Power conversion device

Abstract

To provide a power conversion device which can continue an operation even when instantaneous voltage drop due to a system accident occurs during a linkage operation.SOLUTION: A first voltage command generation unit 307 generates a first voltage command V1 from reactive power Qout obtained by measurement and calculation, and a reactive power command Qo. A current command generation unit 308 generates a current command I* from measurement voltage Vout and the first voltage command V1. A current command restriction unit 309 restricts the current command I* to be output. A second voltage command generation unit 310 generates a second voltage command V* from the restricted current command and measurement current Iout. A control circuit 3 controls a power conversion circuit 2 on the basis of the second voltage command V*.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] Patent Document 1 discloses a power conversion device that can eliminate the need to change the control method, such as current control or voltage control, when switching from independent operation to grid-connected operation in a combined power generation system such as a microgrid. The power conversion device calculates a command value for the output current of a power converter from an internal phase difference angle calculated from an active power control loop and an internal electromotive voltage calculated from a reactive power control loop, and controls the power converter using the command value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 008413 [Non-patent literature]

[0004] [Non-Patent Document 1] "Grid Interconnection Regulations (JEAC 9701-2019)" Grid Interconnection Special Committee of the Japan Electric Association Summary of the Invention [Problem to be solved by the invention]

[0005] For example, the power conversion device for a combined power generation system disclosed in Patent Document 1 uses a power converter that does not require a change in control method when interconnected to a grid, thereby enabling the construction of an easy-to-use independent power supply system. Meanwhile, Non-Patent Document 1 specifies "Requirements for the continued operation performance of distributed power sources during grid disturbances, which are necessary to ensure power quality" (Fault Ride Through: FRT) for grid-connected power sources. That is, continued operation performance during a fault is required to prevent simultaneous parallel-off of power generation equipment or continued output reduction due to widespread instantaneous voltage drops and frequency fluctuations caused by a grid fault. For this reason, the power conversion device for a combined power generation system must satisfy the continued operation performance during a fault in order to operate while connected to a commercial grid.

[0006] However, when a power conversion device for a combined power generation system experiences a sudden change in grid voltage due to a momentary fault or other reason during grid-connected operation, its output current and power may be disrupted. A sudden change in grid voltage also causes a sudden change in the active power output of the power conversion device for a combined power generation system, which may result in a change in the frequency command value. This may result in changes in the frequency difference and phase difference with the grid, which may cause output disruption. Furthermore, if the internal electromotive force command value cannot be changed quickly enough in response to a sudden change in grid voltage, an overcurrent may occur due to the potential difference between the internal electromotive force command value and the grid voltage, which may result in equipment shutdown to protect the equipment during grid-connected operation. In other words, there is a problem in that it is difficult to continue operation during a fault.

[0007] Therefore, one object of the present invention is to provide a power conversion device that can continue to operate even if a momentary voltage drop occurs due to a grid fault during grid-connected operation.

[0008] The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0009] A power conversion device according to one embodiment includes a power conversion circuit that converts DC power to AC power and a control circuit that controls the power conversion circuit. The control circuit has an active power command unit, an angular frequency command generation unit, a phase command generation unit, a reactive power command unit, a first voltage command generation unit, a current command generation unit, a current command constraint unit, and a second voltage command generation unit. The active power command unit determines an active power command. The angular frequency command generation unit generates an angular frequency command from the active power command and an output active power obtained by measurement and calculation. The phase command generation unit generates a phase command from the angular frequency command. The reactive power command unit determines a reactive power command. The first voltage command generation unit generates a first voltage command from the output reactive power obtained by measurement and calculation and the reactive power command. The current command generation unit generates a current command from the measured voltage and the first voltage command. The current command constraint unit constrains and outputs the current command. The second voltage command generation unit generates a second voltage command from the constrained current command and the measured current. The control circuit then controls the power conversion circuit based on the second voltage command. [Effects of the Invention]

[0010] According to the embodiment, even if a momentary voltage drop occurs due to a grid fault during grid-connected operation, operation can be continued. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating a configuration example of a power conversion device according to a first embodiment. [Figure 2] 2 is a block diagram showing a detailed configuration example of each unit in FIG. 1. FIG. [Figure 3] FIG. 10 is a schematic diagram illustrating a configuration example of a power conversion device according to a second embodiment. [Figure 4] 4 is a timing chart showing an example of an active power command and an angular frequency command generated in FIG. 3. [Figure 5] FIG. 13 is a schematic diagram showing an example of a current command constraining method in a current command constraining unit in the third embodiment. [Figure 6]FIG. 10 is a block diagram showing a detailed configuration example of each part in FIG. 1 or 3 in a power conversion device according to a fourth embodiment. [Figure 7] FIG. 10 is a block diagram showing a detailed configuration example of each part in FIG. 1 or 3 in a power conversion device according to a fifth embodiment. [Figure 8] FIG. 13 is a schematic diagram showing a partial configuration example of a power conversion device according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, the same components are generally designated by the same reference numerals, and repeated description thereof will be omitted.

