Power conversion system

Abstract

To provide a power conversion system capable of stably supplying power to a load even when an autonomous operation is performed using a distributed power supply.SOLUTION: A power conversion system comprises: a power storage unit 20 for storing and discharging DC power; a power conversion unit 10 for converting AC power supplied from a power grid 1 to DC power and outputting it to the power storage unit 20 in a grid-connected operation state, and converting DC power supplied from the power storage unit 20 to AC power and outputting it to a load 30 in an autonomous operation state; and a control unit 11 for controlling an operation of the power conversion unit 10. In an autonomous operation state, the control unit 11 acquires a correction target value Pc obtained by correcting an active power target value Pref being a target value of active power output to the load 30 in a grid-connected operation state for the purpose of modifying an output frequency fout that the power conversion unit 10 outputs, and controls the output frequency fout to approach a predetermined set frequency fs on the basis of the correction target value Pc.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 can perform stand-alone operation by cutting off power supplied from a power grid. [Background technology]

[0002] BACKGROUND ART Conventionally, there is known a power conversion system that can perform stand-alone operation by cutting off power supplied from a power grid (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a distributed power supply system (power conversion system) that interconnects a distributed power supply including a solar cell and a power storage unit with a grid power supply 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 supply and the grid power supply, and operates in grid-connected mode with the grid power supply. The power conversion system of Patent Document 1 also includes a detection means for detecting an abnormality in the grid power supply, and controls the opening and closing of a switching means between the load and the grid power supply based on the output of the detection means. In this way, when an abnormality occurs in the grid power supply, the power conversion system of Patent Document 1 switches to stand-alone operation using the distributed power supply by opening the switching means between the load and the grid power supply, and supplies 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, in Patent Document 1, when an abnormality occurs in the grid power supply, switching to stand-alone operation using distributed power sources is performed by opening a switching device between the load and the grid power supply, and power is supplied to the load. Patent Document 1 does not disclose a detailed control configuration of the power conditioner during stand-alone operation. For example, feedback control may be performed with a predetermined voltage as a target value, as in the case of grid-connected operation. However, even if feedback control with a predetermined voltage as a target value is performed during stand-alone operation, if the load balance changes, the amplitude and frequency of the voltage output in the stand-alone system may become unstable, causing the load to stop. Therefore, there is a demand for a power conversion system that can provide a stable power supply to a load even when stand-alone operation is performed using distributed power sources.

[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 can provide a stable power supply to a load even when performing independent operation using distributed power sources. [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 comprises: a 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 it to the storage unit; and, 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 storage unit into AC power and outputs it to a load; and a control unit that controls the operation of the power conversion unit; wherein, in the independent operation state, the control unit acquires a corrected target value for independent operation, which is obtained by correcting a first interconnection target value as a target active power output to the load in the grid-connected operation state in order to change the output frequency output by the power conversion unit, and is configured to perform control to bring the output frequency closer to a predetermined set frequency based on the corrected target value for independent operation.

[0008] In a power conversion system according to one aspect of the present invention, as described above, the control unit is configured to, in the isolated operation state, acquire a corrected target value for isolated operation, which is obtained by correcting the first interconnection target value as the target active power output to the load in the grid-connected operation state in order to change the output frequency output by the power conversion unit, and to perform control to bring the output frequency closer to a predetermined set frequency based on the corrected target value for isolated operation. As a result, in the isolated operation state, a corrected target value for isolated operation for performing isolated operation that is different from the first interconnection target value can be acquired based on the first interconnection target value used in the grid-connected operation state, thereby enabling control suitable for the isolated operation state. As a result, a stable power supply to the load can be achieved even when isolated operation is performed using distributed power sources.

[0009] In the power conversion system according to the above aspect, the control unit is preferably configured to acquire the isolated operation corrected target value by adding a correction value acquired based on the set frequency to the first grid-connection target value. With this configuration, the correction value based on the set frequency can be taken into consideration when controlling the isolated operation state, making it easy to adjust the frequency of the voltage supplied to the load.

[0010] In this case, preferably, the control unit is configured to continuously change the first interconnection target value and the isolated operation corrected target value by adding a correction value and acquiring an isolated operation corrected target value without stopping acquisition of the first interconnection target value when switching from the grid-connected operation state to the isolated operation state. Here, for example, if a switch or the like is used to switch between the first interconnection target value and the isolated operation corrected target value, there may be a period of discontinuity in control, which may cause the load to stop during the period when power supply is stopped. In contrast, with the above configuration, the first interconnection target value and the isolated operation corrected target value are continuously changed, so that even when the grid-connected operation state switches to the isolated operation state, power supply to the load can be stabilized without interruption.

