs dq / 3-phase conversion on the sum value of the output of the first PI control unit and the output of the second PI control unit to generate the third 3-phase voltage value.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a V-connected inverter capable of suppressing voltage distortion of a fundamental wave and harmonics of a specific frequency.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of a V-connected inverter according to the present invention will be described with reference to the accompanying drawings.

[0020] FIG. 1 shows a V-connected inverter 1 according to an embodiment of the present invention. The V-connected inverter 1 includes a main circuit section 10 and a control section 100. The main circuit section 10 includes terminals 1a, 1b, terminals 2u, 2v, 2w, a voltage dividing circuit 11, a switch circuit 12, a filter circuit 13, and a detection circuit 14.

[0021] A DC input voltage Vdc is input to terminals 1a, 1b. The input voltage Vdc is the output of a DC voltage power source, for example, the output of a photovoltaic power generation device or the output of a power storage device.

[0022] Terminals 2u, 2v, 2w are connected to a three-phase power source Vs (for example, a commercial power system) grounded at the V phase via the U-phase line, V-phase line, and W-phase line, respectively. A three-phase load or a single-phase load is connected to the three-phase power source Vs, for example. A line voltage Vuv is output between terminals 2u and 2v, a line voltage Vvw is output between terminals 2v and 2w, and a line voltage Vwu is output between terminals 2w and 2u. Also, a line current Isu is output from terminal 2u, a line current Isv is output from terminal 2v, and a line current Isw is output from terminal 2w. In the V-connected inverter 1, the line voltage and the phase voltage are equal and both are the same physical quantity, and the line current and the phase current are equal and both are the same physical quantity.

[0023] The voltage dividing circuit 11 is composed of a first voltage dividing capacitor C1 and a second voltage dividing capacitor C2 connected in series. The voltage dividing circuit 11 has its positive electrode side connected to terminal 1a and its negative electrode side connected to terminal 1b. The neutral point M, which is the connection point between the first voltage dividing capacitor C1 and the second voltage dividing capacitor C2, is connected to terminal 2v (V-phase line). It is preferably controlled that the first voltage dividing capacitor C1 and the second voltage dividing capacitor C2 have substantially equal capacitances.

[0024] The switch circuit 12 includes a first leg and a second leg connected in parallel, and each leg includes an upper arm and a lower arm connected in series. The upper arm of the first leg includes a switching element S1, the lower arm of the first leg includes a switching element S2, the upper arm of the second leg includes a switching element S3, and the lower arm of the second leg includes a switching element S4. The first leg drives the U-phase and outputs the line voltage Vuv (corresponding to the "first line voltage" of the present invention). The second leg drives the W-phase and outputs the line voltage Vvw (corresponding to the "second line voltage" of the present invention).

[0025] The collector (drain) terminals of the switching elements S1 and S3 are connected to terminal 1a, and the emitter (source) terminals of the switching elements S2 and S4 are connected to terminal 1b, so that an input voltage Vdc is applied to the switch circuit 12. The connection point between the emitter (source) terminal of the switching element S1 and the collector (drain) terminal of the switching element S2 is connected to terminal 2u (U-phase line) via the filter circuit 13, and the connection point between the emitter (source) terminal of the switching element S3 and the collector (drain) terminal of the switching element S4 is connected to terminal 2w (W-phase line) via the filter circuit 13.

[0026] The switching elements S1 to S4 can use power semiconductor elements capable of high-frequency switching, such as IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) using Si (Silicon), SiC (Silicon Carbide), GaN (Gallium Nitride), etc. In the current paths of the switching elements S1 to S4, freewheeling diodes D1 to D4 are connected in parallel in the reverse direction. The diodes D1 to D4 may be built-in diodes (parasitic diodes) of the switching elements S1 to S4, external diodes, or both. Also, partial resonance capacitors for soft switching may be connected in parallel with the diodes D1 to D4 in the current paths of the switching elements S1 to S4. The partial resonance capacitors may be parasitic capacitors of the switching elements S1 to S4, external capacitors, or both.

[0027] The filter circuit 13 is composed of reactors Lu, Lw for output smoothing and capacitors Cu, Cw. The reactor Lu is interposed in the U-phase line connecting the connection point of the switching elements S1, S2 and the terminal 2u. The reactor Lw is interposed in the W-phase line connecting the connection point of the switching elements S3, S4 and the terminal 2w. The capacitor Cu is connected between the U-phase line and the V-phase line on the output side of the reactor Lu to form an LC filter. The capacitor Cw is connected between the V-phase line and the W-phase line on the output side of the reactor Lw to form an LC filter.

