Power conditioner and power control method

Abstract

This power conditioner includes an inverter that converts DC power into AC power and supplies the AC power to a power system, and a control device that controls the inverter. The control device estimates the system voltage on the basis of the output current of the inverter and the characteristics of the impedance between the inverter and the power system. Moreover, the control device generates a correction voltage on the basis of a voltage obtained by removing the high-frequency component from a differential voltage which is the difference between the estimated system voltage and a target voltage. Furthermore, the control device issues an instruction to the inverter on the basis of the voltage obtained by adding the correction voltage to the target voltage.

Description

Power conditioner and power control method

[0001] The present disclosure relates to a technique for controlling a power conditioner.

[0002] Patent Document 1 discloses a power conditioner. Specifically, when the power conditioner detects an overcurrent in which the inverter output current exceeds an allowable current value during an independent operation mode, the power conditioner performs control to change the phase of the inverter output voltage so that the inverter output voltage approaches 0 V.

[0003] Japanese Patent Publication No. 2022-019159

[0004] Consider the case where a power grid fault occurs. If the power conditioner (specifically, the inverter) detects an overcurrent in its output current and stops outputting the inverter, the load on the power grid cannot continue to operate.

[0005] One object of the present disclosure is to provide a technology that can prevent the output current of an inverter from becoming an overcurrent state in the event of a grid fault.

[0006] A first aspect of the present disclosure relates to a power conditioner. The power conditioner includes an inverter that converts DC power into AC power and supplies the AC power to a power grid, and a control device that controls the inverter. The control device estimates a grid voltage based on an output current of the inverter and characteristics of the impedance between the inverter and the power grid. The control device also generates a correction voltage based on a voltage obtained by removing high-frequency components from a differential voltage, which is the difference between the estimated grid voltage and a target voltage. The control device also issues an instruction to the inverter based on a voltage obtained by adding the correction voltage to the target voltage.

[0007] A second aspect of the present disclosure relates to a power control method, which includes: converting DC power into AC power using an inverter and supplying the AC power to a power grid; estimating a grid voltage based on characteristics of an output current of the inverter and an impedance between the inverter and the power grid; generating a correction voltage based on a voltage obtained by removing high-frequency components from a differential voltage that is a difference between the estimated grid voltage and a target voltage; and issuing an instruction to the inverter based on a voltage obtained by adding the correction voltage to the target voltage.

[0008] According to the present disclosure, a grid voltage is estimated based on the output current of an inverter and the characteristics of the impedance between the inverter and the power grid. A correction voltage is then generated based on a voltage obtained by removing high-frequency components from a differential voltage, which is the difference between the estimated grid voltage and a target voltage. Furthermore, an instruction is issued to the inverter based on a voltage obtained by adding the correction voltage to the target voltage. This prevents the inverter's output current from becoming an overcurrent state, allowing AC power to be continuously supplied to the power grid. This makes it possible to stabilize the power grid.

[0009] FIG. 1 is a diagram for explaining an overview of a power conversion system. FIG. 2 is a block diagram showing an example of the functions of a control device. FIG. 3 is a flowchart showing an example of the processing of the control device. FIG. 4 is an explanatory diagram showing an example of the output result of an inverter when a disturbance observer is not applied. FIG. 5 is an explanatory diagram showing an example of the output result of an inverter when a disturbance observer is applied. FIG. 6 is a block diagram showing an example of the functions of a control device according to another embodiment. FIG. 7 is a flowchart showing an example of the processing of a control device according to another embodiment.

[0010] A power conditioner and a power control method according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. Elements common to the drawings will be designated by the same reference numerals, and duplicated descriptions will be omitted.

[0011] 1. Overview of the Power Conversion System Fig. 1 is a diagram for explaining an overview of a power conversion system 1. The power conversion system 1 includes a battery 11, a power conditioner 10, a transformer 20, and a power grid 30. The power conditioner 10 includes an inverter 12 and a control device 100.

[0012] The battery 11 is an electricity storage device that stores electricity generated by renewable energy, such as solar power, wind power, and hydropower.

[0013] The inverter 12 is a device that converts DC power output from the battery 11 into AC power and supplies the AC power to the power grid 30 via a transformer 20. Examples of the inverter 12 include a current-controlled grid-following (GFL) inverter and a voltage-controlled grid-forming (GFM) inverter.

