Power conversion device and inverter control device

Abstract

Provided is a power conversion device comprising: a first voltage command generation unit that generates a first voltage command on the basis of a predetermined rated voltage; an angular frequency command generation unit that generates an angular frequency command for alternating current power on the basis of an active power command input from the outside; a phase command generation unit that generates a phase command on the basis of the angular frequency command; a current command generation unit that generates a current command for the alternating current power on the basis of the phase command and the first voltage command; a harmonic current command generation unit that generates a harmonic current command; and a current control unit that generates a voltage command for the alternating current power on the basis of the current command generated by the current command generation unit and the harmonic current command generated by the harmonic current command generation unit. The harmonic current command generation unit acquires reference information synchronized with a power system or absolute time information, and determines the phase of the harmonic current command on the basis of the reference information or the time information.

Description

Power conversion devices, inverter control devices

[0001] The present invention relates to a power conversion device and an inverter control device.

[0002] Conventionally, there has been known a power conversion device that is connected between a DC power source such as a solar panel or a storage battery and a power grid, converts DC power output from the DC power source into AC power that matches the frequency and phase of the power grid, and inputs the AC power into the power grid. One such power conversion device is known to inject an interharmonic current having a frequency that is a non-integer multiple of the fundamental wave of the power grid into the power grid, and monitor the impedance of the power grid from the measurement results of the voltage corresponding to this interharmonic current, thereby detecting when the power supply from the power grid is stopped and cutting off the connection with the power grid to prevent accidents or the like in the power grid (Patent Document 1).

[0003] When multiple power conversion devices having the above-described functions are connected in parallel, it is necessary to prevent mutual interference between the interharmonic currents of the power conversion devices. Patent Document 2 (Patent Document 2) describes a distributed power supply apparatus that includes a master distributed power supply unit and a slave distributed power supply unit connected to a power grid. The master distributed power supply unit injects a reference signal into the power grid, and the master distributed power supply unit and the slave distributed power supply unit each generate interharmonic signals having the same frequency and synchronized with the reference signal injected into the power grid. This distributed power supply apparatus allows the master distributed power supply unit and the slave distributed power supply unit to synchronize their respective interharmonic signals without the need for communication lines or the like for synchronization.

[0004] Japanese Unexamined Patent Publication No. 10-248168 Japanese Unexamined Patent Application No. 2015-154604

[0005] In the distributed power supply apparatus described in Patent Document 2, if the master distributed power supply unit is unable to generate a reference signal normally due to a failure or the like, it becomes difficult to synchronize the remaining slave distributed power supply units. Therefore, there is a problem in that it is not possible to prevent mutual interference of interharmonic currents between the power conversion devices, making it difficult to detect a power supply interruption in the power system.

[0006] In view of the above-mentioned problems, an object of the present invention is to improve the availability of a function for detecting a power supply interruption in a power system when a plurality of power conversion devices are connected in parallel.

[0007] a current command generation unit that generates a current command for the AC power based on the phase command and the first voltage command; a harmonic current command generation unit that generates a harmonic current command for the harmonic; and a current control unit that generates a voltage command for the AC power based on the current command generated by the current command generation unit and the harmonic current command generated by the harmonic current command generation unit, wherein the harmonic current command generation unit acquires reference information or absolute time information synchronized with the power system, and determines a phase of the harmonic current command based on the reference information or the time information. an inverter control device connected to an electric power system and configured to control an inverter that converts DC power supplied from a DC power source into AC power having a harmonic current superimposed on a fundamental frequency of the power system and outputs the converted AC power to the power system, the inverter control device comprising: a first voltage command generation unit that generates a first voltage command based on a predetermined rated voltage; an angular frequency command generation unit that generates an angular frequency command for the AC power based on an active power command input from outside; a phase command generation unit that generates a phase command based on the angular frequency command; a current command generation unit that generates a current command for the AC power based on the phase command and the first voltage command; a harmonic current command generation unit that generates a harmonic current command for the harmonic current; and a current control unit that generates a voltage command for the AC power based on the current command generated by the current command generation unit and the harmonic current command generated by the harmonic current command generation unit,

[0008] According to the present invention, it is possible to improve the availability of the function for detecting a power supply interruption in the power system when a plurality of power conversion devices are connected in parallel.

[0009] Fig. 1 is a diagram showing an example of the configuration of a power conversion device according to a first embodiment of the present invention. Fig. 2 is a control block diagram showing details of current control in the power conversion device according to the first embodiment of the present invention. Fig. 3 is a diagram showing an example of the configuration of a power conversion device according to a second embodiment of the present invention. Fig. 4 is a control block diagram showing details of current control in the power conversion device according to the second embodiment of the present invention. Fig. 5 is a diagram showing an example of the configuration of a power conversion device according to a third embodiment of the present invention. Fig. 6 is a diagram showing an example of the configuration of a power conversion device according to a fourth embodiment of the present invention.

[0010] 1 is a diagram showing an example of the configuration of a power conversion device according to a first embodiment of the present invention. A power conversion device 100 of this embodiment converts DC power supplied from a DC power source 1 into AC power and outputs the AC power to a power grid 2, thereby realizing power supply from the DC power source 1 to the power grid 2, and includes an inverter 3, a filter 4, a current sensor 5, a voltage sensor 6, and an inverter control device 10.

[0011] The DC power supply 1 is connected to the inverter 3 and outputs a predetermined DC power to the inverter 3. The DC power supply 1 may be, for example, a secondary battery such as a lithium ion battery, a nickel-metal hydride battery, or a lead-acid battery, or may be a renewable energy power supply such as a solar power generation or a wind power generation. The DC power supply 1 may also be configured by a combination of these.

