Control device and control method

Abstract

Provided is a control device that controls an inverter so as to exhibit a frequency fluctuation suppressing effect indicated by a design value even when the specification, the configuration, or the operation state of a connection destination of the inverter changes. A control device (41) controls an inverter (42) so that the frequency of the output voltage of the inverter (42) has a virtual inertial force with respect to active power supplied to a connection destination of the inverter (42). The control device (41) comprises: a first virtual synchronous generator control unit (101) that uses an active power actual measurement value supplied to the connection destination by the inverter (42) to calculate a frequency deviation using a transfer function based on a swing equation in a synchronous generator; a first command value generation unit (102) that generates a frequency command value for the output voltage of the inverter using the frequency deviation; and a first error correction control unit (103) that determines the gain of the transfer function of the first virtual synchronous generator control unit (101) using a first error that is the difference between an active power reference value, which is the active power supplied by the inverter (42) to the connection destination in a predetermined reference state, and the active power actual measurement value.

Description

Control device and control method

[0001] The present disclosure relates to a control device and a control method for controlling an inverter provided in a power supply.

[0002] In a power system that supplies AC power from a power source to a load, control is performed to maintain the output voltage and frequency. In a power system, if the amount of AC power introduced from renewable energy sources increases compared to the amount of AC power introduced from synchronous generators, the inertia of the power source decreases, making it difficult to maintain the frequency when the supply-demand balance suddenly changes.

[0003] In response to this, for example, in a distributed power supply control device disclosed in Patent Document 1, an inverter that connects a distributed power supply to a grid is operated under virtual synchronous generator (hereinafter referred to as VSG, an abbreviation for Virtual Synchronous Generator) control, thereby giving the distributed power supply a pseudo inertial force that a synchronous generator has, thereby suppressing frequency fluctuations in the grid.

[0004] JP 2019-176584 A

[0005] However, conventional distributed power supply control devices have a problem in that, when the specifications, configuration, or operating conditions of the equipment connected to the grid change, it is necessary to change the inverter settings and check them after the change so that the frequency fluctuation suppression effect can be maintained as before the change. This is because the active power output by the inverter, which is the input value for the calculation process related to VSG control, changes due to the influence of the connected equipment. In other words, when the specifications, configuration, or operating conditions of the connected equipment change, it is necessary to perform, for example, inverter gain adjustment to correct the change in active power.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a control device and control method that are configured to be able to calculate an active power reference value to be output by an inverter to a connection destination in a predetermined reference state, and that can control an inverter so as to exert the effect of suppressing frequency fluctuations according to the design value, even when the specifications, configuration, or operating conditions of the connection destination change, by feeding back the difference between the active power reference value and the actual measured active power value, or the difference between the VSG control output based on the active power reference value and the VSG control output based on the actual measured active power value, to calculation processing related to VSG control.

[0007] The control device according to the present disclosure is a control device that controls an inverter so that the frequency of the inverter's output voltage has a virtual inertial force with respect to the active power supplied to a destination connected to the inverter, and includes: a first virtual synchronous generator control unit that calculates a frequency deviation by a transfer function based on an oscillation equation in the synchronous generator using an actual measured value of the active power supplied by the inverter to a destination connected to the inverter; a first command value generation unit that generates a frequency command value for the inverter's output voltage using the frequency deviation calculated by the first virtual synchronous generator control unit; and a first error correction control unit that determines a gain of the transfer function in the first virtual synchronous generator control unit using a first error that is the difference between an active power reference value, which is the active power supplied by the inverter to a destination connected to the inverter in a predetermined reference state, and the actual measured value of the active power.

[0008] Another embodiment of the control device according to the present disclosure includes a first virtual synchronous generator control unit that calculates a first frequency deviation by a transfer function based on an oscillation equation in the synchronous generator using an actual measured value of active power supplied by the inverter to a connected destination; a first command value generation unit that generates a first frequency command value as a frequency command value for an output voltage of the inverter using the first frequency deviation calculated by the first virtual synchronous generator control unit; a second virtual synchronous generator control unit that calculates a second frequency deviation by a transfer function using an active power reference value that is active power supplied by the inverter to a connected destination in a predetermined reference state; and a second error correction control unit that feeds back a second error that is the difference between the first frequency deviation calculated by the first virtual synchronous generator control unit and the second frequency deviation calculated by the second virtual synchronous generator control unit to the first virtual synchronous generator control unit.

[0009] The control method according to the present disclosure is a control method for controlling an inverter so that the frequency of the inverter's output voltage has a virtual inertial force with respect to the active power supplied to a destination connected to the inverter, and includes the steps of: calculating a frequency deviation by a transfer function based on an oscillation equation in a synchronous generator using an actual measured value of the active power supplied by the inverter to a destination; generating a frequency command value for the inverter's output voltage using the frequency deviation; and determining a gain of the transfer function using a first error that is the difference between an active power reference value, which is the active power supplied by the inverter to a destination in a predetermined reference state, and the actual measured value of the active power.

[0010] Another embodiment of the control method according to the present disclosure includes the steps of: calculating a first frequency deviation by a transfer function based on an oscillation equation in a synchronous generator using an actual measured value of active power supplied by the inverter to a connected destination; generating a frequency command value for the output voltage of the inverter using the first frequency deviation; calculating a second frequency deviation by the transfer function using an active power reference value that is active power supplied by the inverter to a connected destination in a predetermined reference state; and feeding back a second error that is the difference between the first frequency deviation and the second frequency deviation to the step of calculating the first frequency deviation.

