Power conversion device

Abstract

An instantaneous voltage command value calculation unit (140) uses a reference operation phase (θop) and a voltage amplitude command value (Ve) to generate instantaneous voltage command values (Vu*, Vv*, Vw*) of an output voltage to an AC power system in which current suppression control is reflected, wherein said reference operation phase (θop) and said voltage amplitude command value (Ve) are calculated by control calculation based on AC detection values (Vsys, Isys) classified as an active component and a reactive component by a coordinate conversion performed by a coordinate conversion unit (105). A PWM calculation unit (150) generates on / off command signals (Sgu, Sgv, Sgw) for switching elements constituting the power conversion device, in accordance with the instantaneous voltage command values (Vu*, Vv*, Vw*). A rotation phase (θdt) used for the coordinate conversion in the coordinate conversion unit (105) is set so that the phase of the instantaneous voltage command values (Vu*, Vv*, Vw*) matches the rotation phase (θdt).

Description

Power Conversion Device

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

[0002] The introduction of power conversion devices that convert renewable energy and energy stored in power storage devices into electric power and exchange it with AC power grids is progressing. However, as the number of such power conversion devices connected to an AC power grid increases, there is a concern that the inertia of the AC power grid against frequency fluctuations will decrease. For this reason, in recent years, attention has been focused on control functions that allow the power conversion devices to behave as voltage sources.

[0003] This control function is also called a virtual generator function because it controls the power conversion device itself to behave like a virtual generator when functioning as a voltage source by determining the output voltage and operating phase. The introduction of the virtual generator function is expected to provide inertia for AC power systems and to form independent systems.

[0004] On the other hand, because power conversion devices realize power interchange through the switching operation of semiconductor elements, there are strict tolerances for input and output currents. For this reason, power conversion devices that operate as voltage sources with virtual generator functionality are also required to be equipped with current suppression control to keep the current within the tolerance range.

[0005] For example, Japanese Patent Application Laid-Open No. 2019-080476 (Patent Document 1) describes that in the calculation of a voltage command value for an AC / DC converter according to an output command value for controlling a virtual synchronous generator, which is an example of a virtual generator function, when a short-circuit accident occurs in an AC power system, control is performed by an output current suppression unit that changes the internal impedance of the virtual synchronous machine so that the output current of the AC / DC converter does not exceed a current limit value.

[0006] Japanese Patent Application Laid-Open No. 2019-080476

[0007] In a power conversion device having a virtual synchronous generator function, a control calculation is generally performed in which detected values ​​of AC output (e.g., current and voltage) to an AC power system are classified into active components (d-axis) and reactive components (q-axis) through coordinate transformation (typically, dq transformation) using a rotation phase. By determining an AC voltage command value (instantaneous value) in accordance with the amplitude and frequency determined with the virtual synchronous generator function, the above-mentioned power conversion device operating as a voltage source having a virtual generator function is realized.

[0008] In Patent Document 1, the virtual generator function and current suppression control are realized by correcting the AC voltage command value (instantaneous value) generated according to the frequency set by the virtual generator function (rotor angular velocity calculation unit) using a control amount from an output current suppression unit.

[0009] However, in the control of Patent Document 1, the rotation phase used in the coordinate transformation (dq inverse transformation) when generating the AC voltage command value (instantaneous value) differs from the phase (rotation phase) of the final AC voltage command value (instantaneous value) after correction by the current suppression control, i.e., the operating phase of the power conversion device.

[0010] As a result, there is a concern that the rotation phase used in the coordinate transformation may deviate from the actual operating phase of the power conversion device, causing errors in the values ​​of the active and reactive components of the AC output (current, voltage, and power) used in the control calculation. If this error becomes large, there is a concern that the control accuracy of the power conversion device operating as a voltage source may decrease, making it impossible to achieve synchronization between the AC power grid and the power conversion device.

[0011] The present disclosure has been made to solve such problems, and an object of the present disclosure is to maintain the control accuracy of a power conversion device operating as a voltage source and to stably ensure synchronization between an AC power system and the power conversion device.

[0012] According to one aspect of the present disclosure, there is provided a power conversion device. The power conversion device includes a main circuit unit connected between a DC power source and an AC power system, and a control circuit. The main circuit unit includes a switching element and performs power conversion between a DC voltage and an AC voltage. The control circuit controls the on / off of the switching element to control the power conversion by the main circuit unit. The control circuit includes a coordinate conversion unit, a voltage control unit, an instantaneous voltage command generation unit, and a switching control unit. The coordinate conversion unit performs coordinate conversion to classify detected values ​​of AC output from the main circuit unit to the AC power system into active and reactive components. The voltage control unit generates, by control calculation based on the active and reactive components obtained by the coordinate conversion, (1) an operating reference phase obtained based on the integral of an operating frequency that is increased or decreased according to the active component of the output power of the main circuit unit, and (2) a voltage amplitude command value that is adjusted to change the amplitude of the output AC voltage of the main circuit unit when the output current of the main circuit unit deviates from a predetermined control range. The instantaneous voltage command generator generates an instantaneous voltage command value for the output AC voltage using the voltage amplitude command value and the operation reference phase from the voltage controller. The switching controller generates on / off command signals for the switching elements in accordance with the instantaneous voltage command value. Furthermore, the control circuit sets the rotation phase so that the rotation phase used in the coordinate transformation matches the phase of the instantaneous voltage command value.

[0013] According to the present disclosure, by matching the phase of the instantaneous voltage command value calculated by a control calculation based on AC detection values ​​classified into active components and reactive components by coordinate transformation with the rotational phase of the coordinate transformation, it is possible to suppress the amount of deviation between the operating phase (phase of the output voltage) of a power conversion device operating as a voltage source and the rotational phase of the coordinate transformation, thereby maintaining the control accuracy of the power conversion device and ensuring stable synchronization between the AC power system and the power conversion device.

[0014] 1 is a block diagram illustrating a schematic configuration of a power conversion apparatus according to the present embodiment. FIG. 12 is a circuit diagram illustrating an example of the configuration of the main circuit shown in FIG. 1. FIG. 13 is a block diagram illustrating an example of the hardware configuration of the control circuit shown in FIG. 1. FIG. 14 is a block diagram illustrating a control circuit of the power conversion apparatus according to embodiment 1. FIG. 15 is a block diagram illustrating an example of the configuration of the active current suppression control unit shown in FIG. 4. FIG. 16 is a block diagram illustrating an example of the configuration of the reactive current suppression control unit shown in FIG. 4. FIG. 17 is a flowchart illustrating processing of active current suppression control in the power conversion apparatus according to embodiment 1. FIG. 18 is a flowchart illustrating processing of reactive current suppression control in the power conversion apparatus according to embodiment 1. FIG. 19 is a first waveform diagram illustrating results of an operation simulation of the power conversion apparatus according to embodiment 1. FIG. 20 is a second waveform diagram illustrating results of an operation simulation of the power conversion apparatus according to embodiment 1. FIG. 21 is a block diagram of a control circuit of a power conversion apparatus according to embodiment 2. FIG. 22 is a block diagram of a control circuit of a power conversion apparatus according to embodiment 3. FIG. 23 is a block diagram illustrating an example of the configuration of the current suppression control unit in FIG. 12. FIG. 24 is a conceptual diagram for illustrating functions of a voltage amplitude command calculation unit and a phase shift amount calculation unit in FIG. 12. FIG. 25 is a flowchart illustrating processing of current suppression control in the power conversion apparatus according to embodiment 3.

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following, identical or corresponding parts in the drawings will be denoted by the same reference numerals, and their description will not be repeated in principle.

[0016] First Embodiment Fig. 1 is a block diagram illustrating a schematic configuration of a power conversion device 10 according to this embodiment.

[0017] 1, power conversion device 10 includes a main circuit unit 20, a current detector 40, a voltage detector 50, and a control circuit 100. Main circuit unit 20 is connected between a power storage element 30, which is an example of a "DC power source," and a transmission line 7 of an AC power system 5, and performs power conversion between DC voltage and AC voltage. In the following, in this embodiment, an example will be described in which AC power system 5 is configured with three-phase AC, but it can also be configured with single-phase AC.

[0018] Fig. 2 shows a circuit diagram illustrating an example of the configuration of main circuit unit 20. Referring to Fig. 2, power storage element 30 includes capacitors 31 and 32 connected in series. Note that, in addition to a capacitor, any DC power storage element such as a secondary battery can be used as power storage element 30.

[0019] The main circuit unit 20 has three-level inverters 21u, 21v, and 21w as a three-level converter. Each of the three-level inverters 21u, 21v, and 21w has a known configuration including four switching elements configured with an IGBT (Insulated Gate Bipolar Transistor) or a SiC (Silicon Carbide)-MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), and converts the DC voltage of a capacitor connected in parallel with the power storage element 30 into a sinusoidal AC voltage by PWM (Pulse Width Modulation) control of the four switching elements.