[0012] The inverter 3 is configured using, for example, a three-phase full-bridge circuit, and operates under the control of the inverter control device 10 to convert DC power input from the DC power source 1 into AC power in which predetermined harmonics are superimposed on the fundamental frequency of the power grid 2, and outputs the AC power to the power grid 2 via the filter 4. The filter 4 removes unnecessary high-frequency components from the AC power output from the inverter 3. The harmonics superimposed on the AC power will be described in detail later.

[0013] The current sensor 5 measures the current value of the AC power output from the inverter 3. The voltage sensor 6 measures the voltage value (AC voltage value of the power grid 2) of the AC power output from the inverter 3 after it has passed through the filter 4. The measurement results from the current sensor 5 and the voltage sensor 6 are input to the inverter control device 10 as a measured current value Iout and a measured voltage value Vout of the AC power output from the power conversion device 100, respectively.

[0014] The inverter control device 10 includes functional blocks, such as a power calculation unit 11, an islanding operation detection unit 12, a reactive power command unit 13, a first voltage command generation unit 14, an angular frequency command generation unit 15, a phase command generation unit 16, a phase detector 17, a harmonic current command phase generation unit 18, a harmonic current command generation unit 19, a current command generation unit 20, a current command constraint unit 21, a current command addition unit 22, a current control unit 23, and a main circuit control unit 24. The inverter control device 10 is configured, for example, by a microcomputer, and these functional blocks can be realized by executing a predetermined program on the microcomputer. Alternatively, some or all of these functional blocks may be realized using hardware circuits such as logic ICs or FPGAs.

[0015] The power calculation unit 11 calculates active power P and reactive power Q, which respectively represent the active component and reactive component of the AC power actually output by the power conversion device 100, from the current measurement value Iout and voltage measurement value Vout obtained from the current sensor 5 and voltage sensor 6, respectively.

[0016] The islanding operation detection unit 12 detects whether the power conversion device 100 is in an islanding operation state based on the measured current value Iout and the measured voltage value Vout acquired from the current sensor 5 and the voltage sensor 6, respectively. Specifically, the islanding operation detection unit 12 measures the impedance of the power grid 2 when the power conversion device 100 outputs AC power based on predetermined harmonic components of the measured voltage value Vout and the measured current value Iout. When this impedance exceeds a preset threshold, the islanding operation detection unit 12 determines that the power conversion device 100 is in an islanding operation state. In this case, the islanding operation detection unit 12 switches off a circuit breaker (not shown) connected between the power conversion device 100 and the power grid 2 to disconnect the power conversion device 100 from the power grid 2. This prevents accidents such as unexpected electric shock in the power grid 2 due to the output of the power conversion device 100. Note that the superposition control of harmonics on AC power is performed in the inverter control device 10 by a harmonic current command Im* (described later) generated by a harmonic current command generation unit 19.

[0017] The reactive power command unit 13 generates a command value for the reactive component of the AC power output from the power conversion device 100 based on the measured voltage value Vout acquired from the voltage sensor 6, and outputs the command value as a reactive power command Q*. Specifically, the reactive power command unit 13 generates the reactive power command Q* by multiplying the deviation (V0-Vout) between the rated voltage V0 (for example, V0=200 V) and the measured voltage value Vout by a predetermined proportional gain KQ.

[0018] The first voltage command generation unit 14 uses the reactive power Q calculated by the power calculation unit 11 and the reactive power command Q* output from the reactive power command unit 13 to generate a first voltage command E*, which is a voltage command value before harmonics are superimposed on the AC power output from the power conversion device 100. Specifically, the first voltage command generation unit 14 generates the first voltage command E* based on the rated voltage V0 by PI control of the deviation (Q*-Q) between the reactive power command Q* and the reactive power Q.

[0019] The angular frequency command generation unit 15 generates a command value for the angular frequency of the AC power output from the power conversion device 100 based on the active power P calculated by the power calculation unit 11 and an externally input active power command P0, and outputs the command value as an angular frequency command ω*. Specifically, the angular frequency command generation unit 15 calculates a value by multiplying the deviation (P0-P) between the active power command P0 and the active power P by the reciprocal of a predetermined proportional gain, 1 / KP, and performs first-order lag and first-order lead compensation on this value to calculate an angular frequency deviation Δω to which pseudo-inertia has been imparted. The angular frequency command ω* is then generated by adding the angular frequency deviation Δω to the rated angular frequency ω0 (e.g., 2π × 50 Hz).

[0020] The phase command generating unit 16 generates a phase command θ*, which is a command value for the phase of the AC power output from the power conversion device 100, based on the angular frequency command ω* output from the angular frequency command generating unit 15. Specifically, the phase command generating unit 16 generates the phase command θ* by integrating the angular frequency command ω*. This makes it possible to obtain the phase command θ* based on the angular frequency command ω*. Note that the phase command θ* may be the remainder obtained when the value obtained by integrating the angular frequency command ω* is divided by 2π.

[0021] The phase detector 17 detects the voltage phase θ of the power system 2 from the voltage measurement value Vout by the voltage sensor 6. Specifically, the phase detector 17 detects the voltage phase θ of the power system 2 by a well-known frequency locked loop (FLL) circuit or phase locked loop (PLL) circuit.

