Power conversion system

Abstract

To provide a power conversion system capable of synchronizing a power conversion unit and a power system so as to stably shift from a self-sustained operation state to a grid-connected operation state.SOLUTION: A control unit 11 is, in a transition period of switching from a self-sustained operation state to a grid-connected operation state, configured to perform a control such that a difference between a value corresponding to each of an amplitude value Vout, a frequency fgrid, and a phase θgrid of an output voltage and a value corresponding to each of an amplitude value Vgrid, a frequency fgrid, and a phase θgrid of a voltage of an interconnection point is equal to or less than a predetermined interconnection threshold value on the basis of a value of an amplitude value Vout of the output voltage detected by an output detection unit D2, a frequency fout, and a phase θout, and a value of an amplitude value Vgrid of an interconnection point voltage detected by an interconnection point detection unit D1 in an interconnection point where a power system 1 and a power conversion unit 10 are connected, a frequency fgrid, and a phase θgrid.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power conversion system, and more particularly to a power conversion system that switches between stand-alone operation and grid-connected operation to supply power to a load. [Background technology]

[0002] BACKGROUND ART Conventionally, there is known a power conversion system that switches between an independent operation and a grid-connected operation to supply power to a load (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a distributed power system (power conversion system) that interconnects a distributed power source including a solar cell and a power storage unit with a grid power source to supply power to household appliances as a load. The power conversion system of Patent Document 1 also includes a power conditioner that transfers power between the distributed power source and the grid power source, and operates in grid-connected mode with the grid power source. The power conversion system of Patent Document 1 also includes a detection means for detecting an abnormality in the grid power source and controls the opening and closing of a switching means between the load and the grid power source based on the output of the detection means. Thus, when an abnormality occurs in the grid power source, the power conversion system of Patent Document 1 switches to stand-alone operation using the distributed power source by opening the switching means between the load and the grid power source, thereby supplying power to the load. Furthermore, when the power conversion system of Patent Document 1 detects restoration of the grid power source during stand-alone operation, it closes the switching means between the load and the grid power source and switches to grid-connected operation, thereby supplying power to the load. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-23673 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, Patent Document 1 discloses a configuration in which, when restoration of the grid power supply is detected during isolated operation, a switching device between the load and the grid power supply is closed to switch to grid-connected operation. However, Patent Document 1 does not disclose a detailed control configuration for switching from isolated operation to grid-connected operation. Therefore, if at least one of the amplitude, frequency, and phase of the voltage in the local grid and the power grid is not synchronized, the voltage supplied to the load may become unstable when grid-connected operation is started, which may result in the load stopping. Therefore, there is a demand for a power conversion system that can synchronize the power conversion unit with the power grid so as to stably transition from an isolated operation state to a grid-connected operation state.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a power conversion system that is capable of synchronizing a power conversion unit with a power grid so as to stably transition from an independent operation state to a grid-connected operation state. [Means for solving the problem]

[0007] In order to achieve the above object, a power conversion system according to one aspect of the present invention includes: a storage unit that stores DC power supplied from the power grid in a grid-connected operation state in which AC power is supplied from the power grid; a power conversion unit that converts the AC power supplied from the power grid into DC power in the grid-connected operation state, and that converts the DC power supplied from the storage unit into AC power and outputs it to a load in an independent operation state in which the AC power supplied from the power grid is cut off; and a control unit, wherein during a transition period when switching from the independent operation state to the grid-connected operation state, the control unit is configured to perform control to keep differences between values ​​corresponding to the amplitude, frequency, and phase of the output voltage supplied from the storage unit, output by the power conversion unit, and detected by the output detection unit, and values ​​of the amplitude, frequency, and phase of a interconnection point voltage detected by a interconnection point detection unit at an interconnection point where the power grid and the power conversion unit are connected, to be equal to or less than a predetermined interconnection threshold value.

[0008] In a power conversion system according to one aspect of the present invention, as described above, the control unit is configured to perform control during a transition period from an isolated operation state to a grid-connected operation state, based on the amplitude, frequency, and phase values ​​of the output voltage supplied from the power storage unit, output by the power conversion unit, and detected by the output detection unit, and the amplitude, frequency, and phase values ​​of the interconnection point voltage detected by the interconnection point detection unit at the interconnection point where the power grid is connected to the power conversion unit, to control the differences between the amplitude, frequency, and phase of the output voltage and the amplitude, frequency, and phase of the voltage at the interconnection point to be equal to or less than a predetermined interconnection threshold. This allows for synchronization by detecting and comparing all of the amplitude, frequency, and phase of the output voltage output from the power conversion unit and the voltage at the interconnection point connected to the power grid during the transition period from the isolated operation state to the grid-connected operation state, thereby enabling control to be performed to prevent voltage instability even when the local grid is connected to the power grid. As a result, the power conversion unit and the power grid can be synchronized to ensure a stable transition from the isolated operation state to the grid-connected operation state.

[0009] In the power conversion system according to the above aspect, the control unit is preferably configured to generate control coefficients based on transition input values ​​generated based on the amplitude, frequency, and phase of the voltage at the interconnection point when generating target values ​​for the amplitude, frequency, and phase of the output voltage during the transition period, and to perform control based on the control coefficients to keep differences between the values ​​corresponding to the amplitude, frequency, and phase of the output voltage and the values ​​corresponding to the amplitude, frequency, and phase of the voltage at the interconnection point equal to or less than a predetermined interconnection threshold. With this configuration, the control coefficients are used to correct the target values ​​based on the transition input values ​​used during the transition period, making it possible to easily synchronize the output voltage output from the power conversion unit with the voltage at the interconnection point connected to the power grid.

[0010] In this case, the control unit is preferably configured to generate a control coefficient during the transition period by additionally inputting a transition input value without switching the target value in the isolated operation state. Here, for example, if a switch or the like is used to switch between the target value in the isolated operation state and the corrected target value in the transition period, there may be a period of discontinuity in control, which may result in the load being stopped during the period when power supply is stopped. In contrast, with the above configuration, the target value in the isolated operation state and the corrected target value in the transition period are continuously changed, so that power can be supplied to the load without interruption even when transitioning to the grid-connected operation state.

[0011] In the power conversion system that generates a control coefficient by additionally inputting a transition input value, the control unit is preferably configured to acquire the control coefficient during the transition period based on the transition input value that is generated based on a value corresponding to the phase of the voltage at the interconnection point and a value corresponding to a phase target value for the generated output voltage. With this configuration, the control coefficient for synchronizing the output voltage output from the power conversion unit and the voltage at the interconnection point connected to the power grid can be easily generated based on the transition input value that is generated based on the output voltage output from the power conversion unit and the target value of the voltage at the interconnection point connected to the power grid, thereby facilitating synchronization.

[0012] In the power conversion system that generates a control coefficient by additionally inputting a transition input value, the control unit is preferably configured to generate a corrected active power target value during the transition period by inputting a value corresponding to frequency from the transition input values ​​to an active power target value used to generate a frequency target value for the output voltage, and to perform control based on the corrected active power target value to keep the difference between the value corresponding to the frequency of the output voltage and the value corresponding to the frequency of the voltage of the power grid equal to or less than a frequency threshold value serving as a predetermined interconnection threshold. With this configuration, the frequency of the output voltage output from the power conversion unit can be easily synchronized with the frequency of the voltage at an interconnection point connected to the power grid based on the corrected active power target value used during the transition period.

