Power conversion device and method for controlling power conversion device

Abstract

A power conversion device (1) is provided with DC terminals (7a, 7b) to which DC power is input and output, AC terminals (5a, 5b, 5c) to which AC power is input and output, a main circuit (2) that mutually converts the DC power and the AC power, and a control circuit (3) that controls the main circuit. The control circuit (3) has a power calculation unit (31) that calculates an active power indicating an active component of the AC power, and an active power output command setting unit (33) that sets an active power output command indicating a command value for the active power. And a phase command generation unit (32) that calculates a deviation between the active power and the active power output command and determines an angular frequency and a phase of the AC power on the basis of the deviation, the phase command generation unit (32) having a droop characteristic indicating a relationship between the deviation and the angular frequency. When the angular frequency determined by the droop characteristic exceeds a preset upper limit value, the deviation is calculated by decreasing the active power output command, and when the angular frequency determined by the droop characteristic falls below a preset lower limit value, the deviation is calculated by increasing the active power output command.

Description

Technical Field

[0001] The present invention relates to a power conversion device and a control method thereof. Background Art

[0002] As the background art of the present invention, the technology described in Patent Document 1 is known. Patent Document 1 describes a power conversion device for a hybrid power generation system. In a power supply system composed of a plurality of power generation devices including a power storage device having a power storage device and a power converter, it has a voltage measurement unit for measuring the voltage of the power supply system, a frequency measurement unit for measuring the frequency of the power supply system, a power measurement unit for measuring the active power and reactive power at the output terminal of the power storage device, and a system control device. The system control device includes: a frequency command value calculation unit having a first proportional calculator for performing proportional calculation on the deviation between the active power command value and the active power measured by the power measurement unit, and a first adder for adding a reference frequency to the output of the first proportional calculator to calculate the frequency command value; an internal phase difference angle calculation unit for accumulating the deviation between the frequency command value calculated by the frequency command value calculation unit and the frequency measured by the frequency measurement unit to calculate the internal phase difference angle; an internal electromotive force command value calculation unit having a second proportional calculator for performing proportional calculation on the deviation between the reactive power command value and the reactive power measured by the power measurement unit, and a second adder for adding a reference voltage to the output of the second proportional calculator to calculate the internal electromotive force command value; and a current command value calculation unit for calculating the command value of the output current of the power converter based on the internal phase difference angle, the internal electromotive force command value, and the voltage measured by the voltage measurement unit, and outputting the command value of the output current to control the power converter.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2013 / 008413 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the power conversion device for the above-mentioned combined power generation system, the target value of the output current of the power conversion device is calculated based on the internal phase difference angle calculated according to the active power control loop and the internal electromotive force calculated according to the reactive power control loop, so as to provide a power converter that does not require a change in the control method during system grid connection, etc., and an independent power supply system that is easy to use is constructed. However, since the upper and lower limit values of the output angular frequency are set in the limiter, there is a possibility that the command value of the active power during independent operation is different from the actual output active power of the power conversion device for the combined power generation system. In such a case, after the angular frequency becomes the value set in the limiter, even if the actual output active power increases or decreases due to the increase or decrease of the power consumed by the load, the angular frequency does not approach the reference angular frequency but remains stable at the value set in the limiter. As a result, the frequency quality during independent operation deteriorates.

[0008] In view of the above problems, an object of the present invention is to provide a power conversion device and its control method that can transfer between system grid-connected operation and independent operation without control switching and improve the frequency quality during independent operation.

[0009] Technical solution for solving the problem

[0010] The power conversion device of the present invention includes: a DC terminal for inputting and outputting DC power; an AC terminal for inputting and outputting AC power; a main circuit for mutually converting the DC power and the AC power; and a control circuit for controlling the main circuit. The control circuit has: a power operation unit for calculating the active power representing the active component of the AC power; an active power output command setting unit for setting an active power output command representing the command value for the active power; and a phase command generation unit for calculating the deviation between the active power and the active power output command and determining the angular frequency and phase of the AC power based on the deviation. The phase command generation unit has a droop characteristic representing the relationship between the deviation and the angular frequency. When the angular frequency determined by the droop characteristic exceeds a preset upper limit value, the active power output command is reduced to calculate the deviation. When the angular frequency determined by the droop characteristic is lower than a preset lower limit value, the active power output command is increased to calculate the deviation.

[0011] The control method of the power conversion device of the present invention is a control method for a power conversion device that mutually converts DC power and AC power. The active power representing the active component of the AC power is calculated, an active power output command representing the command value for the active power is set, the deviation between the active power and the active power output command is calculated, and based on the droop characteristic representing the relationship between the deviation and the angular frequency of the AC power, the angular frequency of the AC power is determined; in the case where the angular frequency determined by the droop characteristic exceeds a preset upper limit value, the active power output command is reduced to calculate the deviation, and in the case where the angular frequency determined by the droop characteristic is lower than a preset lower limit value, the active power output command is increased to calculate the deviation.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to provide a power conversion device and its control method that can transfer between grid-connected operation and independent operation of the system without control switching and improve the frequency quality during independent operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing a structural example of the power conversion device according to the first embodiment of the present invention.

[0015] Figure 2 It is a diagram showing a structural example of the phase command generation unit in the first embodiment of the present invention.

[0016] Figure 3 It is an example of a droop characteristic diagram showing the relationship between the deviation between the active power and the active power output command and the angular frequency change amount command without correcting the active power output command.

[0017] Figure 4 It is an example of a droop characteristic diagram showing the relationship between the deviation between the active power and the active power output command and the angular frequency change amount command when the active power output command is corrected.

[0018] Figure 5 It is a diagram showing a structural example of the power conversion device according to the second embodiment of the present invention.

[0019] Figure 6 It is a diagram showing a structural example of the phase command generation unit in the third embodiment of the present invention.

[0020] Figure 7 It is a diagram showing a structural example of the power conversion device according to the fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in each of the embodiments described below, for the sake of simplicity of description, it is assumed that the efficiency of the circuit and the device is 100%, but in reality, the efficiency may not be 100%.

[0022] In addition, the present invention is not limited to the following embodiments. Those skilled in the art can make various additions and changes within the scope of the present invention.

[0023] (First Embodiment)

[0024] Figure 1 It is a diagram showing a structural example of a power conversion device according to the first embodiment of the present invention. Figure 1 The power conversion device 1 shown includes a main circuit 2, a control circuit 3, and an AC filter 4. In addition, it has AC terminals 5a, 5b, 5c for inputting and outputting AC power by being connected to an AC system 5 and an AC load 6, and DC terminals 7a, 7b for inputting and outputting DC power by being connected to a DC power supply 7.

