Control device, power conversion device, and control method

Abstract

A technology is provided that enables a power conversion device that exchanges power with a power system to appropriately respond to a power system accident. A control device (60) according to an embodiment of the present disclosure controls a voltage V at a connection point GCP between a power supply system (10) including a power conversion device (40) and a power grid (20). D Based on the measured value, the voltage V at the grid connection point GCP D and a phase detector 603 for detecting the phase θ of the voltage V D and the command value of the output current of the power conversion device 40 (current command value I * ) based on the measured value of the positive-phase voltage of the grid-connection point GCP (steady-state component sV d + and a current command limiting unit 604 that limits the output current of the power conversion device 40 in response to a decrease in the output voltage Vcc.

Description

[Technical Field]

[0001] The present disclosure relates to a control device and the like. [Background technology]

[0002] For example, a technology is known in which a power supply system including a DC power source and a power conversion device that converts power between DC and AC is interconnected with a power grid, and power is exchanged between the power supply system and the power grid (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-220409 [Patent Document 2] Japanese Patent Application Publication No. 2019-004651 Summary of the Invention [Problem to be solved by the invention]

[0004] However, depending on conditions such as impedance between a power supply system and a power grid, in the event of an accident such as a short circuit or a ground fault in the power grid, the power supply system may continue to output transient currents and voltages that are not synchronized with the phase of the power grid for a long period of time. As a result, for example, when the power grid recovers from the accident in this state, a current with an inappropriate phase may flow from the power supply system to the power grid, causing fluctuations in the voltage of the power grid and resulting in overvoltages and overcurrents.

[0005] In view of the above-mentioned problems, an object of the present invention is to provide a technology for a power conversion device that exchanges power with a power grid, capable of appropriately responding to a fault in the power grid. [Means for solving the problem]

[0006] In order to achieve the above object, in one embodiment of the present disclosure, A control device for controlling a power conversion device having one end connected to a DC power source and the other end connected to a power grid, the control device performing power conversion between DC on the one end side and AC on the other end side, a phase detection unit that detects a phase based on a measurement value of a voltage at an interconnection point between the power supply system including the power conversion device and the power grid; a current control unit that controls the output current based on the phase and a command value of the output current of the power conversion device; a first limiting unit that limits the output current in response to a decrease in the magnitude of the measured positive-phase voltage at the interconnection point. 、 When a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is established, the phase detection unit detects the phase of the voltage at the interconnection point by updating the phase of the voltage at the interconnection point so as to advance it at an angular frequency corresponding to a rated frequency of the power grid or a predetermined value based on a past detection value of the frequency of the power grid. Ru, A control device is provided.

[0007] In another embodiment of the present disclosure, a main circuit unit having one end connected to a DC power source and the other end connected to a power grid, and performing power conversion between DC at the one end and AC at the other end; a phase detector that detects a phase based on a measured value of a voltage at an interconnection point between a power supply system including a power conversion device and the power grid; a current control unit that controls the output current based on the phase and a command value of the output current of the power conversion device; a first limiting unit that limits the output current in response to a decrease in the magnitude of the measured positive-phase voltage at the interconnection point. 、 When a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is established, the phase detection unit detects the phase of the voltage at the interconnection point by updating the phase of the voltage at the interconnection point so as to advance it at an angular frequency corresponding to a rated frequency of the power grid or a predetermined value based on a past detection value of the frequency of the power grid. Ru, A power converter is provided.

[0008] In still another embodiment of the present disclosure, A control method for controlling a power conversion device having one end connected to a DC power source and the other end connected to a power grid, the power conversion device performing power conversion between DC on the one end side and AC on the other end side, the method comprising: a phase detection step of detecting a phase based on a measurement value of a voltage at an interconnection point between the power supply system including the power conversion device and the power grid; a current control step of controlling the output current based on the phase and a command value of the output current of the power conversion device; a first limiting step of limiting the output current in response to a decrease in the magnitude of the measured positive-phase voltage of the interconnection point. fruit , In the phase detection step, when a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied, the phase of the voltage at the interconnection point is detected by updating the phase so as to advance the phase of the voltage at the interconnection point at an angular frequency corresponding to a rated frequency of the power grid or a predetermined value based on a past detection value of the frequency of the power grid. A control method is provided. [Effects of the Invention]

[0009] According to the above-described embodiment, a power conversion device that exchanges power with a power grid can appropriately respond to a fault in the power grid. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an example of a power system. [Figure 2] FIG. 2 is a control block diagram illustrating a configuration of an example of a control device. [Figure 3] FIG. 2 is a diagram illustrating an example of a configuration of a phase detection unit. [Figure 4] FIG. 2 is a diagram illustrating an example of a configuration of a freewheel determining unit and a PLL unit. [Figure 5] 10A and 10B are diagrams illustrating an example of upper and lower limit values ​​of a current command value. [Figure 6] FIG. 2 is a diagram illustrating an example of a current command on / off switching unit. [Figure 7] FIG. 2 is a control block diagram showing an example of a configuration of a current control unit. [Figure 8] FIG. 2 is a control block diagram showing an example of the configuration of an AC-ACR unit. [Figure 9] 6 is a time chart showing an example of a phase detection result by a phase detection section according to a first comparative example. [Figure 10] 10 is a time chart showing an example of a phase detection result by a phase detection section according to a second comparative example. [Figure 11] 4 is a time chart showing an example of a phase detection result by a phase detection unit according to the embodiment; [Figure 12] FIG. 10 is a time chart illustrating an example of a result of control of an output current of a power conversion device by a control device according to a comparative example. [Figure 13] 5 is a time chart illustrating an example of a result of control of an output current of a power conversion device by a control device according to an embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment will be described with reference to the drawings.

[0012] [Power system configuration] The configuration of a power system 1 according to this embodiment will be described with reference to FIG.

[0013] FIG. 1 is a diagram illustrating an example of the configuration of a power system 1. As shown in FIG.

[0014] As shown in FIG. 1, the power system 1 includes a power supply system 10 and a power grid 20.

[0015] In the power system 1, power is exchanged between a power supply system 10 and a power grid 20.

[0016] In the power system 1, the exchange of power between the power supply system 10 and the power grid 20 is, for example, a bidirectional exchange of power. Furthermore, the exchange of power between the power supply system 10 and the power grid 20 may be only a supply of power from one side to the other, such as only a supply of power from the power supply system 10 to the power grid 20 or only a supply of power from the power grid 20 to the power supply system 10.

[0017] The power supply system 10 includes a DC power supply 30 , a power conversion device 40 , an AC filter 50 , and a control device 60 .

[0018] The power supply system 10 uses a power conversion device 40 to exchange power between a DC power supply 30 and a power grid 20. For example, as shown in Fig. 1 , a current flows between the power conversion device 40 and the power grid 20 via a reactor L1, a filter capacitor C, and a reactor L2 of an AC filter 50, a resistance R of the line, and an impedance Z of the line.

[0019] The power system 20 supplies three-phase AC power to an electrical load (not shown).

[0020] The DC power supply 30 is electrically connected to one end of the power conversion device 40 by a DC link.

[0021] The DC power supply 30 is, for example, a secondary battery. The secondary battery is, for example, a liquid-type lithium-ion battery or an all-solid-state battery.

[0022] Furthermore, the DC power supply 30 may be a wind power generator included in a wind power generation system as the power supply system 10. The wind power generator as the DC power supply 30 includes a wind turbine, a generator (for example, a PM (Permanent Magnet) synchronous generator) mechanically coupled to the wind turbine by a rotating shaft, and a power converter that converts AC power generated and output by the generator into DC power. In this case, the only exchange between the power supply system 10 and the power grid 20 is the supply of power from the power supply system 10 to the power grid 20.

[0023] Furthermore, the DC power supply 30 may be, for example, a solar power generator (specifically, a solar panel) included in a solar power generation system as the power supply system 10. In this case, the only exchange between the power supply system 10 and the power grid 20 is the supply of power from the power supply system 10 to the power grid 20.

[0024] One end of the power conversion device 40 is electrically connected to the DC power supply 30 through a DC link, and the other end is electrically connected to the power grid 20 via an AC filter 50. The power conversion device 40 performs power conversion between DC on the DC power supply 30 side and three-phase AC on the power grid 20 side.

[0025] Specifically, when power is supplied from the power supply system 10 to the power grid 20, the DC is converted into three-phase AC of a desired voltage (amplitude) and frequency and output to the power grid 20 via the AC filter 50. When power is supplied from the power grid 20 to the power supply system 10, the three-phase AC is converted into DC and the power is supplied to the DC power supply 30 via a DC link.

[0026] The power conversion device 40 includes, for example, an inverter circuit 42 capable of converting DC power into three-phase AC power of a desired voltage and frequency, or converting three-phase AC power into DC power, and a gate circuit 44 for driving the inverter circuit 42.

[0027] For example, the inverter circuit is a three-phase full-bridge inverter circuit including six semiconductor switches (also referred to as "switching elements"), and each semiconductor switch is connected in parallel with a free wheel diode.

[0028] The gate circuit 44 drives the semiconductor switch of the inverter circuit 42 to turn on and off under the control of the control device 60 .

[0029] The AC filter 50 passes the AC output from the power conversion device 40 and the three-phase AC supplied (input) from the power grid 20 to the power supply system 10, and attenuates unnecessary frequency components (e.g., harmonic components). For example, the AC filter 50 is an LCL filter that includes reactors L1 and L2 of the power conversion device 40 and a filter capacitor C provided between the reactors L1 and L2.

