POWER CONVERSION DEVICE, CONTROL METHOD FOR POWER CONVERSION DEVICE, AND PROGRAM

Abstract

To provide a power conversion device, a method for controlling a power conversion device, and a program that enable a desired amount of reactive power to be supplied to an interconnection point even in a case where an unbalance accident occurs in a power system.SOLUTION: A power conversion device of an embodiment includes a power converter, a control device, a voltage detector, and a current detector. The power converter supplies reactive power to an interconnection point with an interconnected power system, or consumes reactive power. The control device controls the power converter. The voltage detector is installed on an AC side of the power converter, and detects an AC voltage at the interconnection point. The current detector is installed on the AC side of the power converter, and detects an AC current at the interconnection point. The control device detects a positive phase AC voltage and a negative phase AC voltage based on the AC voltage, and controls output of a positive phase AC current and a negative phase AC current based on the positive phase AC voltage and the negative phase AC voltage, and predetermined AC current upper and lower limit values and a reactive power command value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a power conversion device, a control method for the power conversion device, and a program. [Background technology]

[0002] In recent years, the introduction of renewable energy sources such as solar power generation and wind power generation has been expanding. There is concern that the supply of power from renewable energy sources may cause the voltage of the power grid to become unstable. For this reason, there is an increasing demand for static synchronous compensators (STATCOMs) to ensure stable operation of the power grid. STATCOMs compensate for reactive power using a self-commutated converter. STATCOMs are introduced, for example, in power transmission and distribution systems installed in substations and are operated continuously. During normal operation, STATCOMs contribute to stabilizing the system voltage by controlling the reactive power at the interconnection point.

[0003] STATCOM is required to continue the operation of the power system and control the reactive current to suppress voltage drops at the interconnection point even when a system fault occurs due to, for example, lightning strike. In other words, STATCOM is required to improve its resistance (robustness) against factors that adversely affect the power system.

[0004] If the fault that occurs in the power system is a balanced fault, where the voltage drop is equal across all three phases, the STATCOM can supply a constant amount of reactive power to the interconnection point by controlling all three phases to the rated positive-sequence current. However, if the fault that occurs in the power system is an unbalanced fault, where the voltage drop differs across the three phases (different for each phase), even if the STATCOM controls the flow of positive-sequence reactive current, the reactive current that is flowing may pulsate due to the unbalanced voltage, and the desired amount of reactive power may not be supplied. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-021848 A Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a power conversion device, a control method for the power conversion device, and a program that can supply a desired amount of reactive power to an interconnection point even when an unbalance fault occurs in a power system. [Means for solving the problem]

[0007] A power conversion device according to an embodiment includes a power converter, a control device, a voltage detector, and a current detector. The power converter supplies reactive power to an interconnection point with an interconnected power system, or consumes the reactive power. The control device controls the power converter. The voltage detector is installed on the AC side of the power converter and detects an AC voltage at the interconnection point. The current detector is installed on the AC side of the power converter and detects an AC current at the interconnection point. The control device detects a positive-phase AC voltage and a negative-phase AC voltage based on the AC voltage, and controls outputs of a positive-phase AC current and a negative-phase AC current based on the positive-phase AC voltage and the negative-phase AC voltage, predetermined AC current upper and lower limits, and a reactive power command value. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a power conversion device according to an embodiment. [Diagram 2] FIG. 1 is a diagram showing an example of the configuration of a power converter. [Diagram 3] FIG. 2 is a diagram showing an example of the configuration of a converter. [Figure 4] 4 is a flowchart showing an example of a process of positive-phase and negative-phase current control in the control device. [Diagram 5]FIG. 4 is a schematic waveform diagram showing an example of waveforms at a grid-connection point when positive-phase / negative-phase current control is executed in a first current control mode in the control device. [Figure 6] FIG. 4 is a schematic waveform diagram showing an example of waveforms at a grid-connection point when positive-phase / negative-phase current control is executed in a second current control mode in the control device. [Figure 7] FIG. 4 is a schematic waveform diagram showing an example of waveforms at a grid-connection point when positive-phase / negative-phase current control is executed in a third current control mode in the control device. [Figure 8] FIG. 1 is a diagram showing an example of another configuration of a power converter (part 1). [Figure 9] FIG. 2 is a diagram showing an example of another configuration of the power converter (part 2). [Figure 10] FIG. 3 is a diagram showing an example of another configuration of the power converter (part 3). [Figure 11] FIG. 2 is a diagram showing an example of a configuration of a cell included in a converter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a power conversion device, a control method for the power conversion device, and a program according to an embodiment will be described with reference to the drawings.

[0010] [Power conversion device configuration] FIG. 1 is a diagram showing an example of a configuration of a power conversion device according to an embodiment. FIG. 1 shows an example of a power conversion device 1 that is installed (connected) in parallel with a power system 2 and stabilizes AC power of the power system 2 by compensating (adjusting) reactive power output (supplied) to the power system 2. The power system 2 is, for example, a three-phase AC system including an AC power source and an AC load. The power conversion device 1 is, for example, a static synchronous compensator (STATCOM). In the following description, a connection point between the power conversion device 1 and the power system 2 is referred to as an interconnection point. Furthermore, in the following description, unless otherwise specified, each of the three phases is not distinguished from one another. The power conversion device 1 includes, for example, a power converter 10, a control device 20, a voltage detector 30, and a current detector 40.

[0011] The power converter 10 stabilizes the system voltage in the power system 2 by supplying AC power (reactive power) to the interconnection point or consuming the reactive power at the interconnection point in response to control from the control device 20. The power converter 10 includes, for example, a transformer 11 and a converter 12. The transformer 11 and the converter 12 have a general configuration. The converter 12 may be, for example, a modular multilevel converter (MMC) that converts AC power and DC power mutually. A DC power source (not shown) is connected to the converter 12 for supplying DC power to be converted into AC power.

[0012] FIG. 2 is a diagram showing an example of the configuration of the power converter 10. The power converter 10a shown in FIG. 2(a) is configured to apply a general three-phase converter. The power converter 10a includes, for example, a transformer 11a and one converter 12. The transformer 11a is, for example, a three-phase transformer. The transformer 11a may be configured to connect three single-phase transformers corresponding to each of the three phases. The converter 12 is, for example, a three-phase converter configured of a converter unit. The AC side terminal of the converter 12 is connected to the transformer 11a. The power converter 10a outputs an AC voltage from the converter 12 according to the control from the control device 20 from the transformer 11a arranged on the AC side, thereby causing an AC current according to the control from the control device 20 to flow. The power converter 10b shown in FIG. 2(b) is configured to apply a multiplexed transformer. Power converter 10b includes, for example, transformer 11b and a plurality of converters 12 (converters 12-1 to 12-n (n is a natural number)). Power converter 10b has a configuration in which transformer 11a in power converter 10a is replaced with transformer 11b which is a multiplexed type transformer. Accordingly, power converter 10b is configured to include a plurality (at least two) of three-phase converters which are the same as converter 12 included in power converter 10a. The AC side terminals of each converter 12 are connected to transformer 11b. In power converter 10b, by multiplexing the AC side outputs of the plurality of converters 12, it is possible to multiply the voltage levels of the AC voltage output to the AC side from transformer 11b arranged on the AC side.

