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

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a power conditioner. Specifically, when the power conditioner detects an overcurrent in which the current value of the output current of the inverter exceeds the allowable current value during the self-operating mode, the power conditioner performs control to change the phase of the output voltage so as to bring the output voltage of the inverter closer to 0V.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Consider the case where a system accident occurs in the power system. When the output current of the power conditioner (specifically, the inverter) detects an overcurrent and the output of the inverter stops, the load of the power system cannot continue to operate. Being When the output current of the inverter detects an overcurrent and the output of the inverter stops, the load of the power system cannot continue to operate.

[0005] One object of the present disclosure is to provide a technique capable of suppressing the output current of the inverter from becoming an overcurrent state during a system accident.

Means for Solving the Problems

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

[0007] A second aspect of this disclosure relates to a power control method. The power control method includes: using an inverter to convert DC power to AC power and supply 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 voltage obtained by removing the high-frequency components of the differential voltage, which is the difference between the estimated system voltage and the target voltage; and issuing an instruction to the inverter based on the voltage obtained by adding the correction voltage to the target voltage. [Effects of the Invention]

[0008] According to this disclosure, the grid voltage is estimated based on the inverter's output current and the impedance characteristics between the inverter and the power grid. A correction voltage is then generated based on the difference voltage, which is the difference between the estimated grid voltage and the target voltage, with the high-frequency components removed. Furthermore, an instruction is issued to the inverter based on the voltage obtained by adding the correction voltage to the target voltage. This suppresses the inverter's output current from becoming overcurrent, allowing for a continuous supply of AC power to the power grid. Consequently, it becomes possible to stabilize the power grid. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram illustrating the overview of a power conversion system. [Figure 2]This is a block diagram showing examples of control device functions. [Figure 3] This flowchart shows an example of the control device's processing. [Figure 4] This is an explanatory diagram showing an example of the inverter output result when a disturbance observer is not applied. [Figure 5] This is an explanatory diagram showing an example of the inverter output result when a disturbance observer is applied. [Figure 6] This block diagram shows examples of functions of a control device according to other embodiments. [Figure 7] This flowchart shows an example of processing by a control device according to another embodiment. [Modes for carrying out the invention]

[0010] A power conditioner and power control method according to the embodiments of this disclosure will be described with reference to the attached drawings. Furthermore, elements common to each figure are denoted by the same reference numerals, and redundant explanations are omitted.

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

[0012] Battery 11 is an energy storage device that stores electricity generated from renewable energy sources. Examples of renewable energy sources include solar power, wind power, hydropower, etc.

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

[0014] 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. Note that 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 Vs detected value) and the detected value of the output current Io (hereinafter referred to as the Io detected value). The Vs detected value and the Io detected 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 Vs detected value and the Io detected value are detected between the power conditioner 10 and the transformer 20. However, it is not limited to this. The Vs detected value and the Io detected value may be detected, for example, between the transformer 20 and the power system 30.

[0015] Also, 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). That is, the above-described Vs detected value includes the Vsu detected value, the Vsv detected value, and the Vsw detected value, and the above-described Io detected value includes the Iou detected value, the Iov detected value, and the Iow detected 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 detected value and Io detected value. Then, the power control unit 110 calculates a current command (also referred to as a target current) of the inverter 12 based on the AC power. Details of an example of calculating the target current will be described later.

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

[0018] Furthermore, the control device 100 may calculate a voltage command for the inverter 12 based on VSG (Virtual Synchronous Generator) control. VSG is a virtual synchronous generator that pseudo-poses the dynamic characteristics of a synchronous generator to the inverter 12. That is, VSG control means controlling a virtual synchronous generator.

[0019] Based on the voltage command obtained by the current control unit 120, the control device 100 gives an instruction ins to the inverter 12 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.