[0025] The main circuit 2 is constituted by, for example, a three-phase full-bridge inverter, and operates in response to the control of the control circuit 3, thereby mutually converting the DC power input and output via the DC terminals 7a, 7b and the AC power input and output via the AC terminals 5a, 5b, 5c. The AC side of the main circuit 2 is connected to the AC system 5 and the AC load 6 via the AC filter 4 and the AC terminals 5a, 5b, 5c. The AC system 5 is, for example, a 50 Hz three-phase 200 V power supply, and the AC load 6 is, for example, a device owned by a consumer such as an air conditioner. The AC filter 4 is constituted by, for example, an inductor or an X capacitor. In order to enable the power conversion device 1 and the AC load 6 to be off-grid from the AC system 5, a relay 51 is provided at the point of common coupling of the AC system 5.

[0026] The DC side of the main circuit 2 is connected to the DC power supply 7 via the DC terminals 7a, 7b. The DC power supply 7 can be, for example, a secondary battery such as a lithium-ion battery, a nickel-metal hydride battery, or a lead-acid battery, or can also be a renewable energy power supply such as solar power generation or wind power generation. In addition, the DC power supply 7 can also be constituted by a combination thereof. In this embodiment, the DC power supply 7 is described as including a secondary battery.

[0027] A voltage measurer 21 is provided on the AC system 5 and AC load 6 side of the AC filter 4. A current measurer 22 is provided on the main circuit 2 side of the AC filter 4. The control circuit 3 respectively obtains an AC voltage measurement value Vout from the voltage measurer 21 and an AC current measurement value Iout from the current measurer 22.

[0028] The control circuit 3 includes a power operation unit 31, a phase command generation unit 32, an active power output command setting unit 33, a reactive power command generation unit 34, a reactive power control unit (AQR) 35, and a main circuit control unit 36.

[0029] Based on the AC voltage measurement value Vout and the AC current measurement value Iout obtained from the voltage measurer 21 and the current measurer 22 respectively, the power operation unit 31 calculates the active power Pout and the reactive power Qout, which respectively represent the active component and the reactive component of the AC power actually input and output by the power conversion device 1 via the AC terminals 5a, 5b, and 5c at present. In addition, in this embodiment, the active power Pout and the reactive power Qout are defined such that the direction of the power flow when the power conversion device 1 receives power from the AC system 5 is positive, and the direction of the power flow when the power conversion device 1 supplies power to the AC system 5 and the AC load 6 is negative. However, the opposite definition is also possible.

[0030] Using the active power Pout calculated by the power operation unit 31 and the active power output command Pref output from the active power output command setting unit 33, the phase command generation unit 32 generates a command value for the phase of the AC power output from the AC terminals 5a, 5b, and 5c of the power conversion device 1, that is, the phase command θref. By generating the phase command θref for each specified operation cycle in the phase command generation unit 32, the phase of the AC power input and output to the power conversion device 1 is controlled sequentially, and the frequency (angular frequency ω) of the AC power is determined. The details of the method for generating the phase command θref by the phase command generation unit 32 will be described later. In addition, in this embodiment, the phase command θref is defined such that the leading direction of the phase is positive. However, the opposite definition is also possible.

[0031] The active power output command setting unit 33 sets a command value for the active component of the AC power input and output via the AC terminals 5a, 5b, and 5c of the power conversion device 1, and outputs this command value as the active power output command Pref to the phase command generation unit 32. The active power output command setting unit 33 can receive the active power value Pref1 from the outside of the power conversion device 1 (for example, an energy management system) through wired communication or wireless communication, and output this active power value Pref1 as the active power output command Pref to the phase command generation unit 32. The reception frequency of the active power value Pref1 at this time can be arbitrarily determined, such as at 1-minute intervals, etc., or it can be received non-periodically. Alternatively, the power value preset in the power conversion device 1 can also be output as the active power output command Pref to the phase command generation unit 32.

[0032] The reactive power command generation unit 34 generates a command value for the reactive component of the AC power input and output via the AC terminals 5a, 5b, and 5c in the power conversion device 1 based on the measured AC voltage value Vout obtained from the voltage measurer 21, and outputs this command value as the reactive power command Qref to the reactive power control unit 35. The reactive power command generation unit 34 can generate the reactive power command Qref by multiplying the deviation V0 - Vout between the rated voltage V0 (e.g., V0 = 200 [V]) and the measured AC voltage value Vout by a specified proportional gain Kq (Kq > 0).

[0033] The reactive power control unit 35 uses the reactive power Qout calculated by the power operation unit 31 and the reactive power command Qref output from the reactive power command generation unit 34 to generate a command value for the voltage of the AC power input and output via the AC terminals 5a, 5b, and 5c in the power conversion device 1, that is, the voltage command Vref. The reactive power control unit 35 can generate the voltage command Vref by performing PI control on the deviation Qref - Qout between the reactive power command Qref and the reactive power Qout. The voltage command Vref generated in the reactive power control unit 35 is output to the main circuit control unit 36.

[0034] The main circuit control unit 36 uses the phase command θref output from the phase command generation unit 32 and the voltage command Vref output from the reactive power control unit 35 to control the operation of the main circuit 2. The main circuit control unit 36 generates gate signals for each switching element included in the main circuit 2 by performing PWM control based on the phase command θref and the voltage command Vref, and outputs these gate signals to the main circuit 2, thereby enabling the driving of the main circuit 2.

[0035] As described above, the power conversion device 1 can perform system grid connection operation with the AC system 5 in a state of virtually having inertia. In this system grid connection operation, the main circuit 2 is driven using the phase command θref and the voltage command Vref. Therefore, the power conversion device 1 operates as a voltage source and can also independently perform power supply to the AC load 6.

[0036] Next, for the details of the method for generating the phase command θref by the phase command generation unit 32, the following Figure 2 is described. Figure 2 FIG. is a diagram showing a structural example of the phase command generation unit 32 in the first embodiment of the present invention. The phase command generation unit 32 includes a subtractor 321, a proportional controller 322, a virtual inertia addition filter 323, an adder 324, an integrator 325, and an active power output command correction unit 326. The active power output command correction unit 326 includes a correction value setting unit 3261 and an adder 3262.

[0037] The active power Pout output from the power operation unit 31 is respectively input to the subtractor 321 and the active power output command correction unit 326 in the phase command generation unit 32. In addition, the active power output command Pref output from the active power output command setting unit 33 is respectively input to the adder 327 and the active power output command correction unit 326 in the phase command generation unit 32.

[0038] In the active power output command correction unit 326, the correction value setting unit 3261 determines the correction value Pbias for the active power output command Pref and outputs the correction value Pbias to the adder 3262. The adder 3262 corrects the active power output command Pref by adding the correction value Pbias to the active power output command Pref, and outputs the obtained sum Pref + Pbias as the corrected active power output command to the subtractor 321.

[0039] The subtractor 321 calculates the deviation between the active power Pout and the corrected active power output command by subtracting the sum Pref + Pbias from the active power Pout, and outputs the calculation result to the proportional controller 322. The proportional controller 322 performs proportional calculation by multiplying the deviation obtained by the subtractor 321 by a prescribed gain Kp (for example, Kp = 0.023 [(rad / s) / kW]), and outputs the calculation result as the angular frequency change amount command Δωref' representing the command value of the output frequency of the AC power for the power conversion device 1 to the virtual inertia addition filter 323 and the active power output command correction unit 326.