[0011] According to the present disclosure, it is possible to provide a control device and a control method that controls an inverter so as to achieve the effect of suppressing frequency fluctuations according to the design value, even when the specifications, configuration, or operating conditions of the inverter's connected destination change.

[0012] FIG. 1 is a diagram showing a configuration example of a microgrid in the first embodiment. FIG. 2 is a block diagram showing a control system including a control device and an inverter to be controlled in the first embodiment. FIG. 3 is a flowchart showing control processing performed by the control device in the first embodiment. FIG. 4 is a diagram showing the relationship between an inverter to be controlled in the first embodiment and a connection destination. FIG. 5 is a block diagram showing a hardware configuration of a PLC realizing the control device in the first embodiment. FIG. 6 is a block diagram showing a control system including a control device and an inverter to be controlled in the second embodiment.

[0013] Embodiment 1. Embodiment 1 will be described in detail with reference to Fig. 1. Fig. 1 is a diagram showing an example of the configuration of a microgrid 1 in embodiment 1. In Fig. 1, the microgrid 1 is an autonomous power system that independently generates and consumes power, and includes a power generation facility 11, a load 12, a storage battery 13, a power conversion device 14, and a transducer 15, which are connected to each other by a power transmission and distribution network 21. Of these, the operation of the power conversion device 14, i.e., the operation of supplying the amount of power generated by the power generation facility 11 to the storage battery 13 and the operation of supplying the amount of power charged in the storage battery 13 to the load 12, is controlled by an integrated controller 31.

[0014] The power generation facility 11 is a renewable energy power source whose output is difficult to control, such as wind power generation, solar power generation, or hydroelectric power generation, and includes a watt-hour meter that measures the amount of power generated and a communication device that transmits the measured value of the amount of power.

[0015] The load 12 is a device that consumes power, and includes a watt-hour meter that measures the amount of power consumed and a communication device that transmits the measured value of the amount of power.

[0016] The storage battery 13 is a secondary battery such as a lead storage battery, a nickel-metal hydride battery, a lithium ion battery, a sodium-sulfur battery, or a redox flow battery, and has a communication device for transmitting an SOC (State Of Charge) and receiving control commands related to charging and discharging.

[0017] The power conversion device 14 includes a control device 41, an inverter 42, and a communication device (not shown). In the power conversion device 14, the inverter 42 is an inverter capable of AC / DC interconversion. When the storage battery 13 discharges, the inverter 42 converts the DC voltage output from the storage battery 13 to the power transmission / distribution network 21 into AC voltage, and when the storage battery 13 charges, the inverter 42 converts the AC voltage received from the power transmission / distribution network 21 into DC voltage. The control device 41 controls the AC / DC interconversion performed by the inverter 42 and also controls the inverter 42 so that the frequency of the output voltage of the inverter 42 has a virtual inertial force with respect to the active power supplied to the inverter's connected destination. The communication device receives an output command value transmitted from the integrated controller 31. Based on the output command value transmitted from the integrated controller 31, the power conversion device 14 causes the storage battery 13 to function as a voltage source and functions as a grid forming (GFM) inverter.

[0018] The transducer 15 detects the actual active power P, which is the active power actually output by the inverter 42 of the power conversion device 14. ｍｅａｓｕｒｅ The transducer 15 is connected to the control device 41 by a signal line such as a coaxial cable, and measures the actual active power value P ｍｅａｓｕｒｅ is output to the control device 41 via a signal line.

[0019] The integrated controller 31 is connected to the power generation equipment 11, the load 12, the storage battery 13, and the power conversion device 14, and controls the storage battery 13 and the power conversion device 14 based on information on power supply and demand, such as the amount of power generated and the amount of power consumed, transmitted from communication devices provided in each device. Specifically, when the amount of power consumed by the load 12 is small relative to the amount of power generated by the power generation equipment 11, the integrated controller 31 controls the power conversion device 14 to convert the AC voltage supplied by the power generation equipment 11 to a DC voltage, and charges the storage battery 13 with the amount of power generated by the power generation equipment 11 converted to DC by the power conversion device 14. On the other hand, when the amount of power consumed by the load 12 is large relative to the amount of power generated by the power generation equipment 11, the integrated controller 31 discharges the storage battery 13 within the range permitted by the SOC so as to compensate for the difference between the amount of power generated by the power generation equipment 11 and the amount of power consumed by the load 12, and controls the power conversion device 14 to convert the DC voltage supplied by the storage battery 13 to an AC voltage. When controlling the storage battery 13 and the power conversion device 14 to the discharge side, the integrated controller 31 sets an active power command value P ｒｅｆ is output to the power conversion device 14.

[0020] Here, the above-mentioned actual measured active power value P ｍｅａｓｕｒｅ , active power command value P ｒｅｆ , and the active powers described hereinafter are values ​​calculated in the PU method (PU: Per Unit) unless otherwise specified, and the unit is pu rather than W. For example, the active power is expressed in the PU method by dividing it by the rated output of the inverter 42.

[0021] Here, the integrated controller 31 is realized by a computer system having an arithmetic unit such as a CPU (Central Processing Unit), a storage device such as a memory such as a RAM (Random Access Memory) and a storage such as an HDD (Hard Disc Drive), a communication device, and a system bus connecting these. Specifically, the storage device stores a program that expresses the above-mentioned control processing, the arithmetic unit executes the above-mentioned program stored in the storage device, and the communication device communicates with the power generation facility 11, the load 12, the storage battery 13, and the power conversion device 14. Furthermore, the integrated controller 31 is not limited to a single computer system, and may be realized by multiple computer systems or a cloud system.