[0020] The on / off command signals Sgu, Sgv, and Sgw shown in FIG. 2 input to the three-level inverters 21u, 21v, and 21w, respectively, collectively represent the on / off command signals (four signals) of the four switching elements in each three-level inverter, which are generated by the PWM control described above.

[0021] The three-level inverters 21u, 21v, and 21w output sinusoidal AC voltages, each having a phase difference of 120 degrees, to the three-phase transmission line 7 (FIG. 1) on the AC side, so that the main circuit unit 20 operates as a three-phase three-level converter.

[0022] The main circuit unit 20 can be configured with a self-excited converter such as a two-level converter or a modular multilevel converter, as long as it has a DC / AC power conversion function. On the DC side, instead of the power storage element 30, a power generation element using renewable energy such as a solar cell, or a DC system using a DC transmission line may be connected as a "DC power source."

[0023] Although not shown in FIG. 2, the main circuit section 20 may further include a filter circuit that removes high frequency components.

[0024] 1 again, current detector 40 detects three-phase AC currents in transmission line 7 of AC power system 5. Specifically, current detector 40 detects U-phase AC current Iu, V-phase AC current Iv, and W-phase AC current Iw of AC power system 5 (more specifically, an interconnection point on transmission line 7). AC currents Iu, Iv, and Iw are input to control circuit 100. Hereinafter, AC currents Iu, Iv, and Iw will also be collectively referred to as AC current Isys.

[0025] The voltage detector 50 detects three-phase AC voltages of the AC power system 5 (more specifically, an interconnection point on the transmission line 7). For example, the voltage detector 50 detects an AC voltage Vu of a U phase, an AC voltage Vv of a V phase, and an AC voltage Vw of a W phase of the AC power system 5. The AC voltages Vu, Vv, and Vw are input to the control circuit 100. Hereinafter, the AC voltages Vu, Vv, and Vw are also collectively referred to as an AC voltage Vsys. In this way, the current detector 40 and the voltage detector 50 can obtain the "detected values ​​of AC output (current, voltage, and power obtained by multiplying both)" from the power conversion device 10 (main circuit unit 20) to the AC power system 5.

[0026] The control circuit 100 controls the power conversion operation of the main circuit unit 20 by generating on / off command signals for the main circuit unit 20, for example, on / off command signals Sgu, Sgv, and Sgw for the three-level inverters 21u, 21v, and 21w shown in Figure 2.

[0027] The control circuit 100 can be configured to have a communication function for transmitting and receiving signals to and from the outside of the power conversion device 10. For example, the communication function makes it possible to receive various command values ​​from the outside and output performance data based on detected values ​​to the outside.

[0028] Fig. 3 is a block diagram showing an example of the hardware configuration of the control circuit 100. Fig. 3 shows an example in which the control circuit 100 is configured by a computer.

[0029] 3, the control circuit 100 includes one or more input converters 70, one or more sample-and-hold (S / H) circuits 71, a multiplexer (MUX) 72, an A / D converter 73, one or more central processing units (CPUs) 74, a random access memory (RAM) 75, a read-only memory (ROM) 76, one or more input / output interfaces (I / Fs) 77, and an auxiliary storage device 78. The control circuit 100 also includes a bus 79 that interconnects the components.

[0030] The input converter 70 has an auxiliary transformer for each input channel, which converts, for example, the signals detected by the current detector 40 and the voltage detector 50 in FIG. 1 into signals of a voltage level suitable for subsequent signal processing.

[0031] A sample-and-hold circuit 71 is provided for each input converter 70. The sample-and-hold circuit 71 samples and holds a signal representing an electrical quantity received from the corresponding input converter 70 at a specified sampling frequency.

[0032] The multiplexer 72 sequentially selects the signals held in the plurality of sample-and-hold circuits 71. The A / D converter 73 converts the signal selected by the multiplexer 72 into a digital value. Note that by providing a plurality of A / D converters 73, A / D conversion may be performed in parallel on detection signals of a plurality of input channels.

[0033] The CPU 74 controls the entire control circuit 100 and executes arithmetic processing in accordance with a program. A RAM 75 as a volatile memory and a ROM 76 as a nonvolatile memory are used as the main memory of the CPU 74. The ROM 76 stores programs, setting values ​​for signal processing, etc. The auxiliary storage device 78 is a nonvolatile memory with a larger capacity than the ROM 76, and stores programs, data on detected values ​​of electricity, etc.

[0034] The input / output interface 77 is an interface circuit for communication between the CPU 74 and an external device. As described above, the input / output interface 77 can be configured to have a communication interface function for data communication with the outside of the power conversion device 10.

[0035] Unlike the example of FIG. 2, at least a part of the control circuit 100 can be configured using circuits such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit).

[0036] 4 is a block diagram of a control circuit 100 in the power conversion device according to embodiment 1. The control circuit 100 includes a coordinate conversion unit 105, an operation reference phase determination unit 110 a, a current suppression control unit 120 a, a voltage amplitude command calculation unit 130, an instantaneous voltage command value calculation unit 140, and a PWM calculation unit 150.

[0037] The functions of the blocks in the block diagrams of the control circuit 100, including those in FIG. 4, are realized by hardware processing and / or software processing by the control circuit 100.

[0038] The coordinate transformation unit 105 classifies the AC current Isys (Iu, Iv, Iw) detected by the current detector 40 and the AC voltage Vsys (Vu, Vv, Vw) detected by the voltage detector 50 into an active component (d-axis) and a reactive component (q-axis component) by coordinate transformation (typically, dq transformation from the UVW phases to the dq axes) using the detection phase θdt described below.

[0039] Through this coordinate conversion, the coordinate conversion unit 105 can calculate an active component Id (hereinafter also referred to as active current Id) and a reactive component Iq (hereinafter also referred to as reactive current Iq) of the output current from the main circuit unit 20, i.e., the power conversion device 10, to the AC power grid 5, an active component Vd (hereinafter also referred to as active voltage Vd) and a reactive component Vq (hereinafter also referred to as reactive voltage Vq) of the output voltage, and an active component Pd (hereinafter also referred to as active power Pd) and a reactive component Pq (hereinafter also referred to as reactive power Pq) of the output power.

[0040] In this embodiment, the active current Id is expressed as a positive value (Id>0) in the current direction (discharge direction) from the power conversion device 10 to the AC power grid 5, and as a negative value (Id<0) in the opposite current direction (charge direction). Furthermore, the reactive current Iq is expressed in pu units as a negative value (Iq<0) during capacitive operation of the power conversion device 10 and as a positive value (Iq>0) during inductive operation.

[0041] That is, the AC current Isys and the AC voltage Vsys correspond to an example of an "AC detected value," and the detected phase θdt corresponds to an example of a "rotation phase" used for coordinate conversion in the coordinate conversion unit 105.

[0042] The operating reference phase determiner 110a includes an operating frequency controller 111, an adder 112, and an integrator 113. The operating frequency controller 111 calculates a frequency control amount f1 based on the deviation between an active power command value Pd* given in advance to the power conversion device 10 and the active power Pd calculated by the coordinate converter 105.

[0043] In general, when the active power Pd is larger than the active power command value Pd*, f1 is calculated to be less than 0 in order to decrease the system frequency, whereas when the active power Pd is smaller than the active power command value Pd*, f1 is calculated to be greater than 0 in order to increase the system frequency.

[0044] For example, the operating frequency control unit 111 can calculate the frequency control amount f1 for feedback control of the active power Pd in ​​accordance with the active power command value Pd* by applying various known control methods such as VSG (Virtual Synchronous Generator) control or VSM (Virtual Synchronous Machine) control to realize a virtual generator function.

[0045] The current suppression control unit 120a includes an active current suppression control unit 121a and a reactive current suppression control unit 122. The active current suppression control unit 121a generates a frequency control amount f2 for reducing the absolute value of the active current Id when the active current Id calculated by the coordinate conversion unit 105 falls outside a predetermined control range.

[0046] The reactive current suppression control unit 122 generates a voltage amplitude control amount V1 for reducing the absolute value of the reactive current Iq when the reactive current Iq calculated by the coordinate conversion unit 105 deviates from a predetermined control range. The control range of the active current Id and the control range of the reactive current Iq can be set individually, with at least one of them having a different upper limit value and lower limit value.

[0047] 5 and 6 are block diagrams illustrating examples of the configuration of the active current suppression control unit 121a and the reactive current suppression control unit 122. In FIG.

[0048] 5, the active current suppression control unit 121a includes a polarity determination unit 201a, multipliers 202a and 204a, a deviation calculator 203a, and a PI controller 206a. The polarity determination unit 201a outputs "1" or "-1" depending on the polarity of the active current Id calculated by the coordinate conversion unit 105. For example, the polarity determination unit 201a is configured to output "1" when Id≧0, and to output "-1" when Id<0.