[0022] The harmonic current command phase generator 18 determines the current phase of the harmonics to be superimposed on the AC power output by the power conversion device 100 based on the voltage phase θ of the power grid 2 detected by the phase detector 17, and outputs the determined value as the harmonic current phase θgrid(m). Here, the value of m in the harmonic current phase θgrid(m) represents the order of the harmonic with respect to the fundamental frequency of the power grid 2 (where m is a real number greater than 1), and is, for example, 2.5. Specifically, the harmonic current command phase generator 18 can calculate the remainder when multiplying the voltage phase θ of the power grid 2 by m and dividing the result by 2π, and output the value obtained by this calculation as the harmonic current phase θgrid(m). In addition, if the current phase of the mth harmonic can be appropriately determined from the voltage phase θ of the power system 2, the harmonic current command phase generating unit 18 may determine the current phase of the mth harmonic by another method and output the value as the harmonic current phase θgrid(m).

[0023] The harmonic current command generating unit 19 generates a harmonic current command Im*, which is a current command for a harmonic to be superimposed on the AC power output by the power conversion device 100. At this time, the harmonic current command generating unit 19 acquires reference information synchronized with the power grid 2 and determines the phase of the harmonic current command Im* based on this reference information. Specifically, in this embodiment, the harmonic current command generating unit 19 acquires the harmonic current phase θgrid(m) for the m-th harmonic determined by the harmonic current command phase generating unit 18 as reference information synchronized with the power grid 2. Then, the harmonic current command generating unit 19 generates the harmonic current command Im* for the m-th harmonic based on the acquired value of the harmonic current phase θgrid(m) and harmonic setting information indicating preset amplitudes and orders of the harmonics.

[0024] The current command generating unit 20 generates a current command I* before high-frequency superposition for the AC power output from the power conversion device 100, based on the first voltage command E* generated by the first voltage command generating unit 14 and based on the rated voltage V0, the phase command θ* based on the angular frequency command ω* obtained by the phase command generating unit 16, and the voltage measurement value Vout obtained by the voltage sensor 6. Specifically, the current command generating unit 20 obtains a deviation between the first voltage command E* and a value obtained by dq transforming the voltage measurement value Vout based on the phase command θ*, and calculates the current command I* before high-frequency superposition based on this deviation. In this way, the current command generating unit 20 can generate the current command I* for the AC power before high-frequency superposition, based on the angular frequency command ω* generated by the angular frequency command generating unit 15 and the predetermined rated voltage V0.

[0025] When the current command I* generated by the current command generating unit 20 exceeds a predetermined limit value, the current command restricting unit 21 restricts the current command I* so that the current command I* is equal to or less than the limit value. If it is not necessary to restrict the current command I* to be equal to or less than the limit value, the current command restricting unit 21 may be omitted from the inverter control device 10.

[0026] The current command adder 22 adds the harmonic current command Im* generated by the harmonic current command generator 19 to the current command I* generated by the current command generator 20 and further constrained by the current command constrainer 21 as necessary.Then, the added value is output to the current controller 23 as a harmonic added current command I+*.

[0027] The current control unit 23 generates a voltage command V* for the AC power output from the power conversion device 100, based on the harmonic added current command I+* input from the current command adder 22 and the current measurement value Iout by the current sensor 5. Specifically, the current control unit 23 calculates the deviation between the harmonic added current command I+* and a value obtained by dq transforming the current measurement value Iout based on the phase command θ*, and calculates the voltage command V* based on this deviation. This allows the current control unit 23 to generate a voltage command V* for the AC power after high-frequency superposition, based on the current command I* generated by the current command generator 20 and the harmonic current command Im* generated by the harmonic current command generator 19.

[0028] The main circuit control unit 24 controls the operation of the inverter 3 based on the voltage command V* generated by the current control unit 23 and the phase command θ* determined by the phase command generation unit 16. At this time, the main circuit control unit 24 performs PWM control based on the voltage command V* and the phase command θ* to generate gate signals for each switching element of the inverter 3 and output these gate signals to the inverter 3. This allows the inverter 3 to be driven to convert DC power to AC power so that the voltage and phase of the AC power output from the inverter 3 to the power grid 2 change in accordance with the voltage command V* and the phase command θ*.

[0029] As described above, the power conversion device 100 can operate in a grid-connected state with the power grid 2 while virtually having inertia. It is also possible to switch off a circuit breaker (not shown) connected between the power conversion device 100 and the power grid 2 to terminate the grid-connected operation with the power grid 2 and transition to stand-alone operation.

[0030] FIG. 2 is a control block diagram showing details of current control in the power conversion device according to the first embodiment of the present invention.

[0031] The harmonic current command generator 19 generates a three-phase m-th harmonic current command for each of the U, V, and W phases based on the harmonic current phase θgrid(m) input from the harmonic current command phase generator 18 and the amplitude and order of the harmonic represented by preset harmonic setting information. The generated three-phase m-th harmonic current command is then three-phase / two-phase converted to calculate an α-axis harmonic current command Im*_α and a β-axis harmonic current command Im*_β for the m-th harmonic. These values ​​are then subjected to dq conversion based on the phase command θ* to calculate a d-axis harmonic current command Im*_d and a q-axis harmonic current command Im*_q for the m-th harmonic based on the phase of the AC power output from the power conversion device 100.

[0032] Current command generating unit 20 performs dq transformation based on phase command θ* on the α-axis component Vout_α and β-axis component Vout_β of the measured voltage value Vout input from voltage sensor 6, and outputs the calculation result via a low-pass filter to obtain a d-axis voltage Vout_d and a q-axis voltage Vout_q. Then, deviations between the obtained d-axis voltage Vout_d and q-axis voltage Vout_q and the d-axis component E*_d and q-axis component E*_q of the first voltage command E* input from first voltage command generating unit 14 are calculated, and a d-axis current command I*_d and a q-axis current command I*_q are calculated from these deviations.