[0014] The control device 100 is connected to the inverter 12 and controls the inverter 12. The control device 100 receives the output voltage Vs (also referred to as the system voltage Vs) and the output current Io output from the inverter 12. The output voltage Vs and the output current Io input to the control device 100 are the detected values ​​of the output voltage Vs (hereinafter referred to as the detected Vs value) and the output current Io (hereinafter referred to as the detected Io value). The detected Vs value and the detected Io value are detected by a detector (not shown) provided between the power conditioner 10 and the power system 30. In the example shown in FIG. 1 , the detected Vs value and the detected Io value are detected between the power conditioner 10 and the transformer 20. However, this is not limiting. The detected Vs value and the detected Io value may be detected, for example, between the transformer 20 and the power system 30.

[0015] Furthermore, the output voltage Vs output from the inverter 12 is made up of three-phase voltages (Vsu, Vsv, Vsw), and the output current Io output from the inverter 12 is made up of three-phase currents (Iou, Iov, Iow). That is, the above-mentioned Vs detection value includes the Vsu detection value, the Vsv detection value, and the Vsw detection value, and the above-mentioned Io detection value includes the Iou detection value, the Iov detection value, and the Iow detection value.

[0016] The control device 100 includes a power control unit 110 and a current control unit 120. The power control unit 110 calculates the AC power output from the inverter 12 based on the input Vs detection value and Io detection value. The power control unit 110 then calculates a current command (also referred to as a target current) for the inverter 12 based on the AC power. An example of calculating the target current will be described in detail later.

[0017] The current control unit 120 calculates a voltage command (also referred to as a target voltage) for the inverter 12 based on the target current and the Io detection value obtained by the power control unit 110. An example of calculating the target voltage will be described in detail later.

[0018] The control device 100 may calculate the voltage command for the inverter 12 based on VSG (Virtual Synchronous Generator) control. A VSG is a virtual synchronous generator that simulates the dynamic characteristics of a synchronous generator in the inverter 12. In other words, VSG control means controlling a virtual synchronous generator.

[0019] The control device 100 issues an instruction ins to the inverter 12 so as to bring the output voltage Vs of the inverter 12 closer to the target voltage, based on the voltage instruction obtained by the current control unit 120. The instruction ins may be a voltage instruction or a current instruction.

[0020] Here, consider that during a grid fault, a disturbance voltage Vdis caused by a disturbance is included in the output voltage Vs (grid voltage Vs) of the inverter 12. The disturbance voltage Vdis is a disturbance that cannot be observed in the Vs detection value, for example, a voltage that causes the grid voltage Vs to momentarily rise. In this case, it is assumed that the output current Io becomes an overcurrent state. As a result, the power conditioner 10 activates an overcurrent trip function to prevent AC power from being supplied to the power grid 30, for example, to protect the inverter 12. The overcurrent trip function, for example, opens (turns off) a circuit breaker (not shown) provided on the output side of the inverter 12 when the output current Io of the inverter 12 is equal to or greater than a reference current value. This prevents AC power from being supplied to the power grid 30.

[0021] However, even in the event of a grid fault, it is required to supply stable AC power to the power grid 30. For example, this is the case when the power conditioner 10 is required to have a low voltage ride-through (LVRT) function. The LVRT is a function that, when an instantaneous voltage drop occurs due to a grid fault, maintains the output current Io before the grid fault occurred to minimize the impact on the power grid 30, as long as the magnitude and duration of the voltage drop do not satisfy an output stop condition.

[0022] The control device 100 further executes a disturbance observer control unit 140. The disturbance observer control unit 140 generates a correction voltage for canceling out a disturbance voltage Vdis included in the system voltage Vs. The control device 100 then issues a command ins to the inverter 12 based on a voltage obtained by adding the correction voltage obtained by the disturbance observer control unit 140 to a target voltage. This prevents the output current Io of the inverter 12 from becoming an overcurrent state, thereby enabling AC power to be continuously supplied to the power system 30. This makes it possible to stabilize the power system. Details of the disturbance observer control unit 140 will be described later.

[0023] 2. Examples of Control Devices 2-1. Configuration Examples The control device 100 has hardware that realizes various functions. The hardware includes a processing circuit capable of high-speed calculations. Examples of the processing circuit include an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). In addition to the processing circuit, the hardware may also include a computing unit (e.g., a CPU or a GPU) that executes a program stored in a storage device.