[0049] The multiplier 202a calculates an active current command value Id* by multiplying the output value of the polarity determination unit 201a by a predetermined target value Idmax (e.g., Idmax=1.0 [p.u]) of the active current (absolute value) in the active current suppression control. The deviation calculator 203a calculates a current deviation ΔId by subtracting the active current Id from the coordinate conversion unit 105 from the active current command value Id* from the multiplier 202a.

[0050] The multiplier 204a multiplies a control flag Fdcn, which is set to 1 when active current suppression control is being executed and to 0 when the motor is stopped, by the current deviation ΔId from the deviation calculator 203a. For example, the control flag Fdcn is changed from 0 to 1 as the active current Id calculated by the coordinate converter 105 changes from within a predetermined control range to outside the control range.

[0051] The PI controller 206a calculates the frequency control amount f2 by a predetermined proportional-integral (PI) control calculation using the current deviation ΔId multiplied by the control flag Fdcn as an input. Therefore, when Fdcn=0, ΔId=0 is input to the PI controller 206a, so basically, when the active current suppression control is stopped, f2=0 is set.

[0052] On the other hand, when active current suppression control is executed (Fdcn=1), the frequency control amount f2 is calculated to be f2<0 in the direction of decreasing the operating frequency fop for ΔId<0.

[0053] 6, the reactive current suppression control unit 122 includes a polarity determination unit 201b, multipliers 202b and 204b, a deviation calculator 203b, and a PI controller 206b. The polarity determination unit 201b outputs "1" or "-1" depending on the polarity of the reactive current Iq calculated by the coordinate conversion unit 105. For example, the polarity determination unit 201b is configured to output "1" when Iq≧0, and to output "-1" when Iq<0.

[0054] The multiplier 202b calculates a reactive current command value Iq* by multiplying a predetermined target value Iqmax (for example, Iqmax=1.0 [p.u]) of the reactive current (absolute value) in the reactive current suppression control by the output value of the polarity determination unit 201b. The deviation calculator 203b calculates a current deviation ΔIq by subtracting the reactive current Iq from the coordinate conversion unit 105 from the reactive current command value Iq* from the multiplier 202a.

[0055] The multiplier 204b multiplies a control flag Fqcn, which is set to 1 when reactive current suppression control is being executed and set to 0 when the inverter is stopped, by the current deviation ΔIq from the deviation calculator 203b. For example, the control flag Fqcn is changed from 0 to 1 as the reactive current Iq calculated by the coordinate converter 105 changes from within a predetermined control range to outside the control range.

[0056] The PI controller 206b calculates the voltage amplitude control amount V1 by a predetermined proportional-integral (PI) control calculation using the current deviation ΔIq multiplied by the control flag Fqcn as an input. Therefore, when Fqcn=0, ΔIq=0 is input to the PI controller 206b, so basically, V1=0 is set when the reactive current suppression control is stopped.

[0057] In contrast, when reactive current suppression control is executed (Fqcn=1), the voltage amplitude control amount V1 is calculated to be V1<0 so as to reduce the output voltage amplitude (AC) of the power conversion device 10 for ΔIq<0.

[0058] 4 again, in the operation reference phase determiner 110a, the adder 112 adds the frequency control amount f1 from the operating frequency controller 111 and the frequency control amount f2 from the active current suppression controller 121a to the reference frequency fr to calculate the operating frequency fop of the power conversion device 10. In the first embodiment, the frequency control amount f1 corresponds to the "first frequency control amount," and the frequency control amount f2 corresponds to the "second frequency control amount."

[0059] The reference frequency fr can be, for example, the nominal value of the grid frequency (50 [Hz] or 60 [Hz]) or the detected value of the grid frequency (current actual value). In the former case, the operating frequency control unit 111 operates to feedback control the active power Pd so that the grid frequency matches the nominal value. In contrast, in the latter case, the operating frequency control unit 111 operates to feedback control the active power Pd so that the active power Pd matches the active power command value Pd* under the current grid frequency.

[0060] The integrator 113 calculates the operating reference phase θop of the power conversion device 10 by integrating the angular velocity according to the operating frequency fop from the adder 112. As a result, when the active current suppression control is stopped, f2 = 0 is basically established, and therefore the operating reference phase θop is set according to the operating frequency fop = fr + f1 reflecting the frequency control amount f1 for virtual generator control. On the other hand, when the active current suppression control is executed, it is understood that the operating reference phase θop is set to fop = fr + f1 + f2, further reflecting the frequency control amount f2 (f2 < 0) for lowering the operating frequency fop, in order to delay the operating phase of the power conversion device 10 and thereby reduce the discharge current (i.e., the active current) to the AC power grid 5.

[0061] The voltage amplitude command calculation unit 130 includes a voltage amplitude determination unit 131 and an adder 132. The voltage amplitude determination unit 131 outputs a base voltage amplitude Vamp to be output by the power conversion device 10. Strictly speaking, the voltage amplitude Vamp is expressed as a vector sum of an active component and a reactive component. However, in this embodiment, it is basically assumed that the base voltage amplitude Vamp is set as a value of the active component that does not include the reactive component. Note that the voltage amplitude Vamp may be a predetermined fixed value (a system nominal value) or may be determined according to the reactive power to be output. That is, in this embodiment, the method of determining the voltage amplitude Vamp by the voltage amplitude determination unit 131 is not particularly limited and may be arbitrary.

[0062] The adder 132 adds the voltage amplitude Vamp from the voltage amplitude determination unit 131 and the voltage amplitude control amount V1 from the reactive current suppression control unit 122 to calculate the voltage amplitude command value Ve of the power conversion device 10. Therefore, it can be understood that when the reactive current suppression control is stopped, V1=0 basically, so Ve=Vamp is set, whereas when the reactive current suppression control is executed, Ve=Vamp+V1 is set, reflecting the voltage amplitude control amount V1 (V1<0) for reducing the voltage amplitude.

[0063] The instantaneous voltage command value calculation unit 140 calculates instantaneous voltage command values ​​Vu*, Vv*, and Vw* for each phase (U, V, and W phases) of the main circuit unit 20 using the voltage amplitude command value Ve from the voltage amplitude command calculation unit 130 and the operating reference phase θop from the operating reference phase determination unit 110a. More specifically, the instantaneous voltage command values ​​Vu*, Vv*, and Vw* are calculated by performing coordinate transformation (a dq inverse transformation from the dq axes to three-phase AC) on the voltage amplitude command value Ve on the dq axes using the operating reference phase θop from the integrator 113. As described above, in the first embodiment, the operating reference phase determination unit 110a, the current suppression control unit 120a, and the voltage amplitude command calculation unit 130 collectively constitute one example of a "voltage control unit" that generates the voltage amplitude command value Ve and the operating reference phase θop.

[0064] In the first embodiment, since both the voltage amplitude Vamp and the voltage amplitude control amount V1 are composed only of active component voltages, the voltage amplitude command value Ve also contains only active components. As a result, the instantaneous voltage command values ​​Vu*, Vv*, and Vw* are sinusoidal voltages with phases shifted by 120 degrees, as shown in the following equations (1) to (3):

[0065] Vu*=Ve·sin(θop) (1) Vv*=Ve·sin(θop-2 / 3π) (2) Vw*=Ve·sin(θop+2 / 3π) (3) Furthermore, when a filter circuit is provided, the instantaneous voltage command value calculating unit 140 can generate the instantaneous voltage command values ​​Vu*, Vv*, Vw* by further reflecting the circuit constant values ​​of the passive elements of the filter circuit. Alternatively, the instantaneous voltage command values ​​Vu*, Vv*, Vw* can be calculated by incorporating feedback control such as voltage control or current control.

[0066] The PWM calculation unit 150 performs PWM calculation to compare each of the three-phase instantaneous voltage command values ​​Vu*, Vv*, and Vw* from the instantaneous voltage command value calculation unit 140 with a carrier signal, thereby generating on / off command signals Sgu, Sgv, and Sgw for the four switching elements of each of the three-level inverters 21u, 21v, and 21v shown in FIG. 2. As a result, the actual operating phase of the power conversion device 10 depends on the phases of the instantaneous voltage command values ​​Vu*, Vv*, and Vw*. In this embodiment illustrating a three-phase AC, the voltage phase of the U phase (i.e., the phase of the instantaneous voltage command value Vu*) corresponds to the actual operating phase of the power conversion device 10.

[0067] The PWM calculation unit 150 corresponds to an example of a “switching control unit.” In practice, in addition to the PWM calculation, the on / off command signals Sgu, Sgv, and Sgw are generally generated so as to provide a so-called dead time.

