Voltage control device and voltage control method

Abstract

A 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 connected to the inverter. The control device executes: a process for calculating a first virtual impedance using various variables when the voltage drop of the output voltage of the inverter is equal to or greater than a threshold value due to a variation in the AC voltage of the power system; a process for calculating a second virtual impedance temporarily added to the first virtual impedance so that the output current of the inverter does not exceed a rated value; a process for calculating a virtual effective voltage and a virtual ineffective voltage by multiplying an effective current and an ineffective current calculated from the output current of the inverter by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance, respectively; and performing voltage control on the basis of the virtual effective voltage and the virtual ineffective voltage so that the effective current and the ineffective current approach an effective current command value and an ineffective current command value required by the power system, respectively.

Description

Technical Field

[0001] The present invention relates to a technology for controlling the output voltage of an inverter. Background Art

[0002] Patent document 1 discloses a technology that enables stable and continuous operation in a power converter (i.e., inverter) that performs simulated control of a synchronous generator. In this prior art, when the AC voltage of the power system fluctuates, voltage control is performed to reduce the effective power input and output between the power system and the power converter.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 7183486 Summary of the invention

[0006] Problems to be solved by the invention

[0007] As an inverter for supplying AC voltage to the power system, a voltage-controlled GFM (Grid Forming Inverter) inverter can be considered. In this case, as shown in Patent Document 1, when the AC voltage of the power system changes, voltage control is performed to reduce the difference in effective power input and output between the power system and the power converter.

[0008] However, even if voltage control is performed to stabilize effective power, the output current of the inverter may not reach the reference current required by the power system, and the power system may become unstable. Therefore, in order to supply stable effective power to the power system, voltage control is required to output the effective current and reactive current required by the power system.

[0009] An object of the present invention is to provide a technology capable of performing voltage control so as to output active current and reactive current required by the power system when the AC voltage of the power system fluctuates.

[0010] Means for solving problems

[0011] A first aspect of the present invention 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 the AC power to a power system. Furthermore, the voltage control device includes a control device connected to the inverter. The control device performs the following processing: when the voltage drop of the output voltage of the inverter exceeds a threshold value due to the change of the AC voltage of the power system, a first virtual impedance is calculated using variables including an effective voltage command value and an invalid voltage command value calculated based on a voltage command value, and an effective current command value and an invalid current command value calculated based on the output voltage of the inverter and the voltage command value; a second virtual impedance temporarily added to the first virtual impedance is calculated so that the output current of the inverter does not exceed the rated value; a virtual effective voltage and a virtual invalid voltage are calculated by multiplying the effective current and the invalid current calculated based on the output current of the inverter by virtual impedances obtained by adding the first virtual impedance and the second virtual impedance; and a voltage control is performed based on the virtual effective voltage and the virtual invalid voltage so that the effective current and the invalid current are close to the effective current command value and the invalid current command value required by the power system.

[0012] The second aspect of the present invention has the following features in addition to the first aspect. 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 when the voltage drop of the output voltage of the inverter is greater than a threshold value. In addition, in the process of calculating the second virtual impedance, the control device sets the second virtual impedance to zero when the voltage drop of the output voltage of the inverter is less than a threshold value.

[0013] The third viewpoint of the present invention has the following characteristics on the basis of the second viewpoint. The second virtual impedance is a reactance composed of an amplitude set by a first variable and a frequency set by a second variable. In addition, when the voltage drop of the output voltage of the inverter is above a threshold value, the control device sets the value of the first variable in a manner that increases as the output voltage of the inverter decreases and decreases the value of the second variable. Furthermore, when the voltage drop of the output voltage of the inverter is above a threshold value, the control device sets the value of the first variable in a manner that decreases as the output voltage of the inverter increases and increases the value of the second variable.

[0014] The fourth aspect of the present invention is characterized by the following features based on any one of the first to third aspects. The variable also includes an effective voltage and an invalid voltage calculated based on the output voltage. In the process of calculating the virtual impedance, the control device calculates the virtual impedance based on the conditions that the invalid voltage is zero, the invalid voltage command value is zero, the voltage value obtained by subtracting the virtual effective voltage and the effective voltage from the effective voltage command value is zero, and the voltage value obtained by subtracting the virtual invalid voltage and the invalid voltage from the invalid voltage command value is zero.

