Power conditioner and power control method

Abstract

A power conditioner is provided with 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. The control device generates a correction voltage on the basis of a voltage obtained by removing a high-frequency component of a differential voltage, which is the difference between the estimated system voltage and the target voltage. Furthermore, the control device instructs the inverter on the basis of a voltage obtained by adding the correction voltage to the target voltage.

Description

Technical Field

[0001] The present disclosure relates to techniques for controlling a power regulator. Background Art

[0002] Patent Document 1 discloses a power conditioner that, when detecting an overcurrent exceeding an allowable current value in the output current of an inverter in a standalone operation mode, controls the phase of the output voltage to change so that the output voltage of the inverter approaches 0V.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-019159 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] Consider a case where a power system failure occurs and an overcurrent is detected in the output current of a power conditioner (specifically, an inverter) and the inverter output is stopped, causing the load of the power system to be unable to continue operating.

[0008] One object of the present disclosure is to provide a technology capable of suppressing an output current of an inverter from becoming an overcurrent state during a power system failure.

[0009] Means for solving problems

[0010] The 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 system, and a control device that controls the inverter. The control device estimates the system voltage based on the output current of the inverter and the impedance characteristics between the inverter and the power system. Furthermore, the control device generates a correction voltage based on the difference between the estimated system voltage and a target voltage, i.e., the voltage obtained by removing the high-frequency components of the differential voltage. Furthermore, the control device issues an instruction to the inverter based on the voltage obtained by adding the correction voltage to the target voltage.

[0011] A second aspect of the present disclosure relates to a power control method. The power control method includes: using an inverter to convert DC power into AC power and supplying the AC power to a power system; estimating the system voltage based on the output current of the inverter and the impedance characteristics between the inverter and the power system; generating a correction voltage based on the difference between the estimated system voltage and a target voltage, i.e., the voltage after removing the high-frequency component of the differential voltage; and issuing an instruction to the inverter based on the voltage obtained by adding the correction voltage to the target voltage.

[0012] Effects of the Invention

[0013] According to the present disclosure, the system voltage is estimated based on the inverter's output current and the impedance characteristics between the inverter and the power system. Furthermore, a correction voltage is generated based on the difference between the estimated system voltage and the target voltage, i.e., the voltage obtained by removing the high-frequency components of the differential voltage. Furthermore, an instruction is issued to the inverter based on the voltage obtained by adding the correction voltage to the target voltage. This prevents the inverter's output current from reaching an overcurrent state, allowing AC power to continue to be supplied to the power system. Consequently, the power system can be stabilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram for explaining the outline of a power conversion system.

[0015] Figure 2 This is a block diagram showing a functional example of a control device.

[0016] Figure 3 This is a flowchart showing an example of processing performed by the control device.

[0017] Figure 4 This is an explanatory diagram showing an example of an inverter output result when the disturbance observer is not applied.

[0018] Figure 5 It is an explanatory diagram showing an example of an output result of an inverter when a disturbance observer is applied.

[0019] Figure 6 This is a block diagram showing a functional example of a control device according to another embodiment.

[0020] Figure 7 This is a flowchart showing a processing example of a control device according to another embodiment. DETAILED DESCRIPTION

[0021] The power conditioner and the power control method according to the embodiment of the present disclosure will be described with reference to the accompanying drawings. Elements common to the various drawings are denoted by the same reference numerals, and duplicate descriptions will be omitted.

[0022] 1. Overview of Power Conversion System

[0023] Figure 1 1 is a diagram for explaining the outline 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 system 30. The power conditioner 10 includes an inverter 12 and a control device 100.

[0024] The battery 11 is a power storage device that stores electricity generated by renewable energy. Examples of renewable energy include sunlight, wind power, and water power.

[0025] The inverter 12 converts DC power output from the battery 11 into AC power and supplies the AC power to the power grid 30 via the transformer 20. Examples of the inverter 12 include a current-controlled GFL (Grid Following) inverter and a voltage-controlled GFM (Grid Forming) inverter.