[0013] FIG. 3 is a diagram showing an example of the configuration of the converter 12. The converter 12a shown in FIG. 3(a) includes three legs 121 (legs 121-1 to 121-3) and one DC capacitor 122. The legs 121 include at least two or more self-extinguishing semiconductor switching elements. The semiconductor switching elements are, for example, insulated gate bipolar transistors (IGBTs). The semiconductor switching elements operate (switching operation) in response to control (switching control) from the control device 20. In the converter 12a, DC side terminals of the respective legs 121 are connected in parallel with each other, and a phase voltage of each phase is output from an AC side terminal of each leg 121. In the converter 12a, both ends of the DC capacitor 122 are connected to the corresponding DC side terminals of each leg 121. With this configuration, in the converter 12a, the voltage level of the phase voltage output by each leg 121 is two levels. The converter 12b shown in FIG. 3(b) includes three legs 123 (legs 123-1 to 123-3) and two DC capacitors 122 (DC capacitor 122-1 and DC capacitor 122-2). The legs 123 are configured to have a neutral terminal. The legs 123 include at least two or more self-extinguishing semiconductor switching elements, and a semiconductor switching element or a diode connected to a midpoint of the semiconductor switching elements to form a neutral point. The semiconductor switching elements included in the legs 123 are, for example, insulated gate bipolar transistors (IGBTs) like the semiconductor switching elements included in the legs 121. The semiconductor switching elements included in the legs 123 also perform switching operations in response to switching control from the control device 20. In the converter 12b, like the converter 12a, the DC side terminals of the legs 123 are connected in parallel with each other, and the phase voltages of the respective phases are output from the AC side terminals of the legs 123. In the converter 12 a , one end of the DC capacitor 122 - 1 is connected to one corresponding DC side terminal of each leg 123 , and one end of the DC capacitor 122 - 2 is connected to the other corresponding DC side terminal of each leg 123 .The other ends of the DC capacitors 122-1 and 122-2 are connected to each other and to the neutral terminals of the respective legs 123. With this configuration, in the converter 12b, the phase voltages output by the respective legs 123 have three voltage levels.

[0014] Returning to FIG. 1 , the voltage detector 30 detects the AC voltage Vac at the interconnection point. The voltage detector 30 is disposed on the interconnection point side (AC side) of the power converter 10, and detects the AC voltage Vac at the position where it is disposed. The voltage detector 30 detects the AC voltage Vac of each phase. The voltage detector 30 outputs the detected value of the AC voltage Vac of each phase to the control device 20.

[0015] The current detector 40 detects the AC current Iac flowing from the power converter 10 to the interconnection point. The current detector 40 is disposed on the interconnection point side (AC side) of the power converter 10, and detects the AC current Iac at the position where it is disposed. The current detector 40 outputs the detection value of the detected AC current Iac to the control device 20.

[0016] The control device 20 controls the operation of the power converter 10 based on the rated value of the power converter 10, the inputted set value, the AC voltage Vac detected by the voltage detector 30, and the AC current Iac detected by the current detector 40. That is, the control device 20 controls the switching of the switching element in the converter 12 included in the power converter 10. The control device 20 controls the operation of the power converter 10 by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). The control device 20 may be realized by hardware (including a circuit section; circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by cooperation between software and hardware. The control device 20 may be realized by a dedicated LSI. The program may be stored in advance in a storage device (storage device with a non-transient storage medium) such as an HDD (Hard Disk Drive) or flash memory provided in the control device 20 or the power conversion device 1, or may be stored in a removable storage medium (non-transient storage medium) such as a DVD or CD-ROM, and installed in the HDD or flash memory provided in the control device 20 or the power conversion device 1 by attaching the storage medium to a drive device provided in the control device 20 or the power conversion device 1.

[0017] The control device 20 controls the operation of the power converter 10, thereby causing the power converter 10 to output (supply) reactive power to an interconnection point with the power system 2. More specifically, the control device 20 generates a control signal for controlling the operation of the power converter 10 based on a rated value of the power converter 10 or an inputted set value. The rated value of the power converter 10 is, for example, a voltage value of an AC voltage or an upper or lower limit value of an AC current (hereinafter referred to as an "AC current upper and lower limit value Ilim") that the power converter 10 outputs (supplies) to the interconnection point. The AC current upper and lower limit values ​​Ilim may be input (set) from a higher-level control device such as a power company that operates the power system 2. For example, a command value of reactive power to be output by the power converter 10 (hereinafter referred to as a "reactive power command value Q*") is input (set) to the control device 20 as a set value from a higher-level control device such as a power company that operates the power system 2. The set value set in the control device 20 may be a command value of reactive voltage or a command value of reactive current. Furthermore, the set value set in the control device 20 may be a command value (AC voltage command value) of the AC voltage at the interconnection point. The control device 20 generates a control signal for supplying reactive power according to the set reactive power command value Q* to the interconnection point. The control device 20 outputs the generated control signal to the power converter 10, thereby causing the power converter 10 to output (supply) reactive power. The control signal generated by the control device 20 and output to the power converter 10 is, for example, a switching pulse signal for controlling the operation of a switching element provided in the converter 12 in order to cause the converter 12 provided in the power converter 10 to flow a desired positive-phase converter AC current Icc. The positive phase means that, for example, when the power system 2 has three phases, a first phase (A phase), a second phase (B phase), and a third phase (C phase), the phase order of the AC voltage in the AC power supplied to the interconnection point according to the converter AC current Icc is shifted by 120° in the order of A phase, B phase, and C phase. The control device 20 generates a control signal for causing the same converter AC current Icc to flow in all three phases, and outputs the control signal to the power converter 10. More specifically, the control device 20 generates a control signal for causing the converter AC current Icc to follow the set reactive power command value Q*, and outputs the control signal to the power converter 10.This allows the power conversion device 1 to output (supply) reactive power to the interconnection point during normal operation.

[0018] For example, even if a system fault occurs in the power system 2 due to a lightning strike or the like, the control device 20 controls the operation of the power converter 10 to output (supply) reactive power to the interconnection point, thereby suppressing a drop in the AC voltage at the interconnection point. This allows the power conversion device 1 to adjust reactive power not only during normal operation but also when a system fault occurs in the power system 2, thereby allowing the operation of the power system 2 to be continued. For this reason, the power conversion device 1 has a function of detecting a system fault that occurs in the power system 2 (hereinafter referred to as an "accident detection function"). The accident detection function may be a function provided in the control device 20.