[0068] In this way, the power conversion device 10 operates as a voltage source by outputting AC voltages (three-phase voltages) according to the instantaneous voltage command values ​​Vu*, Vv*, and Vw*, and by turning on current suppression control (active current suppression control and / or reactive current suppression control) when the current increases, the power conversion device 10 can operate so that the output current of the power conversion device 10 does not exceed a predetermined current limit value. Furthermore, by generating the instantaneous voltage command values ​​Vu*, Vv*, and Vw* reflecting the frequency control amount f1 by the operating frequency control unit 111, the power conversion device 10 can operate as a voltage source having a virtual generator function (frequency control).

[0069] In this case, in the power conversion device of embodiment 1, by making the operating reference phase θop and the detection phase θdt common (θop = θdt), it is possible to suppress the deviation between the rotational phase (detection phase θdt) used for coordinate transformation to classify active and reactive components in the coordinate transformation unit 105 and the actual operating phase of the power conversion device 10.

[0070] As a result, even if the power conversion device 10 operates according to the instantaneous voltage command values ​​Vu*, Vv*, Vw* that are combined with control variables for current suppression control based on the virtual generator function (frequency control), synchronization between the power conversion device 10 and the AC power system 5 can be stably ensured.

[0071] Next, the processing of the active current suppression control and the reactive current suppression control in the control configuration of Fig. 4 will be described using the flowcharts of Fig. 7 and Fig. 8. The control processing in each step (hereinafter also simply referred to as "S") of the flowcharts shown in Fig. 7 and Fig. 8 can be executed by the control circuit 100 using software processing, hardware processing, or a combination of both.

[0072] FIG. 7 is a flowchart illustrating the process of active current suppression control in the power conversion device according to the first embodiment.

[0073] 7, the control circuit 100 periodically acquires the detected value of the AC current Isys by the current detector 40 in S110, and then classifies the AC current Isys into an active component and a reactive component using the detected phase θdt at that time point in S120 to acquire the active current Id and the reactive current Iq. Then, in S130, it is determined whether the active current Id acquired in S120 is outside a predetermined control range.

[0074] When the active current Id is outside the control range (YES determination in S130), the control circuit 100 proceeds to S140 to execute active current suppression control. On the other hand, when the active current Id is within the control range (NO determination in S130), the process returns to S110. When the determination in S130 is NO, the processes in S110 to S130 are executed at regular intervals. When the determination in S130 is NO, the control circuit 100 maintains the control flag Fdcn in FIG. 5 at 0, whereas when the determination in S130 is YES, the control circuit 100 sets the control flag Fdcn to 1.

[0075] In S140, the control circuit 100 calculates an AC parameter for suppressing the active current by the active current suppression control unit 121a. In the first embodiment, as shown in Figures 4 and 5, the frequency control amount f2 (basically, f2<0) is calculated as the "AC parameter." As described above, the frequency control amount f2 corresponding to the "AC parameter" is reflected in the operating reference phase θop via the operating frequency fop, and acts to change the phases of the instantaneous voltage command values ​​Vu*, Vv*, and Vw* in a direction that reduces the active current Id.

[0076] Even during execution of the active current suppression control, the control circuit 100 acquires the detection value of the AC current Isys by the current detector 40 at regular intervals in S150, and acquires the active current Id and the reactive current Iq from the AC current Isys using the detection phase θdt at that time in S160.

[0077] In S170, the control circuit 100 determines whether a stop command for the active current suppression control has been generated. For example, the stop command for the active current suppression control is generated when it is difficult to continue the operation of the power conversion device 10, when a predetermined time has elapsed, when a command is issued by a higher-level management device or a user, when the operation of the active current suppression control is mismatched, etc.

[0078] Specifically, when the voltage of the capacitors 31, 32 (FIG. 2) deviates from a predetermined range, or when the charge amount of the power storage element 30 (FIGS. 1 and 2) deviates from a predetermined range (risk of overcharging or overdischarging), it is determined that it is difficult to continue operating the power conversion device 10, and a stop command can be generated. Also, when the time limit for the user to request output from the power conversion device 10 of the present invention is exceeded (for example, after about 10 seconds have elapsed), a stop command can be generated.

[0079] Alternatively, a stop command can be generated by a higher-level management device or a user as needed for maintenance, etc. Furthermore, when the active current suppression control is stopped but the active current Id does not deviate from the upper or lower limit, and the active current suppression control is operating unnecessarily, for example, when the frequency control variable f2 set by the active current suppression control unit 121a is a positive value (f2>0) but the frequency control variable f2 is set to follow the active current command value Id*, the above-mentioned mismatch can be detected and a stop command can be generated. In this way, the active current suppression control is started when the active current Id deviates from a predetermined control range, and when a predetermined stop condition is met during the execution of the active current suppression control, the active current suppression control is terminated by making a YES determination in S170.

[0080] When a stop command has not been generated (NO in S170), the control circuit 100 returns the process to S140. As a result, until a stop command is generated, the AC parameters calculated in S140 are reflected in the instantaneous voltage command values ​​Vu*, Vv*, and Vw*, thereby executing active current suppression control at a constant cycle.

[0081] On the other hand, when a stop command is generated (YES in S170), the control circuit 100 stops the active current suppression control in S180. In S180, the control flag Fdcn is reset to 0, and in FIGS. 4 and 5, the frequency control amount f2 corresponding to the AC parameter is reset to 0.

[0082] Thereafter, the control circuit 100 restarts the processing from S110 onwards, thereby operating the power conversion device 10 so as to perform active current suppression control every time the active current Id deviates from the control range.

[0083] FIG. 8 is a flowchart illustrating the reactive current suppression control process in the power conversion device according to the first embodiment.

[0084] 8, the control circuit 100 acquires the detection value of the AC current Isys by the current detector 40 at a constant period in S210, which is the same as S110 (FIG. 7), and then classifies the AC current Isys into an active component and a reactive component using the detected phase θdt at that time in S220, which is the same as S120 (FIG. 7), to acquire the active current Id and the reactive current Iq. Then, in S230, the control circuit 100 determines whether the reactive current Iq acquired in S220 is outside a predetermined control range.

[0085] When the reactive current Iq is outside the control range (YES determination in S230), the control circuit 100 proceeds to S240 to execute reactive current suppression control. On the other hand, when the reactive current Iq is within the control range (NO determination in S230), the process returns to S210. When the determination in S230 is NO, the processes of S210 to S230 are executed at regular intervals. When the determination in S230 is NO, the control circuit 100 maintains the control flag Fqcn in FIG. 6 at 0, while when the determination in S230 is YES, the control flag Fqcn is set to 1.

[0086] In S240, the control circuit 100 calculates a voltage amplitude control amount V1 (basically V1<0) for suppressing the reactive current by the reactive current suppression control unit 122. During execution of the reactive current suppression control, the control circuit 100 acquires the detection value of the AC current Isys by the current detector 40 at regular intervals in S250, which is the same as S150 (FIG. 7), and acquires the active current Id and the reactive current Iq from the AC current Isys using the detected phase θdt at that time in S260, which is the same as S160 (FIG. 7).

[0087] In S270, the control circuit 100 determines whether a command to stop the reactive current suppression control has been generated. For example, the command to stop the reactive current suppression control is generated when a recovery of the system voltage (voltage recovery) is detected after a fault in the AC power system 5, when a command is issued by a higher-level management device or a user, when there is a mismatch in the operation of the reactive current suppression control, etc.

[0088] Specifically, after an accident occurs in the AC power grid 5, a stop command can be generated when voltage recovery is detected based on a comparison between the voltage detected by the voltage detector 50 or its derivative and a predetermined judgment value. Furthermore, when continued operation of the power conversion device 10 is undesirable due to maintenance or other reasons, a stop command can be generated by a higher-level management device or a user. Alternatively, when the reactive current suppression control is stopped but the reactive current Iq does not deviate from its upper or lower limit, a control output with a polarity that causes the reactive current Iq to follow the reactive current command value Iq* is set, the above-mentioned mismatch can be detected and a stop command can be generated. In this way, the reactive current suppression control is initiated when the reactive current Iq deviates from a predetermined control range, and is terminated by determining YES in S270 when a predetermined stop condition is met during the execution of the reactive current suppression control.

[0089] When a stop command has not been generated (NO in S270), the control circuit 100 returns the process to S240. As a result, until a stop command is generated, the reactive current suppression control is executed at regular intervals by reflecting the voltage amplitude control amount V1 calculated in S240 in the instantaneous voltage command values ​​Vu*, Vv*, and Vw*.

[0090] On the other hand, when a stop command is generated (YES in S270), the control circuit 100 stops the reactive current suppression control in S280. In S280, the control flag Fqcn is reset to 0, and in FIGS. 4 and 6, the voltage amplitude control amount V1 is reset to 0.

[0091] Thereafter, the control circuit 100 can operate the power conversion device 10 so as to execute reactive current suppression control every time the reactive current Iq deviates from the control range by restarting the processing from S210 onwards.