[0026] The control device 100 is connected to the inverter 12 and controls the inverter 12. The output voltage Vs (also referred to as the system voltage Vs) and the output current Io output from the inverter 12 are input to the control device 100. In addition, the output voltage Vs and the output current Io input to the control device 100 are the detection value of the output voltage Vs (hereinafter referred to as the Vs detection value) and the detection value of the output current Io (hereinafter referred to as the Io detection value). The Vs detection value and the Io detection value are detected by a detector (not shown) provided between the power conditioner 10 and the power system 30. Figure 1 In the example shown, the Vs detection value and the Io detection value are detected between the power conditioner 10 and the transformer 20. However, this is not limiting. The Vs detection value and the Io detection value may also be detected between the transformer 20 and the power system 30, for example.

[0027] Furthermore, the output voltage Vs output from the inverter 12 is composed of three-phase voltages (Vsu, Vsv, Vsw), and the output current Io output from the inverter 12 is composed of three-phase currents (Iou, Iov, Iow). Specifically, the Vs detection value includes the Vsu detection value, the Vsv detection value, and the Vsw detection value, and the Io detection value includes the Iou detection value, the Iov detection value, and the Iow detection value.

[0028] Control device 100 includes a power control unit 110 and a current control unit 120. Power control unit 110 calculates the AC power to be output from inverter 12 based on the input Vs and Io detection values. Power control unit 110 then calculates a current command (also called a target current) for inverter 12 based on the AC power. Details of an example of target current calculation will be described later.

[0029] 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. Details of an example of calculation of the target voltage will be described later.

[0030] Furthermore, control device 100 may calculate a voltage command for 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 inverter 12. In other words, VSG control refers to controlling a virtual synchronous generator.

[0031] The control device 100 issues an instruction ins to the inverter 12 based on the voltage command obtained by the current control unit 120 so that the output voltage Vs of the inverter 12 approaches the target voltage. The instruction ins may be a voltage instruction or a current instruction.

[0032] Here, in the event of a system accident, it is considered that the interference voltage Vdis caused by the interference is included in the output voltage Vs of the inverter 12 (system voltage Vs). The interference voltage Vdis is an interference that cannot be observed in the Vs detection value, etc., for example, it is a voltage that instantly rises in the system voltage Vs. In this case, it is assumed that the output current Io becomes an overcurrent state. Therefore, the power conditioner 10 operates the overcurrent tripping function in a manner that does not supply AC power to the power system 30 for the purpose of protecting the inverter 12. The overcurrent tripping function, for example, disconnects (OFF) the circuit breaker (not shown) provided on the output side of the inverter 12 when the output current Io of the inverter 12 is greater than the reference current value. As a result, AC power is not supplied to the power system 30.

[0033] However, even in the event of a system failure, stable AC power is required to be supplied to the power system 30. For example, the power conditioner 10 is required to have an LVRT (Low Voltage Ride Through) function. LVRT is a function that minimizes the impact on the power system 30 by maintaining the output current Io at the level before the system failure, as long as the magnitude and duration of the voltage drop do not meet the output stop conditions, when a system failure causes a momentary voltage drop.

[0034] The control device 100 also executes a disturbance observer control unit 140. This unit generates a correction voltage for canceling the disturbance voltage Vdis included in the system voltage Vs. The control device 100 then issues an instruction ins to the inverter 12 based on the voltage obtained by adding the correction voltage generated by the disturbance observer control unit 140 to the target voltage. This prevents the output current Io of the inverter 12 from becoming overcurrent, allowing AC power to continue to be supplied to the power system 30. Consequently, the power system can be stabilized. The details of the disturbance observer control unit 140 will be described later.

[0035] 2. Examples of control devices

[0036] 2-1. Structural example

[0037] The control device 100 includes hardware that implements various functions. The hardware includes a processing circuit capable of high-speed computing. Examples of processing circuits include FPGAs (Field Programmable Gate Arrays) and ASICs (Application Specific Integrated Circuits). In addition to the processing circuits, the hardware may also include a computing unit (e.g., a CPU or GPU) that executes programs stored in a storage device.