[0040] The virtual inertia addition filter 323 virtually adds the inertia of the synchronous generator to the angular frequency change amount command Δωref' obtained by the proportional controller 322, and outputs the result as the corrected angular frequency change amount command Δωref. The virtual inertia addition filter 323 is constituted by, for example, a first-order lead-lag filter. By determining its time constant using the unit inertia constant and the unit damping constant of the synchronous generator, the inertia of the synchronous generator can be virtually added to the angular frequency change amount command Δωref'. Through this virtual inertia addition filter 323, even when the deviation Pout - Pref between the active power output command Pref and the active power Pout changes stepwise, the angular frequency change amount command Δωref' that instantaneously changes stepwise accordingly can be made to change smoothly as the corrected angular frequency change amount command Δωref. Thereby, an angular frequency change with inertia can be realized in the AC power input and output for the power conversion device 1.

[0041] The corrected angular frequency change command Δωref obtained by the virtual inertia addition filter 323 is input to the adder 324. The adder 324 obtains the angular frequency command ωref by adding the corrected angular frequency change command Δωref to the reference angular frequency ω0. For example, when the reference frequency of the AC power is set to 50 Hz, the reference angular frequency ω0 is ω0 = 2π×50 [rad / s].

[0042] The angular frequency command ωref obtained by the adder 324 is input to the integrator 325. The integrator 325 generates a phase command θref by integrating the angular frequency command ωref. The generated phase command θref is output to the main circuit control unit 36.

[0043] The correction value setting unit 3261 determines a correction value Pbias for correcting the active power output command Pref based on the angular frequency change command Δωref' obtained by the proportional controller 322 and the active power Pout and the active power output command Pref, and outputs it to the adder 3262. In the adder 327, the correction value Pbias is used to calculate the sum Pref + Pbias as the corrected active power output command as described above.

[0044] At the start of the operation of the control circuit 3, the correction value setting unit 3261 of the active power output command correction unit 326 determines the correction value Pbias as the initial value 0. Then, when the angular frequency change command Δωref' satisfies the following conditional expressions (1) or (2), the correction value Pbias is updated with a value calculated by the method described later. In the conditional expressions (1) and (2), ωlow and ωup represent the lower limit value and the upper limit value of the angular frequency ω of the AC power corresponding to the reference angular frequency ω0, respectively.

[0045] Δωref' < ωlow - ω0......(1)

[0046] Δωref' > ωup - ω0......(2)

[0047] In the active power output command correction unit 326, when the correction value Pbias has been calculated by the correction value setting unit 3261 by satisfying the conditional expression (1) or (2), the calculated value is continuously output as the correction value for the active power output command Pref until the correction value Pbias is calculated again as described later, or the active power output command setting unit 33 updates the active power output command Pref. On the other hand, when the correction value setting unit 3261 calculates the correction value Pbias again, the correction value for the active power output command Pref is updated with this value and continuously output. In addition, when the active power output command setting unit 33 updates the active power output command Pref, the correction value for the active power output command Pref is reset to the initial value 0 with Pbias = 0.

[0048] In the power conversion device 1 of the present embodiment, in the phase command generation unit 32 of the control circuit 3, the correction value Pbias calculated by the correction value setting unit 3261 of the active power output command correction unit 326 is used as described above to generate the phase command θref. Thereby, the improvement of the frequency quality during independent operation is achieved. This will be described below.

[0049] Figure 3 It is an example of a droop characteristic diagram showing the relationship between the deviation Pout - Pref of the active power Pout and the active power output command Pref and the angular frequency change amount command Δωref' when the correction of the active power output command Pref is not performed. When the correction value Pbias for the active power output command Pref is the initial value 0, in the phase command generation unit 32, based on Figure 3 the shown droop characteristic, the droop control corresponding to the above deviation Pout - Pref is performed, and thereby the angular frequency change amount command Δωref' is determined according to the following formula (3). In addition, Figure 3 the slope of the shown droop characteristic diagram is the gain Kp of the proportional controller 322.

[0050] Δωref' = Kp(Pout - Pref)......(3)

[0051] In formula (3), when Pout < Pref, Δωref' < 0. In this case, the control circuit 3 performs control to increase the active power Pout, that is, to increase the power received by the power conversion device 1 or decrease the discharge power, by reducing the angular frequency ω of the AC power input and output by the power conversion device 1.

[0052] In addition, in Equation (3), when Pout > Pref, Δωref' > 0. In this case, the control circuit 3 performs control to increase the angular frequency ω of the AC power input and output by the power conversion device 1, thereby reducing the active power Pout, that is, reducing the received power of the power conversion device 1 or increasing the discharge power.

[0053] For example, when Pref = -10 [kW] (10 kW discharge) and Pout = -9 [kW] (9 kW discharge), using the above-mentioned value of the gain Kp (Kp = 0.023 [(rad / s) / kW]), the angular frequency change command Δωref' is calculated according to Equation (3) as shown in the following Equation (4).

[0054] Δωref' = 0.023 × {(-9) - (-10)} = 0.023 [rad / s]... (4)

[0055] That is, according to the calculation result of Equation (4), the power conversion device 1 discharges while increasing the angular frequency ω of the AC power, so the discharge power increases.

[0056] For example, when the value of the active power output command Pref is Pref = 50 [kW] (50 kW charging) and the power consumption of the AC load 6 is 50 kW, the AC system 5 supplies a total of 100 kW to the power conversion device 1 and the AC load 6. Here, when an accident / power outage occurs in the AC system 5, the relay 51 becomes in the open state, and the power conversion device 1 operates independently to supply power to the AC load 6. At this time, the power conversion device 1 needs to output the power consumption of the AC load 6 regardless of the value of the active power output command Pref. Therefore, the value of the active power Pout is Pout = -50 [kW] (50 kW discharge). Thus, the deviation Pout - Pref between the active power output command Pref and the active power Pout in the above Equation (3) is Pout - Pref = -100 [kW].

[0057] As described above, when the value of the gain Kp is set to Kp = 0.023 [(rad / s) / kW], for the above deviation value of Pout - Pref, the value of the angular frequency change command Δωref' determined by the droop control of the phase command generation unit 32 is obtained as Δωref' = -2.30 [rad / s] according to Equation (3). That is, at this time, when the reference frequency of the AC power is set to 50 Hz, the power conversion device 1 operates independently at 49.63 Hz.

[0058] Here, when the frequency of the AC power supplied by the power conversion device 1 to the AC load 6 varies significantly compared to the reference frequency of 50 Hz, there is a case where it affects the operation of the AC load 6. It is generally considered that when a frequency variation of ±0.2 Hz or more occurs in a 50 Hz system, it will affect some consumer equipment. Therefore, when the power conversion device 1 transfers from grid-connected operation to independent operation, it is necessary to suppress the angular frequency variation and frequency variation of the AC power determined by the angular frequency change amount command Δωref'.