[0022] Next, the configuration and operation of the control device 41 will be described in detail with reference to Figs. 2 and 3. Fig. 2 is a block diagram showing a control system including the control device 41 and the inverter 42 to be controlled in the first embodiment, and Fig. 3 is a flowchart showing the control processing performed by the control device 41 in the first embodiment. The control device 41 includes a subtractor 111, a first virtual synchronous generator control unit 101 (hereinafter referred to as the first VSG control unit 101), a first governor control unit 113, a first command value generation unit 102, a ZOH circuit 116 (ZOH: Zero Order Hold), a reference output calculation unit 117, a subtractor 118, and a first error correction control unit 103. The control device 41 calculates the active power command value P ｒｅｆ The control unit 41 controls the frequency of the output voltage of the inverter 42 based on the above. The operation of each functional block of the control unit 41 will now be described.

[0023] The subtractor 111 subtracts the active power command value P ｒｅｆ The first governor control unit 113 subtracts the output value of the first governor control unit 113 from the calculated value and outputs the result to the first VSG control unit 101. Here, the first governor control unit 113 is a functional block that performs calculations simulating a governor (speed governor) for maintaining a constant rotation speed in a synchronous generator, and its operation will be described later.

[0024] The first VSG control unit 101 includes a subtractor 121, a multiplier 122, and a first-order lag circuit 123. The first VSG control unit 101 performs VSG control to stabilize the power system by imitating the inertial force resulting from the rotor inertia moment of a synchronous generator in the output voltage of the inverter 42. Stabilizing the power system refers to gradual frequency fluctuations in the P-f droop characteristic, in which the frequency of the power supply's output voltage decreases when the load on the AC power supply increases and increases when the load decreases. Taking a synchronous generator as an example, for example, in a rotor with a large mass and strong inertial force, load fluctuations have little effect on the rotor's rotation speed. Because the rotation speed of the rotor of a synchronous generator and the frequency of the output voltage are synchronized, fluctuations in the output voltage frequency in response to an increase in load are gradual in the case of a rotor with a large moment of inertia. In VSG control, by simulating such rotor inertia force, fluctuations in the frequency of the output voltage are made gentler in response to fluctuations in active power corresponding to load fluctuations, thereby stabilizing the power system.

[0025] In step S11 shown in FIG. 3, the first VSG control unit 101 calculates the actual measured active power value P ｍｅａｓｕｒｅ Using the frequency deviation Δω １ In detail, in the first VSG control unit 101, the subtractor 121 calculates the actual measured active power value P ｍｅａｓｕｒｅ The signal value indicating the active power deviation ΔP is subtracted from the output value of the subtractor 111. １ Furthermore, the subtractor 121 subtracts the calculated active power deviation ΔP １ is output to the multiplier 122. Here, the zero-order hold refers to holding a certain signal value at a constant value until the next sampling point.

[0026] In the first VSG control unit 101, a multiplier 122 calculates the effective power deviation ΔP １ by a gain (1 / D) and outputs the result to a first-order lag circuit 123. Subsequently, the first-order lag circuit 123 multiplies the output value of the multiplier 122 by a transfer function {1 / (1+sM / D)} formed by an inertia constant M and a damping constant D to obtain a frequency deviation Δω １is calculated and output to the first governor control unit 113 and the first command value generation unit 102. Here, s is the Laplace operator in the transfer function.

[0027] Here, the transfer function that the first VSG control unit 101 applies to the input value will be described. As described above, the first VSG control unit 101 performs control that simulates the inertial force caused by the moment of inertia of the rotor in a synchronous generator. This control is based on the rotor oscillation equation for a synchronous generator, which is expressed by equation (1-1). Here, equation (1-1) is expressed using the PU method, where M is the rotor inertia constant (unit: s), D is a damping constant (unitless), and ω is the rotor rotation speed (unit: pu).

[0028]

[0029] When formula (1-1) is transformed using formula (1-2) and then subjected to Laplace transformation to find the transfer function from ΔP to Δω, formula (1-3) is obtained. In light of the description in FIG. 2, it can be seen that the transfer function that the first VSG control unit 101 applies to the input value corresponds to the transfer function expressed by formula (1-3). Also, ΔP and Δω in formula (1-3) are ΔP in this embodiment. １ and Δω １ correspond to the following:

[0030]

[0031] 2, the first governor control unit 113 simulates the operation of a governor in a synchronous generator. Specifically, the first governor control unit 113 calculates the frequency deviation Δω output from the first VSG control unit 101. １ is multiplied by a transfer function {K / (1+sT)} and the value is output to a subtractor 111. Here, T is a time constant corresponding to the integral time, and K is the governor gain.

[0032] In step S12 shown in FIG. 3, the first command value generating unit 102 generates a frequency deviation Δω calculated by the first VSG control unit 101. １ is used to obtain the frequency command value f of the output voltage as the control command value of the inverter 42. ｖ Furthermore, the first command value generating unit 102 generates the generated frequency command value fｖ to the inverter 42 and the reference output calculation unit 117. The first command value generation unit 102 includes a constant multiplier 114a, a ZOH circuit 114b, and an adder 115, as shown in FIG.