[0024] 2-2. Functional Example FIG. 2 is a block diagram showing a functional example of the control device 100 according to the embodiment. The control device 100 executes a power control unit 110. The power control unit 110 calculates actual measured values ​​of active power and reactive power based on the detected Vs value and the detected Io value. Then, based on the actual measured value of active power and the target value of active power, the power control unit 110 performs control (also referred to as APR (Automatic Power Regulator) control) so that the actual measured value of active power becomes the target value of active power. Furthermore, based on the actual measured value of reactive power and the target value of reactive power, the power control unit 110 performs control (also referred to as AQR (Automatic Reactive Power Regulator) control) so that the actual measured value of reactive power becomes the target value of reactive power. The power control unit 110 calculates a target current Iref based on the target value of active current obtained by APR control and the target value of reactive current obtained by AQR control.

[0025] The Vs detection value input to the power control unit 110 may be acquired, for example, via a PLL (Phase Locked Loop) provided in the control device 100. The PLL is a circuit that synchronizes the phase of an input voltage signal with that of an output voltage signal. This allows the Vs detection value to be synchronized with the phase of the output voltage Vs of the inverter 12, thereby properly connecting the inverter 12 with the power grid 30.

[0026] After executing the power control unit 110, the control device 100 executes the current control unit 120. Based on a differential current ΔI, which is the difference between the target current Iref obtained by the power control unit 110 and the detected Io value, the current control unit 120 performs control (also referred to as ACR (Automatic Current Regulator) control) so that the differential current ΔI becomes the target current Iref. The ACR control is a constant current control that performs feedback control of PI control including proportional action and integral action. In the ACR control, the current control unit 120 outputs a target voltage Vref.

[0027] After executing the current control unit 120, the control device 100 executes the output control unit 130. The output control unit 130 generates three-phase voltages (Vsu, Vsv, Vsw) and performs PWM control, which performs pulse width modulation on each of the three-phase voltages. The control device 100 then outputs an instruction "ins" generated by the PWM control to the inverter 12.

[0028] The output control unit 130 receives a voltage obtained by adding the target voltage Vref and the Vs detection value. The voltage received by the output control unit 130 may be changed depending on whether a grid fault occurs. For example, the output control unit 130 may receive a voltage obtained by adding the target voltage Vref and the Vs detection value when a grid fault occurs, and may receive either the target voltage Vref or the Vs detection value when no grid fault occurs.

[0029] After executing the current control unit 120, the control device 100 executes the disturbance observer control unit 140. The disturbance observer control unit 140 includes a Vs estimating unit 141, a noise removing unit 142, and a correction voltage calculating unit 143.

[0030] The Vs estimator 141 estimates the system voltage Vs based on the Io detection value and the characteristics of the impedance between the inverter 12 and the power system 30. The estimated system voltage Vs is referred to as the estimated system voltage Vse. The impedance includes the inductance L of the reactor shown in FIG. 1. The estimated system voltage Vse is estimated by multiplying the Io detection value by a predetermined constant. The predetermined constant is a value obtained by multiplying the angular frequency ω by the inductance L. In other words, the predetermined constant is expressed as ωL (=2πfL), where f is 50 Hz or 60 Hz. This makes it possible to estimate the voltage when the output current Io flows through the reactor without using a sensor.

[0031] The noise removal unit 142 removes high-frequency components from the differential voltage ΔVdis, which is the difference between the estimated system voltage Vse obtained by the Vs estimation unit 141 and the target voltage Vref obtained by the current control unit 120. A low-pass filter (LPF) is used to remove the high-frequency components from the differential voltage ΔVdis. When a system fault occurs and the system voltage Vs includes a disturbance voltage Vdis, the differential voltage ΔVdis is estimated to be the disturbance voltage Vdis.

[0032] The correction voltage calculation unit 143 generates the correction voltage Vdisc based on the voltage obtained by removing high-frequency components from the differential voltage ΔVdis. Specifically, the correction voltage calculation unit 143 controls the voltage obtained by removing high-frequency components from the differential voltage ΔVdis so that it stays within a target range. This control may be, for example, feedback control of P control including proportional operation. Note that the disturbance observer control unit 140 may be enabled only when a grid fault occurs.

[0033] The control device 100 then executes a process (disturbance compensation) of adding the correction voltage Vdisc obtained by the disturbance observer control unit 140 to the target voltage Vref. As a result, when a grid fault occurs, the disturbance voltage Vdis included in the estimated grid voltage Vse is suppressed by the correction voltage Vdisc. This prevents the output current Io of the inverter 12 from becoming an overcurrent state, allowing AC power to be continuously supplied to the power grid 30. This makes it possible to stabilize the power grid 30.