[0013] (First embodiment) <Outline of power conversion device> FIG. 1 is a schematic diagram showing an example of the configuration of a power conversion device according to a first embodiment. The power conversion device 1 shown in FIG. 1 is configured, for example, by a housing in which various internal components are mounted. As part of the internal components, the power conversion device 1 includes a power conversion circuit 2, a control circuit 3, and an AC filter 4. However, the AC filter 4 may be an external component. The power conversion circuit 2 is, for example, a three-phase full-bridge inverter that converts DC power into AC power. The AC terminal of the power conversion circuit 2 is connected to an AC system 5 and an AC load 6 via the AC filter 4.

[0014] The AC system 5 is, for example, a 50 Hz, three-phase 200 V commercial system. The AC load 6 is, for example, a consumer-owned device such as an air conditioner. Here, multiple AC loads 6 are collectively described as one load, but in detail, there may be multiple loads. The AC filter 4 is composed of an inductor and an X capacitor. Although not shown, a relay may be installed at the interconnection point with the AC system 5 so that the power conversion device 1 and the AC load 6 can be disconnected from the AC system 5.

[0015] The DC end of the power conversion circuit 2 is connected to a DC power supply 7. The DC power supply 7 is, for example, a secondary battery such as a lithium ion battery, a nickel-metal hydride battery, or a lead storage battery, a capacitor, or a renewable energy power supply such as solar power generation. Note that instead of the DC power supply 7, a power supply in which a device capable of storing energy in a form other than electrical energy, such as a CAES (Compressed Air Energy Storage) or a flywheel, is connected to a device that converts that energy into electrical energy may be used.

[0016] A voltage meter 10 is installed on the AC system 5 and AC load 6 side of the AC filter 4. A current meter 11 is installed on the power conversion circuit 2 side of the AC filter 4. The control circuit 3 receives the measured AC voltage value from the voltage meter 10 and the measured AC current value from the current meter 11. The control circuit 3 includes a measurement unit 301, a power calculation unit 302, an active power command unit 303, an angular frequency command generation unit 304, a phase command generation unit 305, a reactive power command unit 306, a first voltage command generation unit 307, a current command generation unit 308, a current command constraint unit 309, a second voltage command generation unit 310, and a main circuit control unit 311.

[0017] Specifically, the control circuit 3 may be realized by, for example, a microcontroller including a processor and a memory. In this case, the measurement unit 301 may be realized by, for example, an analog-to-digital converter built into the microcontroller. The other units may be realized by the processor executing a program stored in the memory. Alternatively, the control circuit 3 may be realized by a programmable logic device such as an FPGA (Field Programmable Gate Array). In this case, the measurement unit 301 may be realized by, for example, an analog-to-digital converter built into the FPGA. The other units may be realized by logic circuits programmed within the FPGA.

[0018] The measurement unit 301 measures the AC voltage and AC current measurements as V out and I outThe measurement unit 301 outputs V out ,I out When outputting the voltage and current, measurement noise may be removed using a low-pass filter or the like. The time constants of the low-pass filter may be set separately for the voltage and current.

[0019] The power calculation unit 302 calculates the V out ,I out From this, the output active power P out and reactive power Q out In this embodiment, the active power P out Regarding the reactive power Q, the power flow discharging the DC power supply 7 is positive. out For example, the three-phase voltage and three-phase current V out ,I out can be converted into two-phase voltages and two-phase currents in the α-β coordinate system by a three-phase to two-phase transformation.

[0020] The active power command unit 303 receives an active power command value P o Based on the active power command P o In this embodiment, P o =P o '. The active power command value P o The active power command value P' can be received via wired or wireless communication from a higher-level command device, such as an energy management system, that is provided outside the power conversion device 1. The reception frequency can be set arbitrarily, for example, every minute. o ' may be received aperiodically or may be arbitrarily input by the user of the power conversion device 1.

[0021] The angular frequency command generator 304 generates an active power command P o and the active power P out The angular frequency command ω is calculated by droop control based on the deviation from * Generates the angular frequency command ω * is expressed by the following equation (1), where K pis the droop coefficient of the active power-angular frequency change command. o is the reference angular frequency, for example 2π×50.

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[0022] Here, the angular frequency command ω * In order to give a pseudo inertia to the droop control part, a first-order lag filter or a first-order lag-lead filter may be set. For example, when a first-order lag-lead filter is set, the angular frequency command ω * is expressed by the following equation (2): where T1 and T2 are time constants.

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[0023] For example, in equation (2), P out <P o When ω * >ω o Therefore, by increasing the angular frequency, the effective power P out On the other hand, P out >P o When ω * <ω o Therefore, by lowering the angular frequency, the effective power P out This droop control setting and filter result in a behavior that reduces ω * The gradual change in the voltage allows the behavior of a virtual synchronous generator to be simulated.