[0030] The control device 60 controls the power conversion device 40 to realize the exchange of power between the power supply system 10 (specifically, the DC power supply 30) and the power grid 20. Specifically, the control device 60 controls a main circuit (for example, the above-mentioned inverter circuit 42) that performs power conversion between DC on the DC power supply 30 side and three-phase AC on the power grid 20 side.

[0031] 1, the control device 60 is built into the power conversion device 40. The control device 60 may be a programmable logic controller (PLC), an edge controller, an edge server, or the like, installed in the same facility as the power conversion device 40. The control device 60 may be a server device installed in a location different from the facility where the power conversion device 40 is installed.

[0032] In the power system 1, the voltage V of each part on the AC side of the power supply system 10 B ,V C ,V D is the current I B ,I C ,I D , and the impedance of each part.

[0033] Voltage V B is the voltage of the line between the power converter 40 and the AC filter 50, and corresponds to the output voltage of the power converter 40. B is the current in the line between the power converter 40 and the AC filter 50, and corresponds to the output current of the power converter 40. When the output current of the power converter 40 is a positive value, it is a current flowing from the power converter 40 to the power grid 20 as shown in the figure, and when it is a negative value, it is a current flowing from the power grid 20 to the power converter 40, in the opposite direction to the figure. C corresponds to the voltage across the filter capacitor C. The current I C corresponds to the current of the filter capacitor C. When the current of the filter capacitor C is a positive value, it flows out of the line between the power conversion device 40 and the power system 20 as shown in the figure, and when it is a negative value, it flows into the line in the opposite direction to the figure. D corresponds to the voltage (connection point voltage) at the interconnection point GCP between the power supply system 10 and the power grid 20. D corresponds to the current at the grid connection point GCP.

[0034] [Control device configuration] An example of the configuration of the control device 60 will be described with reference to FIGS. 2 to 8 in addition to FIG.

[0035] FIG. 2 is a control block diagram showing an example of the configuration of the control device 60. FIG. 3 is a diagram showing an example of the configuration of the phase detection unit 603. FIG. 4 is a diagram showing an example of the configuration of the freewheel determination unit 6036 and the PLL unit 6037. FIG. 5 is a diagram showing an example of the configuration of the current command value I * Upper limit of I HL and lower limit I LL Fig. 6 is a diagram showing an example of the configuration of a current command on / off switching unit 605. Fig. 7 is a control block diagram showing an example of the configuration of a current control unit 606. Fig. 8 is a control block diagram showing an example of an AC-ACR unit 6063a.

[0036] Specifically, Fig. 5 shows the current command value I * Upper limit of I HL 7A and the current command value I * Lower limit of I LL 7B, which represents the same.

[0037] The configurations of the b-phase AC-ACR section 6063b and the c-phase AC-ACR section 6063c are the same as the a-phase AC-ACR section 6063a, so they are not shown in the figures and FIG. 8 is used instead.

[0038] It includes a line-to-three-phase converter 602 , a phase detector 603 , a current command limiter 604 , a current command on / off switcher 605 , a current controller 606 , and a PWM converter 607 .

[0039] Some or all of the functions of each unit of the control device 60 may be realized solely by hardware such as electrical circuits or electronic circuits. Alternatively, some or all of the functions of each unit of the control device 60 may be realized by a combination of hardware and software, such as a program, an auxiliary storage device corresponding to an installation destination, a load destination, and an execution unit of the program, a memory device, and a processor. Examples of the auxiliary storage device include a hard disk drive (HDD), a solid state drive (SSD), an electrically erasable programmable read-only memory (EEPROM), and a flash memory. Examples of the memory device include a static random access memory (SRAM), a dynamic random access memory (DRAM), and the like. Examples of the processor include a central processing unit (CPU). Examples of the processor may also include a graphics processing unit (GPU), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and the like.

[0040] The line-to-three-phase converter 602 converts the line voltage V DL The measured value (also referred to as the "actual measured value", "actual value", or "detected value") (hereinafter, for convenience, the "measured line voltage V DL ) is the phase voltage (voltage V D ) measurement value (hereinafter, for convenience, it is called "voltage measurement value V D ") to convert the line voltage measurement V DL is the measured line voltage V between phase a and phase b D_ab and the measured line voltage V between phase b and phase c D_bc Also, the line voltage measurement value V DL is the measured line voltage V between phase c and phase a D_ca The voltage measurement V D is the measured a-phase voltage V D_a , b-phase voltage measurement value V D_b , and the c-phase voltage measurement value VD_c Includes.

[0041] The phase detector 603 detects the voltage measurement value V D Specifically, the phase detector 603 detects the phase θ of the voltage measurement value V of the grid-connection point GCP at each predetermined processing cycle. D The phase θ of

[0042] For example, as shown in FIG. 3, the phase detector 603 detects the voltage measurement value V D Specifically, the phase detection unit 603 includes a three-phase to two-phase conversion unit 6031, a positive phase dq conversion unit 6032, a positive phase decoupling cell 6033, a negative phase dq conversion unit 6034, a negative phase decoupling cell 6035, a freewheel determination unit 6036, and a PLL unit 6037.

[0043] The three-phase to two-phase converter 6031 converts the three-phase AC into two-phase AC in a stationary coordinate system defined by orthogonal α-axis and β-axis (hereinafter referred to as "αβ stationary coordinate system") using a known method.

[0044] For example, the three-phase to two-phase conversion unit 6031 calculates the a-phase component A of the electrical physical quantity A of the three-phase AC by using the following equation (1): a , b-phase component A b , and c-phase component A c α-axis component A of electrical physical quantity A in the αβ stationary coordinate system α , and the β-axis component A β Convert to.

[0045]

number

[0046] In this example, the three-phase to two-phase conversion unit 6031 converts the three-phase AC at the grid connection point GCP into a voltage measurement value V D (i.e., the measured voltage of phase a, V D_a , b-phase voltage measurement value V D_b, and the c-phase voltage measurement value V D_c ) is expressed as the α-axis voltage measurement value V in the αβ stationary coordinate system. α and the measured β-axis voltage V β Convert to.

[0047] The positive-phase dq transformation unit 6032 converts the two-phase AC in the αβ stationary coordinate system into the voltage measurement value V at the interconnection point GCP. D into a two-phase AC in the positive rotation direction (positive phase) in a dq rotating coordinate system (hereinafter simply referred to as "dq rotating coordinate system") based on the phase θ of the

[0048] For example, the positive-phase dq transformation unit 6032 calculates the α-axis component A of the electrical physical quantity A in the αβ stationary coordinate system using the following equation (2): α and β-axis component A β is the positive-phase d-axis component A of electrical physical quantity A in the dq rotating coordinate system. d + and the positive-phase q-axis component A q + Convert to.

[0049]

number

[0050] In this example, the positive phase dq conversion unit 6032 converts the α-axis voltage measurement value V in the αβ stationary coordinate system output from the three-phase to two-phase conversion unit 6031 into α and the measured β-axis voltage V β is expressed as the measured positive-phase d-axis voltage V in the dq rotating coordinate system. d + and the positive-phase q-axis voltage measurement value V q + At this time, the positive phase dq transformation unit 6032 can use the cosine cos θ and sine sin θ of the detected value of the phase θ (hereinafter, for convenience, the "detected phase value θ") acquired in the previous detection process of the phase θ.

[0051] The positive-phase decoupling cell 6033 converts the positive-phase d-axis voltage measurement value V d + and the positive-phase q-axis voltage measurement value V q+ The double harmonic components originating from the negative-phase d-axis voltage and q-axis voltage are removed or attenuated from the positive-phase d-axis voltage measurement value V d +* and the positive-phase q-axis voltage measurement value V q +* Output.

[0052] For example, the positive-phase non-interfering cell 6033 detects the stationary component sV of the negative-phase d-axis voltage measurement value acquired during the previous detection process of the phase θ of the phase detector 603. d - and the steady-state component sV of the negative-phase q-axis voltage measurement q - , and the cosine cos2θ and sine sin2θ of the phase twice the detected value of the phase θ (phase detected value θ) are used to calculate the positive-phase d-axis voltage measurement value V d +* and the positive-phase q-axis voltage measurement value V q +* Get.

[0053] Positive-phase d-axis voltage measurement value V d +* and the positive-phase q-axis voltage measurement value V q +* is passed through a low pass filter (LPF) and is output as the steady-state component sV of the positive-phase d-axis voltage measurement value. d + and the steady-state component sV of the positive-phase q-axis voltage measurement q + The steady-state component sV of the positive-phase d-axis voltage measurement is output. d + and the steady-state component sV of the positive-phase q-axis voltage measurement q + is stored in a memory device or the like of the control device 60 and will be used in the next detection process of the phase θ, as will be described later.

[0054] The reverse-phase dq transformer 6034 transforms the two-phase AC current in the αβ stationary coordinate system into a two-phase AC current in the reverse rotation direction (reverse phase) in the dq rotating coordinate system.

[0055] For example, the antiphase dq transform unit 6034 calculates the α-axis component A of the electrical physical quantity A in the αβ stationary coordinate system using the following equation (3):α and β-axis component A β is the d-axis component A of the opposite phase of the electrical physical quantity A in the dq rotating coordinate system. d - and the opposite-phase q-axis component A q - Convert to.

[0056]

number

[0057] In this example, the anti-phase dq transformation unit 6034 converts the α-axis voltage measurement value V in the αβ stationary coordinate system output from the three-phase to two-phase transformation unit 6031 into α and the q-axis voltage measurement value V β is expressed as the negative-phase d-axis voltage measurement value V in the dq rotating coordinate system. d - and the negative phase q-axis voltage measurement value V q - At this time, the antiphase dq transform unit 6034 can use the cosine cos θ and sine sin θ of the phase detection value θ acquired in the previous detection process of the phase θ.