[0034] 3 is a flowchart showing a processing example of the control device 100 according to the embodiment. Specifically, FIG. 3 shows an outline of an example of disturbance compensation control for compensating for the disturbance voltage Vdis.

[0035] In step S100, the control device 100 estimates the system voltage Vs, i.e., calculates the estimated system voltage Vse, based on the detected Io value and the characteristics of the impedance between the inverter 12 and the power system 30. Thereafter, the process proceeds to step S101.

[0036] In step S101, the control device 100 calculates a differential voltage ΔVdis, which is the difference between the estimated grid voltage Vse and the target voltage Vref. Then, the process proceeds to step S102. When a grid fault occurs and the grid voltage Vs includes a disturbance voltage Vdis, the differential voltage ΔVdis is estimated to be the disturbance voltage Vdis.

[0037] In step S102, the control device 100 removes high frequency components from the differential voltage ΔVdis, and then the process proceeds to step S103.

[0038] In step S103, the control device 100 calculates the correction voltage Vdisc based on the voltage obtained by removing the high frequency components from the differential voltage ΔVdis, and then the process proceeds to step S104.

[0039] In step S104, the control device 100 executes a process (disturbance compensation) of adding the correction voltage Vdisc to the target voltage Vref.

[0040] 3. Example of inverter output result Fig. 4 is an explanatory diagram showing an example of the output result of the inverter 12 when a grid fault occurs and the disturbance observer control unit 140 is not applied. On the other hand, Fig. 5 is an explanatory diagram showing an example of the output result of the inverter 12 when a grid fault occurs and the disturbance observer control unit 140 is applied.

[0041] (A) in FIG. 4 and (A) in FIG. 5 show examples of waveforms of the Vs detection value. (B) in FIG. 4 and (B) in FIG. 5 show examples of waveforms of the Io detection value. (C) in FIG. 4 and (C) in FIG. 5 show examples of waveforms of the correction voltage Vdisc. Note that the waveforms of the Vs detection value and the Io detection value in FIG. 4 and FIG. 5 indicate one of the three phases (U, V, W). The vertical axes of the graphs shown in FIG. 4 and FIG. 5 are expressed in PU (Per Unit). However, this is not limiting. The vertical axes of the graphs shown in FIG. 4 and FIG. 5 may also represent PU as a percentage.

[0042] When the disturbance observer control unit 140 is not applied, the correction voltage Vdisc remains at "0PU" and is not generated around the time when the grid fault occurs and around the time when the grid recovers from the fault, as shown in (C) of Fig. 4. On the other hand, when the disturbance observer control unit 140 is applied, the correction voltage Vdisc for canceling out the disturbance voltage Vdis is generated around the time when the grid fault occurs, as shown in (C) of Fig. 5. Furthermore, when the Vs detection value is smaller than the target voltage Vref around the time when the grid recovers from the fault, the correction voltage Vdisc for canceling out the undervoltage, which is the difference between the Vs detection value and the target voltage Vref, is generated as shown in (C) of Fig. 5.

[0043] In the examples shown in (B) of Figure 4 and (B) of Figure 5, when a grid fault occurs, the peak value of the Io detection value when the disturbance observer control unit 140 is applied is lower than when the disturbance observer control unit 140 is not applied. In other words, by applying the disturbance observer control unit 140 when a grid fault occurs, it is possible to suppress an overcurrent in the output current Io of the inverter 12. Therefore, the inverter 12 can continue to supply AC power to the power grid 30, and it is possible to minimize the impact on the power grid 30.

[0044] 4. Effects According to the power conditioner 10 of this embodiment, the system voltage Vs is estimated based on the output current Io of the inverter 12 and the characteristics of the impedance between the inverter 12 and the power grid 30. Then, a correction voltage Vdisc is generated based on a voltage obtained by removing high-frequency components from a differential voltage ΔVdis, which is the difference between the estimated system voltage Vs (estimated system voltage Vse) and a target voltage Vref. Furthermore, a command ins is issued to the inverter 12 based on a voltage obtained by adding the correction voltage Vdisc to the target voltage Vref. This prevents the output current Io of the inverter 12 from becoming an overcurrent state, allowing AC power to be continuously supplied to the power grid 30. This makes it possible to stabilize the power grid.

[0045] 6 is a block diagram showing an example of functions of a control device 100 according to another embodiment. The difference from the control device 100 according to the above-described embodiment is the presence or absence of a threshold determination unit 144 in the disturbance observer control unit 140.