[0020] Here, consider that during a power system accident, a disturbance voltage Vdis caused by a disturbance is included in the output voltage Vs (power system voltage Vs) of the inverter 12. The disturbance voltage Vdis is a disturbance that cannot be observed in the Vs detection value or the like, and for example, is a voltage that instantaneously increases the power system voltage Vs. In this case, it is assumed that the output current Io enters an overcurrent state. As a result, the power conditioner 10 activates an overcurrent trip function so as not to supply AC power to the power system 30 for the purpose of protecting the inverter 12 or the like. 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. Thereby, AC power is not supplied to the power system 30.

[0021] However, even when a power system accident occurs, it is required to supply stable AC power to the power system 30. For example, in the power conditioner 10, it may be required to have a LVRT (Low Voltage Ride Through) function. LVRT is a function that, when an instantaneous voltage drop occurs due to a power system accident, maintains the output current Io before the occurrence of the power system accident and minimizes the impact on the power system 30 as long as the width and duration of the voltage drop do not satisfy the output stop condition.

[0022] According to the control device 100, the disturbance observer control unit 140 is also executed. The disturbance observer control unit 140 generates a correction voltage to cancel out the disturbance voltage Vdis included in the system voltage Vs. Then, the control device 100 issues an instruction ins to the inverter 12 based on the voltage obtained by adding the correction voltage obtained by the disturbance observer control unit 140 to the target voltage. This prevents the output current Io of the inverter 12 from becoming an overcurrent state, and allows AC power to be continuously supplied to the power system 30. 30 This makes it possible to stabilize the system. Details of the disturbance observer control unit 140 will be described later.

[0023] 2. Examples of control devices 2-1. Example Configuration The control device 100 has hardware that implements various functions. The hardware includes processing circuits capable of high-speed calculations. Examples of processing circuits include FPGAs (Field Programmable Gate Arrays) and ASICs (Application Specific Integrated Circuits). In addition to processing circuits, the hardware may also include arithmetic units (e.g., CPUs, GPUs) that execute programs stored in memory.

[0024] 2-2. Examples of Functions Figure 2 is a block diagram illustrating an example of the functions of the control device 100 according to an 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 detected Vs value and the detected Io value. The power control unit 110 then controls the system so that the measured value of active power becomes the target value of active power (also referred to as APR (Automatic Power Regulator) control) based on the measured value of active power and the target value of active power. The power control unit 110 also controls the system so that the measured value of reactive power becomes the target value of reactive power (also referred to as AQR (Automatic Reactive Power Regulator) control) based on the measured value of reactive power and 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.

[0025] Furthermore, the Vs detection value input to the power control unit 110 may be obtained, for example, via a PLL (Phase Locked Loop) provided in the control device 100. A PLL is a circuit that synchronizes the phase of the input voltage signal and the output voltage signal. This allows the phase of the Vs detection value and the output voltage Vs of the inverter 12 to be synchronized, and the inverter 12 and the power system 30 to be properly connected.

[0026] After the power control unit 110 has finished operating, the control device 100 operates the current control unit 120. The current control unit 120 controls the current so that the differential current ΔI, which is the difference between the target current Iref obtained by the power control unit 110 and the detected Io value, becomes the target current Iref (also called ACR (Automatic Current Regulator) control). ACR control is a constant current control and performs feedback control of PI control, which includes proportional and integral operation. In ACR control, the current control unit 120 outputs a target voltage Vref.

[0027] After the current control unit 120 has finished operating, 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 modulates the pulse width of each of the three-phase voltages. The control device 100 then outputs the instruction ins generated by the PWM control to the inverter 12.

[0028] Furthermore, the output control unit 130 receives a voltage that is the sum of the target voltage Vref and the detected Vs value. The voltage input to the output control unit 130 may be changed depending on whether or not there is a grid fault. For example, the output control unit 130 may receive a voltage that is the sum of the target voltage Vref and the detected Vs value if a grid fault occurs, and receive either the target voltage Vref or the detected Vs value if there is no grid fault.

