Voltage control device and voltage control method

Abstract

This voltage control device is provided with: an inverter that converts DC power output from a battery into AC power and supplies the AC power to a power system; and a control device that is connected to the inverter. The control device executes: a process of calculating a first virtual impedance by using various variables when a voltage drop of an output voltage of the inverter is equal to or greater than a threshold value due to a fluctuation in an AC voltage of the power system; a process of calculating a second virtual impedance to be temporarily added to the first virtual impedance so that an output current of the inverter is not greater than a rated value; a process of calculating a virtual effective voltage and a virtual reactive voltage by multiplying each of an effective current and a reactive current calculated by the output current of the inverter by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance; and a process of performing a voltage control so that the effective current and the reactive current respectively approach an effective current command value and a reactive current command value required for the power system on the basis of the virtual effective voltage and the virtual reactive voltage.

Description

Technical Field

[0001] This disclosure relates to a technique for controlling the output voltage of an inverter.

Background Art

[0002] Patent Document 1 discloses a technique that enables a power converter (i.e., an inverter) that executes control simulating a synchronous generator to continue operating stably. In this prior art, when the AC voltage of the power grid fluctuates, voltage control is performed so that the active power input and output between the power grid and the power converter decreases.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Consider the case of using a voltage-controlled GFM (Grid Forming Inverter) inverter as an inverter that supplies an AC voltage to the power grid. In this case, as shown in Patent Document 1, when the AC voltage of the power grid fluctuates, voltage control is performed to reduce the difference in active power input and output between the power grid and the power converter.

[0005] However, even when voltage control is performed to stabilize the active power, the output current of the inverter may not reach the reference current required by the power grid, and the power grid may become unstable. Therefore, in order to supply stable active power to the power grid, it is necessary to perform voltage control so as to output the active current and reactive current required by the power grid.

[0006] One object of this disclosure is to provide a technology that enables voltage control to output the active and reactive currents required by a power system when the AC voltage of the power system fluctuates. [Means for solving the problem]

[0007] The first aspect of this disclosure relates to a voltage control device. The voltage control device includes an inverter that converts DC power output from a battery into AC power and supplies AC power to a power system. Furthermore, the voltage control device includes a control device connected to the inverter. When the voltage drop of the inverter's output voltage exceeds a threshold due to fluctuations in the AC voltage of the power system, the control device performs the following processes: calculates a first virtual impedance using variables including an active voltage command value and a reactive voltage command value calculated from a voltage command value, and an active current command value and a reactive current command value calculated from the inverter's output voltage and the voltage command value; calculates a second virtual impedance that is temporarily added to the first virtual impedance so that the inverter's output current does not exceed its rated value; calculates a virtual active voltage and a virtual reactive voltage by multiplying the active current and reactive current, respectively, calculated from the inverter's output current, by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance; and performs voltage control based on the virtual active voltage and virtual reactive voltage so that the active current and reactive current, respectively, approach the active current command value and reactive current command value required by the power system.

[0008] The second aspect of this disclosure, in addition to the first aspect, further has the following features: In the process of calculating the second virtual impedance, the control device sets the second virtual impedance to a value corresponding to the output voltage if the voltage drop of the inverter's output voltage is greater than or equal to a threshold. Also, in the process of calculating the second virtual impedance, the control device sets the second virtual impedance to zero if the voltage drop of the inverter's output voltage is less than a threshold.

[0009] A third aspect of this disclosure, in addition to the second aspect, further has the following features: The second virtual impedance is a reactance composed of the amplitude set by the first variable and the frequency set by the second variable. Furthermore, when the voltage drop of the inverter output voltage is greater than or equal to a threshold, the control device is configured to increase the value of the first variable and decrease the value of the second variable as the inverter output voltage decreases. Furthermore, when the voltage drop of the inverter output voltage is greater than or equal to a threshold, the control device is configured to decrease the value of the first variable and increase the value of the second variable as the inverter output voltage increases.

[0010] A fourth aspect of this disclosure has the following features in addition to any one of the first to third aspects: The variables further include an active voltage and a reactive voltage calculated from the output voltage. The control device calculates the virtual impedance in the process of calculating the virtual impedance based on the conditions that the reactive voltage is zero, the reactive voltage command value is zero, the voltage value obtained by subtracting the virtual active voltage and the active voltage from the active voltage command value is zero, and the voltage value obtained by subtracting the virtual reactive voltage and the reactive voltage from the reactive voltage command value is zero.

[0011] A fifth aspect of this disclosure has the following additional features in addition to any one of the first to third aspects: The first virtual impedance includes resistance and reactance. In the process of calculating the first virtual impedance, the control device calculates the resistance and reactance, respectively, corresponding to the output voltage.