[0028] The detection circuit 14 is composed of a first voltage detection means V1, a second voltage detection means V2, a first current detection means CT1, and a second current detection means CT2. The first voltage detection means V1 detects the line voltage Vuv, and the second voltage detection means V2 detects the line voltage Vvw. The first current detection means CT1 detects the line current Isu, and the second current detection means CT2 detects the line current Isw. As the first current detection means CT1 and the second current detection means CT2, current sensors such as current transformers and Hall elements can be used, for example.

[0029] The control unit 100 controls the on / off of the switching elements S1 to S4 to control the output voltage and output current of the main circuit unit 10. The control unit 100 includes a processing unit that generates control signals G1 to G4 for on / off control, and a driving unit (not shown) that turns on and off the switching elements S1 to S4 based on the control signals G1 to G4. The control unit 100 may be composed of a digital circuit such as a microprocessor or a digital signal processor (including peripheral elements such as a memory), an analog circuit, or a circuit combining a digital circuit and an analog circuit. Note that descriptions regarding communication such as start / stop instructions, output start, etc. from the upper system of the control unit 100, and target voltage output commands or target current output commands are omitted.

[0030] FIG. 2 shows a block diagram of the control unit 100. As shown in the figure, the control unit 100 includes a voltage command value output unit 110, a voltage value / frequency output unit 120, an average command value output unit 130, a first voltage correction unit 140, a second voltage correction unit 150, a dq-axis voltage value output unit 160, a dq-axis command value output unit 170, a limiter unit 180, a current value output unit 190, a dq-axis current value output unit 200, an amplification unit 210, a three-phase command value output unit 220, and a switch control unit 230. In the following description, the word "signal" is omitted from the signal names of various signals input to and output from each unit of the control unit 100. For example, "signals related to the line-to-line voltages Vuv and Vvw" are simply expressed as "line-to-line voltages Vuv and Vvw".

[0031] The voltage command value output unit 110 outputs a d-axis voltage command value Vd* and a q-axis voltage command value Vq* in response to an instruction from an upper system (not shown). The d-axis voltage command value Vd* and the q-axis voltage command value Vq* correspond to the "dq-axis voltage command values" of the present invention.

[0032] The voltage value / frequency output unit 120 receives the line-to-line voltages Vuv and Vvw from the detection circuit 14, calculates the line-to-line voltage Vwu, and outputs the three line-to-line voltages Vuv, Vvw, and Vwu (corresponding to the "first three-phase voltage values" of the present invention). Further, the voltage value / frequency output unit 120 outputs the fundamental angular frequency ω (= 2πf) of the fundamental wave of the commercial frequency f, the specific angular frequency kω (= 2πkf) of the k-th harmonic (k: an integer of 2 or more), and the double specific angular frequency 2kω (= 4πkf) of its second harmonic. Note that the double specific angular frequency 2kω can be omitted depending on the configuration of the second voltage correction unit 150 described later (the configuration of Example 1 shown in FIG. 6 and the configuration of Example 2 shown in FIG. 7).

[0033] As shown in FIG. 3, the voltage value / frequency output unit 120 includes a voltage value calculation unit 121 and a frequency detection unit 122. The voltage value calculation unit 121 calculates and outputs the line-to-line voltage Vwu from the line-to-line voltages Vuv and Vvw (Vwu = -Vuv - Vvw). The frequency detection unit 122 detects and outputs the fundamental angular frequency ω, the specific angular frequency kω, and the double specific angular frequency 2kω from the line-to-line voltages Vuv and Vvw. The frequency detection unit 122 includes, for example, a synchronization circuit such as a PLL (Phase Locked Loop) or a discrete Fourier transform circuit.

[0034] The average command value output unit 130 generates and outputs a single-phase average value command Va based on the d-axis voltage command value Vd* and the q-axis voltage command value Vq*. The single-phase average value command Va is a value obtained by the following equation (1).

Equation

[0035] The first voltage correction unit 140 generates and outputs correction values Vuv2, Vvw2, and Vwu2 (corresponding to the "second three-phase voltage values" of the present invention) for the line-to-line voltages Vuv, Vvw, and Vwu at the fundamental angular frequency ω based on the three line-to-line voltages Vuv, Vvw, Vwu and the single-phase average value command Va. Details of the first voltage correction unit 140 will be described later.

[0036] The positive part 150 of the second voltage generates and outputs positive values Vuv3, Vvw3, Vwu3 (corresponding to the "third three-phase voltage value" of the present invention) for the line voltages Vuv, Vvw, Vwu at the specific angular frequency kω and the double specific angular frequency 2kω based on the three line voltages Vuv, Vvw, Vwu, the specific angular frequency kω, and the double specific angular frequency 2kω. Details of the positive part 150 of the second voltage will be described later.