[0019] Incidentally, system faults occurring in the power system 2 include a balanced fault in which the amount of AC voltage drop is the same in the three phases, and an unbalanced fault in which the amount of AC voltage drop is different in the three phases (different for each phase). When the system fault is a balanced fault, the control device 20 outputs a control signal to the power converter 10 to cause the converter 12 included in the power converter 10 to flow a positive-phase converter AC current Icc having the same current value for all three phases, although the current value is different from that during normal operation of the power conversion device 1, thereby making it possible to cause the power converter 10 to output (supply) reactive power corresponding to the balanced fault to the interconnection point. In other words, the control device 20 controls the operation of the power converter 10 to cause the same converter AC current Icc to flow in all three phases, as in the case of normal operation of the power conversion device 1, thereby adjusting the reactive power corresponding to the balanced fault that has occurred and allowing the operation of the power system 2 to continue.

[0020] On the other hand, when the system fault is an unbalanced fault, the control device 20 outputs a control signal to the power converter 10 to cause the converter AC current Icc, which takes into account not only the positive phase but also the negative phase, to flow through the converter 12 included in the power converter 10. The negative phase means that the phase order of the AC voltage is supplied in an order different from the positive phase, such as phase A, phase C, phase B, etc.

[0021] When the system fault is an unbalanced fault, the control device 20 detects a positive-phase AC voltage component (hereinafter referred to as "positive-phase AC voltage Vp") and a negative-phase AC voltage component (hereinafter referred to as "negative-phase AC voltage Vn") at the interconnection point based on the detection value of the AC voltage Vac output by the voltage detector 30 and the detection value of the AC current Iac output by the current detector 40. In the following description, the function of the control device 20 to detect the positive-phase AC voltage Vp and the negative-phase AC voltage Vn is referred to as a "positive-phase / negative-phase voltage detection function." In this positive-phase / negative-phase voltage detection function, for example, the AC voltage Vac is subjected to a positive-phase dq conversion to remove pulsation of twice the frequency in the AC voltage at the interconnection point, and the result is detected as the positive-phase AC voltage Vp. Similarly, in the positive-phase / negative-phase voltage detection function, for example, the AC voltage Vac is subjected to a negative-phase dq conversion to remove pulsation of twice the frequency in the AC voltage at the interconnection point, and the result is detected as the negative-phase AC voltage Vn.

[0022] Then, the control device 20 calculates a current command value (hereinafter referred to as "positive-phase current command value Ip*") for causing a positive-phase AC current to flow from the power converter 10 to the interconnection point and a current command value (hereinafter referred to as "negative-phase current command value In*") for causing a negative-phase AC current to flow from the power converter 10 based on the set reactive power command value Q* and the detected positive-phase AC voltage Vp and negative-phase AC voltage Vn. The control device 20 generates a control signal such that the positive-phase component of the AC current Iac flowing from the power converter 10 to the interconnection point (hereinafter referred to as "positive-phase AC current Ip") follows the calculated positive-phase current command value Ip* and the negative-phase component of the AC current Iac (hereinafter referred to as "negative-phase AC current In") follows the calculated negative-phase current command value In*, and outputs the control signal to the power converter 10. In other words, the control device 20 generates a control signal such that not only the positive-phase AC current Ip but also an AC current superimposed with the negative-phase AC current In flows as a reactive current, and outputs the control signal to the power converter 10. In the following description, the control performed by the control device 20 to make the positive-phase AC current Ip and the negative-phase AC current In follow the calculated positive-phase current command value Ip* and the negative-phase current command value In*, respectively, is referred to as "positive-phase and negative-phase current control."

[0023] The control device 20 can output (supply) reactive power corresponding to an unbalanced fault occurring in the power system 2 from the power converter 10 to the interconnection point by switching the control method of the power converter 10 by positive-phase / negative-phase current control. That is, the control device 20 has a plurality of modes (current control modes) for switching the reactive power supply method when an unbalanced fault occurs. The current control mode in the control device 20 is switched, for example, by a mode switching signal (hereinafter referred to as "switching signal Mode"). The switching signal Mode is input (set) to the control device 20 from, for example, a higher-level control device based on the reactive power supply method determined by the power company that operates the power system 2 or a higher-level control device. For example, a number corresponding to each current control mode is assigned to the switching signal Mode, and the higher-level control device inputs the assigned number to the control device 20 as the switching signal Mode, whereby the control device 20 executes positive-phase / negative-phase current control in the current control mode corresponding to the input number. The reactive power supply method switched by the control device 20 according to the current control mode will be described later.

[0024] [Positive and negative sequence current control processing] FIG. 4 is a flowchart showing an example of the process of the positive-phase and negative-phase current control in the control device 20. FIG. 4 shows an example of the flow of the process executed by the control device 20 when calculating the positive-phase current command value Ip* and the negative-phase current command value In* in the positive-phase and negative-phase current control. The process of this flowchart may be repeatedly executed while the power conversion device 1 is operating. In the following description, it is assumed that the AC current upper and lower limit values ​​Ilim in the power converter 10 are determined in advance, and the reactive power command value Q* and the switching signal Mode are input (set) to the control device 20. Furthermore, in the following description, it is assumed that the control device 20 acquires the AC voltage Vac detected by the voltage detector 30 and the AC current Iac detected by the current detector 40, and the positive-phase and negative-phase voltage detection function based on the acquired AC voltage Vac and AC current Iac is completed, that is, the detection of the positive-phase AC voltage Vp and the negative-phase AC voltage Vn is completed.

[0025] When the control device 20 starts the positive-phase / negative-phase current control, it first calculates the reactive power limit value Qlim according to the input switching signal Mode based on the current control mode represented by the switching signal Mode and the positive-phase AC voltage Vp and the negative-phase AC voltage Vn (step S1). At this time, the control device 20 calculates the reactive power limit value Qlim so that the AC current Iac does not exceed the AC current upper and lower limits Ilim.

[0026] The control device 20 compares the calculated reactive power limit value Qlim with the absolute value |Q*| of the input reactive power command value Q*, and judges whether the reactive power limit value Qlim is equal to or greater than the absolute value |Q*| of the reactive power command value Q* (step S2). If the reactive power limit value Qlim is equal to or greater than the absolute value |Q*| of the reactive power command value Q* in step S2, the control device 20 determines a command value (hereinafter referred to as "reactive power limit command value Qlim*") for outputting reactive power to the power converter 10 in consideration of the AC current upper and lower limits Ilim, as the reactive power command value Q* (step S3-1). Then, the control device 20 substitutes the value of the reactive power command value Q* for the value of the reactive power limit command value Qlim*.

[0027] On the other hand, in step S2, if the reactive power limit value Qlim is not equal to or greater than the absolute value |Q*| of the reactive power command value Q* (that is, if the reactive power limit value Qlim is smaller than the absolute value |Q*| of the reactive power command value Q*), the control device 20 determines the reactive power limit command value Qlim* to be the reactive power limit value Qlim (step S3-2). Then, the control device 20 substitutes the value of the reactive power limit value Qlim for the value of the reactive power limit command value Qlim*.

[0028] The control device 20 calculates a positive-phase current command value Ip* and a negative-phase current command value In* based on the current control mode indicated by the switching signal Mode, the reactive power limit command value Qlim*, and the positive-phase AC voltage Vp and the negative-phase AC voltage Vn (step S4-1). The positive-phase current command value Ip* is a command value representing the amplitude of a positive-phase AC current to be caused to flow from the power converter 10 to the interconnection point, and the negative-phase current command value In* is a command value representing the amplitude of a negative-phase AC current to be caused to flow from the power converter 10 to the interconnection point.