[0024] The phase command generation unit 305 generates an angular frequency command ω * is integrated to obtain the phase command θ * The reactive power command unit 306 generates a reactive power command Q o Generates and outputs reactive power command Q o For example, the rated voltage V o (for example, 200V) and the output of the measurement unit 301, V out Deviation V o -V out , the proportional gain Kq (K q It should be noted that the reactive power command unit 306 does not use the output of this droop control but uses the reactive power command value Q input from outside the power conversion device 1. o ' is used as the reactive power command Q o It may be output as

[0025] In addition, the reactive power command unit 306 outputs a reactive power command Q o is input from the outside of the power conversion device 1, o ', the rated power of the power conversion device 1, and the desired power factor. In this case, behavior conforming to power factor control is possible. Furthermore, the reactive power command unit 306 controls the active power command P o The reactive power command Q is calculated from the rated power of the power conversion device 1 and the desired power factor. o may be determined.

[0026] The first voltage command generator 307 generates a reactive power command Q o and reactive power Q out The current command generating unit 308 calculates the deviation between the first voltage command V1 and the AC voltage measurement value V out and impedance Z, the AC current that flows when the AC end voltage of the power conversion circuit 2 is the first voltage command V1 is calculated using the following equation (3), and the current command I * Generate.

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[0027] Equation (3) is a phasor expression, and V1 = (V1, 0). In practice, the current command generator 308 calculates the d-axis component and the q-axis component in the dq transformation. That is, I * =(I d * ,I q *) is calculated using the following equations (4) and (5). Here, impedance Z is expressed as resistance r and reactance x. Also, V out =(V out_d ,V out_q ) dq transformation is performed using the phase command θ * is used.

[0028]

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[0029] The impedance Z, in other words the virtual impedance value, is determined by the impedance Z of the AC filter 4, which is known in advance. filter =r filter +jx filter The impedance Z of the AC filter 4 may be used. filter In addition, the impedance Z inside the synchronous generator is virtual You can set Z=Z filter +Z virtual =(r filter +r virtual )+j(x filter +x virtual )

[0030] The current command constraint unit 309 constrains the current command I generated by the current command generation unit 308. * =(I d * ,I q * ) is constrained. For example, the current command constraint unit 309 sets limiters for the d-axis component and the q-axis component so that the upper limit threshold current and the lower limit threshold current are the upper and lower limits. In this case, the upper limit threshold current is, for example, the rated current of the power conversion circuit 2. The lower limit threshold current is, for example, the value obtained by multiplying the rated current of the power conversion circuit 2 by -1.

[0031] The second voltage command generator 310 generates the current command (I d* ,I q * ) and the AC current measurement value I out Phase command θ * The d-axis and q-axis components (I out_d ,I out_q ) and the second voltage command V * =(V d * ,V q * Specifically, the second voltage command generator 310 calculates the constrained current command I * =(I d * ,I q * ) and the AC current measurement value I out =(I out_d ,I out_q ) and perform PI control.

[0032] Here, the gain of the PI control is the proportional gain K vp , integral gain K vi Then, the second voltage command V * =(V d * ,V q * ) is expressed by the following equations (6) and (7).

[0033]

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[0034] Furthermore, the second voltage command generator 310 performs non-interference control to generate the second voltage command V * =(V d * ,V q * ) may be generated. When decoupling control is added, the second voltage command V * =(V d * ,V q* ) is expressed by the following equations (8) and (9).

[0035]

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[0036] The main circuit control unit 311 outputs a second voltage command V * =(V d * ,V q * ) as the phase command θ * Then, an inverse dq transform is performed on the power converter circuit 2, and an inverse three-phase to two-phase transform is performed on the power converter circuit 2 to generate a voltage command for each of the three phases (R, S, T). The main circuit control unit 311 generates a gate signal G pwm (R, S, T) is generated and drives the power conversion circuit 2.

[0037] <Power conversion device details> Fig. 2 is a block diagram showing a detailed configuration example of each part in Fig. 1. In Fig. 2, a current command generating unit 308 generates a measured AC voltage V in an α-β coordinate system obtained by three-phase to two-phase conversion. out_α ,V out_β , the phase command θ * Using the AC voltage measurement value V in the dq coordinate system out_d ,V out_d The current command generator 308 converts the converted AC voltage measurement value V out_d ,V out_d Then, the current command generator 308 calculates the current command I based on the equations (4) and (5). * d-axis component I d * and the q-axis component I q * Calculate the following.

[0038] The second voltage command generator 310 generates a measured AC current I in the α-β coordinate system obtained by three-phase to two-phase transformation.out_α ,I out_β , the phase command θ * Using the AC current measurement value I in the dq coordinate system out_d ,I out_d The second voltage command generator 310 converts the converted AC current measurement value I out_d ,I out_d , and removes noise from the measured current using a low-pass filter 313. Then, in this example, the second voltage command generating unit 310 generates the second voltage command V * d-axis component V d * and the q-axis component V q * Calculate the following.