[0012] The sixth aspect of this disclosure has the following additional features in addition to any one of the first to third aspects: The active current command value is calculated by multiplying the difference voltage, which is the difference between the voltage command value and the output voltage, by a constant value. The reactive current command value is calculated such that the sum of the squares of the active current command value and the squares of the reactive current command value is 1.

[0013] The seventh aspect of this disclosure, in addition to the sixth aspect, further has the following features: The active current command value is expressed as a percentage. If the calculated result of the active current command value exceeds 100%, the control device sets the active current command value to 100%.

[0014] The eighth aspect of this disclosure relates to a voltage control method. The voltage control method includes: using an inverter to convert DC power output from a battery into AC power and supply AC power to a power system; calculating a first virtual impedance using variables including an active voltage command value and a reactive voltage command value calculated from a voltage command value, and an active current command value and a reactive current command value calculated from the inverter's output voltage and voltage command value, when the voltage drop of the inverter's output voltage exceeds a threshold due to fluctuations in the AC voltage of the power system; calculating a second virtual impedance to be temporarily added to the first virtual impedance so that the inverter's output current does not exceed its rated value; calculating a virtual active voltage and a virtual reactive voltage by multiplying the active current and reactive current, respectively, calculated from the inverter's output current, by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance; and voltage control based on the virtual active voltage and virtual reactive voltage so that the active current and reactive current, respectively, approach the active current command value and reactive current command value required by the power system. [Effects of the Invention]

[0015] According to this disclosure, if the voltage drop of the inverter's output voltage exceeds a threshold due to fluctuations in the AC voltage of the power system, a first virtual impedance is calculated based on the voltage command value and the inverter's output voltage. A second virtual impedance is also calculated, which is temporarily added to the first virtual impedance to ensure that the inverter's output current does not exceed its rated value. A virtual active voltage and a virtual reactive voltage are then generated based on the virtual impedance obtained by adding the first and second virtual impedances. Based on these virtual active and reactive voltages, voltage control is performed so that the active current and reactive current output from the inverter approach the active current command value and reactive current command value required by the power system. As a result, even if the AC voltage of the power system fluctuates, the inverter can output the active current and reactive current required by the power system. Therefore, it becomes possible to stabilize the power system. [Brief explanation of the drawing]

[0016] [Figure 1] This is a diagram illustrating the overview of a power conversion system. [Figure 2] This is a block diagram showing an example of the functions of the control device in the voltage control device according to the embodiment. [Figure 3] This is a block diagram showing an example of the function of a circuit that generates the second virtual impedance (Xα) of the control device in a voltage control device according to an embodiment. [Figure 4] This figure illustrates an example of the output result of the virtual impedance of the control device in a voltage control device according to an embodiment. [Figure 5] This figure illustrates an example of the output result of an inverter in a voltage control device according to an embodiment. [Figure 6] This flowchart shows an example of processing by the control device in the voltage control device according to the embodiment. [Modes for carrying out the invention]

[0017] Referring to the accompanying drawings, a voltage control device and a voltage control method according to embodiments of the present disclosure will be described. In addition, elements common to each figure are denoted by the same reference numerals, and redundant descriptions are omitted.

[0018] 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 voltage control device 10, a transformer 20, and a power grid 30. The voltage control device 10 is configured to include a battery 11, an inverter 12, and a control device 100.

[0019] The inverter 12 is a device that converts the DC power output from the battery 11 into AC power and supplies the AC power to the power grid 30 via the transformer 20. As the inverter 12, a voltage control type GFM inverter is exemplified.

[0020] The control device 100 is a device connected to the inverter 12 and configured to control the output power output from the inverter 12. Specifically, the control device 100 inputs a detected value of the output voltage Vs (hereinafter referred to as the Vs detected value) and a detected value of the output current Io (hereinafter referred to as the Io detected value) output from the inverter 12. The Vs detected value and the Io detected value are detected by a detector (not shown) provided between the voltage control device 10 and the power grid 30. In the example shown in FIG. 1, the Vs detected value and the Io detected value detected between the voltage control device 10 and the transformer 20 are input to the control device 100, but the Vs detected value and the Io detected value detected between the transformer 20 and the power grid 30 may be input. Thus, the detected value of the AC voltage of the power grid 30 may be the Vs detected value. Also, the detected value of the AC current of the power grid 30 may be the Io detected value.

