Power system

Abstract

Stable operation is achieved immediately after the circuit breaker opens or immediately after load fluctuations while the circuit is open. [Solution] The power system 100 is connected to the power grid 10 via a circuit breaker 11. The power system 100 includes a load device 22, a power generation system 30 that performs governor-free operation in which the output power changes according to the frequency deviation in the power system 100, a storage device 41 that outputs DC power, a power converter 42 that converts DC power to AC power, and a storage system 40 that includes a control device 45 that performs pseudo-inertia control to simulate inertia response in the power converter 42. Immediately after the circuit breaker 11 changes from a closed state to an open state, or immediately after the load of the load device changes while the circuit breaker 11 is open, the frequency fluctuation is suppressed by pseudo-inertia control in the storage system 40.

Description

Technical Field

[0001] The present disclosure relates to a power system connected to a power grid via a circuit breaker.

Background Art

[0002] Power systems connected to a power grid such as a commercial grid via a circuit breaker have been proposed in the past. For example, Patent Document 1 discloses a self-generation facility including a generator driven by a prime mover such as a gas engine and power storage means capable of charge and discharge. The in-house distribution line of the self-generation facility is connected to the commercial grid via a circuit breaker for system separation. By closing / open the circuit breaker, the connection and separation of the self-generation facility to / from the commercial grid can be switched.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Immediately after the circuit breaker changes from the closed state to the open state, the power that the power generation device should output can increase rapidly. Similarly, when the load fluctuates rapidly in the open state of the circuit breaker, the power that the power generation device should output can increase rapidly. In the above situations, even if the power is assisted by the discharge of the power storage means, as a whole, the self-generation facility may instantaneously or transiently lack power, and as a result, it may not be possible to appropriately maintain the operation of the self-generation facility due to fluctuations in frequency. Considering the above circumstances, one aspect of the present disclosure aims to realize stable operation immediately after the circuit breaker opens or immediately after a load fluctuation in the open state.

Means for Solving the Problems

[0005] To solve the above problems, a power system according to one aspect of the present disclosure is a power system connected to a power grid via a circuit breaker, comprising: a load device; a power generation system that performs governor-free operation in which the output power changes according to the frequency deviation in the power system; a power storage device that outputs DC power; a power conversion device that converts the DC power into AC power; and a power storage system that performs pseudo-inertia control to simulate inertia response in the power conversion device, wherein the frequency fluctuation is suppressed by pseudo-inertia control in the power storage system immediately after the circuit breaker changes from a closed state to an open state, or immediately after the load of the load device fluctuates while the circuit breaker is in an open state.

[0006] A power system according to one aspect of the present disclosure is a power system connected to a power grid via a circuit breaker, comprising a load device and an energy storage system, wherein the energy storage system includes an energy storage device that outputs DC power, a power converter that converts the DC power to AC power, and a control device that controls the power converter, wherein the control device causes the numerical values ​​of one or more control parameters applied to the control of the power converter to differ between the closed state and the open state of the circuit breaker. [Brief explanation of the drawing]

[0007] [Figure 1] This is a block diagram illustrating the configuration of a power system according to the first embodiment. [Figure 2] This is a diagram illustrating the operation of the reference system. [Figure 3] This is a diagram illustrating the operation of the reference system. [Figure 4] This is a diagram illustrating the operation of the power system immediately after a circuit breaker is opened. [Figure 5] This is a diagram illustrating the operation of the power system immediately after a circuit breaker is opened. [Figure 6] This is a diagram illustrating the operation of a power system when the load suddenly increases while the circuit breaker is open. [Figure 7]This is a diagram illustrating the operation of a power system when the load suddenly decreases while the circuit breaker is open. [Figure 8] This is a block diagram illustrating the functional configuration of a control device. [Figure 9] This is an explanatory diagram of the conversion (adjustment frequency characteristics) performed by the conversion processing unit. [Figure 10] This is a block diagram illustrating a part of the functional configuration of the control device in the third embodiment. [Figure 11] This is a block diagram of the drive processing unit in a modified example. [Figure 12] This is a block diagram illustrating the configuration of a power system in a modified example. [Figure 13] This is a block diagram illustrating the configuration of a power system in a modified example. [Modes for carrying out the invention]

[0008] The embodiments for implementing this disclosure will be described with reference to the drawings. The embodiments described below are exemplary embodiments that may be envisioned when implementing this disclosure. Therefore, the scope of this disclosure is not limited to the embodiments described below.

[0009] A: First Embodiment Figure 1 is a block diagram illustrating the configuration of a power system 100 according to the first embodiment. The power system 100 is a private power generation facility connected to the power grid 10 via a circuit breaker 11. The power grid 10 is a commercial grid (distribution grid or transmission grid) for supplying AC power generated by power generation facilities such as thermal power plants or nuclear power plants to businesses or consumers such as ordinary households.

[0010] The circuit breaker 11 is a switchgear that switches the electrical connection and disconnection between the power grid 10 and the power system 100. Specifically, one end of the circuit breaker 11 is connected to the power grid 10, and the other end of the circuit breaker 11 is connected to the interconnection point 21 of the power system 100. The circuit breaker 11 may also be installed as an element constituting the power system 100.

[0011] The breaker 11 is controlled to be either in a closed state or an open state. The closed state is a state in which the power system 100 is electrically connected to the power grid 10. The open state is a state in which the power system 100 is electrically separated from the power grid 10. The breaker 11 is maintained in the closed state during normal operation and is changed from the closed state to the open state when an abnormality such as a power outage occurs in the power grid 10. In the open state of the breaker 11, the supply of power from the power grid 10 to the power system 100 stops, and the power system 100 transitions to an autonomous operation independent of the power grid 10.

[0012] As illustrated in FIG. 1, the power system 100 includes a load device 22, a control device 23, a power generation system 30, and a power storage system 40.

[0013] The load device 22 is various loads (in-house loads) electrically connected to the connection point 21. The load device 22 operates by consuming the power supplied from the power grid 10 and the power supplied from the power generation system 30 and the power storage system 40. Note that the load device 22 may include equipment that supplies control power or auxiliary power to each element of the power system 100.

[0014] The control device 23 is a controller that controls the power generation system 30 and the power storage system 40. Specifically, the control device 23 measures the AC power at the connection point 21 and sets a power command value Px and a power command value Py according to the measurement result so that the AC power at the connection point 21 becomes the target value. The power command value Px is a command value for the active power that the power generation system 30 should output and is transmitted from the control device 23 to the power generation system 30. The power command value Py is a command value for the active power that the power storage system 40 should output and is transmitted from the control device 23 to the power storage system 40.

[0015] The power generation system 30 is connected to the connection point 21 via the circuit breaker 24. The circuit breaker 24 is a switching device that switches the electrical connection and disconnection between the connection point 21 and the power generation system 30. In the following description, it is assumed for convenience that the circuit breaker 24 maintains a closed circuit.

[0016] The power generation system 30 is a power generation facility that outputs AC power according to the power command value Px, and includes a prime mover 31, a power generation device 32, a transformer 33, and a control device 34.

[0017] The prime mover 31 is a power source that drives the power generation device 32. The prime mover 31 in the first embodiment is a lean combustion engine such as a gas engine type home power generation facility. A lean combustion engine is an internal combustion engine that burns in a state where the air excess ratio in the air-fuel mixture exceeds the theoretical air-fuel ratio. While a lean combustion engine can achieve high-efficiency power generation, it tends to have low performance (hereinafter referred to as "load following performance") in quickly responding to load fluctuations. However, a combustion engine other than a lean combustion engine may be adopted as the prime mover 31. Also, the prime mover 31 may be adopted as a power generation facility other than a home power generation facility.

[0018] The control device 34 controls the rotational force of the prime mover 31 according to the power command value Px received from the control device 23. Note that part of the functions of the control device 34 may be mounted on the control device 23, or part of the functions of the control device 23 may be mounted on the control device 34.

[0019] The power generation device 32 is a synchronous generator that generates AC power by being driven by the prime mover 31. Specifically, the power generation device 32 is mechanically connected to the rotation shaft of the prime mover 31 and outputs three-phase AC power according to the rotational force of the prime mover 31. Note that the synchronous reactance of the generator is included in the power generation device 32. The output terminals of the power generation device 32 are connected to one end of the transformer 33. The transformer 33 is a power facility for boosting or降压 that matches the output voltage of the power generation device 32 to the received power voltage of the power grid 10 or the load device 22. The other end of the transformer 33 is connected to the connection point 21.