[0015] A fifth aspect of the present invention is characterized in that, in addition to any one of the first to third aspects, the first virtual impedance includes resistance and reactance, and the control device calculates each of the resistance and reactance corresponding to the output voltage in the process of calculating the first virtual impedance.

[0016] The sixth aspect of the present invention is based on any one of the first to third aspects and has the following features. The effective current command value is calculated by multiplying the differential voltage obtained by differentiating the voltage command value from the output voltage by a constant value. In addition, the ineffective current command value is calculated so that the sum of the square value of the effective current command value and the square value of the ineffective current command value is 1.

[0017] The seventh aspect of the present invention has the following characteristics in addition to the sixth aspect: the effective current command value is expressed as a percentage, and the control device sets the effective current command value to 100% when the calculation result of the effective current command value exceeds 100%.

[0018] The eighth aspect of the present invention 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 supplying AC power to a power system; when the voltage drop of the output voltage of the inverter exceeds a threshold value due to the change of the AC voltage of the power system, using variables including an effective voltage command value and an ineffective voltage command value calculated based on the voltage command value, and an effective current command value and an ineffective current command value calculated based on the output voltage of the inverter and the voltage command value, calculating a first virtual impedance; calculating a second virtual impedance temporarily added to the first virtual impedance in such a way that the output current of the inverter does not exceed the rated value; multiplying the effective current and the ineffective current calculated based on the output current of the inverter by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance, respectively, to calculate a virtual effective voltage and a virtual ineffective voltage; and performing voltage control based on the virtual effective voltage and the virtual ineffective voltage so that the effective current and the ineffective current are close to each of the effective current command value and the ineffective current command value required by the power system.

[0019] Effects of the Invention

[0020] According to the present invention, when the voltage drop of the output voltage of the inverter is above the threshold value due to the change of the AC voltage of the power system, the first virtual impedance is calculated based on the voltage command value and the output voltage of the inverter. In addition, the second virtual impedance temporarily added to the first virtual impedance is calculated in such a way that the output current of the inverter does not exceed the rated value. Then, a virtual effective voltage and a virtual invalid voltage are generated based on the virtual impedance obtained by adding the first virtual impedance to the second virtual impedance, and voltage control is performed based on the virtual effective voltage and the virtual invalid voltage so that the effective current and the invalid current output from the inverter are respectively close to the effective current command value and the invalid current command value required by the power system. As a result, even if the AC voltage of the power system changes, the effective current and the invalid current required by the power system can be output. Therefore, the power system can be stabilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram for explaining the outline of a power conversion system.

[0022] Figure 2 It is a block diagram showing a functional example of a control device in the voltage control device according to the embodiment.

[0023] Figure 3 1 is a block diagram showing a functional example of a circuit for generating a second virtual impedance (Xα) of a control device in the voltage control device according to the embodiment.

[0024] Figure 4 This is a diagram for explaining an example of an output result of a virtual impedance of a control device in the voltage control device according to the embodiment.

[0025] Figure 5 It is a diagram for explaining an example of an output result of an inverter in the voltage control device according to the embodiment.

[0026] Figure 6 1 is a flowchart showing a processing example of the control device in the voltage control device according to the embodiment. DETAILED DESCRIPTION

[0027] A voltage control device and a voltage control method according to an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the same reference numerals are given to common elements in each figure, and duplicate descriptions are omitted.

[0028] 1. Overview of power conversion system

[0029] Figure 11 is a diagram for explaining the outline of the power conversion system 1. The power conversion system 1 includes a voltage control device 10, a transformer 20, and a power system 30. The voltage control device 10 includes a battery 11, an inverter 12, and a control device 100.

[0030] The inverter 12 is a device that converts DC power output from the battery 11 into AC power and supplies the AC power to the power system 30 via the transformer 20. As the inverter 12, a voltage-controlled GFM inverter is exemplified.

[0031] The control device 100 is a device connected to the inverter 12 and controls the output power output from the inverter 12. Specifically, the control device 100 inputs 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) output from the inverter 12. The Vs detection value and the Io detection value are detected by a detector (not shown) provided between the voltage control device 10 and the power system 30. Figure 1 In the example shown, the Vs detection value and the Io detection value detected between the voltage control device 10 and the transformer 20 are input to the control device 100, but the Vs detection value and the Io detection value detected between the transformer 20 and the power system 30 may be input. In this way, the detection value of the AC voltage of the power system 30 may also be the Vs detection value. In addition, the detection value of the AC current of the power system 30 may also be the Io detection value.