[0021] Furthermore, the output voltage Vs from inverter 12 is composed of three-phase voltages (Vsu, Vsv, Vsw), and the output current Io from inverter 12 is composed of three-phase currents (Iou, Iov, Iow). In other words, the Vs detection value mentioned above includes the Vsu detection value, the Vsv detection value, and the Vsw detection value, and the Io detection value mentioned above includes the Iou detection value, the Iov detection value, and the Iow detection value.

[0022] The control device 100 performs VSG (Virtual Synchronous Generator) control based on the input Vs detection value and Io detection value. 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 the virtual synchronous generator. The dynamic characteristics of the synchronous generator include the inertia constant M, the braking constant D, etc. This prevents the power system 30 from becoming unstable in the event of a grid fault, i.e., when an LVRT (Low Voltage Ride Through) occurs.

[0023] Furthermore, based on the results of the VSG control, the control device 100 performs voltage control on the inverter 12 so that the output current Io output from the inverter 12 becomes the current value required by the power system 30 when an LVRT occurs. The voltage control includes the generation of three-phase voltages (Vsu, Vsv, Vsw) and PWM control, which modulates the pulse width for each of the three-phase voltages. The control device 100 then outputs the voltage control signal generated by the PWM control to the inverter 12. As a result, the inverter 12 can reduce the difference in AC power between the power system 30 and the inverter 12 based on the voltage control signal.

[0024] 2. Specific Examples of Voltage Control Devices 2-1. Example of Control Device Configuration The control device 100 has hardware that implements various functions. The hardware may be a processing circuit or a computer that executes a program stored in a memory device using a CPU. Examples of processing circuits include FPGAs (Field Programmable Gate Arrays) and ASICs (Application Specific Integrated Circuits).

[0025] 2-2. Examples of Control Device Functions Figure 2 is a block diagram showing an example of the functions of the control device 100 in the voltage control device 10 according to the embodiment. The control device 100 includes an active / reactive voltage calculation processing unit 101, an active / reactive current calculation processing unit 102, a VSG control unit 103, a dq-axis voltage conversion unit 104, a dq-axis current command calculation unit 105, a virtual impedance generation unit 106, a first virtual impedance generation unit 106a, a second virtual impedance generation unit 106b, a virtual voltage generation unit 107, a first output selection circuit 108, a second output selection circuit 109, a switching determination circuit 110, an addition / subtraction circuit 111, and a voltage control circuit 112.

[0026] The active / reactive voltage calculation processing unit 101 calculates the active voltage Vd and reactive voltage Vq based on the Vs detection value input to the control device 100. The active voltage Vd and reactive voltage Vq calculated by the active / reactive voltage calculation processing unit 101 can be expressed, for example, by the following equation (1).

[0027]

number

[0028] The active / reactive current calculation processing unit 102 calculates the active current Id and reactive current Iq based on the Io detection value input to the control device 100. The active current Id and reactive current Iq calculated by the active / reactive current calculation processing unit 102 are, for example, expressed by the following equation (2).

[0029]

number

[0030] The VSG control unit 103 generates a voltage command value Vref for the output voltage Vs of the inverter 12. The voltage command value Vref is a fixed value determined, for example, according to the power system 30 connected to the inverter 12. The voltage command value Vref includes a d-axis voltage command value Vdref and a q-axis voltage command value Vqref.

[0031] The d-axis voltage command value Vdref is also called the active voltage command value Vdref, and the q-axis voltage command value Vqref is also called the reactive voltage command value Vqref. The dq-axis voltage conversion unit 104 converts the voltage command value Vref generated by the VSG control unit 103 into the active voltage command value Vdref and the reactive voltage command value Vqref.

[0032] The dq-axis current command calculation unit 105 calculates the d-axis current command value Idref and the q-axis current command value Iqref required for the power system 30 based on the voltage command value Vref and the Vs detection value when LVRT occurs due to fluctuations in the AC voltage of the power system 30. The d-axis current command value Idref is also called the effective current command value Idref. q Axis current command value I q ref is also called the reactive current command value Iqref. The active current command value Idref and the reactive current command value Iqref, calculated by the dq-axis current command calculation unit 105, are expressed, for example, by the following equations (3) and (4). k is a constant value determined by the specifications of the inverter 12. ΔV is the differential voltage Vdiff, which is the difference between the voltage command value Vref and the detected Vs value.

[0033]

number

[0034]

number

[0035] Here, when each variable used in equations (3) and (4) is expressed as a percentage, the active current command value Idref is calculated so as not to exceed 100%. Specifically, when the voltage drop of the detected Vs value falls to 60%, ΔV becomes Vdref - Vs = 100% - 60% = 40%. Also, when k is a constant value of "2", Iqref becomes 2 × 40% = 80%. In this case, Iqref does not exceed 100%, so it becomes 80%. Furthermore, the reactive current command value Iqref is calculated so that the sum of the squares of the active current command value Idref and the reactive current command value Iqref is 1. Therefore, when the active current command value Idref is 80%, the reactive current command value Iqref becomes 60% according to equation (4).