[0013] In the power conversion system that generates a control coefficient by additionally inputting a transition input value, the control unit is preferably configured to generate a phase correction value during the transition period by inputting a value corresponding to the phase of the transition input value for an active power target value used to generate a phase target value for the output voltage, and to perform control based on the phase correction value to keep the difference between the value corresponding to the phase of the output voltage and the value corresponding to the phase of the voltage of the power grid equal to or less than a phase threshold as a predetermined interconnection threshold. With this configuration, the phase of the frequency of the output voltage output from the power conversion unit can be easily synchronized with the phase of the frequency of the voltage at an interconnection point connected to the power grid based on the phase correction value used during the transition period.

[0014] In this case, the control unit preferably performs control to provide a virtual synchronous generator function that applies a virtual inertial force to the operation of the power conversion unit, and incorporates a value corresponding to the phase of the transition input value into an inertia term, which is a control term for generating the inertial force, thereby controlling the difference between the value corresponding to the phase of the output voltage and the value corresponding to the phase of the power grid voltage to be equal to or less than a phase threshold. This configuration allows the power conversion unit to generate an inertial force similar to that of a power grid using a synchronous generator, thereby reducing power instability even when load fluctuations occur, compared to when a generator without inertial force is used. Here, if the value corresponding to the phase of the transition input value is input before the inertia term, the gain setting value for the value corresponding to the phase of the transition input value is affected by a coefficient related to the generation of inertial force in the inertia term, making it difficult to adjust the value corresponding to the phase of the transition input value. Therefore, by inputting the value corresponding to the phase of the transition input value so that it is incorporated into the inertia term, the value corresponding to the phase of the transition input value can be easily adjusted.

[0015] In the power conversion system that generates the control coefficients, the control unit is preferably configured to generate the control coefficients during a transition period based on transition input values ​​generated based on values ​​corresponding to the amplitude, frequency, and phase of the voltage at the interconnection point and values ​​corresponding to the amplitude, frequency, and phase of a boosted output voltage obtained by boosting the output voltage using a transformer. Here, due to resistance components contained in the transformer, the output voltage boosted by the transformer may differ from the design value of the output voltage output from the power conversion unit. However, with the above configuration, the output voltage boosted by the transformer can be taken into account when synchronizing the output voltage output from the power conversion unit with the voltage at the interconnection point to which power supplied from the power grid is applied, thereby enabling more accurate synchronization of the output voltage and the interconnection point voltage.

[0016] In the power conversion system that generates the control coefficients, the control unit is preferably configured to start acquiring transition input values ​​when, in an isolated operation state, the difference between values ​​corresponding to the amplitude, frequency, and phase of the output voltage and values ​​corresponding to the amplitude, frequency, and phase of the voltage at the interconnection point becomes equal to or less than a predetermined transition operation threshold value that is greater than a predetermined interconnection threshold value. This configuration allows the transition operation control to be started based on a relatively small value that is equal to or less than the transition operation threshold value that is greater than the predetermined interconnection threshold value, eliminating the need to wait for the difference between the output voltage and the voltage at the interconnection point to narrow to or below the interconnection threshold value. As a result, the transition operation control for synchronizing the output voltage and the voltage at the interconnection point can be started in a relatively short time.

[0017] In the power conversion system according to the above aspect, the control unit is preferably configured to start control for the grid-connected operation state when, during the transition period, differences between values ​​corresponding to the amplitude, frequency, and phase of the output voltage and values ​​corresponding to the amplitude, frequency, and phase of the voltage of the power grid become equal to or less than a predetermined grid-connected threshold. With this configuration, control for the grid-connected operation state is started only when the difference between the output voltage output from the power conversion unit and the voltage at the grid-connected point connected to the power grid becomes a sufficiently small value equal to or less than the grid-connected threshold, thereby enabling grid-connected operation without destabilizing the power.

[0018] In the power conversion system according to the above aspect, the control unit is preferably configured to start control in a grid-connected operation state when, during the transition period, a state in which differences between values ​​corresponding to the amplitude, frequency, and phase of the output voltage and values ​​corresponding to the amplitude, frequency, and phase of the voltage of the power grid remain equal to or less than a predetermined interconnection threshold value for a predetermined set time or more. With this configuration, it is possible to prevent grid-connected operation from being started, for example, when, despite insufficient recovery of the power grid, the difference between the output voltage output from the power conversion unit and the voltage at the interconnection point connected to the power grid momentarily becomes equal to or less than the interconnection threshold value. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a power conversion system that can synchronize a power conversion unit with a power grid so as to stably transition from an isolated operation state to a grid-connected operation state. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing a power conversion system according to a first embodiment. [Figure 2] FIG. 2 is a diagram for explaining the configuration of a power conversion unit according to the first embodiment. [Figure 3] FIG. 3 is a diagram for explaining the operation of a frequency / phase control block according to the first embodiment. [Figure 4] FIG. 3 is a diagram for explaining the operation of a voltage control block according to the first embodiment. [Figure 5] FIG. 10 is a diagram for explaining the configuration of a power conversion unit according to a second embodiment. [Figure 6] FIG. 10 is a diagram for explaining the operation of the frequency / phase control block according to the second embodiment. [Figure 7] FIG. 10 is a diagram for explaining the operation of the voltage control block according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings.

[0022] [First embodiment] The configuration of a power conversion system 100 according to a first embodiment will be described with reference to FIGS.

[0023] As shown in FIG. 1 , the power conversion system 100 includes a power conversion unit 10 and a power storage unit 20. The power conversion system 100 is connected to the power grid 1 via a transformer 40 and an interconnection point switch 41. When the AC power supplied from the power grid 1 is normal, the power conversion system 100 controls the power conversion unit 10 to output power synchronized with the power supplied from the power grid 1 to the load 30 or the power grid 1. In other words, the power conversion system 100 is a system that not only supplies power to the load 30 but also performs reverse power flow to the power grid 1. Furthermore, when an abnormality such as a power outage occurs in the power grid 1, the power conversion system 100 is configured to control the power conversion unit 10 to supply the power supplied from the power storage unit 20 to the load 30. That is, the power conversion system 100 is a system that supplies power supplied by the power system 1 or the power storage unit 20 and controlled by the power conversion unit 10 to the load 30 via the bus 100a and the load switch 31.

[0024] Power system 1 is a power generation system managed by an electric power company, and supplies three-phase AC power generated by a synchronous generator that uses a steam turbine, such as in a thermal power plant. That is, the power generation system of power system 1 has a large inertial force due to the synchronous generator. The voltage amplitude of the AC power supplied from power system 1 to bus 1a is, for example, 6600V.