[0032] In addition, 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-mentioned Vs detection value includes a Vsu detection value, a Vsv detection value, and a Vsw detection value, and the above-mentioned Io detection value includes an Iou detection value, an Iov detection value, and an Iow detection value.

[0033] The control device 100 performs VSG (Virtual Synchronous Generator) control based on the input Vs detection value and Io detection value. VSG refers to a virtual synchronous generator that allows the inverter 12 to virtually have the dynamic characteristics of a synchronous generator. That is, VSG control refers to controlling the virtual synchronous generator. The dynamic characteristics of the synchronous generator include an inertia constant M, a braking constant D, etc. As a result, when a system accident occurs, that is, when LVRT (Low Voltage Ride Through) occurs, the power system 30 can be prevented from becoming unstable.

[0034] Moreover, the control device 100 performs voltage control on the inverter 12 based on the execution result of the VSG control so that the output current Io output from the inverter 12 when the LVRT is generated becomes the current value required by the power system 30. The voltage control includes the generation of three-phase voltages (Vsu, Vsv, Vsw) and PWM control for performing pulse width modulation on the three-phase voltages. Moreover, the control device 100 outputs the voltage control signal generated by the PWM control to the inverter 12. Thus, 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.

[0035] 2. Specific example of voltage control device

[0036] 2-1. Example of control device configuration

[0037] The control device 100 has hardware for realizing various functions. The hardware may be a processing circuit or a computer in which a CPU executes a program stored in a storage device. Examples of the processing circuit include FPGA (Field Programmable Gate Array) and ASIC (Application Specific Integrated Circuit).

[0038] 2-2. Example of control device functions

[0039] Figure 2 1 is a block diagram showing a functional example of the control device 100 in the voltage control device 10 according to the embodiment. The control device 100 includes an effective and ineffective voltage calculation processing unit 101, an effective and ineffective 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 and subtraction circuit 111, and a voltage control circuit 112.

[0040] The effective / ineffective voltage calculation processing unit 101 calculates the effective voltage Vd and the ineffective voltage Vq based on the Vs detection value input to the control device 100. The effective voltage Vd and the ineffective voltage Vq calculated by the effective / ineffective voltage calculation processing unit 101 are expressed by the following equation (1) as an example.

[0041]

Number 1

[0042]

[0043] The effective and reactive current calculation processing unit 102 calculates the effective current Id and the reactive current Iq based on the Io detection value input to the control device 100. The effective current Id and the reactive current Iq calculated by the effective and reactive current calculation processing unit 102 are expressed by the following equation (2) as an example.

[0044]

Number 2

[0045]

[0046] The VSG control unit 103 generates a voltage command value Vref of the output voltage Vs of the inverter 12. The voltage command value Vref is, for example, a fixed value determined 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.

[0047] The d-axis voltage command value Vdref is also referred to as an effective voltage command value Vdref, and the q-axis voltage command value Vqref is also referred to as an ineffective voltage command value Vqref. The dq-axis voltage converter 104 converts the voltage command value Vref generated by the VSG controller 103 into an effective voltage command value Vdref and an ineffective voltage command value Vqref.

[0048] 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 by the power system 30 based on the voltage command value Vref and the Vs detection value when LVRT occurs as the AC voltage of the power system 30 changes. The d axis current command value Idref is also called the effective current command value Idref, and the d axis current command value Idref is also called the reactive current command value Iqref. The effective current command value Idref and the reactive current command value Iqref calculated by the dq axis current command calculation unit 105 are respectively represented by the following equations (3) and (4) as an example. K is a constant value determined according to the specifications of the inverter 12. ΔV is a differential voltage Vdiff obtained by differentiating the voltage command value Vref from the Vs detection value.

[0049]

Number 3

[0050] Iqref=kΔV…(3)

[0051]

Number 4

[0052]

[0053] Here, when the variables used in equations (3) and (4) are expressed as percentages, the effective current command value Idref is calculated in a manner that does not exceed 100%. Specifically, when the voltage drop of the Vs detection value is reduced to 60%, ΔV becomes Vdref-Vs=100%-60%=40%. In addition, when k is set to the constant value of "2", Iqref becomes 2×40%=80%. In this case, Iqref does not exceed 100%, so it becomes 80%. In addition, the ineffective current command value Iqref is calculated in a manner that the sum of the square value of the effective current command value Idref and the square value of the ineffective current command value Iqref becomes 1. Therefore, when the effective current command value Idref is 80%, the ineffective current command value Iqref becomes 60% according to equation (4).