[0011] In the power conversion system according to the above aspect, the control unit is preferably configured to, in an autonomous operation state, acquire a frequency correction coefficient based on an actual measurement value of the active power output to the load and a correction target value, and to control the output frequency of the power conversion unit to approach a predetermined set frequency based on the rated frequency and the acquired frequency correction coefficient. Here, since the actual measurement value of the active power output to the load changes as the load fluctuates, the frequency correction coefficient based on the actual measurement value of the active power output to the load also changes. Therefore, with the above configuration, the frequency output by the power conversion unit can be controlled using a frequency correction coefficient that fluctuates depending on the load. As a result, frequency control depending on the load can be performed.

[0012] In this case, the control unit is preferably configured to perform control to impart a virtual synchronous generator function to the operation of the power conversion unit such that a virtual inertial force is generated, and to acquire a frequency correction coefficient based on the correction target value and an inertia term that is a control term for generating the inertial force in an independent operation state. With this configuration, it is possible to generate an inertial force in the power conversion unit similar to that in a power system that uses a synchronous generator, and therefore it is possible to prevent the power supply from becoming unstable even when a load fluctuation occurs, compared to when there is no inertial force.

[0013] In the power conversion system according to the above aspect, the control unit is preferably configured to control the amplitude value of the load voltage output by the power conversion unit to approach a predetermined set voltage amplitude value in the isolated operation state, without controlling the reactive power output to the load. Here, in the grid-connected operation state, it is necessary to output reactive power that will achieve a desired power factor due to the convenience of the power grid (electric power company). However, in the isolated operation state, since the system is not connected to the power grid, it is not necessary to output reactive power unnecessary for the operation of the load. Therefore, with the above configuration, it is possible to perform control to output the voltage required by the load in the isolated operation state, thereby enabling efficient power supply.

[0014] In this case, the control unit is preferably configured to control, when switching from the grid-connected operation state to the isolated operation state, to bring the amplitude value of the load voltage output by the power conversion unit closer to a predetermined set voltage amplitude value by cutting off the input of the second grid-connection target value, which is a target value of reactive power added in the grid-connected operation state. With this configuration, by cutting off the second grid-connection target value added for use only in the grid-connected operation state, it is possible to continuously change the target value used in the grid-connected operation state and the target value used in the isolated operation state. As a result, it is possible to prevent interruptions in the power supply to the load.

[0015] In the power conversion system according to the above aspect, the control unit is preferably configured to control the output frequency of the power conversion unit to match a predetermined set frequency. With this configuration, the predetermined set frequency can be set to an optimal frequency required for stable operation of the load, thereby making it possible to set the output frequency of the power conversion unit to an optimal frequency required for stable operation of the load. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a power conversion system that can stably supply power to a load even when performing stand-alone operation using distributed power sources. [Brief explanation of the drawings]

[0017] [Figure 1] 1 illustrates a power conversion system according to one embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration of a power conversion unit according to an embodiment. [Figure 3] FIG. 3 is a diagram for explaining the operation of a frequency / phase control block according to an embodiment. [Figure 4] FIG. 4 is a diagram illustrating an operation of a voltage control block according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings.

[0019] The configuration of a power conversion system 100 according to this embodiment will be described with reference to FIGS.

[0020] 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, and controls the power conversion unit 10 to output power synchronized with the power supplied by the power grid 1 to the load 30 or the power grid 1. That is, 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, the power conversion system 100 is configured to control the power conversion unit 10 to supply power supplied from the power storage unit 20 to the load 30 when an abnormality such as a power outage occurs in the power grid 1. That is, the power conversion system 100 is a system that supplies power supplied by the power grid 1 or the power storage unit 20 and controlled by the power conversion unit 10 to the load 30 via the bus 100 a and the load switch 31.

[0021] 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.

[0022] 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 or the power grid 1. As shown in FIG. 2 , the power conversion unit 10 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 by an inductor L1, an inductor L2, and a capacitor C, and converts the rectangular voltage signal (square wave) output from the switching circuit 10a into a sine wave. The switch 10c is controlled by the control unit 11 to open and close so as to cut off the supply of the power output from the filter circuit 10b to the load 30.