[0058] The negative-sequence decoupling cell 6035 measures the negative-sequence d-axis voltage V d - and the negative phase q-axis voltage measurement value V q - The double harmonic components originating from the positive-phase d-axis voltage and q-axis voltage are removed or attenuated from the negative-phase d-axis voltage measurement value V d -* and the negative phase q-axis voltage measurement value V q -* Output.

[0059] For example, the negative-phase non-interference cell 6035 detects the steady-state component sV of the positive-phase d-axis voltage measurement value acquired during the previous detection process of the phase θ of the phase detector 603. d + and the steady-state component sV of the positive-phase q-axis voltage measurement q + , and the cosine cos2θ and sine sin2θ of the phase twice the detected value of the phase θ (phase detected value θ) are used to calculate the positive-phase d-axis voltage measurement value Vd +* and the positive-phase q-axis voltage measurement value V q +* Get.

[0060] Negative-phase d-axis voltage measurement value V d -* and the negative phase q-axis voltage measurement value V q -* is passed through the LPF and is output as the steady-state component sV of the negative-phase d-axis voltage measurement. q - and the steady-state component sV of the negative-phase q-axis voltage measurement q - The steady-state component of the negative-phase d-axis voltage measurement value sV is output. d - and the steady-state component sV of the negative-phase q-axis voltage measurement q - is temporarily stored in a memory device or the like of the control device 60 and is used in the next detection process of the phase θ as described above.

[0061] The freewheel determining unit 6036 determines whether or not to cause the PLL unit 6037 to perform a freewheel operation.

[0062] The freewheeling operation of the PLL unit 6037 is an operation of detecting the phase θ, assuming that the phase θ advances (i.e., rotates) at a fixed value of an angular frequency ω1 corresponding to the rated frequency f1 (e.g., 50 Hz) of the power grid 20 or a predetermined value based on past detected values ​​of the frequency of the power grid 20. The predetermined value based on past detected values ​​of the frequency of the power grid 20 is, for example, a frequency trend value of the power grid 20. The frequency trend value of the power grid 20 is a representative value of the past frequency of the power grid 20. For example, the control device 60 stores past detected values ​​of the frequency of the power grid 20 as time-series data and calculates the frequency trend value of the power grid 20 by averaging values ​​at N points from n cycles ago to (n+N-1) cycles ago (n: a positive integer, N: an integer greater than or equal to 2).

[0063] For example, as shown in FIG. 4, the freewheel determining unit 6036 includes a positive-phase voltage amplitude calculation unit 6036A and a determining unit 6036B.

[0064] The positive-phase voltage amplitude calculation unit 6036A calculates the steady-state component sV of the positive-phase d-axis voltage measurement value output during the previous phase θ detection process. d + and the steady-state component sV of the positive-phase q-axis voltage measurement q + Based on this, the amplitude of the positive sequence voltage at the GCP interconnection point |sV + |(hereinafter referred to as "positive-sequence voltage amplitude |sV + Calculates |

[0065] The determination unit 6036B determines the positive-sequence voltage amplitude |sV + The determining unit 6036B determines whether the positive-sequence voltage amplitude |sV + The threshold value Th1 may be determined based on the phase θ detected by the normal operation of the PLL unit 6037 and the voltage V of the power system 20. E (Hereinafter, "system voltage V E ") phase Θ (hereinafter referred to as "system phase Θ") to the extent that it is impossible to synchronize the positive-sequence voltage amplitude |sV + The positive-sequence voltage amplitude |sV + The threshold value Th1 can be set arbitrarily. For example, the positive-sequence voltage amplitude |sV + When | is expressed in a PU (Per Unit) system based on a rated value (for example, the rated voltage of the power system 20), that is, in a PU value, the threshold value Th1 is, for example, "0.2."

[0066] The determination unit 6036B determines the positive-sequence voltage amplitude |sV + is equal to or less than the threshold value Th1, the determination unit 6036B outputs a value of "0", which means that a freewheel operation is to be performed, to the PLL unit 6037. On the other hand, in all other cases, the determination unit 6036B outputs a value of "1", which means that a freewheel operation is not to be performed (i.e., normal operation is to be performed), to the PLL unit 6037.

[0067] The determination unit 6036B determines the positive-phase voltage amplitude |sV +Instead of |, it may be determined whether another index (for example, the effective value of the positive-sequence voltage) indicating the magnitude of the positive-sequence voltage at the interconnection point GCP is equal to or less than the threshold value. Furthermore, the determination unit 6036B may determine whether or not to perform the freewheel operation based on an index other than the magnitude of the positive-sequence voltage. That is, the determination unit 6036B may determine whether or not to perform the freewheel operation depending on whether or not any condition is satisfied that allows it to be determined that the phase detection value θ is clearly out of sync with the phase Θ of the power grid 20 (i.e., any condition that allows it to be determined that the phase detection value θ cannot be synchronized with the phase Θ of the power grid 20 by the PLL unit 6037).

[0068] The PLL unit 6037 controls the voltage V D and outputs the detected value of the phase θ.

[0069] For example, as shown in FIG. 4, the PLL unit 6037 includes a PI adjuster 6037A with a limiter, a multiplier 6037B, and a phase calculation unit 6037C.

[0070] The limiter-equipped PI (Proportional Integral) regulator 6037A calculates the positive-phase q-axis voltage measurement value V output from the positive-phase non-interference cell 6033. q +* The voltage V at the grid connection point GCP is set to zero. D The frequency f of the power grid 20 is adjusted based on the rated frequency f1 of the power grid 20. For example, the PI regulator 6037A with limiter adjusts the voltage V of the grid connection point GCP, which is expressed as a PU value based on the rated frequency f1. D frequency f PU The adjustment amount Δf is used to adjust the PU value to "1.0" as the standard. PU Output.

[0071] Specifically, the PI regulator with limiter 6037A calculates the positive-phase q-axis voltage measurement value V q +*The PI regulator includes a proportional and an integrator connected in parallel, and a limiter unit that limits the output of the PI regulator between an upper limit value ULim and a lower limit value LLim. The PI regulator with limiter 6037A adjusts the output of the limiter unit by an adjustment amount Δf PU Output as

[0072] The upper limit value ULim is appropriately set to a positive value, and the lower limit value LLim is appropriately set to a negative value. The upper limit value ULim and the lower limit value LLim may be fixed values ​​or may be variable values ​​that change depending on the situation. The upper limit value ULim and the lower limit value LLim are, for example, "0.1" and "-0.1" in PU values.

[0073] Furthermore, the PI regulator with limiter 6037A receives an inverted signal of value "0" or "1" output from the freewheel determination unit 6036. If the inverted signal input is "1", that is, if the freewheel determination unit 6036 outputs a value of "0" indicating the execution of a freewheel operation, the PI regulator with limiter 6037A resets the integrator to "0".

[0074] The multiplier 6037B multiplies the adjustment amount Δf output from the PI regulator with limiter 6037A. PU The CPU 6034 multiplies the value output from the freewheel determining unit 6036 by the value indicating whether or not a freewheel operation is being performed, and outputs the multiplied value.

[0075] When the value output from the freewheel determination unit 6036 is "1", that is, when the freewheel operation is not performed, the multiplier 6037B multiplies the adjustment amount Δf PU On the other hand, if the value output from the freewheel determination unit 6036 is "0", that is, if the freewheel operation is to be performed, the multiplier 6037B outputs "0".

[0076] The phase calculation unit 6037C calculates a phase detection value θ based on the output of the multiplier 6037B.

[0077] For example, the phase calculation unit 6037C adds the PU value "1.0" corresponding to the rated frequency f1 to the output of the multiplier 6037B, and further multiplies it by the rated frequency f1 and "2π" (=2πf1), thereby obtaining the voltage V at the grid-connection point GCP. D The phase calculation unit 6037C then calculates the angular frequency ω of the phase detected value θ by integrating the angular frequency ω.

[0078] When the freewheeling operation of the PLL unit 6037 is not performed, that is, when normal operation is performed, the phase calculation unit 6037C adjusts the PU value to "1.0" by the adjustment amount Δf PU By adding these, the voltage V at the grid connection point GCP D On the other hand, when the freewheeling operation of the PLL unit 6037 is performed, the output of the multiplier 6037B is "0", so the phase calculation unit 6037C calculates the voltage V D The frequency f of the grid connection point GCP can be regarded as the rated frequency f1. D is considered to be leading (that is, rotating) at an angular frequency ω1 corresponding to the rated frequency f1 of the power system 20, the phase detection value θ can be calculated.

[0079] The phase detection unit 603 calculates the cosine cos θ and sine sin θ of the phase detection value θ output from the PLL unit 6037 and outputs the result as a reference voltage signal.

[0080] Furthermore, the phase detection unit 603 calculates the cosine cos2θ and sine sin2θ of the phase (2θ) twice the phase detection value θ output from the PLL unit 6037.

[0081] The cosine cos θ and sine sin θ, as well as the cosine cos2θ and sine sin2θ as reference voltage signals, are temporarily stored in a memory device or the like of the control device 60, and are used in the next detection process of the phase θ, as described above.

[0082] The current command limiting unit 604 is configured to limit the output current command value I* (Hereinafter, "current command value I * ") size.

[0083] Current command value I * is the d-axis component I in the dq rotating coordinate system d * (hereinafter referred to as "d-axis current command value I d * ") and the q-axis component I q * (Hereinafter, the q-axis current command value I q * The control device 60 calculates the current command value I * For example, the control device 60 generates the voltage V D and current I D The current command value I * Generate.

[0084] The current command limiting unit 604 limits the d-axis current command value I d * and q-axis current command value I q * The d-axis current command value I d * This allows the current command limiting unit 604 to reduce the active current of the power conversion device 40.

[0085] For example, the current command limiting unit 604 may limit the active current command value of the power conversion device 40, i.e., the d-axis current command value I d * The upper limit I HL Less than or equal to lower limit I LL It is limited to the above range.

[0086] Specifically, the current command limiting unit 604 limits the input d-axis current command value I d * is the upper limit I HL Less than or equal to lower limit I LL If it is within the above range, the input d-axis current command value I d *That is, the current command limiting unit 604 outputs the input d-axis current command value I d * is the upper limit I HL Less than or equal to lower limit I LL When the d-axis current command value I d * On the other hand, the current command limiting unit 604 does not limit the input d-axis current command value I d * is the upper limit I HL Less than or equal to lower limit I LL If it is outside the above range, the d-axis current command value I d * The upper limit I HL Or lower limit I LL The d-axis current command value I d * More specifically, the current command limiting unit 604 outputs the input d-axis current command value I d * is the upper limit I HL If the d-axis current command value I d * The upper limit I HL and limit (i.e., correct) the lower limit I LL If it is less than the d-axis current command value I d * Lower limit I LL Limit (i.e., correct)

[0087] Upper limit I HL is a positive value (I HL >0), is set to limit the output current of the power conversion device 40 that flows from the power conversion device 40 to the power grid 20. LL is a negative value (I LL <0), is provided to limit the output current of the power conversion device 40 that flows from the power grid 20 toward the power conversion device 40.

[0088] For example, the current command value I d * is expressed as a PU value based on the rated current of the power conversion device 40, and the steady-state component sV d+ Let us consider the case where is expressed as a PU value based on the rated voltage of the power system 20.

[0089] As shown in Figure 5A, the steady-state component sV of the measured positive-phase d-axis voltage d + If is less than "1.0" and greater than or equal to the threshold Th2 (<1.0), the upper limit I HL is set to "1.0", and the lower limit I LL is set to "-1.0". In other words, the current command limiting unit 604 limits the steady-state component sV d + is equal to or less than "1.0" and equal to or greater than the threshold value Th2, the d-axis current command value I d * does not substantially restrict

[0090] On the other hand, the steady-state component sV of the positive-phase d-axis voltage measurement d + If is greater than or equal to "0" and less than or equal to the threshold Th2 (>0), the upper limit I HL is the steady-state component sV of the measured positive-phase d-axis voltage d + It is set to decrease linearly from "1.0" to "0" as the value of decreases. Similarly, the steady-state component sV of the measured positive-phase d-axis voltage d + If is greater than or equal to "0" and less than or equal to the threshold value Th2, the lower limit I LL is the steady-state component sV of the measured positive-phase d-axis voltage d + In other words, the current command limiting unit 604 is configured to linearly increase from "-1.0" to "0" as the steady-state component sV of the measured positive-phase d-axis voltage d + When is greater than or equal to "0" and less than or equal to the threshold value Th2, the steady-state component sV of the measured positive-phase d-axis voltage d + The current command value I d * Limit.

[0091] The threshold value Th2 is, for example, a fixed value that is set as appropriate. Alternatively, the threshold value Th2 may be a variable value that is changed according to a predetermined condition. For example, the threshold value Th2 is "0.8."

[0092] The current command limiting unit 604 limits the d-axis current command value I d * , and the q-axis current command value I q * is output to the current control unit 606.

[0093] The current command limiting unit 604 limits the steady-state component sV of the positive-phase d-axis voltage measurement value. d + Instead, the positive-phase d-axis voltage measurement value V d + Another index that represents the magnitude of the positive-phase d-axis voltage (for example, V d +* The current command value I d * may be restricted.

[0094] The current command on / off switching unit 605 controls the current command value I * (i.e., d-axis current command value I d * and q-axis current command value I q * ) is enabled or disabled (i.e., turned on or off).

[0095] Specifically, the current command on / off switching unit 605 controls the voltage V D When the condition indicating that the phase detection value θ of the phase detection value θ is clearly out of sync with the phase Θ of the power grid 20 by the PLL unit 6037 is satisfied, the d-axis current command value I d * and q-axis current command value I q *On the other hand, if the above condition is not met, the current command ON / OFF switching unit 605 disables (i.e., turns OFF) the d-axis current command value I d * and q-axis current command value I q * Enable (i.e., turn ON).

[0096] For example, as shown in FIG. 6, the current command on / off switching unit 605 includes comparators 6051 and 6052, an AND operator 6053, a comparator 6054, a monostable 6055, an AND operator 6056, and an on-delay 6057.

[0097] In this example, the steady-state component sV of the positive-phase d-axis voltage measurement d + and the steady-state component sV of the normal q-axis voltage measurement q + is expressed as a PU value based on the rated voltage of the power grid 20.

[0098] Comparator 6051 detects the steady-state component sV of the positive-phase d-axis voltage measurement value. d + is compared with the threshold value Th3, and the steady-state component sV d + If is greater than the threshold value Th3, it outputs "1" (TRUE), otherwise it outputs "0" (FALSE).

[0099] The threshold value Th3 is a value greater than 0 and less than 1. The threshold value Th3 is a value greater than the voltage V D The steady-state component sV of the positive-phase d-axis voltage measurement value, which can be determined to be clearly out of sync with the grid phase Θ, d + is the upper limit of the value of

[0100] Comparator 6052 detects the steady-state component sV of the positive-phase q-axis voltage measurement value. q + Absolute value of |sV q + | is compared with the threshold value Th4, and the steady-state component sV q+ If is smaller than the threshold value Th4, it outputs "1" (TRUE), otherwise it outputs "0" (FALSE).

[0101] The threshold value Th4 is a value greater than 0 and less than 1. The threshold value Th4 is a value greater than the voltage V D The steady-state component sV of the positive-sequence q-axis voltage measurement value, which can be determined to be clearly out of sync with the grid phase Θ, q + Absolute value of |sV q + is the lower limit of |.

[0102] The AND operator 6053 outputs "1" (TRUE) when the outputs of the comparators 6051 and 6052 are both "1" (TRUE), and outputs "0" (FALSE) in all other cases.

[0103] The comparator 6054 compares the inverted value of the output of the AND operator 6053 with the value "0.5", and outputs "1" (TRUE) if the inverted value of the output of the AND operator 6053 is greater than "0.5", and outputs "0" otherwise. In other words, the comparator 6054 outputs "1" (TRUE) if the output of the AND operator 6053 is "0", and outputs "0" (FALSE) if the output of the AND operator 6053 is "1".

[0104] Monostable 6055 holds the output of comparator 6054 for a predetermined waiting time T1 and outputs the held value. As a result, even if a different value is input from comparator 6054 during the holding period (waiting time T1), monostable 6055 does not switch to a state in which it outputs a different value until the holding period has elapsed. Therefore, for example, even if the output of AND operator 6053 switches from "0" to "1" and its inverted value switches from "1" to "0", the output value of monostable 6055 does not switch from "1" to "0" until waiting time T1 has elapsed.

[0105] The AND operator 6056 outputs "1" (TRUE) if both the output of the AND operator 6053 and the inverted value of the output of the monostable 6055 are "1", and outputs "0" (FALSE) otherwise. In other words, the AND operator 6056 outputs "1" if the state in which the output of the AND operator 6053 is "1" has elapsed for the waiting time T1 or more, and outputs "0" otherwise.

[0106] The waiting time T1 is determined based on, for example, the rated frequency f1 of the power grid 20. Specifically, for example, the waiting time T1 is a time equivalent to half of one cycle (half cycle), which is the reciprocal of the rated frequency f1 of the power grid 20.

[0107] The on-delay 6057 outputs "1" only when the output of the AND operator 6056 switches from "0" to "1" after a predetermined waiting time T2 (also referred to as "delay time") has elapsed, and otherwise outputs the output of the AND operator 6056 as is. The output of the on-delay 6057 is the d-axis current command value I d * and q-axis current command value I q * ON signal (="1") to enable, or d-axis current command value I d * and q-axis current command value I q * This makes it possible to prevent, for example, chattering, in which the output of the on-delay 6057 immediately switches to an ON signal in the next processing cycle after it has switched from an ON signal to an OFF signal.

[0108] The waiting time T2 is determined based on, for example, the rated frequency f1 of the power grid 20. Specifically, for example, the waiting time T1 is a time equivalent to one cycle, which is the reciprocal of the rated frequency f1 of the power grid 20.

[0109] The current control unit 606 controls the current command value I *and a signal (ON signal or OFF signal) input from the current command ON / OFF switching unit 605, the output current of the power conversion device 40 is controlled.

[0110] For example, the current control unit 606 includes a switch unit 6061 , a two-phase to three-phase conversion unit 6062 , and an AC-ACR unit 6063 .

[0111] Based on the signal input from the current command on / off switching unit 605, the switch unit 6061 sets the d-axis current command value I input from the current command limiting unit 604 as the target value of the output current of the power conversion device 40. d * and q-axis current command value I q * Switches between selecting "0" and "1".