[0054] Next, consider the case where the voltage drop of the Vs detection value decreases to 10%. In this case, ΔV becomes Vdref-Vs=100%-10%=90%. In addition, when k is set to the constant value of "2", Iqref becomes 2×90%=180%. In this case, Iqref exceeds 100%, so it becomes 100% of the upper limit. In addition, when the effective current command value Idref is 100%, the ineffective current command value Iqref becomes 0% according to formula (4).

[0055] The virtual impedance generating unit 106 includes a first virtual impedance generating unit 106a and a second virtual impedance generating unit 106b. The first virtual impedance generating unit 106a calculates the first virtual impedance in such a manner that the output voltage Vs of the inverter 12 increases when the voltage drop of the Vs detection value is greater than a threshold value, that is, when the differential voltage Vdiff obtained by differentiating the Vs detection value and the voltage command value Vref is greater than a threshold value. The first virtual impedance includes a resistor Rv and a reactance Xv. The resistor Rv and the reactance Xv are calculated based on the effective voltage command value Vdref, the ineffective voltage command value Vqref, the effective current command value Idref, the ineffective current command value Iqref, the effective voltage Vd, and the ineffective voltage Vq, respectively.

[0056] The second virtual impedance generating unit 106b is a circuit for generating a second impedance. The second impedance refers to 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 generating unit 106a. That is, the virtual impedance generating unit 106 calculates the reactance Xv2 obtained by adding the reactance Xv to the reactance Xα. Moreover, the virtual impedance generating unit 106 outputs the resistor Rv and the reactance Xv2 to the virtual voltage generating unit 107 described later. The details of the calculation of the resistor Rv and the reactance Xv2 and the generation of the reactance Xα will be described in detail later.

[0057] The virtual voltage generating unit 107 generates a virtual effective voltage Vud and a virtual ineffective voltage Vuq for increasing the output voltage Vs of the inverter 12 based on the resistor Rv and the reactance Xv2, the effective current Id, and the ineffective current Iq. The virtual effective voltage Vud calculated by the virtual voltage generating unit 107 and the virtual voltage generating unit 107 are respectively represented by the following formula (5) as an example.

[0058]

Number 5

[0059]

[0060] The first output selection circuit 108 is a switching switch having two input terminals and one output terminal. The first output selection circuit 108 switches in a manner that selects one of the two input terminals. Specifically, when the switching determination 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, when the switching determination result input to the first output selection circuit 108 is "1", the first output selection circuit 108 switches to select the second input terminal. Figure 2 In the illustrated example, 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 .

[0061] The switching determination result is generated by the switching determination circuit 110. When the differential voltage Vdiff between the Vs detection value and the voltage command value Vref is lower than the threshold value, that is, when the AC voltage of the power system 30 is not in the LVRT state, the switching determination circuit 110 outputs "0" as the switching determination result. On the other hand, when the differential voltage Vdiff between the Vs detection value and the voltage command value Vref is higher than the threshold value, that is, when the AC voltage of the power system 30 is in the LVRT state, the switching determination circuit 110 outputs "1" as the switching determination result. 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.

[0062] The second output selection circuit 109 is a switching switch having two input terminals and one output terminal. The second output selection circuit 109 switches in a manner that selects one of the two input terminals. Specifically, when the switching determination 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, when the switching determination result input to the second output selection circuit 109 is "1", the second output selection circuit 109 switches to select the second input terminal. Figure 2 In the example shown, a fixed value (zero value) is input to the first input terminal of the second output selection circuit 109 , and a virtual null voltage Vuq is input to the second input terminal of the second output selection circuit 109 .

[0063] As described above, the switching determination result is generated by the switching determination circuit 110. 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 a selection invalid voltage Vqsel.