[0046] In the control device 100 according to another embodiment, the disturbance observer control unit 140 includes a threshold determination unit 144. Specifically, the threshold determination unit 144 determines whether the correction voltage Vdisc obtained by the correction voltage calculation unit 143 satisfies a threshold condition. If it is determined that the correction voltage Vdisc satisfies the threshold condition, the threshold determination unit 144 outputs the correction voltage Vdisc. On the other hand, if it is determined that the correction voltage Vdisc does not satisfy the threshold condition, the threshold determination unit 144 does not output the correction voltage Vdisc.

[0047] The threshold condition includes that the absolute value of the correction voltage Vdisc is equal to or greater than a threshold, or that the absolute value of the voltage obtained by removing low-frequency components from the correction voltage Vdisc is equal to or greater than a threshold. A high-pass filter (HPF) is used to remove the low-frequency components from the correction voltage Vdisc.

[0048] Fig. 7 is a flowchart showing an example of processing by a control device according to another embodiment. Only the parts that differ from Fig. 3 will be explained here. Specifically, S200 to S203 and S205 are the same as S100 to S104 described above, and therefore their explanation will be omitted.

[0049] In step S204, the control device 100 determines whether the correction voltage Vdisc is equal to or greater than the threshold value. If it is determined that the correction voltage Vdisc is equal to or greater than the threshold value (step S204; Yes), the process proceeds to step S205. Otherwise (step S204; No), the process ends.

[0050] According to the control device 100 of the other embodiment, the disturbance observer control unit 140 includes a threshold determination unit 144. When the correction voltage Vdisc satisfies the threshold condition, the threshold determination unit 144 outputs the correction voltage Vdisc. As a result, the disturbance voltage Vdis contained in the estimated system voltage Vse and exceeding a certain level is suppressed by the correction voltage Vdisc. In this case, the same effects as those of the above-described embodiment can be obtained.

[0051] REFERENCE SIGNS LIST 1... power conversion system, 10... power conditioner, 11... battery, 12... inverter, 20... transformer, 30... power system, 100... control device, 110... power control unit, 120... current control unit, 130... output control unit, 140... disturbance observer control unit

Claims

1. an inverter that converts DC power into AC power and supplies the AC power to a power grid; a control device that controls the inverter; Equipped with The control device Estimating a grid voltage based on an output current of the inverter and characteristics of an impedance between the inverter and the power grid; generating a correction voltage based on a voltage obtained by removing high-frequency components from a differential voltage, which is a difference between the estimated grid voltage and a target voltage; An instruction is issued to the inverter based on a voltage obtained by adding the correction voltage to the target voltage. It was configured as A power conditioner characterized by the above.

2. The power conditioner according to claim 1, In the process of outputting the instruction to the inverter, the control device determining whether the correction voltage satisfies a threshold condition; When it is determined that the correction voltage satisfies the threshold condition, the instruction is issued to the inverter based on a voltage obtained by adding the correction voltage to the target voltage. A power conditioner characterized by the above.

3. The power conditioner according to claim 2, The threshold condition includes that the absolute value of the correction voltage is equal to or greater than a threshold, or that the absolute value of the voltage obtained by removing low-frequency components from the correction voltage is equal to or greater than a threshold. A power conditioner characterized by the above.

4. The power conditioner according to claim 1, The target voltage is a voltage obtained by controlling the differential current, which is the difference between the target current and the output current of the inverter, to be the target current. A power conditioner characterized by the above.

5. The power conditioner according to claim 1, The correction voltage is a voltage obtained by removing high frequency components from the differential voltage and controlling the voltage to stay within a target range. A power conditioner characterized by the above.

6. The power conditioner according to claim 1, The impedance includes the inductance of a reactor, The estimated system voltage is estimated by multiplying the output current of the inverter by a predetermined constant. A power conditioner characterized by the above.

7. The power conditioner according to claim 6, The predetermined constant is a value obtained by multiplying the angular frequency by the inductance. A power conditioner characterized by the above.

8. converting DC power into AC power using an inverter and supplying the AC power to a power grid; estimating a grid voltage based on characteristics of an output current of the inverter and an impedance between the inverter and the power grid; generating a correction voltage based on a voltage obtained by removing high frequency components from a differential voltage, which is a difference between the estimated grid voltage and a target voltage; issuing an instruction to the inverter based on a voltage obtained by adding the correction voltage to the target voltage; Contains A power control method comprising: