Power conversion device

Abstract

To enable the setting of limit to an active power and a reactive power at different ratios.SOLUTION: A current command value correction part 44 includes a command value conversion part 441 that converts a d-axis current command value Iref_d and a q-axis current command value Iref_q having an internal phase θvsg into a first d-axis current command value Iref_d(1) and a first q-axis current command value Iref_q(1) having a system phase θg in consideration of a phase difference between the internal phase θvsg and the system phase θg, a current limiter 442 that limits at least one of the first d-axis current command value Iref_d(1) and the first q-axis current command value Iref_q(1), and a command value inverse converter 444 that inversely converts a third d-axis current command value Iref_d(3) and the third q-axis current command value Iref_q(3) having the system phase θg after the limit into the corrected d-axis current command value I'ref_d and the corrected q-axis current command value I'ref_q having the internal phase θvsg.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] There are power supply systems in which distributed power sources such as solar power generation systems, fuel cell power generation systems, wind power generation systems, and storage battery systems are connected to a grid via inverters. Many of these distributed power sources do not have inertial forces, which can reduce the inertial forces of the power supply system. Therefore, virtual synchronous generators, which simulate the inertial forces of a synchronous generator in an inverter (power conversion unit), have become widespread. A current-controlled virtual synchronous generator is one example of a virtual synchronous generator. A current-controlled virtual synchronous generator simulates a synchronous generator by controlling the current using a current command value. This prevents the current output from a power conversion device from becoming an overcurrent, thereby protecting the power conversion device.

[0003] Patent Document 1 discloses an inverter control system equipped with a dq absolute value limiting unit. The dq absolute value limiting unit limits the current command value (restricts the current command value). By limiting the current command value to a desired magnitude, it is possible to operate the system voltage stably. Specifically, in Patent Document 1, by limiting the current command value using the dq absolute value limiter, active power and reactive power are restricted at the same rate, thereby preventing the current output from the power conversion device from becoming an overcurrent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-141704 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, limits are applied to active power and reactive power at the same rate. However, there is a difference between them in that active power mainly affects the system frequency and reactive power mainly affects the system voltage. Therefore, there are cases where it is desired to apply limits to active power and reactive power at different rates, taking into consideration the state of the system, the purpose of system control, the remaining amount of energy stored on the DC side, the magnitude of the DC voltage, etc.

[0006] Therefore, a primary object of the present invention is to provide a power conversion device capable of imposing limits on active power and reactive power at different rates. [Means for solving the problem]

[0007] The power conversion device according to the present invention comprises: an inverter that converts DC power from a DC power supply into AC power and outputs the AC power to a grid via an output line; and an inverter control unit that controls the inverter so that virtual synchronous generator control is performed by a virtual synchronous generator that simulates a synchronous generator. The inverter control unit a dq transformation unit that derives d-axis current, d-axis voltage, q-axis current, and q-axis voltage on an internal phase synchronous dq coordinate system that rotates in synchronization with the internal phase of the virtual synchronous generator from an output voltage and an output current measured on an output line of the inverter, the d-axis current, d-axis voltage, q-axis current, and q-axis voltage having internal phases; an internal phase derivation unit that derives an internal frequency deviation of the virtual synchronous generator from the deviation between an active power derived from the d-axis current, the d-axis voltage, the q-axis current, and the q-axis voltage and an active power command value input from the outside to the inverter control unit, and that derives an internal phase from the internal frequency deviation and an external frequency command value input from the outside to the inverter control unit; an AVR unit that derives an internal voltage of the virtual synchronous generator from reactive power derived from the d-axis current, d-axis voltage, q-axis current and q-axis voltage, a reactive power command value input from the outside to the inverter control unit, an output voltage absolute value derived from the d-axis voltage and q-axis voltage, and an external voltage command value input from the outside to the inverter control unit, and performs automatic voltage control in the virtual synchronous generator; a current command value derivation unit that derives a d-axis current command value having an internal phase and a q-axis current command value having an internal phase from the internal voltage, the d-axis voltage, the q-axis voltage, and the internal impedance of the virtual synchronous generator; a current command value correcting unit that converts the d-axis current command value and the q-axis current command value into a first d-axis current command value and a first q-axis current command value, respectively, in consideration of a phase difference between an internal phase and a system phase of the system, and then derives a corrected d-axis current command value and a corrected q-axis current command value by using a value obtained by applying a limit to at least one of the first d-axis current command value and the first q-axis current command value; and a switching control unit that derives a switching control signal that controls the switching of the inverter so that currents corresponding to the corrected d-axis current command value and the corrected q-axis current command value are output to the output line of the inverter. The current command value correction unit is a command value converter that converts each of the d-axis current command value having an internal phase and the q-axis current command value having an internal phase into a first d-axis current command value having a grid phase and a first q-axis current command value having a grid phase, respectively; a current limiting unit that derives a second d-axis current command value having a grid phase by multiplying the first d-axis current command value by the d-axis current limiting value, and a second q-axis current command value having a grid phase by multiplying the first q-axis current command value by the q-axis current limiting value, using a d-axis current limiting value and a q-axis current limiting value that are input from outside to the inverter control unit to adjust active power and reactive power, respectively, and wherein the d-axis current limiting value and the q-axis current limiting value are different values ​​that are equal to or greater than 0; and a command value inverse converter that inversely converts each of the second d-axis current command value having the system phase and the second q-axis current command value having the system phase into a corrected d-axis current command value having an internal phase and a corrected q-axis current command value having the internal phase, respectively.

[0008] In the power conversion device according to the present invention, it is possible to apply limits to the active power and the reactive power at different rates. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a power conversion device capable of imposing limits on active power and reactive power at different rates.

[0010] The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a configuration diagram of a power conversion system according to an embodiment of the present invention. [Figure 2] 10 is an explanatory diagram showing current command values ​​in an αβ coordinate, an internal phase synchronization dq coordinate, and a system phase synchronization dq coordinate. FIG. [Figure 3] FIG. 2 is a configuration diagram of a measurement value calculation unit in FIG. 1. [Figure 4] FIG. 4 is a configuration diagram of a power calculation unit in FIG. 3. [Figure 5] FIG. 2 is a configuration diagram of a control signal derivation unit in FIG. [Figure 6] FIG. 6 is a configuration diagram of a current command value derivation unit in FIG. 5. [Figure 7] FIG. 6 is a configuration diagram of a current command value correction unit in FIG. 5. [Figure 8] FIG. 10 is a schematic diagram showing the ranges of active power and reactive power on the system phase-synchronized dq coordinates after the d-axis current command value and the q-axis current command value are multiplied by current absolute value limit values. [Figure 9] FIG. 10 is a configuration diagram of a control signal derivation unit that does not correct the d-axis current command value and the q-axis current command value in consideration of the phase difference between the internal phase and the system phase. [Figure 10] FIG. 10 is a configuration diagram of a current command value correction unit in FIG. 9. [Figure 11] 10 is a schematic diagram showing the range of active power and reactive power on the system phase-synchronized dq coordinate obtained by the control signal derivation unit of FIG. 9 and the range of active power and reactive power on the system phase-synchronized dq coordinate obtained by the control signal derivation unit of this embodiment. [Figure 12] FIG. 4 is a schematic diagram showing the range of active power and reactive power on the system phase-synchronized dq coordinate system obtained by the control signal derivation unit according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1. Power Conversion System (1) Overview of the power conversion system 1 is a configuration diagram of a power conversion system according to an embodiment of the present invention. Power conversion system 1 includes a DC power supply 2 and a power conversion device 3. Power conversion system 1 is connected to a system (a so-called commercial power system) 4, and controls the interchange of power between DC power supply 2 and system 4.

[0013] The DC power source 2 is a distributed power source such as a solar power generation device, a fuel cell power generation device, a wind power generation device, a storage battery device, a gas engine generator, etc. The power conversion device 3 is connected between the DC power source 2 and a grid 4.

[0014] The power conversion device 3 performs power conversion between DC power, which is the output or input of the DC power source 2, and AC power, which is the output or input of the grid 4. The power conversion device 3 is configured to enable grid-connected operation, in which the DC power source 2 and the grid 4 are interconnected and operated, and stand-alone operation, in which the DC power source 2 is operated independent of the grid 4. In grid-connected operation, the power conversion device 3 operates to supply power to a load in a state where power is shared between the DC power source 2 and the grid 4. In stand-alone operation, the DC power source 2 is disconnected from the grid 4, and the power conversion device 3 operates to supply power from the DC power source 2 to the load.

[0015] The power conversion device 3 according to this embodiment performs virtual synchronous generator control using a virtual synchronous generator that simulates the operation of a synchronous generator during grid-connected operation. In particular, the power conversion device 3 performs virtual synchronous generator control using a current-controlled virtual synchronous generator. Virtual synchronous generator control virtually simulates the inertia and other properties of a synchronous generator, thereby making it possible to improve the stability of the system frequency and system voltage of the system 4. The power in the power conversion system 1 and the system 4 includes active power and reactive power. In this embodiment, the current-controlled virtual synchronous generator imposes limits at different rates on the d-axis current command value and the q-axis current command value, respectively, thereby imposing limits at different rates on the active power and the reactive power. The power conversion device 3 ensures the stability of the system frequency and system voltage in the system 4 even in the above-mentioned case.

[0016] In current-controlled virtual synchronous generator control, the power conversion device 3 is controlled by the internal phase θvsg of the virtual synchronous generator (hereinafter simply referred to as the internal phase θvsg). Meanwhile, the system 4 has a system phase θg of the system 4 (hereinafter simply referred to as the system phase θg). The internal phase θvsg may deviate from the system phase θg. The deviation between the internal phase θvsg and the system phase θg can be explained, for example, as follows: The synchronous generator and the virtual synchronous generator operate to move along a power-phase difference angle curve. The power-phase difference angle curve is a sinusoidal curve that represents the relationship between the active power, reactive power, and phase difference angle when the internal voltage, output voltage, and internal impedance are given. The phase difference angle is the difference between the internal phase θvsg and the system phase θg. According to the power-phase difference angle curve, the phase difference angle generally becomes a non-zero value depending on the values ​​of the active power and reactive power. A non-zero phase difference angle indicates a deviation between the internal phase θvsg and the system phase θg. If the power conversion device 3 performs control so as to limit the active power and the reactive power at different rates while the internal phase θvsg and the system phase θg are misaligned in this way, it may not be possible to limit at least one of the active power and the reactive power in the system 4 to a desired magnitude. This point will be further explained below with reference to FIG. 2.

[0017] FIG. 2 is an explanatory diagram showing current command values ​​in αβ coordinates, internal phase-synchronized dq coordinates, and system phase-synchronized dq coordinates. In this embodiment, system 4 uses the a-phase current, b-phase current, c-phase current, a-phase voltage, b-phase voltage, and c-phase voltage of each of the three phases (a-phase, b-phase, and c-phase). The current and voltage of each of the three phases can be expressed in a three-phase coordinate system in which the a-axis, b-axis, and c-axis are shifted by 120°. The αβ coordinate system shown in FIG. 2 is obtained by converting these three-phase coordinate systems into coordinate systems in which the α-axis and β-axis are orthogonal to each other through a three-phase-to-two-phase transformation. In the αβ coordinate system, the direction of the vector of the current component (or voltage component) changes over time.