[0029] Furthermore, after the current control unit 120 has finished operating, the control device 100 operates the disturbance observer control unit 140. The disturbance observer control unit 140 includes a Vs estimation unit 141, a noise reduction unit 142, and a corrected voltage calculation unit 143.

[0030] The Vs estimation unit 141 estimates the system voltage Vs based on the detected Io value and the impedance characteristics between the inverter 12 and the power system 30. The estimated system voltage Vs is called the estimated system voltage Vse. The impedance includes the inductance L of the reactor shown in Figure 1. The estimated system voltage Vse is estimated by multiplying the detected Io value by a predetermined constant. The predetermined constant is the 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 50Hz or 60Hz. This makes it possible to estimate the voltage when the output current Io flows through the reactor without using a sensor.

[0031] The noise reduction unit 142 removes the high-frequency components of the differential voltage ΔVdis, which is obtained by differentiating the estimated system voltage Vse obtained by the Vs estimation unit 141 with the target voltage Vref obtained by the current control unit 120. A low-pass filter (LPF) is used to remove the high-frequency components of the differential voltage ΔVdis. In the event of a system fault, if 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 a correction voltage Vdisc based on the voltage obtained by removing the high-frequency components of the differential voltage ΔVdis. Specifically, the correction voltage calculation unit 143 controls the voltage obtained by removing the high-frequency components of the differential voltage ΔVdis to move within a target range. This control is performed, for example, as feedback control of P control including proportional action. Note that the disturbance observer control unit 140 may be enabled only when a system fault occurs.

[0033] The control device 100 then performs a process (disturbance compensation) in which it adds the correction voltage Vdisc obtained by the disturbance observer control unit 140 to the target voltage Vref. As a result, in the event of a grid fault, the disturbance voltage Vdis included in the estimated grid voltage Vse is suppressed by the correction voltage Vdisc. Therefore, the output current Io of the inverter 12 is prevented from becoming an overcurrent state, and AC power can be continuously supplied to the power system 30. Thus, the power system 30 can be stabilized.

[0034] 2-3. Processing Example Figure 3 is a flowchart showing an example of processing by the control device 100 according to the embodiment. Specifically, Figure 3 summarizes an example of disturbance compensation control that compensates for disturbance voltage Vdis.

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

[0036] In step S101, the control device 100 calculates the differential voltage ΔVdis by subtracting the estimated system voltage Vse from the target voltage Vref. The process then proceeds to step S102. When a system fault occurs, if the system voltage Vs includes the disturbance voltage Vdis, the differential voltage ΔVdis is estimated to be the disturbance voltage Vdis.

[0037] In step S102, the control device 100 removes the high-frequency component of the differential voltage ΔVdis. The process then proceeds to step S103.

[0038] In step S103, the control device 100 calculates a corrected voltage Vdisc based on the voltage obtained by removing the high-frequency component of the differential voltage ΔVdis. Then, the process proceeds to step S104.

[0039] In step S104, the control device 100 performs a process (disturbance compensation) in which it adds the correction voltage Vdisc to the target voltage Vref.

[0040] 3. Example of inverter output results Figure 4 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 during a grid fault. On the other hand, Figure 5 is an explanatory diagram showing an example of the output result of the inverter 12 when the disturbance observer control unit 140 is applied during a grid fault.

[0041] Figures 4(A) and 5(A) show examples of waveforms for the Vs detection value. Figures 4(B) and 5(B) show examples of waveforms for the Io detection value. Figures 4(C) and 5(C) show examples of waveforms for the correction voltage Vdisc. Note that the waveforms for the Vs detection value and the Io detection value in Figures 4 and 5 represent one of the three phases (U, V, W). Also, the vertical axis of the graphs shown in Figures 4 and 5 is: pu ( per unit It is represented as follows: However, it is not limited to this. The vertical axis of the graphs shown in Figures 4 and 5 is puIt may also be expressed as a percentage.