[0092] Next, the results of an operation simulation of the power conversion device 10 according to the first embodiment using a simulator will be described. In the simulation, the AC power system 5 in Fig. 1 was modeled using a three-phase ideal voltage, and the transmission line 7 of each phase was simply modeled using a resistance component and a reactor component. The reactor component of the transmission line 7 represents an AC reactor, leakage impedance of a transformer (not shown), impedance of an electric wire, etc., and the circuit constant values ​​for the simulation were determined so as to be set to a value sufficiently larger than the resistance component.

[0093] Fig. 9 is a first waveform diagram showing the results of an operation simulation of the power conversion device 10. Fig. 9 shows the results of a simulation of the power conversion device 10 when active current suppression control is activated when the system frequency fgr (bottom row), which corresponds to the frequency of an ideal voltage source simulating the AC power system 5, decreases at a constant rate from 60 [Hz] to 58 [Hz] due to a load fluctuation, a generator tripping, or the like.

[0094] In FIG. 9, the active current Id is expressed in pu units, and the threshold value for determining whether or not active current suppression control is required is ±1.1 [pu].

[0095] 9 , in the initial state, the active current Id is 0.5 [pu], i.e., the power conversion device 10 (main circuit unit 20) is discharging toward the AC power grid 5, and therefore the operating phase of the power conversion device 10 leads the phase of the AC power grid 5. If the system frequency drops from this state due to, for example, the tripping of a generator on the AC power grid 5 side, the phase of the AC power grid 5 further lags, and the phase difference between the operating phase of the power conversion device 10 and the phase of the AC power grid 5 further increases.

[0096] As a result, the operating phase of the power conversion device 10 leads the phase of the AC power grid 5, and the active current Id increases in the discharge direction (positive direction). As a result, when the active current Id exceeds the threshold value (1.1 [pu]), the control flag Fdcn is changed from 0 to 1, and active current suppression control is executed.

[0097] In response to an increase in the active power Pd, the frequency control variable f1 is set to a negative value by the operating frequency control unit 111. In addition, in response to the control flag Fdcn being set to 1, the active current suppression control unit 121a calculates the frequency control variable f2 (f2<0) so as to control the active current Id to the active current command value Id* (here, Id*=1.0 [pu]).

[0098] As a result, the output frequency fcv of the power conversion device 10 gradually decreases in accordance with the operating frequency fop (FIG. 4) that reflects the frequency control variables f1 and f2. At this time, by applying the control configuration shown in FIG. 4, the output frequency fcv of the power conversion device 10 changes without increasing the difference with the system frequency fgr (AC power system 5), and it can be confirmed from the simulation results that synchronization between the AC power system 5 and the power conversion device 10 is ensured.

[0099] Fig. 10 is a second waveform diagram showing the results of an operation simulation of the power conversion device 10. When an accident such as a ground fault occurs on the AC power grid 5 side and the grid voltage drops, a capacitive reactive current Iq (Iq<0) is generated depending on the wiring impedance or the leakage impedance of the transformer in order to maintain a constant output voltage of the power conversion device 10. In the example of Fig. 10, such an initial state where Id<0 is assumed.

[0100] 10 shows a simulation result of the power conversion device 10 when the reactive current suppression control is activated when the voltage amplitude Vgr of the ideal voltage source simulating the AC power system 5 drops from 1.0 [pu] to 0.2 [pu] due to a system fault such as a ground fault from the above-mentioned initial state. The voltage amplitude at the bottom of FIG. 10 indicates the active component (Vd).

[0101] In FIG. 10, the reactive current Iq is shown in pu units, and the threshold value for determining whether or not reactive current suppression control is required is ±1.1 [pu].

[0102] Referring to FIG. 10 , in response to a sudden drop in the voltage amplitude Vgr of the AC power system 5 due to the occurrence of a system fault, the reactive current Iq becomes less than −1.1 [pu], and falls outside the range of −1.1 [pu]≦Iq≦1.1 [pu]. In response, the control flag Fqcn is changed from 0 to 1, and reactive current suppression control is executed.

[0103] When the control flag Fqcn is set to 1, the reactive current suppression control unit 122 calculates the voltage amplitude control amount V1 (V1<0) so as to control the reactive current Iq to the reactive current command value Iq* (here, Iq*=-1.0 [pu]).

[0104] As a result, the output voltage amplitude Vcv of the power conversion device 10 decreases in accordance with the voltage amplitude command value Ve (FIG. 4) that reflects the voltage amplitude control amount V1. At this time, it can be seen that by applying the control configuration shown in FIG. 4, the output voltage amplitude Vcv of the power conversion device 10 changes without increasing the difference with the voltage amplitude Vgr of the AC power grid 5.

[0105] From the simulation results of FIGS. 9 and 10 , it can be confirmed that, according to the power conversion device of embodiment 1, when operating as a voltage source having a virtual generator function (frequency control), and when current suppression control (active current suppression control and / or reactive current suppression control) is performed during current increase, the control accuracy of the power conversion device is maintained and synchronization between the AC power system and the power conversion device is stably ensured.

[0106] Second Embodiment In a second embodiment, another example of the control configuration by the control circuit 100 will be described.

[0107] Fig. 11 is a block diagram of a control circuit of a power conversion device according to embodiment 2. As shown in Fig. 11, the power conversion device according to embodiment 2 differs from embodiment 1 in that the control circuit 100 includes an operating reference phase determiner 110b and a current suppression control unit 120b instead of the operating reference phase determiner 110a and the current suppression control unit 120a (Fig. 4).

[0108] The current suppression control unit 120b differs from the current suppression control unit 120a in that it includes an active current suppression control unit 121b instead of the active current suppression control unit 121a.

[0109] 5, the active current suppression control unit 121b differs from the active current suppression control unit 121a in that the PI controller 206a is configured to calculate the phase control amount θ2 instead of the frequency control amount f2. Specifically, it is possible to configure the active current suppression control unit 121b to calculate the phase control amount θ2 by adjusting the gain values ​​(proportional gain and integral gain) used in the control calculation in the PI controller 206a.

[0110] Like the active current suppression control unit 121a, the active current suppression control unit 121b sets θ2 = 0 when the active current suppression control is stopped (Fdcn = 0). In contrast, when the active current suppression control is executed (Fdcn = 1), the phase control amount θ2 is calculated to be θ2 < 0 in order to reduce the discharge current (i.e., the active current) to the AC power grid 5 by delaying the operating phase of the power conversion device 10 relative to ΔId < 0.

[0111] Meanwhile, in current suppression control unit 120b, the configuration and operation of reactive current suppression control unit 122 are the same between the first embodiment and the second embodiment, and therefore detailed description thereof will not be repeated. That is, in the second embodiment, voltage amplitude command value Ve input to instantaneous voltage command value calculation unit 140 is calculated in the same way as in the first embodiment.

[0112] The operating reference phase determiner 110b includes an operating frequency controller 111, adders 112 and 114, and an integrator 113, similar to those in FIG.

[0113] 4 and the frequency control amount f1 from the operating frequency control unit 111, and outputs the operating frequency fop. The integrator 113 integrates the angular velocity according to the operating frequency fop to calculate the phase θ1.

[0114] In the operating reference phase determiner 110b, the adder 114 calculates the operating reference phase θop of the power conversion device 10 by adding the phase control amount θ2 from the active current suppression controller 121b to the phase θ1 from the integrator 113. That is, it can be understood that also in the second embodiment, the operating reference phase θop is obtained based on the integration of the operating frequency fop.

[0115] Instantaneous voltage command value calculation unit 140 generates instantaneous voltage command values ​​Vu*, Vv*, and Vw* using voltage amplitude command value Ve from voltage amplitude command calculation unit 130 and operating reference phase θop from operating reference phase determiner 110b. In the second embodiment, the operations of instantaneous voltage command value calculation unit 140 and PWM calculation unit 150 are similar to those in the first embodiment, and therefore detailed description will not be repeated. In this way, in the second embodiment, the ensemble of operating reference phase determiner 110b, current suppression control unit 120b, and voltage amplitude command calculation unit 130 constitutes one example of a "voltage control unit" that generates voltage amplitude command value Ve and operating reference phase θop.

[0116] As can be understood from the above explanation, the only difference between embodiment 1 and embodiment 2 is whether the output from the active current suppression control units 121a, 121b in the control circuit 100 is a frequency control amount f2 that is reflected in the operating reference phase θop via the operating frequency θop, or a phase control amount θ2 that is directly reflected in the operating reference phase θop; the other parts of embodiment 2 are the same as those of embodiment 1.

[0117] Therefore, in the power conversion device according to the second embodiment, as in the first embodiment, the operating reference phase θop and the detection phase θdt used for coordinate conversion in the coordinate conversion unit 105 are made common (θop = θdt), thereby providing the same effects as the power conversion device according to the first embodiment and enabling stable synchronization between the power conversion device 10 and the AC power system 5 to be ensured.