[0018] The dq coordinates are coordinates obtained by converting the αβ coordinates so that the direction of the vector of the current component (or voltage component) does not change over time by rotating the dq coordinates themselves with time. Here, the current and voltage in the virtual synchronous generator control have an internal phase θvsg. Figure 2 shows the dq coordinates (hereinafter referred to as the internal phase synchronized dq coordinates (d θvsg q θvsg The internal phase-synchronized dq coordinate is d θvsg axis and q θvsg In Figure 2, the coordinate system is a Cartesian coordinate system with axes d θvsg axis and q θvsg The intersection with the α-axis coincides with the intersection with the β-axis. The internal phase-synchronized dq coordinate is shifted by the internal phase θvsg from the αβ coordinate. In other words, the internal phase-synchronized dq coordinate is a coordinate where the reference phase θref (described later) is the internal phase θvsg (reference phase θref = internal phase θvsg). The internal phase θvsg changes over time, and the internal phase-synchronized dq coordinate rotates in synchronization with the internal phase θvsg.

[0019] On the other hand, the system current and system voltage of system 4 have a system phase θg. The system phase θg may be out of sync with the internal phase θvsg. Figure 2 shows a dq coordinate system (hereinafter referred to as a system phase synchronized dq coordinate system (d in Figure 2)) that rotates in synchronization with the system phase θg. θg q θg The system phase synchronization dq coordinate is dθg axis and q θg In Figure 2, the coordinate system is a Cartesian coordinate system with axes d θg axis and q θg The intersection point with the axis is d θvsg axis and q θvsg The points of intersection with the α-axis and the β-axis coincide with the points of intersection with the α-axis and the β-axis. The system phase synchronized dq coordinate is shifted by the system phase θg from the αβ coordinate. In other words, the system phase synchronized dq coordinate is a coordinate where the reference phase θref is the system phase θg (reference phase θref = system phase θg). The system phase θg changes over time, and the system phase synchronized dq coordinate rotates in synchronization with the system phase θg.

[0020] In Fig. 2, the vector of the current command value Iref is shown. In the internal phase synchronization dq coordinate, the d θvsg The axis component is Iref_d with internal phase θvsg θvsg and the q of the current command value Iref θvsg The axis component is Iref_q with internal phase θvsg θvsg On the other hand, in the grid phase synchronization dq coordinate, the d θg The axis component is Iref_d with system phase θg θg and the q of the current command value Iref θg The axis component is Iref_q with system phase θg θg Therefore, when the system phase θg and the internal phase θvsg are out of sync, Iref_d θvsg and Iref_d θg is a different value from Iref_q θvsg and Iref_q θg is a different value.

[0021] Typically, the power conversion device 3 has an internal phase θvsg. θvsg and Iref_q θvsg The desired limit is applied to each of them using the d-axis current limit value and the q-axis current limit value. As a result, the current command value after limiting is I'ref_d with the internal phase θvsg. θvsg and I'ref_q θvsgIn this embodiment, the d-axis current limit value and the q-axis current limit value are limit values ​​with different ratios, and for example, the d-axis current limit value may be 1.0 and the q-axis current limit value may be 0.5. Then, the power conversion device 3 calculates I'ref_d θvsg and I'ref_q θvsg However, the active power and reactive power based on I'ref_d θvsg and I'ref_q θvsg The active power and reactive power based on Iref_d may not be limited to the desired magnitude based on the desired limit in the grid 4. This is thought to be due to the fact that the internal phase θvsg and the grid phase θg are misaligned due to the relationship between the power and phase difference angle curve of the synchronous generator as described above. In other words, when Iref_d has an internal phase θvsg that is misaligned from the grid phase θg, θvsg and Iref_q θvsg This is thought to be because the active power and reactive power are derived by applying a limit to the system phase θg, and therefore the active power and reactive power are not limited to match the system phase θg.

[0022] Therefore, before imposing limits on the d-axis current command value and the q-axis current command value, the power conversion device 3 according to this embodiment converts the phases of the d-axis current command value and the q-axis current command value from the internal phase θvsg to the grid phase θg. That is, the d-axis current command value having the internal phase θvsg and the q-axis current command value having the internal phase θvsg are converted into a first d-axis current command value having the grid phase θg and a first q-axis current command value having the grid phase θg, respectively.

[0023] Then, a second d-axis current command value having the grid phase θg and a second q-axis current command value having the grid phase θg are derived by multiplying the first d-axis current command value having the grid phase θg and the first q-axis current command value having the grid phase θg by a d-axis current limit value and a q-axis current limit value, respectively. In this embodiment, the d-axis current limit value and the q-axis current limit value are different from each other. Then, the second d-axis current command value having the grid phase θg and the second q-axis current command value having the grid phase θg are inversely converted into a corrected d-axis current command value having the internal phase θvsg and a corrected q-axis current command value having the internal phase θvsg, respectively. In this way, the d-axis current command value and the q-axis current command value are converted into a first d-axis current command value and a first q-axis current command value having the grid phase θg, not a value having the internal phase θvsg, and then different limits are applied to the converted values. Then, by supplying the active power and reactive power based on the corrected d-axis current command value and the corrected q-axis current command value to the grid 4, it is possible to limit the active power and reactive power to desired levels in the grid 4 even when the internal phase θvsg and the grid phase θg are misaligned.

[0024] (2) Specific configuration of the power conversion system An example of a specific configuration of the power conversion system 1 according to this embodiment will be described below. Fig. 3 is a configuration diagram of the measurement value calculation unit in Fig. 1. Fig. 4 is a configuration diagram of the power calculation unit in Fig. 3. Fig. 5 is a configuration diagram of the control signal derivation unit in Fig. 1. Fig. 6 is a configuration diagram of the current command value derivation unit in Fig. 5. Fig. 7 is a configuration diagram of the current command value correction unit in Fig. 5.

[0025] The power conversion system 1 is connected to a grid 4 and includes a DC power supply 2 and a power conversion device 3. The power conversion device 3 performs virtual synchronous generator control using a virtual synchronous generator. The power conversion device 3 includes a grid interconnection unit 10 and an inverter control unit 20. Each unit will be described below.

[0026] (2-1) Grid Interconnection Section The grid interconnection unit 10 is connected between the DC power source 2 and the grid 4, and adjusts power interchangeably between the DC power source 2 and the grid 4. The grid interconnection unit 10 includes an inverter (power conversion unit) 11 and an output line 12 extending from the output of the inverter 11 and connected to the grid 4.

[0027] The inverter 11 converts DC power from the DC power source 2 into AC power and outputs the AC power to the system 4 via an output line 12. The inverter 11 includes six transistors, first to sixth, T1 to T6, each having, for example, a diode. The first transistor T1 and the second transistor T2 are connected in series by connecting the source of the first transistor T1 to the drain of the second transistor T2. The drain of the first transistor T1 is connected to one side of the DC power source 2, and the source of the second transistor T2 is connected to the other side of the DC power source 2. Similarly, the third transistor T3 and the fourth transistor T4 are connected in series, and the drain of the third transistor T3 is connected to one side of the DC power source 2, and the source of the fourth transistor T4 is connected to the other side of the DC power source 2. Similarly, the fifth transistor T5 and the sixth transistor T6 are connected in series, and the drain of the fifth transistor T5 is connected to one side of the DC power source 2, and the source of the sixth transistor T6 is connected to the other side of the DC power source 2.

[0028] Switching control signals g1 to g6 (described later) are input to gates G1 to G6 of the first to sixth transistors T1 to T6, respectively. The first to sixth transistors T1 to T6 are turned ON and OFF by the switching control signals g1 to g6, respectively, causing the inverter 11 to convert DC power from the DC power supply 2 into AC power. The output line 12 includes a first output line 12a connected to a connection portion between the first transistor T1 and the second transistor T2, a second output line 12b connected to a connection portion between the third transistor T3 and the fourth transistor T4, and a third output line 12c connected to a connection portion between the fifth transistor T5 and the sixth transistor T6. The first to third output lines 12a to 12c are supplied with three-phase AC power output from the inverter 11.

[0029] The grid interconnection unit 10 includes a filter inductor 13, a filter capacitor 14, an inverter current sensor 15, an output current sensor 16, and an output voltage sensor 17. In this embodiment, the filter inductor 13, the inverter current sensor 15, the filter capacitor 14, the output current sensor 16, and the output voltage sensor 17 are provided on the output line 12 in this order from the inverter 11 side toward the grid 4 side.

[0030] The filter inductor 13 includes first to third filter inductors 13a to 13c. The first to third filter inductors 13a to 13c are connected to the first to third output lines 12a to 12c, respectively. The first to third filter inductors 13a to 13c are configured to filter noise in the AC power on the first to third output lines 12a to 12c, respectively, and function as, for example, a low-pass filter.

[0031] The filter capacitor 14 includes first to third filter capacitors 14a to 14c. The first to third filter capacitors 14a to 14c are connected to the first to third output lines 12a to 12c, respectively. The first to third filter capacitors 14a to 14c are configured to filter noise from the AC power by charging the AC power of the first to third output lines 12a to 12c, respectively.

[0032] Inverter current sensor 15 includes first to third inverter current sensors 15a to 15c. First to third inverter current sensors 15a to 15c are connected to first to third output lines 12a to 12c, respectively, on the side closer to inverter 11 than to power grid 4. In this embodiment, first to third inverter current sensors 15a to 15c are connected to the filter inductor 13 side between filter inductor 13 and power grid 4. First to third inverter current sensors 15a to 15c measure inverter output currents Iinv_a, Iinv_b, and Iinv_c, respectively, which are measurement values ​​of the inverter currents of the three phases (a phase, b phase, and c phase) output from inverter 11.

[0033] The output current sensor 16 includes first to third output current sensors 16a to 16c. In this embodiment, the first to third output current sensors 16a to 16c are connected to the first to third output lines 12a to 12c, respectively, between the filter capacitor 14 and the power system 4. The first to third output current sensors 16a to 16c measure output currents Iga, Igb, and Igc, which are measurement values ​​of the output currents of the three phases (a-phase, b-phase, and c-phase) output from the inverter 11, respectively.

[0034] The output voltage sensor 17 includes first to third output voltage sensors 17a to 17c. In this embodiment, the first to third output voltage sensors 17a to 17c are connected to the first to third output lines 12a to 12c, respectively, between the filter capacitor 14 and the system 4. The first to third output voltage sensors 17a to 17c measure output voltages Vga, Vgb, and Vgc, respectively, which are measurement values ​​of the output voltages of the three phases (a-phase, b-phase, and c-phase) output from the inverter 11.

[0035] The output voltages Vga, Vgb, Vgc, the output currents Iga, Igb, Igc, and the inverter output currents Iinv_a, Iinv_b, Iinv_c are input to the inverter control unit 20.