[0020] When the circuit breaker 11 is closed, if the output power of the generator 32 falls below the power command value Px from the control device 23, the fuel supply increases due to the characteristics of the governor of the prime mover 31, and as a result, the output power of the generator 32 increases. On the other hand, if the output power of the generator 32 exceeds the power command value Px from the control device 23, the fuel supply decreases, resulting in a decrease in the output power of the generator 32. As described above, the power generation system 30 operates in accordance with the power command value Px.

[0021] When the circuit breaker 11 is open, the output power of the power generator 32 changes autonomously according to the deviation between the frequency at the interconnection point 21 and a predetermined reference frequency Fn. The reference frequency Fn is the standard frequency (rated frequency) for AC power in the power system 10, for example, 50 Hz or 60 Hz. When the frequency is below the reference frequency Fn, the fuel supply amount increases due to the governor characteristics of the prime mover 31, resulting in an increase in the output power of the power system 100. On the other hand, when the frequency is above the reference frequency Fn, the fuel supply amount to the prime mover 31 decreases, resulting in a decrease in the output power of the power system 100. As described above, the power generator 30 performs governor-free operation in which the output power changes according to the frequency deviation. Governor-free operation by the power generator 30 enables autonomous output adjustment in accordance with the power supply and demand balance in the power system 10 or the load device 22.

[0022] The energy storage system 40 is connected to the interconnection point 21 via a circuit breaker 25. The circuit breaker 25 is a switchgear that switches the electrical connection and disconnection between the interconnection point 21 and the energy storage system 40. For the purposes of the following explanation, it will be assumed that the circuit breaker 25 remains closed.

[0023] The energy storage system 40 is a power facility that exchanges AC power with the interconnection point 21 through charging and discharging, and comprises an energy storage device 41, a power converter 42, an interconnection reactor 43, a transformer 44, and a control device 45.

[0024] The energy storage device 41 is a secondary battery that discharges and charges DC power. In other words, the energy storage device 41 outputs DC power. The type of energy storage device 41 is arbitrary, but examples of energy storage devices 41 include lithium-ion batteries and redox flow batteries.

[0025] The power converter 42 is an AC / DC converter that converts DC power and AC power to each other. For example, the power converter 42 is a three-phase inverter that converts DC power output from the energy storage device 41 into AC power. The transformer 44 transforms the voltage of the AC power. Specifically, the power converter 42 converts the DC power supplied by the discharge of the energy storage device 41 into AC power, and the transformer 44 transforms the voltage of the AC power after conversion by the power converter 42. The transformer 44 also transforms the voltage of the AC power supplied from the interconnection point 21, and the power converter 42 converts the AC power after transformation by the transformer 44 into DC power and supplies it to the energy storage device 41.

[0026] The interconnection reactor 43 is an inductance element connected between the power converter 42 and the transformer 44, and suppresses harmonic components in the output current from the power converter 42. Note that the interconnection reactor 43 and the transformer 44 may be omitted.

[0027] The control device 45 is a controller that controls the power converter 42. Specifically, the control device 45 controls the power converter 42 to generate active power corresponding to the power command value Py received from the control device 23. The power converter 42 and the control device 45 constitute a Power Conditioning System (PCS) that controls the power exchanged between the energy storage system 40 and the interconnection point 21. Some or all of the functions of the control device 45 may be incorporated into the control device 23, or some or all of the functions of the control device 23 may be incorporated into the control device 45.

[0028] In the first embodiment, the control device 45 performs pseudo-inertia control and governor-free equivalent control on the power converter 42.

[0029] The pseudo-inertia control of the control device 45 is a control process that causes the power converter 42 to simulate the inertia response of a synchronous generator. Specifically, the pseudo-inertia control simulates the rotational inertia of a synchronous generator and controls the frequency of the power converter 42 according to the output power of the power converter 42, the deviation of the output power from the target value, and the set value of the inertia constant. For example, the control device 45 increases the frequency of the power converter 42 when the output power of the power converter 42 is decreasing from a predetermined value, and decreases the frequency of the power converter 42 when the output power of the power converter 42 is increasing from a predetermined value. As a result of the pseudo-inertia control by the control device 45, abrupt fluctuations in frequency are suppressed.

[0030] The governor-free equivalent control of the control device 45 is a control process that causes the power converter 42 to simulate the response of a synchronous generator's governor. Specifically, the governor-free equivalent control simulates the governor of a synchronous generator, controlling the output power of the power converter 42 according to the deviation of the power converter 42's frequency and the reference frequency Fn, and the set value of the adjustment ratio. For example, the control device 45 increases the output power of the power converter 42 when the frequency falls below the reference frequency Fn, and decreases the output power of the power converter 42 when the frequency exceeds the reference frequency Fn. As a result of the governor-free equivalent control by the control device 45, the frequency is stably maintained. Note that an inverter equipped with pseudo-inertia control and governor-free equivalent control is also called a virtual synchronous generator (VSG) control.

[0031] Figure 2 is an explanatory diagram of the operation of a comparative power system (hereinafter referred to as the "reference system") in which the energy storage system 40 is not installed. In the reference system, the load device 22 and the power generation system 30 are connected to the interconnection point 21, similar to the first embodiment.

[0032] Figure 2 illustrates the operation of the reference system immediately after the circuit breaker 11 changes from a closed state to an open state, when the circuit breaker 11 is closed and the power generation system 30 is supplying some power to the load device 22 while the remaining power is supplied from the power grid 10. Because the circuit breaker 11 opens at time t1, separating it from the power grid 10, the active power output from the power generation system 30 of the reference system increases sharply at time t1 to compensate for the power that was supplied from the power grid 10. In a configuration where only the power generation system 30 supplies power to the load device 22, the inertia of the power generation system 30 and the response of the governor cannot keep up with the increase in power due to the separation from the power grid 10, causing the frequency to drop, and as illustrated in Figure 2, the active power supplied from the power generation system 30 to the load device 22 may decrease sharply.

[0033] Figure 3 illustrates the operation of the reference system immediately after the circuit breaker 11 changes from a closed state to an open state, when the circuit breaker 11 is closed and the power generation system 30 is supplying all the power to the load device 22 while supplying the surplus power to the power grid 10. Because the circuit breaker 11 opens at time t1, separating the reference system from the power grid 10, the active power output from the power generation system 30 of the reference system decreases sharply at time t1 because the power supplied to the power grid 10 is interrupted. In a configuration where only the power generation system 30 supplies power to the load device 22, the inertia of the power generation system 30 and the response of the governor cannot keep up with the decrease in power due to the separation from the power grid 10, causing the frequency to rise, and as shown in Figure 3, the active power supplied from the power generation system 30 to the load device 22 may decrease sharply.

[0034] Figure 4 is an explanatory diagram of the operation of the power system 100 in the first embodiment, in which a power generation system 30 and an energy storage system 40 are installed. In Figure 4, as in Figure 2, it is assumed that the circuit breaker 11 changes from a closed state to an open state at time t1. In Figure 4, the time change of the active power consumed by the load device 22, the time change of the active power output by the power generation system 30, the time change of the active power output by the energy storage system 40, and the time change of frequency are shown together on a common time axis.

[0035] When circuit breaker 11 opens, the power system 100 is separated from the power grid 10, resulting in the cessation of power supply from the power grid 10 to the power system 100 (interconnection point 21) at time t1. To compensate for the power shortage at connection point 21 caused by the cessation of power supply from the power grid 10, the active power output from the power generation system 30 and the energy storage system 40 increases sharply at time t1. The total increase in active power output from the power generation system 30 and the energy storage system 40 is equivalent to the power supplied from the power grid 10 immediately before time t1.

[0036] Immediately after time t1, the frequency at the interconnection point 21 begins to decrease. The power system 100 eliminates the frequency decrease that occurred after time t1 over time through governor-free operation by the power generation system 30 and pseudo-inertia control and governor-free equivalent control by the energy storage system 40.