[0118] The processing of active power suppression control in the power conversion device according to the second embodiment is realized by calculating the phase control amount θ2 (FIG. 11) as an "AC parameter" in S140 according to the flowchart of FIG. 8. That is, also in the second embodiment, the phase control amount θ2 corresponding to the "AC parameter" is directly reflected in the operating reference phase θop, and acts to change the phases of the instantaneous voltage command values ​​Vu*, Vv*, Vw* in a direction that reduces the active current Id.

[0119] Third Embodiment In a third embodiment, still another example of the control configuration by the control circuit 100 will be described.

[0120] 12 is a block diagram of a control circuit of a power conversion device according to embodiment 3. As shown in FIG. 12, in the power conversion device according to embodiment 3, a control circuit 100 includes an operation reference phase determiner 110c, a current suppression controller 120c, a coordinate converter 105, a voltage amplitude command calculator 130, an instantaneous voltage command value calculator 140, and a PWM calculator 150 similar to those in FIGS. 4 and 11 , and further includes a phase adjuster 160 that calculates a detected phase θdt. The phase adjuster 160 includes a phase shift calculator 162 and an adder 164.

[0121] The operating reference phase determiner 110c has an operating frequency control unit 111, an adder 112, and an integrator 113, similar to those in Fig. 11. Therefore, the operating frequency fop of the power conversion device 10 is output by adding the reference frequency fr and the frequency control amount f1 from the operating frequency control unit 111, similar to Fig. 11. The operating reference phase θop is calculated by integrating the operating frequency θop from the adder 112 using the integrator 113, and is therefore equivalent to the operating reference phase θop in Fig. 11 (embodiment 1).

[0122] The current suppression control section 120c, unlike the current suppression control sections 120a and 120c, generates the voltage amplitude control amount V1 by classifying it into an active component Vd1 and a reactive component Vq1.

[0123] 13 is a block diagram illustrating an example of the configuration of the current suppression control unit 120c. As shown in FIG. 13, the current suppression control unit 120c includes deviation calculators 210a and 210b, PI controllers 212a and 212b, decoupling controllers 214a and 214b, a subtractor 216a, an adder 216b, and multipliers 218a and 218b.

[0124] The deviation calculator 210a calculates a current deviation ΔId by subtracting the active current Id calculated by the coordinate converter 105 from the active current command value Id* similar to that in Fig. 5. Similarly, the deviation calculator 210b calculates a current deviation ΔIq by subtracting the reactive current Iq calculated by the coordinate converter 105 from the reactive current command value Iq* similar to that in Fig. 6.

[0125] The PI controller 212a receives the current deviation ΔId as an input and outputs a controlled variable Vd0 calculated by a predetermined proportional-integral (PI) control calculation. Similarly, the PI controller 212b receives the current deviation ΔIq as an input and outputs a controlled variable Vq0 calculated by a predetermined proportional-integral (PI) control calculation.

[0126] The decoupling controller 214a outputs a value obtained by multiplying the active current command value Id* by the decoupling term (jωL). Similarly, the decoupling controller 214b outputs a value obtained by multiplying the reactive current command value Iq* by the decoupling term (jωL).

[0127] The subtractor 216a subtracts the output value of the decoupling controller 214b from the output value (Vd0) of the PI controller 212a, while the adder 216b adds the output value (Vq0) of the PI controller 212a and the output value of the decoupling controller 214b.

[0128] The multiplier 218a multiplies the output value of the subtractor 216a by a control flag Fcn, which is set to 1 when current suppression control is being executed and to 0 when the current suppression control is stopped, to calculate a voltage amplitude control amount Vd1. Similarly, the multiplier 218b multiplies the output value of the adder 216b by the control flag Fcn to calculate a voltage amplitude control amount Vq1.

[0129] For example, the control flag Fcn is changed from 0 to 1 when at least one of the active current Id and the reactive current Iq calculated by the coordinate conversion unit 105 changes from within a predetermined control range to outside the control range.

[0130] In the current suppression control 120c, when Fcn=0 (current suppression control is stopped), Vd1=0 and Vq1=0 are set. On the other hand, when Fcn=1 (current suppression control is being executed), Vd1=Vd0-jωL·Iq* and Vq1=Vq0+jωL·Id* are set for current suppression.

[0131] The configuration of the current suppression control unit 120c is not limited to the example shown in Figure 13, and can be configured according to any control method that uses the active current Id and the reactive current Iq as inputs to calculate voltage amplitude control amounts Vd1 (active component) and Vq1 (reactive component) for suppressing the current. For example, as in Patent Document 1, a virtual impedance can be set and the voltage amplitude control amounts Vd1 and Vq1 can be calculated according to the following equations (4) and (5), which are linear combinations of the active current Id and the reactive current Iq with the resistance components (Rd, Rq) and the inductance components (Ld, Lq). In this way, the voltage amplitude control amounts Vd1 and Vq1 are calculated to be 0, a positive value, or a negative value.

[0132] Vd1=Id·Rd−Iq·jω(Lq) (4) Vq1=Iq·Rq+Id·jω(Ld) (5) Referring again to FIG. 12 , in voltage amplitude command calculation unit 130, adder 132 adds voltage amplitude Vamp determined by voltage amplitude determination unit 131 to voltage amplitude control amounts Vd1 and Vq1 by current suppression control unit 120c for both the active component (d-axis) and the reactive component (q-axis). Therefore, in the third embodiment, voltage amplitude command value Ve of power conversion device 10 is set so as to include both the active component and the reactive component. Furthermore, phase shift calculation unit 162 calculates phase shift θdf caused by voltage amplitude control amounts Vd1 and Vq1 by current suppression control unit 120c.

[0133] FIG. 14 is a conceptual diagram illustrating the functions of the voltage amplitude command calculation unit 130 and the phase shift amount calculation unit 162.

[0134] 14, voltage amplitude command calculation unit 130 calculates voltage amplitude command value Ve as the vector sum of an active component indicated by the sum of voltage amplitude Vamp from voltage amplitude determination unit 131 and voltage amplitude control amount Vd1, and a reactive component indicated by voltage amplitude control amount Vq1. That is, voltage amplitude Veamp indicated by voltage amplitude command value Ve is expressed by the following equation (6).

[0135] Veamp=√((Vamp+Vd1) ２ +Vq1 ２) (6) The phase shift calculation unit 162 can calculate the phase shift θdf by the following equation (7) in accordance with the ratio between the active component and the reactive component of the voltage amplitude command value Ve. The phase shift calculation unit 162 may calculate the phase shift θdf by further taking into account the effects of calculation delay, dead time, and the like.

[0136] θdf=tan －１ (Vq1 / (Vamp+Vd1)) (7) Referring again to FIG. 12 , instantaneous voltage command value calculation unit 140 calculates instantaneous voltage command values ​​Vu*, Vv*, and Vw* using voltage amplitude command value Ve from voltage amplitude command calculation unit 130 and operating reference phase θop from operating reference phase determiner 110c. Specifically, as described in the first embodiment, voltage amplitude command value Ve is subjected to coordinate transformation (inverse dq transformation) using operating reference phase θop to calculate instantaneous voltage command values ​​Vu*, Vv*, and Vw* for each phase (U, V, W phase) of main circuit unit 20. In the third embodiment, an ensemble of operating reference phase determiner 110c, current suppression control unit 120c, and voltage amplitude command calculation unit 130 constitutes one example of a “voltage control unit” that generates voltage amplitude command value Ve and operating reference phase θop.

[0137] The PWM calculation unit 150 operates in the same manner as in the first and second embodiments, and generates on / off command signals Sgu, Sgv, Sgw (Figures 1 and 2) by PWM calculation that compares each of the instantaneous voltage command values ​​Vu*, Vv*, Vw* with a carrier signal.

[0138] Therefore, in embodiment 3, if the voltage amplitude command value Ve has a reactive component due to the voltage amplitude control amount Vq1, a phase shift will occur between the phase of the instantaneous voltage command values ​​Vu*, Vv*, Vw*, i.e., the actual operating phase of the power conversion device 10, and the operating reference phase θop.

[0139] In the phase adjustment section 160 , the adder 164 adds the operating reference phase θop from the integrator 113 and the phase shift amount θdf from the phase shift amount calculation section 162 to calculate the detection phase θdt used in the coordinate conversion section 105 .

[0140] As a result, the detection phase θdt is generated to reflect the phase shift θdf between the operating reference phase θop and the instantaneous voltage command values ​​Vu*, Vv*, Vw* due to the reactive component of the voltage amplitude command value Ve, and to suppress the shift from the actual output phase of the power conversion device 10.

[0141] As a result, even when the voltage amplitude command value Ve includes both the active component and the reactive component, it is possible to obtain the same effect as when the operating reference phase θop and the detection phase θdt are standardized in the first and second embodiments in which the voltage amplitude command value Ve includes only the active component. That is, in the power conversion device according to the third embodiment, it is possible to prevent the phase used for the coordinate conversion for classifying the active component and the reactive component in the coordinate conversion unit 105 from shifting from the actual operating phase of the power conversion device 10.