[0023] 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 this 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.

[0024] The control unit 11 is configured to acquire the voltages detected by the interconnection point detection unit D1 and the output detection unit D2. The control unit 11 also controls the inverter operation of the power conversion unit 10 so that the power conversion unit 10 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 power fluctuations) of a system that generates power using a synchronous generator, such as the power system 1. In this embodiment, the control unit 11 is configured to input control blocks such as a governor block B2, an inertia block B3, and a braking block B4 as shown in FIG. 3 as the synchronous generator simulation model. The detailed operation of the control unit 11 will be described later.

[0025] The power storage unit 20 is a secondary battery capable of storing and discharging DC power. For example, the power storage unit 20 is a lithium-ion secondary battery. In a grid-connected operation state in which the power system 1 and the power conversion unit 10 operate in cooperation with each other, the power storage unit 20 stores power supplied from the power system 1 and converted into DC power by the power conversion unit 10. In an isolated operation state in which the power system 1 and the power conversion unit 10 are disconnected by the interconnection point switch 41 and in a grid-connected operation state, the power storage unit 20 discharges power so as to supply DC power to the power conversion unit 10, 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.

[0026] 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 operate with a voltage amplitude of, for example, 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.

[0027] 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 embodiment, for example, the transformer 40 is configured to have a winding ratio of 33:1 between the primary side and the secondary side in order to step down the voltage of 6600 V on the power system 1 side, which is the primary side, to 200 V on the load 30 side, which is 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 cutting off the exchange of power at the interconnection point where the power system 1 and the power conversion system 100 are connected.

[0028] (Operations of power conversion unit 10 and control unit 11) Here, with reference to Figs. 2 to 4, the control operation of the control unit 11 on the power conversion unit 10 in 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 will be described below.

[0029] When the power supplied from the power grid 1 is normal, the power conversion unit 10 performs grid-connected operation to synchronize the frequency, phase, and voltage amplitude with the power supplied from the power grid 1 in order to supply the amount of power required by the load 30. This state is referred to as a grid-connected operation state. In this embodiment, the control unit 11 generates pulse signals for controlling the operation of the switching circuit 10a in the power conversion unit 10, using a frequency / phase control block 11a, a voltage control block 11b, a current control block 11c, and a PWM pulse generation block 11d.

[0030] The frequency / phase control block 11a included in the control unit 11 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 generates an active power target value P of the voltage generated by the frequency / phase control block 11a. ref , phase target value θref , 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 load 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. ref is an example of a "first grid-connection target value" in the claims.

[0031] 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 out and 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 correction coefficient A1 to be multiplied by the actual measured value of the active power P out and the target active power value P ref For example, a normalized value such as a percentage when the set maximum value is "1" is used for the frequency correction coefficient A1. In addition, in order to function as a virtual synchronous generator, the outputs of the governor block B2, inertia block B3, and braking block B4, which are set as control terms having predetermined values ​​in the frequency / phase control block 11a, are incorporated into the generation of the frequency correction coefficient A1. The inertia block B3 is an example of an "inertia term" in the claims.

[0032] 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 interconnection point detection unit D1, which 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.

[0033] The control unit 11 switches the switching unit 110a in the ALFC (Automatic Load Frequency Control) block B1 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 correction coefficient A1. This ALFC block B1 is a control model for frequency control that is different from the simulation model used for virtual synchronous power generation.

[0034] Specifically, the addition 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 is set based on the frequency for stably operating the load 30, and for example, a value normalized to "1" is input, which is the frequency of 59.9 Hz of the power supply when the power grid 1 is supplying power normally. n For example, a value normalized to "1" for the AC power frequency of 60 Hz used in Western Japan is input.

[0035] 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. GOVHowever, 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 an integral term 1 / s are included inside, and the output 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.

[0036] Here, the correction value S c is the frequency ratio f from the frequency weighting 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 ref The input signal S via the governor block B2 is added in the 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 target value P c The correction target value P c is an example of the "corrected target value for autonomous driving" in the claims.

[0037] In this embodiment, in the autonomous operation state, the correction target value P c and the actual measured value P of the effective power in the power output from the power conversion unit 10 to the load 30. out At the addition point a5, the difference between the correction target value P c and the measured value of the active power P out The value obtained by multiplying the frequency correction coefficient A1 by the value output from the braking block B4 is the signal S DThen, the value of the summing point a5 is multiplied by the inertia block B3 to generate the frequency correction 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.