[0059] In the power conversion device 1 of the present embodiment, under the control of the control circuit 3, the upper limit value of the frequency is set to Fup, the lower limit value is set to Flow, and the frequency of the AC power output by the power conversion device 1 is suppressed to be not less than Flow and not more than Fup. At this time, the upper limit value ωup of the angular frequency ω in the above conditional expressions (1) and (2) is ωup = 2π × Fup, and the lower limit value ωlow is ωlow = 2π × Flow. That is, in the power conversion device 1 of the present embodiment, by suppressing the angular frequency ω of the input / output AC power to be not less than ωlow and not more than ωup, the improvement of the frequency quality when transferring from grid-connected operation to independent operation is achieved. In the present embodiment, for example, Fup is set to 50.2 Hz and Flow is set to 49.8 Hz respectively.

[0060] As described above, by setting the upper limit value ωup and the lower limit value ωlow for the angular frequency ω of the AC power input / output to the power conversion device 1, and thus limiting the value of the angular frequency change amount command Δωref' within the range from the upper limit threshold ωup - ω0 to the lower limit threshold ωlow - ω0 by a limiter, the variation of the angular frequency command ωref can be suppressed within the range of the following formula (5).

[0061] ωlow ≤ ωref ≤ ωup......(5)

[0062] However, even if the power consumption of the AC load 6 decreases when the angular frequency command ωref is suppressed to the lower limit value ωlow by the above limiter, or the power consumption of the AC load 6 increases when the angular frequency command ωref is suppressed to the upper limit value ωup, the value of the angular frequency change amount command Δωref' obtained by formula (3) remains unchanged. Therefore, the value of the angular frequency command ωref still remains at the lower limit value ωlow or the upper limit value ωup and does not asymptote to the reference angular frequency ω0, thus causing a problem that the power conversion device 1 cannot input / output AC power corresponding to the load state.

[0063] A specific example of the above problem will be described below. Under the above conditions (Pref = 50 [kW], Pout = -50 [kW], Kp = 0.023 [(rad / s) / kW]), the value of the angular frequency change amount command Δωref' when the power conversion device 1 transfers to independent operation is Δωref' = -2.30 [rad / s]. On the other hand, the lower limit threshold ωlow - ω0 of the angular frequency change amount command Δωref' at this time is ωlow - ω0 = -1.26 [rad / s]. Therefore, Δωref' is suppressed by the limiter to the lower limit threshold -1.26 [rad / s].

[0064] Here, it is assumed that when the power consumption of the AC load 6 decreases from 50 kW to 20 kW, the active power Pout is Pout = -20 [kW]. Therefore, the value of the angular frequency change amount command Δωref' determined by the droop control of Equation (3) is Δωref' = -1.61 [rad / s]. This value, similar to the case where the power consumption is 50 kW, is less than the above lower limit threshold ωlow - ω0 = -1.26 [rad / s]. Therefore, the angular frequency change amount command Δωref' is still suppressed by the limiter to the lower limit threshold -1.26 [rad / s]. That is, even if the load state of the AC load 6 changes to a light load, the angular frequency ω of the power conversion device 1 remains at the lower limit value ωlow.

[0065] Thus, in the power conversion device 1 of the present embodiment, in order to solve the above problem, when the angular frequency change amount command Δωref' satisfies the above conditional expression (1) or (2), the correction value Pbias is updated in the active power output command correction unit 326, and the active power output command Pref is corrected by calculating the sum of it and the active power output command Pref, and droop control is implemented. Thereby, the following control is performed: Even when the power consumption of the AC load 6 decreases after the angular frequency ω of the AC power reaches the lower limit value ωlow during independent operation, or the power consumption of the AC load 6 increases after the angular frequency ω of the AC power reaches the upper limit value ωup, the angular frequency ω does not stay at the lower limit value ωlow or the upper limit value ωup but approaches the reference angular frequency ω0.

[0066] As described above, in the active power output command correction unit 326, the correction value Pbias is added to the active power output command Pref by the adder 3262, and the sum Pref + Pbias is input to the subtractor 321 to calculate the deviation Pout - Pref - Pbias from the active power Pout. That is, after correcting the active power output command Pref by the correction value Pbias, the angular frequency change amount command Δωref' is determined by droop control. Thus, when the correction value Pbias is not the initial value 0, the angular frequency change amount command Δωref' is determined according to the following Equation (6).

[0067] Δωref' = Kp(Pout - Pref - Pbias)……(6)

[0068] Figure 4 This is an example of a droop characteristic diagram showing the relationship between the deviation Pout - Pref - Pbias between the active power Pout and the active power output command Pref when the active power output command Pref is corrected and the angular frequency change amount command Δωref'. Figure 4 Among them, the dotted line 41 respectively represents the droop characteristic in the case of Pbias = 0 described above Figure 3 Among them, the solid lines 42 and 43 represent the droop characteristics when Pbias is not 0. That is, the dotted line 41 represents the above formula (3), and the solid lines 42 and 43 represent formula (6).

[0069] In addition Figure 4 Among them, an example of a droop characteristic diagram is shown in which the solid lines 42 and 43 are the cases where the angular frequency change amount command Δωref' satisfies the conditional formula (1), that is, the value of Δωref' is lower than the lower limit threshold ωlow - ω0. However, a droop characteristic diagram in the case where the angular frequency change amount command Δωref' satisfies the conditional formula (2), that is, the value of Δωref' is higher than the upper limit threshold ωup - ω0, can also be shown in the same way.

[0070] As described above in the active power output command correction unit 326, when the angular frequency change amount command Δωref' satisfies the conditional formula (1) or (2), the correction value Pbias output from the correction value setting unit 3261 to the adder 3262 is updated. Thus, the droop characteristic can be changed corresponding to the corrected active power output command, that is, the value of the sum Pref + Pbias of the active power output command Pref and the correction value Pbias, and the angular frequency change amount characteristic Δωref' is determined according to the changed droop characteristic in such a manner that the angular frequency change amount command Δωref' does not reach the lower limit threshold ωlow - ω0.

[0071] Let the value of the active power Pout at the moment when the angular frequency change amount command Δωref' becomes less than the lower limit threshold ωlow - ω0 be Pout1, and let the correction value Pbias when Δωref' = ωlow - ω0 be Pbias1. According to the above formula (6), it can be known that these values satisfy the following formula (7).

[0072] ωlow - ω0 = Kp(Pout1 - Pref - Pbias1)……(7)

[0073] By transforming formula (7), the following formula (8) is obtained for the above correction value Pbias1.