[0038] 2-2. Function Example

[0039] Figure 2 : This is a block diagram showing a functional example of the control device 100 according to the embodiment. The control device 100 executes the power control unit 110. The power control unit 110 calculates the measured value of active power and the measured value of reactive power based on the Vs detection value and the Io detection value. Then, the power control unit 110 performs control (also called APR (Automatic Power Regulator) control) based on the measured value of active power and the target value of active power so that the measured value of active power becomes the target value of active power. In addition, the power control unit 110 performs control (also called AQR (Automatic Reactive Power Regulator) control) based on the measured value of reactive power and the target value of reactive power so that the measured value of reactive power becomes the target value of reactive power. The power control unit 110 calculates the 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.

[0040] The Vs detection value input to the power control unit 110 can also be obtained via, for example, a PLL (Phase Locked Loop) provided in the control device 100. A PLL is a circuit that synchronizes the phases of the input voltage signal and the output voltage signal. This allows the Vs detection value to be synchronized with the phase of the output voltage Vs of the inverter 12, allowing the inverter 12 to be properly interconnected with the power system 30.

[0041] After power control unit 110 executes, control device 100 executes current control unit 120. Based on the differential current ΔI, the difference between the target current Iref and the detected value Io obtained by power control unit 110, current control unit 120 performs control (also known as ACR (Automatic Current Regulator) control) so that differential current ΔI reaches the target current Iref. ACR control is constant current control, performing feedback control using PI control, which includes proportional and integral actions. During ACR control, current control unit 120 outputs a target voltage Vref.

[0042] After executing current control unit 120, control device 100 executes output control unit 130. Output control unit 130 generates three-phase voltages (Vsu, Vsv, Vsw) and performs PWM control to pulse-width modulate each of the three-phase voltages. Control device 100 then outputs instruction ins generated by PWM control to inverter 12.

[0043] Furthermore, a voltage obtained by adding the target voltage Vref and the Vs detection value is input to the output control unit 130. The voltage input to the output control unit 130 may also be changed depending on whether a system failure has occurred. For example, the output control unit 130 may input a voltage obtained by adding the target voltage Vref and the Vs detection value when a system failure has occurred, and input either the target voltage Vref or the Vs detection value when no system failure has occurred.

[0044] 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 estimation unit 141 , a noise removal unit 142 , and a correction voltage calculation unit 143 .

[0045] The Vs estimation unit 141 estimates the system voltage Vs based on the Io detection value and the impedance characteristics between the inverter 12 and the power system 30. The estimated system voltage Vs is referred to as the estimated system voltage Vse. Figure 1 The inductance L of the reactor shown. The estimated system voltage Vse is estimated by multiplying the detected value Io by a predetermined constant. The predetermined constant is the value obtained by multiplying the inductance L by the angular frequency ω. Specifically, the predetermined constant is represented by ωL (= 2πfL). f is 50 Hz or 60 Hz. This allows the voltage when the output current Io flows through the reactor to be estimated without using a sensor.

[0046] Noise removal unit 142 removes high-frequency components from differential voltage ΔVdis, which is the difference between estimated system voltage Vse obtained by Vs estimation unit 141 and target voltage Vref obtained by current control unit 120. A low-pass filter (LPF) is used to remove high-frequency components from differential voltage ΔVdis. Furthermore, if a system failure occurs and system voltage Vs includes interference voltage Vdis, differential voltage ΔVdis is estimated to be interference voltage Vdis.

[0047] The correction voltage calculator 143 generates the correction voltage Vdisc based on the voltage obtained by removing the high-frequency components of the differential voltage ΔVdis. Specifically, the correction voltage calculator 143 controls the voltage such that the voltage after removing the high-frequency components of the differential voltage ΔVdis falls within a target range. This control, for example, employs feedback control including P control with proportional action. Furthermore, the disturbance observer controller 140 may be activated only when a system failure occurs.