[0033] In the first command value generating unit 102, a constant multiplier 114a calculates the frequency deviation Δω １ is multiplied by the rated frequency fn (unit: Hz) to convert the unit to Hz, and the frequency deviation df １ The ZOH circuit 114b outputs the frequency deviation df １ The signal value obtained by zero-order holding of the frequency command value f is output to the adder 115. The adder 115 adds the rated frequency fn to the signal value output from the ZOH circuit 114b to obtain the frequency command value f ｖ and outputs the calculated value as a control command value for the inverter 42 to the inverter 42 and the reference output calculation unit 117. Here, the rated frequency fn is a system frequency that is set to 50 Hz in eastern Japan and 60 Hz in western Japan, for example.

[0034] The inverter 42 operates in response to the frequency command value f output from the first command value generating unit 102. ｖ The effective power is output based on the frequency command value f ｖ When the frequency command value f fluctuates, the effective power output by the inverter 42 changes depending on, for example, the voltage or frequency of the inverter 42. ｖ The relationship between the effective power output by the inverter 42 and the effective power output by the inverter 42 will be described in detail with reference to Fig. 4. Fig. 4 is a diagram showing the relationship between the inverter 42, which is the control target, and the connection destination of the inverter 42. Fig. 4 schematically shows the inverter 42 controlled by the control device 41 and the connection destination (hereinafter simply referred to as the connection destination), such as the load 12, connected to the inverter 42 via the line reactance L. Here, the connection destination is not limited to the load 12, and if, for example, a plurality of storage batteries 13 and power conversion devices 14 are connected, these are also included as the connection destination.

[0035] In FIG. 4, the AC voltage output from the inverter 42 is V ｖ, the line reactance of the power transmission and distribution network 21 is L, the current flowing through the power transmission and distribution network 21 is i, and the AC voltage at the connection destination is v ｏ Then, these relations are expressed as the following equation (1-4): ｖ is the frequency of the AC voltage output from the inverter 42, f ｏ is the frequency of the AC voltage at the connection point, θ ｏ is the current i and the voltage v at the connection ｏ is the phase difference between

[0036]

[0037] Furthermore, to facilitate subsequent transformations, equation (1-5) is introduced, and solving equation (1-4) for the current i yields the following equation (1-6). Furthermore, given that apparent power S is expressed as in equation (1-7), the active power P output by the inverter 42 is expressed as in equation (1-8). Here, Q is the reactive power output by the inverter 42.

[0038]

[0039] In the effective power P expressed by the formula (1-8), the controllable parameters are the amplitude V of the AC voltage output by the inverter 42, ｖ and a frequency command value f of the AC voltage output by the inverter 42 ｖ Of these, the amplitude of the AC voltage is V ｖ In VSG control, the frequency command value f of the AC voltage is determined based on the Q-v drooping characteristic, which is the relationship between the reactive power Q and the voltage v in the synchronous generator. ｖ By controlling only the inverter 42, the active power P output by the inverter 42 is changed.

[0040] On the other hand, the effective power P expressed by equation (1-8) is the voltage amplitude V ｏ , frequency f ｏ , phase difference θ ｏ, and line reactance L as variables. These values ​​change depending on the load 12, other inverters 42, and other storage batteries 13 connected to the inverter 42. In other words, the active power P output from the inverter 42 changes depending on, for example, the specifications, configuration, and operating conditions of the connected equipment.

[0041] Returning to FIG. 2, the reference output calculation unit 117 calculates the frequency command value f output from the first command value generation unit 102. ｖ Based on this, the active power output by the inverter 42 when connected to the load 12 in a predetermined reference state is calculated, and the active power reference value P ｓｔ Specifically, the reference output calculation unit 117 calculates the frequency command value f output from the adder 115 as ｖ Using the above, the active power reference value P ｓｔ In equation (1-8a), the voltage amplitude V ｓ , frequency f ｓ , phase difference θ ｓ , and the line reactance L ｓ is a constant representing the connection destination in the reference state. Here, the reference state is a design condition of the control device 41 used when determining the inertial force that the power conversion device 14 realizes by VSG control. That is, when the connection destination is a voltage amplitude V ｓ , frequency f ｓ , phase difference θ ｓ , and the line reactance L ｓ In the state represented by (1), the control device 41 can cause the power conversion device 14 to exert the effect of suppressing frequency fluctuations as designed.

[0042]

[0043] Next, the subtractor 118 subtracts the active power reference value P ｓｔ From the measured active power value P ｍｅａｓｕｒｅ The first error dP is obtained by subtracting １ and outputs it to the first error correction control unit 103. Here, the first error dP calculated by the subtractor 118 is １ is the active power reference value P ｓｔ The actual measured value of the active power P ｍｅａｓｕｒｅThis indicates the magnitude relationship between the first error dP and the second error dP, and affects the effect of suppressing frequency fluctuations. １ If is a positive value, the effect of suppressing frequency fluctuations is insufficient, and the first error dP １ If is a negative value, the effect of suppressing frequency fluctuations becomes excessive.

[0044] In step S13 shown in FIG. 3, the first error correction control unit 103 calculates the first error dP １ The gain in the first VSG control unit 101 is determined using the above formula. The first error correction control unit 103 includes a first-order lag circuit 124, an adder 125, and a limiter 126, as shown in FIG.

[0045] In the first error correction control unit 103, the first-order lag circuit 124 calculates the first error dP １ Transfer function {K ｏｂｓ / (1+sT ｏｂｓ )} and outputs the result to an adder 125. The adder 125 adds 1 / D, which is the gain set in the multiplier 122, to the value input from the first-order lag circuit 124 and outputs the result to a limiter 126. ｏｂｓ is the time constant, K ｏｂｓ are gains, and these values ​​may be determined using general control theory, such as the ultimate sensitivity method.