[0038] The frequency / phase control block 11a calculates the frequency correction coefficient A1 and the rated frequency f n The product of these is used to obtain a frequency target value f ref The frequency / phase control block 11a is configured to output the frequency correction 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

[0039] Next, the function of the voltage control block 11b will be described with reference to Fig. 4. The voltage control block 11b includes a load 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 a7, 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 and set to have arbitrary values ​​in advance in the voltage control block 11b. s is set based on the voltage amplitude value for stably operating the load 30, and for example, a value normalized to "1" as the voltage amplitude value of the operating voltage of the load 30 is input.

[0040] Here, in the grid-connected operation state, the power conversion system 100 is connected to 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 limited to a predetermined reactive power Q out Specifically, in this 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 from 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 controls not only the amplitude value of the output voltage but also the reactive power value. Note that the reactive power target value Q ref is an example of a "second interconnection target value" in the claims.

[0041] In this 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 a8 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 a8 receives the load voltage amplitude value V obtained at the summing point a7. out and the set voltage amplitude value V s Only the difference value is entered.

[0042] In this embodiment, in the state of independent operation, the amplitude value V of the load voltage at the summing point a8 out and the set voltage amplitude value V sThe difference between the load voltage V and the power converter 10 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 load 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

[0043] At the summing point a9, the set voltage amplitude value V s and the output value A2 of the AVR block B7 are added together. Also, the value of the summing point a9 is directly added to the amplitude target value V ref This amplitude target value V ref Based on this, a PWM pulse wave for driving the switching circuit 10a is generated.

[0044] As described above, the power conversion system 100 of this embodiment has different frequency target values ​​f ref and the amplitude target value V ref Since the power generating condition is used, the power required for the operation of the load 30 is supplied in the local grid even in an isolated operation state.

[0045] (Effects of this embodiment) Next, the effects of this embodiment will be described.

[0046] The power conversion system 100 of this embodiment 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 a 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 that controls the operation of the power conversion unit 10, and the control unit 11 controls an active power target value P as a target active power to be output to the load 30 in the grid-connected operation state in the independent operation state. ref The output frequency f outThe correction target value P c and obtain the correction target value P c Based on the output frequency f out The predetermined set frequency f s As a result, in the isolated operation state, the effective power target value P ref Based on this, the active power target value P ref Corrected target value P for autonomous operation different from c As a result, even when the load 30 is operated independently using the power storage unit 20, which is a distributed power source, a stable power supply can be provided to the load 30.

[0047] In this embodiment, the control unit 11 controls the effective power target value P ref For the set frequency f s The correction value S obtained based on c By adding c This allows the set frequency f s Correction value S based on c Therefore, the output frequency f out The adjustment can be easily performed.

[0048] In this embodiment, when switching from the grid-connected operation state to the self-sustained operation state, the control unit 11 adjusts the active power target value P ref Without stopping the acquisition of the correction value S c Add the correction target value P c By obtaining the target active power value P ref and the correction target value P c Here, for example, the active power target value P ref and the correction target value P cIn contrast, if the active power target value P ref and the correction target value P c Since the power supply voltage is continuously changed, even when the grid-connected operation state is switched to the independent operation state, the power supply to the load 30 can be stabilized without interruption.

[0049] In this embodiment, the control unit 11 calculates the actual measured value P of the active power output to the load 30 in the self-sustained operation state. out and the correction target value P c and obtain the frequency correction factor A1 based on the rated frequency f n and the acquired frequency correction coefficient A1, the output frequency f output by the power conversion unit 10 is calculated. out The predetermined set frequency f s Here, the actual measured value P of the active power output to the load 30 due to the fluctuation of the load 30 is out Since the actual measured value P of the effective power output to the load 30 changes, out Therefore, by configuring as above, the frequency correction coefficient A1 based on the output frequency f output by the power conversion unit 10 also changes. out can be controlled using the frequency correction coefficient A1 that varies depending on the load 30. As a result, the frequency can be controlled in accordance with the load 30.