[0036] Next, let's consider the case where the voltage drop of the detected Vs value decreases to 10%. In this case, ΔV becomes Vdref - Vs = 100% - 10% = 90%. Also, if k is a constant value of "2", then Iqref becomes 2 × 90% = 180%. In this case, since Iqref exceeds 100%, it becomes the upper limit of 100%. Note that when the active current command value Idref is 100%, the reactive current command value Iqref becomes 0% according to equation (4).

[0037] The virtual impedance generation unit 106 includes a first virtual impedance generation unit 106a and a second virtual impedance generation unit 106b. The first virtual impedance generation unit 106a calculates a first virtual impedance to increase the output voltage Vs of the inverter 12 when the voltage drop of the detected Vs value is greater than or equal to a threshold, that is, when the differential voltage Vdiff obtained by differentiating the detected Vs value and the voltage command value Vref is greater than or equal to a threshold. The first virtual impedance includes resistance Rv and reactance Xv. The resistance Rv and reactance Xv are calculated based on the active voltage command value Vdref, the reactive voltage command value Vqref, the active current command value Idref, the reactive current command value Iqref, the active voltage Vd, and the reactive voltage Vq, respectively.

[0038] The second virtual impedance generation unit 106b is a circuit that generates a second impedance. The second impedance is the reactance Xα. The reactance Xα is calculated based on the Vs detection value and added to the reactance Xv generated by the first virtual impedance generation unit 106a. In other words, the virtual impedance generation unit 106 calculates a reactance Xv2 by adding the reactance Xv and the reactance Xα. The virtual impedance generation unit 106 then outputs the resistance Rv and the reactance Xv2 to the virtual voltage generation unit 107, which will be described later. Details of the calculation of resistance Rv and reactance Xv2, and details of the generation of reactance Xα will be described later.

[0039] The virtual voltage generation unit 107 generates a virtual active voltage Vud and a virtual reactive voltage Vuq to increase the output voltage Vs of the inverter 12, based on the resistance Rv and reactance Xv2, the active current Id, and the reactive current Iq. The virtual active voltage Vud and the virtual voltage generation unit 107 calculated by the virtual voltage generation unit 107 are each represented by the following equation (5) as an example.

[0040]

number

[0041] The first output selection circuit 108 is a toggle switch with two input terminals and one output terminal. The first output selection circuit 108 switches to select one of the two input terminals. Specifically, if the switching judgment result input to the first output selection circuit 108 is "0", the first output selection circuit 108 switches to select the first input terminal. On the other hand, if the switching judgment result input to the first output selection circuit 108 is "1", the first output selection circuit 108 switches to select the second input terminal. In the example shown in Figure 2, a fixed value (zero value) is input to the first input terminal of the first output selection circuit 108, and a virtual effective voltage Vud is input to the second input terminal of the first output selection circuit 108.

[0042] The switching determination result is generated by the switching determination circuit 110. The switching determination circuit 110 outputs "0" as the switching determination result if the difference voltage Vdiff between the detected Vs value and the voltage command value Vref is less than the threshold, that is, if the AC voltage of the power system 30 is not in the LVRT state. On the other hand, the switching determination circuit 110 outputs "1" as the switching determination result if the difference voltage Vdiff between the detected Vs value and the voltage command value Vref is greater than or equal to the threshold, that is, if the AC voltage of the power system 30 is in the LVRT state. The first output selection circuit 108 outputs the voltage input to the selected input terminal. The voltage output from the first output selection circuit 108 is called the selection effective voltage Vdsel.

[0043] The second output selection circuit 109 is a toggle switch with two input terminals and one output terminal. The second output selection circuit 109 switches to select one of the two input terminals. Specifically, if the switching judgment result input to the second output selection circuit 109 is "0", the second output selection circuit 109 switches to select the first input terminal. On the other hand, if the switching judgment result input to the second output selection circuit 109 is "1", the second output selection circuit 109 switches to select the second input terminal. In the example shown in Figure 2, a fixed value (zero value) is input to the first input terminal of the second output selection circuit 109, and a virtual reactive voltage Vuq is input to the second input terminal of the second output selection circuit 109.

[0044] The switching determination result is generated by the switching determination circuit 110, as described above. The second output selection circuit 109 outputs the voltage input to the selected input terminal. The voltage output from the second output selection circuit 109 is called the selection inactive voltage Vqsel.

