Power conversion device

Abstract

To appropriately control a current output by a power conversion device.SOLUTION: The power-converting device 10 includes the separation calculator (the first converter 122 and the separator 124) that calculates the positive-phase voltages Vp α and Vp β and the negative-phase voltages Vn α and Vn β from the three phase AC voltage of the power system, the PLL circuit 142 that calculates the positive-phase sequence θ p from the positive-phase voltages Vp α and Vp β, the PLL circuit 162 that calculates the negative-phase sequence θ n and the negative-phase voltage amplitude Vn from the negative-phase voltages Vn α and Vn β, the negative-phase sequence current amplitude command generator 168 that calculates the negative-phase sequence current amplitude command value In based on the negative-phase sequence voltage amplitude Vn, and the negative-phase sequence current command generator 169 that calculates the negative-phase sequence current command values Ina, Inb, and Inc based on the positive-phase sequence θ p. And a current control part 180 and a pulse generation part 190 for generating the control signal PLS.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] A grid-connected system that connects a DC power supply that outputs DC power to a grid power supply included in a power system includes, for example, a power conversion device that converts the DC power supplied from the DC power supply into AC power. This type of power conversion device may be required to have a dynamic reactive current control function, a so-called DVS (Dynamic Voltage Support) function, that supplies reactive current to the power system in order to mitigate and recover from voltage drops during a grid fault. For example, Patent Document 1 discloses a technology for suppressing negative-phase voltage when an unbalanced short circuit occurs in a grid-connected power system. Note that an example of an unbalanced short circuit is a short circuit between two phases that occurs in a three-phase AC power system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 070295 Summary of the Invention [Problem to be solved by the invention]

[0004] In the event of an unbalanced fault such as an unbalanced short circuit, it is necessary to appropriately control the current output by the power conversion device in order to suppress the negative-phase voltage. In consideration of the above circumstances, one aspect of the present invention aims to appropriately control the current output by the power conversion device when an unbalanced fault occurs in the power system. [Means for solving the problem]

[0005] A preferred aspect of the present invention provides a power conversion device that converts DC power supplied from a DC power source into three-phase AC power based on a control signal and supplies the converted three-phase AC power to a three-phase AC power system, and includes: a separation calculation unit that calculates a positive-sequence voltage and a negative-sequence voltage from a three-phase AC voltage of the power system; a first calculation unit that calculates a positive-sequence phase from the positive-sequence voltage; a second calculation unit that calculates a negative-sequence phase and a negative-sequence voltage amplitude from the negative-sequence voltage; a negative-sequence current amplitude command unit that calculates a negative-sequence current command value based on the negative-sequence current amplitude command value and the negative-sequence phase; and a signal generation unit that generates the control signal based on a result of adding the positive-sequence current command value based on the positive-sequence phase and the negative-sequence current command value.

[0006] A power conversion device according to another preferred aspect of the present invention is a power conversion device that converts DC power supplied from a DC power source into three-phase AC power based on a control signal and supplies the converted three-phase AC power to a three-phase AC power system, and includes: a separation calculation unit that calculates a positive-phase voltage and a negative-phase voltage from a three-phase AC voltage of the power system; a third calculation unit that calculates a cosine and sine of a positive-phase phase from the positive-phase voltage; a fourth calculation unit that calculates a cosine and sine of a negative-phase phase and a negative-phase voltage amplitude from the negative-phase voltage; a negative-phase current amplitude command unit that calculates a negative-phase current command value based on the negative-phase voltage amplitude; a negative-phase current command unit that calculates a negative-phase current command value based on the negative-phase current amplitude command value and the cosine and sine of the negative-phase phase; and a signal generation unit that generates the control signal based on a result of adding the positive-phase current command value based on the positive phase and the negative-phase current command value. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an explanatory diagram for explaining an example of a grid-connected system 1 including a power conversion device 10 according to an embodiment. [Figure 2] 2 is an explanatory diagram for explaining an example of the configuration of a control unit shown in FIG. 1. FIG. [Figure 3] 3 is an explanatory diagram for explaining an example of the configuration of a positive phase control unit shown in FIG. 2.

[0023] FIG. [Figure 4]3 is an explanatory diagram for explaining an example of the configuration of a reverse phase control unit shown in FIG. 2.

[0023] FIG. [Figure 5] 10 is an explanatory diagram illustrating an example of a relationship between a negative-phase-sequence voltage amplitude and a negative-phase-sequence current amplitude command value. FIG. [Figure 6] FIG. 10 is an explanatory diagram for explaining an example of the configuration of a reverse phase control unit according to a first modified example. [Figure 7] FIG. 10 is an explanatory diagram illustrating an example of the configuration of a control unit according to a second modified example. [Figure 8] 8 is an explanatory diagram for explaining an example of the configuration of a positive phase control section and a negative phase control section shown in FIG. 7.

[0023] FIG. [Figure 9] FIG. 10 is an explanatory diagram illustrating an example of the configuration of a control unit according to a third modified example. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the dimensions and scale of each part are appropriately different from those of the actual parts. Furthermore, the embodiments described below are preferred examples of the present invention, and therefore various technically preferable limitations are applied. However, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

[0009] A. Embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an example of an outline of a grid-connected system 1 including a power conversion device 10 according to an embodiment will be described with reference to FIG.

[0010] FIG. 1 is an explanatory diagram illustrating an example of a grid-connected system 1 including a power conversion device 10 according to an embodiment.

[0011] The grid-connected system 1, for example, connects a DC power supply 12 that outputs DC power to a grid power supply 20 included in a three-phase AC power system. For example, the grid-connected system 1 includes a power conversion device 10, a DC power supply 12, the grid power supply 20, a reactor 22, and a transformer 30. The DC power supply 12 is connected to the grid power supply 20 via the power conversion device 10, the transformer 30, and the reactor 22. The grid power supply 20 outputs three-phase AC power, for example, U-phase, V-phase, and W-phase. The reactor 22 is a reactor in a line between the grid power supply 20 and the transformer 30.

[0012] The DC power supply 12 is, for example, a distributed power supply such as a storage battery. However, the DC power supply 12 is not limited to a storage battery. For example, the DC power supply 12 may be a solar cell or a fuel cell.

[0013] The power conversion device 10 converts DC power supplied from a DC power source 12 into AC power. An example of the power conversion device 10 is a power conditioner system (PCS), also known as an inverter. The power conversion device 10 includes, for example, a power conversion circuit 100, a control unit 102, reactors 104 and 106, a filter capacitor 108, a voltage measurement unit 110, and a current measurement unit 112.