[0025] The power conversion unit 10 is a PCS (Power Conditioning System) and includes functions as a converter that converts AC power to DC power and an inverter that converts DC power to AC power. This allows the power conversion unit 10 to convert AC power supplied from the power grid 1 into DC power and output it to the power storage unit 20, and also convert DC power supplied from the power storage unit 20 into AC power and output it to the load 30. As shown in FIG. 2 , the power conversion unit 10 also includes a switching circuit 10a, a filter circuit 10b, and a switch 10c. The switching circuit 10a includes a plurality of switching elements (not shown) configured as a three-phase, three-wire bridge circuit, and performs power conversion operations under the control of a control unit 11 (described later). The filter circuit 10b is formed of an inductor L1, an inductor L2, and a capacitor C, and converts a rectangular voltage signal (square wave) output from the switching circuit 10a into a sine wave. The control unit 11 controls the opening and closing of the switch 10c to block the power output from the filter circuit 10b from being supplied to the load 30.

[0026] The power conversion unit 10 also includes a control unit 11 for controlling the power conversion operation. The control unit 11 includes a CPU (Central Processing Unit) as a processor and a storage unit such as a memory having a ROM (Read Only Memory) and a RAM (Random Access Memory). In the first embodiment, as shown in FIG. 2, the control unit 11 includes a frequency / phase control block 11a, a voltage control block 11b, a current control block 11c, and a PWM pulse generation block 11d as functional blocks configured by software to control the switching circuit 10a of the power conversion unit 10.

[0027] The control unit 11 is configured to acquire voltages detected by the interconnection point detection unit D1 and the output detection unit D2 shown in FIG. 1. The control unit 11 also controls the inverter operation of the power conversion unit 10 so that it operates as a virtual synchronous generator. Here, the virtual synchronous generator is a synchronous generator simulation model input as a functional block in the inverter control system so as to virtually realize the inertia (e.g., the resistance of frequency to fluctuations in response to power fluctuations) of a system that generates power using a synchronous generator, such as the power system 1. In this first embodiment, the control unit 11 includes, for example, control blocks such as a governor block B2, an inertia block B3, and a braking block B4 as shown in FIG. 3 in the frequency / phase control block 11a as the simulation model of the synchronous generator.

[0028] The frequency / phase control block 11a included in the control unit 11 shown in FIG. 2 is a functional block that generates a command value (target value) for controlling the frequency and phase output from the power conversion unit 10. The voltage control block 11b is a functional block that generates a command value (target value) for controlling the amplitude of the voltage output from the power conversion unit 10. The current control block 11c is a functional block that performs current control to suppress overcurrent, and controls the active power target value P generated by the frequency / phase control block 11a. ref , phase target value θ ref , and the amplitude target value V generated by the voltage control block 11b ref Based on the inputs, the target value V of the voltage applied to the inductor L1 is calculated. Lref The PWM pulse generation block 11d generates V Lref and the amplitude value V of the output voltage output from the power conversion unit 10 to the load 30. out Based on this, the switching circuit 10a outputs a PWM signal as an operation command value for a switching element (not shown) included in the switching circuit 10a.

[0029] The function of the frequency / phase control block 11a will be described with reference to Fig. 3. The frequency / phase control block 11a receives an actual measured value P outand the active power target value P of the power output from the power conversion unit 10 to the load 30. ref and are input, and the rated frequency f is calculated based on the difference between them. n The frequency target value coefficient A1 to be multiplied by the actual measured value P out and the target active power value P ref For example, a normalized value expressed as a percentage when the set maximum value is set to "1" is used for the frequency target value coefficient A1. The frequency target value coefficient A1 is an example of a "control coefficient" in the claims.

[0030] Furthermore, in order for the power conversion unit 10 to function as a virtual synchronous generator, the generation of the frequency target value coefficient A1 incorporates the outputs of the governor block B2, the inertia block B3, and the braking block B4, which are set in advance as control terms having arbitrary values ​​in the frequency / phase control block 11a. The inertia block B3 is an example of the "inertia term" in the claims. A detailed description of the operation of the control unit 11 to control the voltage frequency and phase will be given later.

[0031] Next, the function of the voltage control block 11b will be described with reference to Fig. 4. The voltage control block 11b includes an output voltage amplitude value V out and a set voltage amplitude value V of the voltage output from the power conversion unit 10 to the load 30. s The difference is acquired at the summing point a11, and the amplitude target value V ref In addition, in the grid-connected operation state, the amplitude target value V ref To generate the set voltage amplitude value V, a power factor control block B5 and a reactive power control block B6 are incorporated as functional blocks configured by software. sis set based on the amplitude value of the voltage for stably operating the load 30, and for example, a value normalized by setting 200V as "1" is input as the voltage amplitude value of the operating voltage of the load 30. A detailed explanation of the operation of the control unit 11 to control the amplitude of the voltage will be given later.

[0032] 1 is a secondary battery capable of charging and discharging (outputting) DC power. For example, the power storage unit 20 is a lithium-ion secondary battery. In a grid-connected operating state in which the power system 1 and the power conversion unit 10 are interconnected and operating, the power storage unit 20 is charged with power supplied from the power system 1 and converted into DC by the power conversion unit 10. In an isolated operating state in which the power system 1 and the power conversion unit 10 are disconnected by the interconnection point switch 41, or in a grid-connected operating state, for example, when the amount of power required by the load 30 increases or when reverse power flow to the power system 1 is performed, the power storage unit 20 discharges power so as to supply DC power to the power conversion unit 10.

[0033] The load 30 is configured to use (consume) AC power supplied from the power system 1 or the power conversion unit 10 via the bus 100a, and includes, for example, various electrical devices in a facility. Note that a plurality of electrical devices are connected as the load 30, and the load 30 operates, for example, with a voltage amplitude of 200V. The load switch 31 is provided to cut off the power supply to the load 30 by controlling the opening and closing operation by the control unit 11, and is controlled by the control unit 11.

[0034] The transformer 40 is a transformer that steps down the voltage amplitude of the AC power supplied from the power system 1 to a voltage amplitude required for the operation of the load 30. In this first embodiment, for example, in order to step down a voltage of 6600 V on the power system 1 side, which is the primary side, to a voltage of 200 V on the load 30 side, which is the secondary side, the transformer 40 is configured to have a winding ratio of 33:1 between the primary side and the secondary side. The interconnection point switch 41 is configured such that its opening and closing operation is controlled by the control unit 11, thereby interrupting the transfer of power at the interconnection point where the power system 1 and the power conversion system 100 are connected.

[0035] (Operations of power conversion unit 10 and control unit 11) 2 to 4, the operation of the power conversion unit 10 controlled by the control unit 11 will be described below. Specifically, the control methods of the control unit 11 will be described in a grid-connected operation state in which the voltage output by the power conversion unit 10 is synchronized with the voltage supplied from the power grid 1, an independent operation state in which the load 30 is operated only by power supply within the local grid in the power conversion system 100, and a transition period in which the independent operation state is transitioned to the grid-connected operation state.

[0036] (Regarding grid-connected operation status) When the power supplied from the power grid 1 is normal, in order to supply the amount of power required by the load 30 or to cause a reverse flow of power to the power grid 1, the control unit 11 in the power conversion unit 10 detects the frequency f of the voltage supplied from the power grid 1 and detected by the interconnection point detection unit D1. grid , phase θ grid , and the amplitude value V grid and obtains the frequency f of the voltage output by the power conversion unit 10. out , phase θ out , and the amplitude value V out In the first embodiment, the control unit 11 uses a frequency / phase control block 11a, a voltage control block 11b, a current control block 11c, and a PWM pulse generation block 11d to generate pulse signals for controlling the operation of the switching circuit 10a in the power conversion unit 10. As a result, the control unit 11 controls the power conversion unit 10 to operate at a frequency f out , phase θ out , and the amplitude value V out The frequency target value f ref , phase target value θ ref , and the amplitude target value V ref is generated.