[0036] (2-2) Inverter control unit The inverter control unit 20 controls the inverter 11 so that virtual synchronous generator control is performed by a virtual synchronous generator that simulates a synchronous generator. The inverter control unit 20 includes a measurement value calculation unit 30 and a control signal derivation unit 40.

[0037] (a) Measurement value calculation section The measurement value calculation unit 30 is configured as shown in Fig. 3 and derives various voltages, power, and the like required by the control signal derivation unit 40 based on the output voltages Vga, Vgb, and Vgc, output currents Iga, Igb, and Igc, and inverter output currents Iinv_a, Iinv_b, and Iinv_c from the grid interconnection unit 10. The measurement value calculation unit 30 includes a dq conversion unit 31, a gain unit 32, a power calculation unit 33, and a power absolute value calculation unit 34. The dq conversion unit 31 includes a voltage dq conversion unit 311, a current dq conversion unit 312, and an inverter current dq conversion unit 313. The gain unit 32 includes a first gain unit 321, a second gain unit 322, and a third gain unit 323.

[0038] The voltage dq converter 311 performs dq conversion on the output voltages Vga, Vgb, and Vgc multiplied by a first gain K1 by the first gain unit 321 using the internal phase θvsg. As a result, the voltage dq converter 311 derives a d-axis voltage Vgd, which is the d-axis component of the output voltages Vga, Vgb, and Vgc on the internal phase-synchronized dq coordinate, and a q-axis voltage Vgq, which is the q-axis component. As described above, the internal phase-synchronized dq coordinate rotates in synchronization with the internal phase θvsg. The d-axis voltage Vgd and the q-axis voltage Vgq have the internal phase θvsg.

[0039] The voltage dq conversion unit 311 derives the d-axis voltage Vgd and the q-axis voltage Vgq, for example, as expressed by the following equation (6).

[0040]

number

[0041] Here, the constant k is an arbitrary positive real number, and θ is a real constant. Moreover, θref in the equation (6) is the reference phase θref.

[0042] In this embodiment, the d-axis voltage Vgd and the q-axis voltage Vgq on the internal phase-synchronized dq coordinate are derived using the following equation (7) with k=1, θ0=0 rad, and the reference phase θref=the internal phase θvsg in equation (6).

[0043]

number

[0044] The current dq converter 312 performs dq conversion on the output currents Iga, Igb, and Igc multiplied by a second gain K2 using the internal phase θvsg in the second gain unit 322. As a result, the current dq converter 312 derives a d-axis current Igd, which is the d-axis component of the output currents Iga, Igb, and Igc on the internal phase-synchronized dq coordinate, and a q-axis current Igq, which is the q-axis component. The d-axis current Igd and the q-axis current Igq have the internal phase θvsg.

[0045] The current dq conversion unit 312 derives the d-axis current Igd and the q-axis current Igq, for example, as expressed by the following equation (8).

[0046]

number

[0047] Here, as in equation (6), the constant k is an arbitrary positive real number, and θ0 is a real constant. Similarly to equation (6), θref in equation (8) is the reference phase θref.

[0048] In this embodiment, the d-axis current Igd and the q-axis current Igq on the internal phase-synchronized dq coordinates are derived using the following equation (9) with k=1, θ0=0 rad, and the reference phase θref=internal phase θvsg in equation (8).

[0049]

number

[0050] The inverter current dq converter 313 performs dq conversion using the internal phase θvsg on the inverter output currents Iinv_a, Iinv_b, and Iinv_c multiplied by a third gain K3 by the third gain unit 323. As a result, the inverter current dq converter 313 derives a d-axis inverter current Iinv_d, which is the d-axis component of the inverter output currents Iinv_a, Iinv_b, and Iinv_c on the internal phase-synchronized dq coordinate, and a q-axis inverter current Iinv_q, which is the q-axis component. The d-axis inverter current Iinv_d and the q-axis inverter current Iinv_q have the internal phase θvsg.

[0051] The d-axis inverter current Iinv_d and the q-axis inverter current Iinv_q are derived by the inverter current dq conversion unit 313, for example, as expressed by the following equation (10).

[0052]

number

[0053] Here, as in equation (6), the constant k is an arbitrary positive real number, and θ0 is a real constant. Similarly to equation (6), θref in equation (10) is the reference phase θref.

[0054] In this embodiment, the d-axis inverter current Iinv_d and the q-axis inverter current Iinv_q on the internal phase synchronized dq coordinates are derived using the following equation (11) with k = 1, θ0 = 0 rad, and reference phase θref = internal phase θvsg in equation (10).

[0055]

number

[0056] The power calculation unit 33 derives active power Pdet and reactive power Qdet from the d-axis current Igd, d-axis voltage Vgd, q-axis current Igq, and q-axis voltage Vgq, for example, using the configuration shown in Fig. 4. In the configuration of Fig. 4, the power calculation unit 33 includes multipliers 331a to 331d and adder-subtractors 332a and 332b. The active power Pdet and reactive power Qdet are derived, for example, using the following equations (12-1) and (12-2). The active power Pdet and reactive power Qdet have an internal phase θvsg.

[0057] Pdet=Vgd·Igd+Vgq·Igq (12-1) Qdet=Vgd·Igq-Vgq·Igd (12-2)

[0058] The power absolute value calculation unit 34 can derive the output voltage absolute value Vg_det from the d-axis voltage Vgd and the q-axis voltage Vgq, for example, by the following equation (13): The output voltage absolute value Vg_det has an internal phase θvsg.

[0059]

number

[0060] The d-axis voltage Vgd, the q-axis voltage Vgq, the active power Pdet, the reactive power Qdet, the d-axis inverter current Iinv_d, the q-axis inverter current Iinv_q, and the output voltage absolute value Vg_det are input to a control signal derivation unit 40.

[0061] (b) Control signal derivation section The control signal derivation unit 40 derives switching control signals g1 to g6 that control the inverter 11. The control signal derivation unit 40 is configured as shown in FIG. 5. The control signal derivation unit 40 receives inputs of a d-axis voltage Vgd, a q-axis voltage Vgq, an active power Pdet, a reactive power Qdet, a d-axis inverter current Iinv_d, a q-axis inverter current Iinv_q, and an output voltage absolute value Vg_det from the measurement value calculation unit 30. The control signal derivation unit 40 also receives inputs of an active power command value Pref, a reactive power command value Qref, an external frequency command value Fref, and an external voltage command value Vref from the outside. The control signal derivation unit 40 also receives inputs of a d-axis current limit value Id_lim, a q-axis current limit value Iq_lim, and a current absolute value limit value Iabs_lim from the outside. The outside refers to an external device, such as a microgrid control device. The microgrid control device is a device that controls a system called a microgrid that supplies power to loads in a specific area using a DC power source 2.

[0062] The control signal derivation unit 40 includes an internal phase derivation unit 41 , an AVR unit 42 , a current command value derivation unit 43 , a current command value correction unit 44 , and a switching control unit 45 .

[0063] (b1) Internal phase derivation section The internal phase derivation unit 41 derives the internal phase θvsg. Specifically, the internal phase derivation unit 41 derives the internal frequency deviation ΔFvsg of the virtual synchronous generator from the deviation between the active power Pdet and an active power command value Pref input from the outside to the internal phase derivation unit 41 (an example of the inverter control unit 20). Furthermore, the internal phase derivation unit 41 derives the internal phase θvsg from the internal frequency deviation ΔFvsg and an external frequency command value Fref input from the outside to the internal phase derivation unit 41 (an example of the inverter control unit 20).

[0064] The internal phase derivation unit 41 includes a simulation calculation unit 411, an angular frequency integrator 412, an adder-subtractor 413a, and an adder-subtractor 413b. The simulation calculation unit 411 includes a unit inertia constant unit 411a, an integrator 411b, a braking control unit 411c, and an adder-subtractor 411d.

[0065] The adder-subtractor 413a derives the deviation between the active power Pdet and the active power command value Pref.

[0066] The simulation calculation unit 411 (part of the internal phase derivation unit 41) performs a predetermined calculation process using the deviation between the active power Pdet and the active power command value Pref and the oscillation equation to derive the internal frequency deviation ΔFvsg.

[0067] The derivation of the internal frequency deviation ΔFvsg will be further explained. First, the adder-subtractor 411d subtracts the product of the internal frequency deviation ΔFvsg multiplied by a unit damping coefficient D from the deviation between the active power Pdet and the active power command value Pref. The unit damping coefficient D is a coefficient that determines the FP droop characteristics of the active power Pdet and the internal frequency deviation ΔFvsg. The product of the internal frequency deviation ΔFvsg multiplied by the unit damping coefficient D is set by the damping control unit 411c based on the internal frequency deviation ΔFvsg. The unit inertia constant unit 411a subtracts the product of the internal frequency deviation ΔFvsg multiplied by the unit damping coefficient D from the deviation between the active power Pdet and the active power command value Pref, and multiplies the result by 1 / 2H. H is the unit inertia constant that simulates the inertia of the virtual synchronous generator. The integrator 411b integrates the multiplication result. In this way, the internal frequency deviation ΔFvsg is derived.

[0068] Next, the adder / subtractor 413b (part of the internal phase derivation unit 41) derives the internal frequency Fvsg (unit: pu) of the virtual synchronous generator by adding the external frequency command value Fref (unit: pu) to the internal frequency deviation ΔFvsg (unit: pu). Furthermore, the angular frequency integrator 412 (part of the internal phase derivation unit 41) derives the internal phase θvsg (unit: rad) by integrating the angular frequency 2πFvsgFn (unit: rad / s) obtained by multiplying the internal frequency Fvsg (unit: pu) of the virtual synchronous generator by 2πFn (unit: rad / s). Fn is the rated frequency (unit: Hz).

[0069] The internal phase θvsg derived by the internal phase derivation unit 41 is used when deriving the d-axis voltage Vgd and the q-axis voltage Vgq in the voltage dq conversion unit 311, when deriving the d-axis current Igd and the q-axis current Igq in the current dq conversion unit 312, and when deriving the d-axis inverter current Iinv_d and the q-axis inverter current Iinv_q in the inverter current dq conversion unit 313. The internal phase θvsg is also used when deriving the switching control signals g1 to g6 in the switching control unit 45.

[0070] (b2) AVR section The AVR unit 42 performs automatic voltage control in the virtual synchronous generator. The AVR unit 42 derives an internal voltage Eref of the virtual synchronous generator from the reactive power Qdet, a reactive power command value Qref input from the outside to the AVR unit 42 (an example of the inverter control unit 20), the output voltage absolute value Vg_det, and an external voltage command value Vref input from the outside to the AVR unit 42 (an example of the inverter control unit 20).

[0071] AVR unit 42 includes a droop / first-order lag calculation unit 421, an internal voltage calculation unit 422, an adder / subtractor 423a, and an adder / subtractor 423b.

[0072] To further explain the AVR unit 42, the adder / subtractor 423a (part of the AVR unit 42) derives the deviation between the reactive power Qdet and the reactive power command value Qref. The droop / first-order lag calculation unit 421 (part of the AVR unit 42) performs a predetermined calculation on the deviation between the reactive power Qdet and the reactive power command value Qref based on the AVR's VQ droop characteristic (an example of an AVR droop characteristic) and adds a first-order lag element to the calculation result. The VQ droop characteristic is a negative proportional characteristic between reactive power and output voltage that enables the virtual synchronous generator to control reactive power during grid-connected operation and output voltage during stand-alone operation. Specifically, the VQ droop characteristic controls the output reactive power to decrease when the output voltage of the virtual synchronous generator increases, and controls the output reactive power to increase when the output voltage of the virtual synchronous generator decreases. The first-order lag element is added to prevent the response from becoming too sensitive to the deviation between the reactive power Qdet and the reactive power command value Qref.

[0073] The adder-subtractor 423b (part of the AVR unit 42) subtracts the output voltage absolute value Vg_det from the sum of the result to which the first-order lag element has been added and the external voltage command value Vref. The internal voltage calculation unit 422 (part of the AVR unit 42) derives the internal voltage Eref by performing feedback control processing on the output of the adder-subtractor 423b. Examples of the feedback control processing include PI control. For example, the feedback control by the internal voltage calculation unit 422 is to apply the output of the adder-subtractor 423b to a transfer function K A This is done by calculating the proportional and integral gain using (s)=Kp+Ki / s, where Kp is the proportional gain and Ki is the integral gain.

[0074] (b3) Current command value derivation part The current command value derivation unit 43 derives current command values ​​Iref_d and Iref_q. As shown in FIG. 5 , the current command value derivation unit 43 receives an input of the internal voltage Eref from the AVR unit 42. The current command value derivation unit 43 also receives an input of the d-axis voltage Vgd and the q-axis voltage Vgq from the measurement value calculation unit 30. The current command value derivation unit 43 also has an internal impedance z of the virtual synchronous generator to simulate the impedance of the synchronous generator. The current command value derivation unit 43 derives a d-axis current command value Iref_d and a q-axis current command value Iref_q from the internal voltage Eref, the d-axis voltage Vgd, the q-axis voltage Vgq, and the internal impedance z of the virtual synchronous generator. The d-axis current command value Iref_d and the q-axis current command value Iref_q each have an internal phase θvsg.

[0075] Specifically, the current command value derivation unit 43 derives the d-axis current command value Iref_d and the q-axis current command value Iref_q using the configuration shown in Fig. 6. Here, in the configuration shown in Fig. 6, the d-axis current command value Iref_d and the q-axis current command value Iref_q can be derived, for example, using the following equation (14).

[0076]

number

[0077] Here, r is the winding resistance of the virtual armature of the virtual synchronous generator, and x is the winding reactance of the virtual armature of the virtual synchronous generator. The internal impedance z of the virtual synchronous generator is virtually simulated based on the winding resistance r and the winding reactance x.

[0078] (b4) Current command value correction section The current command value corrector 44 converts the d-axis current command value Iref_d and the q-axis current command value Iref_q into a first d-axis current command value Iref_d(1) and a first q-axis current command value Iref_q(1), respectively, taking into account the phase difference between the internal phase θvsg and the grid phase θg. Thereafter, the current command value corrector 44 derives a corrected d-axis current command value I'ref_d and a corrected q-axis current command value I'ref_q by using a value obtained by applying a limit to at least one of the first d-axis current command value Iref_d(1) and the first q-axis current command value Iref_q(1). The current command value corrector 44 will be described in detail below.

[0079] As shown in FIG. 7, the current command value corrector 44 includes a command value converter 441, a current limiter 442, an absolute value limiter 443, and a command value inverse converter 444.

[0080] (i) The command value converter 441 converts the d-axis current command value Iref_d having the internal phase θvsg and the q-axis current command value Iref_q having the internal phase θvsg into a first d-axis current command value Iref_d(1) having the system phase θg and a first q-axis current command value Iref_q(1) having the system phase θg, respectively.

[0081] Here, the conversion performed by the command value conversion unit 441 is not limited to this, but examples thereof include: first, coordinate conversion of coordinate points of the d-axis current command value and the q-axis current command value on the internal phase-synchronized dq coordinate; second, rotational conversion of the internal phase-synchronized dq coordinate; and third, conversion using a mathematical formula.

[0082] In the first conversion, the command value converter 441 converts the coordinate points of the d-axis current command value Iref_d and the q-axis current command value Iref_q on the internal phase-synchronized dq coordinate into the coordinate points of the first d-axis current command value Iref_d(1) and the first q-axis current command value Iref_q(1) on the system phase-synchronized dq coordinate. That is, the command value converter 441 converts the coordinate point of the d-axis current command value Iref_d having the internal phase θvsg on the internal phase-synchronized dq coordinate into the coordinate point of the first d-axis current command value Iref_d(1) having the system phase θg on the system phase-synchronized dq coordinate. The command value converter 441 also converts the coordinate point of the q-axis current command value Iref_q having the internal phase θvsg on the internal phase-synchronized dq coordinate into the coordinate point of the first q-axis current command value Iref_q(1) having the system phase θg on the system phase-synchronized dq coordinate.

[0083] In the second conversion, the command value converter 441 converts the internal phase synchronized dq coordinates into system phase synchronized dq coordinates that rotate in synchronization with the system phase θg by performing rotational conversion from the internal phase θvsg to the system phase θg. As a result, the command value converter 441 converts the d-axis current command value Iref_d having the internal phase θvsg and the q-axis current command value Iref_q having the internal phase θvsg into a first d-axis current command value Iref_d(1) having the system phase θg and a first q-axis current command value Iref_q(1) having the system phase θg, respectively.

[0084] Explaining this with reference to FIG. 2, in the case of the second conversion, the command value conversion unit 441 converts d θvsg axis and q θvsg Intersection of the axes (or d θg axis and q θg The internal phase synchronization dq coordinates are rotated around the intersection of the axes (δ = θvsg - θg) so that they coincide with the system phase synchronization dq coordinates. In the case of Figure 2, δ = φvsg. In the case of Figure 11, which will be described later, this rotation causes the d θvsg Iref_d is the axis component θvsg(corresponding to the d-axis current command value Iref_d with the internal phase θvsg mentioned above) is the d θg Iref_d is the axis component θg (corresponding to the first d-axis current command value Iref_d(1) having the system phase θg described above). Similarly, the q θvsg Axis component Iref_q θvsg (corresponding to the q-axis current command value Iref_q with the internal phase θvsg mentioned above) is the q θg Axis component Iref_q θg (corresponding to the first q-axis current command value Iref_q(1) having the grid phase θg described above).

[0085] In the case of the third conversion, the command value conversion unit 441 derives the first d-axis current command value Iref_d(1) having the system phase θg and the first q-axis current command value Iref_q(1) having the system phase θg by the following equation (1).

[0086]

number

[0087] (ii) The current limiting unit 442 limits the first d-axis current command value Iref_d(1) and the first q-axis current command value Iref_q(1) to adjust the active power Pdet and the reactive power Qdet, respectively. Specifically, the current limiting unit 442 derives a second d-axis current command value Iref_d(2) having the grid phase θg and a second q-axis current command value Iref_q(2) having the grid phase θg using the d-axis current limit value Id_lim and the q-axis current limit value Iq_lim input from the outside to the current limiting unit 442 (a part of the inverter control unit 20) and the first d-axis current command value Iref_d(1) and the first q-axis current command value Iref_q(1). The second d-axis current command value Iref_d(2) having the grid phase θg is obtained by multiplying the first d-axis current command value Iref_d(1) by the d-axis current limit value Id_lim. The second q-axis current command value Iref_q(2) having the grid phase θg is obtained by multiplying the first q-axis current command value Iref_q(1) by the q-axis current limit value Iq_lim. The d-axis current limit value Id_lim and the q-axis current limit value Iq_lim are each a value equal to or greater than 0, and are different from the d-axis current limit value Id_lim and the q-axis current limit value Iq_lim.

[0088] The current limiter 442 derives a second d-axis current command value Iref_d(2) having the system phase θg and a second q-axis current command value Iref_q(2) having the system phase θg using the following equation (2).

[0089]

number

[0090] (iii) The absolute value limiter 443 limits the second d-axis current command value Iref_d(2) and the second q-axis current command value Iref_q(2) to commonly adjust the active power Pdet and the reactive power Qdet. Specifically, the absolute value limiter 443 derives a third d-axis current command value Iref_d(3) having the grid phase θg and a third q-axis current command value Iref_q(3) having the grid phase θg using a current absolute value limit value Iabs_lim input from the outside to the absolute value limiter 443 (part of the inverter control unit 20), the second d-axis current command value Iref_d(2), and the second q-axis current command value Iref_q(2). The third d-axis current command value Iref_d(3) having the grid phase θg is obtained by multiplying the second d-axis current command value Iref_d(2) by the current absolute value limit value Iabs_lim. The third q-axis current command value Iref_q(3) having the grid phase θg is obtained by multiplying the second q-axis current command value Iref_q(2) by the current absolute value limit value Iabs_lim, which is a value equal to or greater than 0.

[0091] The absolute value limiter 443 derives the third d-axis current command value Iref_d(3) having the system phase θg and the third q-axis current command value Iref_q(3) having the system phase θg using the following equation (4).

[0092]

number

[0093] (iv) The command value inverse converter 444 inversely converts the third d-axis current command value Iref_d(3) having the system phase θg and the third q-axis current command value Iref_q(3) having the system phase θg into a corrected d-axis current command value I'ref_d having the internal phase θvsg and a corrected q-axis current command value I'ref_q having the internal phase θvsg, respectively.

[0094] Here, the inverse transformation performed by the command value inverse transformation unit 444 is not limited to the above, but examples thereof include first, coordinate inverse transformation of the coordinate points of the third d-axis current command value Iref_d(3) and the third q-axis current command value Iref_q(3) on the system phase-synchronized dq coordinate system; second, inverse rotational transformation of the system phase-synchronized dq coordinate system; and third, inverse transformation using a mathematical formula. The command value inverse transformation unit 444 performs an inverse transformation corresponding to the transformation performed by the command value transformation unit 441. For example, if the command value transformation unit 441 performs coordinate transformation of the coordinate points, the command value inverse transformation unit 444 performs coordinate inverse transformation of the coordinate points. Furthermore, for example, if the command value transformation unit 441 performs rotational transformation of the internal phase-synchronized dq coordinate system, the command value inverse transformation unit 444 performs inverse rotational transformation of the system phase-synchronized dq coordinate system. Furthermore, for example, if the command value transformation unit 441 performs transformation using a mathematical formula, the command value inverse transformation unit 444 performs inverse transformation using a mathematical formula.

[0095] In the first inverse transformation, the command value inverse transformation unit 444 inversely transforms the coordinate points of the third d-axis current command value Iref_d(3) and the third q-axis current command value Iref_q(3) on the system phase synchronized dq coordinate system into the coordinate points of the corrected d-axis current command value I'ref_d and the corrected q-axis current command value I'ref_q on the internal phase synchronized dq coordinate system. Specifically, the command value inverse transformation unit 444 inversely transforms the coordinate point of the third d-axis current command value Iref_d(3) having the system phase θg on the system phase synchronized dq coordinate system into the coordinate point of the corrected d-axis current command value I'ref_d having the internal phase θvsg on the internal phase synchronized dq coordinate system. In addition, the command value inverse conversion unit 444 performs an inverse coordinate conversion on the coordinate point of the third q-axis current command value Iref_q(3) having the system phase θg on the system phase synchronized dq coordinate, into the coordinate point of the corrected q-axis current command value I'ref_q having the internal phase θvsg on the internal phase synchronized dq coordinate.

[0096] In the case of the second inverse transformation, the command value inverse converter 444 inversely transforms the system phase-synchronized dq coordinates after the rotational transformation in the command value converter 441 into internal phase-synchronized dq coordinates by performing an inverse rotational transformation from the system phase θg to the internal phase θvsg. As a result, the command value inverse converter 444 inversely transforms the third d-axis current command value Iref_d(3) having the system phase θg and the third q-axis current command value Iref_q(3) having the system phase θg into a corrected d-axis current command value I'ref_d having the internal phase θvsg and a corrected q-axis current command value I'ref_q having the internal phase θvsg, respectively.

[0097] Explaining this with reference to FIG. 2, in the case of the second inverse conversion, the command value inverse conversion unit 444 converts d θvsg axis and q θvsg Intersection of the axes (or d θg axis and q θg The system phase synchronization dq coordinates are rotated in the reverse direction around the intersection of the axes (δ = θvsg - θg) so that they coincide with the internal phase synchronization dq coordinates. In the case of Figure 2, δ = φvsg. In the case of Figure 11, which will be described later, this reverse rotation causes the d θg Iref_d is the axis component θg (corresponding to the third d-axis current command value Iref_d(3) having the grid phase θg mentioned above) is the d θvsg Iref_d is the axis component θvsg (corresponding to the d-axis current command value I'ref_d after the correction described above). Similarly, the q θg Axis component Iref_q θg (corresponding to the third q-axis current command value Iref_q(3) having the grid phase θg mentioned above) is the q θvsg Axis component Iref_q θvsg (corresponding to the corrected q-axis current command value I'ref_q described above).

[0098] In the case of the third inverse transformation, the command value inverse transformation unit 444 derives the corrected d-axis current command value I'ref_d having the internal phase θvsg and the corrected q-axis current command value I'ref_q having the internal phase θvsg using the following equation (5).

[0099]

number

[0100] (b5) Switching control section The switching control unit 45 derives switching control signals g1 to g6 that control the switching of the inverter 11 so that currents corresponding to the corrected d-axis current command value I'ref_d and the corrected q-axis current command value I'ref_q are output to the output line 12 of the inverter 11.

[0101] The switching control unit 45 includes a current control unit 451 , an inverse dq conversion unit 452 , a gain unit 453 , and a PWM unit 454 .

[0102] The current control unit 451 performs current control based on the d-axis inverter current Iinv_d, the q-axis inverter current Iinv_q, the corrected d-axis current command value I'ref_d, and the corrected q-axis current command value I'ref_q, and derives the d-axis inverter voltage command value Vinv_ref_d and the q-axis inverter voltage command value Vinv_ref_q. The current control is feedback control that causes desired output currents Iga, Igb, and Igc to be output from the first to third output lines 12a to 12c. Examples of current control include PID control.

[0103] An inverse dq transformation unit 452 performs inverse dq transformation on the d-axis inverter voltage command value Vinv_ref_d and the q-axis inverter voltage command value Vinv_ref_q using the internal phase θvsg. A gain unit 453 multiplies the inverse dq transformed results by a fourth gain K4, thereby deriving inverter voltage command values ​​Vinv_ref_a, Vinv_ref_b, and Vinv_ref_c for each phase (a-phase, b-phase, and c-phase) to be output to the output line 12 of the inverter 11.

[0104] The inverter voltage command values ​​Vinv_ref_a, Vinv_ref_b, and Vinv_ref_c of the respective phases are expressed by, for example, the following equation (15).

[0105]

number

[0106] Here, the constant k is an arbitrary positive real number, and θ is a real constant. Also, as in equation (6), θref in equation (15) is the reference phase θref.

[0107] In this embodiment, the inverter voltage command values ​​Vinv_ref_a, Vinv_ref_b, and Vinv_ref_c are derived by the following equation (16) using equation (15) where k=1, θ0=0 rad, and reference phase θref=internal phase θvsg.

[0108]

number

[0109] The PWM unit 454 generates switching control signals g1 to g6 by PWM controlling the inverter voltage command values ​​Vinv_ref_a, Vinv_ref_b, and Vinv_ref_c of the respective phases.

[0110] The switching control signals g1 to g6 generated in this manner are input to gates G1 to G6 of six transistors, first to sixth, T1 to T6, of the inverter 11. The inverter 11, controlled by the switching control signals g1 to g6, converts the DC power of the DC power supply 2 into AC power. In this case, the active power and reactive power in the AC power are limited in desired proportions, so that the stability of the system frequency and system voltage of the system 4 can be ensured.

[0111] 2. Action and Effects According to this embodiment, it is possible to provide a power conversion device 3 that can impose limits on active power and reactive power at different rates. The power conversion device 3 can ensure the stability of the system frequency and system voltage of the system 4. This will be specifically described below.

[0112] FIG. 8 is a schematic diagram showing the ranges of active power and reactive power on the system phase-synchronized dq coordinates after multiplying the d-axis current command value and the q-axis current command value by current absolute value limit values. FIG. 9 is a configuration diagram of a control signal derivation unit that does not correct the d-axis current command value and the q-axis current command value taking into account the phase difference between the internal phase and the system phase. FIG. 10 is a configuration diagram of a current command value correction unit of FIG. 9. FIG. 11 is a schematic diagram showing the ranges of active power and reactive power on the system phase-synchronized dq coordinates obtained by the control signal derivation unit of FIG. 9 and the ranges of active power and reactive power on the system phase-synchronized dq coordinates obtained by the control signal derivation unit according to this embodiment. FIG. 12 is a schematic diagram showing the ranges of active power and reactive power on the system phase-synchronized dq coordinates obtained by the control signal derivation unit according to this embodiment.

[0113] In the above embodiment, the current command values ​​(d-axis current command value and q-axis current command value) are subjected to conversion and inverse conversion taking into account the phase difference between the internal phase θvsg and the grid phase θg. Specifically, the current command value having the internal phase θvsg is converted into a current command value having the grid phase θg. Furthermore, after limiting the current command value having the grid phase θg, the current command value having the grid phase θg after the limit is inversely converted into a current command value having the internal phase θvsg. Hereinafter, a current command value “with conversion” refers to a current command value that has been converted and inversely converted taking into account the phase difference between the internal phase θvsg and the grid phase θg. Furthermore, a range “with conversion” refers to a range on the dq coordinate of active power and reactive power calculated based on the current command value “with conversion.” On the other hand, a current command value “without conversion” refers to a current command value that has not been converted and inversely converted taking into account the phase difference between the internal phase θvsg and the grid phase θg. Furthermore, the term "range without transformation" refers to the range on the dq coordinate of the active power and reactive power calculated based on the current command value "without transformation."

[0114] First, a case where both active power and reactive power are limited at the same rate will be described. In virtual synchronous generator control simulating a current-controlled virtual synchronous generator, when both active power and reactive power are limited at the same rate, the power conversion device 3 typically applies a current absolute value limit value to a pre-limiting current command value having an internal phase θvsg. The current absolute value limit value is equal to or greater than 0. Specifically, the post-limiting d-axis current command value "without transformation" is obtained by multiplying the pre-limiting d-axis current command value by the current absolute value limit value. Furthermore, the post-limiting q-axis current command value "without transformation" is obtained by multiplying the pre-limiting q-axis current command value by the current absolute value limit value. The pre-limiting active power and reactive power are indicated by a circular pre-limiting range R_origi on a grid phase-synchronized dq coordinate system, as shown in FIG. 8, for example. The pre-limiting range R_origi is calculated based on the pre-limiting d-axis current command value and the pre-limiting q-axis current command value. Furthermore, the post-limit "no transformation" active power and the post-limit "no transformation" reactive power are indicated by a circular post-limit "no transformation" range R_con_lim on the grid phase-synchronized dq coordinate. The post-limit "no transformation" range R_con_lim is calculated based on the post-limit "no transformation" d-axis current command value and the post-limit "no transformation" q-axis current command value. As shown in Figure 8, the pre-limit range R_origi is limited to the post-limit "no transformation" range R_con_lim. The d of the pre-limit range R_origi θg The "no conversion" range R_con_lim after limiting from the axis component θg The ratio of the limit to the axis component is the q of the range R_origi before the limit. θg q of the "no conversion" range R_con_lim after limiting from the axis component θg The ratio of the limit to the axis component is the same. In other words, the range before limit R_origi and the "without conversion" range after limit R_con_lim are d θg axis and q θg They are concentric circles with the intersection with the axis as the center.

[0115] Here, there is a case where the internal phase θvsg is misaligned with the system phase θg. When the internal phase θvsg is misaligned with the system phase θg, if the limited active power "without conversion" and the limited reactive power "without conversion" are supplied to the system 4, there is a case where the system 4 cannot limit at least one of the active power and the reactive power to a desired magnitude.

[0116] However, in the example of Fig. 8, the power conversion device 3 applies the current absolute value limit value to both the pre-limiting d-axis current command value having the internal phase θvsg and the pre-limiting q-axis current command value having the internal phase θvsg. In this case, even if the internal phase θvsg is misaligned with the grid phase θg, the active power and the reactive power after the limit "without conversion" can be limited to desired levels in the grid 4 by outputting the post-limiting "without conversion" active power and the post-limiting "without conversion" reactive power to the grid 4 without performing correction according to the phase difference between the internal phase θvsg and the grid phase θg. More specifically, as described above, the post-limiting "without conversion" active power and the post-limiting "without conversion" reactive power are indicated by a circular post-limiting "without conversion" range R_con_lim on the grid phase-synchronized dq coordinate system as shown in Fig. 8. Here, on the grid phase synchronization dq coordinate, the range R_lim "with conversion" after limiting is set to the range R_con_lim "without conversion" after limiting so as to correct the phase difference between the internal phase θvsg and the grid phase θg. θg axis and q θgThe limit range R_con_lim is obtained by rotating the range R_con_lim "without transformation" around the intersection with the axis. The limit range R_con_lim "without transformation" is circular on the grid phase-synchronized dq coordinate system. Therefore, even if the limit range R_con_lim "without transformation" is rotated by the phase difference between the internal phase θvsg and the grid phase θg, the limit range R_lim "with transformation" is the same as the limit range R_con_lim "without transformation" after limiting. In other words, even if the active power and reactive power defined by the limit range R_con_lim "without transformation" after limiting are supplied to grid 4, which is controlled by the grid phase θg, when the internal phase θvsg and the grid phase θg are misaligned, the active power and reactive power are limited to the desired magnitude in grid 4.

[0117] Next, a case where different ratios of limits are applied to active power and reactive power will be described. In this case, if the internal phase θvsg and the system phase θg are misaligned, when the limited active power "without conversion" and the limited reactive power "without conversion" are supplied to the system 4, it may not be possible to limit at least one of the active power and the reactive power to a desired magnitude in the system 4.

[0118] A case where at least one of the active power and the reactive power in the system 4 cannot be limited to a desired magnitude will be described as an example with reference to FIGS. 9 and 10 . As shown in FIG. 9 , the control signal derivation unit 40A includes an internal phase derivation unit 41, an AVR unit 42, a current command value derivation unit 43, a current command value correction unit 44A, and a switching control unit 45. As shown in FIG. 10 , the current command value correction unit 44A includes a current limit unit 442 and an absolute value limit unit 443. The current command value correction unit 44 shown in FIGS. 5 and 7 according to this embodiment includes a command value conversion unit 441 and a command value inverse conversion unit 444, but the current command value correction unit 44A shown in FIGS. 9 and 10 does not include the command value conversion unit 441 and the command value inverse conversion unit 444.

[0119] 10 derives a first d-axis current command value Icon_ref_d(1) and a first q-axis current command value Icon_ref_q(1) “without conversion” using the d-axis current limit value Id_lim, the q-axis current limit value Iq_lim, the d-axis current command value Iref_d having the internal phase θvsg, and the q-axis current command value Iref_q having the internal phase θvsg. Specifically, the first d-axis current command value Icon_ref_d(1) “without conversion” is obtained by multiplying the d-axis current command value Iref_d by the d-axis current limit value Id_lim. Also, the first q-axis current command value Icon_ref_q(1) “without conversion” is obtained by multiplying the q-axis current command value Iref_q by the q-axis current limit value Iq_lim. The first d-axis current command value Icon_ref_d(1) "without conversion" and the first q-axis current command value Icon_ref_q(1) "without conversion" are not converted by the command value converter 441 shown in FIGS. 5 and 7 , which takes into account the phase difference between the internal phase θvsg and the grid phase θg. Therefore, the first d-axis current command value Icon_ref_d(1) "without conversion" and the first q-axis current command value Icon_ref_q(1) "without conversion" have the internal phase θvsg. The d-axis current limit value Id_lim and the q-axis current limit value Iq_lim are input from the outside to a current limiter 442 (a part of the inverter control unit 20). The d-axis current limit value Id_lim and the q-axis current limit value Iq_lim are each a value equal to or greater than 0, and are different from the d-axis current limit value Id_lim and the q-axis current limit value Iq_lim.

[0120] The absolute value limit unit 443 derives a second d-axis current command value I'con_ref_d(2) "without conversion" and a second q-axis current command value I'con_ref_q(2) "without conversion" using the current absolute value limit value Iabs_lim input from outside to the absolute value limit unit 443 (part of the inverter control unit 20), and the first d-axis current command value Icon_ref_d(1) "without conversion" and the first q-axis current command value Icon_ref_q(1). Specifically, the second d-axis current command value I'con_ref_d(2) "without conversion" is obtained by multiplying the first d-axis current command value Icon_ref_d(1) "without conversion" by the current absolute value limit value Iabs_lim. The second q-axis current command value I'con_ref_q(2) "without conversion" is obtained by multiplying the first q-axis current command value Icon_ref_q(1) "without conversion" by the current absolute value limit value Iabs_lim. The second d-axis current command value I'con_ref_d(2) "without conversion" and the second q-axis current command value I'con_ref_q(2) "without conversion" have an internal phase θvsg.

[0121] Based on the second d-axis current command value I'con_ref_d(2) "without conversion" and the second q-axis current command value I'con_ref_q(2) "without conversion," a range R_con_lim of the active power and reactive power "without conversion" is determined. In FIG. 11, the range R_con_lim "without conversion" is shown in the system phase synchronized dq coordinates. Note that although the system phase synchronized dq coordinates are shown in FIG. 11, for reference, the range R_con_lim is shown in the internal phase synchronized dq coordinates shown in FIG. 2. θvsg axis and q θvsgThe axes are aligned. In FIG. 11 , the d-axis current limit value Id_lim is 1.0 and the q-axis current limit value Iq_lim is 0.5. The “no conversion” range R_con_lim is the region enclosed between the lines α1 and β1 in the circular pre-limit range R_origi on the grid phase-synchronized dq coordinate. FIG. 11 also shows the “conversion” range R_lim according to this embodiment. The “conversion” range R_lim is the range of active power and reactive power calculated based on the corrected d-axis current command value I′ref_d and the corrected q-axis current command value I′ref_q described above. The corrected d-axis current command value I′ref_d and the corrected q-axis current command value I′ref_q are current command values ​​that have been converted and inversely converted in consideration of the phase difference between the internal phase θvsg and the grid phase θg. The range R_lim "with transformation" is the region enclosed between the straight lines α0 and β0 in the circular pre-limit range R_origi on the system phase-synchronized dq coordinate system.

[0122] The range "with conversion" R_lim is the range "without conversion" R_con_lim. θg axis and q θg The phase difference between the internal phase θvsg and the system phase θg is rotated (transformed) around the intersection O of the axes. In this embodiment, the phase difference is φvsg (=θvsg-θg). This phase difference corresponds to δ in FIG. 2. In other words, the range R_con_lim "without transformation" is d θg axis and q θg With the intersection O of the axes as the center, it is shifted to a position corresponding to the phase difference (φvsg) between the internal phase θvsg and the system phase θg with respect to the range R_lim "with conversion".

[0123] Here, the system phase φg based on the reference phase θref and the internal phase φvsg based on the reference phase θref are respectively expressed by the following equations (17-1) and (17-2). Also, in the system phase synchronized dq coordinates of Figures 11 and 12, the reference phase θref = system phase θg. Therefore, the following equations (17-1) and (17-2) become the following equations (17-3) and (17-4) in the system phase synchronized dq coordinates of Figures 11 and 12. φg=θg-θref (17-1) φvsg=θvsg-θref (17-2) φg=θg-θref=θg-θg=0 (17-3) φvsg=θvsg-θref=θvsg-θg=δ(17-4)

[0124] Next, the lines α1 and β1 that define the range R_con_lim "without conversion" and the lines α0 and β0 that define the range R_lim "with conversion" will be explained below. As mentioned above, the d-axis current limit value Id_lim is 1.0 and the q-axis current limit value Iq_lim is 0.5. The line α1 is the q-axis current limit value Igq. θg In the positive region of the q-axis, the line α1 passes through the part corresponding to the q-axis current limit value Iq_lim = 0.5. The line α1 is inclined with respect to the line α0, with the intersection point O as the center, by the phase difference φvsg (=δ) between the internal phase θvsg and the grid phase θg. The line α0 is inclined with respect to the line α0, with the intersection point O as the center. θg In the positive region of the q-axis, the part corresponding to the q-axis current limit value Iq_lim = 0.5 is passed, and θg In the example of Figure 11, the line α1 is inclined upward to the right relative to the line α0. On the other hand, the line β1 is inclined upward to the right relative to the line α0. θg In the negative region of the q-axis, the line β1 passes through the area corresponding to the q-axis current limit value -Iq_lim = -0.5. The line β1 is inclined with respect to the line β0, with the intersection point O as the center, by the phase difference φvsg (=δ) between the internal phase θvsg and the grid phase θg. The line β0 is inclined with respect to the line β0, with the intersection point O as the center. θg In the negative region of the q-axis, the current passes through the area corresponding to the q-axis current limit value -Iq_lim=-0.5, and θg In the example of Figure 11, the line β1 is inclined upward to the right relative to the line β0.

[0125] As described above, the "no conversion" range R_con_lim determined by the lines α1 and β1 is shifted from the "conversion" range R_lim determined by the lines α0 and β0 by the phase difference φvsg (=δ) between the internal phase θvsg and the system phase θg. Therefore, when the active power and reactive power specified in the "no conversion" range R_con_lim are output to the system 4 controlled by the system phase θg, at least one of the active power and reactive power may not be limited to the desired magnitude in the system 4. In the example of FIG. 11 , the q-axis components of the active power and reactive power are output to the system 4 without being limited by the desired limit (q-axis current limit value ±Iq_lim = ±0.5). Specifically, in a region γ1 of the "no conversion" range R_con_lim that exceeds the line α0 (a region γ1 of the "no conversion" range R_con_lim that is surrounded by the lines α0 and α1), the q-axis components of the active power and reactive power are not limited to the desired magnitude when output to the system 4. Furthermore, in the region γ2 of the range R_con_lim "without conversion" that exceeds the line β0 (the region γ2 of the range R_con_lim "without conversion" that is surrounded by the lines β0 and β1), the q-axis components of the active power and reactive power are not limited to the desired magnitude when output to system 4.

[0126] 11, the d-axis current limit value ±Id_lim = ±1.0, so the d-axis components of the active power and reactive power are not limited. However, if the d-axis current limit value ±Id_lim is set to less than ±1.0, the d-axis components of the active power and reactive power may not be limited to the desired magnitude when output to grid 4, as described above.

[0127] Furthermore, in a region γ3 of the range R_lim "involving conversion" that exceeds the line α1 (a region γ3 of the range R_lim "involving conversion" that is surrounded by the lines α0 and α1), when the q-axis components of the active power and reactive power are output to the grid 4, they exceed the desired limit (here, the q-axis current limit value Iq_lim = 0.5), resulting in an excessively restricted state. Furthermore, in a region γ4 of the range R_lim "involving conversion" that exceeds the line β1 (a region γ4 of the range R_lim "involving conversion" that is surrounded by the lines β0 and β1), when the q-axis components of the active power and reactive power are output to the grid 4, they exceed the desired limit (here, the q-axis current limit value -Iq_lim = -0.5), resulting in an excessively restricted state.

[0128] According to the above-described configuration of the present embodiment, the power conversion device 3 has the current command value corrector 44. Therefore, even if limits are imposed on the active power and the reactive power at different rates in a state where the internal phase θvsg and the system phase θg are misaligned, the active power and the reactive power can be limited to desired levels in the system 4. A brief description will be given below.

[0129] The current command value corrector 44 converts, limits, and inversely converts the d-axis current command value Iref_d and the q-axis current command value Iref_q, taking into account the phase difference φvsg (=δ) between the internal phase θvsg and the grid phase θg. The current command value corrector 44 includes a command value converter 441, a current limiter 442, an absolute value limiter 443, and a command value inverse converter 444.