[0014] The power conversion circuit 100 is an inverter circuit that converts DC power supplied from a DC power supply 12 into three-phase AC power based on a control signal PLS. For example, the power conversion circuit 100 includes a plurality of switching elements (not shown) that are switched on and off based on the control signal PLS. Examples of the switching elements include power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).

[0015] The control unit 102 controls the power conversion circuit 100 using, for example, a control signal PLS that drives each of the multiple switching elements of the power conversion circuit 100. Details of the control unit 102 will be described later with reference to FIG.

[0016] The reactors 104 and 106 are connected in series to each other. The reactor 104 is connected to the power conversion circuit 100, and the reactor 106 is connected to the transformer 30. A filter capacitor 108 is connected between the reactor 104 and the reactor 106.

[0017] The voltage measurement unit 110 measures the inter-phase voltages Vab and Vbc of the three phases and outputs the measurement results to the control unit 102. The inter-phase voltage Vab is the voltage between phase A and phase B, and the inter-phase voltage Vbc is the voltage between phase B and phase C. In this embodiment, it is assumed that phase A, phase B, and phase C correspond to the above-mentioned phase U, phase V, and phase W, respectively.

[0018] The current measurement unit 112 measures, for example, the current Ime flowing through the reactor 104 and outputs the measurement result to the control unit 102. For example, the current measurement unit 112 identifies the current Ime flowing through the reactor 104 based on the voltage difference between the output voltage of the power conversion circuit 100 and the voltage of the filter capacitor 108 and the impedance of the reactor 104. Note that in FIG. 1, for ease of viewing the drawing, the currents of the a-phase, b-phase, and c-phase are collectively shown as the current Ime.

[0019] Here, a fault such as a short circuit may temporarily occur due to a lightning strike or the like in the grid-connected system 1. For this reason, the grid-connected system 1 is configured to satisfy the so-called FRT (Fault Ride Through) requirement, which allows the DC power source 12 (distributed power source) to continue operating even during a grid fault. Furthermore, the power conversion device 10 has a dynamic reactive current control function (DVS function) that supplies reactive current to the power grid to mitigate and recover from a voltage drop during a grid fault.

[0020] For example, when an unbalanced fault occurs at point PTfa, causing a short circuit between two wires of phases A and B, the power conversion device 10 supplies reactive current to the power grid. As a result, when DVS control is performed, the decrease in grid voltage is suppressed compared to when DVS control is not performed, as shown in the parenthesized diagram in FIG.

[0021] While known voltage control methods can adequately address a three-phase balanced fault, known voltage control methods cannot adequately determine the current to be output by the power conversion device 10 when an unbalanced fault occurs. For example, regardless of whether a DVS function is present or not, a typical PCS detects a positive phase θp, which is the phase of a positive signal, from a three-phase signal of a power grid. Then, a typical PCS converts the positive signal into a DC value by rotating the αβ signal, which is a converted three-phase signal, by “−θp,” and converts the negative signal into a DC value by rotating the αβ signal by “+θp.” That is, a typical PCS considers “−θp” to be the phase of the negative signal. However, when an unbalanced fault occurs, the phase of the negative signal does not necessarily become “−θp.”

[0022] For example, if two wires, A and B, are short-circuited and an unbalanced fault occurs that reduces the residual voltage between phases A and B to 20%, the amplitude of the positive-sequence voltage will decrease from 1.0 pu to 0.6 pu, and a negative-sequence voltage with an amplitude of 0.4 pu and a phase of 240° will be superimposed. The phase of the positive-sequence voltage will remain unchanged from 0°. The unit pu indicates a value relative to a specified base value.

[0023] In this way, when an unbalanced fault occurs, the phase of the negative-sequence signal does not necessarily become "-θp" specified from the positive-sequence phase θp. For this reason, in this embodiment, the control unit 102 of the power conversion device 10 detects the negative-sequence phase θn, which is the phase of the negative-sequence voltage, separately from the positive-sequence phase θp, as shown in Fig. 4 etc., and determines an appropriate negative-sequence current using the detected negative-sequence phase θn.

[0024] Next, an example of the configuration of the control unit 102 will be described with reference to FIG.

[0025] FIG. 2 is an explanatory diagram illustrating an example of the configuration of the control unit 102 shown in FIG.

[0026] The control unit 102 has a phase voltage calculation unit 120, a first conversion unit 122, a separation unit 124, a positive phase control unit 140, a negative phase control unit 160, a current control unit 180, and a pulse generation unit 190. The first conversion unit 122 and the separation unit 124 are an example of a "separation calculation unit." Note that the separation unit 124 may also be considered as a "separation calculation unit."

[0027] Based on the inter-phase voltages Vab and Vbc measured by the voltage measurement unit 110, the phase voltage calculation unit 120 calculates the A-phase voltage Va, the B-phase voltage Vb, and the C-phase voltage Vc.

[0028] The first conversion unit 122 performs αβ conversion to convert three-phase AC into two-phase AC equivalent to the three-phase AC. For example, the first conversion unit 122 converts three-phase AC voltages Va, Vb, and Vc into two-phase AC voltages Vα and Vβ in a stationary coordinate system.

[0029] The separator 124 calculates positive-phase voltages Vpα and Vpβ and negative-phase voltages Vnα and Vnβ from the two-phase AC voltages Vα and Vβ. The positive-phase control unit 140 calculates positive-phase current command values ​​Ipa, Ipb, and Ipc based on the positive-phase voltages Vpα and Vpβ calculated by the separator 124. The negative-phase control unit 160 calculates negative-phase current command values ​​Ina, Inb, and Inc based on the negative-phase voltages Vnα and Vnβ calculated by the separator 124. Details of the positive-phase control unit 140 will be described later with reference to FIG. 3, and details of the negative-phase control unit 160 will be described later with reference to FIG. 4.

[0030] The current control unit 180 is, for example, an ACR (Automatic Current Regulator) that performs feedback control so that the current Ime measured by the current measurement unit 112 coincides with the sum of the positive-phase current command values ​​Ipa, Ipb, and Ipc and the negative-phase current command values ​​Ina, Inb, and Inc. For example, the current control unit 180 has an adder 182 that adds the positive-phase current command values ​​Ipa, Ipb, and Ipc calculated by the positive-phase control unit 140 and the negative-phase current command values ​​Ina, Inb, and Inc calculated by the negative-phase control unit 160. The current control unit 180 generates a three-phase current command signal λsig based on the difference between the sum of the adder 182 and the current Ime measured by the current measurement unit 112, and outputs the current command signal λsig to the pulse generation unit 190.