[0037] In addition, in the grid-connected operation state, the power conversion system 100 is synchronized with the power grid 1 and receives requests from the power company that manages the power grid 1. Therefore, the power output from the power conversion unit 10 is controlled by a predetermined reactive power Q out Specifically, in the first embodiment, in the grid-connected operation state, the reactive power target value Q is set to a predetermined power factor so that the power output by the power conversion unit 10 has a predetermined power factor. ref and the output reactive power Q out The difference between these is the gain coefficient Ki AQR and the integral term 1 / s are input. That is, in the grid-connected operation state, the power conversion system 100 receives the output from the reactive power control block B6 and outputs the amplitude value V out The load 30 is supplied with power in which not only the reactive power value but also the reactive power value is controlled.

[0038] (Regarding autonomous operation) Here, if some abnormality occurs in the power grid 1 and the AC power supplied from the power grid 1 becomes unstable, the control unit 11 receives a signal from the output detection unit D2 that measures the voltage supplied by the power grid 1, and opens the interconnection point switch 41. That is, an isolated operation is started in which the load 30 is operated only by power transfer within the power conversion system 100. This state is called an isolated operation state.

[0039] The control unit 11 switches the switching unit 110a in the ALFC (Automatic Load Frequency Control) block B1 shown in FIG. 6 to "T" in the grid-connected operation state, and switches the switching unit 110a to "F" in the isolated operation state. That is, in the isolated operation state, a control value that was not input in the grid-connected operation state is input to generate the frequency target value coefficient A1. This ALFC block B1 is a control model for frequency control that differs from the simulation model used for virtual synchronous power generation. Note that "F" is input to the switching units 110b and 110c in both the grid-connected state and the isolated operation state, and is switched to "T" only during a transition period, which will be described later.

[0040] In the isolated operation state, the summing point a1 has a set frequency f s and rated frequency f n and the active power target value P ref The correction value S for correcting c The frequency ratio f used to generate s / f n is added and input (subtracted). Note that the set frequency f s The value corresponding to the rated frequency f is set based on the frequency for stably operating the load 30, and for example, the frequency of the supplied power when the power grid 1 is supplying power normally, 59.9 Hz, is used. n As a value corresponding to this, for example, the AC power frequency of 60 Hz used in western Japan is used.

[0041] In addition, in a grid-connected operation state in which the switching unit 110a sets the control mode to "T", the summing point a2 receives the signal S output from the governor block B2. GOV However, in the autonomous operation state where the control mode is set to "F", the correction value Sc is additionally input to the addition point a2. Note that the ALFC block B1 has a coefficient Ki as a gain that can be arbitrarily set by an operator or the like. ALFC and the integral term 1 / s are multiplied, and the frequency f output from the power conversion unit 10 to the load 30 is out at a predetermined set frequency f s The governor block B2 also includes a gain and an integral term, and has the function of suppressing frequency fluctuations.

[0042] Here, the correction value S c is the frequency ratio f from the frequency target value coefficient A1 s / f n The coefficient Ki as the gain inside ALFC block 1 is added to the value obtained by subtracting ALFC and the integral term 1 / s. In the islanded operation state, the active power target value P refSignal S via governor block B2 added in grid-connected operation state from GOV In addition, the correction value S c Therefore, in the isolated operation state, the active power target value P ref Correction value S c The corrected active power target value Pc corrected based on the above is input.

[0043] In the first embodiment, in the state of independent operation, the corrected active power target value Pc and the actual measured value P of the active power in the power output from the power conversion unit 10 to the load 30 are calculated at the summing point a4. out At the summing point a5, the difference between the corrected active power target value Pc and the actual measured value P out The value obtained by multiplying the frequency target value coefficient A1 by the value output from the braking block B4 is the signal S D Then, the value of the summing point a5 is multiplied by the inertia block B3 to generate the frequency target value coefficient A1, which is output to the connection point j2. The inertia block B3 and the braking block B4 contain gain and integral terms and have the function of suppressing frequency fluctuations.

[0044] The frequency / phase control block 11a also calculates the frequency target value coefficient A1 and the rated frequency f n The product of these is used to calculate the frequency target value f for controlling the frequency of the power waveform output from the power conversion unit 10. ref The frequency / phase control block 11a is configured to output the frequency target value coefficient A1 and the rated frequency f n The phase target value θ for controlling the phase of the power waveform output from the power conversion unit 10 is calculated by multiplying the product of ref It is configured to output as

[0045] In this first embodiment, the control unit 11 of the power conversion unit 10 switches the switching unit 110b in the reactive power control block B6 to "T" in the grid-connected operation state, and switches the switching unit 110b to "F" in the independent operation state. As a result, a command input to the summing point a13 in the grid-connected operation state is not input in the independent operation state. That is, in the independent operation state, the voltage control block 11b ref Therefore, in the isolated operation state, the summing point a13 receives the amplitude value V of the output voltage acquired at the summing point a11. out and the set voltage amplitude value V s Only the difference value is entered.

[0046] In the first embodiment, in the independent operation state, the amplitude value V of the output voltage at the summing point a13 out and the set voltage amplitude value V s The difference ΔV between the power converter 10 and the load 30 is multiplied by a control term of an AVR (Automatic Voltage Regulator) block B7. The AVR block B7 includes a proportional control term and an integral term, and calculates the amplitude value V of the voltage output from the power converter 10 to the load 30. out The predetermined voltage amplitude value V s It has the function of bringing it closer to

[0047] At the summing point a14, the set voltage amplitude value V s and the output value A2 of the AVR block B7 are added together. The value of the summing point a14 is directly added to the amplitude target value V ref This amplitude target value V ref A PWM pulse wave for driving the switching circuit 10a is generated based on the output value A2. The output value A2 is an example of the "control coefficient" in the claims.

[0048] (Regarding the transition period) Here, when the power of the power grid 1 starts to be restored and the AC power supplied from the power grid 1 gradually stabilizes, the control unit 11 starts a control mode for a transition period to synchronize and connect the voltage in the power conversion system 100 with the voltage of the power grid 1. Specifically, the control unit 11 controls the frequency f grid and the output voltage frequency f out Difference between the phase θ grid and the phase of the output voltage θ out The difference between the amplitude and the amplitude V grid and the output voltage amplitude V out The difference between these is the frequency f of the output voltage out , phase θ out , and the amplitude value V out If the time period during which the value is within 0.2% of the transition operation threshold continues for 1 second, the control mode for the transition period will be started.

[0049] When the control mode for the transition period is started, the control unit 11 switches the switching units 110b and 110c in the frequency / phase control block 11a and the switching unit 110a in the ALFC block B1 from "F" to "T." As a result, in the frequency / phase control block 11a, the frequency control function in the ALFC block B1 is turned off and input values ​​related to the voltage frequency and phase for the transition period are added. Specifically, at the addition point a7, the frequency f of the voltage at the interconnection point acquired at the addition point a6 is added. grid and the set frequency f as the target value output from the frequency / phase control block 11a. s Therefore, during the transition period, unlike the isolated operation state, the difference Δf between the input and output is input to the summing point a1. s +Δf) / f n is input, and the value multiplied by the control term of the governor block B2 is the active power target value P ref to obtain a corrected active power target value Pc that does not include the correction value Sc. This difference Δf is an example of the "transition input value" and the "value corresponding to the frequency among the transition input values" in the claims.