[0029] Furthermore, the control device 20 calculates a command value for the phase of the positive-phase AC current to be caused to flow from the power converter 10 to the interconnection point (hereinafter referred to as the "positive-phase current phase command value Φp*") and a command value for the phase of the negative-phase AC current to be caused to flow from the power converter 10 to the interconnection point (hereinafter referred to as the "negative-phase current phase command value Φn*") based on the current control mode represented by the switching signal Mode, the reactive power limit command value Qlim*, and the positive-phase AC voltage Vp and the negative-phase AC voltage Vn (step S4-2).

[0030] In this way, the control device 20 calculates command values ​​of AC currents (positive-phase current command value Ip*, positive-phase current phase command value Φp*, negative-phase current command value In*, and negative-phase current phase command value Φn*) to be flowed from the power converter 10 to the interconnection point, based on the set reactive power command value Q* and the positive-phase AC voltage Vp and negative-phase AC voltage Vn detected from the AC voltage Vac detected by the voltage detector 30 and the AC current Iac detected by the current detector 40. Then, the control device 20 uses the calculated command values ​​of the AC currents to generate control signals to be output to the power converter 10, and controls the operation of the power converter 10.

[0031] For example, the control device 20 calculates a positive-phase current command value Icp* for causing a positive-phase converter AC current Icc (hereinafter referred to as "positive-phase current Icp") to flow through the converter 12 by the following equation (1), and calculates a negative-phase current command value Icn* for causing a negative-phase converter AC current Icc (hereinafter referred to as "negative-phase current Icn") to flow through the converter 12 by the following equation (2). Then, the control device 20 generates a control signal (switching pulse signal) such that the positive-phase current Icp follows the calculated positive-phase current command value Icp* and the negative-phase current Icn follows the calculated negative-phase current command value Icn*, and outputs the control signal to the converter 12.

[0032] Icp*=Ip*×sin(ωt+Φp*) ···(1)

[0033] Icn*=In*×sin(ωt+Φn*) ···(2)

[0034] For example, the control device 20 may calculate a current command value Ic* for causing the converter AC current Icc to flow through the converter 12 using the following equation (3), generate a control signal (switching pulse signal) such that the converter AC current Icc follows the calculated current command value Ic*, and output the control signal to the converter 12.

[0035] Ic*=Ip*×sin(ωt+Φp*)+In*×sin(ωt+Φn*) (3)

[0036] As a control method for the converter 12 in the control device 20, for example, PID control which combines P (Proportional) control, I (Integral) control, and D (Differential) control, feedback control, PR control which combines P (Proportional) control and R (Resonance) control, repetitive control, and other control methods can be applied.

[0037] In this way, the control device 20 calculates the positive-phase current command value Icp* and the negative-phase current command value Icn* for causing the positive-phase and negative-phase converter AC currents Icc corresponding to the input (set) switching signal Mode to flow through the converter 12, and controls the converter 12, thereby causing the power converter 10 to output (supply) reactive power to the interconnection point according to the current control mode.

[0038] [First current control mode] Here, an example of a method of supplying reactive power to be output (supplied) to the interconnection point according to the current control mode will be described. FIG. 5 is a schematic waveform diagram showing an example of a waveform at the interconnection point when the control device 20 executes positive-phase / negative-phase current control in the first current control mode. The first current control mode is a control mode that suppresses pulsation of reactive power. The example of the waveform at the interconnection point shown in FIG. 5 is an example when an unbalanced fault occurs in the B phase and the C phase of the three phases (A phase, B phase, and C phase). In FIG. 5, an example of the waveform of the AC voltage of each phase at the interconnection point is shown in the upper part, and an example of the waveform of the AC current of each phase at the interconnection point is shown in the middle part. The waveform of the AC current of each phase at the interconnection point shown in the middle part of FIG. 5 is an AC current waveform in which the positive-phase AC current Ip and the negative-phase AC current In are superimposed, which are caused to flow from the power converter 10 to the interconnection point by the control device 20 controlling the operation. In the lower part of Fig. 5, an example of changes in the reactive power limit value Qlim calculated by the control device 20, the reactive power Q at the interconnection point controlled by the control device 20, and the active power P at the interconnection point are shown in correspondence with the AC voltage waveform shown in the upper part of Fig. 5 and the AC current waveform shown in the middle part of Fig. 5. In Fig. 5, the horizontal axis is time t.

[0039] In the case of an unbalanced fault occurring in the system between the B phase and the C phase, the AC voltage at the interconnection point has a lower AC voltage component of the B phase (B phase AC voltage Vb) and a lower AC voltage component of the C phase (C phase AC voltage Vc) than the AC voltage component of the A phase (A phase AC voltage Va) as shown in the upper part of Fig. 5. Therefore, when the control device 20 calculates the reactive power limit value Qlim in step S1 such that the AC current Iac does not exceed the AC current upper and lower limits Ilim, the control device 20 determines in step S2 that the reactive power limit value Qlim is equal to or greater than the absolute value |Q*| of the reactive power command value Q*, and substitutes the value of the reactive power command value Q* as the value of the reactive power limit command value Qlim* (Qlim*=Q*) in step S3-1.

[0040] Then, in steps S4-1 and S4-2, the control device 20 calculates the positive-sequence current command value Ip*, the positive-sequence current phase command value Φp*, the negative-sequence current command value In*, and the negative-sequence current phase command value Φn* of the AC current to be caused to flow from the power converter 10 to the interconnection point, and generates a control signal to control the operation of the power converter 10. At this time, in the first current control mode, the reactive power is controlled to be constant. As a result, the AC current at the interconnection point becomes unbalanced as shown in the middle part of FIG. More specifically, the amplitude of the A-phase AC current component (A-phase AC current Ia) of the AC current at the interconnection point is the entire width between the upper limit value (+Ilim) and the lower limit value (-Ilim) of the AC current upper and lower limits Ilim, and the amplitudes of the B-phase AC current component (B-phase AC current Ib) and the C-phase AC current component (C-phase AC current Ic) are each narrower than the entire width between the upper limit value (+Ilim) and the lower limit value (-Ilim).

[0041] As a result, in the positive-phase / negative-phase current control of the first current control mode in the control device 20, the reactive power Q at the interconnection point is controlled to match the reactive power limit value Qlim, as shown in the lower part of Fig. 5. That is, the reactive power Q is controlled to a substantially constant amount of power with pulsation suppressed, similar to the reactive power limit value Qlim. On the other hand, in the positive-phase / negative-phase current control of the first current control mode in the control device 20, the active power P pulsates at a frequency twice that of the AC voltage at the interconnection point, while the average value (time average value) of the amount of power is set to zero.