[0033] Current command constraint unit 21 compares the d-axis current command I*_d and the q-axis current command I*_q calculated by current command generation unit 20 with predetermined limit values, and if the limit values ​​are exceeded, it imposes constraints on the d-axis current command I*_d and the q-axis current command I*_q, respectively. Then, it outputs the constrained d-axis current command I*_d and the q-axis current command I*_q. On the other hand, if the d-axis current command I*_d and the q-axis current command I*_q do not exceed the limit values, it outputs these values ​​as they are without imposing constraints.

[0034] Current command adder 22 adds d-axis harmonic current command Im*_d and q-axis harmonic current command Im*_q input from harmonic current command generator 19 to d-axis current command I*_d and q-axis current command I*_q input from current command generator 20 via current command constraint unit 21. That is, current command adder 22 adds d-axis harmonic current command Im*_d and q-axis harmonic current command Im*_q corresponding to the active current command (active harmonic current command) and reactive current command (reactive harmonic current command) for the harmonics, respectively, to d-axis current command I*_d and q-axis current command I*_q corresponding to the active current command and reactive current command for the AC power before harmonics are superimposed. In this way, d-axis harmonic added current command I+*_d and q-axis harmonic added current command I+*_q corresponding to the active current command and reactive current command for the AC power after harmonics are superimposed are calculated.

[0035] The current control unit 23 has a positive-phase sequence calculation unit 231 and a negative-phase sequence compensation calculation unit 232. The positive-phase sequence calculation unit 231 obtains a positive-phase sequence voltage command V+* representing a positive-phase sequence component of the voltage command V* for the AC power output from the power conversion device 100. The negative-phase sequence compensation calculation unit 232 obtains a negative-phase sequence voltage command V-* representing a negative-phase sequence compensation component of the voltage command V* for the AC power output from the power conversion device 100.

[0036] The positive-phase calculation unit 231 obtains the positive-phase d-axis current I+out_d and the q-axis current I+out_q by performing dq transformation based on the phase command θ* on the α-axis component Iout_α and the β-axis component Iout_β of the measured current value Iout input from the current sensor 5. The positive-phase calculation unit 231 then calculates the deviations between the obtained positive-phase d-axis current I+out_d and q-axis current I+out_q and the d-axis harmonic added current command I+*_d and the q-axis harmonic added current command I+*_q input from the current command adder 22. Furthermore, a PI control calculation is performed on each of these deviations, and a feedforward calculation and a decoupling control calculation are performed using the d-axis voltage Vout_d and the q-axis voltage Vout_q calculated by current command generating unit 20 to calculate a positive-phase d-axis voltage command V+*_d and a q-axis voltage command V+*_q representing the d-axis component and the q-axis component of the positive-phase voltage command V+*, respectively. Then, an inverse αβ transformation based on the phase command θ* is performed on the calculated positive-phase d-axis voltage command V+*_d and q-axis voltage command V+*_q to calculate a positive-phase α-axis voltage command V+*_α and a β-axis voltage command V+*_β.

[0037] The negative-phase-sequence compensation calculation unit 232 calculates the negative-phase d-axis current I-out_d and the q-axis current I-out_q by performing dq transformation based on the negative-phase command -θ* obtained by inverting the sign of the phase command θ* on the α-axis component Iout_α and the β-axis component Iout_β of the measured current Iout input from the current sensor 5. Then, the negative-phase compensation calculation unit 232 calculates values ​​obtained by subtracting the calculated negative-phase d-axis current I-out_d and q-axis current I-out_q from 0, and performs a PI control calculation and a decoupling control calculation on these subtracted values ​​to calculate the negative-phase d-axis voltage command V-*_d and the q-axis voltage command V-*_q, which respectively represent the d-axis component and the q-axis component of the negative-phase voltage command V-*. Furthermore, the calculated negative-phase d-axis voltage command V-*_d and q-axis voltage command V-*_q are subjected to inverse αβ transformation based on the negative-phase command -θ* to obtain negative-phase α-axis voltage command V-*_α and β-axis voltage command V-*_β.

[0038] In the current control unit 23 of this embodiment, the negative-phase α-axis voltage command V-*_α and the negative-phase β-axis voltage command V-*_β calculated by the negative-phase compensation calculation unit 232 are added to the positive-phase α-axis voltage command V+*_α and the positive-phase β-axis voltage command V+*_β calculated by the positive-phase calculation unit 231. This calculates the α-axis component V*_α and the β-axis component V*_β of the voltage command V* to which the negative-phase compensation has been added. Note that if negative-phase compensation is not required, the negative-phase compensation calculation unit 232 may be omitted from the current control unit 23.

[0039] In the power conversion device 100 of this embodiment, the inverter control device 10 performs the control described above to synchronize the phase of the harmonics superimposed on the AC power output by the inverter 3 with the voltage phase of the power grid 2. Specifically, in the inverter control device 10, the harmonic current command generator 19 acquires the harmonic current phase θgrid(m) generated by the harmonic current command phase generator 18 as reference information synchronized with the power grid 2. Here, the harmonic current command phase generator 18 determines the harmonic current phase θgrid(m) based on the phase θ of the AC voltage detected from the measured voltage value Vout by the phase detector 17. Therefore, the harmonic current phase θgrid(m) is synchronized with the voltage of the power grid 2. Then, the harmonic current command generator 19 generates a harmonic current command Im* for the m-th harmonic using the acquired harmonic current phase θgrid(m). As a result, when the current control unit 23 generates a voltage command V* based on the current command I* and the harmonic current command Im*, and the inverter 3 is operated in accordance with this voltage command V*, harmonics synchronized with the voltage phase of the power system 2 are superimposed on the AC power output from the inverter 3.