[0037] The addition values of the positive values Vuv2, Vvw2, Vwu2 and the positive values Vuv3, Vvw3, Vwu3 are input to the dq-axis voltage value output unit 160, and the basic angular frequency ω is input from the voltage value / frequency output unit 120. The dq-axis voltage value output unit 160 performs a three-phase / dq conversion on the above addition value, and generates and outputs a d-axis voltage value Vd2 and a q-axis voltage value Vq2. The d-axis voltage value Vd2 and the q-axis voltage value Vq2 correspond to the "dq-axis voltage value" of the present invention. The d-axis voltage value Vd2 and the q-axis voltage value Vq2 are added to the d-axis voltage command value Vd* and the q-axis voltage command value Vq* as negative feedback signals.

[0038] As described above, the difference obtained by subtracting the d-axis voltage value Vd2 from the d-axis voltage command value Vd* and the difference obtained by subtracting the q-axis voltage value Vq2 from the q-axis voltage command value Vq* are input to the dq-axis command value output unit 170. The dq-axis command value output unit 170 performs PI control so that these differences approach zero, and generates and outputs a d-axis current command value Isd* and a q-axis current command value Isq*. The d-axis current command value Isd* and the q-axis current command value Isq* correspond to the "dq-axis command value" of the present invention.

[0039] The limiter unit 180 limits the d-axis current command value Isd* so that the d-axis current command value Isd* does not exceed a preset d-axis upper current value, and also limits the d-axis current command value Isd* so that the q-axis current command value Isq* does not exceed a preset q-axis upper current value.

[0040] The line current value output unit 190 receives the line currents Isu and Isw from the detection circuit 14, calculates the line current Isv, and outputs the three-phase line currents Isu, Isv, and Isw. As shown in FIG. 4, the line current value output unit 190 includes a line current value calculation unit 191, and the line current value calculation unit 191 calculates and outputs the line current Isv from the line currents Isu and Isw (Isv = -Isu - Isw).

[0041] The dq-axis line current value output unit 200 receives the three-phase line currents Isu, Isv, and Isw from the line current value output unit 190 and the fundamental angular frequency ω from the voltage value / frequency output unit 120. As shown in FIG. 4, the dq-axis line current value output unit 200 includes a three-phase / dq conversion unit 201, and the three-phase / dq conversion unit 201 performs a three-phase / dq conversion on the three-phase line currents Isu, Isv, and Isw to generate and output a d-axis line current value Isd and a q-axis line current value Isq. The d-axis line current value Isd and the q-axis line current value Isq are added to a d-axis line current command value Isd* and a q-axis line current command value Isq* as negative feedback signals.

[0042] As described above, the amplification unit 210 receives the difference obtained by subtracting the d-axis line current value Isd from the d-axis line current command value Isd* and the difference obtained by subtracting the q-axis line current value Isq from the q-axis line current command value Isq*. The amplification unit 210 amplifies these differences at a preset amplification factor to generate and output a d-axis line current amplification value Ifd and a q-axis line current amplification value Ifq.

[0043] The three-phase command value output unit 220 receives the d-axis line current amplification value Ifd and the q-axis line current amplification value Ifq from the amplification unit 210 and the fundamental angular frequency ω from the voltage value / frequency output unit 120. The three-phase command value output unit 220 performs a dq / three-phase conversion on the d-axis line current amplification value Ifd and the q-axis line current amplification value Ifq to generate and output a command value Ifuv and a command value Ifvw. The command value Ifuv and the command value Ifvw correspond to the "three-phase command value" of the present invention.

[0044] The switch control unit 230 generates and outputs control signals (for example, gate signals) G1 to G4 for performing on / off control of the switching elements S1 to S4 based on the command value Ifuv and the command value Ifvw. For example, the switching element S1 turns on when the control signal G1 is at a high level and turns off when the control signal G1 is at a low level. The same applies to the relationship between the switching elements S2 to S4 and the control signals G2 to G4.

[0045] FIG. 5 shows a block diagram of the first voltage correction unit 140. As shown in the figure, the first voltage correction unit 140 includes a block 140u that generates a corrected value Vuv2 based on the line voltage Vuv and the single-phase average value command Va, a block 140v that generates a corrected value Vvw2 based on the line voltage Vvw and the single-phase average value command Va, and a block 140w that generates a corrected value Vwu2 based on the line voltage Vwu and the single-phase average value command Va. Since the configurations of the blocks 140u, 140v, and 140w are the same, only the block 140u will be described below.

[0046] The block 140u includes a rectifier section 141, an LPF (low-pass filter) 142, a PI control section 143, a deviation rate calculation section 144, a limiter section 145, a first calculation section 146, and an inverse calculation section 147 (second calculation section 148, third calculation section 149).

[0047] The rectifier section 141 performs a rectification process (in this embodiment, a full-wave rectification process) on the line voltage Vuv and outputs the line voltage Vuv after full-wave rectification.