[0074] Pbias1 = Pout1 - Pref - (ωlow - ω0) / Kp……(8)

[0075] For example, consider a situation where the value of the active power output command Pref as described above is Pref = 50 [kW] (50 kW charging), the relay 51 becomes open from the state where the AC load 6 is operating in parallel with the AC system 5 consuming 50 kW of power, and thus the power conversion device 1 transfers to independent operation to supply power to the AC load 6. In this case, as described above, Δωref' = -2.30 [rad / s], which is lower than the lower limit threshold ωlow - ω0 = -1.26 [rad / s] of the angular frequency change amount command Δωref'. Therefore, the active power output command correction unit 326 determines that the conditional expression (1) is satisfied, sets the correction value Pbias1 obtained by the formula (8) using the correction value setting unit 3261, and corrects the active power output command Pref using this correction value Pbias1.

[0076] In the above case, Pout1 = -50 [kW], Kp = 0.023 [(rad / s) / kW], so the value of the correction value Pbias1 obtained according to the formula (8) is Pbias1 = -45 [kW]. According to the value of this correction value Pbias1, the value of the active power output command Pref in the next operation cycle is corrected to Pref + Pbias1 = 50 - 45 = 5 [kW], and thus the value of the angular frequency change amount command Δωref' output from the proportional controller 322 is corrected to Δωref' = ωlow - ω0. Figure 4 The droop characteristic shown by the solid line 42 in the figure represents the relationship between the active power value Pout1 obtained after correcting the active power output command Pref with the correction value Pbias1 and the frequency change amount command Δωref'.

[0077] As described above, when changing the droop characteristic by correcting the active power output command Pref with the correction value Pbias, the value of the angular frequency change command Δωref' output from the proportional controller 322 changes as follows. First, before the value of the correction value Pbias is updated from the initial value 0, Δωref' is a value less than the lower limit threshold ωlow - ω0, that is, -2.30 [rad / s]. In the next operation cycle, the value of the correction value Pbias is updated from the initial value 0 to Pbias1, and thus Δωref' becomes equal to the lower limit threshold ωlow - ω0. In this way, even if the value of the angular frequency change command Δωref' becomes Δωref' < ωlow - ω0 in one operation cycle, the value of the angular frequency change command Δωref after adding inertia by the virtual inertia addition filter 323 will not be less than the lower limit threshold ωlow - ω0. That is, by using the virtual inertia addition filter 323, even if the value of the angular frequency change command Δωref' temporarily becomes the lower limit threshold ωlow - ω0, it is possible to prevent the corrected angular frequency change command Δωref from decreasing to less than the lower limit threshold ωlow - ω0.

[0078] In addition, when the value of the angular frequency change command Δωref' becomes 0, by resetting the value of the correction value Pbias to 0 in the active power output command correction unit 326, the droop characteristic can be restored to the state before the change. That is, the active power output command correction unit 326 can also update the correction value Pbias when Pbias ≠ 0 and Δωref' = 0, or when the value of the active power output command Pref is updated, except when the angular frequency change command Δωref' satisfies the conditional expressions (1) or (2).

[0079] Here, when the power consumption of the AC load 6 increases compared to the above 50 kW, the active power Pout decreases (increases in the negative direction). In this case, the angular frequency change command Δωref' becomes as shown in the following equation (9).

[0080] Δωref' = Kp(Pout - Pref - Pbias1) < ωlow - ω0......(9)

[0081] For example, when the power consumption of the AC load 6 increases from 50 kW to 60 kW, Pout = -60 [kW], and the value of the angular frequency change command Δωref' at this time is Δωref' = -1.50 [rad / s], which is lower than the above lower limit threshold ωlow - ω0 = -1.26 [rad / s]. In this case, similar to the above when transferring to independent operation, in the active power output command correction unit 326, the correction value Pbias is recalculated by the correction value setting unit 3261.

[0082] In the above case, when the value of the active power Pout at the instant when the angular frequency change amount command Δωref' becomes less than the lower limit threshold ωlow - ω0 is Pout2, Pout2 = -60 [kW]. When the correction value Pbias2 is recalculated by the correction value setting unit 3261 using this active power value Pout2 instead of the active power value Pout1 in the above formula (8), Pbias2 = -55.4 [kW]. According to the value of this correction value Pbias2, in the next operation cycle, the value of the active power output command Pref is corrected to Pref + Pbias2 = 50 - 55.4 = -5.4 [kW], and thus the value of the angular frequency change amount command Δωref' output from the proportional controller 322 is corrected to Δωref' = ωlow - ω0. Figure 4 The droop characteristic shown by the solid line 43 in the figure represents the relationship between the active power value Pout2 obtained after correcting the active power output command Pref with the correction value Pbias2 and the angular frequency change amount command Δωref'.

[0083] Furthermore, when the power consumption of the AC load 6 is reduced compared to 50 kW, the active power Pout increases (decreases in the negative direction). In this case, the angular frequency change amount command Δωref' becomes as shown in the following formula (10). Therefore, the condition formulas (1) and (2) are not satisfied and the correction value Pbias is not recalculated, and the droop characteristic at this time remains as Figure 4 the droop characteristic shown by the solid line 42 in the figure.

[0084] Δωref' = Kp(Pout - Pref - Pbias2) > ωlow - ω0 ……(10)

[0085] For example, when the power consumption of the AC load 6 is reduced from 60 kW to 50 kW, Pout = -50 [kW], and the value of the angular frequency change amount command Δωref' at this time is Δωref' = -1.02 [rad / s], which is higher than the above lower limit threshold ωlow - ω0 = -1.26 [rad / s]. Thus, the power conversion device 1 outputs AC power at an angular frequency ω3 = 313.1 [rad / s] higher than the above lower limit value ωlow = 312.9 [rad / s] according to the droop characteristic shown by the solid line 42 in the figure. Figure 4 If the control of the present embodiment is not applied and the angular frequency ω of the AC power is set only by the limiter as described above, the droop characteristic representing the relationship between the active power Pout and the angular frequency change amount command Δωref' remains

[0086] Figure 4 ​The droop characteristic shown by the dashed line 41 remains unchanged. As described above, when the power consumption of the AC load 6 decreases from 60 kW to 50 kW, the value of the angular frequency change amount command Δωref' at the droop characteristic of the dashed line 41 is less than the lower limit threshold ωlow - ω0. According to Equation (3), the calculated value of Δωref' is Δωref' = -2.30 [rad / s], but the value of Δωref' is limited by the limiter to the lower limit threshold ωlow - ω0, so Δωref' = -1.26 [rad / s]. At this time, the power conversion device 1 outputs AC power at the lower limit value ωlow = 312.9 [rad / s] of the angular frequency ω.

[0087] On the other hand, when the control of the present embodiment is applied, the power conversion device 1 corrects the active power output command Pref with the correction value Pbias as described above, thereby changing the droop characteristic and determining the value of the angular frequency change amount command Δωref'. As a result, Δωref' = -1.02 [rad / s]. Compared with the case where the control of the present embodiment is not applied, the angular frequency command ωref obtained by the adder 324 can be made closer to the reference angular frequency ω0. Thus, the angular frequency ω of the AC power input and output to the power conversion device 1 can be gradually close to the reference angular frequency ω0, improving the frequency quality.