[0050] At the summing point a8, the voltage phase θ grid and the phase target value θ as a target value output from the frequency / phase control block 11a. ref The difference Δθ between the phase and the proportional gain Kp ph After being multiplied by this, it is input to the summing point a9 between the control constant 1 / (2H) of the inertia block B3 and the integral term, and is used to generate the frequency target value coefficient A1. As described above, the control unit 11 calculates the frequency f of the output voltage using the input values ​​for the transition period (the difference Δf, the difference Δθ, and the difference ΔV) based on the voltage of the interconnection point. out and phase θ out and the frequency of the voltage at the interconnection point f grid and phase θ grid The difference Δθ is an example of the "transition input value" and the "value corresponding to the phase of the transition input value" in the claims.

[0051] Furthermore, when the control mode for the transition period is started, the control unit 11 switches the switching unit 110d in the reactive power control block B6 in the voltage control block 11b from "F" to "T." This causes an input value related to the voltage amplitude for the transition period to be added to the voltage control block 11b. Specifically, at the summing point a10, the amplitude value V of the voltage at the interconnection point acquired at the summing point a9 is added to grid and the set voltage amplitude value V s The difference ΔV between the input value and the output value is input. The difference ΔV is an example of the "transition input value" in the claims.

[0052] During the transition period, unlike the isolated operation state, the addition points a11 and a13 have (V s +ΔV)-V out is input, and the value multiplied by the control term of the AVR block B7 is input as the output value A2 at the summing point a14. Also, during this transition period, (V s +ΔV)-V outis added to the amplitude target value V ref As described above, the control unit 11 uses the input value for the transition period based on the voltage at the interconnection point to calculate the amplitude value V of the output voltage. out and the amplitude value of the voltage at the interconnection point V grid The control is performed to match the two in order to synchronize them.

[0053] Thereafter, the control unit 11 adjusts the frequency f of the voltage of the power grid 1. grid and the output voltage frequency f out Difference between the phase θ grid and the phase of the output voltage θ out The difference between the amplitude and the amplitude V grid and the output voltage amplitude V out The difference between these is the frequency f of the output voltage out , phase θ out , and the amplitude value V out If the time period during which the values ​​of the power supply voltage, power output, and power supply voltage are within 0.05% of the interconnection thresholds (frequency threshold, phase threshold, and amplitude threshold) continues for one second, the control mode for grid-connected operation is initiated. At this time, the control unit 11 closes the interconnection point switch 41 (see FIG. 1).

[0054] As described above, the power conversion system 100 of the first embodiment is configured to generate target values ​​for the voltage amplitude, frequency, and phase using the added input values ​​for the transition period when the transition period begins, and therefore transitions the control mode to a grid-connected operation state while supplying the power required for the operation of the load 30 within the local grid in an autonomous operation state.

[0055] (Effects of the first embodiment) Next, the effects of the first embodiment will be described.

[0056] The power conversion system 100 of the first embodiment described above includes a power storage unit 20 that stores and discharges DC power, a power conversion unit 10 that converts AC power supplied from the power system 1 into DC power and outputs it to the power storage unit 20 in a grid-connected operation state in which AC power is supplied from the power system 1, and converts DC power supplied from the power storage unit 20 into AC power and outputs it to the load 30 in an independent operation state in which the AC power supplied from the power system 1 is cut off, and a control unit 11, and the control unit 11 controls a frequency f of an output voltage supplied from the power storage unit 20 and output by the power conversion unit 10 and detected by an output detection unit D2 during a transition period when switching from the independent operation state to the grid-connected operation state. out , phase θ out , and the amplitude value V out and the frequency f of the interconnection point voltage detected by the interconnection point detection unit D1 at the interconnection point where the power system 1 and the power conversion unit 10 are connected. grid , phase θ grid , and the amplitude value V grid Based on the value of and the frequency of the output voltage f out , phase θ out , and the amplitude value V out and the frequency f of the voltage at the interconnection point. grid , phase θ grid , and the amplitude value V grid and performs control to keep the difference between the values ​​corresponding to each of these at or below a predetermined grid-connection threshold. This makes it possible to detect, compare, and synchronize all of the amplitude, frequency, and phase of the output voltage output from the power conversion unit 10 and the voltage at the interconnection point connected to the power grid 1 during the transition period, thereby enabling control to be performed so that voltage does not become unstable even when the local grid is connected to the power grid 1. As a result, the power conversion unit 10 and the power grid 1 can be synchronized so as to stably transition from an isolated operation state to a grid-connected operation state.

[0057] In the first embodiment, the control unit 11 controls the frequency f of the output voltage during the transition period. out , phase θ out , and the amplitude value V out The target values ​​of each (f ref , θref , V ref ) when generating the voltage frequency f grid , phase θ grid , and the amplitude value V grid and generating a frequency target value coefficient A1 or an output value A2 based on the transition input values ​​(difference Δf, difference Δθ, and difference ΔV) generated based on each of the above. out , phase θ out , and the amplitude value V out and the frequency f of the voltage at the interconnection point. grid , phase θ grid , and the amplitude value V grid The control is configured to control the difference between the values ​​corresponding to each of the above to be equal to or less than a predetermined interconnection threshold value. As a result, the target value (frequency target value f ref , phase target value θ ref and the amplitude target value V ref ) is used, the output voltage output from the power conversion unit 10 and the interconnection point voltage connected to the power grid 1 can be easily synchronized.

[0058] In the first embodiment, the control unit 11 is configured to generate the frequency target value coefficient A1 or the output value A2 by additionally inputting transition input values ​​(differences Δf, Δθ, and ΔV) without switching the target value in the autonomous operation state during the transition period. ref , phase target value θ ref and the set voltage amplitude value V s) and the frequency target value coefficient A1 or output value A2 during the transition period using the switching unit 110a or the like, there may be a period of time when the control is discontinuous, which may cause the load 30 to stop during the period when the power supply is stopped. In contrast, with the above configuration, the target value during the isolated operation state and the target value during the transition period are continuously changed, so that even when performing a transition operation to the grid-connected operation state, power can be supplied to the load 30 without interruption.

[0059] In the first embodiment, the control unit 11 controls the phase θ of the voltage at the interconnection point during the transition period. grid and the phase target value θ for the generated output voltage ref and acquires a frequency target value coefficient A1 based on a difference Δθ which is a transition input value generated based on values ​​corresponding to each of the above. This allows the frequency target value coefficient A1 for synchronizing the output voltage output from the power conversion unit 10 with the voltage at the interconnection point connected to the power grid 1 to be easily generated based on the difference Δθ which is a transition input value generated based on the output voltage output from the power conversion unit 10 and the target value of the voltage at the interconnection point connected to the power grid 1, thereby making it possible to easily perform synchronization.