[0112] When an ON signal, i.e., a value of "1", is input from the current command ON / OFF switching unit 605, the switch unit 6061 uses the d-axis current command value I input from the current command limiting unit 604 as the target values ​​of the d-axis component and the q-axis component of the output current of the power conversion device 40. d * and q-axis current command value I q * On the other hand, when an OFF signal, i.e., a value of "0", is input from the current command ON / OFF switching unit 605, the switch unit 6061 selects "0" as the target values ​​of the d-axis component and the q-axis component of the output current of the power conversion device 40.

[0113] The two-phase to three-phase conversion unit 6062 converts the electrical physical quantity of two-phase AC in the dq rotating coordinate system into an equivalent expression of three-phase AC.

[0114] For example, the two-phase to three-phase conversion unit 6062 calculates the d-axis component A of the electrical physical quantity of the two-phase AC based on the reference voltage signal output from the phase detection unit 603 using the following equation (4): d and q-axis component A q a-phase component A of three-phase AC a , b-phase component A b , and c-phase component A c Convert to.

[0115]

number

[0116] In this example, the two-phase to three-phase conversion unit 6062 selects and outputs target values ​​of the d-axis component and the q-axis component of the output current of the power conversion device 40 (hereinafter referred to as the current target value I ** ) to the three-phase AC current target value I ** (i.e., a-phase current target value I a ** , b-phase current target value I b ** , and the c-phase current target value I c ** )

[0117] The AC-ACR unit 6063 is a known AC (Alternating Current) type ACR (Auto Current Regulator: current controller), and performs current control so as to reduce the deviation between the target value and the measured value of each output current of the a-phase, b-phase, and c-phase of the three-phase AC, and outputs a voltage Δv. That is, the AC-ACR unit 6063 calculates the a-phase current measurement value I of the current measurement value I a , b-phase current measurement value I b , and the c-phase current measurement value I c Each of these is the a-phase current target value I a ** , b-phase current target value I b ** , and the c-phase current target value I c ** The current is controlled to follow the a-phase voltage Δv, and the voltage Δv is output. a , b-phase voltage Δv b , and c-phase voltage Δv c Includes.

[0118] Specifically, the AC-ACR section 6063 includes an a-phase AC-ACR section 6063a, a b-phase AC-ACR section 6063b, and a c-phase AC-ACR section 6063c.

[0119] The AC-ACR unit 6063a calculates the a-phase current target value I a ** and the a-phase current measurement value I a The current is controlled to reduce the deviation from the a-phase voltage Δv a Output.

[0120] Measured a-phase voltage at the GCP interconnection point V D_a and a-phase voltage Δv a are added together, and the output voltage command value V * (hereinafter referred to as "voltage command value V * ") of the a-phase component (hereinafter referred to as "voltage command value V a * ") and output to the PWM conversion unit 607.

[0121] The AC-ACR unit 6063b calculates the b-phase current target value I b ** and the b-phase current measurement value I b The current is controlled to reduce the deviation from the b-phase voltage Δv b Output.

[0122] Measured b-phase voltage at the GCP interconnection point V D_b and b-phase voltage Δv b are added together, and the three-phase AC voltage command value V * b-phase component of the voltage command value V b * ") and output to the PWM conversion unit 607.

[0123] The AC-ACR unit 6063c calculates the c-phase current target value I c ** and the measured c-phase current I c The current is controlled to reduce the deviation from the c-phase voltage Δv c Output.

[0124] Measured c-phase voltage at the GCP interconnection point V D_c and c-phase voltage Δv c are added together, and the three-phase AC voltage command value V * The c-phase component of the voltage command value V c *") and output to the PWM conversion unit 607.

[0125] For example, as shown in FIG. 8, the AC-ACR unit 6063a calculates the a-phase current target value I a ** and the a-phase current measurement value I a It is a PR (Proportional Resonant) controller in which a proportional term 6063a_P and a resonant term 6063a_R that resonates at the rated frequency f1 of the power system 20 are provided in parallel, with the deviation from the rated frequency f1 of the power system 20 as an input. In addition, for example, the AC-ACR units 6063b and 6063c also have a similar configuration.

[0126] The transfer function R(s) of the resonance term in the PR controller is, for example, the resonance gain K r and angular frequency ω1, it is expressed by the following equations (5.1) and (5.2), and the maximum gain is achieved at angular frequency ω1.

[0127]

number

[0128] The AC-ACR units 6063a, 6063b, and 6063c may be P (Proportional) controllers, in which case the resonance term is omitted.

[0129] The PWM conversion unit 607 converts the output voltage command value of the power conversion device 40 (voltage command value V * ) into a PWM (Pulse Width Modulation) signal.

[0130] The PWM signal is a rectangular wave signal that corresponds to a carrier frequency, and is input to a gate circuit 44 for driving a semiconductor switch of the power conversion device 40 (specifically, the inverter circuit 42).

[0131] As a result, the control device 60 sets the current target value I ** Voltage command value V according to *Therefore, the control device 60 can drive the power conversion device 40 via the gate circuit 44 based on the current target value I. ** Specifically, the current command value I * is valid, the control device 60 determines whether the measured value of the output current of the power conversion device 40 (the measured current value I) is equal to the current command value I * In addition, the current command value I * is invalid, the control device 60 can perform current control so that the measured value of the output current of the power conversion device 40 (measured current I) follows zero.

[0132] [Specific example of phase detection result by phase detection unit according to first comparative example] A specific example of a phase detection result by the phase detection section according to the first comparative example will be described with reference to FIG.

[0133] FIG. 9 is a time chart showing an example of a phase detection result of the phase detection section according to the first comparative example.

[0134] Specifically, FIG. 9 shows FIG. 9A, which shows the time variation of the phase detection value θ and the system phase Θ, and FIG. 9B shows the time variation of the phase detection value θ and the voltage V at the interconnection point GCP when it is assumed that the power system 20 is in a normal state. E 9B shows the change over time of the phase shift between the phase θ of the

[0135] The phase detector according to the first comparative example differs from the phase detector 603 according to the embodiment in that the freewheel determination unit 6036 and the reset function of the multiplier 6037B and integrator of the PLL unit 6037 are omitted. In other words, unlike the phase detector 603 according to the embodiment, the phase detector according to the first comparative example is able to detect the voltage V D The phase θ of

[0136] In this example, a short circuit or ground fault occurs in the power grid 20 at time t11, and the grid voltage V EAfter the phase θ falls to zero and it becomes impossible to detect the phase θ accurately, the system voltage V E has returned to normal.

[0137] As shown in Figure 9, when an accident occurs in the power system 20 at time t11, the phase detection value θ increases the angular frequency ω (corresponding to the gradient of the time change in the phase detection value θ in the figure) by an amount equivalent to the upper limit value ULim due to the action of the PI regulator 6037A with limiter.

[0138] System voltage V E Even if the voltage V at the grid connection point GCP drops to zero, the voltage V at the grid connection point GCP may increase due to the influence of the impedance Z. D remains relatively high, and as a result, the steady-state component V of the positive-phase q-axis voltage measurement q +* is maintained to be greater than zero. Therefore, after time t11, when it is assumed that the power system 20 is in a normal state, the voltage V D The phase difference between the phase θ of the inverter and the actual phase detection value θ increases over time. At time t12, a relatively large phase difference occurs, and the system voltage V E has returned.

[0139] In this state, if the power conversion device 40 outputs a current, an unexpected reactive current flows between the power conversion device 40 and the power grid 20, and the grid voltage V E may fluctuate significantly, resulting in overvoltage.

[0140] [Phase detection result of the phase detection unit according to the second comparative example] A specific example of a phase detection result according to the second comparative example will be described with reference to FIG.

[0141] FIG. 10 is a time chart showing an example of a phase detection result of the phase detection section 603 according to the second comparative example.

[0142] Specifically, FIG. 10A shows the time variation of the phase detection value θ and the system phase Θ, and FIG. 10B shows the time variation of the phase detection value θ and the voltage V at the interconnection point GCP when it is assumed that the power system 20 is in a normal state. E 10B shows the change over time of the phase shift between the phase θ of the signal and the phase of the signal.

[0143] The phase detection unit of the second comparative example differs from the phase detection unit 603 of this embodiment in that, when the same condition for performing freewheel operation (hereinafter, for convenience, referred to as the "update stop condition") is met, the phase detection unit stops updating the phase detection value θ and fixes the phase detection value θ to the state immediately before transitioning to freewheel operation.

[0144] In this example, a short circuit or ground fault occurs in the power grid 20 at time t21, and the grid voltage V E After the phase θ becomes impossible to detect accurately, the system voltage V E has returned to normal.

[0145] As shown in Fig. 10, when a fault occurs in the power grid 20 at time t21, the phase detection value θ increases the angular frequency ω by an amount corresponding to the upper limit value ULim due to the action of the PI regulator 6037A with limiter. Therefore, after time t21, when it is assumed that the power grid 20 is in a normal state, the voltage V D The phase difference between the phase θ and the actual phase detection value θ increases with time.

[0146] In contrast, in this example, the update stop condition is met at time t22, and the phase detection value θ is fixed at the most recent value. Therefore, the phase shift temporarily decreases between times t22 and t23. However, assuming that the power system 20 is in a normal state, the voltage V at the interconnection point GCP D Since the phase θ of the power grid 20 changes at an angular frequency ω1 corresponding to the rated frequency f1, the phase shift increases in the negative direction between times t23 and t24, and then decreases again between times t24 and t25. Then, at time t25, when a relatively large phase shift occurs, the system voltage V E has returned.