[0037] Figure 5 is an explanatory diagram of the operation of the power system 100 in the first embodiment, in which a power generation system 30 and an energy storage system 40 are installed. In Figure 5, as in Figure 3, it is assumed that the circuit breaker 11 changes from a closed state to an open state at time t1. In Figure 5, the time change of the active power consumed by the load device 22, the time change of the active power output by the power generation system 30, the time change of the active power output by the energy storage system 40, and the time change of frequency are shown together on a common time axis.

[0038] When circuit breaker 11 opens, the power system 100 is separated from the power grid 10, resulting in the cessation of power supply from power system 100 (interconnection point 21) to power grid 10 at time t1. To compensate for the surplus power from power generation system 30 resulting from the opening of circuit breaker 11, the active power output from power generation system 30 and energy storage system 40 decreases sharply at time t1. The total decrease in active power output from power generation system 30 and energy storage system 40 is equivalent to the power supplied to power grid 10 immediately before time t1.

[0039] Immediately after time t1, the frequency at the interconnection point 21 begins to rise. The power system 100 eliminates the frequency rise after time t1 over time through governor-free operation by the power generation system 30 and pseudo-inertia control and governor-free equivalent control by the energy storage system 40.

[0040] The pseudo-inertia control by the energy storage system 40 in the first embodiment allows for a faster response compared to governor-free equivalent control. Therefore, in the period T1 immediately following time t1, the pseudo-inertia control by the energy storage system 40 becomes dominant compared to governor-free operation by the power generation system 30 and governor-free equivalent control by the energy storage system 40. In other words, in period T1, frequency fluctuations are suppressed by the pseudo-inertia control by the energy storage system 40. However, in period T1, governor-free operation by the power generation system 30 and governor-free equivalent control by the energy storage system 40 also contribute to suppressing frequency fluctuations.

[0041] On the other hand, with only the pseudo-inertia control by the energy storage system 40, a steady-state frequency deviation (steady-state error) may remain in the frequency. That is, the effect of the pseudo-inertia control by the energy storage system 40 decreases over time, and the governor-free operation by the power generation system 30 and the governor-free equivalent control by the energy storage system 40 become relatively more effective. Therefore, in period T2 after the elapsed period T1, the governor-free operation by the power generation system 30 and the governor-free equivalent control by the energy storage system 40 become dominant compared to the pseudo-inertia control. In other words, in period T2, the power system 100 reduces the residual frequency deviation through the governor-free operation by the power generation system 30 and the governor-free equivalent control by the energy storage system 40. In addition, in period T2, the pseudo-inertia control by the energy storage system 40 also contributes to the reduction of the frequency deviation.

[0042] Figures 6 and 7 illustrate a scenario where the load on the load device 22 changes rapidly while the circuit breaker 11 remains open. Figure 6 is an explanatory diagram of the operation of the power system 100 when the load on the load device 22 increases rapidly while the circuit breaker 11 is open. Time t1 in Figure 6 is the point in time when the load on the load device 22 increases rapidly. To compensate for the rapid increase in load, the active power output from the power generation system 30 and the energy storage system 40 increases rapidly at time t1. The sum of the increases in active power output from the power generation system 30 and the energy storage system 40 corresponds to the increase in load at time t1.

[0043] Immediately after time point t1, the frequency at the interconnection point 21 begins to decrease over time. The power system 100 eliminates the frequency decrease after time point t1 over time through governor-free operation by the power generation system 30 and pseudo-inertia control and governor-free equivalent control by the energy storage system 40.

[0044] The power generation system 30 and the energy storage system 40 operate in the same manner as in Figure 4. That is, in the period T1 immediately following time t1, the pseudo-inertia control by the energy storage system 40 becomes dominant compared to the governor-free operation by the power generation system 30 and the governor-free equivalent control by the energy storage system 40. In other words, during period T1, frequency fluctuations are suppressed by the pseudo-inertia control by the energy storage system 40.

[0045] On the other hand, in period T2 after period T1 has elapsed, governor-free operation by the power generation system 30 and governor-free equivalent control by the energy storage system 40 become dominant compared to pseudo-inertia control. That is, in period T2, the power system 100 reduces the frequency deviation remaining in the frequency by governor-free operation by the power generation system 30 and governor-free equivalent control by the energy storage system 40.

[0046] Figure 7 is an explanatory diagram of the operation of the power system 100 when the load on the load device 22 decreases rapidly while the circuit breaker 11 is open. Time t1 in Figure 7 is the time when the load on the load device 22 decreases rapidly. To compensate for the rapid decrease in load, the active power output from the power generation system 30 and the energy storage system 40 decreases rapidly at time t1. The sum of the decreases in active power output from the power generation system 30 and the energy storage system 40 corresponds to the decrease in load at time t1.

[0047] Immediately after time point t1, the frequency of the interconnection point 21 begins to rise over time. The power system 100 eliminates the rise in frequency after time point t1 over time through governor-free operation by the power generation system 30 and pseudo-inertia control and governor-free equivalent control by the energy storage system 40.

[0048] In the period T1 immediately following time t1, the pseudo-inertia control by the energy storage system 40 becomes dominant compared to the governor-free operation by the power generation system 30 and the governor-free equivalent control by the energy storage system 40. In other words, in period T1, the rise in frequency is suppressed by the pseudo-inertia control by the energy storage system 40.

[0049] On the other hand, in period T2 after period T1 has elapsed, governor-free operation by the power generation system 30 and governor-free equivalent control by the energy storage system 40 become dominant compared to pseudo-inertia control. That is, in period T2, the power system 100 reduces the frequency deviation remaining in the frequency by governor-free operation by the power generation system 30 and governor-free equivalent control by the energy storage system 40.

[0050] As described above, in the first embodiment, immediately after the circuit breaker 11 opens (Figures 4 and 5) or immediately after load fluctuations while the circuit is open (Figures 6 and 7), frequency fluctuations are suppressed by pseudo-inertia control in the energy storage system 40. Furthermore, the frequency deviation remaining in the frequency during pseudo-inertia control is reduced by governor-free operation of the power generation system 30 and governor-free equivalent control of the energy storage system 40. Therefore, compared to the reference system (Figure 2) in which the power generation system 30 alone provides power to the load device 22, stable operation can be achieved quickly by suppressing frequency fluctuations immediately after the circuit breaker 11 opens or immediately after load fluctuations while the circuit is open.

[0051] As mentioned above, lean-combustion engines used as prime movers 31 in the power generation system 30 can achieve highly efficient power generation, but tend to have poor load-following capabilities. According to the first embodiment, immediately after the circuit breaker 11 is opened (Figures 4 and 5) or immediately after load fluctuations in the open state (Figures 6 and 7), frequency fluctuations are suppressed by pseudo-inertia control in the energy storage system 40. Therefore, the lack of load-following capability of the power generation system 30 is compensated for by the load-following capability provided by pseudo-inertia control, and stable power supply can be achieved even in a configuration in which a lean-combustion engine is used as the prime mover 31 in the power generation system 30.

[0052] In the first embodiment, in particular, frequency fluctuations are suppressed by pseudo-inertia control immediately after the circuit breaker 11 opens or immediately after load fluctuations in the open state, while residual frequency deviations after pseudo-inertia control are reduced by governor-free operation by the power generation system 30 and governor-free equivalent control by the energy storage system 40. Therefore, it is possible to converge the frequency more quickly and stably while reducing the load on the power generation system 30.

[0053] [Functional configuration of the control device 45] Figure 8 is a block diagram illustrating the functional configuration of the control device 45. Each element illustrated in Figure 8 is implemented by one or more types of processors, such as a PLD (Programmable Logic Device), CPU (Central Processing Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit). As illustrated in Figure 8, the control device 45 implements multiple functions (output control unit 50, inertia control unit 60, voltage control unit 70, reactive power control unit 80, drive unit 90) for controlling the power converter 42.

[0054] [Output control unit 50] The output control unit 50 implements governor-free equivalent control of the power converter 42. Specifically, the output control unit 50 calculates the power command value Pz according to the frequency command value (hereinafter referred to as "frequency command value Fref") related to the AC power of the power converter 42. As illustrated in Figure 8, the output control unit 50 includes an arithmetic processing unit 51, a conversion processing unit 52, a control processing unit 53, a range limiting unit 54, and an arithmetic processing unit 55.

[0055] The calculation processing unit 51 calculates the deviation between the frequency command value Fref and the reference frequency Fn (hereinafter referred to as "frequency deviation ΔF") (ΔF = Fref - Fn). The reference frequency Fn is also expressed as the target value of the frequency command value Fref. The conversion processing unit 52 converts the frequency deviation ΔF into a power change amount ΔPa.