[0050] In this embodiment, the control unit 11 performs control to provide the power conversion unit 10 with a virtual synchronous generator function that generates a virtual inertial force, and in the stand-alone operation state, the correction target value P cand an inertia block B3, which is a control term for generating an inertial force. This allows the power conversion unit 10 to generate an inertial force similar to that of the power system 1 using a synchronous generator, so that even when a fluctuation occurs in the load 30, the supplied power can be prevented from becoming unstable compared to when there is no inertial force.

[0051] In this embodiment, the control unit 11 also controls the reactive power Q output to the load 30 in the self-sustained operation state. out Without performing the control of the load voltage amplitude value V out The predetermined voltage amplitude value V s Here, in the grid-connected operation state, it is necessary to output reactive power that results in a desired power factor due to the circumstances of the power grid 1 side (electric power company), but in the stand-alone operation state, since it is not connected to the power grid 1, it is not necessary to output reactive power that is unnecessary for the operation of the load 30. Therefore, by configuring as described above, it is possible to perform control to output the voltage required by the load 30 in the stand-alone operation state, thereby enabling efficient power supply.

[0052] In this embodiment, when switching from the grid-connected operation state to the independent operation state, the control unit 11 adjusts the reactive power target value Q ref By cutting off the input of out The predetermined voltage amplitude value V s This allows the reactive power target value Q ref By interrupting the power supply, it is possible to continuously change the target value used in the grid-connected operation state and the target value used in the isolated operation state. As a result, it is possible to eliminate interruptions in the power supply to the load 30 and stabilize the power supply to the load 30.

[0053] In this embodiment, the control unit 11 controls the output frequency f out The predetermined set frequency f s This allows the frequency to be controlled to match the predetermined set frequency f s By setting the frequency f to the optimum frequency required for stable operation of the load 30, the output frequency f out can be set to the optimum frequency required for stable operation of the load 30.

[0054] [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 above description of the embodiments, and further includes all modifications (variations) within the meaning and scope of the claims.

[0055] For example, in the above embodiment, an example has been shown in which power is supplied within power conversion system 100 by power storage unit 20 and 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 power storage unit 20 and power conversion unit 10 and connected in parallel to bus 100a. Furthermore, the amplitude of the drive voltage of load 30 may be other than 200 V, and the frequency may be other than 60 Hz.

[0056] In the above embodiment, 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.

[0057] Furthermore, in the above embodiment, an example has been shown in which the control unit 11 is included inside the power conversion unit 10, but the present invention is not limited to this. In the present invention, for example, a higher-level control device may be provided outside the power conversion unit 10, and the higher-level control device may be configured to receive voltage signals detected by the interconnection point detection unit D1 or the output detection unit D2, to control the opening and closing of the interconnection point switch 41, and to control the power conversion unit 10, etc.

[0058] In the above embodiment, in the autonomous operation state, the correction target value P c and the measured value of the active power P out The present invention is not limited to this example. For example, a limiter circuit is provided to determine upper and lower limits of the effective power that can be output based on the performance of the power conversion unit 10, and the correction target value P c is greater than the upper limit set in the limiter circuit, the upper limit of the limiter circuit and the actual measured value of the active power P out Similarly, the frequency correction coefficient A1 may be derived based on the difference between the correction target value P c is smaller than the lower limit set in the limiter circuit, the lower limit of the limiter circuit and the actual measured value of the active power P out The frequency correction coefficient A1 may be derived based on the difference between

[0059] In the above embodiment, the control unit 11 detects whether the autonomous operation state has been established by a so-called passive method, in which the control unit 11 detects whether the autonomous operation state has been established 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 whether the autonomous operation state has been established 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 whether the autonomous operation state has been established based on the fluctuations.

[0060] In the above embodiment, the control unit 11 controls the effective power target value P ref The correction value S obtained based on the set frequency fs is c By adding cHowever, the present invention is not limited to this. s The correction value S obtained based on c By adding out Set the frequency f s The target value may be obtained so as to approach the above.

[0061] In the above embodiment, the control unit 11 adjusts the active power target value P ref Without stopping the acquisition of the correction value S c Add the correction target value P c By obtaining the target active power value P ref and the correction target value P c In the present invention, the active power target value P ref and the correction target value P c Alternatively, control may be performed so that the change between the two is switched as quickly as possible.