[0064] The addition and subtraction circuit 111 includes four addition and subtraction circuits (a first addition and subtraction circuit 111a, a second addition and subtraction circuit 111b, a third addition and subtraction circuit 111c, and a fourth addition and subtraction circuit 111d). The first addition and subtraction circuit 111a is an addition and subtraction circuit that adds the effective voltage command value Vdref and performs addition and subtracts the selected effective voltage Vdsel. The second addition and subtraction circuit 111b is an addition and subtraction circuit that adds the invalid voltage command value Vqref and performs addition and subtracts the selected invalid voltage Vqsel. The third addition and subtraction circuit 111c is an addition and subtraction circuit that adds the output of the first addition and subtraction circuit 111a and performs addition and subtracts the effective voltage Vd. The fourth addition and subtraction circuit 111d is an addition and subtraction circuit that adds the output of the second addition and subtraction circuit 111b and performs addition and subtracts the invalid voltage Vq.

[0065] When the effective voltage output from the third adder-subtractor circuit 111c is taken as the abnormal effective voltage Errd and the invalid voltage output from the fourth adder-subtractor circuit 111d is taken as the abnormal invalid voltage Errq, the relational expression (6) shown below holds.

[0066]

Number 6

[0067]

[0068] In addition, when equation (5) is substituted into equation (6), it is expressed by the following equation (7).

[0069]

Number 7

[0070]

[0071] In this case, if the abnormal effective voltage Errd and the abnormal invalid voltage Errq are both zero values, it means that the virtual effective voltage Vud and the virtual invalid voltage Vuq are both appropriate voltage values. That is, by setting the abnormal effective voltage Errd and the abnormal invalid voltage Errq to zero in advance, the optimal values ​​of the virtual effective voltage Vud and the virtual invalid voltage Vuq can be calculated.

[0072] Moreover, the power factor expressed by percentage of the effective voltage Vd relative to the output voltage Vs of the inverter 12 is preferably high. Accordingly, the invalid voltage Vq and the invalid voltage command value Vqref are both set to zero. Therefore, in the formula (7), when Errd=0, Errq=0, the invalid voltage Vq=0, and the invalid voltage command value Vqref=0, the resistance Rv and the reactance Xv2 are each expressed by the following formula (8) as an example.

[0073]

Number 8

[0074]

[0075] Thus, the calculation formula of the virtual impedance that adds the first virtual impedance to the second virtual impedance includes the effective current command value Idref and the reactive current command value Iqref, so the voltage control device 10 can output appropriate effective current Id and reactive current Iq to the power system 30. In addition, since the second virtual impedance is included in the virtual impedance, the impedance becomes larger, so the output current Io of the inverter 12 can be controlled not to exceed the rated value. Thus, the overcurrent in the output current Io of the inverter 12 can be suppressed.

[0076] The voltage control circuit 112 is a circuit that performs voltage control based on a virtual effective voltage Vud and a virtual ineffective voltage Vuq calculated from virtual impedance (resistance Rv and reactance Xv2) so that the effective current Id and the ineffective current Iq are close to the effective current command value Idref and the ineffective current command value Iqref required by the power system 30. In addition, the voltage control circuit 112 outputs a voltage control signal Vsc generated by the voltage control.

[0077] In addition, as described above, voltage control includes processing for generating three-phase voltages (Vsu, Vsv, Vsw) and PWM control for performing pulse width modulation on the three-phase voltages. In PWM control, the generated three-phase voltages are controlled to have a predetermined pulse width and a predetermined frequency. In addition, PI control is used, for example, in the generation of the three-phase voltage based on voltage control.

[0078] 2-3. Calculation example of the second virtual impedance (Xα)

[0079] Figure 3 1 is a block diagram showing a functional example of a circuit for generating a second virtual impedance (Xα) of the control device 100 in the voltage control device 10 according to the embodiment. Specifically, Figure 3 The second virtual impedance generator 106 b includes a variable setting unit 200 , a third output selection circuit 201 , a switching determination circuit 202 , and a high-pass filter unit 203 .

[0080] 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 generating unit 106b. Furthermore, the variable setting unit 200 outputs the reactance Xα generated based on the first variable and the second variable. The first variable is a variable for setting the amplitude of the reactance Xα, and is set to an amplitude corresponding to the Vs detection value. The second variable is a variable for setting the frequency of the reactance Xα, and is set to a frequency corresponding to the Vs detection value.