[0056] FIG. 9 is an explanatory diagram of the conversion by the conversion processing unit 52. Specifically, the relationship between the frequency deviation ΔF and the power change amount ΔPa (hereinafter referred to as "regulation rate characteristic") is illustrated in FIG. 9.

[0057] As illustrated in FIG. 9, the numerical range of the frequency deviation ΔF is divided into a high region BH, a low region BL, and a dead band B0. The high region BH is a range where the frequency command value Fref exceeds the reference frequency Fn (Fref>Fn). Specifically, the high region BH is a region where the frequency deviation ΔF exceeds the threshold value ΔFH. The threshold value ΔFH is a predetermined positive number. The low region BL is a range where the frequency command value Fref is lower than the reference frequency Fn (Fref<Fn). Specifically, the low region BL is a region where the frequency deviation ΔF is lower than the threshold value ΔFL. The threshold value ΔFL is a predetermined negative number. The dead band B0 is a region between the high region BH and the low region BL. The threshold value ΔFH is the upper limit value of the dead band B0, and the threshold value ΔFL is the lower limit value of the dead band B0.

[0058] In the high region BH, the power change amount ΔPa changes according to the frequency deviation ΔF within the range of negative numbers that mean charging of the power storage system 40. Specifically, the power change amount ΔPa linearly decreases with an increase in the frequency deviation ΔF within the high region BH. That is, as the frequency command value Fref increases with respect to the reference frequency Fn, the charging power by the power storage system 40 increases. The gradient Gr of the power change amount ΔPa with respect to the frequency deviation ΔF in the high region BH is expressed by the following mathematical formula (1).

Equation

[0059] The symbol Pn in the mathematical formula (1) is a reference value (rated output) regarding the output power of the power conversion device 42. The symbol Rr in the mathematical formula (1) means the regulation rate on the charging side of the power storage system 40. The regulation rate Rr is a ratio representing the relationship between the frequency deviation ΔF and the power change amount ΔPa, and is an index regarding the degree of autonomously changing the output power of the power conversion device 42 with respect to the frequency deviation ΔF.

[0060] In the low-range BL, the power change ΔPa varies according to the frequency deviation ΔF within a range of positive numbers that represent the discharge of the energy storage system 40. Specifically, the power change ΔPa decreases linearly with increasing frequency deviation ΔF within the low-range BL. That is, the lower the frequency command value Fref is relative to the reference frequency Fn, the greater the discharge power from the energy storage system 40. The slope Gd of the power change ΔPa with respect to frequency deviation ΔF in the low-range BL is expressed by the following equation (2).

number

[0061] In equation (2), the symbol Rd represents the drop rate on the discharge side of the energy storage system 40. The drop rate Rd is a ratio that represents the relationship between the frequency deviation ΔF and the power change ΔPa, and is an indicator of the degree to which the output power of the power converter 42 is autonomously changed in response to the frequency deviation ΔF.

[0062] The dead zone B0 is the range within the numerical range of the frequency deviation ΔF in which the power change ΔPa does not depend on the frequency deviation ΔF. Specifically, the power change ΔPa in the dead zone B0 is fixed at zero regardless of the numerical value of the frequency deviation ΔF. The width W of the dead zone B0 corresponds to the interval between the threshold ΔFH and the threshold ΔFL. The width W of the dead zone B0, the threshold ΔFH, and the threshold ΔFL are the dead zone parameters that define the dead zone B0.

[0063] The conversion processing unit 52 in Figure 8 identifies the power change amount ΔPa corresponding to the frequency deviation ΔF in the adjustment ratio characteristics described above. As illustrated above, multiple conversion parameters are applied to the conversion by the conversion processing unit 52. These conversion parameters include, for example, the adjustment ratios Rr and Rd, and the dead zone parameters (range width W, threshold ΔFH, threshold ΔFL) mentioned above.

[0064] The control processing unit 53 performs deviation suppression control to stabilize the transient response of the power change amount ΔPa. The deviation suppression control by the control processing unit 53 applies a proportional gain Kg_P, an integral gain Kg_I, and a differential gain Kg_D. Specifically, the control processing unit 53 performs the following: (1) Proportional calculation of the power change ΔPa by applying the proportional gain Kg_P, (2) The integral calculation of the power change ΔPa to which the integral gain Kg_I is applied, (3) Differential calculation of the power change ΔPa with the differential gain Kg_D applied, (4) An operation to calculate the power change ΔPb by adding the output values ​​from each operation and The following is performed: The proportional gain Kg_P, integral gain Kg_I, and differential gain Kg_D are control gains applied to the control of the power converter 42.

[0065] The range limiting unit 54 calculates the power change amount ΔPc by limiting the range of the power change amount ΔPb. Specifically, the range limiting unit 54 limits the range of the power change amount ΔPb to the range between the upper limit value EH and the lower limit value EL. That is, the range limiting unit 54 sets the upper limit value EH for the power change amount ΔPb if the value exceeds the upper limit value EH, and sets the lower limit value EL for the power change amount ΔPc if the value falls below the lower limit value EL. If the power change amount ΔPb is a value within the range between the upper limit value EH and the lower limit value EL, the range limiting unit 54 outputs the power change amount ΔPb as the power change amount ΔPc. The power change amount ΔPc is a command value for the change in output power of the power converter 42. The upper limit value EH and the lower limit value EL are limiting parameters applied to the control of the power converter 42. Furthermore, the upper limit EH and lower limit EL may be applied to the control processing unit 53 to restrict, for example, the range of the numerical value obtained by the integral calculation.

[0066] The arithmetic processing unit 55 calculates the power command value Pz by adding the power change amount ΔPc and the power command value Py. As mentioned above, the power command value Py is the command value of the active power transmitted from the control device 23 to the energy storage system 40.

[0067] [Inertia control unit 60] The inertia control unit 60 in Figure 8 implements pseudo-inertia control for the power converter 42. Specifically, the inertia control unit 60 is a mathematical model that simulates the equations of motion (oscillation equations) that describe the mechanical behavior and characteristics of a rotating body in a synchronous generator. Specifically, the inertia control unit 60 calculates the frequency command value Fref according to the power command value Pz. The frequency command value Fref is the command value of the frequency at the AC output of the power converter 42. The frequency command value Fref is also supplied to the output control unit 50 (arithmetic processing unit 51) mentioned above. As illustrated in Figure 8, the inertia control unit 60 comprises an arithmetic processing unit 61, an inertia processing unit 62, and a damping processing unit 63.

[0068] The arithmetic processing unit 61 calculates the power deviation δP by subtracting the power measurement value Pm and the damping control value Pd from the power command value Pz set by the output control unit 50. The power measurement value Pm is the actual measured value of the active power output by the power converter 42.

[0069] The inertia processing unit 62 calculates the frequency command value Fref by applying the inertia constant M. The inertia constant M is a parameter that represents the degree of inertia in pseudo-inertia control. Specifically, the inertia constant M is a constant that defines the degree of change (inertia effect) when the output power from the power converter 42 changes in accordance with the time rate of change of the frequency related to the output power. That is, for example, the larger the inertia constant M, the more the frequency fluctuation in response to the fluctuation of output power is suppressed. Specifically, the inertia processing unit 62 divides the power deviation δP by the inertia constant M and calculates the frequency command value Fref by integrating the result of the division.

[0070] The braking processing unit 63 suppresses transient fluctuations of the frequency command value Fref (damping control) by applying a braking coefficient D to the calculation. The braking coefficient D is a parameter that represents the degree of braking in pseudo-inertia control. Specifically, the braking coefficient D is a constant that defines the degree of change (braking effect) when the output power from the power converter 42 changes in accordance with the frequency deviation δF of the output power. That is, the larger the braking coefficient D, the greater the correction amount of the output power for frequency fluctuations, and the more transient frequency fluctuations are attenuated. The braking processing unit 63 calculates the deviation δF between the frequency command value Fref and the reference frequency Fn (δF = Fref - Fn), and calculates the aforementioned braking control value Pd by multiplying the deviation δF by the braking coefficient D. The braking control value Pd is a value that is subtracted from the power command value Pz.