[0042] [Second current control mode] FIG. 6 is a schematic waveform diagram showing an example of a waveform at a grid point when the control device 20 executes positive-phase / negative-phase current control in the second current control mode. The second current control mode is a control mode that suppresses pulsation of active power. The example of the waveform at the grid point shown in FIG. 6 is an example when an unbalanced fault occurs in the grid in the B phase and the C phase among the three phases, A phase, B phase, and C phase, as in the example of the waveform at the grid point shown in FIG. 5. In FIG. 6, as in FIG. 5, an example of the waveform of the AC voltage of each phase at the grid point is shown in the upper part, and an example of the waveform of the AC current of each phase at the grid point is shown in the middle part. In FIG. 6, as in FIG. 5, an example of the change in the reactive power limit value Qlim, the reactive power Q at the grid point, and the active power P at the grid point is shown in correspondence with the waveforms of the AC voltage and the AC current shown in the upper part and the middle part of FIG. 6. In FIG. 6, the horizontal axis is also time t.

[0043] The AC voltages (A-phase AC voltage Va, B-phase AC voltage Vb, and C-phase AC voltage Vc) at the interconnection point shown in the upper part of Fig. 6 are similar to the AC voltages shown in the upper part of Fig. 5. That is, the B-phase AC voltage Vb and the C-phase AC voltage Vc are each lower than the A-phase AC voltage Va. Therefore, in the second current control mode as well, similar to the first current control mode, the control device 20 assigns the value of the reactive power command value Q* to the value of the reactive power limit command value Qlim* (Qlim*=Q*) in step S3-1.

[0044] Then, in steps S4-1 and S4-2, the control device 20 calculates a positive-phase current command value Ip*, a positive-phase current phase command value Φp*, a negative-phase current command value In*, and a negative-phase current phase command value Φn*, and generates a control signal to control the operation of the power converter 10, in the same manner as in the first current control mode. At this time, in the second current control mode, the active power is controlled to be constant. As a result, in the second current control mode, as in the first current control mode, the AC current at the interconnection point is in an unbalanced state. However, in the second current control mode, as shown in the middle part of FIG. 6, the amplitude of the A-phase AC current Ia at the interconnection point is narrower than the entire width between the upper limit value (+Ilim) and the lower limit value (-Ilim) of the AC current upper and lower limit values ​​Ilim, and the amplitudes of the B-phase AC current Ib and the C-phase AC current Ic are the entire width between the upper limit value (+Ilim) and the lower limit value (-Ilim).

[0045] As a result, in the positive-phase / negative-phase current control of the second current control mode in the control device 20, the active power P at the interconnection point is controlled to approximately zero, as shown in the lower part of Fig. 6. In other words, the active power P is controlled to a constant amount of power at approximately zero, with pulsation suppressed. On the other hand, in the positive-phase / negative-phase current control of the second current control mode in the control device 20, the reactive power Q pulsates at a frequency twice that of the AC voltage at the interconnection point, while keeping the average value (time average value) of the amount of power the same as the reactive power limit value Qlim.

[0046] [Third current control mode] FIG. 7 is a schematic waveform diagram showing an example of a waveform at the interconnection point when the control device 20 executes positive-phase / negative-phase current control in the third current control mode. The third current control mode is a control mode for controlling so that the AC currents of all three phases are balanced. The example of the waveform at the interconnection point shown in FIG. 7 is an example when an unbalanced fault occurs in the B phase and the C phase among the three phases, A phase, B phase, and C phase, as in the example of the waveform at the interconnection point shown in FIG. 5 and FIG. 6. In FIG. 7, as in FIG. 5 and FIG. 6, an example of the waveform of the AC voltage of each phase at the interconnection point is shown in the upper part, and an example of the waveform of the AC current of each phase at the interconnection point is shown in the middle part. In FIG. 7, as in FIG. 5 and FIG. 6, an example of the change in the reactive power limit value Qlim, the reactive power Q of the interconnection point, and the active power P of the interconnection point is shown in the lower part in correspondence with the AC voltage and AC current waveforms shown in the upper part and the middle part of FIG. 7. In FIG. 7, the horizontal axis is also time t.

[0047] The AC voltages (A-phase AC voltage Va, B-phase AC voltage Vb, and C-phase AC voltage Vc) at the interconnection point shown in the upper part of Fig. 7 are similar to the AC voltages shown in the upper parts of Fig. 5 and Fig. 6. That is, the B-phase AC voltage Vb and the C-phase AC voltage Vc are each lower than the A-phase AC voltage Va. Therefore, in the third current control mode as well, similarly to the first current control mode and the second current control mode, the control device 20 assigns the value of the reactive power command value Q* to the value of the reactive power limit command value Qlim* (Qlim*=Q*) in step S3-1.

[0048] Then, in steps S4-1 and S4-2, the control device 20 calculates a positive-phase current command value Ip*, a positive-phase current phase command value Φp*, a negative-phase current command value In*, and a negative-phase current phase command value Φn*, and generates a control signal to control the operation of the power converter 10, in the third current control mode. At this time, in the third current control mode, the current values ​​of the three phases are controlled to be balanced. As a result, in the third current control mode, unlike the first current control mode and the second current control mode, the AC current at the interconnection point is in a balanced state (three-phase balanced state) for all three phases as shown in the middle part of FIG. 7. More specifically, in the third current control mode, the amplitudes of all of the A-phase AC current Ia, the B-phase AC current Ib, and the C-phase AC current Ic at the interconnection point are the entire width between the upper limit value (+Ilim) and the lower limit value (-Ilim) of the AC current upper and lower limit values ​​Ilim.

[0049] As a result, in the positive-phase / negative-phase current control of the third current control mode in the control device 20, the active power P at the interconnection point pulsates at twice the frequency of the AC voltage at the interconnection point while keeping the average value (time average value) of the power amount at zero, as shown in the lower part of Fig. 7. Furthermore, in the positive-phase / negative-phase current control of the third current control mode in the control device 20, the reactive power Q pulsates at twice the frequency of the AC voltage at the interconnection point while keeping the average value (time average value) of the power amount similar to the reactive power limit value Qlim.

[0050] Incidentally, the third current control mode is also a control mode that performs control equivalent to the positive-phase / negative-phase current control when the grid fault is a balanced fault. Therefore, in the power conversion device 1, the process of controlling the power converter 10 so as to output (supply) reactive power to the interconnection point when the grid fault is a balanced fault may be made common to the positive-phase / negative-phase current control by the third current control mode, or the control when the grid fault is a balanced fault may be performed instead of the third current control mode.