[0046] In the first error correction control unit 103, the limiter 126 compares whether the value input from the adder 125 is greater than a predetermined lower limit value, and if it is greater than the lower limit value, sets that value, and if it is equal to or less than the lower limit value, sets the lower limit value as the gain of the multiplier 122. That is, the limiter 126 changes the gain of the multiplier 122 depending on whether the value input from the adder 125 is greater than the predetermined lower limit value, and the multiplier 122 calculates the changed gain as the active power deviation ΔP １ Here, the lower limit value is set so that the value input from the adder 125 does not become 0, and 0 must not be set. If the lower limit value is set to 0 and the value input from the adder 125 is 0 or less, 0 is set as the gain of the multiplier 122, and the output value of the first VSG control unit 101 becomes 0, causing the first VSG control unit 101 to stop functioning.

[0047] The first error correction control unit 103 calculates the actual measured active power value P ｍｅａｓｕｒｅ and the active power reference value P ｓｔ The gain of the multiplier 122 is set to compensate for the difference between the voltage amplitude V ｏ , frequency f ｏ , phase difference θ ｏ , and the first error dP １ acts to make it smaller.

[0048] Here, the hardware configuration of the control device 41 will be described. The control device 41 is realized by a PLC (Programmable Logic Controller). The hardware configuration of the PLC will be described using FIG. 5. FIG. 5 is a block diagram showing the hardware configuration of the PLC that realizes the control device 41. Each functional block of the control device 41 shown in FIG. 2 is realized by executing a program (hereinafter referred to as a control program) on the PLC that describes the processing to be performed by the control device 41. As shown in FIG. 5, this PLC includes an arithmetic unit 51, a storage device 52, and a communication device 53, which are connected via a system bus 54. Here, FIG. 5 is an example, and the configuration of the PLC is not limited to the example of FIG. 5.

[0049] In the PLC, the arithmetic unit 51 is a processor such as a CPU and executes a control program. The storage device 52 includes a volatile memory such as a RAM and a nonvolatile memory such as a flash memory. The storage device 52 stores the control program executed by the arithmetic unit 51 and data obtained during processing, and is also used as a temporary storage area for the program. The communication device 53 is, for example, a receiver and transmitter that communicates with the integrated controller 31. Unlike computer systems with similar hardware configurations, PLCs do not include an operating system (OS) and are therefore less susceptible to processing delays or slowdowns due to, for example, resident program interrupts caused by the operation of the OS. Based on these characteristics, the present embodiment illustrates an example in which the control device 41 is implemented by a PLC. However, the present invention is not limited to this example and may be implemented by a computer system.

[0050] In this way, the first VSG control unit 101 calculates the frequency deviation Δω using a transfer function based on the oscillation equation in a synchronous generator. １ The first command value generating unit 102 calculates the frequency deviation Δω １ The frequency command value f of the output voltage of the inverter 42 is calculated using ｖ The reference output calculation unit 117 generates a frequency command value f ｖ The active power reference value P output by the inverter 42 to the connection destination in a predetermined reference state based on ｓｔ and the subtractor 118 calculates the active power reference value P ｓｔ From the measured active power value P ｍｅａｓｕｒｅ The first error dP is obtained by subtracting １ The first error correction control unit 103 calculates the first error dP １ Since the gain of the transfer function of the first VSG control unit 101 is set using the above, it is possible to provide a control device 41 that controls the inverter 42 so as to exert the effect of suppressing frequency fluctuations according to the design value even when the specifications, configuration, or operating conditions of the connected device change.

[0051] In this embodiment, an example has been shown in which the first error correction control unit 103 determines the gain in the first VSG control unit 101, but the present invention is not limited to this example, and (M / D), which corresponds to the time constant of the first VSG control unit 101, may be changed in accordance with the determined gain. In detail, the first error correction control unit 103 sets the reciprocal of the determined gain as D, and determines the value of M so that the transfer function {1 / (1+sM / D)} when this D is used is stable. The method for determining the value of M may use general control theory such as Nyquist's stability criterion, or a pattern of values ​​of M relative to D may be stored in advance and the value of M may be determined by fitting this pattern. As a result, the actual measured active power value P ｍｅａｓｕｒｅ and the active power reference value P ｓｔ The first error dP is the difference between １ becomes large, and the gain set in the multiplier 122 becomes large, it is possible to prevent the occurrence of control oscillation.

[0052] Furthermore, in the example shown, limiter 126 compares whether the input value is greater than a predetermined lower limit value, and if the input value is equal to or less than the lower limit value, sets the lower limit value to multiplier 122. However, the present invention is not limited to this example, and an upper limit value may also be set, and the input value may be further compared to whether the input value is less than the upper limit value, and if the input value is equal to or greater than the upper limit value, the upper limit value may be set to multiplier 122. This makes it possible to prevent control oscillation from occurring due to an excessively high gain setting.

[0053] Second Embodiment The second embodiment will be described in detail with reference to Figures 6 and 7. Figure 6 is a block diagram showing a control system including a control device 41 and an inverter 42 to be controlled in the second embodiment, and Figure 7 is a flowchart showing the control process performed by the control device 41 in the second embodiment. Of the components shown in Figure 6, the same reference numerals as in Figure 2 indicate the same or equivalent parts, and their description will be omitted. Furthermore, the configuration of the microgrid 1 in the second embodiment is the same as that in the first embodiment, and therefore will not be shown or described again.