[0045] The addition / subtraction circuit 111 includes four addition / subtraction circuits (first addition / subtraction circuit 111a, second addition / subtraction circuit 111b, third addition / subtraction circuit 111c, and fourth addition / subtraction circuit 111d). The first addition / subtraction circuit 111a controls the effective voltage command value Vdref add Calculate and select the effective voltage Vdsel ReduceThis is an addition / subtraction circuit that performs calculations. The second addition / subtraction circuit 111b is an addition / subtraction circuit that calculates the reactive voltage command value Vqref add Calculate and select the invalid voltage Vqsel Reduce This is an addition and subtraction circuit that performs calculations. The third addition and subtraction circuit 111c is the output of the first addition and subtraction circuit 111a. add Calculate the effective voltage Vd Reduce This is an addition / subtraction circuit that performs calculations. The fourth addition / subtraction circuit 111d is the output of the second addition / subtraction circuit 111b. add Calculate the reactive voltage Vq Reduce This is an addition and subtraction circuit.

[0046] If the effective voltage output from the third addition / subtraction circuit 111c is denoted as the abnormal effective voltage Errd, and the reactive voltage output from the fourth addition / subtraction circuit 111d is denoted as the abnormal reactive voltage Errq, then the following relationship (6) holds true.

[0047]

number

[0048] Furthermore, when equation (5) is substituted into equation (6), it is expressed as equation (7) below.

[0049]

number

[0050] In this case, if both the abnormal active voltage Errd and the abnormal reactive voltage Errq are zero, it means that both the virtual active voltage Vud and the virtual reactive voltage Vuq are at appropriate voltage values. In other words, by setting both the abnormal active voltage Errd and the abnormal reactive voltage Errq to zero beforehand, the optimal values ​​for the virtual active voltage Vud and the virtual reactive voltage Vuq can be calculated.

[0051] Furthermore, it is desirable that the power factor, which is the effective voltage Vd of the inverter 12 expressed as a percentage with respect to the output voltage Vs, be high. For this reason, both the reactive voltage Vq and the reactive voltage command value Vqref are set to zero. Accordingly, in equation (7), when Errd=0, Errq=0, reactive voltage Vq=0, and reactive voltage command value Vqref=0, the resistance Rv and reactance Xv2 are expressed, for example, by the following equation (8).

[0052]

number

[0053] As a result, the formula for calculating the virtual impedance, which is the sum of the first virtual impedance and the second virtual impedance, includes the active current command value Idref and the reactive current command value Iqref. Therefore, the voltage control device 10 can output appropriate active current Id and reactive current Iq to the power system 30. Furthermore, by including the second virtual impedance in the virtual impedance, the impedance becomes larger, so the output current Io of the inverter 12 can be controlled so as not to exceed the rated value. This makes it possible to suppress overcurrent in the output current Io of the inverter 12.

[0054] The voltage control circuit 112 is a circuit that controls the voltage so that the active current Id and reactive current Iq approach the active current command value Idref and reactive current command value Iqref required by the power system 30, respectively, based on the virtual active voltage Vud and virtual reactive voltage Vuq calculated based on the virtual impedance (resistance Rv and reactance Xv2). The voltage control circuit 112 then outputs a voltage control signal Vsc generated by the voltage control.

[0055] Furthermore, as described above, voltage control includes the process of generating three-phase voltages (Vsu, Vsv, Vsw) and PWM control, which performs pulse width modulation on each of the three-phase voltages. In PWM control, the generated three-phase voltages are controlled to have a predetermined pulse width and frequency. In addition, PI control, for example, is used to generate the three-phase voltages by voltage control.

[0056] 2-3. Example of calculating the second virtual impedance (Xα) Figure 3 is a block diagram showing an example of the function of a circuit that generates a second virtual impedance (Xα) of the control device 100 in the voltage control device 10 according to the embodiment. Specifically, Figure 3 shows an example of the function of the second virtual impedance generation unit 106b. The second virtual impedance generation unit 106b includes a variable setting unit 200, a third output selection circuit 201, a switching determination circuit 202, and a high-pass filter unit 203.

[0057] The variable setting unit 200 sets the first variable and the second variable based on the Vs detection value input to the second virtual impedance generation unit 106b. The variable setting unit 200 then outputs the reactance Xα generated based on the first variable and the second variable. The first variable is a variable that sets the amplitude of the reactance Xα, and the amplitude is set according to the Vs detection value. The second variable is a variable that sets the frequency of the reactance Xα, and the frequency is set according to the Vs detection value.