[0081] Consider the setting value of the first variable. For example, when the Vs detection value is small, in order to reduce the difference in AC power between the power system 30 and the inverter 12, it is necessary to increase the rise of the output current Io. Therefore, in this case, the control device 100 sets the value of the first variable to a larger value. On the other hand, when the Vs detection value is large, in order to reduce the difference in AC power between the power system 30 and the inverter 12, it is necessary to reduce the rise of the output current Io. Therefore, in this case, the control device 100 sets the value of the first variable to a smaller value.

[0082] Next, the setting value of the second variable is considered. For example, when the Vs detection value is small, as described above, it is necessary to increase the degree of increase of the output current Io. In this case, it is assumed that a certain time is required to increase the output current Io to a predetermined current value. Therefore, when the Vs detection value is small, the control device 100 sets the value of the frequency as the second variable to a small value to prolong the time for the reactance Xα to become effective.

[0083] On the other hand, when the Vs detection value is large, as described above, it is necessary to reduce the degree of increase of the output current Io. In this case, it is assumed that the time required to increase the output current Io to a predetermined current value is short. Therefore, when the Vs detection value is large, the control device 100 sets the value of the frequency as the second variable to a large value to shorten the time when the reactance Xα becomes effective.

[0084] Thus, the setting is such that the value of the first variable is increased and the value of the second variable is decreased as the Vs detection value is smaller, and the setting is such that the value of the first variable is decreased and the value of the second variable is increased as the Vs detection value is larger.

[0085] The third output selection circuit 201 is a switching switch having two input terminals and one output terminal. The third output selection circuit 201 switches to select one of the two input terminals. Specifically, when the switching determination 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, when the switching determination result input to the third output selection circuit 201 is "1", the third output selection circuit 201 switches to select the second input terminal. Figure 3 In the example shown, a fixed value (zero value) is input to the first input terminal of the third output selection circuit 201 , and a reactance Xα generated by the variable setting unit 200 is input to the second input terminal of the third output selection circuit 201 .

[0086] The switching determination result is generated by the switching determination circuit 202. When the Vs detection value is greater than the threshold value th2, that is, when the output current Io of the inverter 12 is less than the rated value of the inverter 12, the switching determination circuit 202 outputs "0" as the switching determination result. On the other hand, when the Vs detection value is less than the threshold value th2, that is, when the output current Io of the inverter 12 exceeds the rated value of the inverter 12, the switching determination circuit 202 outputs "1" as the switching determination result. The reactance Xα output from the third output selection circuit 201 outputs the value (reactance Xα or zero) input to the selected input terminal.

[0087] The high-pass filter unit 203 is a high-pass filter that removes unnecessary signal components before the reactance Xα is output from the second virtual impedance generator 106 b .

[0088] In addition, the variable setting unit 200 described above is provided on the input side of the third output selection circuit 201 , but may be provided on the output side of the third output selection circuit 201 .

[0089] 2-4. Example of output results of virtual impedance

[0090] Figure 4 This is a diagram for explaining an example of an output result of a virtual impedance of the control device 100 in the voltage control device 10 according to the embodiment. Figure 4 (A) shows an example of a waveform of the reactance Xα output from the second virtual impedance generating unit 106 b . Figure 4 (B) shows an example of the waveform of the reactance Xv2 input to the virtual voltage generating unit 107. Figure 4 (A) and Figure 4 In the example shown in (B) of FIG. 1 , the value of each reactance is expressed as PU (Per Unit), but it may also be expressed as a percentage.

[0091] In addition, Figure 4 In the example shown in (A), the waveform of the reactance Xα is shown when the first variable used in generating the reactance Xα is set to "0.5 pu" and the second variable is set to "0.7 Hz". The first variable is set, for example, between 0.2 pu and 0.6 pu, and the second variable is set, for example, between 0.3 Hz and 2 Hz.

[0092] like Figure 4 As shown in (A), the reactance Xα rises sharply when the first variable is set, and then decays gently. That is, the reactance Xα is a temporarily set impedance, and decays to zero at the value set by the first variable based on the frequency set by the second variable. Therefore, Figure 4 As shown in (B), the reactance Xv2 also attenuates in accordance with the change of the reactance Xα. Moreover, when the reactance Xα attenuates to zero, the reactance Xv2 only includes the reactance Xv. Figure 4 In the example shown in (B), the resistance Rv becomes 0.0 pu.