[0031] The pulse generating unit 190 generates control signals PLS for driving the multiple switching elements of the power conversion circuit 100, based on the three-phase current command signal λsig received from the current control unit 180. Then, the pulse generating unit 190 outputs the control signals PLS to the power conversion circuit 100. The current control unit 180 and the pulse generating unit 190 are an example of a "signal generating unit."

[0032] Next, an example of the configuration of the positive phase control section 140 will be described with reference to FIG.

[0033] FIG. 3 is an explanatory diagram for explaining an example of the configuration of the positive phase control unit 140 shown in FIG.

[0034] The positive phase control unit 140 has a PLL (Phase Locked Loop) circuit 142, a positive sequence current amplitude command generation unit 148, and a positive sequence current command generation unit 149. The PLL circuit 142 is an example of a "first calculation unit."

[0035] The PLL circuit 142 detects a positive phase θp, which is the phase of the positive-sequence voltage, based on the positive-sequence voltages Vpα and Vpβ calculated by the separator 124. For example, the PLL circuit 142 includes a second converter 142a, a proportional-plus-integral controller 142b, and an integrator 142c.

[0036] The second conversion unit 142a performs dq transformation to convert voltages in the stationary coordinate system into voltages in a synchronous rotating coordinate system defined by the d-axis and q-axis. For example, the second conversion unit 142a converts the positive-phase voltages Vpα and Vpβ calculated by the separation unit 124 into voltages Vpd and Vpq using the positive-phase phase θp output from the integrator 142c. Specifically, the second conversion unit 142a calculates the voltages Vpd and Vpq by rotating the positive-phase voltages Vpα and Vpβ by "-θp" with a gain of 1. In this case, the voltages Vpd and Vpq are expressed by equations (1) and (2), respectively.

[0037] Vpd=Vpα·cos(θp)+Vpβ·sin(θp) …(1) Vpq=-Vpα·sin(θp)+Vpβ·cos(θp) …(2)

[0038] The proportional-plus-integral control unit 142b calculates an angular frequency by, for example, performing proportional-plus-integral control (so-called PI control) so that the voltage Vpq calculated by the second conversion unit 142a becomes zero. The integrator 142c calculates a positive phase θp by integrating the angular frequency calculated by the proportional-plus-integral control unit 142b. The positive phase θp is fed back to the second conversion unit 142a. Furthermore, the positive phase θp is used by the positive-sequence current command generator 149.

[0039] In this way, the PLL circuit 142 calculates the positive sequence phase θp and the voltages Vpd and Vpq based on the positive sequence voltages Vpα and Vpβ. Furthermore, as described above, the PLL circuit 142 performs feedback control so that the voltage Vpq becomes zero. Therefore, the PLL circuit 142 can calculate the amplitude of the positive sequence voltage by calculating the voltage Vpd. Hereinafter, the amplitude of the positive sequence voltage is also referred to as the positive sequence voltage amplitude Vp. For example, in this embodiment, the voltage Vpd is output from the PLL circuit 142 to the positive sequence current amplitude command generator 148 as the positive sequence voltage amplitude Vp.

[0040] The positive-sequence current amplitude command generator 148 calculates a positive-sequence current amplitude command value Ip based on the positive-sequence voltage amplitude Vp. For example, the positive-sequence current amplitude command generator 148 calculates the positive-sequence current amplitude command value Ip from the positive-sequence voltage amplitude Vp based on predetermined voltage-current characteristics (the relationship between voltage and current). Specifically, for example, the positive-sequence current amplitude command generator 148 may calculate the positive-sequence current amplitude command value Ip by multiplying the positive-sequence voltage amplitude Vp by a predetermined coefficient.

[0041] The positive sequence current command generator 149 calculates three-phase positive sequence current command values ​​Ipa, Ipb, and Ipc based on the phase φp, the positive sequence phase θp calculated by the PLL circuit 142, and the positive sequence current amplitude command value Ip calculated by the positive sequence current amplitude command generator 148. The phase φp indicates, for example, the phase angle of the positive sequence current relative to the positive sequence voltage (a leading phase is positive, and a lagging phase is negative). In this embodiment, it is assumed that the phase φp is a leading phase of 90°. The positive sequence current command values ​​Ipa, Ipb, and Ipc are expressed, for example, by equations (3), (4), and (5), respectively.

[0042] Ipa=Ip·cos(θp+φp) …(3) Ipb=Ip·cos(θp-120°+φp) …(4) Ipc=Ip·cos(θp+120°+φp) …(5)

[0043] In this way, the positive phase control unit 140 calculates the three-phase positive sequence current command values ​​Ipa, Ipb, and Ipc based on the positive sequence voltages Vpα and Vpβ calculated by the separation unit 124. Note that the method of calculating the three-phase positive sequence current command values ​​Ipa, Ipb, and Ipc is not limited to the example shown in Fig. 3, and any known method can be used.

[0044] Next, an example of the configuration of the reverse phase control section 160 will be described with reference to FIG.

[0045] FIG. 4 is an explanatory diagram for explaining an example of the configuration of the reverse phase control section 160 shown in FIG.

[0046] The negative-phase control unit 160 has a PLL circuit 162, a negative-phase voltage amplitude calculation unit 163, a negative-phase current amplitude command generation unit 168, and a negative-phase current command generation unit 169. The PLL circuit 162 is an example of a "second calculation unit." The negative-phase current amplitude command generation unit 168 is an example of a "negative-phase current amplitude command unit," and the negative-phase current command generation unit 169 is an example of a "negative-phase current command unit."

[0047] The PLL circuit 162 detects the antiphase phase θn, which is the phase of the antiphase voltage, based on the antiphase voltages Vnα and Vnβ calculated by the separator 124. For example, the PLL circuit 162 includes a third converter 162a, a proportional-plus-integral controller 162b, and an integrator 162c.