[0054] In the second embodiment, the control device 41 includes a subtractor 111a, a first VSG control unit 101a (hereinafter referred to as the first VSG control unit 101a), a first governor control unit 113, a first command value generation unit 102, a ZOH circuit 116, a subtractor 211, a second VSG control unit 201, a second governor control unit 213, a second command value generation unit 202, a reference output calculation unit 117, a ZOH circuit 216, a subtractor 217, and a second error correction control unit 218. The operation of each functional block of the control device 41 in the second embodiment will be described below.

[0055] The subtractor 111a subtracts the active power command value P ｒｅｆ and the second error dP output from the second error correction control unit 218, the details of which will be described later. ２ The output value of the first governor control unit 113 is subtracted from the sum of the above and the result is output to the first VSG control unit 101a.

[0056] The first VSG control unit 101a has a subtractor 121, a multiplier 122a, and a first-order lag circuit 123, and is similar to the first VSG control unit 101 in the first embodiment in that it performs VSG control to impart a pseudo inertial force of a synchronous generator to the power conversion device 14. On the other hand, the multiplier 122a differs from the first embodiment in that the gain (1 / D) by which the input value is multiplied is a fixed value.

[0057] In step S21 shown in FIG. 7, the first VSG control unit 101a calculates the actual measured active power value P ｍｅａｓｕｒｅ The first frequency deviation Δω is calculated using １ In detail, in the first VSG control unit 101a, the multiplier 122a multiplies the active power deviation ΔP calculated by the subtractor 121 by １ is multiplied by a gain (1 / D) and output to the first-order lag circuit 123. Subsequently, the first-order lag circuit 123 multiplies the output value of the multiplier 122a by a transfer function {1 / (1+sM / D)} to obtain the first frequency deviation Δω １ and outputs it to the first governor control unit 113, the first command value generation unit 102, and the subtractor 217.

[0058] The first governor control unit 113 is the same functional block as that in the first embodiment, and controls the first frequency deviation Δω output from the first VSG control unit 101a.１ is multiplied by a transfer function {K / (1+sT)} and the resulting value is output to the subtractor 111a, where the time constant T and the gain K are the same as those in the first embodiment.

[0059] In step S22 shown in FIG. 7, the first command value generating unit 102 calculates the first frequency deviation Δω calculated by the first VSG control unit 101a. １ is used to obtain a first frequency command value f which is a frequency command value for the output voltage as a control command value for the inverter 42. ｖ１ Furthermore, the first command value generator 102 generates the generated first frequency command value f ｖ１ to the inverter 42. As in the first embodiment, the first command value generator 102 includes a constant multiplier 114a, a ZOH circuit 114b, and an adder 115. In detail, the constant multiplier 114a multiplies the first frequency deviation Δω by １ The ZOH circuit 114b multiplies the frequency deviation df1 by the rated frequency fn to calculate the frequency deviation df1 and outputs the result to the ZOH circuit 114b. The ZOH circuit 114b performs zero-order hold on the frequency deviation df1 and outputs the result to the adder 115. The adder 115 adds the rated frequency fn to the signal value output from the ZOH circuit 114b to calculate the first frequency command value f ｖ１ is calculated and output to the inverter 42 as a control command value for the inverter 42.

[0060] The inverter 42 generates the first frequency command value f ｖ１ In this manner, the active power output by the inverter 42 is controlled by the frequency command value, as in the first embodiment.

[0061] In the second embodiment, the active power command value P ｒｅｆ is also input to the subtractor 211. The subtractor 211 subtracts the active power command value P ｒｅｆ The output value of the second governor control unit 213 is subtracted from the calculated value, and the result is output to the second VSG control unit 201.

[0062] In step S23 shown in FIG. 7, the second VSG control unit 201 calculates an active power reference value P ｓｔThe second frequency deviation Δω is calculated using ２ As shown in FIG. 6, the second VSG control unit 201 has the same functional blocks as the first VSG control unit 101a, that is, a subtractor 121, a multiplier 122a, and a first-order lag circuit 123, and performs the same arithmetic processing as the first VSG control unit 101a to calculate the second frequency deviation Δω. ２ and outputs it to the second governor control unit 213, the second command value generation unit 202, and the subtractor 217. Here, the gain (1 / D) by which the second VSG control unit 201 multiplies the input value, the transfer function {1 / (1+sM / D)}, and the inertia constant M and the braking constant D that constitute these are the same as those of the first VSG control unit 101a.

[0063] The second governor control unit 213, like the first governor control unit 113, calculates the second frequency deviation Δω output from the second VSG control unit 201. ２ is multiplied by a transfer function {K / (1+sT)} and the resultant value is output to the subtractor 211. Here, the time constant T and the gain K are the same values ​​as those of the first governor control unit 113.

[0064] The second command value generating unit 202 has a constant multiplier 214a, a ZOH circuit 214b, and an adder 215, and generates a second frequency command value f as a frequency command value, similarly to the first command value generating unit 102. ｖ２ Specifically, the constant multiplier 214a calculates the frequency deviation df2 by the same calculation process as the constant multiplier 114a, and outputs the frequency deviation df2 to the ZOH circuit 214b. The ZOH circuit 214b performs zero-order hold on the frequency deviation df2 and outputs the signal value to the adder 215. The adder 215 adds the rated frequency fn to the signal value output from the ZOH circuit 214b to obtain the second frequency command value f ｖ２ and outputs it to the reference output calculation unit 117.