[0093] 2-5. Example of inverter output results

[0094] Figure 5 It is a diagram for explaining an example of an output result of the inverter 12 in the voltage control device 10 according to the embodiment. Figure 5 (A) shows an example of a waveform of the output voltage Vs when the Vs detection value decreases to 45%. Figure 5 (B) shows an example of the waveform of the output current Io output from the inverter 12 to the power system 30 , the waveform of the effective current Id, and the waveform of the reactive current Iq when the Vs detection value is reduced to 45% and the reactance Xα is set to zero. Figure 5(C) shows an example of a waveform of an output current Io output from the inverter 12 to the power system 30, a waveform of an effective current Id, and a waveform of a reactive current Iq when the Vs detection value is reduced to 45% and the first variable and the second variable are set for the reactance Xα.

[0095] exist Figure 5 In the example shown in (B), when the Vs detection value drops to 45% and the reactance Xα is set to zero, the output current Io composed of the effective current Id and the reactive current Iq exceeds 100% and is output at 140%.

[0096] exist Figure 5 In the example shown in (C), when the Vs detection value decreases to 45% and the first variable and the second variable are set for the reactance Xα, the output current Io composed of the effective current Id and the reactive current Iq is output at less than 100%.

[0097] In this way, when the AC voltage of the power system 30 changes, the effective current Id and the reactive current Iq required by 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. In addition, the first variable and the second variable are set for the reactance Xα according to the voltage drop of the output voltage of the inverter 12. In this way, the overcurrent in the output current Io of the inverter 12 can be suppressed.

[0098] 3. Processing example

[0099] Figure 6 1 is a flowchart showing a processing example of the control device 100 in the voltage control device 10 according to the embodiment.

[0100] 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 value. If the voltage drop of the output voltage is greater than or equal to the threshold value (step S100; Yes), the process proceeds to step S110. Otherwise (step S100; No), the control device 100 ends the process.

[0101] In step S110 , the control device 100 calculates the first virtual impedance based on various variables. Thereafter, the process proceeds to step S120 .

[0102] In addition, the first virtual impedance is calculated based on the prescribed conditions. The prescribed conditions are the following conditions: the invalid voltage Vq is zero, the invalid voltage command value Vqref is zero, the voltage value obtained by subtracting the virtual effective voltage Vud and the effective voltage Vd from the effective voltage command value Vdref is zero, and the voltage value obtained by subtracting the virtual invalid voltage Vuq and the invalid voltage Vq from the invalid voltage command value Vqref is zero.

[0103] In step S120, the control device 100 calculates the second virtual impedance to be temporarily added to the first virtual impedance. Thereafter, the process proceeds to step S130.

[0104] In step S130, the control device 100 calculates a virtual effective voltage Vud and a virtual reactive voltage Vuq by multiplying the effective current Id and the reactive current Iq 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. Then, the process proceeds to step S140.

[0105] In step S140 , the control device 100 performs voltage control based on the virtual effective voltage Vud and the virtual reactive voltage Vuq so that the effective current Id and the reactive current Iq output from the inverter 12 approach the effective current command value Idref and the reactive current command value Iqref required by the power system 30 , respectively.

[0106] 4. Effect

[0107] According to the voltage control device 10 involved in the embodiment, when the voltage drop of the output voltage Vs of the inverter 12 is greater than or equal to the threshold value due to the change of the AC voltage of the power system 30, the first virtual impedance is calculated based on the voltage command value Vref and the output voltage Vs of the inverter 12. In addition, the second virtual impedance temporarily added to the first virtual impedance is calculated so that the output current Io of the inverter 12 does not exceed the rated value. Moreover, in the voltage control device 10, based on the virtual impedance obtained by adding the first virtual impedance to the second virtual impedance, a virtual effective voltage Vud and a virtual ineffective voltage Vuq are generated. Moreover, in the voltage control device 10, voltage control is performed based on the virtual effective voltage Vud and the virtual ineffective voltage Vuq so that the effective current Id and the ineffective current Iq output from the inverter 12 are close to the effective current command value Idref and the ineffective current command value Iqref required by the power system 30, respectively. As a result, even when the AC voltage of the power system 30 changes, the effective current Id and the ineffective current Iq required by the power system 30 can be output. Therefore, the power system 30 can be stabilized. Furthermore, the second virtual impedance is used to control the output current Io so that it does not exceed the rated value. This can also suppress overcurrent.