[0042] If the disturbance observer control unit 140 is not applied, as shown in (C) in Figure 4, the correction voltage Vdisc is "0" around the time the system fault occurred and around the time the system recovered from the fault. pu It remains as is and is not generated. On the other hand, when the disturbance observer control unit 140 is applied, as shown in (C) in Figure 5, a correction voltage Vdisc is generated to cancel out the disturbance voltage Vdis around the time the system fault occurred. Also, around the time the system recovered from the fault, if the detected Vs value is smaller than the target voltage Vref, a correction voltage Vdisc is generated to cancel out the undervoltage, which is the difference between the detected Vs value and the target voltage Vref, as shown in (C) in Figure 5.

[0043] In the examples shown in Figure 4(B) and Figure 5(B), when the disturbance observer control unit 140 is applied during a system fault, the peak value of the detected Io is... Applicable The level will be lower compared to when this is not done. In other words, by applying the disturbance observer control unit 140 when a grid fault occurs, the overcurrent of the inverter 12's output current Io can be suppressed. Therefore, the inverter 12 can continue to supply AC power to the power grid 30, minimizing 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 impedance characteristics between the inverter 12 and the power system 30. Then, a correction voltage Vdisc is 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 suppresses the output current Io of the inverter 12 from becoming an overcurrent state, and allows AC power to be continuously supplied to the power system 30. 30This makes it possible to stabilize it.

[0045] 5. Other Embodiments Figure 6 is a block diagram showing an example of the functions of the control device 100 according to another embodiment. The difference from the control device 100 according to the embodiment described above is the presence or absence of the threshold determination unit 144 in the disturbance observer control unit 140.

[0046] In other embodiments of the control device 100, 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 the 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 the absolute value of the correction voltage Vdisc being greater than or equal to the threshold, or the absolute value of the voltage obtained by removing the low-frequency components of the correction voltage Vdisc being greater than or equal to the threshold. A High Pass Filter (HPF) is used to remove the low-frequency components of the correction voltage Vdisc.

[0048] Figure 7 shows a control device according to another embodiment. 100 This is a flowchart showing an example of the process. Here, we will only explain the parts that differ from Figure 3 described above. Specifically, steps S200 to S203 and S205 are the same processes as S100 to S104 described above, so we will omit their explanation.

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

[0050] In the control device 100 according to another 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, disturbance voltages Vdis above a certain level included in the estimated system voltage Vse are suppressed by the correction voltage Vdisc. In this case, the same effects as in the embodiment described above can be obtained. [Explanation of Symbols]

[0051] 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 to AC power and supplies the AC power to the power grid, A control device for controlling the inverter, Equipped with, The control device is Based on the output current of the inverter and the impedance characteristics between the inverter and the power system, the system voltage is estimated. A correction voltage is generated based on the voltage obtained by removing the high-frequency components from the differential voltage, which is the difference between the estimated system voltage and the target voltage. Based on the voltage obtained by adding the correction voltage to the target voltage, an instruction is issued to the inverter. It is configured in such a way A power conditioner characterized by the following.

2. A power conditioner according to claim 1, In the process of outputting the instruction to the inverter, the control device, Determine whether the correction voltage satisfies the threshold condition. If it is determined that the correction voltage satisfies the threshold condition, the inverter is issued an instruction based on the voltage obtained by adding the correction voltage to the target voltage. A power conditioner characterized by the following.

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

4. A 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, so that the differential current equals the target current. A power conditioner characterized by the following.

5. A power conditioner according to claim 1, The correction voltage is a voltage obtained by controlling the voltage obtained by removing the high-frequency components of the differential voltage to move within a target range. A power conditioner characterized by the following.

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

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

8. Using an inverter, converts DC power to AC power and supplies the AC power to the power grid. The system voltage is estimated based on the output current of the inverter and the impedance characteristics between the inverter and the power system. A correction voltage is generated based on the voltage obtained by removing the high-frequency component from the differential voltage, which is the difference between the estimated system voltage and the target voltage. Based on the voltage obtained by adding the correction voltage to the target voltage, an instruction is issued to the inverter. including A power control method characterized by the following features.

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