[0147] In this way, when the phase detector according to the second comparative example is adopted, the temporary phase shift is reduced, but the system voltage V E Depending on the time required for the system voltage V to recover, the phase shift may then repeatedly increase and decrease. E Depending on the timing of the restoration, a relatively large phase shift may occur, and an overvoltage may occur, as in the case of the phase detection unit according to the first comparative example described above.

[0148] [Phase detection results of the phase detection unit according to the embodiment] A specific example of a phase detection result by the phase detection unit 603 according to this embodiment will be described with reference to FIG.

[0149] FIG. 11 is a time chart showing an example of a phase detection result of the phase detection unit 603 according to the embodiment.

[0150] Specifically, FIG. 11A shows the time variation of the phase detection value θ and the system phase Θ, and FIG. 11B shows the time variation of the phase detection value θ and the voltage V at the interconnection point GCP when it is assumed that the power system 20 is in a normal state. E 11B shows the change over time of the phase shift between the phase θ of the signal and the phase of the signal.

[0151] In this example, a short circuit or ground fault occurs in the power grid 20 at time t31, and the grid voltage V E After the phase θ falls to zero and it becomes impossible to detect the phase θ accurately, the system voltage V E has returned to normal.

[0152] As shown in FIG. 11, when a fault occurs in power system 20 at time t31, PI regulator 6037A with limiter increases angular frequency ω of phase detection value θ by an amount equivalent to upper limit value ULim.

[0153] In contrast to this, in this example, at time t32, the conditions for performing the above-mentioned freewheel operation are met, and a signal indicating the execution of the freewheel operation (i.e., a signal with a value of "0") is output from the freewheel determination unit 6036 to the PLL unit 6037. Therefore, after time t32, the action of the PI regulator with limiter 6037A is stopped, and the angular frequency ω of the phase detection value θ is fixed to the angular frequency ω1 corresponding to the rated frequency f1 of the power system 20. As a result, the phase shift is prevented from increasing after time t32, and the amount of phase shift is maintained in the state it was in immediately before the start of the freewheel operation. Therefore, thereafter, at time t33, the system voltage V E The amount of phase shift when the signal returns can be kept relatively small.

[0154] In this way, in this example, the phase detection unit 603 detects the system voltage V E Therefore, the phase detector 603 can prevent the phase shift from increasing in a situation where the phase θ cannot be accurately detected due to a decrease in the system voltage V E This can suppress the occurrence of overvoltage when the power is restored.

[0155] Furthermore, when the freewheeling operation is performed, the integrator of the PI regulator with limiter 6037A is reset to zero as described above. E When the system voltage V E Therefore, the phase detector 603 can prevent the system voltage V from suddenly canceling the phase shift due to the action of the integrator when the system voltage V is restored. E When the power is restored, the PLL unit 6037 operates to eliminate the sudden phase shift, thereby preventing the system from falling into an unstable state.

[0156] [Control results by the control device according to the comparative example] A specific example of the control result of the output current of the power conversion device 40 by the control device according to the comparative example will be described with reference to FIG.

[0157] FIG. 12 is a time chart showing an example of the control result of the output current of the power conversion device 40 by the control device according to the comparative example.

[0158] The control device according to the comparative example differs from the control device 60 according to the present embodiment in that the freewheel determination unit 6036 of the phase detection unit 603 is omitted, the PLL unit 6037 does not perform freewheel operation, the current command limiting unit 604 is omitted, and the current command on / off switching unit 605 is omitted.

[0159] In this example, an accident such as a short circuit or a ground fault occurs in the power grid 20 at time t41 in the time chart of FIG. 12, and the grid voltage V E falls to zero, and then at time t42, the grid voltage V E has returned to normal.

[0160] As shown in FIG. 12, when a fault occurs in the power grid 20 at time t41, the grid voltage V E However, as described above, due to the influence of the impedance Z between the interconnection point GCP and the power system 20, the voltage measurement value V D Therefore, after time t41, the phase difference Δθ between the phase detection value θ and the system phase Θ increases, and as a result, the frequency detection value f inside the PLL unit 6037 sticks to the upper limit.

[0161] In addition, the positive-phase d-axis voltage measurement value V d + and the positive-phase q-axis voltage measurement value V q + is originally the positive-phase d-axis voltage measurement value V d + becomes "1", and the positive-phase q-axis voltage measurement value V q + Instead of following "0", it is vibrating.

[0162] Also, as in the case of FIG. 9, the phase detection value θ is inappropriate, so the system voltage V E The phase difference Δθ continues to increase after the recovery of the power grid. As a result, the voltage VD is vibrating.

[0163] And the voltage measurement value V at the grid connection point GCP D In this case, distortion occurs and the amplitude of the signal increases to a level at which the power conversion device 40 stops due to overvoltage.

[0164] In this way, the control device according to the comparative example reduces the system voltage V E When an accident occurs in the power grid 20 in which the output voltage drops to zero, the output current of the power conversion device 40 cannot be appropriately controlled. As a result, the power conversion device 40 may stop due to an overvoltage, and the power supply system 10 may not be able to continue operating.

[0165] [Control results by the control device according to the embodiment] A specific example of the control result of the output current of the power conversion device 40 by the control device 60 according to the embodiment will be described with reference to FIG.

[0166] FIG. 13 is a time chart showing an example of the control result of the output current of the power conversion device 40 by the control device 60 according to the embodiment.

[0167] In this example, an accident such as a short circuit or a ground fault occurs in the power grid 20 at time t51 in the time chart of FIG. 13, and the grid voltage V E falls to zero, and then at time t52, the grid voltage V E has returned to normal.

[0168] As shown in FIG. 13, when a time t51 occurs in the power grid 20, the grid voltage V E However, as described above, due to the influence of the impedance Z between the interconnection point GCP and the power system 20, the voltage measurement value V D Therefore, after time t51, the phase difference Δθ between the phase detection value θ and the system phase Θ increases, and as a result, the frequency detection value f inside the PLL unit 6037 sticks to the upper limit.

[0169] However, in this example, the positive-phase d-axis voltage measurement value V d + and the positive-phase q-axis voltage measurement value V q + As the d-axis current command value I d * is greatly limited, and the current command value I * is disabled.

[0170] As a result, after the occurrence of a fault in the power system 20, the amplitude of the output current (current measurement value I) of the power conversion device 40 drops significantly and converges to zero, and the voltage measurement value V of the interconnection point GCP D The amplitude of Vq drops significantly and converges to zero. As a result, the positive-phase q-axis voltage Vq, which had been rising, reverses and drops, and the detected frequency value f, which had been rising, drops. Furthermore, as the positive-phase q-axis voltage Vq drops, the conditions for performing freewheeling are met, and the detected frequency value f is fixed to the rated frequency f1 of the power system 20.

[0171] After that, at time t52, the system voltage V E When the state returns to normal, the output current of the power conversion device 40 increases transiently.

[0172] After power grid 20 recovers from the fault, the positive-phase d-axis voltage measurement value V d + and the positive-phase q-axis voltage measurement value V q + rises and approaches the appropriate value. Also, the positive-phase d-axis voltage measurement value V d + and the positive-phase q-axis voltage measurement value V q + As the voltage rises, the condition for performing the freewheeling operation is no longer met, and the PLL unit 6037 starts normal operation, so the phase difference Δθ decreases, and the phase detection value θ and the frequency detection value f approach their appropriate values. As a result, the transient increase in the output current of the power conversion device 40 subsides.

[0173] In addition, after the power grid 20 recovers from the fault, the positive-phase d-axis voltage measurement value Vd + and the positive-phase q-axis voltage measurement value V q + As the d-axis current command value I increases and approaches the appropriate value, the current command limiting unit 604 operates to limit the d-axis current command value I d * The current command ON / OFF switching unit 605 operates to substantially remove the restriction on the current command value I * As a result, the output current of the power conversion device 40 is restored.

[0174] In this way, the control device 60 according to this embodiment controls the system voltage V E When a fault occurs in the power grid 20, causing the grid voltage V to drop to zero, the output current of the power conversion device 40 can be appropriately controlled by the current command limiting unit 604, the current command ON / OFF switching unit 605, and the PLL unit 6037, which switch between normal operation and freewheeling operation. E In the event of an accident in the power grid 20 in which the voltage V drops to zero, the power system 1 can be stabilized, the power supply system 10 can continue to operate, and the system voltage V E When the control is restored, the normal control state can be restored stably.

[0175] [Other embodiments] Another embodiment will now be described.

[0176] The above-described embodiment may be modified or changed as appropriate. Hereinafter, examples in which the above-described embodiment is modified or changed will be referred to as "modified examples" for convenience.

[0177] For example, in the above-described embodiment, either the current command limiting unit 604 or the current command ON / OFF switching unit 605 may be omitted.

[0178] In the above-described embodiment and its modifications, the freewheel determination unit 6036 may be omitted, and the PLL unit 6037 may not perform the freewheel operation. In this case, the multiplier 6037B may be omitted, and the output of the PI regulator with limiter (adjustment amount ΔfPU ) is directly input to the phase calculation unit 6037C, and the reset function of the integrator of the PI regulator with limiter 6037A is omitted.

[0179] In the above-described embodiment and its modified example, the current command limiting unit 604 limits the d-axis current command value I d * Instead of limiting the output current of the power conversion device 40, the output current of the power conversion device 40 may be limited (specifically, reduced) by changing a control parameter such as a control gain of the current control unit 606. Specifically, for example, the control device 60 (current control unit 606) uses a variable gain, and normally sets the gain to "1", but when the magnitude of the positive-phase voltage drops, changes the gain setting to a value smaller than "1", thereby limiting (i.e., reducing) the output current of the power conversion device 40.