[0051] With such a configuration and processing, in the power conversion device 1, the control device 20 controls the operation of the power converter 10 based on the rated value (reactive power limit value Qlim) of the power converter 10 and the inputted set value (reactive power command value Q*), thereby making it possible to output (supply) reactive power to the interconnection point. Moreover, in the power conversion device 1, even if a system fault occurs in the power system 2, the control device 20 can perform positive-phase and negative-phase current control based on the AC voltage Vac detected by the voltage detector 30 and the AC current Iac detected by the current detector 40. In other words, in the power conversion device 1, the control device 20 controls to flow not only a positive-phase reactive current but also a reactive current superimposed with a negative-phase reactive current. As a result, in the power conversion device 1, not only during normal operation but also when a system fault (balanced fault and unbalanced fault) occurs in the power system 2, the reactive power can be adjusted and the operation of the power system 2 can be continued. Furthermore, in the power conversion device 1, the positive-phase and negative-phase current control when an unbalanced fault occurs can be switched according to the switching signal Mode. As a result, in the power conversion device 1, the operation of the power converter 10 is controlled using a control method suitable for the unbalanced fault that has occurred, and the amount of reactive power (reactive power amount) output (supplied) to the interconnection point can be controlled to the desired amount of power as commanded by the reactive power command value Q*.

[0052] In the power conversion device 1, the voltage detector 30 is disposed near the interconnection point and detects the AC voltage Vac supplied to the interconnection point. However, the voltage detector 30 may be disposed on the secondary side of the transformer 11 included in the power converter 10. In other words, the control device 20 may perform positive-phase / negative-phase current control using the AC voltage on the secondary side of the transformer 11 instead of the AC voltage Vac.

[0053] In the above-described reactive power supply methods in the current control modes (first current control mode, second current control mode, and third current control mode), a case where an unbalance fault occurs in phases B and C among three phases (phases A, B, and C) has been described. However, a system fault occurring in the power system 2 does not necessarily occur in phases B and C. For example, an unbalance fault may occur due to a system fault occurring in phases A and B, phases A and C, phases A only, phase B only, or phase C only. In this case, the positive-phase and negative-phase current control may be equivalent to the above-described positive-phase and negative-phase current control.

[0054] [Alternative configurations of power converters] In the power conversion device 1, the configuration of the power converter 10 is shown in Fig. 2 and Fig. 3 (converter 12). However, as described above, the transformer 11 and converter 12 included in the power converter 10 have a general configuration. In other words, various configurations are possible for the power converter 10. Below, an example of another configuration of the power converter 10 will be described. Figs. 8 to 10 are diagrams showing an example of another configuration of the power converter 10.

[0055] The power converter 10c shown in FIG. 8(a) has a configuration in which a modular multilevel converter (MMC) is applied as the converter 12. The power converter 10c includes, for example, a transformer 11a and a converter 12c. The converter 12c is a star-connected MMC. The power converter 10c has a configuration in which the converter 12 configured as a converter unit in the power converter 10a (see FIG. 2) is replaced with the converter 12c. Therefore, the transformer 11a included in the power converter 10c may be configured to have three single-phase transformers connected to each other, similar to the power converter 10a. The converter 12c includes, for example, three arms 124 (arms 124-1 to 124-3) and three buffer reactors (BR in the figure) 126 (buffer reactors 126-1 to 126-3) connected in series to the respective arms 124. The buffer reactor 126 is an impedance element for suppressing a change in the current flowing through the arm 124. Each arm 124 corresponds to each of the three phases. The arm 124 is configured, for example, by connecting a plurality of cells 125 (cell 125-1 to cell 125-n (n is a natural number)) in series. That is, the arm 124 is configured by a plurality of stages (n stages) of cells 125. Each of the cells 125 is a small-capacity converter. The cell 125 includes at least two or more semiconductor switching elements and a capacitor (DC capacitor). The semiconductor switching element included in the cell 125 is also, for example, an insulated gate bipolar transistor (IGBT), similar to the semiconductor switching elements included in the legs included in the converter 12 in the power converter 10a or the power converter 10b (see FIG. 2), that is, the leg 121 in the converter 12a and the leg 123 in the converter 12b shown in FIG. 3. In the converter 12c, each of the arms 124 is star-connected. The AC side terminals of each phase in the converter 12c are connected to the transformer 11a. The power converter 10c outputs an AC voltage from the converter 12c in response to the control of the control device 20 from the transformer 11a arranged on the AC side, thereby causing an AC current in response to the control of the control device 20 to flow.

[0056] The power converter 10d shown in FIG. 8(b) also has a configuration in which an MMC is applied as the converter 12. The power converter 10d includes, for example, a transformer 11a and a converter 12d. The converter 12d is a delta-connected MMC. The power converter 10d has a configuration in which the converter 12 configured as a converter unit in the power converter 10a (see FIG. 2) is replaced with the converter 12d. Therefore, the transformer 11a included in the power converter 10d may also be configured to have three single-phase transformers connected to each other, similar to the power converters 10a and 10c. The converter 12d includes, for example, three arms 124 (arms 124-1 to 124-3) corresponding to the respective phases of the three phases, and three buffer reactors 126 (buffer reactors 126-1 to 126-3) connected in series to the respective arms 124. In converter 12d, a series circuit of arm 124 and buffer reactor 126 is delta-connected. AC side terminals of each phase in converter 12d are also connected to transformer 11a. Power converter 10d outputs AC voltage from converter 12d in response to control from control device 20 from transformer 11a arranged on the AC side, thereby causing AC current in response to control from control device 20 to flow.

[0057] The power converter 10e shown in FIG. 9 is configured to use a single-phase transformer. The power converter 10e includes, for example, a transformer 11c and a converter 12e. The transformer 11c is configured to have, for example, three single-phase transformers connected to each other, or a three-winding transformer. The converter 12e includes, for example, three arms 124 (arms 124-1 to 124-3). Each arm 124 corresponds to each phase. Both ends of each arm 124 are connected to the converter side terminal of the corresponding phase in the transformer 11c. The power converter 10e outputs an AC voltage from the converter 12e in response to control from the control device 20 from the transformer 11c arranged on the AC side, thereby causing an AC current in response to control from the control device 20 to flow.

[0058] A power converter 10f shown in FIG. 10(a) also has a configuration in which an MMC is applied as the converter 12. The power converter 10f includes, for example, a transformer 11a and a converter 12f. The converter 12f is a double-star type MMC. The power converter 10f has a configuration in which the converter 12 configured as a converter unit in the power converter 10a (see FIG. 2) is replaced with the converter 12f. Therefore, the transformer 11a included in the power converter 10f may also have a configuration in which three single-phase transformers are connected to each other, similar to the power converter 10a. The converter 12f includes, for example, six arms 124 (arms 124-U-1 to 124-U-3 and arms 124-D-1 to 124-D-3), six buffer reactors 126 (buffer reactors 126-U-1 to 126-U-3 and buffer reactors 126-D-1 to 126-D-3), and a DC circuit 127. Each of the buffer reactors 126 is connected in series to the corresponding arm 124. The converter 12f includes the DC circuit 127, and is configured to be used in applications such as DC power transmission that require AC / DC conversion. In the converter 12f, for example, a series circuit of the arm 124-U and the buffer reactor 126-U is configured for the upper side (positive pole), and a series circuit of the arm 124-D and the buffer reactor 126-D is configured for the lower side (negative pole). In the converter 12f, one end (DC side terminal) of the arm 124-U on the side not connected to the buffer reactor 126-U in the upper series circuit is star-connected, and one end (DC side terminal) of the arm 124-D on the side not connected to the buffer reactor 126-D in the lower series circuit is star-connected, thereby forming a double star. In the converter 12f, the connection point of the star connection of the upper series circuit and the connection point of the star connection of the lower series circuit are each connected to the DC circuit 127. In the converter 12f, the connection point between the upper series circuit and the lower series circuit, that is, the connection point between the buffer reactor 126-U and the buffer reactor 126-D, is the AC side terminal of each phase. In the converter 12f, a pair of the upper series circuit and the lower series circuit is one leg, and each leg corresponds to each of the three phases. The AC terminals of each phase of converter 12f are connected to transformer 11a.The power converter 10f outputs an AC voltage from the converter 12f in response to control from the control device 20 from the transformer 11a arranged on the AC side, thereby causing an AC current in response to control from the control device 20 to flow.