[0048] The third conversion unit 162a performs dq transformation in the same way as the second conversion unit 142a. For example, the third conversion unit 162a converts the antiphase voltages Vnα and Vnβ calculated by the separation unit 124 into voltages Vnd and Vnq using the antiphase phase θn output from the integrator 162c. Specifically, the third conversion unit 162a calculates the voltages Vnd and Vnq by rotating the antiphase voltages Vnα and Vnβ by "+θn" with a gain of 1. In this case, the voltages Vnd and Vnq are expressed by equations (6) and (7), respectively.

[0049] Vnd=Vnα·cos(θn)-Vnβ·sin(θn) …(6) Vnq=Vnα·sin(θn)+Vnβ·cos(θn) …(7)

[0050] The proportional-plus-integral control unit 162b calculates an angular frequency by, for example, performing proportional-plus-integral control (PI control) so that the voltage Vnq calculated by the third conversion unit 162a becomes zero. The integrator 162c calculates a negative phase θn by integrating the angular frequency calculated by the proportional-plus-integral control unit 162b. The negative phase θn is fed back to the third conversion unit 162a. Furthermore, the negative phase θn is used by the negative-phase current command generator 169.

[0051] In this way, the PLL circuit 162 calculates the negative-phase phase θn and the voltages Vnd and Vnq based on the negative-phase voltages Vnα and Vnβ. Furthermore, as described above, the PLL circuit 162 performs feedback control so that the voltage Vnq becomes zero. Therefore, the PLL circuit 162 can calculate the amplitude of the negative-phase voltage by calculating the voltage Vnd. Hereinafter, the amplitude of the negative-phase voltage is also referred to as the negative-phase voltage amplitude Vn. For example, in this embodiment, the voltage Vnd is output from the PLL circuit 162 to the negative-phase current amplitude command generator 168 as the negative-phase voltage amplitude Vn.

[0052] The negative-phase-sequence current amplitude command generating unit 168 calculates the negative-phase-sequence current amplitude command value In based on the negative-phase-sequence voltage amplitude Vn. For example, the negative-phase-sequence current amplitude command generating unit 168 calculates the negative-phase-sequence current amplitude command value In from the negative-phase-sequence voltage amplitude Vn based on predetermined voltage-current characteristics (the relationship between voltage and current). Specifically, for example, the negative-phase-sequence current amplitude command generating unit 168 may calculate the negative-phase-sequence current amplitude command value In by multiplying the negative-phase-sequence voltage amplitude Vn by a predetermined coefficient. In this embodiment, as shown in FIG. 5 described later, a dead band is predetermined for the negative-phase-sequence voltage amplitude Vn, and upper and lower limits are predetermined for the negative-phase-sequence current amplitude command value In.

[0053] The negative-phase current command generator 169 calculates three-phase negative-phase current command values ​​Ina, Inb, and Inc based on the phase φn, the negative-phase phase θn calculated by the PLL circuit 162, and the negative-phase current amplitude command value In calculated by the negative-phase current amplitude command generator 168. The phase φn indicates, for example, the phase angle of the negative-phase current relative to the negative-phase voltage (a leading phase is positive, and a lagging phase is negative). In this embodiment, it is assumed that the phase φn is a leading phase of 90°. The negative-phase current command values ​​Ina, Inb, and Inc are expressed, for example, by equations (8), (9), and (10), respectively.

[0054] Ina=In·cos(θn+φn) …(8) Inb=In·cos(θn+120°+φn) …(9) Inc=In·cos(θn-120°+φn) …(10)

[0055] In this manner, in the present embodiment, the three-phase negative-sequence current command values ​​Ina, Inb, and Inc are calculated using the negative-sequence phase θn, etc., calculated based on the negative-sequence voltages Vnα and Vnβ. Therefore, in the present embodiment, when an unbalanced fault occurs, the negative-sequence current command values ​​Ina, Inb, and Inc can be calculated more appropriately than in the comparative example in which "-θp" identified from the positive-sequence phase θp is used as the negative-sequence phase.

[0056] In the comparative example, for example, the negative-sequence voltages Vnα and Vnβ are converted into two-phase negative-sequence dq voltages (voltages Vnd and Vnq) using "-θp" determined from the positive-sequence phase θp. Then, the two-phase negative-sequence dq currents are calculated by rotating the dq voltages by 90° with a predetermined gain. Furthermore, the two-phase negative-sequence dq currents are subjected to two-phase / three-phase conversion to calculate the three-phase negative-sequence current command values ​​Ina, Inb, and Inc. In this way, in the comparative example, the three-phase negative-sequence current command values ​​Ina, Inb, and Inc are calculated by vector calculation on the d-axis and q-axis. Therefore, it is difficult to set a dead zone for the negative-sequence voltages and upper and lower limits for the negative-sequence currents. In contrast, in the present embodiment, the negative-sequence voltage amplitude Vn and the negative-sequence current amplitude command value In are scalar quantities. This makes it easy to set the dead zone for the negative-sequence voltage amplitude Vn and the upper and lower limits for the negative-sequence current amplitude command value In.

[0057] Next, an example of the relationship between the negative-phase-sequence voltage amplitude Vn and the negative-phase-sequence current amplitude command value In will be described with reference to FIG.

[0058] 5 is an explanatory diagram illustrating an example of the relationship between the negative-phase-sequence voltage amplitude Vn and the negative-phase-sequence current amplitude command value In. The horizontal axis of the graph in FIG. 5 represents the negative-phase-sequence voltage amplitude Vn, and the vertical axis represents the negative-phase-sequence current amplitude command value In.

[0059] As shown in Fig. 5, a dead zone DZ is set for the negative-phase sequence voltage amplitude Vn, and an upper limit and a lower limit are set for the negative-phase sequence current amplitude command value In. In the example shown in Fig. 5, the range from voltage amplitude VDZ1 to voltage amplitude VDZ2 is set as the dead zone DZ. Furthermore, the upper limit of the negative-phase sequence current amplitude command value In is set to the current amplitude value ILu, and the lower limit of the negative-phase sequence current amplitude command value In is set to the current amplitude value ILl.

[0060] For example, when the negative-phase-sequence voltage amplitude Vn is within the range of the dead zone DZ (the range of not less than the voltage amplitude VDZ1 and not more than the voltage amplitude VDZ2), the negative-phase-sequence current command generating unit 169 maintains the negative-phase-sequence current amplitude command value In at a predetermined current amplitude value I0. The current amplitude value I0 is, for example, "0." As described above, in this embodiment, the dead zone DZ is set for the negative-phase-sequence voltage amplitude Vn, so that unnecessary charging and discharging can be suppressed. Furthermore, in this embodiment, upper and lower limits are set for the negative-phase-sequence current amplitude command value In, so that excessive charging and discharging can be suppressed.