[0048] The control device 100 then performs a process (disturbance compensation) by adding the correction voltage Vdisc obtained by the disturbance observer control unit 140 to the target voltage Vref. Consequently, when a power system failure occurs, the interference voltage Vdis included in the estimated system voltage Vse is suppressed by the correction voltage Vdisc. This prevents the output current Io of the inverter 12 from becoming overcurrent, allowing AC power to continue to be supplied to the power system 30. Consequently, the power system 30 can be stabilized.

[0049] 2-3. Treatment Example

[0050] Figure 3 1 is a flowchart showing an example of processing by the control device 100 according to the embodiment. Specifically, Figure 3 An example of the interference compensation control for compensating for the interference voltage Vdis is generally shown.

[0051] In step S100 , the control device 100 estimates the system voltage Vs, that is, calculates the estimated system voltage Vse, based on the Io detection value and the impedance characteristics between the inverter 12 and the power system 30 .

[0052] In step S101, control device 100 calculates differential voltage ΔVdis, which is the difference between estimated system voltage Vse and target voltage Vref. The process then proceeds to step S102. When a system failure occurs and system voltage Vs includes disturbance voltage Vdis, differential voltage ΔVdis is estimated to be disturbance voltage Vdis.

[0053] In step S102 , control device 100 removes high-frequency components of differential voltage ΔVdis , and then the process proceeds to step S103 .

[0054] In step S103 , the control device 100 calculates the correction voltage Vdisc based on the voltage obtained by removing the high-frequency component of the differential voltage ΔVdis. The process then proceeds to step S104 .

[0055] In step S104 , the control device 100 performs a process of adding the correction voltage Vdisc to the target voltage Vref (interference compensation).

[0056] 3. Example of inverter output results

[0057] Figure 4 1 is an explanatory diagram showing an example of the output result of the inverter 12 when the disturbance observer control unit 140 is not applied when a system accident occurs. Figure 5 1 is an explanatory diagram showing an example of the output result of the inverter 12 when the disturbance observer control unit 140 is applied when a system failure occurs.

[0058] Figure 4 (A) and Figure 5 (A) in FIG. 1 shows an example of a waveform of a Vs detection value. Figure 4 (B) and Figure 5 (B) in FIG. 1 shows an example of a waveform of the Io detection value. Figure 4 (C) and Figure 5 (C) in FIG. 1 shows an example of a waveform of the correction voltage Vdisc. Figure 4 and Figure 5 The waveform of the Vs detection value and the waveform of the Io detection value in represent one of the three phases (U, V, W). Figure 4 and Figure 5 The vertical axis of the graph shown is represented by PU (Per Unit), but is not limited to this. Figure 4 and Figure 5 The vertical axis of the graph shown may also represent PU in percentage.

[0059] When the disturbance observer control unit 140 is not used, Figure 4 As shown in (C) in FIG. 1 , the correction voltage Vdisc remains at “0 PU” and is not generated near the time when the system accident occurs and near the time when the system accident is recovered. On the other hand, when the disturbance observer control unit 140 is applied, as shown in FIG. Figure 5 As shown in (C) in FIG, near the time when the system accident occurs, the correction voltage Vdisc for eliminating the interference voltage Vdis is generated. In addition, near the time when the system accident is recovered, when the Vs detection value is less than the target voltage Vref, as shown in FIG. Figure 5 As shown in (C) in FIG. 1 , a correction voltage Vdisc is generated to eliminate the difference between the Vs detection value and the target voltage Vref, that is, the undervoltage.

[0060] exist Figure 4 (B) and Figure 5 In the example shown in (B) of FIG, when a power system failure occurs, the peak value of the detected value Io is lower when the disturbance observer control unit 140 is used compared to when the disturbance observer control unit 140 is not used. Specifically, by using the disturbance observer control unit 140 when a power system failure occurs, overcurrent in the output current Io of the inverter 12 can be suppressed. Consequently, the inverter 12 can continue to supply AC power to the power system 30, minimizing the impact on the power system 30.