[0048] The LPF 142 obtains a DC component from the output of the rectifier section 141 and outputs the DC component.

[0049] A difference obtained by subtracting the single-phase average value command Va from the output of the LPF 142 is input to the PI control section 143. The PI control section 143 performs PI control on the difference and outputs a control amount for bringing the difference closer to zero.

[0050] The deviation rate calculation unit 144 receives the added value of the control amount output from the PI control unit 143 and the single-phase average value command Va, and also receives the single-phase average value command Va. The deviation rate calculation unit 144 is a divider that divides the above added value by the single-phase average value command Va and outputs the division value (deviation rate).

[0051] The limiter unit 145 limits the deviation rate so that the deviation rate output from the deviation rate calculation unit 144 does not exceed a preset upper limit value. That is, when the deviation rate output from the deviation rate calculation unit 144 exceeds the upper limit value, the limiter unit 145 limits the deviation rate to the upper limit value and outputs it.

[0052] The first calculation unit 146 multiplies the deviation rate passed through the limiter unit 145 by the line voltage Vuv and outputs the multiplication value as the correction value Vuv2.

[0053] The inverse calculation unit 147 (the second calculation unit 148, the third calculation unit 149) performs the reverse process of the process from the PI control unit 143 to the limiter unit 145. That is, the second calculation unit 148 multiplies the deviation rate by the single-phase average value command Va and outputs the multiplication value. The third calculation unit 149 subtracts the single-phase average value command Va from the multiplication value and outputs the subtraction value. The subtraction value is input to the PI control unit 143, and the PI control unit 143 makes the output control amount approach the subtraction value. That is, the inverse calculation unit 147 makes the output of the deviation rate calculation unit 144 (strictly speaking, the output of the limiter unit 145) coincide with the output of the PI control unit 143. Thereby, for example, when the deviation rate output from the deviation rate calculation unit 144 exceeds the upper limit value, over-control by the integral element in the PI control unit 143 can be canceled, and the transient response characteristics can be improved.

[0054] By controlling in this way, even when an unbalanced load such as a single-phase load is connected to the V-connected inverter 1, the first voltage correction unit 140 can generate correction values Vuv2, Vvw2, and Vwu2 for the line voltages Vuv, Vvw, and Vwu of the fundamental angular frequency ω. In addition, the first voltage correction unit 140 can avoid over-control of the PI control unit 143 even when fluctuations in the fundamental wave occur, for example, at the start of the V-connected inverter 1.

[0055] FIG. 6 shows a block diagram (configuration of Example 1) of the second voltage correction unit 150. Note that, as the second voltage correction unit 150, instead of the configuration of Example 1 shown in FIG. 6, the configuration of Example 2 (second voltage correction unit 250) shown in FIG. 7 or the configuration of Example 3 (second voltage correction unit 350) shown in FIG. 8 can be adopted.

[0056] As shown in FIG. 6, the second voltage correction unit 150 includes a first positive-phase three-phase / dq conversion unit 151, a first LPF (low-pass filter) 152, a first PI control unit 153, a reverse-phase three-phase / dq conversion unit 154, a second LPF (low-pass filter) 155, a second PI control unit 156, a reverse-phase dq / three-phase conversion unit 157, a second positive-phase three-phase / dq conversion unit 158, and a positive-phase dq / three-phase conversion unit 159.

[0057] Three line voltages Vuv, Vvw, and Vwu and a specific angular frequency kω are input to the first positive-phase three-phase / dq conversion unit 151. The first positive-phase three-phase / dq conversion unit 151 performs positive-phase three-phase / dq conversion on the line voltages Vuv, Vvw, and Vwu, and generates and outputs a positive-phase d-axis value d1 and a positive-phase q-axis value q1. The positive-phase three-phase / dq conversion using the specific angular frequency kω is performed based on the following equation (2).

Equation

[0058] The first LPF 152 acquires a DC component (corresponding to the "first DC component" of the present invention) from the positive-phase d-axis value d1 and the positive-phase q-axis value q1, and outputs the DC component.

[0059] The difference between the positive-phase d-axis value d1 and zero and the difference between the positive-phase q-axis value q1 and zero are input to the first PI control unit 153. The first PI control unit 153 performs PI control on the difference, and outputs a control amount for making the difference approach zero.

[0060] Here, when an unbalanced load such as a single-phase load is connected to the V-connected inverter 1, the three-phase unbalance component generated becomes a second harmonic (a harmonic of the second specific angular frequency 2kω), and thus cannot be detected from the DC component obtained via the first positive-phase three-phase / dq conversion unit 151 and the first LPF 152. Therefore, in the second voltage correction unit 150, the three-phase unbalance component of the second harmonic is detected by providing a reverse-phase three-phase / dq conversion unit 154 and a second LPF 155.

[0061] Three line-to-line voltages Vuv, Vvw, Vwu and the specific angular frequency kω are input to the reverse-phase three-phase / dq conversion unit 154. The reverse-phase three-phase / dq conversion unit 154 performs reverse-phase three-phase / dq conversion on the line-to-line voltages Vuv, Vvw, Vwu, and generates and outputs a reverse-phase d-axis value d2 and a reverse-phase q-axis value q2. The reverse-phase three-phase / dq conversion using the specific angular frequency kω is performed based on the following equation (3).

Equation

[0062] The second LPF 155 acquires a DC component (corresponding to the "second DC component" of the present invention) from the reverse-phase d-axis value d2 and the reverse-phase q-axis value q2, and outputs the DC component.

[0063] The difference between the reverse-phase d-axis value d2 and the reverse-phase q-axis value q2 and zero is input to the second PI control unit 156. The second PI control unit 156 performs PI control on the difference, and outputs a control amount for making the difference approach zero.

[0064] The output of the second PI control unit 156 and the specific angular frequency kω are input to the reverse-phase dq / three-phase conversion unit 157. The reverse-phase dq / three-phase conversion unit 157 performs reverse-phase dq / three-phase conversion on the output of the second PI control unit 156, and generates and outputs three-phase voltage values.

[0065] The second positive-phase 3-phase / dq conversion unit 158 receives the output of the reverse-phase dq / 3-phase conversion unit 157 and the specific angular frequency kω. The second positive-phase 3-phase / dq conversion unit 158 performs positive-phase 3-phase / dq conversion on the output of the reverse-phase dq / 3-phase conversion unit (the 3-phase voltage values), generates and outputs the positive-phase d-axis value and the positive-phase q-axis value.

[0066] The positive-phase dq / 3-phase conversion unit 159 receives the added value of the output of the first PI control unit 153 and the output of the second positive-phase 3-phase / dq conversion unit 158, and also receives the specific angular frequency kω. The positive-phase dq / 3-phase conversion unit 159 performs positive-phase dq / 3-phase conversion on the added value, generates and outputs the corrected values Vuv3, Vvw3, and Vwu3.

[0067] By controlling in this way, the corrected values Vuv3, Vvw3, and Vwu3 become the corrected values for the line voltages Vuv, Vvw, and Vwu of the specific angular frequency kω and the double specific angular frequency 2kω. Therefore, the second voltage correction unit 150 can suppress the harmonics of the specific angular frequency kω and the double specific angular frequency 2kω due to the 3-phase unbalance component when an unbalanced load such as a single-phase load is connected to the V-connected inverter 1.

[0068] Fig. 7 shows a block diagram of the second voltage correction unit 250 (configuration of Example 2). The second voltage correction unit 250 includes a 3-phase / dq conversion unit 251, a first HPF (high-pass filter) 252, a first dq conversion unit 253, a first PI control unit 254, a first inverse dq conversion unit 255, a second HPF (high-pass filter) 252', a second dq conversion unit 253', a second PI control unit 254', a second inverse dq conversion unit 255', and a dq / 3-phase conversion unit 256.

[0069] The 3-phase / dq conversion unit 251 receives the three line voltages Vuv, Vvw, and Vwu and the specific angular frequency kω. The 3-phase / dq conversion unit 251 performs 3-phase / dq conversion on the line voltages Vuv, Vvw, and Vwu, generates and outputs the d-axis value d0 and the q-axis value q0.

[0070] Hereinafter, since the processing performed on the d-axis value d0 (the processing performed by the first HPF 252, the first dq conversion unit 253, the first PI control unit 254, and the first inverse dq conversion unit 255) and the processing performed on the q-axis value q0 (the processing performed by the second HPF 252', the second dq conversion unit 253', the second PI control unit 254', and the second inverse dq conversion unit 255') are the same, only the processing performed on the d-axis value d0 will be described.

[0071] The first HPF 252 obtains an AC component d, which is an unbalanced component, by removing the DC component included in the d-axis value d0, and outputs the AC component d.

[0072] The first dq conversion unit 253 performs dq conversion on the AC component d, generates and outputs a d-component value dd and a q-component value dq. The dq conversion using the specific angular frequency kω is performed based on the following equation (4).

Equation

[0073] The first PI control unit 254 performs PI control on the d-component value dd and the q-component value dq, and outputs a control amount dd2 for making the d-component value dd approach zero and a control amount dq2 for making the q-component value dq approach zero.

[0074] The first inverse dq conversion unit 255 performs inverse dq conversion on the control amount dd2 and the control amount dq2, generates and outputs a d-axis correction value d*. The inverse dq conversion is performed based on the following equation (5).

Equation

[0075] The dq / 3 phase conversion unit 256 receives the difference between the d-axis correction value d* generated by the first inverse dq conversion unit 255 and zero, and similarly the difference between the q-axis correction value q* generated by the second inverse dq conversion unit 255' and zero. The dq / 3 phase conversion unit 256 performs dq / 3 phase conversion on these differences, and generates and outputs the correction values Vuv3, Vvw3, and Vwu3.

[0076] By controlling in this way, the correction values Vuv3, Vvw3, and Vwu3 become correction values for the line voltages Vuv, Vvw, and Vwu at the specific angular frequency kω and the twice specific angular frequency 2kω. Therefore, the second voltage correction unit 250 can suppress the harmonics at the specific angular frequency kω and the twice specific angular frequency 2kω due to the three-phase unbalance component when an unbalanced load such as a single-phase load is connected to the V-connected inverter 1.

[0077] FIG. 8 shows a block diagram (configuration of Example 3) of the second voltage correction unit 350. The second voltage correction unit 350 includes a first three-phase / dq conversion unit 351, a first LPF (low-pass filter) 352, a first PI control unit 353, a second three-phase / dq conversion unit 354, a second LPF (low-pass filter) 355, a second PI control unit 356, and a dq / 3 phase conversion unit 357.

[0078] The first three-phase / dq conversion unit 351 receives the three line voltages Vuv, Vvw, and Vwu and the specific angular frequency kω. The first three-phase / dq conversion unit 351 performs three-phase / dq conversion on the line voltages Vuv, Vvw, and Vwu at the specific angular frequency kω, and generates and outputs a first d-axis value d1 and a first q-axis value q1.

[0079] The first LPF 352 obtains the DC components (corresponding to the "first DC component" of the present invention) from the first d-axis value d1 and the first q-axis value q1 respectively, and outputs the DC components. The DC components are harmonic components at the specific angular frequency kω.

[0080] The first PI control unit 353 performs PI control on the difference between the DC component of the first d-axis value d1 and zero, and outputs a control amount d1' for making the difference approach zero. At the same time, the first PI control unit 353 performs PI control on the difference between the DC component of the first q-axis value q1 and zero, and outputs a control amount q1' for making the difference approach zero.

[0081] The second three-phase / dq conversion unit 354 receives three line-to-line voltages Vuv, Vvw, Vwu and a double specific angular frequency 2kω. The second three-phase / dq conversion unit 354 performs three-phase / dq conversion on the line-to-line voltages Vuv, Vvw, Vwu with the double specific angular frequency 2kω, and generates and outputs a second d-axis value d2 and a second q-axis value q2.

[0082] The second LPF 355 obtains the DC components (corresponding to the "second DC component" of the present invention) from the second d-axis value d2 and the second q-axis value q2 respectively, and outputs the DC components. The DC components are harmonic components of the double specific angular frequency 2kω.

[0083] The second PI control unit 356 performs PI control on the difference between the DC component of the second d-axis value d2 and zero, and outputs a control amount d2' for making the difference approach zero. At the same time, the second PI control unit 356 performs PI control on the difference between the DC component of the second q-axis value q2 and zero, and outputs a control amount q2' for making the difference approach zero.

[0084] The dq / three-phase conversion unit 357 receives the sum value of the control amount d1' and the control amount d2', and the sum value of the control amount q1' and the control amount q2'. The dq / three-phase conversion unit 357 performs dq / three-phase conversion on these sum values, and generates and outputs correction values Vuv3, Vvw3, Vwu3.

[0085] By controlling in this way, the correction values Vuv3, Vvw3, and Vwu3 become correction values for the line voltages Vuv, Vvw, and Vwu at the specific angular frequency kω and the double specific angular frequency 2kω. Therefore, when an unbalanced load such as a single-phase load is connected to the V-connected inverter 1, the second voltage correction unit 350 can suppress harmonics at the specific angular frequency kω and the double specific angular frequency 2kω due to the three-phase unbalance component.

[0086] As described above, the control unit 100 of the V-connected inverter 1 includes a first voltage correction unit 140 that generates correction values Vuv2, Vvw2, and Vwu2 for the line voltages Vuv, Vvw, and Vwu at the fundamental angular frequency ω, and a second voltage correction unit 150 (or the second voltage correction units 250 and 350) that generates correction values Vuv3, Vvw3, and Vwu3 for the line voltages Vuv, Vvw, and Vwu at the specific angular frequency kω and the double specific angular frequency 2kω. Then, the control unit 100 performs on / off control of the switching elements S1 to S4 based on a signal obtained by adding the correction values Vuv2, Vvw2, Vwu2 and the correction values Vuv3, Vvw3, Vwu3.