[0061] It is not necessary to set a dead zone DZ for the negative-sequence voltage amplitude Vn. It is also not necessary to set upper and lower limits for the negative-sequence current amplitude command value In. In addition, the positive-phase control unit 140 may also set a dead zone DZ for the positive-sequence voltage amplitude Vp and set upper and lower limits for the positive-sequence current amplitude command value Ip.

[0062] As described above, in this embodiment, the power conversion device 10 is a power conversion device 10 that converts DC power supplied from the DC power source 12 into three-phase AC power based on the control signal PLS and supplies the converted three-phase AC power to a three-phase AC power system, and includes a separation calculation unit (first conversion unit 122 and separation unit 124) that calculates positive-phase voltages Vpα and Vpβ and negative-phase voltages Vnα and Vnβ from the three-phase AC voltage of the power system, a PLL circuit 142 that calculates a positive-phase phase θp from the positive-phase voltages Vpα and Vpβ, and a negative-phase phase θp from the negative-phase voltages Vnα and Vnβ. The inverter circuit 160 includes a PLL circuit 162 that calculates a phase θn and a negative-phase voltage amplitude Vn, a negative-phase current amplitude command generator 168 that calculates a negative-phase current amplitude command value In based on the negative-phase voltage amplitude Vn, a negative-phase current command generator 169 that calculates negative-phase current command values ​​Ina, Inb, and Inc based on the negative-phase current amplitude command value In and the negative-phase phase θn, and a current controller 180 and a pulse generator 190 that generate a control signal PLS based on the sum of the positive-phase current command value based on the positive-phase phase θp and the negative-phase current command values ​​Ina, Inb, and Inc.

[0063] In this manner, in the present embodiment, the three-phase negative-sequence current command values ​​Ina, Inb, and Inc are calculated using the negative-sequence phase θn calculated based on the negative-sequence voltages Vnα and Vnβ. Therefore, in the present embodiment, the negative-sequence current command values ​​Ina, Inb, and Inc can be calculated appropriately. Furthermore, in the present embodiment, the negative-sequence voltage amplitude Vn and the negative-sequence current amplitude command value In are scalar quantities, so that the dead zone of the negative-sequence voltage amplitude Vn and the upper and lower limits of the negative-sequence current amplitude command value In can be easily set.

[0064] For example, in this embodiment, when the negative-phase-sequence voltage amplitude Vn is within a predetermined dead zone DZ (a range from the voltage amplitude VDZ1 to the voltage amplitude VDZ2), the negative-phase-sequence current amplitude command generator 168 may maintain the negative-phase-sequence current amplitude command value In at a predetermined amplitude value (current amplitude value I0). In this case, unnecessary charging and discharging can be suppressed.

[0065] In this embodiment, a lower limit and an upper limit may be set for the negative-phase current amplitude command value In. In this case, excessive charging and discharging can be prevented.

[0066] B: Modified example The above-described exemplary embodiments may be modified in various ways. Specific examples of modifications that may be applied to the above-described embodiments are given below. Two or more of the following examples may be combined together as long as they are not mutually inconsistent.

[0067] B1: First modified example In the above-described embodiment, the PLL circuit 162 is used as the second calculation unit that calculates the negative phase θn and the negative voltage amplitude Vn from the negative voltages Vnα and Vnβ, but the present invention is not limited to this. For example, the negative phase θn may be calculated based on the positive phase θp and the phase difference between the negative phase θn and the positive phase θp.

[0068] Fig. 6 is an explanatory diagram for explaining an example of the configuration of a negative phase control unit 160A according to a first modification. The power conversion device 10 according to this modification is similar to the power conversion device 10 shown in Fig. 1 except that the control unit 102 has a negative phase control unit 160A instead of the negative phase control unit 160 shown in Fig. 4. The negative phase control unit 160A is also similar to the negative phase control unit 160 except that the PLL circuit 162 shown in Fig. 4 is omitted and a fourth conversion unit 164, a polar coordinate conversion unit 165, an inversion unit 166, and an addition unit 167 are provided.

[0069] For example, the negative-phase control unit 160A has a fourth conversion unit 164, a polar coordinate conversion unit 165, an inversion unit 166, an addition unit 167, a negative-phase current amplitude command generation unit 168, and a negative-phase current command generation unit 169. The fourth conversion unit 164, the polar coordinate conversion unit 165, the inversion unit 166, and the addition unit 167 are an example of a "second calculation unit." Furthermore, the addition unit 167 is an example of a "phase calculation unit."

[0070] For example, the fourth conversion unit 164 performs dq conversion on the negative-phase voltages Vnα and Vnβ calculated by the separation unit 124 using the positive-phase phase θp calculated by the PLL circuit 142. This calculates the voltages Vnd and Vnq. For example, the fourth conversion unit 164 calculates the voltages Vnd and Vnq by rotating the negative-phase voltages Vnα and Vnβ by "+θp" with a gain of 1.

[0071] The polar coordinate converter 165 performs polar coordinate conversion on the voltages Vnd and Vnq calculated by the fourth converter 164 to calculate the phase difference between the negative phase θn and the positive phase θp, and the negative phase voltage amplitude Vn. The negative phase voltage amplitude Vn is output to the negative phase current amplitude command generator 168. The negative phase voltage amplitude Vn is expressed by equation (11) using the symbol ^ indicating the power.

[0072] Vn = √(Vnd^2 + Vnq^2) …(11)

[0073] Furthermore, in the case of negative-phase signals such as voltages Vnd and Vnq, the angular velocity is inverted relative to the positive-phase signals. Therefore, the phase difference calculated by polar coordinate conversion unit 165 is inverted by inverter 166. As a result, the difference Δθn between the positive phase θp and the negative phase θn (the value obtained by subtracting the positive phase θp from the negative phase θn) is calculated.

[0074] The adder 167 calculates the negative phase θn by adding the difference Δθn calculated by the polar coordinate converter 165 and the inverter 166 to the positive phase θp calculated by the PLL circuit 142. The negative phase θn is output to the negative phase current command generator 169.

[0075] The negative-phase-sequence current amplitude command generating unit 168 and the negative-phase-sequence current command generating unit 169 are similar to the negative-phase-sequence current amplitude command generating unit 168 and the negative-phase-sequence current command generating unit 169 described in Fig. 4. In this modification as well, the three-phase negative-phase-sequence current command values ​​Ina, Inb, and Inc are calculated using the negative-phase phase θn etc. calculated based on the negative-phase-sequence voltages Vnα and Vnβ.