[0142] As a result, in the power conversion device according to the third embodiment, as in the first and second embodiments, even if the power conversion device 10 operates in accordance with the instantaneous voltage command values ​​Vu*, Vv*, Vw* that are a combination of control variables for current suppression control based on a virtual generator function (frequency control), synchronization between the power conversion device 10 and the AC power system 5 can be stably ensured.

[0143] In particular, in the power conversion device according to the third embodiment, at the stage when the instantaneous voltage command values ​​Vu*, Vv*, Vw* reflecting the voltage amplitude control variables Vd1, Vq1 for current suppression control are calculated, the phase shift amount θdf caused by the voltage amplitude control variables Vd1, Vq1 can be reflected in the detected phase θdt and coordinate transformation can be performed. Therefore, compared to control in which the phase is corrected using the phase shift amount actually measured based on the actual output of the power conversion device 10, it is expected that the occurrence of control errors caused by the phase shift can be suppressed.

[0144] Fig. 15 is a flowchart illustrating the current suppression control process in the power conversion device according to embodiment 3. As with Fig. 7 and Fig. 8, the control process of each step shown in Fig. 15 can be executed by the control circuit 100 using software processing, hardware processing, or a combination of both.

[0145] 15, the control circuit 100 acquires the detection value of the AC current Isys by the current detector 40 at a constant period in S310, which is the same as S110 (FIG. 7), and then classifies the AC current Isys into an active component and a reactive component using the detected phase θdt at that time in S320, which is the same as S120 (FIG. 7), to acquire the active current Id and the reactive current Iq. Then, in S330, the control circuit 100 determines whether at least one of the active current Id and the reactive current Iq acquired in S320 is outside a predetermined control range for each.

[0146] When at least one of the active current Id and the reactive current Iq is outside the control range (YES determination in S330), the control circuit 100 proceeds to S340 to execute current suppression control. On the other hand, when both the active current Id and the reactive current Iq are within the control range (NO determination in S330), the control circuit 100 returns to S310. When the determination in S330 is NO, the processes of S310 to S330 are executed at regular intervals. When the determination in S330 is NO, the control circuit 100 maintains the control flag Fcn in FIG. 13 at 0, whereas when the determination in S330 is YES, the control flag Fcn is set to 1.

[0147] In S340, the control circuit 100 calculates the voltage amplitude control amounts Vd1 and Vq1 for current suppression using the current suppression control unit 120c. Then, in S345, the control circuit 100 calculates the detected phase θdt by reflecting the phase shift amount θdf caused by the voltage amplitude command value Ve that reflects the voltage amplitude control amounts Vd1 and Vq1.

[0148] Then, even while the current suppression control is being executed, the control circuit 100 acquires the detection value of the AC current Isys detected by the current detector 40 at regular intervals by S350, which is similar to S150 (FIG. 7), and acquires the active current Id and the reactive current Iq from the AC current Isys by S360 using the detection phase θdt at that time calculated by S345.

[0149] In S370, the control circuit 100 determines whether a stop command for the current suppression control has been generated. For example, in S320, depending on whether the active current Id or the reactive current Iq has fallen outside the control range, the control circuit 100 can make a YES determination in S370 if the stop condition conforming to S170 (FIG. 7) and / or S270 (FIG. 8) is satisfied.

[0150] When a stop command has not been generated (NO in S370), control circuit 100 returns the process to S340. As a result, current suppression control is executed periodically by reflecting voltage amplitude control amounts Vd1 and Vq1 calculated in S340 in instantaneous voltage command values ​​Vu*, Vv*, and Vw* until a stop command is generated.

[0151] On the other hand, when a stop command is generated (YES in S370), the control circuit 100 stops the current suppression control in S380. In S380, the control flag Fcn is reset to 0, and Vd1=Vq1=0 in FIGS. 12 and 13 .

[0152] Thereafter, the control circuit 100 can restart the processing from S310 onwards, thereby operating the power conversion device 10 to perform current suppression control whenever at least one of the active current Id and the reactive current Iq falls outside the predetermined control range for each.

[0153] <Additional Notes> The present embodiment and the modifications described above include the following technical ideas.

[0154] [Configuration 1] A main circuit unit (20) including a switching element connected between a DC power source (30) and an AC power system (5) for performing power conversion between a DC voltage and an AC voltage, and a control circuit (100) for controlling the on / off of the switching element to control the power conversion, wherein the control circuit comprises: a coordinate transformation unit (105) that performs coordinate transformation to classify a detected value of AC output from the main circuit unit to the AC power system into an active component and a reactive component; and a voltage control unit (110a-110c, 120a-120c, 130) that generates, by control calculation based on the active component and the reactive component obtained by the coordinate transformation, an operating reference phase (θop) obtained based on an integral of an operating frequency (fop) that is controlled to increase or decrease according to the active component (Pd) of the output power of the main circuit unit, and a voltage amplitude command value that is adjusted to change the amplitude of the output AC voltage of the main circuit unit when the output current of the main circuit unit deviates from a predetermined control range. an instantaneous voltage command generating unit (140) that generates instantaneous voltage command values ​​(Vu*, Vv*, Vw*) of the output AC voltage using the voltage amplitude command value (Ve) and the operating reference phase (θop) from the voltage control unit; and a switching control unit (150) that generates on / off command signals (Sgu, Sgv, Sgw) for the switching elements in accordance with the instantaneous voltage command values, wherein the control circuit sets a rotation phase (θdt) used for the coordinate transformation so that the phase of the instantaneous voltage command values ​​coincides with that of the instantaneous voltage command values.

[0155] [Configuration 2] The voltage control unit comprises: an active current suppression control unit (121a, 121b) that executes active current suppression control when an active component (Id) of the output current of the main circuit unit (20) obtained by the coordinate transformation falls outside a predetermined first control range, and calculates AC parameters (f2, θ2) for changing the phase of the instantaneous voltage command value (Vu*, Vv*, Vw*) in a direction to reduce the absolute value of the active component; and a reactive current suppression control unit (122) that executes reactive current suppression control when a reactive component (Id) of the output current of the main circuit unit obtained by the coordinate transformation falls outside a predetermined second control range, and calculates a voltage amplitude control amount (V1) including only the active component, for changing the amplitude of the output AC voltage in a direction to reduce the absolute value of the reactive component. the power conversion device according to configuration 1, further comprising: an operating frequency control unit (111) for increasing or decreasing the operating frequency (fop) in accordance with the effective component (Pd) of the output power obtained by the coordinate transformation; a reference operating phase determination unit (110a, 110b) for determining the operating reference phase (θop) using the operating frequency and the AC parameter; and a voltage amplitude command calculation unit (130) for calculating the voltage amplitude command value (Ve) by reflecting the voltage amplitude control amount, wherein the coordinate transformation unit (105) performs the coordinate transformation using the operating reference phase (θop) and the rotational phase (θdt) set to a common value.

[0156] [Configuration 3] The power conversion device according to Configuration 2, wherein the operating frequency control unit (111) is configured to calculate a first frequency control variable (f1) based on a deviation between an active component (Pd) of the output power and a predetermined active power command value (Pd*), the active current suppression control unit (121a) calculates a second frequency control variable (f2) for changing the operating frequency as the AC parameter when the active current suppression control is performed, and the reference operating phase determination unit (110a) sets the operating frequency (fop) using a reference frequency (fr), the first frequency control variable, and the second frequency control variable, and sets the operating reference phase (θop) by integrating the operating frequency.

[0157] [Configuration 4] The power conversion device according to Configuration 2, wherein the operating frequency control unit (111) is configured to calculate a frequency control amount (f1) based on a deviation between an active component (Pd) of the output power and a predetermined active power command value (Pd*), the active current suppression control unit (121b) calculates, as the AC parameter, a phase control amount (θ2) for delaying the operating reference phase (θop) when the active current suppression control is performed, and the reference operating phase determination unit (110b) sets the operating frequency (fop) using a reference frequency (fr) and the frequency control amount, and sets the operating reference phase using an integral value of the operating frequency and the phase control amount.

[0158] [Configuration 5] The power conversion device according to any one of configurations 2 to 4, wherein the active current suppression control unit (121a, 121b) calculates the AC parameters (f2, θ2) based on a deviation between an active component (Id) of the output current and an active current command value (Id*) when the active current suppression control is executed, and the reactive current suppression control unit (122) calculates the voltage amplitude control amount (V1) based on a deviation between a reactive component (Iq) of the output current and a reactive current command value (Iq*) when the reactive current suppression control is executed.