[0108] Description of Reference Numerals

[0109] 1: power conversion system, 10: voltage control device, 11: battery, 12: inverter, 20: transformer, 30: power system, 100: control device, 101: effective and invalid voltage calculation processing unit, 102: effective and invalid 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 determination circuit, 111: addition and subtraction circuit, 111a: first addition and subtraction circuit, 111b: second addition and subtraction circuit, 111c: third addition and subtraction circuit, 111d: fourth addition and subtraction circuit, 112: voltage control circuit.

Claims

1. A voltage control device, characterized in that: have: an inverter that converts direct current power output from the battery into alternating current power and supplies the alternating current power to the power system; and A control device connected to the inverter, The control device is configured to perform the following processing: When the voltage drop of the output voltage of the inverter exceeds a threshold value due to a change in the AC voltage of the power system, a process of calculating a first virtual impedance using variables including an effective voltage command value and an ineffective voltage command value calculated based on a voltage command value, and an effective current command value and an ineffective current command value calculated based on the output voltage and the voltage command value; Calculating a second virtual impedance temporarily added to the first virtual impedance in such a way that the output current of the inverter does not exceed a rated value; A process of calculating a virtual effective voltage and a virtual invalid voltage by multiplying an effective current and an invalid current calculated according to the output current by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance; as well as A process of performing voltage control based on the virtual effective voltage and the virtual reactive voltage so that the effective current and the reactive current are close to the effective current command value and the reactive current command value respectively required by the electric power system.

2. The voltage control device according to claim 1, characterized in that: The control device is configured such that, in the process of calculating the second virtual impedance, When the voltage drop of the output voltage is equal to or greater than the threshold value, the second virtual impedance is set to a value corresponding to the output voltage, In a case where the voltage of the output voltage drops below the threshold, the second virtual impedance is set to zero.

3. The voltage control device according to claim 2, characterized in that: The second virtual impedance is a reactance composed of an amplitude set by a first variable and a frequency set by a second variable. The control device is configured so that, when the voltage drop of the output voltage is equal to or greater than the threshold value, The first variable is set to increase the value of the first variable and decrease the value of the second variable as the output voltage decreases. The value of the first variable is set to be smaller and the value of the second variable is set to be larger as the output voltage is larger.

4. The voltage control device according to any one of claims 1 to 3, characterized in that: The variables also include effective voltage and invalid voltage calculated according to the output voltage. The control device is configured such that, in the process of calculating the virtual impedance, The virtual impedance is calculated based on the conditions that the invalid voltage is zero, the invalid voltage command value is zero, the voltage value obtained by subtracting the virtual effective voltage and the effective voltage from the effective voltage command value is zero, and the voltage value obtained by subtracting the virtual invalid voltage and the invalid voltage from the invalid voltage command value is zero.

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

6. The voltage control device according to any one of claims 1 to 3, characterized in that: The effective current command value is calculated by multiplying a differential voltage obtained by differentiating the voltage command value from the output voltage by a constant value. The reactive current command value is calculated so that a sum obtained by adding a square value of the effective current command value and a square value of the reactive current command value becomes 1.

7. The voltage control device according to claim 6, characterized in that: The effective current command value is expressed as a percentage, The control device sets the effective current command value to 100% when the calculation result of the effective current command value exceeds 100%.

8. A voltage control method, characterized in that: include: using an inverter to convert direct current power output from a battery into alternating current power, and supplying the alternating current power to a power system; When the voltage drop of the output voltage of the inverter exceeds a threshold value due to a change in the AC voltage of the power system, calculating a first virtual impedance using variables including an effective voltage command value and an ineffective voltage command value calculated based on a voltage command value, and an effective current command value and an ineffective current command value calculated based on the output voltage and the voltage command value; Calculating a second virtual impedance temporarily added to the first virtual impedance in such a way that the output current of the inverter does not exceed a rated value; multiplying the effective current and the ineffective current calculated according to the output current by a virtual impedance obtained by adding the first virtual impedance and the second virtual impedance, respectively, to calculate a virtual effective voltage and a virtual ineffective voltage; as well as Voltage control is performed based on the virtual effective voltage and the virtual reactive voltage so that the effective current and the reactive current are close to the effective current command value and the reactive current command value required by the electric power system, respectively.

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