[0059] A power converter 10g shown in FIG. 10(b) also has a configuration in which an MMC is applied as the converter 12. The power converter 10g includes, for example, a transformer 11c and a converter 12g. The converter 12g is also a double-star type MMC. The power converter 10g has a configuration in which the converter 12e included in the power converter 10e (see FIG. 9) is replaced with a converter 12g. The converter 12g includes, for example, three arms 124 (arms 124-U-1 to 124-U-3) for the upper side, three arms 124 (arms 124-D-1 to 124-D-3) for the lower side, and a DC circuit 127. Like the converter 12f included in the power converter 10f, the converter 12g also includes the DC circuit 127, and is used for applications such as DC power transmission that require AC-DC conversion. In the converter 12g, one end (DC side terminal) of the upper arm 124-U is star-connected, and one end (DC side terminal) of the lower arm 124-D is star-connected, thereby forming a double star. In the converter 12g, the connection point of the star connection of the upper series circuit and the connection point of the star connection of the lower series circuit are each connected to the DC circuit 127. In the converter 12g, the other end (AC side terminal) of the upper arm 124-U and the other end (AC side terminal) of the lower arm 124-D are each connected to the converter side terminal of the corresponding phase in the transformer 11c. In the converter 12g, a pair of the upper arm 124-U and the lower arm 124-D corresponds to each of the three phases. The power converter 10g outputs an AC voltage from a converter 12g in response to control from the control device 20 from a transformer 11a arranged on the AC side, thereby causing an AC current in response to control from the control device 20 to flow.

[0060] FIG. 11 is a diagram showing an example of the configuration of the cell 125 included in the converter 12. The cell 125a shown in FIG. 11(a) has a configuration to which a half bridge is applied. The cell 125a includes, for example, two semiconductor switch units 128 (semiconductor switch unit 128-1 and semiconductor switch unit 128-2) and one DC capacitor 122. The semiconductor switch unit 128 may be, for example, a semiconductor switching element, or may be configured such that a semiconductor switching element and a diode are connected in parallel to each other. In the cell 125a, the semiconductor switch unit 128-1 and the semiconductor switch unit 128-2 are connected in series, and the DC capacitor 122 is connected to both ends of the series. In the cell 125a, the connection point between the semiconductor switch unit 128-1 and the semiconductor switch unit 128-2 and one end of the semiconductor switch unit 128-2 are output terminals. That is, in the cell 125a, the midpoint and one end of the series circuit to which the two semiconductor switch units 128 are connected are output terminals. With this configuration, in the cell 125a, an output voltage with two voltage levels and a single polarity, either positive or negative, is output from the output terminal.

[0061] The cell 125b shown in FIG. 11B has a full-bridge configuration. The cell 125b includes, for example, four semiconductor switch units 128 (semiconductor switch units 128-1 to 128-4) and one DC capacitor 122. In the cell 125b, a series circuit in which the semiconductor switch unit 128-1 and the semiconductor switch unit 128-2 are connected in series and a series circuit in which the semiconductor switch unit 128-3 and the semiconductor switch unit 128-4 are connected in series are connected in parallel, and the DC capacitor 122 is connected to both ends of each series circuit. In the cell 125b, the midpoint of the series circuit in which the semiconductor switch unit 128-1 and the semiconductor switch unit 128-2 are connected and the midpoint of the series circuit in which the semiconductor switch unit 128-3 and the semiconductor switch unit 128-4 are connected are each an output terminal. With this configuration, in the cell 125b, output voltages with three voltage levels of both positive and negative polarities are output from the output terminal.

[0062] In the power conversion device 1, even if the power converter 10 has such a configuration, the control device 20 can perform positive-phase / negative-phase current control by controlling the operation of the power converter 10. In this case, the positive-phase / negative-phase current control of the control device 20 may be equivalent to the above-mentioned positive-phase / negative-phase current control. As a result, even if the power conversion device 1 includes a power converter 10 having a different configuration, not only during normal operation but also when a system fault (balanced fault or unbalanced fault) occurs in the power system 2, the power conversion device 1 can adjust reactive power using a control method suitable for the unbalanced fault that has occurred, and can continue the operation of the power system 2.

[0063] As described above, in the power conversion device of the embodiment, the control device controls the operation of the power converter based on the rated value (reactive power limit value) of the power converter and the inputted set value (reactive power command value). At this time, in the power conversion device of the embodiment, the control device performs positive-phase / negative-phase current control for outputting (supplying) reactive power to the interconnection point based on the AC voltage of the interconnection point detected by the voltage detector and the AC current of the interconnection point detected by the current detector. As a result, in the power conversion device of the embodiment, not only during normal operation but also when a system accident (balanced accident and unbalanced accident) occurs in the power system connected to the interconnection point, the amount of reactive power (reactive power amount) outputted (supplied) to the interconnection point can be adjusted (compensated) to a desired amount of power as commanded by the reactive power command value. Furthermore, in the power conversion device of the embodiment, the control device switches the control method of the power converter by positive-phase / negative-phase current control. As a result, the power conversion device of the embodiment can control the operation of the power converter using a control method suitable for a system fault that occurs in the power system to which the power conversion device is connected, and output (supply) a desired amount of reactive power to the interconnection point. As a result, the power conversion device of the embodiment can improve the continuity of operation of the power system when a system fault occurs.

[0064] According to at least one of the embodiments described above, a power converter (10) is provided that supplies reactive power (Q) to a connection point with a connected power system (2) or consumes reactive power, a control device (20) that controls the power converter, a voltage detector (30) that is installed on the AC side of the power converter and detects an AC voltage (Vac) at the connection point, and a current detector (40) that is installed on the AC side of the power converter and detects an AC current (Iac) at the connection point, and the control device detects a positive-phase AC voltage (Vp) and a negative-phase AC voltage (Vn) based on the AC voltage, and controls the output of a positive-phase AC current (Ip) and a negative-phase AC current (In) based on the positive-phase AC voltage and the negative-phase AC voltage, predetermined AC current upper and lower limits (Ilim) and a reactive power command value (Q*). This makes it possible to realize a power conversion device that can supply a desired amount of reactive power to the connection point even when an unbalanced accident occurs in the power system.