[0088] In addition, when the above control is implemented, when the active power output command setting unit 33 updates the active power output command Pref, preferably in the active power output command correction unit 326, the correction value setting unit 3261 sets the correction value to Pbias = 0 and ends the correction of the active power output command Pref. That is, after the angular frequency ω of the AC power input and output to the power conversion device 1 reaches the lower limit value ωlow or the upper limit value ωup, when the active power output command Pref is changed in consideration of the power consumption of the AC load 6, it is preferable not to implement the correction of the active power output command Pref thereafter, but to operate the power conversion device 1 according to the new active power output command Pref. In addition, when the angular frequency ω of the AC power reaches the lower limit value ωlow or the upper limit value ωup again later, the correction of the active power output command Pref can be implemented.

[0089] Through the above control, the frequency quality during the independent operation of the power conversion device 1 can be improved. When implementing this control, the upper limit value Fup and the lower limit value Flow of the frequency of the AC power input and output by the power conversion device 1 are preferably set to values exceeding the frequency range of the AC power supplied by the AC system 5, that is, values greater than the upper limit of the frequency and less than the lower limit. In other words, the upper limit value ωup and the lower limit value ωlow of the angular frequency ω of the AC power input and output by the power conversion device 1 are preferably set to values exceeding the range of the angular frequency ω corresponding to the frequency range of the AC power supplied by the AC system 5. According to this setting, the above-described control does not work when the power conversion device 1 is connected to the AC system 5, and synchronization with the AC system 5 can be achieved. In addition, there is no need to switch the control between independent operation and grid-connected operation.

[0090] (Second Embodiment)

[0091] Figure 5 FIG. is a structural example diagram of the power conversion device according to the second embodiment of the present invention. Figure 5 The power conversion device 1A shown is different from the power conversion device 1 described in the first embodiment in that the control circuit 3 further has an active power input unit 37. Figure 1 Compared with the power conversion device 1, the control circuit 3 further has an active power input unit 37.

[0092] For the active power input unit 37, an active power value Pref2 different from the above-mentioned active power value Pref1 is input. The active power input unit 37 outputs the active power value Pref2 to the active power output command setting unit 33. The active power input unit 37 is constituted by, for example, an input device installed in the housing of the power conversion device 1A such as a touch panel and a keyboard. The user of the power conversion device 1A sets the active power value Pref2 by operating the active power input unit 37.

[0093] In the present embodiment, the active power output command setting unit 33 selects either the active power value Pref1 received from the outside of the power conversion device 1A or the active power value Pref2 input to the active power input unit 37 as the active power output command Pref and outputs it to the phase command generation unit 32. For example, when the active power value Pref2 is not input, the active power value Pref1 is selected, and when the active power value Pref2 is input using the active power input unit 37, the active power value Pref2 is selected, whereby either the active power value Pref1 or Pref2 can be selected.

[0094] (Third Embodiment)

[0095] In the present embodiment, a description is given of having the same as that described in the first embodiment Figure 2Examples of phase command generators with structures different from that of the phase command generator 32. In addition, the structures other than the phase command generator 32 are the same as those in the first and second embodiments, and thus the description thereof is omitted.

[0096] Figure 6 FIG. shows a structural example of the phase command generator 32B in the third embodiment of the present invention. In the present embodiment, the correction value setting unit 3261 of the active power output command correction unit 326 calculates the correction value Pbias by referring to the angular frequency change amount command Δωref after additional inertia output from the virtual inertia addition filter 323 instead of referring to the angular frequency change amount command Δωref' output from the proportional controller 322.

[0097] In addition, the initial value of Pbias in the present embodiment is 0 as in the first embodiment. Then, when the angular frequency change amount command Δωref after additional inertia satisfies the following conditional expressions (11) or (12), the correction value Pbias calculated by the same method as in the first embodiment is output as the correction value for the active power output command Pref.

[0098] Δωref < ωlow - ω0 …… (11)

[0099] Δωref > ωup - ω0 …… (12)

[0100] In addition, in the present embodiment as well as in the first embodiment, when the active power output command correction unit 326 has already calculated the correction value Pbias, it is preferable to continuously output the most recent calculated value as the correction value Pbias until the correction value Pbias is recalculated or the active power output command setting unit 33 updates the active power output command Pref. When the correction value Pbias is recalculated, the correction value Pbias is updated with the calculation result and continuously output. When the active power output command setting unit 33 updates the active power output command Pref, Pbias = 0 is set. Further, the droop characteristic can be restored to the state before the change by resetting the value of the correction value Pbias to 0 when the value of the angular frequency change amount command Δωref after additional inertia becomes 0.

[0101] The angular frequency change command Δωref' output from the proportional controller 322 instantaneously changes with respect to the change in the power consumption of the AC load 6. Therefore, when the correction value setting unit 3261 in the active power output command correction unit 326 calculates the correction value Pbias with reference to this angular frequency change command Δωref', after satisfying the conditional expressions (1) and (2), the correction of the active power output command Pref can be immediately started, but the correction is performed whenever the power consumption of the AC load 6 changes. On the other hand, the angular frequency change command Δωref output from the virtual inertia addition filter 323 has inertia added, so even if the power consumption of the AC load 6 changes, it does not change instantaneously like Δωref'. That is, the change in Δωref with respect to the power consumption of the AC load 6 gradually changes smoothly, and after a certain amount of time, it reaches the lower limit threshold ωlow - ω0 or the upper limit threshold ωup - ω0.

[0102] As in this embodiment, by calculating the correction value Pbias with reference to Δωref instead of Δωref', during the period until Δωref reaches the lower limit threshold ωlow - ω0 or the upper limit threshold ωup - ω0, regardless of the change in the power consumption of the AC load 6 or Δωref', there is no need to correct the active power output command Pref. Therefore, compared with the first embodiment, the computational amount of the control circuit 3 can be reduced. In addition, after the angular frequency change command Δωref reaches the threshold, the correction value Pbias is calculated in the same manner as in the first embodiment, and the droop characteristic changes.

[0103] (Fourth Embodiment)

[0104] Figure 7 FIG. is a structural example diagram of a power conversion device showing a fourth embodiment of the present invention. Figure 7 The power conversion device 1C shown is different from the Figure 5 power conversion device 1A described in the second embodiment in that the control circuit 3 further includes a current command generation unit 38 and a current control unit 39.

[0105] The current command generation unit 38 generates a current command Iref based on the AC voltage measurement value Vout, the voltage command Vref generated by the reactive power control unit 35, and the phase command θref generated by the phase command generation unit 32, and outputs it to the current control unit 39. This current command Iref is obtained according to the following expressions (13) and (14) based on Vout, Vref, θref, and the resistance component R and reactance X of the AC filter 4.