[0058] Let's consider the setting value of the first variable. For example, if the detected Vs value is small, in order to reduce the difference in AC power between the power system 30 and the inverter 12, the rate of increase in the output current Io needs to be increased. Therefore, in this case, the control device 100 sets the value of the first variable to a large value. On the other hand, if the detected Vs value is large, in order to reduce the difference in AC power between the power system 30 and the inverter 12, the rate of increase in the output current Io needs to be decreased. Therefore, in this case, the control device 100 sets the value of the first variable to a small value.

[0059] Next, let's consider the setting value of the second variable. For example, if the detected Vs value is small, as mentioned above, it is necessary to increase the rate at which the output current Io rises. In this case, it is assumed that a certain amount of time will be required to raise the output current Io to a predetermined current value. Therefore, if the detected Vs value is small, the control device 100 sets the value of the frequency, which is the second variable, to a small value so that the time during which the reactance Xα is effective is extended.

[0060] On the other hand, if the detected Vs value is large, as mentioned above, it is necessary to reduce the rate at which the output current Io rises. In this case, it is assumed that the time required to raise the output current Io to a predetermined current value will be short. Therefore, if the detected Vs value is large, the control device 100 sets the value of the second variable, frequency, to a large value in order to shorten the time during which the reactance Xα is effective.

[0061] Thus, the smaller the Vs detection value, the more the value of the first variable and the smaller the value of the second variable are set to be. Conversely, the larger the Vs detection value, the smaller the value of the first variable and the larger the value of the second variable are set to be.

[0062] The third output selection circuit 201 is a toggle switch with two input terminals and one output terminal. The third output selection circuit 201 switches to select one of the two input terminals. Specifically, if the switching judgment result input to the third output selection circuit 201 is "0", the third output selection circuit 201 switches to select the first input terminal. On the other hand, if the switching judgment result input to the third output selection circuit 201 is "1", the third output selection circuit 201 switches to select the second input terminal. In the example shown in Figure 3, a fixed value (zero value) is input to the first input terminal of the third output selection circuit 201, and the reactance Xα generated by the variable setting unit 200 is input to the second input terminal of the third output selection circuit 201.

[0063] The switching determination result is generated by the switching determination circuit 202. The switching determination circuit 202 outputs "0" as the switching determination result if the detected Vs value is greater than or equal to the threshold th2, that is, if the output current Io of the inverter 12 is less than or equal to the rated value of the inverter 12. On the other hand, the switching determination circuit 202 outputs "1" as the switching determination result if the detected Vs value is less than the threshold th2, that is, if the output current Io of the inverter 12 exceeds the rated value of the inverter 12. The reactance Xα output from the third output selection circuit 201 outputs the value (reactance Xα or zero) input to the selected input terminal.

[0064] The high-pass filter section 203 is a high-pass filter that removes unwanted signal components before the reactance Xα is output from the second virtual impedance generation section 106b.

[0065] Although the variable setting unit 200 described above is provided on the input side of the third output selection circuit 201, it may also be provided on the output side of the third output selection circuit 201.

[0066] 2-4. Example of output results for virtual impedance Figure 4 is a diagram illustrating an example of the output result of the virtual impedance of the control device 100 in the voltage control device 10 according to the embodiment. Figure 4(A) shows an example of the waveform of reactance Xα output from the second virtual impedance generation unit 106b. Figure 4(B) shows an example of the waveform of reactance Xv2 input to the virtual voltage generation unit 107. In the examples shown in Figures 4(A) and 4(B), the values ​​of each reactance are expressed in PU (Per Unit), but they may also be expressed as a percentage.

[0067] Furthermore, the example shown in Figure 4(A) illustrates the waveform of reactance Xα when the first variable used to generate reactance Xα is set to "0.5pu" and the second variable to "0.7Hz". The first variable can be set, for example, between 0.2pu and 0.6pu, and the second variable can be set, for example, between 0.3Hz and 2Hz.

[0068] As shown in Figure 4(A), when the first variable is set, the reactance Xα rises sharply and then gradually decays. In other words, reactance Xα is a temporarily set impedance, and the value set by the first variable decays to zero based on the frequency set by the second variable. Therefore, as shown in Figure 4(B), reactance Xv2 also decays in accordance with the fluctuation of reactance Xα. When reactance Xα decays to zero, reactance Xv2 will contain only reactance Xv. In the example shown in Figure 4(B), the resistance Rv is 0.0pu.