[0040] Here, when a plurality of power conversion devices 100 according to the present embodiment are used and each is connected in parallel to the power grid 2, and the above-described control is performed in each power conversion device 100, each power conversion device 100 outputs AC power on which harmonics are superimposed and which is synchronized with the voltage phase of the power grid 2. Therefore, it is possible to synchronize the harmonics of each power conversion device 100 without mutual exchange of signals or information between the plurality of power conversion devices 100. As a result, even if any one of the power conversion devices 100 becomes unable to operate normally, the other power conversion devices 100 can continue to output AC power on which harmonics are superimposed and which are synchronized with each other. Therefore, when a plurality of power conversion devices 100 are connected in parallel and used, the availability of the function of detecting a power supply interruption (islanding operation detection) in the power grid is improved.

[0041] According to the first embodiment of the present invention described above, the following advantageous effects are achieved.

[0042] (1) The power conversion device 100 is connectable to the power grid 2, converts DC power supplied from a DC power source 1 into AC power having harmonics superimposed on the fundamental frequency of the power grid 2, and outputs the AC power to the power grid 2. The power conversion device 100 includes an inverter control device 10, which includes an angular frequency command generating unit 15, a current command generating unit 20, a harmonic current command generating unit 19, and a current control unit 23. The angular frequency command generating unit 15 generates an angular frequency command ω* for AC power output by the power conversion device 100 based on an active power command P0 input from an external device. The current command generating unit 20 generates a current command I* for AC power output by the power conversion device 100 based on a phase command θ* generated from the angular frequency command ω* generated by the angular frequency command generating unit 15 and a predetermined rated voltage V0. The harmonic current command generating unit 19 generates a harmonic current command Im* for the harmonics superimposed on the AC power output by the power conversion device 100. The current control unit 23 generates a voltage command V* for the AC power output by the power conversion device 100 based on the current command I* generated by the current command generating unit 20 and the harmonic current command Im* generated by the harmonic current command generating unit 19. Here, the harmonic current command generating unit 19 acquires reference information synchronized with the power grid 2 and determines the phase of the harmonic current command Im* based on this reference information. This makes it possible to improve the availability of the function of detecting power supply interruptions in the power grid (islanding operation detection) when multiple power conversion devices 100 are connected in parallel.

[0043] (2) The power conversion device 100 includes, in the inverter control device 10, a harmonic current command phase generator 18 that determines a harmonic current phase θgrid(m), which is a current phase used for the harmonic current command Im*, based on the voltage phase θ of the power grid 2. The harmonic current command generator 19 acquires the harmonic current phase θgrid(m) determined by the harmonic current command phase generator 18 as reference information synchronized with the power grid 2. This configuration allows the harmonic current command generator 19 to reliably acquire reference information synchronized with the power grid 2 and use this to generate the harmonic current command Im*.

[0044] (3) The inverter control device 10 of the power conversion device 100 includes a phase detector 17 that detects the voltage phase θ of the power grid 2 from the voltage measurement value Vout of the AC power output by the power conversion device 100. The harmonic current command phase generator 18 determines the harmonic current phase θgrid(m) based on the voltage phase θ of the power grid 2 detected by the phase detector 17. In this manner, the harmonic current phase θgrid(m) as reference information synchronized with the power grid 2 can be accurately determined based on the voltage phase θ of the power grid 2.

[0045] (4) The power conversion device 100 includes a current command adder 22 in the inverter control device 10 that calculates a harmonic sum current command I+* by adding the harmonic current command Im* to the current command I*. The current control unit 23 generates a voltage command V* based on the harmonic sum current command I+* calculated by the current command adder 22. This configuration allows the current control unit 23 to easily generate a voltage command V* based on the current command I* and the harmonic current command Im*.

[0046] (5) The power conversion device 100 includes an islanding operation detection unit 12 in the inverter control device 10 that detects whether the power conversion device 100 is in an islanding operation state based on a measured voltage value Vout representing a measurement result of the AC voltage in the power grid 2 and a measured current value Iout representing a measurement result of the AC current output from the power conversion device 100 to the power grid 2. This configuration makes it possible to reliably detect when the power conversion device 100 is in an islanding operation state.

[0047] Second Embodiment Fig. 3 is a diagram showing an example of the configuration of a power conversion device according to a second embodiment of the present invention. A power conversion device 100A of this embodiment differs from the power conversion device 100 described in the first embodiment in that the inverter control device 10 does not include a current command adder 22. The following describes the power conversion device 100A of this embodiment, focusing on the differences from the first embodiment.

[0048] In this embodiment, the current command I* generated by the current command generating unit 20 and further constrained by the current command constraining unit 21 as necessary, and the harmonic current command Im* generated by the harmonic current command generating unit 19 are each input to the current control unit 23. The current control unit 23 generates a voltage command V* for the AC power output from the power conversion device 100A based on these current commands, the harmonic current phase θgrid(m) for the m-th harmonic determined by the harmonic current command phase generating unit 18, and the current measurement value Iout by the current sensor 5.

[0049] FIG. 4 is a control block diagram showing details of current control in a power conversion device according to a second embodiment of the present invention.

[0050] The harmonic current command generating unit 19 calculates an α-axis harmonic current command Im*_α and a β-axis harmonic current command Im*_β for the m-th harmonic, as in the first embodiment. Then, in the second embodiment of the present invention, these values ​​are subjected to dq transformation based on the harmonic current phase θgrid(m), thereby calculating a d-axis harmonic current command Im*_d and a q-axis harmonic current command Im*_q for the m-th harmonic based on the phase of the m-th harmonic.

[0051] The current command generating unit 20 and the current command restricting unit 21 each perform the same calculations as in the first embodiment.