[0065] The reference output calculation unit 117 calculates the second frequency command value f output from the second command value generation unit 202. ｖ２ Based on this, the active power output by the inverter 42 when connected to the load 12 in a predetermined reference state is calculated, and the active power reference value P ｓｔ To be more specific, the reference output calculation unit 117 outputs f ｖ= f ｖ２ The effective power reference value P ｓｔ Calculate.

[0066] The subtractor 217 subtracts the second frequency deviation Δω output from the second VSG control unit 201. ２ From this, the first frequency deviation Δω output by the first VSG control unit 101a is １ The subtractor 217 then outputs the calculated difference value of the frequency deviation to the second error correction control unit 218.

[0067] In step S24 shown in FIG. 7, the second error correction control unit 218 calculates the first frequency deviation Δω calculated by the first VSG control unit 101a. １ and the second frequency deviation Δω calculated by the second VSG control unit 201. ２ The second error dP is the difference between ２ and feeds it back to the first VSG control unit 101a. In detail, the second error correction control unit 218 functions as an integrator and applies a transfer function (K ｓ / s) to obtain the second error dP ２ This second error dP ２ is the measured active power value P ｍｅａｓｕｒｅ and the active power reference value P ｓｔ Since this value is generated according to the difference between ｍｅａｓｕｒｅ and the active power reference value P ｓｔ Here, the difference between the transfer function (K ｓ / s), K ｓ is an integral gain in the second error correction control unit 218, and its value may be determined using general control theory so that the entire control system including the second error correction control unit 218 is stable. Also, s is a Laplace operator.

[0068] In this way, the first VSG control unit 101a calculates the actual measured value P of the active power output by the inverter 42. ｍｅａｓｕｒｅ The first frequency deviation Δω is calculated by a transfer function based on the oscillation equation in the synchronous generator. １The second VSG control unit 201 calculates the active power reference value P ｓｔ The second frequency deviation Δω is calculated by a transfer function based on the oscillation equation in the synchronous generator. ２ The first command value generator 102 calculates the first frequency deviation Δω １ is used to obtain a first frequency command value f as a frequency command value for the output voltage of the inverter 42. ｖ１ and outputs the second command value to the inverter 42, and the second command value generator 202 generates a second frequency deviation Δω ２ is used to obtain a second frequency command value f as the frequency command value of the output voltage of the inverter 42. ｖ２ and outputs it to the reference output calculation unit 117, which calculates the second frequency command value f ｖ２ The active power reference value P output by the inverter 42 to the connection destination in a predetermined reference state based on ｓｔ The second error correction control unit 218 calculates the first frequency deviation Δω １ and the second frequency deviation Δω ２ The second error dP ２ is calculated and fed back to the first VSG control unit 101a, it is possible to provide a control device 41 that controls the inverter 42 so as to exert the effect of suppressing frequency fluctuations according to the design value even when the specifications, configuration, or operating state of the connected device changes.

[0069] In the first and second embodiments, an example in which there are a plurality of power generation facilities 11 and a plurality of loads 12 is shown using Fig. 1 , but the present invention is not limited to this example, and there may be only one power generation facility 11 and one load 12. In addition, an example in which there is one storage battery 13 is shown using Fig. 1 , but the present invention is not limited to this example, and there may be a plurality of storage batteries 13, and the plurality of storage batteries 13 may be a combination of a plurality of types of secondary batteries.

[0070] Furthermore, in the first and second embodiments, when there are multiple power generation facilities 11, the multiple power generation facilities 11 may be a combination of multiple types of renewable energy power sources. Furthermore, the power generation facilities 11 do not need to have more than one watt-hour meter and communication device that transmits the watt-hour meter measurement value for each power generation facility 11; when there are multiple power generation facilities 11, they only need to be configured to measure and transmit the total amount of power generated. Similarly, the load 12 does not need to have more than one watt-hour meter and communication device that transmits the watt-hour meter measurement value for each load 12; when there are multiple loads 12, they only need to be configured to measure and transmit the total amount of power consumed.

[0071] In the first and second embodiments, the microgrid 1 includes the power generation facility 11, the load 12, the storage battery 13, the power conversion device 14, and the transducer 15. However, the present invention is not limited to this example, and the microgrid 1 may further include power receiving and distribution facilities such as a circuit breaker, a disconnecting switch, a transformer, etc. The microgrid 1 may be connected to another power system via the power transmission and distribution network 21, i.e., may be interconnected to a grid, and interconnection facilities such as a circuit breaker, a disconnecting switch, a transformer, etc. may be provided between the microgrid 1 and the other power system.

[0072] Furthermore, in the first and second embodiments, an example in which the microgrid 1 has the load 12 has been described, but the present invention is not limited to this example, and the microgrid 1 does not need to have the load 12. However, in this case, it should be noted that the microgrid 1 needs to have a plurality of storage batteries 13. This is because the power charged in the storage batteries 13 needs to be consumed by a destination. In other words, when a storage battery 13 discharges power to charge another storage battery 13, the present control device 41 controls the storage battery 13 that performs the discharge. In this case, the charging and discharging of each storage battery 13 may be controlled by the integrated controller 31.