[0060] In the first embodiment, the control unit 11 adjusts the frequency target value f ref The active power target value P used to generate ref The corrected active power target value P c and the corrected active power target value P c Based on the output voltage frequency f out and the frequency f of the voltage of power system 1. grid The control is configured to control the difference between the corrected active power target value P c Based on this, the frequency f of the output voltage output from the power conversion unit 10 outand the frequency f of the voltage at the interconnection point connected to power grid 1 grid can be easily synchronized.

[0061] In the first embodiment, the control unit 11 adjusts the phase target value θ for the output voltage during the transition period. ref The active power target value P used to generate ref The phase correction value S is obtained by inputting the difference Δθ as a value corresponding to the phase of the transition input value. θ and generate the phase correction value S θ Based on this, the phase of the output voltage θ out and the voltage phase θ of power system 1 grid The phase correction value S used in the transition period is controlled to be equal to or less than the phase threshold value as a predetermined interconnection threshold value. θ Based on this, the phase θ of the frequency of the output voltage output from the power conversion unit 10 out and the phase θ of the voltage frequency at the interconnection point connected to power system 1 grid can be easily synchronized.

[0062] In the first embodiment, the control unit 11 performs control to provide a virtual synchronous generator function that provides a virtual inertial force to the operation of the power conversion unit 10, and incorporates the difference Δθ, which is a value corresponding to the phase among the transition input values, into the inertia block B3, which is a control term for generating an inertial force, thereby controlling the phase θ of the output voltage. out and the voltage phase θ of power system 1 gridThe difference between the value corresponding to the phase difference Δθ and the value corresponding to the phase difference Δθ is controlled to be equal to or less than the phase threshold. This allows the power conversion unit 10 to generate an inertial force similar to that of the power system 1 using a synchronous generator, thereby preventing power instability when fluctuations occur in the load 30 compared to when a generator without inertial force is used. Here, when the difference Δθ as a value corresponding to the phase among the transition input values ​​is input to the upstream stage of the inertia block B3, the gain setting value for the difference Δθ is affected by the coefficient 1 / (2H) related to the generation of inertial force in the inertia block B3, making it difficult to adjust the value corresponding to the difference Δθ. Therefore, by inputting the value corresponding to the phase among the transition input values ​​so that it is incorporated into the inertia block B3, the value corresponding to the difference Δθ can be easily adjusted.

[0063] In the first embodiment, the control unit 11 controls the frequency f of the output voltage in the self-sustained operation state. out , phase θ out , and the amplitude value V out and the frequency f of the voltage at the interconnection point. grid , phase θ grid , and the amplitude value V grid The system is configured to start acquiring the transition input values ​​(differences Δf, Δθ, and ΔV) when the difference between the values ​​corresponding to each of these becomes equal to or less than a predetermined transition operation threshold value that is greater than the predetermined interconnection threshold value. This allows the transition operation control to be started based on a relatively small value that is equal to or less than the transition operation threshold value that is greater than the predetermined interconnection threshold value, so there is no need to wait for the difference between the output voltage and the voltage at the interconnection point to decrease to or below the interconnection threshold value. As a result, the transition operation control for synchronizing the output voltage and the voltage at the interconnection point can be started in a relatively short time.

[0064] In the first embodiment, the control unit 11 controls the frequency f of the output voltage during the transition period. out , phase θ out , and the amplitude value V out and the voltage frequency f of power system 1. grid , phase θ grid, and the amplitude value V grid The control for the grid-connected operation state is started when the difference between the output voltage from the power conversion unit 10 and the voltage at the interconnection point connected to the power grid 1 becomes equal to or less than a predetermined interconnection threshold value. As a result, the control for the grid-connected operation state is started only when the difference between the output voltage from the power conversion unit 10 and the voltage at the interconnection point connected to the power grid 1 becomes a sufficiently small value equal to or less than the interconnection threshold value, so that the grid-connected operation can be performed without causing power instability.

[0065] In the first embodiment, the control unit 11 controls the frequency f of the output voltage during the transition period. out , phase θ out , and the amplitude value V out and the voltage frequency f of power system 1. grid , phase θ grid , and the amplitude value V grid and the difference between the output voltage of the power converter 10 and the voltage at the interconnection point connected to the power grid 1 by chance becomes equal to or less than the interconnection threshold value for a predetermined set time or more, the control in the grid-connected operation state is started. This makes it possible to prevent the grid-connected operation from being started, for example, when the difference between the output voltage of the power converter 10 and the voltage at the interconnection point connected to the power grid 1 by chance becomes equal to or less than the interconnection threshold value, even though the power grid 1 is not fully restored.

[0066] [Second embodiment] Next, a power conversion system 101 according to a second embodiment will be described. As shown in Fig. 5, the power conversion system 101 according to the second embodiment has a similar device configuration to the power conversion system 100 shown in Fig. 1, except that it includes a host control device 50 and an output detection unit D2 detects the power on the primary side (power system 1 side) of the transformer 40. Note that a description of the second embodiment common to the first embodiment will be omitted.

[0067] The second embodiment includes a host control device 50. The host control device 50 includes a CPU (Central Processing Unit) as a processor, and a storage unit such as a memory having a ROM (Read Only Memory) and a RAM (Random Access Memory). In the second embodiment, the host control device 50 is configured to acquire the voltage detected by the interconnection point detection unit D1 and the voltage detected by the output detection unit D2, and to communicate with the control unit 11 of the power conversion unit 10. The host control device 50 is also configured to receive commands from the control unit 11 and perform the opening and closing operation of the interconnection point switch 41.

[0068] In the second embodiment, the amplitude value V of the voltage detected by the output detection unit D2 local is the amplitude value V of the output voltage by the transformer 40. out Here, the transformer 40 includes a resistance component, and some power loss occurs, so the voltage amplitude value V local is the amplitude value of the output voltage V out The amplitude value V of the voltage stepped up by the transformer 40 may differ slightly from the value obtained by simply multiplying it by 33 depending on the winding ratio. local As a value corresponding to this, a value normalized by setting the amplitude value Vgrid of the voltage supplied from the power grid 1, 6600V, to "1" is input.

[0069] As shown in FIG. 6, unlike the first embodiment, the control unit 11 uses a set frequency f s Instead, the frequency of the boosted voltage f local is input, and the phase target value θ is used to generate Δθ input to the switching unit 110c. ref Instead, the phase θ of the boosted voltage local 7, unlike the first embodiment, the voltage control block 11b uses a set voltage amplitude value V s Instead, the amplitude value of the boosted voltage V localTherefore, in the second embodiment, the frequency f of the boosted output voltage obtained by boosting the output voltage by the transformer 40 is local , phase θ local , and the amplitude value V local The other operations are performed in the same manner as in the first embodiment.

[0070] (Effects of the second embodiment) Next, the effects of the second embodiment will be described.

[0071] In the power conversion system 101 of the second embodiment, the control unit 11 controls the frequency f of the voltage at the interconnection point during the transition period. grid , phase θ grid , and the amplitude value V grid and the frequency f of the boosted output voltage obtained by boosting the output voltage by the transformer 40. local , phase θ local , and the amplitude value V local and generate a frequency target value coefficient A1 and an output value A2 based on transition input values ​​(differences Δf, Δθ, and ΔV) that are generated based on values ​​corresponding to each of the above. Here, due to a resistance component included in the transformer 40, the output voltage after being boosted by the transformer 40 may differ from the design value with respect to the output voltage output from the power conversion unit 10. However, with the above configuration, the output voltage after being boosted by the transformer 40 can be taken into consideration when synchronizing the output voltage output from the power conversion unit 10 with the voltage at the interconnection point to which power supplied by the power system 1 is applied, and therefore the output voltage and the voltage at the interconnection point can be synchronized with higher accuracy.