[0069] 2-5. Example of inverter output results Figure 5 is a diagram illustrating an example of the output result of the inverter 12 in the voltage control device 10 according to the embodiment. Figure 5(A) shows an example of the waveform of the output voltage Vs when the Vs detection value drops to 45%. Figure 5(B) shows an example of the waveforms of the output current Io, the active current Id, and the reactive current Iq output from the inverter 12 to the power system 30 when the Vs detection value drops to 45% and the reactance Xα is set to zero. Figure 5(C) shows an example of the waveforms of the output current Io, the active current Id, and the reactive current Iq output from the inverter 12 to the power system 30 when the Vs detection value drops to 45% and the first and second variables are set for the reactance Xα.

[0070] In the example shown in Figure 5(B), when the detected Vs value drops to 45% and the reactance Xα is set to zero, the output current Io, which is composed of the active current Id and the reactive current Iq, exceeds 100% and is output at 140%.

[0071] In the example shown in Figure 5(C), when the detected Vs value decreases to 45% and the first and second variables are set for reactance Xα, the output current Io, which is composed of the active current Id and the reactive current Iq, is output at 100% or less.

[0072] Thus, when the AC voltage of the power system 30 fluctuates, the active current Id and reactive current Iq required for the power system 30 are output based on the virtual impedance to reduce the difference in AC power between the power system 30 and the inverter 12. Furthermore, a first variable and a second variable are set for the reactance Xα according to the voltage drop of the output voltage of the inverter 12. This makes it possible to suppress overcurrent in the output current Io of the inverter 12.

[0073] 3. Processing Example Figure 6 is a flowchart showing an example of processing by the control device 100 in the voltage control device 10 according to the embodiment.

[0074] In step S100, the control device 100 determines whether the voltage drop of the output voltage of the inverter 12 is greater than or equal to a threshold. If the voltage drop of the output voltage is greater than or equal to the threshold (step S100; Yes), the process proceeds to step S110. Otherwise (step S100; No), the control device 100 terminates the process.

[0075] In step S110, the control device 100 teeth, Based on various variables, the first virtual impedance is calculated. Then, the process proceeds to step S120.

[0076] Furthermore, the first virtual impedance is calculated based on predetermined conditions. These predetermined conditions are that the reactive voltage Vq is zero, the reactive voltage command value Vqref is zero, the voltage value obtained by subtracting the virtual active voltage Vud and the active voltage Vd from the active voltage command value Vdref is zero, and the voltage value obtained by subtracting the virtual reactive voltage Vuq and the reactive voltage Vq from the reactive voltage command value Vqref is zero.

[0077] In step S120, the control device 100 calculates a second virtual impedance to be temporarily added to the first virtual impedance. The process then proceeds to step S130.

[0078] In step S130, the control device 100 calculates the virtual active voltage Vud and virtual reactive voltage Vuq by multiplying the active current Id and reactive current Iq, which are calculated from the output current Io of the inverter 12, by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance. The process then proceeds to step S140.

[0079] In step S140, the control device 100 performs voltage control based on the virtual active voltage Vud and virtual reactive voltage Vuq so that the active current Id and reactive current Iq output from the inverter 12 approach the active current command value Idref and reactive current command value Iqref required by the power system 30, respectively.

[0080] 4. Effects According to the voltage control device 10 of this embodiment, if the voltage drop of the output voltage Vs of the inverter 12 exceeds a threshold due to fluctuations in the AC voltage of the power system 30, a first virtual impedance is calculated based on the voltage command value Vref and the output voltage Vs of the inverter 12. A second virtual impedance is also calculated to be temporarily added to the first virtual impedance so that the output current Io of the inverter 12 does not exceed its rated value. The voltage control device 10 then generates a virtual active voltage Vud and a virtual reactive voltage Vuq based on the virtual impedance obtained by adding the first and second virtual impedances. Furthermore, the voltage control device 10 performs voltage control based on the virtual active voltage Vud and virtual reactive voltage Vuq so that the active current Id and reactive current Iq output from the inverter 12 approach the active current command value Idref and reactive current command value Iqref required by the power system 30. As a result, even if the AC voltage of the power system 30 fluctuates, the required active current Id and reactive current Iq can be output. Therefore, it becomes possible to stabilize the power system 30. Furthermore, the second virtual impedance controls the output current Io so that it does not exceed its rated value. This also helps to suppress overcurrent. [Explanation of symbols]