[0039] The main circuit control unit 311 outputs a second voltage command V * =(V d * ,V q * ), phase command θ * By performing an inverse dq transformation using α * ,V β * ) is calculated. After that, although not shown in the figure, the main circuit control unit 311 calculates voltage commands for each of the three phases (R, S, T) by inverse three-phase to two-phase conversion, and generates gate signals Gpwm(R, S, T) which are PWM signals.

[0040] <Major Effects of the First Embodiment> As described above, the power conversion device 1 operates as a voltage source, but by providing the current command generation unit 308, the current command constraint unit 309, and the second voltage command generation unit 310, it becomes a voltage source incorporating current control. This makes it possible to continue operation even if an instantaneous voltage drop occurs due to a grid fault. In particular, by providing the current command constraint unit 309, it becomes possible to operate while suppressing overcurrent.

[0041] (Second embodiment) <Outline of power conversion device> Fig. 3 is a schematic diagram showing a configuration example of a power conversion device according to a second embodiment. In the second embodiment, descriptions of the same parts as in the first embodiment will be omitted as appropriate. The power conversion device 1 shown in Fig. 3 has a different configuration of an active power command unit 303 compared to the case of Fig. 1.

[0042] When the power conversion device 1 shown in FIG. 3 or FIG. 1 is operating in a grid-connected manner with respect to the AC grid 5, the power conversion device 1 outputs an active power command P o As shown below, the effective power P out However, when a fault occurs in the AC system 5 and the voltage of the AC system 5 drops instantaneously, the effective power P out That is, the power conversion device 1 reduces the active power command P o As shown below, the effective power P out In this case, in equation (1) or equation (2), P out <P o Therefore, ω * >ω o As a result, the power conversion device 1 increases the effective power P out We try to increase the

[0043] Here, when the fault is removed from the AC system 5 and the voltage of the AC system 5 is restored, the power conversion device 1 generates an effective power P out However, when the voltage is restored, the angular frequency command ω * is the angular frequency ω of AC system 5 o For ω * >ω o As a result, the angular frequency difference and phase difference between the power conversion device 1 and the AC system 5 become large. out becomes excessively large, and the active power command P o The value of the active power P out If the power rating exceeds the limit, overcurrent and overload operation may occur.

[0044] Meanwhile, Non-Patent Document 1 defines "Requirements for the operation continuity performance of distributed power sources during grid disturbances, which are necessary to ensure power quality" (Fault Ride Through: FRT). According to this, power sources connected to a grid are required to have the operation continuity performance during a fault to prevent disconnection or continuous output reduction due to widespread instantaneous voltage drops and frequency fluctuations caused by a grid fault. In order for the power conversion device 1 to operate in a grid-connected manner, it is necessary to satisfy this operation continuity performance during a fault. However, as described above, if overcurrent / overload operation occurs after recovery from the instantaneous voltage drop, the power conversion device 1 may stop operating, and may not be able to satisfy the operation continuity performance during a fault.

[0045] Therefore, to prevent overcurrent and overload operation after voltage recovery, the angular frequency command ω * As mentioned above, when the voltage of the AC system 5 drops, the effective power P out decreases, so the angular frequency command ω * To reduce the fluctuation of , the voltage drop of AC system 5 is detected and the active power command P o The value of can be reduced.

[0046] Generally, the line-to-line voltage V s , receiving end line voltage V s The effective power P in a three-phase AC with a phase difference δ and a reactance X between the sending and receiving ends is expressed as in equation (10).

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[0047] Based on the equation (10), the active power command unit 303 shown in FIG. 3 calculates the active power command P o That is, the active power command value P o ' is the d-axis component of the AC voltage measurement V out_d However, V in Equation (11) is corrected by the square of o is the AC terminal rated voltage of the power conversion circuit 2.

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[0048] <Details of the active power command section> Fig. 4 is a timing chart showing an example of the active power command and the angular frequency command generated in Fig. 3. In Fig. 4, the horizontal axis represents time t, and from the top, the voltage (measured AC voltage) V of the AC system 5 is out , active power P out , active power command P o , angular frequency command ω * Also, the active power command P o and angular frequency command ω * Regarding the graph, the solid line is an example of a waveform when the method of the second embodiment is applied, and the dashed dotted line is an example of a waveform when the method of the second embodiment is not applied.

[0049] In Figure 4, the AC voltage measurement value V out When decreases, the active power P out As the active power command P decreases, o As a result, when the method of the second embodiment is applied, the value of the angular frequency command ω * As a result, it is possible to suppress the increase in the angular frequency difference and phase difference between the power conversion device 1 and the AC system 5, and it is possible to suppress overcurrent and overload operation after voltage recovery.