[0087] Therefore, according to the V-connected inverter 1 according to the present embodiment, it can be used in a distributed power system that performs not only grid-connected operation but also stand-alone operation. When a single-phase load, which is an unbalanced load, is connected and / or when a non-linear load is connected, it is possible to suppress voltage distortion of the fundamental wave (fundamental angular frequency ω) and harmonics at specific frequencies (specific angular frequency kω and double specific angular frequency 2kω) included in the line voltages Vuv, Vvw, and Vwu of the U-phase line, V-phase line, and W-phase line.

[0088] As described above, the embodiment of the V-connected inverter according to the present invention has been described, but the present invention is not limited to the above embodiment.

[0089] [Modification Example] FIG. 9 shows a V-connected inverter 1' according to a modification example. The V-connected inverter 1' includes a main circuit unit 10' and a control unit 100'. The main circuit unit 10' has the same configuration as that of the above embodiment except that it includes a detection circuit 14' instead of the detection circuit 14.

[0090] The detection circuit 14' has a configuration in which a third voltage detection means V3 for detecting the line voltage Vwu is added to the detection circuit 14 of the above embodiment. Note that the detection circuit 14' may include a third current detection means CT3 for detecting the line current Isv.

[0091] The control unit 100' has the same configuration as that of the above embodiment, except that instead of calculating the line voltage Vwu, the line voltage Vwu detected by the third voltage detection means V3 is used. Note that when the detection circuit 14' includes the third current detection means CT3, the control unit 100' uses the line current Isv detected by the third current detection means CT3 instead of calculating the line current Isv.

[0092] [Other Modification Examples] The main circuit section of the V-connected inverter according to the present invention includes a first leg and a second leg connected in parallel, each leg including an upper arm and a lower arm including a switching element, the first leg outputting a first line voltage between the U-phase line and the V-phase line, and the second leg outputting a second line voltage between the V-phase line and the W-phase line. If it includes a voltage detection means for detecting the first line voltage and the second line voltage, the configuration can be changed as appropriate.

[0093] For example, in the above embodiment, as the switch circuit 12, a full-bridge circuit configuration in which one leg is composed of an upper arm and a lower arm is adopted, but a switch circuit composed of a multi-arm such as a three-level may also be used.

[0094] The control unit of the V-connected inverter according to the present invention includes a voltage command value output unit that outputs dq-axis voltage command values, a voltage value / frequency output unit that outputs a first three-phase voltage value, which is the voltage value of each line voltage of the U-phase line, V-phase line, and W-phase line, based on the detection value of the voltage detection means, and outputs a specific frequency that is a frequency component that is an integer multiple of the fundamental wave, an average command value output unit that outputs a single-phase average command value that is the average value of the dq-axis voltage command values, a first voltage correction unit that outputs a second three-phase voltage value, which is a correction value for each line voltage of the fundamental wave, based on the first three-phase voltage value and the single-phase average command value, a second voltage correction unit that outputs a third three-phase voltage value, which is a correction value for each line voltage of the specific frequency, based on the first three-phase voltage value and the specific frequency, a dq-axis voltage value output unit that performs 3-phase / dq conversion on the addition value of the second three-phase voltage value and the third three-phase voltage value to output a dq-axis voltage value, a dq-axis command value output unit that performs control to bring the difference between the dq-axis voltage value and the dq-axis voltage command value closer to 0 and outputs a dq-axis command value, a three-phase command value output unit that performs dq / 3-phase conversion on the dq-axis command value to output a three-phase command value, and a switch control unit that performs on / off control of the switching element based on the three-phase command value. If so, the configuration can be changed as appropriate.

Explanation of Signs

[0095] 1, 1’ V-connected inverter 10, 10’ Main circuit unit 11 Voltage dividing circuit 12 Switching circuit 13 Filter circuit 14, 14’ Detection circuit 100, 100’ Control unit