[0159] [Configuration 6] The voltage control unit includes: an operating frequency control unit (111) for increasing / decreasing the operating frequency (fop) in accordance with the active component (Pd) of the output power obtained by the coordinate transformation; a reference operating phase determination unit (110c) for determining the operating reference phase (θop) using the operating frequency; a current suppression control unit (120c) for calculating a voltage amplitude control amount (V1) that may include both an active component (Vd1) and a reactive component (Vq1) for changing the amplitude of the output AC voltage by performing current suppression control when at least one of the active component (Id) and the reactive component (Iq) of the output current of the main circuit unit (20) obtained by the coordinate transformation falls outside a predetermined first or second control range; and a voltage amplitude command calculation unit (130) for calculating the voltage amplitude command value (Ve) by reflecting the voltage amplitude control amount (V1). the instantaneous voltage command generating unit (140) generates the instantaneous voltage command values ​​(Vu*, Vv*, Vw*) by using the operating reference phase (θop) to perform an inverse transformation of the coordinate transformation performed by the coordinate transformation unit on the voltage amplitude command values, and the control circuit further includes a phase adjusting unit (160) that sets the rotational phase (θdt) used in the coordinate transformation using the operating reference phase (θop) and a phase shift amount (θdf) based on a ratio of the reactive component (Vq1) to the active component (Vamp+Vd1) of the voltage amplitude command value (Ve) reflecting the voltage amplitude control amount (V1).

[0160] [Configuration 7] The power conversion device according to Configuration 6, wherein the current suppression control unit (120c) calculates an active component (V1d) and a reactive component (V1q) of the voltage amplitude control amount so as to control the active component to an active current command value (Id*) and the reactive component to a reactive current command value (Iq*) when the current suppression control is executed.

[0161] [Configuration 8] The power conversion device according to Configuration 6 or 7, wherein the operating frequency control unit (111) is configured to calculate a frequency control amount (f1) based on a deviation between an active component (Pd) of the output power and a predetermined active power command value (Pd*), and the reference operating phase determination unit (110c) determines the operating reference phase (θop) by integrating the operating frequency set using a reference frequency (fr) and the frequency control amount.

[0162] [Configuration 9] The power conversion device according to any one of Configurations 3, 4, and 8, wherein the reference frequency (fr) is a nominal frequency value of the AC power system (50) or a detected frequency value of the AC power system.

[0163] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0164] 5 AC power system, 7 Transmission line, 10 Power conversion device, 20 Main circuit unit, 21u, 21v, 21w Three-level inverter, 30 Storage element, 31, 32 Capacitor, 40 Current detector, 50 Voltage detector, 100 Control circuit, 105 Coordinate conversion unit, 110a to 110c Operation reference phase determination unit, 111 Operation frequency control unit, 113 Integrator, 120a to 120c Current suppression control unit, 121a, 121b Active current suppression control unit, 122 Reactive current suppression control unit, 130 Voltage amplitude command value calculation unit, 131 Voltage amplitude determination unit, 140 Instantaneous voltage command value calculation unit, 150 PWM calculation unit, 160 Phase adjustment unit, 162 Phase shift amount calculation unit, 214a, 214b Non-interference controller, Fcn, Fdcn, Fqcn Control flag, Id active current, Id* active current command value, Iq reactive current, Iq* reactive current command value, Isys, Iu, Iv, Iw AC current, Pd active power, Pd* active power command value, Pq reactive power, Sgu, Sgv, Sgw on / off command signal, V1, Vd1, Vq1 voltage amplitude control amount, Vamp voltage amplitude (base value), Ve voltage amplitude command value, Vsys, Vu, Vv, Vw AC voltage, Vu*, Vv*, Vw instantaneous voltage command value, f1, f2 frequency control amount, fcv output frequency (power conversion device), fgr system frequency, fop operating frequency, fr reference frequency, θ2 phase control amount, θdf phase shift amount, θdt detected phase, θop operating reference phase.

Claims

1. A power converter comprising: a main circuit section connected between a DC power source and an AC power system and including a switching element for performing power conversion between a DC voltage and an AC voltage; and a control circuit for controlling the on / off of the switching element to control the power conversion, wherein the control circuit comprises: a coordinate conversion section that performs coordinate conversion to classify a detected value of AC output from the main circuit section to the AC power system into an active component and a reactive component; a voltage control section that generates, by control calculation based on the active component and the reactive component obtained by the coordinate conversion, an operating reference phase obtained based on the integral of an operating frequency that is controlled to increase or decrease according to the active component of the output power of the main circuit section, and a voltage amplitude command value that is adjusted to change the amplitude of the output AC voltage of the main circuit section when the output current of the main circuit section deviates from a predetermined control range; an instantaneous voltage command generation section that generates an instantaneous voltage command value of the output AC voltage using the voltage amplitude command value and the operating reference phase from the voltage control section; and a switching control section that generates an on / off command signal for the switching element in accordance with the instantaneous voltage command value. The control circuit sets the rotation phase used in the coordinate transformation so that the rotation phase coincides with the phase of the instantaneous voltage command value.

2. The power conversion device according to claim 1, wherein the voltage control unit is configured to: an active current suppression control unit that executes active current suppression control when the active component of the output current of the main circuit unit obtained by the coordinate transformation falls outside a predetermined first control range, and calculates an AC parameter for changing the phase of the instantaneous voltage command value in a direction that reduces the absolute value of the active component; an reactive current suppression control unit that executes reactive current suppression control when the reactive component of the output current of the main circuit unit obtained by the coordinate transformation falls outside a predetermined second control range, and calculates a voltage amplitude control amount including only the active component, for changing the amplitude of the output AC voltage in a direction that reduces the absolute value of the reactive component; an operating frequency control unit that increases or decreases the operating frequency in accordance with the active component of the output power obtained by the coordinate transformation, and includes: a reference operating phase determination unit that determines the operating reference phase using the operating frequency and the AC parameter; and a voltage amplitude command calculation unit that calculates the voltage amplitude command value reflecting the voltage amplitude control amount; and the coordinate transformation unit performs the coordinate transformation using the operating reference phase and the rotation phase that is set to a common value.

3. A power conversion device according to claim 2, wherein the operating frequency control unit is configured to calculate a first frequency control variable based on the deviation between an active component of the output power and an active power command value, the active current suppression control unit calculates a second frequency control variable as the AC parameter for changing the operating frequency when the active current suppression control is executed, and the reference operating phase determination unit sets the operating frequency using a reference frequency, the first frequency control variable, and the second frequency control variable, and sets the operating reference phase by integrating the operating frequency.

4. A power conversion device as claimed in claim 2, wherein the operating frequency control unit is configured to calculate a frequency control amount based on the deviation between the active component of the output power and an active power command value, the active current suppression control unit calculates a phase control amount for changing the operating reference phase as the AC parameter when the active current suppression control is executed, and the reference operating phase determination unit sets the operating frequency using a reference frequency and the frequency control amount, and sets the operating reference phase using an integral value of the operating frequency and the phase control amount.

5. A power conversion device according to any one of claims 2 to 4, wherein the active current suppression control unit calculates the AC parameter based on the deviation between the active component of the output current and an active current command value when the active current suppression control is being performed, and the reactive current suppression control unit calculates the voltage amplitude control amount based on the deviation between the reactive component of the output current and a reactive current command value when the reactive current suppression control is being performed.

6. The voltage control unit includes: an operating frequency control unit for increasing / decreasing the operating frequency in accordance with the active component of the output power obtained by the coordinate transformation, and a reference operating phase determination unit for determining the operating reference phase using the operating frequency; a current suppression control unit for calculating a voltage amplitude control amount that may include both active and reactive components when at least one of the active and reactive components of the output current of the main circuit unit obtained by the coordinate transformation falls outside a predetermined first or second control range, thereby performing current suppression control to change the amplitude of the output AC voltage in a direction that reduces the absolute value of the active or reactive component; and a voltage amplitude command calculation unit for calculating the voltage amplitude command value by reflecting the voltage amplitude control amount; and the instantaneous voltage command generation unit generates the instantaneous voltage command value by using the operating reference phase to perform an inverse transformation of the coordinate transformation performed by the coordinate transformation unit on the voltage amplitude command value, and the control circuit 2. The power conversion device according to claim 1, further comprising a phase adjustment unit that sets the rotation phase used in the coordinate transformation using the operation reference phase and a phase shift amount based on a ratio of the reactive component to the active component of the voltage amplitude command value in which the voltage amplitude control amount is reflected.

7. A power conversion device according to claim 6, wherein the current suppression control unit calculates the active component and the reactive component of the voltage amplitude control amount so as to control the active component to an active current command value and the reactive component to a reactive current command value when the current suppression control is executed.

8. A power conversion device according to claim 6 or 7, wherein the operating frequency control unit is configured to calculate a frequency control amount based on a deviation between an active component of the output power and a predetermined active power command value, and the reference operating phase determination unit determines the operating reference phase by integrating the operating frequency set using a reference frequency and the frequency control amount.

9. The power conversion device according to any one of claims 3, 4 and 8, wherein the reference frequency is a nominal frequency value of the AC power system or a detected frequency value of the AC power system.

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