[0071] As described above, multiple inertia control parameters are applied to the pseudo-inertia control by the inertia control unit 60. These inertia control parameters include, for example, the inertia constant M and the braking coefficient D.

[0072] [Voltage control unit 70] The voltage control unit 70 is an automatic voltage regulator (AVR) for maintaining a constant output voltage of the power converter 42. Specifically, the voltage control unit 70 calculates a voltage command value Vref according to the measured output voltage Vm of the power converter 42. The voltage command value Vref is the command value of the AC voltage output by the power converter 42. As illustrated in Figure 8, the voltage control unit 70 comprises an arithmetic processing unit 71, a control processing unit 72, and an arithmetic processing unit 73.

[0073] The arithmetic processing unit 71 calculates the deviation (hereinafter referred to as "voltage deviation ΔV") between the measured value Vm of the AC voltage output by the power converter 42 and a predetermined set value Vn (ΔV = Vn - Vm). The set value Vn is the target value of the AC voltage output by the power converter 42.

[0074] The control processing unit 72 performs deviation suppression control to maintain the output voltage of the power converter 42 at a set value Vn. The deviation suppression control by the control processing unit 72 applies a proportional gain Kv_P and an integral gain Kv_I. Specifically, the control processing unit 72 performs the following: (1) Proportional calculation of the voltage deviation ΔV with proportional gain Kv_P applied, (2) The integral calculation of the voltage deviation ΔV to which the integral gain Kv_I is applied, (3) An operation to add the output values ​​from each operation and The following is performed. The proportional gain Kv_P and integral gain Kv_I are control gains applied to the control of the power converter 42 by the voltage control unit 70. Note that the configuration of the deviation suppression control by the control processing unit 72 is not limited to the above example and may be changed as desired. For example, the deviation suppression control by the control processing unit 72 may include differential operations.

[0075] The arithmetic processing unit 73 calculates the voltage command value Vref by adding the calculation result from the control processing unit 72 and the voltage deviation ΔV calculated by the arithmetic processing unit 71.

[0076] [Reactive power control unit 80] The reactive power control unit 80 controls the reactive power output by the power converter 42. The operating mode of the reactive power control unit 80 is set to either the reactive power adjustment mode (AQR: Automatic Reactive Power Regulator) or the power factor adjustment mode (APFR: Automatic Power Factor Regulator). The reactive power adjustment mode is an operating mode that adjusts the reactive power output by the power converter 42 to a set value (hereinafter referred to as "reactive power set value Qn"). The reactive power set value Qn is the target value of the reactive power. The power factor adjustment mode is an operating mode that sets the power factor of the power converter 42 to a predetermined value (hereinafter referred to as "power factor set value PFm"). The power factor set value PFm is the target value of the power factor of the power converter 42. The control device 45 selects either the reactive power adjustment mode or the power factor adjustment mode in response to instructions from the control device 23. Alternatively, the control device 45 may select the operating mode in response to instructions from the operator of the power system 100. The reactive power control unit 80 of the first embodiment includes a reactive power calculation unit 81, a deviation calculation unit 82, a deviation suppression unit 83, and a calculation processing unit 84.

[0077] In power factor adjustment mode, the reactive power calculation unit 81 calculates the reactive power (hereinafter referred to as "reactive power setting value Qn") from the power measurement value Pm of the power converter 42 and the power factor setting value PFm. The reactive power setting value Qn is the target value of reactive power required to generate the active power of the power measurement value Pm under the power factor setting value PFm. In power factor adjustment mode (APFR), the calculation result of the reactive power calculation unit 81 is applied as the reactive power setting value Qn. On the other hand, in reactive power adjustment mode (AQR), the reactive power command value transmitted from the control device 23 to the energy storage system 40 is applied as the reactive power setting value Qn.

[0078] The deviation calculation unit 82 calculates the deviation ΔQ between the reactive power set value Qn and the reactive power measured value Qm (ΔQ = Qn - Qm). The reactive power measured value Qm is the actual value of the reactive power output by the power converter 42. The deviation suppression unit 83 performs deviation suppression control to maintain the reactive power of the power converter 42 at the set value Qn. Specifically, the deviation suppression unit 83 calculates the reactive power command value Qref by multiplying the deviation ΔQ by the integral gain Kq and integrating the multiplication result (Kq·ΔQ). The arithmetic processing unit 84 adds the reactive power command value Qref to the voltage deviation ΔV calculated by the arithmetic processing unit 71. The voltage deviation ΔV after adding the reactive power command value Qref is the target of the deviation suppression control by the control processing unit 72. Note that the configuration of the deviation suppression control by the deviation suppression unit 83 is not limited to the above example and may be changed as desired. For example, the deviation suppression control by the deviation suppression unit 83 may include proportional or differential calculations.

[0079] As described above, multiple reactive power parameters are applied to the control of reactive power by the reactive power control unit 80. These reactive power parameters include, for example, the power factor setpoint PFm and the integral gain Kq.

[0080] [Drive Processing Unit 90] The drive processing unit 90 generates a command value for the three-phase AC voltage according to the frequency command value Fref and the voltage command value Vref. The command value is the voltage value at each instant representing the ideal waveform of the three-phase AC voltage. The drive processing unit 90 also generates a drive signal by pulse width modulation (PWM) applied to the command value for the three-phase AC voltage, and controls the switching of the inverter of the power converter 42 with this drive signal. As a result of the control by the drive signal, the power converter 42 generates AC power corresponding to the frequency command value Fref and the voltage command value Vref from the DC power supplied from the energy storage device 41. Note that the phase command value calculated by the integral of the frequency command value Fref may also be instructed to the drive processing unit 90 together with the voltage command value Vref.

[0081] As described above, multiple control parameters are applied to the control of the power converter 42 by the control device 45. These multiple control parameters include, for example, (1) Multiple conversion parameters (Rr, Rd, W, ΔFH, ΔFL) applied to the conversion processing unit 52, (2) Multiple control gains (Kg_P, Kg_I, Kg_D) applied to the control processing unit 53, (3) Limiting parameters (EH, EL) applied to the range limiting unit 54, (4) Inertia control parameters (M,D) applied to the inertia control unit 60, (5) Multiple control gains (Kv_P, Kv_I) applied to the output control unit 50 (control processing unit 72), (6) Reactive power parameters (PFm, Kq) applied to the reactive power control unit 80 Includes.

[0082] In the first embodiment, the numerical values ​​of each control parameter are set so that the pseudo-inertia control of the energy storage system 40 is quickly activated immediately after the circuit breaker 11 opens (Figures 4 and 5) or immediately after load fluctuations while the circuit is open (Figures 6 and 7).

[0083] B: Second Embodiment A second embodiment of this disclosure will now be described. For elements whose function is the same as in the first embodiment in each of the embodiments described below, the same reference numerals as in the first embodiment will be used, and detailed descriptions of each will be omitted as appropriate.

[0084] The operating conditions required or preferred for the power system 100 differ depending on whether the circuit breaker 11 is closed, connecting the power system 100 to the power grid 10, or whether the circuit breaker 11 is open, separating the power system 100 from the power grid 10. Taking these circumstances into consideration, the control device 45 of the second embodiment sets the numerical values ​​of several control parameters applied to the control of the power converter 42 to be different depending on whether the circuit breaker 11 is closed or open.

[0085] With the above configuration, when the circuit breaker 11 is in a closed state, each control parameter can be set to a value suitable for the operating conditions for connection with the power system 10, and when the circuit breaker 11 is in an open state, the control parameters can be set to a value suitable for the operating conditions when separated from the power system 10. Therefore, for example, the control parameters can be set so that the frequency converges quickly and stably immediately after the circuit breaker 11 opens or immediately after load fluctuations in the open state. Specific examples of setting the control parameters are described in detail below.

[0086] [Output control unit 50] The control device 45 sets the values ​​of the control parameters (Rr, Rd, W, ΔFH, ΔFL, Kg_P, Kg_I, Kg_D, EH, EL) applied to the output control unit 50 to differ depending on whether the circuit breaker 11 is closed or open.

[0087] For example, the control device 45 makes the values ​​of the conversion parameters (Rr, Rd, W, ΔFH, ΔFL) applied to the conversion by the conversion processing unit 52 different for the closed and open states of the circuit breaker 11. Specifically, the values ​​of the adjustment ratio R(Rr, Rd) in the open state of the circuit breaker 11 are lower than the values ​​of the adjustment ratio R in the closed state of the circuit breaker 11. In other words, the control device 45 decreases the value of the adjustment ratio R when the circuit breaker 11 is open and increases the value of the adjustment ratio R when the circuit breaker 11 is closed.