[0050] In FIG. 4, the AC voltage measurement value V out Although the waveform shows an ideal one in which V quickly drops and recovers, in reality, out (V out_d ) chattering may occur. The chattering AC voltage measurement value V out is used as the active power command P o When used to correct the active power command P o and angular frequency command ω * Therefore, the active power command unit 303 outputs the active power command P o When correcting for AC voltage measurement V out_dIt is advisable to set a low-pass filter to remove vibrations caused by chattering before making corrections.

[0051] In addition, in equation (11), the d-axis component V out_d was used, but the three-phase AC voltage measurement value V out The effective value of V out_rms and the d-axis component V out_d and the q-axis component V out_q In addition, in equation (10), the effective power P is calculated by multiplying the line-to-line voltage V s , receiving end line voltage V s Therefore, the active power command unit 303 determines the second voltage command V * d-axis component V d * Using this, the active power command P is expressed in equation (12) instead of equation (11). o may be calculated.

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[0052] The active power command unit 303 also calculates the active power command P o Alternatively, the active power command unit 303 may constantly perform the calculation of the active power command P o The calculation is performed using the AC voltage measurement value V out_d or its effective value V out_rms , or the d-axis component V out_d and the q-axis component V out_q The above-mentioned measurement may be performed only when the square root of the sum of the squares of the voltages is below a threshold voltage that is determined separately, that is, only when it is estimated that a fault has occurred in the AC system 5.

[0053] <Major Effects of the Second Embodiment> As described above, by using the power conversion device 1 according to the second embodiment, it is possible to obtain the same effects as those described in the first embodiment. * To suppress the change of the active power command P oBy correcting this, it is possible to suppress overcurrent and overload operation that can occur after recovery from a momentary voltage drop caused by a grid fault.

[0054] (Third embodiment) <Details of current command constraints> In the third embodiment, the same parts as those in the above-described embodiments will not be described. A schematic configuration example of the power conversion device 1 according to the third embodiment is the same as the configuration example shown in FIG. 1 or 3.

[0055] In FIG. 1 or 3, the current command constraint unit 309 constrains the current command I generated by the current command generation unit 308. * =(I d * ,I q * ) is constrained. As described in FIG. 1, the current command constraint unit 309 constrains the d-axis component I by setting limiters for each of the d-axis component and the q-axis component, for example, so that the rated current of the power conversion circuit 2 is the upper limit and the value obtained by multiplying the rated current by −1 is the lower limit. d * and the q-axis component I q * Each of these can be limited to a rated current or less.

[0056] However, the d-axis component I d * and the q-axis component I q * If we only individually constrain the apparent current command √((I d * ) 2 +(I q * ) 2 ) may exceed the rated current. In this case, current control is performed according to the current command that exceeds the rated current, resulting in operation in an overcurrent state.

[0057] For example, when an accident occurs and the voltage of the AC system 5 drops instantaneously, the current command I * d-axis component I d *and the q-axis component I q * In this case, the d-axis component I d * and the q-axis component I q * Even if each is individually constrained to be less than the rated current, the apparent current command √((I d * ) 2 +(I q * ) 2 ) is √2 times the rated current. Therefore, in the third embodiment, in order to suppress overcurrent, the current is restricted depending on whether the apparent current command exceeds the threshold current.

[0058] FIG. 5 is a schematic diagram showing an example of a current command constraint method in the current command constraint unit 309 in the third embodiment. The current command constraint unit 309 constrains the apparent current command √((I d * ) 2 +(I q * ) 2 ) is the threshold current I lim When the current exceeds the limit, the current command I * =(I d * ,I q * ) into the current command I' * =(I d ' * ,I q ' * )

[0059]

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[0060] The current command constraint unit 309 determines the current command I * =(I d * ,I q* ) is constrained to obtain the current command I * =(I d * ,I q * ) power factor, the apparent current command reaches the threshold current I lim This makes it possible to suppress overcurrent while maintaining the power factor.

[0061] Threshold current I lim is, for example, the rated current of the power conversion circuit 2. However, in order to allow temporary overload operation, the threshold current I lim may be set to, for example, 120% of the rated current of the power conversion circuit 2. In addition, the threshold current I lim may be changed as appropriate depending on the state of the AC grid 5 and the operating state of the power conversion device 1. As an example, the threshold current I lim is the measured AC voltage V out When the threshold voltage is exceeded, the AC voltage measurement value V is set to 120% of the rated current of the power conversion circuit 2. out When the voltage Vcc is lower than the threshold voltage, the current Vcc may be set to the rated current of the power conversion circuit 2.

[0062] <Major Effects of the Third Embodiment> As described above, the use of the power conversion device 1 according to the third embodiment also provides the same effects as those described in the previous embodiments. lim If the current command I * The value of the threshold current I lim By restricting the value of

[0063] (Fourth embodiment) <Power conversion device details> In the fourth embodiment, the same parts as those in the above-described embodiments will not be described. A schematic configuration example of the power conversion device 1 according to the fourth embodiment is the same as the configuration example shown in FIG. 1 or 3.