[0081] 1...Power conversion system, 10...Voltage control device, 11...Battery, 12...Inverter, 20...Transformer, 30...Power system, 100...Control device, 101...Active / Reactive Voltage Calculation Processing Unit, 102...Active / Reactive Current Calculation Processing Unit, 103...VSG Control Unit, 104...dq-axis Voltage Conversion Unit, 105...dq-axis Current Command Calculation Unit, 106...Virtual Impedance Generation Unit, 106a...First Virtual Impedance Generation Unit, 106b...Second Virtual Impedance Generation Unit, 107...Virtual Voltage Generation Unit, 108...First Output Selection Circuit, 109...Second Output Selection Circuit, 110...Switching Judgment Circuit, 111...Addition / Subtraction Circuit, 111a...First Addition / Subtraction Circuit, 111b...Second Addition / Subtraction Circuit, 111c...Third Addition / Subtraction Circuit, 111d...Fourth Addition / Subtraction Circuit, 112...Voltage Control Circuit

Claims

1. An inverter that converts DC power output from a battery into AC power and supplies the AC power to the power grid, The inverter is connected to the aforementioned inverter. If the voltage drop of the output voltage of the inverter exceeds a threshold due to fluctuations in the AC voltage of the power system, a process is performed to calculate a first virtual impedance using variables including an active voltage command value and a reactive voltage command value calculated from the voltage command value, and an active current command value and a reactive current command value calculated from the output voltage and the voltage command value. A process to calculate a second virtual impedance, which is temporarily added to the first virtual impedance, so that the output current of the inverter does not exceed the rated value, A process to calculate the virtual active voltage and virtual reactive voltage by multiplying the active current and reactive current calculated from the output current by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance, A process of controlling the voltage so that the active current and the reactive current, respectively, approach the active current command value and the reactive current command value required by the power system, based on the virtual active voltage and the virtual reactive voltage, A control device configured to perform the following: Equipped with A voltage control device characterized by the following features.

2. A voltage control device according to claim 1, In the process of calculating the second virtual impedance, the control device, If the voltage drop of the output voltage is greater than or equal to the threshold, the second virtual impedance is set to a value corresponding to the output voltage. The system is configured to set the second virtual impedance to zero if the voltage drop of the output voltage is less than the threshold. A voltage control device characterized by the following features.

3. A voltage control device according to claim 2, The second virtual impedance is a reactance composed of the amplitude set by the first variable and the frequency set by the second variable. The control device, when the voltage drop of the output voltage is greater than or equal to the threshold, The smaller the output voltage, the larger the value of the first variable and the smaller the value of the second variable. The system is configured such that the larger the output voltage, the smaller the value of the first variable and the larger the value of the second variable. A voltage control device characterized by the following features.

4. A voltage control device according to any one of claims 1 to 3, The aforementioned variable further includes the active voltage and reactive voltage calculated from the output voltage. In the process of calculating the virtual impedance, the control device, The system is configured to calculate the virtual impedance based on the following conditions: the reactive voltage is zero, the reactive voltage command value is zero, the voltage obtained by subtracting the virtual active voltage and the active voltage from the active voltage command value is zero, and the voltage obtained by subtracting the virtual reactive voltage and the reactive voltage from the reactive voltage command value is zero. A voltage control device characterized by the following features.

5. A voltage control device according to any one of claims 1 to 3, The aforementioned first virtual impedance includes resistance and reactance, The control device is configured to calculate the resistance and reactance corresponding to the output voltage in the process of calculating the first virtual impedance. A voltage control device characterized by the following features.

6. A voltage control device according to any one of claims 1 to 3, The effective current command value is calculated by multiplying the difference voltage, which is the difference between the voltage command value and the output voltage, by a constant value. The reactive current command value is calculated such that the sum of the square of the active current command value and the square of the reactive current command value is 1. A voltage control device characterized by the following features.

7. A voltage control device according to claim 6, The aforementioned active current command value is expressed as a percentage. If the calculation result of the effective current command value exceeds 100%, the control device sets the effective current command value to 100%. A voltage control device characterized by the following features.

8. Using an inverter, the DC power output from the battery is converted to AC power, and the AC power is supplied to the power grid. If the voltage drop of the inverter's output voltage exceeds a threshold due to fluctuations in the AC voltage of the power system, a first virtual impedance is calculated using a variable that includes an active voltage command value and a reactive voltage command value calculated from the voltage command value, and an active current command value and a reactive current command value calculated from the output voltage and the voltage command value. To ensure that the output current of the inverter does not exceed the rated value, a second virtual impedance is calculated to be temporarily added to the first virtual impedance, The virtual active voltage and virtual reactive voltage are calculated by multiplying the active current and reactive current, respectively, calculated from the output current, by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance, Based on the virtual active voltage and the virtual reactive voltage, the voltage is controlled so that the active current and the reactive current, respectively, approach the active current command value and the reactive current command value required by the power system. including A voltage control method characterized by the following:

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