[0072] The other effects of the second embodiment are the same as those of the first embodiment.

[0073] [Variations] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims rather than the description of the above embodiments, and further includes all modifications (variations) within the meaning and scope of the claims.

[0074] For example, in the first and second embodiments, the control unit 11 controls the frequency f of the output voltage during the transition period. out , phase θ out , and the amplitude value V out The target values ​​of each (f ref , θ ref , V ref ) when generating the voltage frequency f grid , phase θ grid , and the amplitude value V grid and generating a frequency target value coefficient A1 or an output value A2 based on the transition input values ​​(difference Δf, difference Δθ, and difference ΔV) generated based on each of the above. out , phase θ out , and the amplitude value V out and the frequency f of the voltage at the interconnection point. grid , phase θ grid , and the amplitude value V grid In the above example, the difference between the output voltage and the voltage at the interconnection point is controlled to be equal to or less than a predetermined interconnection threshold value, but the present invention is not limited to this. In the present invention, the difference between the output voltage and the voltage at the interconnection point may be controlled to be equal to or less than a predetermined interconnection threshold value without generating the frequency target value coefficient A1 or A2 and without using the frequency target value coefficient A1 or A2.

[0075] In the first and second embodiments, the control unit 11 generates the frequency target value coefficient A1 or the output value A2 during the transition period by additionally inputting the transition input values ​​(differences Δf, Δθ, and ΔV) without switching the target value in the autonomous operation state, but the present invention is not limited to this. In the present invention, for example, the control unit 11 may be configured to acquire the target value for the transition period by switching the control mode using a separately prepared switching unit or the like.

[0076] In the first and second embodiments, the control unit 11 controls the frequency f of the voltage at the interconnection point during the transition period. grid , phase θ grid , and the amplitude value V grid and the frequency f of the measured output voltage. out , phase θ out , and the amplitude value V out In the above example, the frequency target value coefficient A1 or the output value A2 is obtained based on the transition input values ​​(differences Δf, Δθ, and ΔV) generated based on the values ​​corresponding to each of the above, but the present invention is not limited to this. In the present invention, the frequency target value coefficient A1 or the output value A2 may be obtained based on a specified input value that is preset as control for the transition period, for example.

[0077] In the first and second embodiments, the control unit 11 adjusts the frequency target value f ref The active power target value P used to generate ref The corrected active power target value P c and the corrected active power target value P c Based on the output voltage frequency f out and the frequency f of the voltage of power system 1. grid In the above example, the difference between the set frequency f and the value corresponding to the set frequency f is controlled to be equal to or less than the frequency threshold value as a predetermined interconnection threshold value, but the present invention is not limited to this. s Instead of adding the difference Δf to the set frequency fs In the place where you enter the frequency f of the voltage at the interconnection point grid and input the target active power value P ref may be corrected, and the output voltage and the voltage of the power system 1 may be made closer to each other based on the corrected target value.

[0078] In the first and second embodiments, the control unit 11 adjusts the phase target value θ for the output voltage during the transition period. ref The active power target value P used to generate ref The phase correction value S is obtained by inputting a value corresponding to the phase among the transition input values. θ and generate the phase correction value S θ Based on this, the phase of the output voltage θ out and the voltage phase θ of power system 1 grid However, the present invention is not limited to this. For example, a preset phase correction value may be used as control for the transition period.

[0079] In the first and second embodiments, the control unit 11 performs control to provide a virtual synchronous generator function that provides a virtual inertial force to the operation of the power conversion unit 10, and incorporates a value corresponding to the phase among the transition input values ​​into the inertia block B3, which is a control term for generating an inertial force, thereby controlling the phase θ of the output voltage. out and the voltage phase θ of power system 1 grid In the above example, the difference between the value corresponding to the virtual synchronous generator and the value corresponding to the virtual synchronous generator is controlled to be equal to or less than the phase threshold value, but the present invention is not limited to this. In the present invention, for example, when a load 30 that is not easily affected by frequency fluctuations is connected, the control of the above embodiment may be performed using a power conversion unit 10 that does not have a virtual synchronous generator function.

[0080] In the first and second embodiments, the control unit 11 controls the frequency f of the output voltage in the self-sustained operation state. out , phase θ out , and the amplitude value V out and the frequency f of the voltage at the interconnection point.grid , phase θ grid , and the amplitude value V grid In the above example, acquisition of a transition input value is started when the difference between the output voltage and the voltage at the interconnection point remains within 0.2%, which is a predetermined transition operation threshold value that is greater than the predetermined interconnection threshold value, for one second or more. However, the present invention is not limited to this. In the present invention, the transition operation threshold value is not limited to 0.2% and may be set to any value. The duration of the transition operation threshold value during the determination may also be set arbitrarily, or the duration itself may not be set. Furthermore, for example, the acquisition of a transition input value may be started when the ratio between the output voltage and the voltage at the interconnection point reaches a predetermined ratio.

[0081] In the first and second embodiments, the control unit 11 controls the frequency f of the output voltage during the transition period. out , phase θ out , and the amplitude value V out and the voltage frequency f of power system 1. grid , phase θ grid , and the amplitude value V grid In the above example, control for the grid-connected operation state is initiated when the difference between the output voltage and the voltage at the grid-connection point becomes equal to or less than a predetermined grid-connection threshold of 0.05%, but the present invention is not limited to this. In the present invention, the grid-connection threshold is not limited to 0.05% and may be set to any value. Also, for example, the system may be configured to initiate control for the grid-connected operation state when the ratio between the output voltage and the voltage at the grid-connection point becomes a predetermined ratio.

[0082] In the first and second embodiments, the control unit 11 controls the frequency f of the output voltage during the transition period. out , phase θ out , and the amplitude value V out and the voltage frequency f of power system 1. grid , phase θ grid , and the amplitude value V gridIn the example shown, when the difference between the values ​​corresponding to the frequency f of the output voltage and the frequency f of the output voltage is equal to or less than the predetermined interconnection threshold value for a predetermined set time of 1 second or more, the control in the grid-connected operation state is started, but the present invention is not limited to this. In the present invention, the set time is not limited to 1 second, and may be set to any time. Also, without setting a set time, the control in the grid-connected operation state is started when the difference between the values ​​corresponding to the frequency f of the output voltage and the frequency f of the output voltage is equal to or less than the predetermined interconnection threshold value for a predetermined set time of 1 second or more. out , phase θ out , and the amplitude value V out and the voltage frequency f of power system 1. grid , phase θ grid , and the amplitude value V grid The control in the grid-connected operation state may be started at the moment when the difference between the values ​​corresponding to the grid-connected operation state and the grid-connected operation state becomes equal to or smaller than a predetermined grid-connected threshold value.