[0073] In the first and second embodiments, the transducer 15 detects the actual measured active power value P ｍｅａｓｕｒｅ However, the present invention is not limited to this example. Actual measured values ​​of voltage and current are measured and output to the control device 41, and the control device 41 uses the output measured values ​​to calculate the actual measured active power value P ｍｅａｓｕｒｅThe transducer 15 may also calculate VT (V ｏ ltageTransf ｏ rmer) and CT (Current Transfer ｏ rmer) may be connected to the power transmission and distribution network 21.

[0074] Furthermore, in the first and second embodiments, the method of connecting the integrated controller 31 to the power generation equipment 11, the load 12, the storage battery 13, and the power conversion device 14 is not limited in any way, and they may be connected by a signal line such as a coaxial cable, by wireless communication, or via the Internet or an intranet.

[0075] In the first and second embodiments, the integrated controller 31 may be configured as, for example, a Community Energy Management System (CEMS), an Area Energy Management System (AEMS), or a Building and Energy Management System (BEMS), and may also control the supply and demand of electricity in another power system in parallel.

[0076] Furthermore, although multiple embodiments have been described, in addition to the above disclosure, as long as the features described in each embodiment are not contradictory, the embodiments can be freely combined, any components of each embodiment can be modified, or each embodiment can be omitted. For example, in both embodiments 1 and 2, the order of the constant multiplier 114a and the ZOH circuit 114b can be reversed. In addition, in embodiment 2, the second error correction control unit 218 calculates the second error dP ２ may be output to the subtractor 121 instead of to the subtractor 111a.

[0077] REFERENCE SIGNS LIST 1 Microgrid, 11 Power generation equipment, 12 Load, 13 Storage battery, 14 Power conversion device, 15 Transducer, 21 Power transmission and distribution network, 31 Integrated controller, 41 Control device, 42 Inverter, 101, 101a First VSG control unit, 102 First command value generation unit, 103 First error correction control unit, 117 Reference output calculation unit, 201 Second VSG control unit, 202 Second command value generation unit, 218 Second error correction control unit

Claims

1. A control device that controls an inverter so that the frequency of the inverter's output voltage has a virtual inertial force with respect to the active power supplied to a destination of the inverter, comprising: a first virtual synchronous generator control unit that calculates a frequency deviation by a transfer function based on an oscillation equation in a synchronous generator using an actual measured value of the active power supplied by the inverter to the destination; a first command value generation unit that generates a frequency command value for the inverter's output voltage using the frequency deviation calculated by the first virtual synchronous generator control unit; and a first error correction control unit that determines a gain of the transfer function in the first virtual synchronous generator control unit using a first error that is the difference between an active power reference value, which is the active power supplied by the inverter to the destination of the inverter in a predetermined reference state, and the actual measured value of the active power.

2. The control device according to claim 1, further comprising: a reference output calculation unit that calculates the active power reference value using the frequency command value generated by the first command value generation unit.

3. The control device according to claim 1 or 2, wherein the first error correction control section further determines a time constant of the transfer function using the determined gain of the transfer function.

4. A control device according to any one of claims 1 to 3, wherein the first error correction control section sets at least one of an upper limit and a lower limit for the gain of the transfer function to be determined.

5. A control device that controls an inverter so that the frequency of the inverter's output voltage has a virtual inertial force with respect to the active power supplied to a destination of the inverter, comprising: a first virtual synchronous generator control unit that calculates a first frequency deviation using a transfer function based on an oscillation equation of a synchronous generator, using an actual measured value of the active power supplied by the inverter to the destination of the inverter; a first command value generation unit that generates a first frequency command value as a frequency command value for the output voltage of the inverter, using the first frequency deviation calculated by the first virtual synchronous generator control unit; a second virtual synchronous generator control unit that calculates a second frequency deviation using the transfer function, using an active power reference value that is the active power supplied by the inverter to the destination of the inverter in a predetermined reference state; and a second error correction control unit that calculates a second error from the difference between the first frequency deviation calculated by the first virtual synchronous generator control unit and the second frequency deviation calculated by the second virtual synchronous generator control unit, and feeds the second error back to the first virtual synchronous generator control unit.

6. The control device according to claim 5, comprising: a second command value generation unit that generates a second frequency command value as a frequency command value for the output voltage of the inverter using the second frequency deviation calculated by the second virtual synchronous generator control unit; and a reference output calculation unit that calculates the active power reference value using the second frequency command value generated by the second command value generation unit.

7. A control method for controlling an inverter so that the frequency of the inverter's output voltage has a virtual inertial force with respect to the active power supplied to a destination of the inverter, the control method comprising: a step of calculating a frequency deviation by a transfer function based on an oscillation equation for a synchronous generator using an actual measured value of the active power supplied by the inverter to the destination; a step of generating a frequency command value for the output voltage of the inverter using the frequency deviation; and a step of determining a gain of the transfer function using a first error that is the difference between an active power reference value, which is the active power supplied by the inverter to the destination of the inverter in a predetermined reference state, and the actual measured value of the active power.

8. A control method for controlling an inverter so that the frequency of the inverter's output voltage has a virtual inertial force with respect to the active power supplied to a destination of the inverter, the control method comprising: a step of calculating a first frequency deviation by a transfer function based on an oscillation equation of a synchronous generator using an actual measured value of the active power supplied by the inverter to the destination; a step of generating a frequency command value for the output voltage of the inverter by using the first frequency deviation; a step of calculating a second frequency deviation by the transfer function using an active power reference value which is the active power supplied by the inverter to the destination of the inverter in a predetermined reference state; and a step of calculating a second error from the difference between the first frequency deviation and the second frequency deviation, and feeding the second error back to the step of calculating the first frequency deviation.

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