Claims

1. A V-connected inverter comprising a main circuit section and a control section, wherein the main circuit section comprises a first leg and a second leg connected in parallel, each leg comprising an upper arm and a lower arm including a switching element, the first leg outputting a first line voltage between a U-phase line and a V-phase line, and the second leg outputting a second line voltage between the V-phase line and a W-phase line; a switch circuit voltage detection means for detecting the first line voltage and the second line voltage; and a voltage detection means, wherein the control section comprises a voltage command value output section for outputting a dq-axis voltage command value; a voltage value / frequency output section for outputting a first three-phase voltage value which is a voltage value of each line voltage of the U-phase line, the V-phase line, and the W-phase line based on a detection value of the voltage detection means, and for outputting a specific frequency which is a frequency component that is an integer multiple of a fundamental wave; an average command value output section for outputting a single-phase average command value which is an average value of the dq-axis voltage command values; a first voltage correction section for outputting a second three-phase voltage value which is a correction value for each line voltage of the fundamental wave frequency based on the first three-phase voltage value and the single-phase average command value; a second voltage correction section for outputting a third three-phase voltage value which is a correction value for each line voltage of the specific frequency based on the first three-phase voltage value and the specific frequency; a dq-axis voltage value output section for performing a three-phase / dq conversion on an added value of the second three-phase voltage value and the third three-phase voltage value to output a dq-axis voltage value; a dq-axis command value output section for performing control to bring a difference between the dq-axis voltage value and the dq-axis voltage command value closer to zero and outputting a dq-axis command value; a three-phase command value output section for performing a dq / three-phase conversion on the dq-axis command value to output a three-phase command value; and a switch control section for performing on / off control of the switching element based on the three-phase command value. A V-connected inverter characterized by the above.

2. The first voltage correction section comprises a rectification section for performing rectification processing on the first three-phase voltage value and outputting the result; a low-pass filter for obtaining and outputting a DC component from an output of the rectification section; a PI control section for performing PI control on a difference between an output of the low-pass filter and the single-phase average command value; a deviation rate calculation section for calculating a deviation rate between an output of the PI control section and the single-phase average command value; and a calculation section for multiplying an output of the deviation rate calculation section by the first three-phase voltage value to generate the second three-phase voltage value. A reverse calculation unit that suppresses over-control of the integral element of the PI control unit by making the output of the deviation rate calculation unit match the output of the PI control unit. The V-connected inverter according to claim 1, characterized in that.

3. The second voltage correction unit includes A first positive-phase three-phase / dq conversion unit that performs positive-phase three-phase / dq conversion on the first three-phase voltage value; A first low-pass filter that acquires and outputs a first DC component from the output of the first positive-phase three-phase / dq conversion unit; A first PI control unit that performs PI control to bring the first DC component closer to 0; A reverse-phase three-phase / dq conversion unit that performs reverse-phase three-phase / dq conversion on the first three-phase voltage value; A second low-pass filter that acquires and outputs a second DC component from the output of the reverse-phase three-phase / dq conversion unit; A second PI control unit that performs PI control to bring the second DC component closer to 0; A reverse-phase dq / three-phase conversion unit that performs reverse-phase dq / three-phase conversion on the output of the second PI control unit; A second positive-phase three-phase / dq conversion unit that performs positive-phase three-phase / dq conversion on the output of the reverse-phase dq / three-phase conversion unit; A positive-phase dq / three-phase conversion unit that performs positive-phase dq / three-phase conversion on the sum value of the output of the first PI control unit and the output of the second positive-phase three-phase / dq conversion unit to generate the third three-phase voltage value. The V-connected inverter according to claim 1, characterized in that.

4. The second voltage correction unit includes A three-phase / dq conversion unit that performs three-phase / dq conversion on the first three-phase voltage value and outputs a d-axis value and a q-axis value; A first high-pass filter that acquires and outputs an AC component from the d-axis value; A first dq conversion unit that performs dq conversion on the output of the first high-pass filter; A first PI control unit that performs PI control to bring the output of the first dq conversion unit closer to 0; A first inverse dq conversion unit that performs inverse dq conversion on the output of the first PI control unit to generate a d-axis correction value; A second high-pass filter that acquires and outputs an AC component from the q-axis value; A second dq conversion unit that performs dq conversion on the output of the second high-pass filter; A second PI control unit that performs PI control to bring the output of the second dq conversion unit closer to 0; A second inverse dq conversion unit that performs inverse dq conversion on the output of the second PI control unit to generate a q-axis correction value; A dq / three-phase conversion unit that performs dq / three-phase conversion on the d-axis correction value and the q-axis correction value to generate the third three-phase voltage value. The V-connected inverter according to claim 1, characterized in that...

5. The second voltage positive part is... A first three-phase / dq conversion unit that performs three-phase / dq conversion on the first three-phase voltage value using the specific frequency and outputs a first dq-axis value; A first low-pass filter that obtains and outputs a first DC component from the first dq-axis value; A first PI control unit that performs PI control to bring the first DC component closer to 0; A second three-phase / dq conversion unit that performs three-phase / dq conversion on the first three-phase voltage value using a frequency that is two times or more the specific frequency and outputs a second dq-axis value; A second low-pass filter that obtains and outputs a second DC component from the second dq-axis value; A second PI control unit that performs PI control to bring the second DC component closer to 0; And a dq / three-phase conversion unit that performs dq / three-phase conversion on the added value of the output of the first PI control unit and the output of the second PI control unit to generate the third three-phase voltage value. The V-connected inverter according to claim 1, characterized in that...

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