[0052] The current control unit 23 further includes a harmonic calculation unit 233 in addition to the positive-phase calculation unit 231 and the negative-phase compensation calculation unit 232 described in the first embodiment. In this embodiment, the positive-phase calculation unit 231 determines a positive-phase voltage command V+* representing a positive-phase component before superimposition of harmonic currents, out of the voltage command V* for the AC power output from the power conversion device 100A. The negative-phase compensation calculation unit 232, as in the first embodiment, determines a negative-phase voltage command V-* used for negative-phase compensation, out of the voltage command V* for the AC power output from the power conversion device 100A. The harmonic calculation unit 233 determines a harmonic voltage command Vm* representing a harmonic component, out of the voltage command V* for the AC power output from the power conversion device 100A.

[0053] Positive-phase calculation unit 231 calculates the deviations between the positive-phase d-axis current I+out_d and q-axis current I+out_q calculated in the same manner as in the first embodiment and the d-axis current command I*_d and q-axis current command I*_q input from current command generation unit 20 via current command constraint unit 21. Then, PI control calculations are performed on these deviations, and a feedforward calculation and a decoupling control calculation are performed using the d-axis voltage Vout_d and q-axis voltage Vout_q calculated by current command generation unit 20, thereby calculating positive-phase d-axis voltage commands V+*_d and q-axis voltage commands V+*_q which respectively represent the d-axis component and the q-axis component of the positive-phase voltage command V+* before the harmonic current is superimposed. Furthermore, the calculated positive-phase d-axis voltage command V+*_d and q-axis voltage command V+*_q are subjected to inverse αβ transformation based on the phase command θ* to determine the positive-phase α-axis voltage command V+*_α and β-axis voltage command V+*_β before the harmonic current is superimposed.

[0054] The negative phase compensation calculation section 232 calculates the negative phase α-axis voltage command V-*_α and the negative phase β-axis voltage command V-*_β by the same calculation as in the first embodiment.

[0055] The harmonic calculation unit 233 obtains the d-axis harmonic current Imout_d and the q-axis harmonic current Imout_q, which respectively represent the d-axis component and the q-axis component of the m-th harmonic contained in the measured current Iout, by performing dq transformation based on the harmonic current phase θgrid(m) on the α-axis component Iout_α and the β-axis component Iout_β of the measured current Iout input from the current sensor 5. The harmonic calculation unit 233 then calculates the deviations between the obtained d-axis harmonic current Imout_d and q-axis harmonic current Imout_q and the d-axis harmonic current command Im*_d and q-axis harmonic current command Im*_q input from the harmonic current command generation unit 19. Furthermore, by performing a PI control calculation and a decoupling control calculation on these deviations, a d-axis harmonic voltage command Vm*_d and a q-axis harmonic voltage command Vm*_q, which respectively represent the d-axis component and the q-axis component of the harmonic voltage command Vm*, are calculated. Then, by performing an inverse αβ transformation based on the harmonic current phase θgrid(m) on the calculated d-axis harmonic voltage command Vm*_d and q-axis harmonic voltage command Vm*_q, the α-axis harmonic voltage command Vm*_α and the β-axis harmonic voltage command Vm*_β are obtained.

[0056] In the current control unit 23 of this embodiment, the negative-phase α-axis voltage command V-*_α and the negative-phase β-axis voltage command V-*_β calculated by the negative-phase compensation calculation unit 232 are added to the positive-phase α-axis voltage command V+*_α and the positive-phase β-axis voltage command V+*_β before superimposing the harmonic currents calculated by the positive-phase calculation unit 231. In this way, the α-axis component and the β-axis component of the voltage command before superimposition of harmonics are calculated by adding negative-phase compensation to the AC power before superimposing the harmonic currents. Note that if negative-phase compensation is not required, the negative-phase compensation calculation unit 232 may be omitted from the current control unit 23. Furthermore, the α-axis component V*_α and β-axis component V*_β of the voltage command V* with high frequency superimposed thereon are calculated by calculating the sum of the α-axis component and β-axis component of the calculated voltage command before harmonics are superimposed and the α-axis harmonic voltage command Vm*_α and β-axis harmonic voltage command Vm*_β calculated by the harmonic calculation unit 233.

[0057] In the power conversion device 100A of the present embodiment, the inverter control device 10 performs the control as described above, so that the current control unit 23 generates the voltage command V* based on the current command I* and the harmonic current command Im*. As a result, similar to the first embodiment, when the inverter 3 is operated in accordance with the voltage command V*, harmonics synchronized with the phase of the power grid 2 are superimposed on the AC power output from the inverter 3. Therefore, the availability of the islanding operation detection function is improved when a plurality of power conversion devices 100A are connected in parallel for use.

[0058] According to the second embodiment of the present invention described above, in addition to the advantages (1) to (3) and (5) described in the first embodiment, the following advantages are further achieved.

[0059] (6) In the current control unit 23, the positive-phase calculation unit 231 and the negative-phase-sequence compensation calculation unit 232 calculate a pre-harmonic superimposition voltage command for the AC power before the harmonic current is superimposed based on the current command I*, and the harmonic calculation unit 233 calculates a harmonic voltage command Vm* for the harmonic current based on the harmonic current command Im*. Then, the voltage command V* is generated based on the sum of the calculated pre-harmonic superimposition voltage command and the harmonic voltage command Vm*. In this manner, the current control unit 23 can easily generate the voltage command V* based on the current command I* and the harmonic current command Im* without using the current command adder 22.

[0060] 5 is a diagram showing an example of the configuration of a power conversion device according to a third embodiment of the present invention. A power conversion device 100B of this embodiment differs from the power conversion device 100A described in the second embodiment in that the inverter control device 10 does not include a phase detector 17. The following describes the power conversion device 100B of this embodiment, focusing on the differences from the second embodiment.