[0083] In the first and second embodiments, the power supply in the power conversion system 100 is performed by the power storage unit 20 and the power conversion unit 10, but the present invention is not limited to this. In the present invention, for example, a distributed power source and a power conversion device may be provided separately from the power storage unit 20 and the power conversion unit 10 and connected in parallel to the bus 100a. In addition, the amplitude of the drive voltage of the load 30 may be other than 200 V, and the frequency may be other than 60 Hz.

[0084] In the first and second embodiments, the power conversion unit 10 controls the operation of the switching circuit 10a using a signal generated by performing current control using the current control block 11c included as a function in the control unit 11, but the present invention is not limited to this. In the present invention, the operation of the switching circuit 10a may be controlled using a signal generated by performing only voltage control using the frequency / phase control block 11a and the voltage control block 11b.

[0085] In the first and second embodiments, in the stand-alone operation state, the corrected active power target value Pc and the actual measured value P outThe present invention is not limited to this example, but for example, a limiter circuit is provided to determine upper and lower limits of the active power that can be output based on the performance of the power conversion unit 10, and when the corrected active power target value Pc is greater than the upper limit set in the limiter circuit, the upper limit of the limiter circuit and the actual measured value Pc of the active power are calculated. out Similarly, if the corrected active power target value Pc is smaller than the lower limit value set in the limiter circuit, the frequency target value coefficient A1 may be derived based on the difference between the lower limit value of the limiter circuit and the actual measured value P out The frequency target value coefficient A1 may be derived based on the difference between the

[0086] In the first and second embodiments, the control unit 11 detects the establishment of an isolated operation state by a so-called passive method, in which the control unit 11 detects the establishment of an isolated operation state based on fluctuations in the voltage signal detected by the interconnection point detection unit D1, but the present invention is not limited to this. In the present invention, the control unit 11 may also detect the establishment of an isolated operation state by a so-called active method, in which the control unit 11 transmits a signal that causes a minute fluctuation to the power grid 1 and detects the establishment of an isolated operation state based on the fluctuations. [Explanation of symbols]

[0087] 1 Power system 10 Power conversion section 11 Control section 20 Power storage unit 30 Load 40 Transformer 41 Interconnection point switch 100, 101 Power conversion system A1 Frequency target value coefficient (control coefficient) A2 Output value (output coefficient) B3 Inertia block (inertia term) f out , f local Output Frequency f ref Target Frequency P c Corrected active power target value P refActive power target value V out , V local Voltage Amplitude Value V ref Amplitude Target Value θ out , θ local Voltage Phase Value θ ref Phase Target Value Δf Frequency difference (input value for transition) Δθ Phase difference (input value for transition) ΔV: Difference in amplitude (input value for transition)

Claims

1. a power storage unit that stores and discharges DC power; a power conversion unit that, in a grid-connected operation state in which AC power is supplied from the power grid, converts the AC power supplied from the power grid into DC power and outputs the DC power to the power storage unit, and that, in an independent operation state in which the AC power supplied from the power grid is cut off, converts the DC power supplied from the power storage unit into AC power and outputs the AC power to a load; a control unit; the control unit is configured to perform control during a transition period when switching from the independent operation state to the grid-connected operation state, based on the values ​​of amplitude, frequency, and phase of the output voltage supplied from the storage unit, output by the power conversion unit, and detected by an output detection unit, and the values ​​of amplitude, frequency, and phase of a grid-connection point voltage detected by a grid-connection point detection unit at a grid-connection point where the power grid and the power conversion unit are connected, to keep the differences between the values ​​corresponding to each of the amplitude, frequency, and phase of the output voltage below a predetermined grid-connection threshold.

2. 2. The power conversion system according to claim 1, wherein the control unit is configured to generate a control coefficient based on a transition input value generated based on each of the amplitude, frequency, and phase of the voltage at the interconnection point when generating target values ​​for each of the amplitude, frequency, and phase of the output voltage during the transition period, and to perform control based on the control coefficient to keep differences between values ​​corresponding to each of the amplitude, frequency, and phase of the output voltage and values ​​corresponding to each of the amplitude, frequency, and phase of the voltage at the interconnection point equal to or less than the predetermined interconnection threshold.

3. The power conversion system of claim 2, wherein the control unit is configured to generate the control coefficient during the transition period by additionally inputting the transition input value without switching the target value in the independent operation state.

4. 4. The power conversion system according to claim 3, wherein the control unit is configured to acquire the control coefficient based on the transition input value generated based on a value corresponding to a phase of the voltage at the interconnection point and a generated phase target value for the output voltage during the transition period.

5. 4. The power conversion system according to claim 3, wherein the control unit is configured to generate a corrected active power target value during the transition period by inputting a value corresponding to a frequency among the transition input values ​​into an active power target value used to generate a frequency target value for the output voltage, and to perform control based on the corrected active power target value so that a difference between a value corresponding to a frequency of the output voltage and a value corresponding to a frequency of the voltage of the power grid is equal to or less than a frequency threshold value serving as the predetermined interconnection threshold value.

6. 4. The power conversion system according to claim 3, wherein the control unit is configured to generate a phase correction value during the transition period by inputting a value corresponding to a phase among the transition input values ​​for an active power target value used to generate a phase target value for the output voltage, and to perform control based on the phase correction value so that a difference between a value corresponding to the phase of the output voltage and a value corresponding to the phase of the voltage of the power grid is equal to or less than a phase threshold value serving as the predetermined interconnection threshold value.

7. 7. The power conversion system according to claim 6, wherein the control unit performs control to provide a virtual synchronous generator function that imparts a virtual inertial force to the operation of the power conversion unit, and performs control to make a difference between a value corresponding to the phase of the output voltage and a value corresponding to the phase of the voltage of the power grid equal to or less than the phase threshold by incorporating a value corresponding to a phase among the transition input values ​​into an inertia term that is a control term for generating the inertial force.

8. 3. The power conversion system according to claim 2, wherein the control unit is configured to generate the control coefficient based on the transition input value generated based on values ​​corresponding to the amplitude, frequency, and phase of the voltage at the interconnection point and values ​​corresponding to the amplitude, frequency, and phase of a boosted output voltage obtained by boosting the output voltage by a transformer during the transition period.

9. 3. The power conversion system of claim 2, wherein the control unit is configured to start acquiring the transition input value when, in the independent operation state, a difference between a value corresponding to each of the amplitude, frequency, and phase of the output voltage and a value corresponding to each of the amplitude, frequency, and phase of the voltage at the interconnection point becomes equal to or less than a predetermined transition operation threshold value that is greater than the predetermined interconnection threshold value.

10. 2. The power conversion system according to claim 1, wherein the control unit is configured to start control for a grid-connected operation state when, during the transition period, differences between values ​​corresponding to an amplitude, a frequency, and a phase of the output voltage and values ​​corresponding to an amplitude, a frequency, and a phase of the voltage of the power grid become equal to or less than the predetermined grid-connected threshold value.

11. 2. The power conversion system according to claim 1, wherein the control unit is configured to start control in the grid-connected operation state when, during the transition period, a state in which differences between values ​​corresponding to an amplitude, a frequency, and a phase of the output voltage and values ​​corresponding to an amplitude, a frequency, and a phase of the voltage of the power grid are equal to or less than the predetermined interconnection threshold continues for a predetermined set time or more.

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