[0106] Iref d = R / (R 2 + X 2 )·(0 - Voutd )+X / (R 2 +X 2 )·(Vref-Vout q )……(13)

[0107] Iref q =X / (R 2 +X 2 )·(0-Vout d )+R / (R 2 +X 2 )·(Vref-Vout q )……(14)

[0108] In formula (13) and (14), Vout d 、Vout q They represent the reactive component and active component of the AC voltage measurement value Vout, respectively. They are obtained by performing three-phase to two-phase conversion on Vout and dq conversion based on θref. Similarly, Iref d 、Iref q They represent the reactive component and active component of the current command Iref, respectively. That is, Iref=(Iref d ,Iref q ).

[0109] The current control unit 39 generates a voltage command Vref' based on the current command Iref obtained by the current command generation unit 38 and the AC current measurement value Iout. Specifically, first, the AC current measurement value Iout is converted into two phases and dq based on θref, thereby obtaining Iout which represents the reactive component and active component of Iout respectively. d , Iout q Then, by comparing it with the components Iref of the above current command Iref d 、Iref q Deviation Iref d -Iout d 、Iref q -Iout q The PI control for the input generates a voltage command Vref'=(Vref d ',Vref q The voltage command Vref' generated by the current control unit 39 is Vref d ',Vref q ') is output to the main circuit control unit 36.

[0110] The main circuit control unit 36 uses the phase command θref output from the phase command generation unit 32 and the voltage command Vref' output from the current control unit 39, and performs PWM control in the same manner as in the first embodiment, thereby generating the gate signal of the switching element included in the main circuit 2. Then, the generated gate signal is output to the main circuit 2 to drive the main circuit.

[0111] As described above, the power conversion device 1C of the present embodiment can operate as a voltage source having a small loop for current control. In such a power conversion device 1C, it is also possible to suppress the angular frequency ωref of the AC power input and output to the power conversion device 1C within the range of ωlow ≤ ωref ≤ ωup by implementing the changes in the droop characteristics described in the first to third embodiments using the phase command generation unit 32. In addition, in the current command generation unit 38, the current command Iref is generated using the phase command θref generated by the phase command generation unit 32. Thereby, the current command Iref can be generated in such a manner that the angular frequency ωref of the AC power input and output to the power conversion device 1C becomes ωlow ≤ ωref ≤ ωup. Thus, it is possible to more appropriately control the AC power input and output to the power conversion device 1C.

[0112] According to the embodiments of the present invention described above, the following operational effects are achieved.

[0113] (1) The power conversion devices 1, 1A, and 1C include DC terminals 7a and 7b for inputting and outputting DC power, AC terminals 5a, 5b, and 5c for inputting and outputting AC power, a main circuit 2 for mutually converting DC power and AC power, and a control circuit 3 for controlling the main circuit 2. The control circuit 3 includes a power operation unit 31 that calculates the active power Pout representing the active component of the AC power, an active power output command setting unit 33 that sets the active power output command Pref representing the command value for the active power Pout, and phase command generation units 32 and 32B that calculate the deviation between the active power Pout and the active power output command Pref and determine the angular frequency ω and phase of the AC power based on the deviation. The phase command generation units 32 and 32B have a droop characteristic ( Figure 4 ) representing the relationship between the above deviation and the angular frequency ω. When the angular frequency ω determined by this droop characteristic exceeds a preset upper limit value ωup, the active power output command Pref is decreased to calculate the deviation. When the angular frequency ω determined by the droop characteristic is lower than a preset lower limit value ωlow, the active power output command Pref is increased to calculate the deviation. Because of this, it is possible to provide a power conversion device and its control method that can transfer between grid-connected operation and independent operation of the system without control switching and improve the frequency quality during independent operation.

[0114] (2) The phase command generation units 32 and 32B include a subtractor 321 for calculating a deviation, a proportional controller 322, a virtual inertia addition filter 323, an adder 324, an integrator 325, and an active power output command correction unit 326. The proportional controller 322 performs a proportional operation based on the droop characteristic on the deviation calculated by the subtractor 321 to generate an angular frequency change amount command Δωref' representing a change amount of the angular frequency ω with respect to the AC power. The virtual inertia addition filter 323 virtually adds inertia to the angular frequency change amount command Δωref' generated by the proportional controller 322 and outputs a corrected angular frequency change amount command Δωref. The adder 324 generates an angular frequency command ωref representing a command value of the angular frequency ω with respect to the AC power based on the corrected angular frequency change amount command Δωref output from the virtual inertia addition filter 323. The integrator 325 generates a phase command θref representing a command value of the phase with respect to the AC power based on the angular frequency command ωref generated by the adder 324. The active power output command correction unit 326 determines a correction value Pbias for the active power output command Pref, and calculates the sum Pref + Pbias of the correction value Pbias and the active power output command Pref, thereby correcting the active power output command Pref. The subtractor 321 calculates the deviation Pout - Pref - Pbias using the active power output command Pref + Pbias corrected by the active power output command correction unit 326. Because of this, in the case where the angular frequency ω exceeds the upper limit value ωup and the case where it is lower than the lower limit value ωlow, the active power output command Pref can be appropriately increased or decreased.

[0115] (3) In the phase command generation units 32 and 32B, the active power output command correction unit 326 determines the correction value Pbias based on the angular frequency change amount command Δωref' ( Figure 2 ) or the corrected angular frequency change amount command Δωref ( Figure 6 ). Because of this, even without changing the active power output command Pref, the correction value Pbias can be appropriately determined corresponding to the change in the active power Pout.

[0116] (4) The active power output command correction unit 326 sets an upper limit threshold ωup - ω0 based on the upper limit value ωup of the angular frequency ω and a lower limit threshold ωlow - ω0 based on the lower limit value ωlow. When the angular frequency change amount command Δωref' or the corrected angular frequency change amount command Δωref exceeds the upper limit threshold ωup - ω0 (Equation (2)) or is lower than the lower limit threshold ωlow - ω0 (Equation (1)), the correction value Pbias is updated and the active power output command Pref is corrected. Because of this, the correction of the active power output command Pref can be performed at an appropriate timing.

[0117] (5) The active power output command correction unit 326 can reset the correction value Pbias to 0 when the angular frequency change amount command Δωref' or the corrected angular frequency change amount command Δωref becomes 0. In addition, the active power output command correction unit 326 can reset the correction value Pbias to 0 when the active power output command setting unit 33 updates the active power output command Pref. If so, it is possible to end the correction of the active power output command Pref at an appropriate timing.

[0118] (6) The active power output command setting unit 33 can set the active power output command Pref based on the first set value (active power value Pref1) for the active power Pout sent from the outside. In addition, the control circuit 3 has an active power input unit 37 ( Figure 5 , Figure 7 ), and the active power input unit 37 can receive the input of the second set value (active power value Pref2) for the active power Pout from the outside. In this case, the active power output command setting unit 33 can select either the active power value Pref1 or Pref2, and set the active power output command Pref based on the selected set value. If so, it is possible to set the active power output command Pref to an arbitrary value.