[0061] In this embodiment, the voltage measurement value Vout by the voltage sensor 6, the active power P calculated by the power calculation unit 11, the first voltage command E* generated by the first voltage command generation unit 14, and the phase command θ* calculated by the phase command generation unit 16 are each input to the harmonic current command phase generation unit 18. Based on these values, the harmonic current command phase generation unit 18 determines the current phase of the harmonics to be superimposed on the AC power output by the power conversion device 100B, and outputs the value as the harmonic current phase θgrid(m).

[0062] When the impedance of the filter 4 is X and the phase difference between the voltage phase of the power grid 2 and the phase command θ* is δ, the active power P of the AC power output by the power conversion device 100B can be expressed by the following equation (1) using a measured voltage Vout, which is the measured voltage on the power grid 2 side of the filter 4, and a first voltage command E*, which is the voltage command on the inverter 3 side of the filter 4. P=(Vout·E* / X) sin δ (1)

[0063] In this embodiment, the harmonic current command phase generating unit 18 pre-stores the value of the impedance X of the filter 4. The harmonic current command phase generating unit 18 calculates the phase difference δ according to the above equation (1) using the value of this impedance X, the measured voltage value Vout, the active power P, and the first voltage command E* input from the voltage sensor 6, the power calculating unit 11, and the first voltage command generating unit 14, respectively. The voltage phase of the power grid 2 can then be determined by subtracting the calculated value of the phase difference δ from the phase command θ* input from the phase command generating unit 16. Based on the voltage phase of the power grid 2 thus determined, the current phase of the harmonics to be superimposed on the AC power output by the power conversion device 100B is determined, and the value is output as the harmonic current phase θgrid(m).

[0064] In the power conversion device 100B of this embodiment, the harmonic current phase θgrid(m) is determined in the harmonic current command phase generating unit 18 of the inverter control device 10 by the method described above. The harmonic current command generating unit 19 uses this harmonic current phase θgrid(m) to generate the harmonic current command Im* in the same manner as in the first and second embodiments. As a result, when the inverter 3 is operated in accordance with the voltage command V* generated by the current control unit 23, harmonics synchronized with the voltage phase of the power grid 2 are superimposed on the AC power output from the inverter 3. Therefore, the availability of the islanding operation detection function is improved when a plurality of power conversion devices 100B are connected in parallel and used.

[0065] In this embodiment, as in the second embodiment, the inverter control device 10 is not provided with the current command adder 22, and the current control unit 23 generates the voltage command V* based on the current command I* and the harmonic current command Im*, but the voltage command V* may be generated in the same manner as in the first embodiment. That is, the inverter control device 10 may be provided with the current command adder 22, which may add the harmonic current command Im* to the current command I* to obtain a harmonic added current command I+*, and the current control unit 23 may generate the voltage command V* based on the harmonic added current command I+* obtained by the current command adder 22. Even in this case, the harmonic current command phase generating unit 18 can determine the current phase of the harmonics to be superimposed on the AC power output by the power conversion device 100B based on the voltage phase of the power system 2 obtained by subtracting the value of the phase difference δ calculated by the above-mentioned equation (1) from the phase command θ* input from the phase command generating unit 16, and output the value as the harmonic current phase θgrid(m).

[0066] According to the third embodiment of the present invention described above, in addition to the advantages (1), (2), and (5) described in the first embodiment and the advantage (6) described in the second embodiment, the following further advantageous effects are achieved.

[0067] (7) The harmonic current command phase generator 18 determines the value δ of the phase used for the harmonic current command Im* by the above-mentioned equation (1), where P is the active power of the AC power output by the power conversion device 100B, X is the impedance of the filter 4 connected between the power conversion device 100B and the electric power grid 2, Vout is the measured voltage of the AC power, and E* is the first voltage command for the reactive component of the AC power before the harmonic current is superimposed. In this way, the harmonic current command phase generator 18 can determine the harmonic current phase θgrid(m) without using the phase detector 17.

[0068] 6 is a diagram showing an example of the configuration of a power conversion device according to a fourth embodiment of the present invention. A power conversion device 100C of this embodiment differs from the power conversion device 100 described in the first embodiment in that the inverter control device 10 does not include the phase detector 17 and the harmonic current command phase generator 18, but instead includes a time information acquisition unit 25. The power conversion device 100C of this embodiment will be described below, focusing on the differences from the first embodiment.

[0069] The time information acquisition unit 25 acquires standard time information, which is absolute time information, and outputs it to the harmonic current command generation unit 19. The time information acquisition unit 25 can acquire, as standard time information, time information included in positioning signals transmitted from GNSS (Global Navigation Satellite System) satellites, time information by NTP (Network Time Protocol), time information provided by the DC (Distributed Clocks) function of EtherCAT (registered trademark), etc. In addition to these, other information may be acquired as standard time information as long as it is absolute time information.

[0070] In this embodiment, the harmonic current command generating unit 19 determines the phase of the harmonic current command Im* based on the standard time information output from the time information acquiring unit 25. That is, since the standard time information output from the time information acquiring unit 25 is absolute time information as described above, the harmonic current command generating unit 19 determines the phase of the harmonic current command Im* based on this standard time information, thereby making it possible to determine the absolute phase of the harmonic current command Im* independent of the operating state of the power conversion device 100C. Then, the current control unit 23 generates a voltage command V* based on the current command I* and the harmonic current command Im*.