[0076] In this modification, a dead zone DZ may be set for the negative-sequence voltage amplitude Vn, and an upper and lower limit may be set for the negative-sequence current amplitude command value In.

[0077] As described above, in this modification, the second calculation unit that calculates the negative phase θn and the negative voltage amplitude Vn from the negative voltages Vnα and Vnβ includes a polar coordinate conversion unit 165 that calculates the difference between the positive phase θp and the negative phase θn (the phase difference before inverting the difference Δθn) from the negative voltages Vnα and Vnβ, and an adder 167 that calculates the negative phase θn based on the difference Δθn and the positive phase θp calculated by the PLL circuit 142. In this modification as well, the same effects as those of the above-mentioned embodiment can be obtained.

[0078] B2: Second variant In the above-described embodiment and modified example, the case where the antiphase θn is calculated has been illustrated, but the present invention is not limited to such an embodiment. For example, instead of calculating the antiphase θn, the cosine and sine of the antiphase θn may be calculated.

[0079] 7 is an explanatory diagram illustrating an example of the configuration of a control unit 102B according to a second modification. The power conversion device 10 according to this modification is similar to the power conversion device 10 shown in FIG. 1 except that it has a control unit 102B instead of the control unit 102 shown in FIG. 1. The control unit 102B is also similar to the control unit 102 except that it has a delay unit 125, a positive phase control unit 150, and a negative phase control unit 170 instead of the separation unit 124, the positive phase control unit 140, and the negative phase control unit 160 shown in FIG. 2.

[0080] For example, the control unit 102B includes a phase voltage calculation unit 120, a first conversion unit 122, a delay unit 125, a positive phase control unit 150, a negative phase control unit 170, a current control unit 180, and a pulse generation unit 190. The phase voltage calculation unit 120, the first conversion unit 122, the current control unit 180, and the pulse generation unit 190 are similar to the phase voltage calculation unit 120, the first conversion unit 122, the current control unit 180, and the pulse generation unit 190 shown in FIG.

[0081] The delay unit 125 delays the voltage Vβ of the two-phase AC voltages Vα and Vβ by 90°. Then, the delay unit 125 outputs a delayed voltage Vβd obtained by delaying the voltage Vβ by 90° to the positive phase control unit 150 and the negative phase control unit 170. Of the two-phase AC voltages Vα and Vβ, the voltage Vα is output from the first conversion unit 122 to the positive phase control unit 150 and the negative phase control unit 170.

[0082] The positive phase control unit 150 calculates positive sequence current command values ​​Ipa, Ipb, and Ipc based on the voltage Vα and the delay voltage Vβd. The negative phase control unit 170 calculates negative sequence current command values ​​Ina, Inb, and Inc based on the voltage Vα and the delay voltage Vβd. Details of the positive phase control unit 150 and the negative phase control unit 170 will be described later with reference to FIG. 8.

[0083] 8 is an explanatory diagram illustrating an example of the configuration of the positive-phase control unit 150 and the negative-phase control unit 170 shown in FIG. 7. The positive-phase control unit 150 and the negative-phase control unit 170 have basically the same configuration except for the difference between subtracting the delay voltage Vβd from the voltage Vα and adding the delay voltage Vβd to the voltage Vα. For this reason, the explanation in FIG. 8 will focus on the negative-phase control unit 170. Note that in FIG. 8, the positive-phase current amplitude command generation unit 158 ​​and the positive-phase current command generation unit 159 are simplified for ease of viewing.

[0084] The negative-phase-sequence control unit 170 has an adder 172, a multiplier 173, an amplitude calculation unit 174, a divider 175, a delay unit 176, a negative-phase-sequence current amplitude command generation unit 178, and a negative-phase-sequence current command generation unit 179. The amplitude calculation unit 174, the divider 175, and the delay unit 176 are an example of a "fourth calculation unit." The negative-phase-sequence current amplitude command generation unit 178 is an example of a "negative-phase-sequence current amplitude command unit," and the negative-phase-sequence current command generation unit 179 is an example of a "negative-phase-sequence current command unit."

[0085] The adder 172 adds the voltage Vα output from the first converter 122 and the delayed voltage Vβd output from the delay unit 125, and outputs the addition result to the multiplier 173. The multiplier 173 multiplies the addition result of the voltage Vα and the delayed voltage Vβd by a coefficient of ½, thereby calculating the negative-phase voltage Vnα. The amplitude calculator 174 calculates the negative-phase voltage amplitude Vn based on the negative-phase voltage Vnα calculated by the multiplier 173. For example, the amplitude calculator 174 calculates the negative-phase voltage amplitude Vn by removing a frequency component twice the frequency of the negative-phase voltage amplitude Vn from the signal of the absolute value of the negative-phase voltage amplitude Vn.

[0086] The divider 175 divides the negative-phase voltage Vnα calculated by the multiplier 173 by the negative-phase voltage amplitude Vn calculated by the amplitude calculator 174 to calculate the cosine (cos θn) of the negative phase θn.

[0087] The delay unit 176 calculates the sine (sin θn) of the antiphase θn based on the cosine (cos θn) of the antiphase θn calculated by the divider 175. For example, the delay unit 176 calculates the sine (sin θn) of the antiphase θn by multiplying the moving average of the cosine (cos θn) of the antiphase θn by "-π / 2".

[0088] The negative-phase-sequence current amplitude command generating unit 178 is similar to the negative-phase-sequence current amplitude command generating unit 168 shown in Fig. 6. For example, the negative-phase-sequence current amplitude command generating unit 178 calculates the negative-phase-sequence current amplitude command value In based on the negative-phase-sequence voltage amplitude Vn calculated by the amplitude calculating unit 174.

[0089] The negative-phase-sequence current command generating unit 179 calculates three-phase negative-phase current command values ​​Ina, Inb, and Inc based on the phase φn, the cosine (cos θn) of the negative-phase phase θn calculated by the dividing unit 175, the sine (sin θn) of the negative-phase phase θn calculated by the delay unit 176, and the negative-phase current amplitude command value In calculated by the negative-phase current amplitude command generating unit 178. The negative-phase-sequence current command generating unit 179 uses the addition theorem of trigonometric functions to calculate the three-phase negative-phase current command values ​​Ina, Inb, and Inc. For example, the addition theorem of trigonometric functions is used to calculate the cosine (cos(θn+φn)) of the sum of the negative-phase phase θn and the phase φn. The cosine (cos(θn+φn)) of the sum of the negative-phase phase θn and the phase φn is expressed by Equation (12).