[0088] As can be understood from the above-mentioned formula (1), in the high-region BH, the smaller the adjustment ratio Rr, the larger the absolute value |Gr| of the gradient Gr of the power change amount ΔPa with respect to the frequency deviation ΔF. That is, the power change amount ΔPa changes more steeply in response to the frequency deviation ΔF. Similarly, in the low-region BL, the smaller the adjustment ratio Rd, the more steeply the power change amount ΔPa changes in response to the frequency deviation ΔF. In the second embodiment, the value of the adjustment ratio R(Rr,Rd) when the circuit breaker 11 is open is lower than the value of the adjustment ratio R when it is closed. Therefore, when the circuit breaker 11 is open (system separation), it is possible to make the output power of the power converter 42 respond more strongly to frequency fluctuations.

[0089] Furthermore, the range width W of the dead zone B0 when the circuit breaker 11 is open is less than the range width W when the circuit breaker 11 is closed. In other words, the control device 45 reduces the dead zone B0 when the circuit breaker 11 is open and expands the dead zone B0 when the circuit breaker 11 is closed. Specifically, when the circuit breaker 11 is open, the control device 45 performs one or both of the following processes: bringing the threshold ΔFH (ΔFH>0), which is the upper limit of the dead zone B0, closer to zero, and bringing the threshold ΔFL (ΔFL<0), which is the lower limit of the dead zone B0, closer to zero.

[0090] As mentioned above, in the dead zone B0, the power change ΔPa is fixed at zero. Therefore, the narrower the dead zone B0, the more sensitively the power change ΔPa fluctuates in accordance with the frequency deviation ΔF. In other words, according to the second embodiment, when the circuit breaker 11 is opened, it is possible to make the output power of the power converter 42 respond sensitively to the frequency fluctuation.

[0091] As described above, in the second embodiment, the conversion parameters (Rr, Rd, W, ΔFH, ΔFL) related to the conversion between the frequency deviation ΔF and the power change amount ΔPa in the governor-free equivalent control of the power converter 42 are set to different values ​​for the closed state and the open state of the circuit breaker 11. Therefore, in the open state of the circuit breaker 11, the values ​​of the conversion parameters are set so that they can respond more strongly and sensitively to frequency fluctuations, thereby appropriately assisting the governor-free operation of the power generation system 30.

[0092] In the above explanation, we focused on the conversion parameters (Rr, Rd, W, ΔFH, ΔFL) applied to the conversion processing unit 52 among the multiple control parameters applied to the output control unit 50. However, the numerical values ​​of each control parameter other than the conversion parameters may also be set to different values ​​depending on whether the circuit breaker 11 is in a closed or open state.

[0093] For example, the control device 45 sets the control gains (Kg_P, Kg_I, Kg_D) applied to the deviation suppression control by the control processing unit 53 to different values ​​for the closed state and the open state of the circuit breaker 11. For example, one of the control gain values ​​in the open state and the control gain value in the closed state is greater than the other.

[0094] Furthermore, the control device 45 sets the upper limit value EH and the lower limit value EL applied to the range limiting unit 54 to different values ​​depending on whether the circuit breaker 11 is closed or open. For example, one of the upper limit value EH in the open state and the upper limit value EH in the closed state exceeds the other, and one of the lower limit value EL in the open state and the lower limit value EL in the closed state exceeds the other.

[0095] [Inertia control unit 60] The control device 45 sets the values ​​of the inertia control parameters (M,D) applied to the inertia control unit 60 to be different depending on whether the circuit breaker 11 is in a closed or open state.

[0096] For example, the control device 45 sets the value of the inertia constant M applied to the inertia processing unit 62 to be different depending on whether the circuit breaker 11 is closed or open. Specifically, the value of the inertia constant M in the open state of the circuit breaker 11 is greater than the value of the inertia constant M in the closed state of the circuit breaker 11. In other words, the control device 45 increases the value of the inertia constant M when the circuit breaker 11 is open and decreases the value of the inertia constant M when the circuit breaker 11 is closed. With this configuration, when the circuit breaker 11 is open, it is possible to quickly adjust the output voltage of the power converter 42 to instantaneous changes in frequency.

[0097] Furthermore, the control device 45 sets the value of the braking coefficient D applied to the braking processing unit 63 to be different depending on whether the circuit breaker 11 is closed or open. Specifically, the value of the braking coefficient D in the open state of the circuit breaker 11 is higher than the value of the braking coefficient D in the closed state of the circuit breaker 11. In other words, the control device 45 increases the value of the braking coefficient D when the circuit breaker 11 is open and decreases the value of the braking coefficient D when the circuit breaker 11 is closed. With this configuration, when the circuit breaker 11 is open, it is possible to attenuate frequency fluctuations caused by the inertia of the power generation system 30 and the pseudo-inertia of the energy storage system 40, and to coordinate the inertial operation of both the power generation system 30 and the energy storage system 40.

[0098] As described above, in the second embodiment, the inertia control parameters (M,D) applied to the pseudo-inertia control of the power converter 42 are set to different values ​​for the closed and open states of the circuit breaker 11. Therefore, for example, in the open state of the circuit breaker 11, the values ​​of the inertia control parameters can be set to respond quickly to frequency fluctuations, thereby appropriately assisting the governor-free operation of the power generation system 30.

[0099] [Voltage control unit 70] The control device 45 sets the value of the control gain Kv(Kv_P, Kv_I) applied to the voltage control unit 70 (control processing unit 72) to be different depending on whether the circuit breaker 11 is closed or open. Specifically, the value of the proportional gain Kv_P when the circuit breaker 11 is open is higher than the value of the proportional gain Kv_P when the circuit breaker 11 is closed. In other words, the control device 45 increases the value of the proportional gain Kv_P when the circuit breaker 11 is open and decreases the value of the proportional gain Kv_P when the circuit breaker 11 is closed.

[0100] Similarly, the value of the integral gain Kv_I when the circuit breaker 11 is open exceeds the value of the integral gain Kv_I when the circuit breaker 11 is closed. In other words, the control device 45 increases the value of the integral gain Kv_I when the circuit breaker 11 is open and decreases the value of the integral gain Kv_I when the circuit breaker 11 is closed. With this configuration, the voltage deviation ΔV of the power converter 42 can be rapidly reduced when the circuit breaker 11 is open.

[0101] [Reactive power control unit 80] The control device 45 sets the values ​​of the reactive power parameters (PFm, Kq) applied to the reactive power control unit 80 to differ between the closed and open states of the circuit breaker 11. For example, the value of the integral gain Kq in the open state of the circuit breaker 11 is greater than the value of the integral gain Kq in the closed state of the circuit breaker 11. That is, the control device 45 increases the value of the integral gain Kq when the circuit breaker 11 is open and decreases the value of the integral gain Kq when the circuit breaker 11 is closed. With this configuration, the high power factor operation of the power generation system 30 can be appropriately assisted when the circuit breaker 11 is open.

[0102] Furthermore, when the circuit breaker 11 is open, the control device 45 sets the operating mode of the reactive power control unit 80 to the reactive power adjustment mode. Therefore, when the circuit breaker 11 is open, the reactive power output by the power converter 42 is adjusted to a predetermined reactive power set value Qn. The operating mode for setting the power factor of the power converter 42 to the power factor set value PFm may also be used when the circuit breaker 11 is open.

[0103] The relationship between the opening and closing of the circuit breaker 11 and the magnitude of the values ​​of each control parameter is not limited to the above examples and may be changed as appropriate. That is, a configuration in which the value of the control parameter in the open state is greater than the value in the closed state, or a configuration in which the value of the control parameter in the open state is less than the value in the closed state is conceivable.

[0104] C: Third Embodiment Figure 10 is a block diagram illustrating a part of the functional configuration of the control device 45 in the third embodiment. As illustrated in Figure 10, the output control unit 50 of the third embodiment includes a low-pass filter 56 and a rate of change limiting unit 57, in addition to the same elements as in the first embodiment. The control device 45 selectively processes the time series of power command values ​​Pz output by the arithmetic processing unit 55 using either the low-pass filter 56 or the rate of change limiting unit 57. The power command value Pz after processing by the low-pass filter 56 or the rate of change limiting unit 57 is input to the inertia control unit 60.