[0130] The d-axis current command value Iref_d and the q-axis current command value Iref_q have an internal phase θvsg, which is shifted with respect to the grid phase θg. The command value converter 441 converts the d-axis current command value Iref_d having the internal phase θvsg and the q-axis current command value Iref_q having the internal phase θvsg into a first d-axis current command value Iref_d(1) having the grid phase θg and a first q-axis current command value Iref_q(1) having the grid phase θg, respectively, taking into account the phase difference φvsg (=δ) between the internal phase θvsg and the grid phase θg.

[0131] Next, the current limit unit 442 limits the first d-axis current command value Iref_d(1) having the system phase θg and the first q-axis current command value Iref_q(1) having the system phase θg using the d-axis current limit value Id_lim and the q-axis current limit value Iq_lim, respectively, to derive a second d-axis current command value Iref_d(2) having the system phase θg and a second q-axis current command value Iref_q(2) having the system phase θg.

[0132] Next, the absolute value limiter 443 multiplies the second d-axis current command value Iref_d(2) having the grid phase θg and the second q-axis current command value Iref_q(2) having the grid phase θg by the current absolute value limit value Iabs_lim in common to derive a third d-axis current command value Iref_d(3) having the grid phase θg and a third q-axis current command value Iref_q(3) having the grid phase θg. The processing by the absolute value limiter 443 can prevent the voltage and current flowing through the inverter 11 from becoming too large. This can prevent malfunction and damage to elements constituting the inverter 11.

[0133] Next, the command value inverse converter 444 inversely converts the third d-axis current command value Iref_d(3) having the system phase θg and the third q-axis current command value Iref_q(3) having the system phase θg into a corrected d-axis current command value I'ref_d having the internal phase θvsg and a corrected q-axis current command value I'ref_q having the internal phase θvsg, taking into account the phase difference φvsg (=δ).

[0134] The switching control unit 45 controls the switching of the inverter 11 using the switching control signals g1 to g6 corresponding to the corrected d-axis current command value I'ref_d and the corrected q-axis current command value I'ref_q.

[0135] With this configuration, even if limits are imposed on the active power and the reactive power at different rates when the internal phase θvsg and the system phase θg are misaligned, the active power and the reactive power can be limited to the desired magnitude in the system 4.

[0136] Fig. 12 shows the range R_lim of active power and reactive power "involving transformation" in Fig. 11. As shown in Fig. 12, the active power and reactive power defined in the range R_lim "involving transformation" have no phase difference with the system phase θg on the system phase-synchronized dq coordinate system and are synchronized with the system phase θg. Therefore, the active power and reactive power defined in the range R_lim "involving transformation" are limited to a desired magnitude when output to the system 4.

[0137] As described above, the embodiment of the present invention has been disclosed in the above description, but the present invention is not limited to this. In other words, various modifications can be made to the above-described embodiments in terms of mechanism, shape, material, quantity, position, arrangement, etc. without departing from the scope of the technical idea and purpose of the present invention, and these modifications are included in the present invention.

[0138] 3. Variations In the above embodiment, the current command value corrector 44 is configured to be able to impose limits on both the d-axis current command value Iref_d and the q-axis current command value Iref_q.

[0139] (a) Limiting only the q-axis current command value However, unlike the above embodiment, the current command value corrector 44 may be configured to limit only the q-axis current command value Iref_q. Specifically, similar to the above embodiment, the command value converter 441 converts the d-axis current command value Iref_d having the internal phase θvsg and the q-axis current command value Iref_q having the internal phase θvsg into a first d-axis current command value Iref_d(1) having the grid phase θg and a first q-axis current command value Iref_q(1) having the grid phase θg, respectively. The current limiter 442 applies the q-axis current limit value Iq_lim only to the first q-axis current command value Iref_q(1). On the other hand, the current limiter 442 does not apply the d-axis current limit value Id_lim to the first d-axis current command value Iref_d(1). In other words, the q-axis current limit value Iq_lim is equal to or greater than 0, and the d-axis current limit value Id_lim=1.0. In this case, the current limiter 442 derives the second d-axis current command value Iref_d(2) having the system phase θg and the second q-axis current command value Iref_q(2) having the system phase θg using the following equation (18).

[0140]

number

[0141] In this modification, the absolute value limit unit 443 derives the third d-axis current command value Iref_d(3) and the third q-axis current command value Iref_q(3) by substituting the second d-axis current command value Iref_d(2) and the second q-axis current command value Iref_q(2) of equation (18) into equation (4) of the above embodiment. In addition, the command value inverse converter 444 derives the corrected d-axis current command value I'ref_d and the corrected q-axis current command value I'ref_q by substituting the third d-axis current command value Iref_d(3) and the third q-axis current command value Iref_q(3) derived in this modification into equation (5) of the above embodiment.

[0142] (b) Limiting only the d-axis current command value Furthermore, unlike the above embodiment, the current command value corrector 44 may be configured to limit only the d-axis current command value Iref_d. Specifically, similar to the above embodiment, the command value converter 441 converts the d-axis current command value Iref_d having the internal phase θvsg and the q-axis current command value Iref_q having the internal phase θvsg into a first d-axis current command value Iref_d(1) having the grid phase θg and a first q-axis current command value Iref_q(1) having the grid phase θg, respectively. The current limiter 442 applies the d-axis current limit value Id_lim only to the first d-axis current command value Iref_d(1). On the other hand, the current limiter 442 does not apply the q-axis current limit value Iq_lim to the first q-axis current command value Iref_q(1). In other words, the d-axis current limit value Id_lim is equal to or greater than 0, and the q-axis current limit value Iq_lim=1.0. In this case, the current limiter 442 derives the second d-axis current command value Iref_d(2) having the system phase θg and the second q-axis current command value Iref_q(2) having the system phase θg using the following equation (19).

[0143]

number

[0144] In this modification, the absolute value limit unit 443 derives the third d-axis current command value Iref_d(3) and the third q-axis current command value Iref_q(3) by substituting the second d-axis current command value Iref_d(2) and the second q-axis current command value Iref_q(2) of equation (19) into equation (4) of the above embodiment. In addition, the command value inverse converter 444 derives the corrected d-axis current command value I'ref_d and the corrected q-axis current command value I'ref_q by substituting the third d-axis current command value Iref_d(3) and the third q-axis current command value Iref_q(3) derived in this modification into equation (5) of the above embodiment.

[0145] In the above embodiment, the current command value corrector 44 includes an absolute value limiter 443. However, if the magnitudes of both the active power and the reactive power do not exceed a predetermined range, the absolute value limiter 443 can be omitted. In this case, the current command value corrector 44 includes a command value converter 441, a current limiter 442, and a command value inverse converter 444. Similarly to the above embodiment, the command value converter 441 converts the d-axis current command value Iref_d having the internal phase θvsg and the q-axis current command value Iref_q having the internal phase θvsg into a first d-axis current command value Iref_d(1) having the grid phase θg and a first q-axis current command value Iref_q(1) having the grid phase θg, respectively. Furthermore, similarly to the above-described embodiment, the current limit unit 442 imposes limits on the first d-axis current command value Iref_d(1) and the first q-axis current command value Iref_q(1), respectively, to derive the second d-axis current command value Iref_d(2) having the system phase θg and the second q-axis current command value Iref_q(2) having the system phase θg.

[0146] Thereafter, the command value inverse converter 444 inversely converts the second d-axis current command value Iref_d(2) having the system phase θg and the second q-axis current command value Iref_q(2) having the system phase θg into a corrected d-axis current command value I'ref_d having the internal phase θvsg and a corrected q-axis current command value I'ref_q having the internal phase θvsg, respectively.

[0147] In the case of the first inverse transformation, the command value inverse transformation unit 444 inversely transforms the coordinate points of the second d-axis current command value Iref_d(2) and the second q-axis current command value Iref_q(2) on the system phase-synchronized dq coordinate into the coordinate points of the corrected d-axis current command value I'ref_d and the corrected q-axis current command value I'ref_q on the internal phase-synchronized dq coordinate.

[0148] In the case of the second inverse transformation, the command value inverse transformation unit 444 inversely transforms the system phase-synchronized dq coordinates after the rotational transformation in the command value transformation unit 441 into internal phase-synchronized dq coordinates by performing an inverse rotational transformation from the system phase θg to the internal phase θvsg. As a result, the command value inverse transformation unit 444 inversely transforms the second d-axis current command value Iref_d(2) having the system phase θg and the second q-axis current command value Iref_q(2) having the system phase θg into a corrected d-axis current command value I'ref_d having the internal phase θvsg and a corrected q-axis current command value I'ref_q having the internal phase θvsg, respectively.

[0149] In the case of the third inverse transformation, the command value inverse transformation unit 444 derives the corrected d-axis current command value I'ref_d having the internal phase θvsg and the corrected q-axis current command value I'ref_q having the internal phase θvsg using the following equation (3).

[0150]

number

[0151] <c> In the above embodiment, the d-axis inverter current Iinv_d and the q-axis inverter current Iinv_q are input to the switching control unit 45. However, the d-axis current Igd and the q-axis current Igq may be input to the switching control unit 45 instead of the d-axis inverter current Iinv_d and the q-axis inverter current Iinv_q.

[0152] In this case, the current control unit 451 performs current control based on the d-axis current Igd, the q-axis current Igq, the corrected d-axis current command value I'ref_d, and the corrected q-axis current command value I'ref_q, and derives the d-axis voltage command value Vref_d and the q-axis voltage command value Vref_q.

[0153] An inverse dq transformation unit 452 performs inverse dq transformation on the d-axis voltage command value Vref_d and the q-axis voltage command value Vref_q using the internal phase θvsg. A gain unit 453 multiplies the inverse dq transformed results by a fourth gain K4, thereby deriving voltage command values ​​Vref_a, Vref_b, and Vref_c for each phase (a-phase, b-phase, and c-phase) to be output to the output line 12 of the inverter 11.

[0154] The voltage command values ​​Vref_a, Vref_b, and Vref_c of the respective phases are derived, for example, by the following equation (20).

[0155]

number

[0156] Here, the constant k is an arbitrary positive real number, and θ is a real constant. Also, as in equation (6), θref in equation (20) is the reference phase θref.

[0157] In this modification, the voltage command values ​​Vref_a, Vref_b, and Vref_c are derived by the following equation (21) using equation (20) where k=1, θ0=0 rad, and the reference phase θref=the internal phase θvsg.

[0158]

number

[0159] The PWM unit 454 generates switching control signals g1 to g6 by PWM controlling the voltage command values ​​Vref_a, Vref_b, and Vref_c of the respective phases.