[0090] cos(θn+φn)=cosθn·cosφn-sinθn·sinφn …(12)

[0091] In this manner, in this modification, the three-phase negative-sequence current command values ​​Ina, Inb, and Inc are calculated using the cosine of the negative-sequence phase θn calculated based on the negative-sequence voltage Vnα, etc. In this modification as well, the negative-sequence current command values ​​Ina, Inb, and Inc are calculated as expressed by equations (8), (9), and (10), respectively, as described in FIG.

[0092] Next, the positive phase control section 150 will be briefly described.

[0093] Positive phase control unit 150 includes subtraction unit 152, multiplication unit 153, amplitude calculation unit 154, division unit 155, delay unit 156, positive sequence current amplitude command generation unit 158, and positive sequence current command generation unit 159. Note that amplitude calculation unit 154, division unit 155, and delay unit 156 are an example of a "third calculation unit."

[0094] The subtraction unit 152 subtracts the delayed voltage Vβd output from the delay unit 125 from the voltage Vα output from the first conversion unit 122, and outputs the subtraction result to the multiplication unit 153. The multiplication unit 153 multiplies the result of subtracting the delayed voltage Vβd from the voltage Vα by a coefficient of ½, thereby calculating the positive-phase voltage Vpα. The amplitude calculation unit 154 calculates the positive-phase voltage amplitude Vp based on the positive-phase voltage Vpα calculated by the multiplication unit 153.

[0095] The divider 155 calculates the cosine (cos θp) of the positive phase θp by dividing the positive phase voltage Vpα calculated by the multiplier 153 by the positive phase voltage amplitude Vp calculated by the amplitude calculator 154. The delay unit 156 calculates the sine (sipθp) of the positive phase θp based on the cosine (cos θp) of the positive phase θp calculated by the divider 155.

[0096] The positive-sequence current amplitude command generating unit 158 ​​calculates a positive-sequence current amplitude command value Ip based on the positive-sequence voltage amplitude Vp calculated by the amplitude calculating unit 154, for example.

[0097] A positive sequence current command generating unit 159 calculates three-phase positive sequence current command values ​​Ipa, Ipb, and Ipc based on the phase φp, the cosine (cos θp) of the positive sequence phase θp calculated by the dividing unit 155, the sine (sin θp) of the positive sequence phase θp calculated by the delay unit 156, and the positive sequence current amplitude command value Ip calculated by the positive sequence current amplitude command generating unit 158. In this modification as well, the positive sequence current command values ​​Ipa, Ipb, and Ipc respectively expressed by equations (3), (4), and (5) described in FIG. 3 are calculated.

[0098] In this modification, a dead zone DZ may be set for the negative-sequence voltage amplitude Vn, and an upper and lower limit may be set for the negative-sequence current amplitude command value In.

[0099] 7 correspond to the "separation calculation unit." Note that the subtraction unit 152, the multiplication unit 153, the addition unit 172, and the multiplication unit 173 may also be considered as the "separation calculation unit."

[0100] As described above, in this modification, the power conversion device 10 includes a separation calculation unit (first conversion unit 122, delay unit 125, subtraction unit 152, multiplication unit 153, addition unit 172, and multiplication unit 173) that calculates the positive-phase voltage Vpα and the negative-phase voltage Vnα from the three-phase AC voltage of the power grid, a third calculation unit (amplitude calculation unit 154, division unit 155, and delay unit 156) that calculates the cosine and sine of the positive-phase phase θp from the positive-phase voltage Vpα, and a fourth calculation unit (amplitude calculation unit 174) that calculates the cosine and sine of the negative-phase phase θn and the negative-phase voltage amplitude Vn from the negative-phase voltage Vnα. , a divider 175 and a delay unit 176), a negative-phase current amplitude command generator 178 that calculates a negative-phase current amplitude command value In based on the negative-phase voltage amplitude Vn, a negative-phase current command generator 179 that calculates negative-phase current command values ​​Ina, Inb and Inc based on the negative-phase current amplitude command value In and the cosine and sine of the negative-phase phase θn, and a current control unit 180 and a pulse generating unit 190 that generate a control signal PLS based on the result of adding the positive-phase current command value based on the positive-phase phase θp and the negative-phase current command values ​​Ina, Inb and Inc. In this modification, the same effects as those of the above-described embodiment can be obtained.

[0101] B3: Third variant The double decoupled synchronous reference frame (DDSRF) method may be used to calculate the positive-phase voltages Vpd and Vpq, the negative-phase voltages Vnd and Vnq, and the positive phase θp of the synchronous rotating coordinate system from the three-phase AC voltages Va, Vb, and Vc.

[0102] 9 is an explanatory diagram illustrating an example of the configuration of a control unit 102C according to a third modification. The power conversion device 10 according to this modification is similar to the power conversion device 10 shown in FIG. 1, except that it has a control unit 102C instead of the control unit 102 shown in FIG.

[0103] For example, the control unit 102C includes a phase voltage calculation unit 120, a first conversion unit 122, a DDSRF circuit 130, a positive-phase current amplitude command generation unit 148, a positive-phase current command generation unit 149, a polar coordinate conversion unit 165, an inversion unit 166, an addition unit 167, a negative-phase current amplitude command generation unit 168, a negative-phase current command generation unit 169, a current control unit 180, and a pulse generation unit 190.

[0104] The phase voltage calculation unit 120, the first conversion unit 122, the current control unit 180, and the pulse generation unit 190 are the same as the phase voltage calculation unit 120, the first conversion unit 122, the current control unit 180, and the pulse generation unit 190 shown in Fig. 2. The positive-sequence current amplitude command generation unit 148 and the positive-sequence current command generation unit 149 are the same as the positive-sequence current amplitude command generation unit 148 and the positive-sequence current command generation unit 149 shown in Fig. 3. The polar coordinate conversion unit 165, the inversion unit 166, the addition unit 167, the negative-sequence current amplitude command generation unit 168, and the negative-sequence current command generation unit 169 are the same as the polar coordinate conversion unit 165, the inversion unit 166, the addition unit 167, the negative-sequence current amplitude command generation unit 168, and the negative-sequence current command generation unit 169 shown in Fig. 6.