[0065] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0066] 1···Power converter, 2···Power system, 10, 10a, 10b, 10c, 10d, 10e, 10f, 10g··Power converter, 11, 11a, 11b, 11c··Transformer, 12, 12-1, 12-n, 12a, 12b, 12c, 12d, 12e, 12f, 12g··Converter, 121, 121-1, 121-2, 121-3, 123-1, 123-2, 123-3··Leg, 122, 122-1, 122-2··DC capacitor, 124, 124-1, 124-2, 124-3, 124-U, 124-U-1, 124-U-2, 124- U-3, 124-D, 124-D-1, 124-D-2, 124-D-3···arm, 125, 125-1, 125-n, 125a, 125b···cell, 126, 126-1, 126-2, 126-3, 126-U, 126-U-1, 126-U-2, 126-U-3, 126-D, 126-D-1, 126-D-2, 126-D-3···buffer reactor, 127···DC circuit, 128, 128-1, 128-2, 128-3, 128-4···semiconductor switch unit, 20···control device, 30···voltage detector, 40···current detector

Claims

1. a power converter that supplies reactive power to a point of interconnection with a connected power system or that consumes the reactive power; A control device that controls the power converter; a voltage detector that is installed on an AC side of the power converter and detects an AC voltage at the interconnection point; a current detector that is installed on an AC side of the power converter and detects an AC current at the interconnection point; Equipped with The control device includes: Detecting a positive-phase AC voltage and a negative-phase AC voltage based on the AC voltage; based on the positive-phase AC voltage and the negative-phase AC voltage, predetermined AC current upper and lower limits, and a predetermined reactive power command value, outputs of a positive-phase AC current and a negative-phase AC current, which are components of the AC current, are controlled so as to follow a positive-phase reactive current command value and a negative-phase reactive current command value obtained from the reactive power command value, respectively; Power conversion equipment.

2. The control device controls outputs of the positive-phase AC current and the negative-phase AC current so that the reactive power at the interconnection point coincides with the reactive power command value. The power conversion device according to claim 1 .

3. The control device controls the output of the positive-phase AC current and the negative-phase AC current so as to make the effective power at the interconnection point substantially zero. The power conversion device according to claim 1 or 2.

4. the control device controls the output of the positive-phase AC current and the negative-phase AC current so as to set the negative-phase AC current to zero and to output only the positive-phase AC current. The power conversion device according to claim 2 or 3.

5. the control device switches a control method for outputting the positive-phase AC current and the negative-phase AC current in response to an input switching signal. The power conversion device according to any one of claims 1 to 4.

6. The control device includes: When a system fault occurring in the power system is detected, an output of the positive-phase AC current and the negative-phase AC current is controlled. When the system fault is not detected, the AC current at the interconnection point is controlled so that the AC voltage follows an AC voltage command value. The power conversion device according to any one of claims 1 to 5.

7. The power converter includes: A transformer disposed on the AC side; A converter unit having an AC side terminal connected to the transformer; The power conversion device according to claim 1 , further comprising:

8. The power converter includes: A multiple transformer disposed on the AC side; At least two converter units each having an AC side terminal connected to the transformer; The power conversion device according to claim 1 , further comprising:

9. The converter unit comprises: Three legs each having at least two self-extinguishing semiconductor switching elements; A DC capacitor; Equipped with The DC side terminals of the legs are connected in parallel to each other, both ends of the DC capacitor are connected to the corresponding DC side terminals of each of the legs; The power converter includes: The AC side terminals of each of the legs are connected to the transformer. The power conversion device according to claim 7 or 8.

10. The converter unit comprises: Three legs each including at least two or more self-extinguishing semiconductor switching elements and a semiconductor switching element or a diode connected to a midpoint of the semiconductor switching elements to form a neutral point; Two DC capacitors, Equipped with The DC side terminals of the legs are connected in parallel to each other, the neutral terminals of the legs are connected in parallel with each other; one end of each of the DC capacitors is connected to the DC side terminal of a corresponding one of the legs; the other end of the DC capacitor is connected to the neutral terminal of each of the legs; The power converter includes: The AC side terminals of each of the legs are connected to the transformer. The power conversion device according to claim 7 or 8.

11. The power converter includes: A transformer disposed on the AC side; three arms, at least one end of which is connected to the transformer; Equipped with Each of the arms includes a plurality of cells connected in series, the cells including at least two or more semiconductor switching elements and a capacitor. The power conversion device according to any one of claims 1 to 6.

12. The power converter includes: A transformer disposed on the AC side; Three legs each having an AC side terminal connected to the transformer and a DC side terminal connected in parallel to each other; a DC circuit having both ends connected to the DC side terminals corresponding to each of the legs; Equipped with Each of the legs comprises: The power supply comprises two series circuits in which an arm is connected in series with a plurality of cells, each cell including at least two semiconductor switching elements and a capacitor, and an impedance element is connected in series, In the series circuit, one end of the cell on a side to which the impedance element is not connected among the plurality of cells included in the arm is the DC side terminal, and a connection point at which the impedance elements included in each of the series circuits are connected to each other is the AC side terminal, Each of the AC side terminals is connected to the transformer. The power conversion device according to any one of claims 1 to 6.

13. The power converter includes: A transformer disposed on the AC side; Six arms, at least one end of which is connected to the transformer; a DC circuit, both ends of which are connected to the corresponding other ends of each of the arms; Equipped with Each of the arms comprises: A plurality of cells each including at least two semiconductor switching elements and a capacitor are connected in series, The one end of each is connected to the transformer. The power conversion device according to any one of claims 1 to 6.

14. a power converter that supplies reactive power to a point of interconnection with a connected power system or that consumes the reactive power; A control device that controls the power converter; a voltage detector that is installed on an AC side of the power converter and detects an AC voltage at the interconnection point; A control method for a power conversion device including: a current detector that is installed on an AC side of the power converter and detects an AC current at the interconnection point, The computer of the control device Detecting a positive-phase AC voltage and a negative-phase AC voltage based on the AC voltage; based on the positive-phase AC voltage and the negative-phase AC voltage, predetermined AC current upper and lower limits, and a predetermined reactive power command value, outputs of a positive-phase AC current and a negative-phase AC current, which are components of the AC current, are controlled so as to follow a positive-phase reactive current command value and a negative-phase reactive current command value obtained from the reactive power command value, respectively; A method for controlling a power conversion device.

15. a power converter that supplies reactive power to a point of interconnection with a connected power system or that consumes the reactive power; A control device that controls the power converter; a voltage detector that is installed on an AC side of the power converter and detects an AC voltage at the interconnection point; A program for controlling a power conversion device including a current detector that is installed on an AC side of the power converter and detects an AC current at the interconnection point, The computer of the control device detecting a positive-phase AC voltage and a negative-phase AC voltage based on the AC voltage; based on the positive-phase AC voltage and the negative-phase AC voltage, predetermined AC current upper and lower limits, and a predetermined reactive power command value, outputs of a positive-phase AC current and a negative-phase AC current, which are components of the AC current, are controlled so as to follow a positive-phase reactive current command value and a negative-phase reactive current command value obtained from the reactive power command value, respectively; program.

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