[0064] 6 is a block diagram showing a detailed configuration example of each unit in FIG. 1 or FIG. 3 in a power conversion device according to the fourth embodiment. In FIG. 6, the configuration example of the second voltage command generating unit 310 is different from that in FIG. 2, and further, a fault determination unit 315 is added. As described above, the second voltage command generating unit shown in FIG. 2 generates the second voltage command V * =(V d * ,V q * ) is calculated. On the other hand, the second voltage command generating unit 310 shown in FIG. 6 calculates the AC voltage measurement value V out By performing the feedforward of the second voltage command V * =(V d * ,V q * ) is calculated.

[0065]

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[0066] In the equations (8) and (9) used by the second voltage command generating unit shown in FIG. 2, the voltage V out =(V out_d ,V out_q ) changes suddenly, the second voltage command V * =(V d * ,V q * ) does not change immediately. Therefore, immediately after the sudden change in the voltage of the AC system 5, the system side voltage (V out_d ,V out_q ) and the second voltage command V corresponding to the voltage on the power conversion circuit 2 side. * =(V d * ,V q *A large potential difference occurs between the value of

[0067] In FIG. 6, the AC voltage measurement value V in the current command generation unit 308 out =(V out_d ,V out_q ) is the output path, and a low-pass filter 312 is applied to the feed-forward path to the second voltage command generation unit 3'10 for noise removal. A time constant Tv1 such as 3 ms is set for the low-pass filter 312. Further, in FIG. 6, an accident determination unit 315 is provided. The accident determination unit 315 can also be applied to the configuration example shown in FIG. 1 or FIG. 3.

[0068] When the accident determination unit 315 determines that a system accident has occurred, it changes the time constant of the low-pass filter 312 from Tv1 to Tv2. The time constant Tv2 satisfies Tv2 < Tv1 and is, for example, 1 ms. By reducing the time constant, the voltage change during a system accident can be more quickly reflected in the current command generation and the second voltage command generation. Note that when Tv2 = 0 ms and it is determined that a system accident has occurred, it is also possible to directly use the measured voltage for command generation and control without passing through the low-pass filter 312, that is, by bypassing the low-pass filter 312.

[0069] The accident determination unit 315, for example, when the d-axis component V out of the AC voltage measurement value V out_d is less than the accident determination threshold voltage, for example, less than 80% of the rated voltage, or when the apparent current command √((I d * ) 2 +(I q * ) 2 ) exceeds the accident determination threshold current, for example, exceeds 120% of the rated current, determines that a system accident has occurred. On the other hand, the accident determination unit 315, for example, when the d-axis component V out of the AC voltage measurement value V out_dis equal to or greater than the fault judgment threshold voltage, and the apparent current command √((I d * ) 2 +(I q * ) 2 ) is equal to or less than the fault determination threshold current, it is determined that no grid fault has occurred or that the grid fault has been removed.

[0070] In this way, the fault determination unit 315 determines whether or not a grid fault has occurred based on two conditions of voltage and current, namely, that the voltage drops when a grid fault occurs and that the current command increases as the voltage drops. When the fault determination unit 315 determines that a grid fault has occurred, it reduces the time constant of the low-pass filter 312, thereby more quickly reflecting the voltage change during the grid fault in the generation of the current command and the second voltage command. This makes it possible to suppress overcurrent when a grid fault occurs and when the grid is restored from the fault.

[0071] <Major Effects of the Fourth Embodiment> As described above, by using the power conversion device 1 according to the fourth embodiment, it is possible to obtain the same effects as those described in the above-described embodiments. * By generating this, it is possible to suppress the potential difference immediately after a sudden voltage change in the AC system 5 due to a system fault, and to suppress overcurrent. Furthermore, by determining whether a system fault has occurred and changing the time constant of the low-pass filter 312 for the measured voltage according to the determination result, it is possible to suppress overcurrent by prioritizing noise removal performance under normal circumstances and responsiveness when a system fault occurs.

[0072] (Fifth embodiment) <Power conversion device details> In the fifth embodiment, the same parts as those in the above-described embodiments will not be described. A schematic configuration example of the power conversion device 1 according to the fifth embodiment is the same as the configuration example shown in FIG. 1 or 3.

[0073] 7 is a block diagram showing a detailed configuration example of each part in FIG. 1 or FIG. 3 in a power conversion device according to a fifth embodiment. In FIG. 1 or FIG. 3, when a fault occurs in the AC system 5 and a voltage imbalance occurs, the AC voltage measurement value V out d-axis component V out_d and the q-axis component V out_q In this case, vibrations at a frequency twice the reference frequency, for example, 50 Hz, appear as negative-phase components. This causes the current command to oscillate, and a negative-phase current is output. As a result, an overcurrent or the like may occur, making it difficult for the power conversion device 1 to continue operating. Therefore, it is beneficial to use the configuration shown in FIG. 7 to operate the power conversion device 1 so as not to output a negative-phase current.