[0180] In the above-described embodiment and its modifications, the control device 60 may employ a known DC-type ACR unit instead of the AC-ACR unit 6063.

[0181] [Effect] A control device, a power conversion device, and a control method according to this embodiment will be described.

[0182] In a first aspect of this embodiment, there is provided a control device for controlling a power conversion device having one end connected to a DC power source and the other end connected to a power grid, the control device performing power conversion between DC at the one end and AC at the other end. The control device is, for example, the control device 60 described above. The DC power source is, for example, the DC power source 30 described above. The power grid is, for example, the power grid 20. The power conversion device is, for example, the power conversion device 40 described above. Specifically, the control device includes a phase detector, a current controller, and a first limiter. The phase detector is, for example, the phase detector 603 described above. The current controller is, for example, the current controller 606 described above. The first limiter is, for example, the current command limiter 604 described above. More specifically, the phase detector detects the phase of the voltage at an interconnection point between a power supply system including the power conversion device and the power grid based on a measured value of the voltage at the interconnection point. The power supply system is, for example, the power supply system 10 described above. The interconnection point is, for example, the above-mentioned interconnection point GCP. The measured voltage of the interconnection point is, for example, the above-mentioned voltage measurement value V D The phase of the voltage at the interconnection point is the above-mentioned phase θ. The current control unit controls the output current based on the phase of the voltage at the interconnection point and a command value of the output current of the power conversion device. The command value is, for example, the above-mentioned current command value I * The first limiting unit limits the output current in response to a decrease in the magnitude of the measured positive-phase voltage at the interconnection point. The magnitude of the measured positive-phase voltage is, for example, a steady-state component sV d + is.

[0183] For example, even if the system voltage drops significantly when an accident such as a short circuit or a ground fault occurs in the power system, the voltage at the interconnection point may be maintained at a relatively high level depending on conditions such as the impedance between the power system and the interconnection point. In this case, if the phase of the voltage at the interconnection point is detected based on the voltage at the interconnection point that is completely unrelated to the phase of the system voltage, a current will continue to be output from the power conversion device, and when the system voltage is restored, this current may fluctuate the phase of the voltage in the power system, which may result in an overcurrent or overvoltage in the power system.

[0184] In response to this, the control device can limit the current command value in accordance with a decrease in the magnitude of the positive-sequence voltage at the interconnection point due to a decrease in the grid voltage. Therefore, when an accident such as a short circuit or a ground fault occurs in the power grid, the control device can suppress (i.e., throttle) the output current from the power conversion device and suppress phase fluctuations in the voltage of the power grid, thereby suppressing overcurrents and overvoltages in the power grid. Therefore, the control device can appropriately respond to accidents in the power grid for power conversion devices that exchange power with the power grid.

[0185] In a second aspect of this embodiment, based on the first aspect described above, the first limiting unit may limit the active current command value to at least one of a positive upper limit value that is smaller than the rated current of the power conversion device and a negative lower limit value that is larger than the inverted value of the rated current, in response to a decrease in the magnitude of the measured positive-phase voltage. HL and lower limit I LL The current control unit may control the output current based on the command value after the limiting by the first limiting unit.

[0186] This allows the control device to limit the current command value in accordance with the decrease in the magnitude of the positive-sequence voltage at the interconnection point.

[0187] In a third aspect of the present embodiment, based on the first or second aspect described above, the first limiting unit may limit the output current when the magnitude of the measured value of the positive-phase voltage is smaller than a first threshold value that is smaller than a value corresponding to a rated voltage of the power grid. The first threshold value is, for example, the threshold value Th2 described above.

[0188] This allows the control device to limit the output current of the power conversion device only when it is necessary to reduce the output current of the power conversion device.

[0189] In addition, in a fourth aspect of this embodiment, based on any one of the first to third aspects described above, the first limiting unit may linearly increase the degree of limiting the output current as the magnitude of the measured value of the positive-phase voltage decreases.

[0190] This allows the control device to mitigate the impact on the power grid caused by limiting the output current of the power conversion device in response to a decrease in the magnitude of the measured positive-phase voltage.

[0191] In a fifth aspect of the present embodiment, assuming any one of the first to fourth aspects described above, when a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied, the phase detector may detect the phase of the voltage at the interconnection point by updating the phase of the voltage at the interconnection point so as to advance it by an angular frequency corresponding to a rated frequency of the power grid or a predetermined value based on a past detected value of the frequency of the power grid. The phase of the power grid is, for example, the phase Θ described above. The rated frequency of the power grid is, for example, the rated frequency f1 described above. The predetermined value based on a past detected value of the frequency of the power grid is, for example, the frequency trend value of the power grid 20 described above.

[0192] This allows the control device to suppress the increase in the deviation between the phase of the voltage at the interconnection point and the phase of the system voltage under conditions where the detected value of the phase of the interconnection point cannot be synchronized with the phase of the system voltage, for example, due to the occurrence of an accident such as a short circuit or ground fault in the power system.

[0193] In a sixth aspect of the present embodiment, based on the fifth aspect described above, the phase detector may detect the phase by updating the phase so as to advance it at an angular frequency corresponding to a rated frequency of the power grid when the magnitude of the measured value of the positive-sequence voltage is equal to or less than a second threshold value that is smaller than a value corresponding to a rated voltage of the power grid, for example, the second threshold value being the threshold value Th1 described above.

[0194] This allows the control device to suppress the increase in the deviation between the phase of the voltage at the interconnection point and the phase of the system voltage under conditions where the detected value of the phase of the interconnection point cannot be synchronized with the phase of the system voltage, for example, due to the occurrence of an accident such as a short circuit or ground fault in the power system.

[0195] Furthermore, in a seventh aspect of this embodiment, on the premise of the fifth or sixth aspect described above, the control device may include a second limiting unit. The second limiting unit is the freewheel determining unit 6036. Specifically, the phase detecting unit may include an adjusting unit and a phase calculating unit. The adjusting unit is, for example, the above-described PI regulator with limiter 6037A. The phase calculating unit is, for example, the above-described phase calculating unit 6037C. More specifically, the adjusting unit may adjust a value corresponding to the frequency or angular frequency of the voltage at the interconnection point based on the rated frequency of the power grid or a rated value of an angular frequency corresponding to the rated frequency, so that the q-axis component of the positive-sequence voltage in a dq rotating coordinate system based on the phase of the voltage at the interconnection point follows zero. The q-axis component of the positive-sequence voltage may be, for example, the above-described positive-sequence q-axis voltage V q +* The rated frequency of the power grid is, for example, the above-mentioned rated frequency f1. The rated value of the angular frequency is, for example, the above-mentioned angular frequency ω1. The phase calculation unit may calculate the phase of the voltage at the interconnection point based on the value adjusted by the adjustment unit. The second limiting unit may limit the operation of the adjustment unit when a condition is established that indicates that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid.

[0196] This allows the control device to suppress the increase in the deviation between the phase of the voltage at the interconnection point and the phase of the system voltage under conditions where the detected value of the phase of the interconnection point cannot be synchronized with the phase of the system voltage, for example, due to the occurrence of an accident such as a short circuit or ground fault in the power system.

[0197] In an eighth aspect of the present embodiment, based on the seventh aspect, the adjusting unit may adjust a value corresponding to a frequency or an angular frequency of the voltage at the interconnection point based on a time integral of a q-axis component of the positive-sequence voltage. The second limiting unit may reset the time integral to zero when a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied.

[0198] As a result, when the control device returns to a state where it can synchronize the phase of the voltage at the interconnection point with the phase of the power system, the time integration of the adjustment unit can prevent the detected value of the phase of the voltage at the interconnection point from being suddenly adjusted.

[0199] In addition, in a ninth aspect of the present embodiment, on the premise of any one of the first to eighth aspects described above, the control device may include a third limiting unit. The third limiting unit is, for example, the above-described current command on / off switching unit 605. Specifically, the third limiting unit may limit the command value to zero when a condition is established indicating that the phase detection unit cannot synchronize the phase of the voltage at the interconnection point with the phase of the power grid.

[0200] As a result, the control device can limit the current command value to zero when, for example, a drop in the grid voltage makes it impossible to synchronize the phase of the voltage at the interconnection point with the phase of the grid voltage. Therefore, the control device can limit the output current from the power conversion device to zero when an accident such as a short circuit or a ground fault occurs in the power grid, thereby suppressing phase fluctuations in the voltage of the power grid. Therefore, the control device can suppress overvoltage in the power grid.

[0201] Furthermore, in a tenth aspect of this embodiment, based on the above-described ninth aspect, when the phase detection unit transitions to a state where a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power system is not satisfied, the third limiting unit may cancel the state where the command value is zero after a predetermined delay time has elapsed, and when the condition transitions to a state where it is satisfied, transition the command value to a state where it is zero without a delay time.

[0202] This allows the control device to prevent frequent switching between a state in which the output current of the power conversion device is limited to zero and a state in which the limit is lifted.

[0203] Furthermore, in an eleventh aspect of this embodiment, assuming either one of the ninth or tenth aspects described above, the third limiting unit may limit the command value to zero when either the d-axis component or the q-axis component of the positive sequence voltage in a dq rotating coordinate system based on the phase of the voltage at the interconnection point detected by the phase detection unit deviates from a predetermined normal range.

[0204] This allows the control device to limit the output current of the power conversion device to zero in a situation where the phase detection value of the voltage at the interconnection point cannot be synchronized with the phase of the interconnection voltage.