[0105] The low-pass filter 56 suppresses high-frequency components included in the time series of the power command value Pz. Specifically, the low-pass filter 56 smooths out sharp changes in the time series by imparting a first-order lag characteristic corresponding to the time constant Tz to the time series of the power command value Pz. The time constant Tz is an example of a control parameter applied to the control of the power converter 42.

[0106] The control device 45 sets the value of the time constant Tz applied to the low-pass filter 56 differently depending on whether the circuit breaker 11 is closed or open. Specifically, the value of the time constant Tz in the open state of the circuit breaker 11 is lower than the value of the time constant Tz in the closed state of the circuit breaker 11. In other words, the control device 45 decreases the time constant Tz when the circuit breaker 11 is open and increases the value of the time constant Tz when the circuit breaker 11 is closed. Therefore, in the open state, the temporal fluctuation of the power command value Pz is reflected more quickly in the output power of the power converter 42 compared to the closed state. That is, in the open state of the circuit breaker 11, the power converter 42 can respond quickly to frequency fluctuations.

[0107] The rate of change limiting unit 57 is a rate limiter that limits the time change of the power command value Pz output by the output control unit 50. Specifically, the rate of change limiting unit 57 limits the rate of change of the power command value Pz to a range below the limit value L. The limit value L is an example of a control parameter applied to the control of the power converter 42.

[0108] The control device 45 sets the value of the limit value L applied to the rate of change limiting unit 57 differently depending on whether the circuit breaker 11 is closed or open. Specifically, the value of the limit value L in the open state of the circuit breaker 11 is greater than the value of the limit value L in the closed state of the circuit breaker 11. In other words, the control device 45 increases the limit value L when the circuit breaker 11 is open and decreases the value of the limit value L when the circuit breaker 11 is closed. Therefore, in the open state of the circuit breaker 11, a steeper change in the power command value Pz is permitted compared to the closed state. That is, in the open state, the temporal fluctuation of the power command value Pz is reflected more quickly in the output power of the power converter 42 compared to the closed state. As described above, in the open state of the circuit breaker 11, the power converter 42 can respond quickly to frequency fluctuations. Note that the low-pass filter 56 and the rate of change limiting unit 57 are examples, and the method for defining the temporal change of the power command value Pz may be changed as appropriate.

[0109] D: Variant The following are examples of specific modifications that may be added to each of the embodiments exemplified above. Two or more embodiments may be arbitrarily selected from the following examples and merged as appropriate, provided they do not contradict each other.

[0110] (1) The control parameters that are set to different values ​​for the open and closed states of the circuit breaker 11 are not limited to the examples given in each of the above embodiments. For example, the control device 45 may set the value of the reference frequency Fn to be different for the open and closed states.

[0111] (2) The drive processing unit 90 may adjust the frequency command value Fref set by the output control unit 50 and the inertia control unit 60, and the voltage command value Vref set by the voltage control unit 70 and the reactive power control unit 80. For example, as illustrated in Figure 11, the drive processing unit 90 may include a synchronization holding unit 91 and an overcurrent suppression unit 92.

[0112] The synchronization holding unit 91 maintains phase synchronization by suppressing the operations of the output control unit 50 and the inertia control unit 60 when the phase synchronization between the output voltage of the power converter 42 and the AC voltage of the power system 10 becomes impossible as a result of the operations of the output control unit 50 and the inertia control unit 60. Specifically, the synchronization holding unit 91 adjusts the frequency command value Fref calculated by the inertia control unit 60 so that the difference between the frequency command value Fref and the frequency measurement value Fm of the output voltage is maintained within a predetermined allowable range. The synchronization parameters applied to the operation by the synchronization holding unit 91 are also examples of control parameters applied to the control of the power converter 42. Therefore, the control device 45 may set different numerical values ​​for the synchronization parameters applied to the synchronization holding unit 91 depending on whether the circuit breaker 11 is closed or open.

[0113] The overcurrent suppression unit 92 limits the output current of the power converter 42 to a predetermined range. Specifically, the overcurrent suppression unit 92 adjusts the voltage command value Vref and frequency command value Fref to the power converter 42 so that the current value of the output current of the power converter 42 does not exceed a predetermined limit value. The limit value applied to the current limit by the overcurrent suppression unit 92 is also an example of a control parameter applied to the control of the power converter 42. Therefore, the control device 45 may set the limit value applied to the overcurrent suppression unit 92 to be different for the closed state and the open state of the circuit breaker 11.

[0114] (3) In each of the above-described embodiments, the power system 100 is shown as comprising one power generation system 30 and one energy storage system 40, but the total number of power generation systems 30 and energy storage systems 40 can be changed as desired. For example, as illustrated in Figure 12, the power system 100 may comprise multiple power generation systems 30 and multiple energy storage systems 40. In the configuration of Figure 12, the numerical values ​​of each control parameter may differ depending on the number of power generation systems 30 or energy storage systems 40 in operation.

[0115] Furthermore, elements other than those exemplified in each of the above-described embodiments (load device 22, power generation system 30, energy storage system 40) may be connected to the interconnection point 21 of the power system 100. For example, as illustrated in Figure 13, various power equipment 26 may be connected to the interconnection point 21 together with the load device 22. The power equipment 26 may be, for example, renewable energy power generation equipment such as solar power generation panels or wind power generation equipment, or phase adjustment equipment that adjusts the reactive power of the power system 100.

[0116] (4) In each of the above-described embodiments, the control device 45 of the energy storage system 40 is shown as performing pseudo-inertia control and governor-free equivalent control on the power converter 42, but the governor-free equivalent control by the energy storage system 40 may be omitted. Specifically, the output control unit 50 in each of the above-described embodiments may be omitted. Also, the reactive power control unit 80 in each of the above-described embodiments may be omitted.

[0117] (5) In the above-described embodiments, examples were given in which the power system 100 is used as a private power generation facility. However, the use and configuration of the power system 100 are not limited to the above examples and may be changed as appropriate. Specifically, the power system 100 may constitute a small-scale power grid such as a microgrid.

[0118] (6) In each of the above-described embodiments, a power generation system 30 equipped with a lean-burn engine as the prime mover 31 has been given as an example. However, the type and method (e.g., combustion method) of the prime mover 31 used in the power generation system 30 is not limited to the above examples and may be changed as appropriate. Specifically, the power generation system 30 may be a power generation facility equipped with, for example, a diesel engine or a gas turbine as the prime mover 31. Such a power generation facility may be used, for example, as an emergency power source in a facility such as a data center.

[0119] (7) The notation "the nth" (where n is a natural number) in this application is used solely as a formal and convenient label to distinguish each element in notation, and has no substantive meaning whatsoever. Therefore, there is no room for restrictive interpretation of the position or order of each element based on the notation "the nth".

[0120] E: Addendum From the embodiments illustrated above, for example, the following configurations can be understood. For the sake of easier understanding of each embodiment, the reference numerals in the drawings are conveniently included in parentheses below; however, the inclusion of these reference numerals does not mean that this disclosure is limited to the illustrated embodiments.

[0121] A power system (100) according to one aspect of the present disclosure (Aspect 1) is a power system (100) connected to a power grid (10) via a circuit breaker (11), and comprises a load device (22), a power generation system (30) that performs governor-free operation in which the output power changes according to the frequency deviation in the power system (100), a power storage device (41) that outputs DC power, a power converter (42) that converts the DC power to AC power, and a power storage system (40) that performs pseudo-inertia control to simulate inertia response in the power converter (42), wherein the frequency fluctuation is suppressed by pseudo-inertia control in the power storage system (40) immediately after the circuit breaker (11) changes from a closed state to an open state, or immediately after the load of the load device (22) fluctuates while the circuit breaker (11) is in an open state.

[0122] In the above embodiment, immediately after the circuit breaker (11) opens or immediately after load fluctuations while it is open, frequency fluctuations are suppressed by pseudo-inertia control in the energy storage system (40). Furthermore, the frequency deviation remaining in the frequency due to the pseudo-inertia control is reduced by governor-free operation of the power generation system (30). Therefore, compared to a configuration in which the power generation system (30) alone provides power to the load device (22), stable operation can be achieved quickly by suppressing frequency fluctuations immediately after the circuit breaker (11) opens or immediately after load fluctuations while it is open.