[0074] 7, the second voltage command generating unit 310, similarly to the case of FIG. 6, receives the AC current measurement value I in the α-β coordinate system from the current command restricting unit 309. out =(I out_α ,I out_β ), phase command θ * By performing a dq transformation using out + =(I out_d + ,I out_q + Then, the second voltage command generating unit 310 calculates the deviation from the current command from the current command constraining unit 309 for each of the d-axis and q-axis components, and calculates the voltage command using the above-mentioned equations (15) and (16).

[0075] However, in the fifth embodiment, the calculation result is not the second voltage command but the positive-phase voltage command V +* =(V d +* ,V q +* The main circuit control unit 311 determines the positive sequence voltage command V +* =(V d +* ,V q +* ), phase command θ * By performing an inverse dq transformation using +* =(V α+* ,V β +* )

[0076] The second voltage command generator 310 also calculates the AC current measurement value I in the α-β coordinate system. out =(I out_α ,I out_β ), phase command θ * multiplied by -1 -θ * By performing a dq transformation using out - =(I out_d - ,I out_q - ) is calculated. That is, the negative-phase current is calculated by such a calculation. In order to prevent the output of the negative-phase current, current control can be performed by setting the current command to 0.

[0077] Therefore, the second voltage command generator 310 calculates the negative-phase current command (0,0) and the negative-phase measurement current I out - =(I out_d - ,I out_q - ) is taken for each d-axis / q-axis component, and the negative-phase voltage command V is calculated using the following equations (17) and (18). -* =(V d -* ,V q -* ) in the dq coordinate system. -* =(V d -* ,V q -* ), phase command θ * multiplied by -1 -θ * By performing an inverse dq transformation using -* =(V α -* ,V β -* )

[0078]

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[0079] Second voltage command V after three-phase to two-phase conversion * =(V α * ,V β * ) is expressed as the positive sequence voltage command V +* =(V α +* ,V β +* ) and negative-phase voltage command V -* =(V α -* ,V β -* ) and

number

[0080] Although not shown in the figure, the main circuit control unit 311 calculates the second voltage command V * =(V α * ,V β * ) is subjected to inverse three-phase to two-phase conversion to generate voltage commands for each of the three phases (R, S, T). Furthermore, the main circuit control unit 311 generates gate signals for the switching elements in the power conversion circuit 2 based on the voltage commands for each of the three phases, and drives the power conversion circuit 2.

[0081] <Major Effects of the Fifth Embodiment> As described above, by using the power conversion device 1 according to the fifth embodiment, it is possible to obtain the same effects as those described in the above-described embodiments. +* and the negative-sequence voltage command V that is controlled so that the negative-sequence current becomes zero. -* The second voltage command V * By generating the negative-phase-sequence current, the power conversion device 1 can continue to operate without outputting a negative-phase-sequence current. As a result, the power conversion device 1 can continue to operate even if an unbalance fault occurs.

[0082] (Sixth embodiment) <Outline of power conversion device> 8 is a schematic diagram showing a partial configuration example of a power conversion device according to a sixth embodiment. The power conversion device 1 shown in FIG. 8 includes a user interface 316 in addition to the current command constraint unit 309 described in FIG. 5 and the fault determination unit 315 described in FIG. 6. The current command constraint unit 309, as described in FIG. 5, determines the threshold current I lim Based on this, the current command I * The fault determination unit 315 determines whether or not a grid fault has occurred based on the fault determination threshold voltage or the fault determination threshold current, as described in FIG.

[0083] Here, the threshold current I lim The optimum values ​​of the fault determination threshold current and the fault determination threshold voltage may change depending on, for example, the state of the AC grid 5. The optimum value of the fault determination threshold voltage may also change depending on, for example, the impedance of the AC grid 5. Therefore, the user interface 316 allows the user 16 to change the threshold current I lim , fault detection threshold voltage V th or fault determination threshold current I th Accepts setting input.

[0084] In this example, the user interface 316 displays the setting screen 17 on the information terminal 15 of the user 16, and acquires the value input by the user 16 on the setting screen 17. Then, the user interface 316 calculates the acquired threshold current I lim is set in the current command constraint unit 309, and the acquired fault determination threshold voltage V th or fault determination threshold current I th is set in the accident determination unit 315.

[0085] This allows flexible adaptation to various system configurations to which the power conversion device 1 is applied. The setting screen 17 may be, for example, an operation panel or the like provided on the power conversion device 1. The setting items include a threshold current I lim , fault detection threshold voltage V th, fault determination threshold current I th It may include, for example, the impedance Z as described in equations (4) and (5).