[0105] The DDSRF circuit 130 calculates the positive sequence phase θp, the positive sequence voltage amplitude Vp, and the voltages Vnd and Vnq by the DDSRF method. Then, the DDSRF circuit 130 outputs the positive sequence phase θp to the positive sequence current command generator 149 and the adder 167, outputs the positive sequence voltage amplitude Vp to the positive sequence current amplitude command generator 148, and outputs the voltages Vnd and Vnq to the polar coordinate converter 165.

[0106] In the DDSRF circuit 130, a positive-sequence signal is calculated by performing dq transformation on the two-phase AC voltages Vα and Vβ using the positive-sequence phase θp. Therefore, in this modification, similarly to the above-described embodiment, the voltage Vpd is output to the positive-sequence current amplitude command generator 148 as the positive-sequence voltage amplitude Vp.

[0107] Furthermore, in the DDSRF circuit 130, a negative phase signal is calculated by performing a dq transformation on the two-phase AC voltages Vα and Vβ using “−θp” determined from the positive phase θp. Therefore, in this modification, similarly to the first modification described above, the voltages Vnd and Vnq are output to the polar coordinate conversion unit 165.

[0108] Here, the DDSRF circuit 130 corresponds to the "separation calculation unit" and the "first calculation unit."

[0109] In this modification, the three-phase negative-sequence current command values ​​Ina, Inb, and Inc are calculated using the negative-sequence phase θn calculated based on the negative-sequence voltages Vnα and Vnβ. In this modification, a dead zone DZ may be set for the negative-sequence voltage amplitude Vn. An upper limit and a lower limit may be set for the negative-sequence current amplitude command value In.

[0110] As described above, in this modified example, the same effects as those of the above-described embodiment can be obtained. [Explanation of symbols]

[0111] 1...grid-connected system, 10...power conversion device, 12...DC power supply, 20...grid power supply, 22...reactor, 30...transformer, 100...power conversion circuit, 102, 102B, 102C...control unit, 104, 106...reactor, 108...filter capacitor, 110...voltage measurement unit, 112...current measurement unit, 120...phase voltage calculation unit, 122...first conversion unit, 124...separation unit, 125...delay unit, 130...DDSRF circuit, 140...positive phase control unit, 142...PLL circuit, 142a...second conversion unit, 142b...proportional-integral control unit, 142c...integration unit, 148...positive phase current amplitude command generation unit, 149...positive phase current command generation unit, 150...positive phase control unit, 152...subtraction unit, 153...multiplication unit, 154...amplitude Width calculation unit, 155... division unit, 156... delay unit, 158... positive-sequence current amplitude command generation unit, 159... positive-sequence current command generation unit, 160, 160A... negative-sequence control unit, 162... PLL circuit, 162a... third conversion unit, 162b... proportional-integral control unit, 162c... integration unit, 163... negative-sequence voltage amplitude calculation unit, 164... fourth conversion unit, 165... polar coordinate conversion unit, 166... ​​inversion unit, 167... addition unit, 168... negative-sequence current amplitude command generation unit, 169... negative-sequence current command generation unit, 170... negative-sequence control unit, 172... addition unit, 173... multiplication unit, 174... amplitude calculation unit, 175... division unit, 176... delay unit, 178... negative-sequence current amplitude command generation unit, 179... negative-sequence current command generation unit, 180... current control unit, 190... pulse generation unit.

Claims

1. 1. A power conversion device that converts DC power supplied from a DC power source into three-phase AC power based on a control signal and supplies the converted three-phase AC power to a three-phase AC power system, a separation calculation unit that calculates a positive-phase voltage and a negative-phase voltage from the three-phase AC voltage of the power system; a first calculation unit that calculates a positive sequence phase from the positive sequence voltage; a second calculation unit that calculates a negative-sequence phase and a negative-sequence voltage amplitude from the negative-sequence voltage; a negative-phase-sequence current amplitude command unit that calculates a negative-phase-sequence current amplitude command value based on the negative-phase-sequence voltage amplitude; a negative-phase-sequence current command unit that calculates a negative-phase-sequence current command value based on the negative-phase-sequence current amplitude command value and the negative-phase-sequence phase; a signal generating unit that generates the control signal based on an addition result of a positive-sequence current command value based on the positive phase and the negative-sequence current command value; Equipped with Power conversion device.

2. 1. A power conversion device that converts DC power supplied from a DC power source into three-phase AC power based on a control signal and supplies the converted three-phase AC power to a three-phase AC power system, a separation calculation unit that calculates a positive-phase voltage and a negative-phase voltage from the three-phase AC voltage of the power system; a third calculation unit that calculates a cosine and a sine of a positive phase from the positive phase voltage; a fourth calculation unit that calculates a cosine and a sine of the negative phase and a negative phase voltage amplitude from the negative phase voltage; a negative-phase-sequence current amplitude command unit that calculates a negative-phase-sequence current amplitude command value based on the negative-phase-sequence voltage amplitude; a negative-phase-sequence current command unit that calculates a negative-phase-sequence current command value based on the negative-phase-sequence current amplitude command value and the cosine and sine of the negative-phase-sequence; a signal generating unit that generates the control signal based on an addition result of a positive-sequence current command value based on the positive phase and the negative-sequence current command value; Equipped with Power conversion device.

3. The negative-phase-sequence current amplitude command unit When the negative-phase-sequence voltage amplitude is within a predetermined dead band, the negative-phase-sequence current amplitude command value is maintained at a predetermined amplitude value. The power conversion device according to claim 1 or 2.

4. A lower limit and an upper limit are determined for the negative-phase-sequence current amplitude command value. The power conversion device according to claim 1 or 2.

5. The negative-phase-sequence current amplitude command unit When the negative-phase-sequence voltage amplitude is within a predetermined dead band, the negative-phase-sequence current amplitude command value is maintained at a predetermined amplitude value. The power conversion device according to claim 4.

6. The second calculation unit a PLL (Phase Locked Loop) circuit that detects the negative phase from the negative phase voltage; The power conversion device according to claim 1 .

7. The second calculation unit a polar coordinate conversion unit that calculates a difference between the positive phase and the negative phase from the negative phase voltage; a phase calculation unit that calculates the negative phase based on the difference and the positive phase calculated by the first calculation unit; Including, The power conversion device according to claim 1 .

Images