[0119] (7) The control circuit 3 can have a current command generation unit 38 that generates a current command Iref representing a command value for the current of the AC power based on the angular frequency ω (phase command θref) of the AC power determined by the phase command generation unit 32, and a current control unit 39 that generates a voltage command Vref' representing a command value for the voltage of the AC power based on the current command Iref generated by the current command generation unit 38 ( Figure 7 ). If so, it is possible to more appropriately control the AC power input and output in the power conversion device.

[0120] (8) The AC terminals 5a, 5b, and 5c are connected to the AC system 5 that supplies AC power. The upper limit value ωup and the lower limit value ωlow of the angular frequency ω of the AC power are preferably set to values that exceed the frequency range of the AC power supplied by the AC system 5. If so, when the power conversion device is connected to the grid of the AC system, the correction of the active power output command Pref is not performed, and synchronization with the AC system can be achieved.

[0121] In addition, the present invention is not limited to the above-described embodiments and modified examples, and can be implemented using any constituent elements without departing from the gist thereof. Further, each of the embodiments and modified examples can be adopted alone, or a plurality of them can be adopted in any combination. That is, in the present invention, by arbitrarily combining the features of each embodiment, the above-described effects can be exhibited.

[0122] The above-described embodiments and modified examples are merely examples, and the present invention is not limited to these as long as the features of the invention are not impaired. In addition, although various embodiments and modified examples have been described above, the present invention is not limited to these. Other modes conceivable within the technical idea of the present invention are also included in the scope of the present invention.

[0123] Description of Reference Numerals

[0124] 1, 1A, 1C... Power conversion device

[0125] 2... Main circuit

[0126] 3... Control circuit

[0127] 4... AC filter

[0128] 5... AC system

[0129] 5a, 5b, 5c... AC terminals

[0130] 6... AC load

[0131] 7... DC power supply

[0132] 7a, 7b... DC terminals

[0133] 31... Power operation unit

[0134] 32, 32B... Phase command generation unit

[0135] 33... Active power output command setting unit

[0136] 34... Reactive power command generation unit

[0137] 35... Reactive power control unit (AQR)

[0138] 36... Main circuit control unit

[0139] 37... Active power input unit

[0140] 38... Current command generation unit

[0141] 39... Current control unit

[0142] 321... Subtractor

[0143] 322... Proportion controller

[0144] 323... Virtual inertia additional filter

[0145] 324... Adder

[0146] 325... Integrator

[0147] 326... Active power output command correction unit.

Claims

1. A power conversion device, characterized in that, Comprising: DC terminals for inputting and outputting DC power; AC terminals for inputting and outputting AC power; A main circuit for converting the DC power and the AC power mutually; and A control circuit for controlling the main circuit, The control circuit having: A power operation unit for calculating the active power representing the active component of the AC power; An active power output command setting unit for setting an active power output command representing a command value for the active power; And A phase command generation unit for calculating a deviation between the active power and the active power output command and determining the angular frequency and phase of the AC power based on the deviation, The phase command generation unit, Having a droop characteristic representing the relationship between the deviation and the angular frequency, When the angular frequency determined by the droop characteristic exceeds a preset upper limit value, reducing the active power output command to calculate the deviation, When the angular frequency determined by the droop characteristic is lower than a preset lower limit value, increasing the active power output command to calculate the deviation.

2. The power conversion device according to claim 1, characterized in that: The phase command generation unit has: A subtractor for calculating the deviation; A proportional controller for performing a proportional operation on the deviation calculated by the subtractor based on the droop characteristic to generate an angular frequency change amount command representing a command value for the change amount of the angular frequency of the AC power; A virtual inertia addition filter for virtually adding inertia to the angular frequency change amount command generated by the proportional controller and outputting a corrected angular frequency change amount command; An adder for generating an angular frequency command representing a command value for the angular frequency of the AC power based on the corrected angular frequency change amount command output from the virtual inertia addition filter; An integrator for generating a phase command representing a command value for the phase of the AC power based on the angular frequency command generated by the adder; And An active power output command correction unit for determining a correction value for the active power output command and using the correction value to correct the active power output command, The subtractor calculates the deviation using the active power output command corrected by the active power output command correction unit.

3. The power conversion device according to claim 2, characterized in that: The active power output command correction unit resets the correction value to 0 when the angular frequency change amount command or the corrected angular frequency change amount command becomes 0.

4. The power conversion device according to claim 2, characterized in that: The active power output command correction unit resets the correction value to 0 when the active power output command is updated by the active power output command setting unit.

5. The power conversion device according to claim 1, characterized in that: The active power output command setting unit sets the active power output command according to a first set value for the active power sent from the outside.

6. The power conversion device according to claim 5, characterized in that: The control circuit has an active power input section that accepts an input of a second set value for the active power from the outside. The active power output command setting section selects either the first set value or the second set value, and sets the active power output command according to the selected set value.

7. The power conversion device according to claim 1, characterized in that: The AC terminal is connected to an AC system that supplies the AC power. The upper limit value and the lower limit value are respectively set to values that exceed the range of the angular frequency corresponding to the frequency range of the AC power supplied by the AC system.

8. A control method for a power conversion device that mutually converts DC power and AC power, characterized in that: Calculate the active power representing the active component of the AC power. Set an active power output command representing a command value for the active power. Calculate the deviation between the active power and the active power output command. Based on the droop characteristic representing the relationship between the deviation and the angular frequency of the AC power, determine the angular frequency of the AC power. When the angular frequency determined by the droop characteristic exceeds a preset upper limit value, reduce the active power output command to calculate the deviation. When the angular frequency determined by the droop characteristic is lower than a preset lower limit value, increase the active power output command to calculate the deviation.

9. The control method for the power conversion device according to claim 8, characterized in that: Perform proportional operation on the deviation based on the droop characteristic to generate an angular frequency change amount command representing a command value for the change amount of the angular frequency of the AC power. Virtually add inertia to the angular frequency change amount command to generate a corrected angular frequency change amount command. Based on the generated corrected angular frequency change amount command, generate an angular frequency command representing a command value for the angular frequency of the AC power. Based on the generated angular frequency command, generate a phase command representing a command value for the phase of the AC power. Determine a correction value for the active power output command. Use the correction value to correct the active power output command. Use the corrected active power output command to calculate the deviation.

10. The control method for the power conversion device according to claim 9, characterized in that: When the angular frequency change amount command or the corrected angular frequency change amount command becomes 0, reset the correction value to 0.

11. The control method for the power conversion device according to claim 9, characterized in that: When the active power output command is updated, reset the correction value to 0.

12. The control method for the power conversion device according to claim 8, characterized in that: Set the active power output command according to a first set value for the active power sent from the outside.

13. The control method for the power conversion device according to claim 12, characterized in that: Accept an input of a second set value for the active power from the outside. Select either the first set value or the second set value, and set the active power output command according to the selected set value.

14. The control method of the power conversion device according to claim 8, characterized in that: The power conversion device is connected to an AC system that supplies the AC power, The upper limit value and the lower limit value are respectively set to values that exceed the range of the angular frequency corresponding to the frequency range of the AC power supplied by the AC system.

Images