[0071] When a plurality of power conversion devices 100C according to the present embodiment are connected in parallel to the power grid 2 and the above-described control is performed in each power conversion device 100C, each power conversion device 100C outputs AC power on which harmonics are superimposed according to a commonly determined absolute phase. Therefore, as in the first embodiment, the harmonics of each power conversion device 100C can be synchronized without the need for signals or information exchange between the plurality of power conversion devices 100C. As a result, even if any one of the power conversion devices 100C cannot operate normally, the other power conversion devices 100C can continue to output AC power on which harmonics are superimposed that are synchronized with each other. Therefore, the availability of the islanding detection function is improved when a plurality of power conversion devices 100C are connected in parallel.

[0072] According to the fourth embodiment of the present invention described above, the harmonic current command generation unit 19 acquires absolute time information and determines the phase of the harmonic current command Im* based on this time information. Specifically, the power conversion device 100C of this embodiment includes a time information acquisition unit 25 that acquires standard time information. The harmonic current command generation unit 19 acquires the standard time information acquired by the time information acquisition unit 25 as absolute time information. As a result, as with the first embodiment, it is possible to improve the availability of the islanding detection function when multiple power conversion devices 100C are connected in parallel for use.

[0073] The present invention is not limited to the above-described embodiments and modifications, and can be implemented using any components within the scope of the present invention. Each embodiment and modification may be employed alone, or multiple embodiments and modifications may be employed in any combination. In other words, the present invention can achieve the above-described effects by combining the features of each embodiment in any combination.

[0074] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0075] DESCRIPTION OF SYMBOLS 1... DC power supply 2... Power system 3... Inverter 4... Filter 5... Current sensor 6... Voltage sensor 10... Inverter control device 11... Power calculation unit 12... Islanding operation detection unit 13... Reactive power command unit 14... First voltage command generation unit 15... Angular frequency command generation unit 16... Phase command generation unit 17... Phase detector 18... Harmonic current command phase generation unit 19... Harmonic current command generation unit 20... Current command generation unit 21... Current command constraint unit 22... Current command addition unit 23... Current control unit 24... Main circuit control unit 25... Time information acquisition unit 100, 100A, 100B, 100C... Power conversion device

Claims

1. A power conversion device connectable to an electric power system, converting DC power supplied from a DC power source into AC power having harmonics superimposed on the fundamental frequency of the power system and outputting the converted AC power to the power system, comprising: a first voltage command generation unit that generates a first voltage command based on a predetermined rated voltage; an angular frequency command generation unit that generates an angular frequency command for the AC power based on an active power command input from outside; a phase command generation unit that generates a phase command based on the angular frequency command; a current command generation unit that generates a current command for the AC power based on the phase command and the first voltage command; a harmonic current command generation unit that generates a harmonic current command for the harmonic; and a current control unit that generates a voltage command for the AC power based on the current command generated by the current command generation unit and the harmonic current command generated by the harmonic current command generation unit, wherein the harmonic current command generation unit obtains reference information or absolute time information synchronized with the power system, and determines the phase of the harmonic current command based on the reference information or the time information.

2. A power conversion device according to claim 1, further comprising a harmonic current command phase generation unit that determines a current phase to be used for the harmonic current command based on the phase of the power system, and the harmonic current command generation unit obtains the current phase determined by the harmonic current command phase generation unit as the reference information.

3. A power conversion device according to claim 2, further comprising a phase detector that detects the phase of the power grid from the voltage measurement value of the AC power, and wherein the harmonic current command phase generation unit determines the current phase based on the phase of the power grid detected by the phase detector.

4. A power conversion device according to claim 2, wherein the harmonic current command phase generation unit calculates a phase difference δ to be used for the harmonic current command by the following equation (1), where P is the active power of the AC power, X is the impedance of a filter circuit connected between the power conversion device and the power grid, Vout is the measured voltage of the AC power, and E* is a first voltage command that is an output voltage command of the power conversion device, and determines the current phase based on a value obtained by subtracting the phase difference δ from the phase command (obtained from an angular frequency command): P=(Vout·E* / X) sin δ (1) 5. A power conversion device according to claim 1, further comprising a time information acquisition unit that acquires standard time information, wherein the harmonic current command generation unit acquires the standard time information acquired by the time information acquisition unit as the time information.

6. A power conversion device according to any one of claims 1 to 5, comprising a current command adder that calculates a harmonic added current command by adding the harmonic current command to the current command, and the current control unit generates the voltage command based on the harmonic added current command calculated by the current command adder.

7. A power conversion device according to any one of claims 1 to 5, wherein the current control section calculates a pre-harmonic superimposition voltage command for the AC power before the harmonic current is superimposed based on the current command, calculates a harmonic voltage command for the harmonic current based on the harmonic current command, and generates the voltage command based on the sum of the pre-harmonic superimposition voltage command and the harmonic voltage command.

8. A power conversion device according to any one of claims 1 to 5, comprising an isolated operation detection unit that detects that the power conversion device is in an isolated operation state based on the measurement results of the AC voltage in the power system and the measurement results of the AC current output from the power conversion device to the power system.

9. A device connectable to an electric power system and controlling an inverter that converts DC power supplied from a DC power source into AC power in which harmonic currents are superimposed on the fundamental frequency of the electric power system and outputs the converted AC power to the electric power system, comprising: a first voltage command generation unit that generates a first voltage command based on a predetermined rated voltage; an angular frequency command generation unit that generates an angular frequency command for the AC power based on an active power command input from outside; a phase command generation unit that generates a phase command based on the angular frequency command; a current command generation unit that generates a current command for the AC power based on the phase command and the first voltage command; a harmonic current command generation unit that generates a harmonic current command for the harmonic current; and a current control unit that generates a voltage command for the AC power based on the current command generated by the current command generation unit and the harmonic current command generated by the harmonic current command generation unit, wherein the harmonic current command generation unit obtains reference information or absolute time information synchronized with the electric power system, and determines the phase of the harmonic current command based on the reference information or the time information.

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