[0086] The invention made by the inventor has been specifically described above based on the embodiments, but the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit of the invention. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0087] 1...power conversion device, 2...power conversion circuit, 3...control circuit, 4...AC filter, 5...AC system, 6...AC load, 7...DC power supply, 301...measurement unit, 302...power calculation unit, 303...active power command unit, 304...angular frequency command generation unit, 305...phase command generation unit, 306...reactive power command unit, 307...first voltage command generation unit, 308...current command generation unit, 309...current command constraint unit, 310...second voltage command generation unit, 311...main circuit control unit, 315...fault determination unit

Claims

1. A power conversion device connected to a DC power source, a power conversion circuit having one end connected to the DC power supply and the other end connected to an AC power supply and an AC load; a measurement unit that outputs a measured voltage and a measured current on the AC side of the power conversion circuit; a power calculation unit that calculates an output active power and an output reactive power from the measured voltage and the measured current; an active power command unit that determines an active power command for the power conversion device; an angular frequency command generation unit that generates an angular frequency command from the output active power and the active power command; a phase command generation unit that generates a phase command from the angular frequency command; a reactive power command unit that determines a reactive power command from the measured voltage or an external input value; a first voltage command generating unit that generates a first voltage command from the output reactive power and the reactive power command; a current command generating unit that generates a current command from the measured voltage and the first voltage command; a current command constraint unit that constrains and outputs the current command; a second voltage command generating unit that generates a second voltage command from the current command constrained by the current command constraining unit and the measured current; Equipped with controlling the power conversion circuit based on the second voltage command; Power conversion device.

2. The power conversion device according to claim 1, the current command generating unit generates the current command by dividing a difference between the measured voltage and the first voltage command by a preset virtual impedance value. Power conversion device.

3. The power conversion device according to claim 1, the active power command unit receives an active power command value and outputs the received active power command value as the active power command; Power conversion device.

4. The power conversion device according to claim 1, the active power command unit receives an active power command value, corrects the received active power command value so as to suppress a change in the angular frequency command, and outputs the corrected active power command value as the active power command; Power conversion device.

5. The power conversion device according to claim 4, the active power command unit corrects the input active power command value by the measured voltage and outputs the corrected value as the active power command. Power conversion device.

6. The power conversion device according to claim 5, the active power command unit calculates the square of a value obtained by dividing the measured voltage by a rated AC terminal voltage of the power conversion circuit, and outputs a value obtained by multiplying the calculated value by the input active power command value as the active power command. Power conversion device.

7. The power conversion device according to claim 1, The current command constraint unit When the square root of the sum of squares of the d-axis component and the q-axis component of the current command exceeds a preset threshold current, the d-axis component and the q-axis component of the current command are each divided by the square root of the sum of squares and then multiplied by the threshold current, and the resulting value is output; When the square root of the sum of squares is equal to or smaller than the threshold current, the current command generated by the current command generating unit is output as is. Power conversion device.

8. The power conversion device according to claim 7, Further, a user interface is provided for accepting a setting input of the threshold current by a user. Power conversion device.

9. The power conversion device according to claim 1, the second voltage command generation unit generates, as the second voltage command, a value obtained by adding the measured voltage to a voltage value calculated from the current command constrained by the current command constraining unit and the measured current. Power conversion device.

10. The power conversion device according to claim 1, further comprising an accident determination unit that determines whether an accident has occurred in the AC power supply, The current command generation unit When the accident determination unit determines that no accident has occurred, the current command is generated by applying a filter to the measured voltage; When the accident determination unit determines that an accident has occurred, the current command is generated without applying the filter to the measured voltage, or the current command is generated by applying a filter having a time constant different from that of the filter to the measured voltage. Power conversion device.

11. The power conversion device according to claim 10, the accident determination unit determines that an accident has occurred when the measured voltage is equal to or lower than a preset threshold voltage or when the root-sum-square of a d-axis component and a q-axis component of the current command exceeds a preset threshold current. Power conversion device.

12. The power conversion device according to claim 11, Further, a user interface is provided for accepting a setting input of the threshold voltage or the threshold current by a user. Power conversion device.

13. The power conversion device according to claim 1, The second voltage command generation unit a positive-sequence measured current having a d-axis component and a q-axis component is calculated by performing a dq transformation on the measured current using the phase command, and a positive-sequence voltage command is generated from the positive-sequence measured current and the current command constrained by the current command constraining unit; a negative-phase-sequence measurement current having a d-axis component and a q-axis component is calculated by performing a dq transformation on the measured current using a value obtained by multiplying the phase command by −1, and a negative-phase-sequence voltage command is generated from the negative-phase-sequence measurement current and a preset negative-phase-sequence current command value; generating the second voltage command as the sum of the positive-sequence voltage command and the negative-sequence voltage command; Power conversion device.

14. The power conversion device according to claim 13, the second voltage command generating unit sets the negative-phase current command value to 0; Power conversion device.

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