[0160] <d> In the above embodiment, the system 4 transmits AC power using a three-phase, three-wire system. However, as in the above embodiment, as long as the active power and reactive power in the system 4 can be limited to desired levels in consideration of the phase difference between the internal phase θvsg and the system phase θg, the system may transmit AC power using any method. For example, the concept of the present invention may be applied to a single-phase, three-wire system or a new system. [Explanation of symbols]

[0161] 1: Power conversion system 2:DC power supply 3: Power conversion device 4: Lineage 10: Grid connection section 11: Inverter 12: Output line 12a~12c: 1st to 3rd output lines 13: Filter inductor 13a to 13c: First to third filter inductors 14: Filter capacitor 14a to 14c: First to third filter capacitors 15: Inverter current sensor 15a to 15c: 1st to 3rd inverter current sensors 16: Output current sensor 16a to 16c: First to third output current sensors 17: Output voltage sensor 17a to 17c: 1st to 3rd output voltage sensors 20: Inverter control unit 30: Measurement value calculation unit 31: dq conversion section 32: Gain section 33: Power calculation section 34: Absolute power calculation unit 40, 40A: Control signal derivation section 41: Internal phase derivation section 42:AVR section 43: Current command value derivation section 44, 44A: Current command value correction section 45: Switching control section 311: Voltage dq conversion unit 312: Current dq conversion section 313: Inverter current dq conversion unit 321 to 323: 1st to 3rd gain sections 331a to 331d: multiplier 332a, 332b: Adder / subtractor 411: Simulation calculation section 411a: Unit inertia constant part 411b: Integrator 411c: Braking control unit 411d: Adder / Subtractor 412: Angular frequency integrator 413a, 413b: adder / subtractor 421: First-order delay calculation unit 422: Internal voltage calculation unit 423a, 423b: Adder / Subtractor 441: Command value conversion unit 442: Current limiter 443: Absolute value limit section 444: Command value inverse conversion unit 451: Current control section 452: Inverse dq transform unit 453: Gain section 454:PWM section G1~G6: Gates T1 to T6: 1st to 6th transistors d θg q θg _coord: System phase synchronization dq coordinate d θvsg q θvsg _coord: Internal phase synchronization dq coordinate< / d> < / c>

Claims

1. an inverter that converts DC power from a DC power supply into AC power and outputs the AC power to a grid via an output line; an inverter control unit that controls the inverter so that virtual synchronous generator control is performed by a virtual synchronous generator that simulates a synchronous generator, The inverter control unit a dq transformation unit that derives, from an output voltage and an output current measured on an output line of the inverter, a d-axis current, a d-axis voltage, a q-axis current, and a q-axis voltage on an internal phase synchronous dq coordinate system that rotates in synchronization with an internal phase of the virtual synchronous generator, wherein the d-axis current, the d-axis voltage, the q-axis current, and the q-axis voltage have the internal phase; an internal phase derivation unit that derives an internal frequency deviation of the virtual synchronous generator from a deviation between an active power derived from the d-axis current, the d-axis voltage, the q-axis current, and the q-axis voltage and an active power command value input from the outside to the inverter control unit, and that derives the internal phase from the internal frequency deviation and an external frequency command value input from the outside to the inverter control unit; an AVR unit that derives an internal voltage of the virtual synchronous generator from reactive power derived from the d-axis current, the d-axis voltage, the q-axis current, and the q-axis voltage, a reactive power command value input from the outside to the inverter control unit, an output voltage absolute value derived from the d-axis voltage and the q-axis voltage, and an external voltage command value input from the outside to the inverter control unit, and performs automatic voltage control in the virtual synchronous generator; a current command value derivation unit that derives a d-axis current command value having the internal phase and a q-axis current command value having the internal phase from the internal voltage, the d-axis voltage, the q-axis voltage, and an internal impedance of the virtual synchronous generator; a current command value correcting unit that converts the d-axis current command value and the q-axis current command value into a first d-axis current command value and a first q-axis current command value, respectively, in consideration of a phase difference between the internal phase and a system phase of the system, and then derives a corrected d-axis current command value and a corrected q-axis current command value by using a value obtained by applying a limit to at least one of the first d-axis current command value and the first q-axis current command value; a switching control unit that derives a switching control signal that controls switching of the inverter so that currents corresponding to the corrected d-axis current command value and the corrected q-axis current command value are output to an output line of the inverter, The current command value correction unit a command value converter that converts the d-axis current command value having the internal phase and the q-axis current command value having the internal phase into the first d-axis current command value having the system phase and the first q-axis current command value having the system phase, respectively; a current limiting unit that derives a second d-axis current command value having the grid phase by multiplying the first d-axis current command value by the d-axis current limit value and a second q-axis current command value having the grid phase by multiplying the first q-axis current command value by the q-axis current limit value, using a d-axis current limit value and a q-axis current limit value that are input from outside to the inverter control unit to adjust the active power and the reactive power, respectively; a command value inverse converter that inversely converts the second d-axis current command value having the grid phase and the second q-axis current command value having the grid phase into the corrected d-axis current command value having the internal phase and the corrected q-axis current command value having the internal phase, respectively.

2. the command value converter converts coordinate points of the d-axis current command value and the q-axis current command value on the internal phase synchronized dq coordinate system into coordinate points of the first d-axis current command value and the first q-axis current command value on a system phase synchronized dq coordinate system that rotates in synchronization with the system phase; 2. The power conversion device according to claim 1, wherein the command value inverse conversion unit inversely converts coordinate points of the second d-axis current command value and the second q-axis current command value on the grid phase synchronized dq coordinate into coordinate points of the corrected d-axis current command value and the corrected q-axis current command value on the internal phase synchronized dq coordinate.

3. the command value converter converts the internal phase synchronized dq coordinates into system phase synchronized dq coordinates that rotate in synchronization with the system phase by performing rotational conversion from the internal phase to the system phase, and converts the d-axis current command value having the internal phase and the q-axis current command value having the internal phase into the first d-axis current command value having the system phase and the first q-axis current command value having the system phase, respectively; 3. The power conversion device according to claim 1, wherein the command value inverse conversion unit inversely converts the system phase synchronized dq coordinates after the rotational conversion in the command value conversion unit into the internal phase synchronized dq coordinates by performing an inverse rotational conversion from the system phase to the internal phase, and inversely converts the second d-axis current command value having the system phase and the second q-axis current command value having the system phase into the corrected d-axis current command value having the internal phase and the corrected q-axis current command value having the internal phase, respectively.

4. The derivation of the first d-axis current command value and the first q-axis current command value by the command value conversion unit is expressed by the following equation (1): [Equation 1] where: Iref_d(1): first d-axis current command value Iref_q(1): first q-axis current command value Vgd: d-axis voltage Vgq: q-axis voltage Iref_d: d-axis current command value The power conversion device according to claim 1 or 2, wherein Iref_q is a q-axis current command value.

5. The current limit unit derives the second d-axis current command value and the second q-axis current command value using the following equation (2): [Equation 2] where: Iref_d(2): second d-axis current command value Iref_q(2): second q-axis current command value Id_lim: d-axis current limit value The power conversion device according to claim 4 , wherein Iq_lim is a q-axis current limit value.

6. The derivation of the corrected d-axis current command value and the corrected q-axis current command value by the command value inverse conversion unit is expressed by the following equation (3): [Equation 3] where: I'ref_d: corrected d-axis current command value The power conversion device according to claim 5 , wherein I′ref_q is the corrected q-axis current command value.

7. The current command value correction unit an absolute value limit unit configured to derive a third d-axis current command value having the grid phase by multiplying the second d-axis current command value by the current absolute value limit value, and to derive a third q-axis current command value having the grid phase by multiplying the second q-axis current command value by the current absolute value limit value, using a current absolute value limit value input to the inverter control unit from outside to commonly adjust the active power and the reactive power, and 3. The power conversion device according to claim 1, wherein the command value inverse converter inversely converts a third d-axis current command value having the grid phase and a third q-axis current command value having the grid phase, instead of the second d-axis current command value having the grid phase and the second q-axis current command value having the grid phase, into the corrected d-axis current command value having the internal phase and the corrected q-axis current command value having the internal phase, respectively.

8. The current command value correction unit an absolute value limit unit configured to derive a third d-axis current command value having the grid phase by multiplying the second d-axis current command value by the current absolute value limit value, and to derive a third q-axis current command value having the grid phase by multiplying the second q-axis current command value by the current absolute value limit value, using a current absolute value limit value input to the inverter control unit from outside to commonly adjust the active power and the reactive power, and the command value inverse converter inversely converts a third d-axis current command value having the grid phase and a third q-axis current command value having the grid phase, instead of the second d-axis current command value having the grid phase and the second q-axis current command value having the grid phase, into the corrected d-axis current command value having the internal phase and the corrected q-axis current command value having the internal phase, respectively; The derivation of the third d-axis current command value and the third q-axis current command value by the absolute value limit unit is expressed by the following formula (4), and the derivation of the corrected d-axis current command value and the corrected q-axis current command value is expressed by the following formula (5). [Equation 4] [Equation 5] where: Iref_d(2): second d-axis current command value Iref_q(2): second q-axis current command value Iref_d(3): Third d-axis current command value Iref_q(3): Third q-axis current command value Iabs_lim: Current absolute limit value I'ref_d: corrected d-axis current command value I'ref_q: corrected q-axis current command value, Vgd: d-axis voltage, The power conversion device according to claim 5, wherein Vgq is a q-axis voltage.

9. 3. The power conversion device according to claim 1, wherein the internal phase derivation unit derives the internal frequency deviation by performing a predetermined arithmetic process using a deviation between the active power and the active power command value and an oscillation equation, derives a rated frequency of the virtual synchronous generator by adding the external frequency command value to the internal frequency deviation, and derives the internal phase by integrating an angular velocity based on the rated frequency of the virtual synchronous generator.

10. 3. The power conversion device according to claim 1, wherein the AVR unit performs a predetermined calculation on a deviation between the reactive power and the reactive power command value based on a droop characteristic of an AVR, adds a first-order lag element to a result of the calculation, and subtracts the output voltage absolute value from a sum of the result to which the first-order lag element is added and the external voltage command value, and then performs feedback control to derive the internal voltage.

11. 3. The power conversion device according to claim 1, wherein the internal impedance is virtually simulated based on a winding resistance and a winding reactance of a generator of the virtual synchronous generator.

12. the dq conversion unit derives a d-axis inverter current and a q-axis inverter current from an inverter output current measured at a position close to the inverter in an output line of the inverter; The switching control unit a current control unit that performs current control based on the d-axis inverter current, the q-axis inverter current, the corrected d-axis current command value, and the corrected q-axis current command value, and derives a d-axis inverter voltage command value and a q-axis inverter voltage command value; an inverse dq transformation unit that performs inverse dq transformation on the d-axis inverter voltage command value and the q-axis inverter voltage command value to derive inverter voltage command values ​​for each phase to be output to an output line of the inverter; The power conversion device according to claim 1 or 2, further comprising: a PWM unit that generates the switching control signal from the inverter voltage command value for each phase by PWM control.

13. The switching control unit a current control unit that performs current control based on the d-axis current, the q-axis current, the corrected d-axis current command value, and the corrected q-axis current command value, and derives a d-axis voltage command value and a q-axis voltage command value; an inverse dq transformation unit that performs inverse dq transformation on the d-axis voltage command value and the q-axis voltage command value to derive voltage command values ​​for each phase to be output to an output line of the inverter; The power conversion device according to claim 1 or 2, further comprising: a PWM unit that generates the switching control signal from the voltage command value of each phase by PWM control.

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