[0062] In the above embodiment, the control unit 11 calculates the actual measured value P of the active power output to the load 30 in the self-sustained operation state. out and the correction target value P c and obtain the frequency correction factor A1 based on the rated frequency f n and the acquired frequency correction coefficient A1, the output frequency f output by the power conversion unit 10 is calculated. out The predetermined set frequency f s However, the present invention is not limited to this. out and the correction target value P c and directly based on the output frequency f out The predetermined set frequency f s The target frequency value f ref may be configured to output:

[0063] In the above embodiment, the control unit 11 performs control to provide the power conversion unit 10 with a virtual synchronous generator function that generates a virtual inertial force, and in the stand-alone operation state, the correction target value P c In the above example, the frequency correction coefficient A1 is obtained based on the inertia block B3, which is a control term for generating an inertial force, 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.

[0064] In the above embodiment, the control unit 11 controls the reactive power Q output to the load 30 in the self-sustained operation state. out Without performing the control of the load voltage amplitude value V out The predetermined voltage amplitude value V s However, the present invention is not limited to this. out Without controlling the load voltage amplitude V out , a predetermined set voltage amplitude value V s It is also possible to perform control to bring the temperature closer to .

[0065] In the above embodiment, when switching from the grid-connected operation state to the independent operation state, the control unit 11 adjusts the reactive power target value Q ref By cutting off the input of out The predetermined voltage amplitude value V s However, the present invention is not limited to this. s In generating the reactive power target value Q ref Two control blocks may be prepared, one for using the control signal and one for not using the control signal, and the control blocks may be configured to switch between them in a short time.

[0066] In the above embodiment, the control unit 11 controls the output frequency fout The predetermined set frequency f s However, the present invention is not limited to this. out and a predetermined set frequency f s The difference may be controlled to be equal to or less than a certain value. [Explanation of symbols]

[0067] 1 Power system 10 Power conversion section 11 Control section 20 Power storage unit 30 Load 40 Transformer 41 Interconnection point switch 100 Power Conversion System A1 Frequency correction factor B3 Inertia block (inertia term) f s Setting frequency f out Output Frequency f ref Target Frequency P c Correction target value (correction target value for autonomous operation) P ref Active power target value (target value for first interconnection) Q ref Reactive power target value (target value for second interconnection) V s Set voltage amplitude value V out Load voltage amplitude V ref Amplitude Target Value

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 that controls the operation of the power conversion unit, The control unit is configured to acquire a corrected target value for independent operation in the independent operation state by correcting a first grid-connected target value as the target active power output to the load in the grid-connected operation state in order to change the output frequency output by the power conversion unit, and to perform control to bring the output frequency closer to a predetermined set frequency based on the corrected target value for independent operation.

2. The power conversion system of claim 1, wherein the control unit is configured to acquire the isolated operation corrected target value by adding a correction value acquired based on the set frequency to the first grid-connection target value in the isolated operation state.

3. The power conversion system of claim 2, wherein the control unit is configured to continuously change the first grid-connected target value and the independent operation corrected target value by adding the correction value and acquiring the independent operation corrected target value without stopping acquisition of the first grid-connected target value when switching from the grid-connected operation state to the independent operation state.

4. 2. The power conversion system according to claim 1, wherein the control unit is configured to acquire a frequency correction coefficient based on an actual measured value of the active power output to the load and the autonomous operation correction target value in the autonomous operation state, and to perform control to bring the output frequency output by the power conversion unit closer to the predetermined set frequency based on a rated frequency and the acquired frequency correction coefficient.

5. 5. The power conversion system according to claim 4, wherein the control unit is configured to perform control to give the operation of the power conversion unit a virtual synchronous generator function that generates a virtual inertial force, and to acquire the frequency correction coefficient in the independent operation state based on the independent operation correction target value and an inertia term that is a control term for generating the inertial force.

6. 2. The power conversion system according to claim 1, wherein the control unit is configured to control the amplitude value of the load voltage output by the power conversion unit to approach a predetermined set voltage amplitude value without controlling the reactive power output to the load in the autonomous operation state.

7. 7. The power conversion system according to claim 6, wherein the control unit is configured to, when switching from the grid-connected operation state to the independent operation state, perform control to bring the amplitude value of the load voltage output by the power conversion unit closer to the predetermined set voltage amplitude value by cutting off input of a second grid-connection target value, which is a target value of reactive power added in the grid-connected operation state.

8. The power conversion system according to claim 1 , wherein the control unit is configured to perform control so that the output frequency output by the power conversion unit coincides with the predetermined set frequency.

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