[0061] 4. Effect

[0062] 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 impedance characteristics between the inverter 12 and the power system 30. A correction voltage Vdisc is then generated based on the voltage obtained by removing the high-frequency components of the differential voltage ΔVdis, which is the difference between the estimated system voltage Vs (estimated system voltage Vse) and the target voltage Vref. Furthermore, an instruction ins is issued to the inverter 12 based on the 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 overcurrent, allowing AC power to continue to be supplied to the power system 30. Consequently, the power system can be stabilized.

[0063] 5. Other Implementation Methods

[0064] Figure 6 1 is a block diagram showing a functional example of a control device 100 according to another embodiment. The difference from the control device 100 according to the above embodiment lies in the presence or absence of a threshold determination unit 144 in the disturbance observer control unit 140 .

[0065] The control device 100 of another embodiment includes a threshold determination unit 144 in the disturbance observer control unit 140. 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 the correction voltage Vdisc is determined to satisfy the threshold condition, the threshold determination unit 144 outputs the correction voltage Vdisc. On the other hand, if the correction voltage Vdisc is determined not to satisfy the threshold condition, the threshold determination unit 144 does not output the correction voltage Vdisc.

[0066] The threshold condition includes that the absolute value of the correction voltage Vdisc is greater than the threshold, or that the absolute value of the voltage obtained by removing the low-frequency component of the correction voltage Vdisc is greater than the threshold. The method of removing the low-frequency component of the correction voltage Vdisc uses an HPF (High Pass Filter).

[0067] Figure 7 This is a flowchart showing an example of processing of a control device in another embodiment. Figure 3 Specifically, S200 to S203 and S205 are the same processes as those of S100 to S104 described above, and therefore their description is omitted.

[0068] In step S204, the control device 100 determines whether the correction voltage Vdisc is greater than or equal to a threshold value. If the correction voltage Vdisc is determined to be greater than or equal to the threshold value (step S204; Yes), the process proceeds to step S205. Otherwise (step S204; No), the process ends.

[0069] According to another embodiment of the control device 100, the disturbance observer control unit 140 includes a threshold determination unit 144. When the correction voltage Vdisc satisfies a threshold condition, the threshold determination unit 144 outputs the correction voltage Vdisc. This suppresses the disturbance voltage Vdis above a certain level contained in the estimated system voltage Vse. In this case, the same effects as those of the aforementioned embodiment can be achieved.

[0070] Description of Reference Numerals

[0071] 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. A power regulator, characterized in that: have: an inverter that converts DC power into AC power and supplies the AC power to the power system; and a control device for controlling the inverter, The control device is configured as follows: estimating a system voltage based on an output current of the inverter and a characteristic of an impedance between the inverter and the power system; generating a correction voltage based on a voltage obtained by removing a high-frequency component of a differential voltage that is a difference between the estimated system voltage and the target voltage; An instruction is issued to the inverter based on a voltage obtained by adding the correction voltage to the target voltage.

2. The power conditioner according to claim 1, wherein: The control device is configured to output the instruction to the inverter: 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.

3. The power conditioner according to claim 2, wherein: The threshold condition includes that the absolute value of the correction voltage is greater than or equal to a threshold, or that the absolute value of the voltage after removing the low-frequency component of the correction voltage is greater than or equal to a threshold.

4. The power conditioner according to claim 1, wherein: The target voltage is a voltage obtained by controlling the target current so that a differential current, which is a difference between a target current and the output current of the inverter, becomes the target current.

5. The power conditioner according to claim 1, wherein: The correction voltage is a voltage controlled so that the voltage obtained by removing the high-frequency component of the differential voltage moves within a target range.

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

7. The power conditioner according to claim 6, wherein: The predetermined constant is a value obtained by multiplying the diagonal frequency by the inductance.

8. A power control method, characterized in that: include: converting DC power into AC power using an inverter, and supplying the AC power to the power system; estimating a system voltage based on an output current of the inverter and a characteristic of an impedance between the inverter and the power system; generating a correction voltage based on a voltage obtained by removing a high-frequency component of a differential voltage that is a difference between the estimated system voltage and the target voltage; as well as An instruction is issued to the inverter based on a voltage obtained by adding the correction voltage to the target voltage.

Images