[0205] Also, in a twelfth aspect of the present embodiment, there is provided a power conversion device including a main circuit unit, a phase detection unit, a current control unit, and a first limiting unit. The power conversion device is, for example, the above-described power conversion device 40. The main circuit unit is, for example, the above-described inverter circuit 42. The phase detection unit is, for example, the above-described phase detection unit 603. The current control unit is, for example, the above-described current control unit 606. The first limiting unit is, for example, the above-described current command limiting unit 604. Specifically, the main circuit unit has one end connected to a DC power source and the other end connected to a power grid, and performs power conversion between DC on the one end side and AC on the other end side. Furthermore, the phase detection unit detects the phase of the voltage at a grid-connection point between a power supply system including the power conversion device and the power grid based on a measured value of the voltage at the grid-connection point. The power supply system is, for example, the above-described power supply system 10. The grid-connection point is, for example, the above-described grid-connection point GCP. The measured value of the voltage at the grid-connection point is, for example, the above-described voltage measurement value V D The phase of the voltage at the interconnection point is the above-mentioned phase θ. The current control unit controls the output current based on the phase of the voltage at the interconnection point and a command value of the output current of the power conversion device. The command value is, for example, the above-mentioned current command value I * The first limiting unit limits the output current in response to a decrease in the magnitude of the measured positive-phase voltage at the interconnection point. The magnitude of the measured positive-phase voltage is, for example, a steady-state component sV d + is.

[0206] As a result, the power conversion device achieves the same functions and effects as the control device of the first aspect described above.

[0207] Furthermore, with respect to the power conversion device, on the premise of the twelfth aspect, aspects similar to the second to eleventh aspects of the control device can be realized.

[0208] As a result, the power conversion device achieves the same functions and effects as the control devices of the second to eleventh aspects described above.

[0209] In addition, a thirteenth aspect of the present embodiment provides a control method for controlling a power conversion device having one end connected to a DC power source and the other end connected to a power grid, the power conversion device performing power conversion between DC at the one end and AC at the other end. The DC power source is, for example, the DC power source 30 described above. The power grid is, for example, the power grid 20. The power conversion device is, for example, the power conversion device 40 described above. Specifically, the control method includes a phase detection step, a current control step, and a first limiting step. More specifically, in the phase detection step, the phase of the voltage at a grid connection point between a power supply system including the power conversion device and the power grid is detected based on a measurement value of the voltage at the grid connection point. The power supply system is, for example, the power supply system 10 described above. The grid connection point is, for example, the grid connection point GCP described above. The measurement value of the voltage at the grid connection point is, for example, the measurement value of the voltage V described above. D The phase of the voltage at the interconnection point is the above-mentioned phase θ. In the current control step, the output current is controlled based on the phase of the voltage at the interconnection point and a command value of the output current of the power conversion device. The command value is, for example, the above-mentioned current command value I * In the first limiting step, the output current is limited in accordance with a decrease in the magnitude of the measured value of the positive-phase voltage at the interconnection point.

[0210] As a result, the control method has the same functions and effects as the control device of the first aspect described above.

[0211] Also, with regard to the control method, on the premise of the above-mentioned thirteenth aspect, aspects similar to the second to eleventh aspects of the control device can be realized.

[0212] As a result, the control method has the same functions and effects as the control devices of the second to eleventh aspects described above.

[0213] Although the embodiments have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist described in the claims. [Explanation of symbols]

[0214] 1. Power System 10 Power System 20 Power system 30 DC power supply 40 Power conversion device 42 Inverter circuit 44 Gate Circuit 50 AC filter 60 Control device 602 Line-to-3 phase converter 603 Phase detection unit 604 Current command limiter 605 Current command on / off switching unit 606 Current control section 607 PWM conversion unit 6031 3-phase to 2-phase converter 6032 Positive sequence dq conversion unit 6033 Positive Phase Non-Interfering Cell 6034 Inverted phase dq conversion unit 6035 Reverse Phase Non-Interference Cell 6036 Freewheel Judgment Unit 6036A Positive-Sequence Voltage Amplitude Calculation Unit 6036B Judgment section 6037 PLL section 6037A PI Regulator with Limiter 6037B Multiplier 6037C Phase calculation section 6051 Comparator 6052 Comparator 6053 AND operator 6054 Comparator 6055 Monostable 6056 AND operator 6057 On Delay 6061 Switch section 6062 2-phase to 3-phase converter 6063 AC-ACR section 6063a AC-ACR section 6063b AC-ACR section 6063c AC-ACR section

Claims

1. A control device for controlling a power conversion device having one end connected to a DC power source and the other end connected to a power grid, the control device performing power conversion between DC on the one end side and AC on the other end side, a phase detection unit that detects a phase of a voltage at an interconnection point between the power supply system including the power conversion device and the power grid based on a measured value of the voltage at the interconnection point; a current control unit that controls the output current based on a phase of the voltage at the interconnection point and a command value of the output current of the power conversion device; a first limiting unit that limits the output current in response to a decrease in the magnitude of a measured value of a positive-phase voltage at the interconnection point; When a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied, the phase detection unit detects the phase of the voltage at the interconnection point by updating the phase so as to advance the phase of the voltage at the interconnection point at an angular frequency corresponding to a rated frequency of the power grid or a predetermined value based on a past detection value of the frequency of the power grid. Control device.

2. the first limiting unit limits the active current command value to at least one of a positive upper limit value that is smaller than a rated current of the power conversion device and a negative lower limit value that is larger than a positive / negative inverted value of the rated current, in response to a decrease in the magnitude of the measured positive-phase voltage; the current control unit controls the output current based on the command value after the limiting by the first limiting unit. The control device according to claim 1 .

3. the first limiting unit limits the output current when the magnitude of the measured positive-phase voltage is smaller than a first threshold value that is smaller than a value corresponding to a rated voltage of the power grid. The control device according to claim 1 or 2.

4. the first limiting unit linearly increases the degree of limiting the output current as the magnitude of the measured positive-phase voltage decreases; The control device according to claim 1 or 2.

5. the phase detection unit detects the phase by updating the phase so as to advance it at an angular frequency corresponding to a rated frequency of the power grid when the magnitude of the measured value of the positive-sequence voltage is equal to or less than a second threshold value that is smaller than a value corresponding to a rated voltage of the power grid, or is less than the second threshold value. The control device according to claim 1 or 2.

6. a second restriction; The phase detection unit an adjustment unit that adjusts a value corresponding to the frequency or angular frequency of the voltage at the interconnection point based on a rated frequency of the power grid or a rated value of an angular frequency corresponding to the rated frequency so that a q-axis component of the positive-phase-sequence voltage in a dq rotating coordinate system based on the phase of the voltage at the interconnection point follows zero; a phase calculation unit that calculates a phase of the voltage at the interconnection point based on the value adjusted by the adjustment unit, the second limiting unit limits the operation of the adjusting unit when a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied. The control device according to claim 1 or 2.

7. the adjusting unit adjusts a value corresponding to a frequency or an angular frequency of the voltage at the interconnection point based on a time integral of a q-axis component of the positive-sequence voltage; The second limiting unit resets the time integral to zero when a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied. The control device according to claim 6.

8. a third limiting unit that limits the command value to zero when a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid by the phase detection unit is satisfied; The control device according to claim 1 or 2.

9. the third limiting unit, when the phase detection unit transitions to a state where a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power system is not satisfied, cancels the state where the command value is zero after a predetermined delay time has elapsed, and when the condition transitions to a state where the condition is satisfied, transitions the command value to a state where it is zero without a delay time; The control device according to claim 8.

10. the third limiting unit limits the command value to zero when either a d-axis component or a q-axis component of the positive-sequence voltage in a dq rotating coordinate system based on the phase of the voltage at the interconnection point detected by the phase detecting unit deviates from a predetermined normal range. The control device according to claim 8.

11. a main circuit unit having one end connected to a DC power source and the other end connected to a power grid, and performing power conversion between DC at the one end and AC at the other end; a phase detection unit that detects the phase of a voltage at an interconnection point between a power supply system including a power conversion device and the power grid based on a measurement value of the voltage at the interconnection point; a current control unit that controls the output current based on a phase of the voltage at the interconnection point and a command value of the output current of the power conversion device; a first limiting unit that limits the output current in response to a decrease in the magnitude of a measured value of a positive-phase voltage at the interconnection point; When a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied, the phase detection unit detects the phase of the voltage at the interconnection point by updating the phase so as to advance the phase of the voltage at the interconnection point at an angular frequency corresponding to a rated frequency of the power grid or a predetermined value based on a past detection value of the frequency of the power grid. Power conversion device.

12. A control method for controlling a power conversion device having one end connected to a DC power source and the other end connected to a power grid, the power conversion device performing power conversion between DC on the one end side and AC on the other end side, the method comprising: a phase detection step of detecting a phase of a voltage at an interconnection point between the power supply system including the power conversion device and the power grid based on a measurement value of the voltage at the interconnection point; a current control step of controlling the output current based on a phase of the voltage at the interconnection point and a command value of the output current of the power conversion device; a first limiting step of limiting the output current in response to a decrease in the magnitude of a measured positive-sequence voltage at the grid-connection point; In the phase detection step, when a condition indicating that the phase of the voltage at the interconnection point cannot be synchronized with the phase of the power grid is satisfied, the phase of the voltage at the interconnection point is detected by updating the phase so as to advance the phase of the voltage at the interconnection point at an angular frequency corresponding to a rated frequency of the power grid or a predetermined value based on a past detection value of the frequency of the power grid. Control method.

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