[0123] The power generation system (30) includes, for example, a prime mover (31) including a lean-burn engine and a power generation device (32) driven by the prime mover (31). While lean-burn engines can achieve highly efficient power generation, they tend to have poor load-following capabilities. According to this disclosure, immediately after the circuit breaker (11) opens or immediately after load fluctuations in the open state, frequency fluctuations are suppressed rapidly by pseudo-inertia control in the energy storage system (40). Therefore, the lack of load-following capability in the power generation system (30) is compensated for by the responsiveness of the energy storage system (40), and stable power supply can be achieved even in a configuration in which a lean-burn engine is used as the prime mover (31) of the power generation system (30). However, the type and method (e.g., combustion method) of the power generation system (30) are not limited to the above examples and may be changed as desired.

[0124] A "lean-burn engine" is an internal combustion engine that burns fuel in a mixture of fuel and air with an excess air ratio exceeding the stoichiometric air-fuel ratio. In other words, a lean-burn engine achieves reduced combustion temperature and high-efficiency operation by burning a mixture with a larger amount of air and a leaner fuel mixture compared to the stoichiometric air-fuel ratio. Specifically, gas engine-type private power generators are given as an example of a "lean-burn engine."

[0125] In a specific example of Embodiment 1 (Embodiment 2), the control device (45) performs governor-free equivalent control, which controls the output power of the power converter (42) according to the frequency deviation. In the above embodiment, frequency fluctuations are suppressed by pseudo-inertia control immediately after the circuit breaker (11) opens or immediately after load fluctuations in the open state, and the frequency deviation remaining after the pseudo-inertia control is reduced by governor-free operation by the power generation system (30) and governor-free equivalent control by the energy storage system (40). Therefore, it is possible to converge the frequency more quickly and stably while reducing the load on the power generation system (30).

[0126] In a specific example of Embodiment 1 or Embodiment 2 (Embodiment 3), the control device (45) sets the numerical values ​​of one or more control parameters applied to the control of the power converter (42) to differ between the closed state and the open state of the circuit breaker (11). In the above embodiments, when the circuit breaker (11) is in the closed state, the control parameters can be set to numerical values ​​suitable for operating conditions for connection with the power system (10), and when the circuit breaker (11) is in the open state, the control parameters can be set to numerical values ​​suitable for operating conditions when isolated from the power system (10). Therefore, for example, the control parameters can be set so that the frequency converges quickly and stably immediately after the circuit breaker (11) opens or immediately after load fluctuations in the open state.

[0127] In a specific example of Embodiment 3 (Embodiment 4), the control device (45) includes a conversion processing unit (52) that converts the frequency deviation (ΔF) between the command value (Fref) and the set value (Fn) of the frequency into a change in output power (ΔPa) of the power converter (42), and the one or more control parameters include one or more conversion parameters applied to the conversion by the conversion processing unit (52). In the above embodiments, the conversion parameters relating to the conversion between the frequency deviation (ΔF) and the change in output power (ΔPa) in the governor-free equivalent control of the power converter (42) are set to different values ​​for the closed state and the open state of the circuit breaker (11). Therefore, for example, in the open state of the circuit breaker (11), the conversion parameters can be set to be able to respond quickly and sensitively to frequency fluctuations, thereby appropriately assisting the governor-free operation of the power generation system (30).

[0128] In a specific example of Embodiment 4 (Embodiment 5), the one or more conversion parameters include a regulating ratio (Rr,Rd) that represents the relationship between the frequency deviation (ΔF) and the change in output power (ΔPa), and the value of the regulating ratio (Rr,Rd) in the open state of the circuit breaker (11) is lower than the value of the regulating ratio (Rr,Rd) in the closed state of the circuit breaker (11). In the above embodiment, the value of the regulating ratio (Rr,Rd) in the open state of the circuit breaker (11) is lower than the value of the regulating ratio (Rr,Rd) in the closed state of the circuit breaker (11). Therefore, when the circuit breaker (11) is opened, it is possible to quickly adjust the output power of the power converter (42) to the frequency fluctuation.

[0129] In a specific example of Embodiment 4 or Embodiment 5 (Embodiment 6), the one or more conversion parameters include a dead zone parameter that defines a dead zone (B0) in the numerical range of the frequency deviation (ΔF) in which the change in output power (ΔPa) is maintained at zero, and the range width (W) of the dead zone (B0) in the open state of the circuit breaker (11) is less than the range width (W) of the dead zone (B0) in the closed state of the circuit breaker (11). In the above embodiments, the range width (W) of the dead zone (B0) in the open state of the circuit breaker (11) is less than the range width (W) of the dead zone (B0) in the closed state of the circuit breaker (11). Therefore, when the circuit breaker (11) is open, it is possible to make the output power of the power converter (42) respond sensitively to frequency fluctuations.

[0130] In any specific example of embodiments 3 to 6 (embodiment 7), the control device (45) includes an inertia control unit (60) for the pseudo-inertia control of the power converter (42), and the one or more control parameters include one or more inertia control parameters applied to the pseudo-inertia control. In the above embodiments, the inertia control parameters applied to the pseudo-inertia control of the power converter (42) are set to different values ​​for the closed state and the open state of the circuit breaker (11). Therefore, for example, in the open state of the circuit breaker (11), the governor-free operation of the power generation system (30) can be appropriately assisted by setting the value of the inertia control parameter so that it can respond quickly to frequency fluctuations.

[0131] In a specific example of Embodiment 7 (Embodiment 8), the one or more inertia control parameters include an inertia constant (M) representing the degree of inertia in the pseudo-inertia control, and the value of the inertia constant (M) in the open state of the circuit breaker (11) exceeds the value of the inertia constant (M) in the closed state of the circuit breaker (11). In the above embodiment, the value of the inertia constant (M) in the open state of the circuit breaker (11) exceeds the value of the inertia constant (M) in the closed state of the circuit breaker (11). Therefore, when the circuit breaker (11) is opened, it is possible to quickly respond to instantaneous changes in frequency with the power converter (42).

[0132] In a specific example of Embodiment 7 or Embodiment 8 (Embodiment 9), the one or more inertia control parameters include a braking coefficient (D) representing the degree of braking in the pseudo-inertia control, and the value of the braking coefficient (D) in the open state of the circuit breaker (11) exceeds the value of the braking coefficient (D) in the closed state of the circuit breaker (11). In the above embodiments, the value of the braking coefficient (D) in the open state of the circuit breaker (11) exceeds the value of the braking coefficient (D) in the closed state of the circuit breaker (11). Therefore, when the circuit breaker (11) is open, it is possible to attenuate frequency fluctuations due to the inertia of the power generation system (30) and the pseudo-inertia of the energy storage system (40), and to coordinate the inertial movements of both.

[0133] In any specific example of embodiments 3 to 9 (embodiment 10), the control device (45) includes a voltage control unit (70) for maintaining the output voltage of the power converter (42) at a set value (Vn), and the one or more control parameters include control gains (Kv_P, Kv_I) applied to the voltage control unit (70), and the numerical value of the control gains (Kv_P, Kv_I) in the open state of the circuit breaker (11) exceeds the numerical value of the control gains (Kv_P, Kv_I) in the closed state of the circuit breaker (11). In the above embodiment, the numerical value of the control gains (Kv_P, Kv_I) in the open state of the circuit breaker (11) exceeds the numerical value of the control gains (Kv_P, Kv_I) in the closed state of the circuit breaker (11). Therefore, when the circuit breaker (11) is opened, the deviation of the output voltage of the power converter (42) can be quickly reduced.

[0134] In any specific example of embodiments 3 to 10 (embodiment 11), the control device (45) includes a deviation suppression unit (83) that integrates the deviation (ΔQ) between a set value (Qn) and a measured value (Qm) of reactive power output by the power converter (42), and the one or more control parameters include an integral gain (Kq) applied to the deviation suppression unit (83), and the value of the integral gain (Kq) in the open state of the circuit breaker (11) exceeds the value of the integral gain (Kq) in the closed state of the circuit breaker (11). In the above embodiment, the value of the integral gain (Kq) in the open state of the circuit breaker (11) exceeds the value of the integral gain (Kq) in the closed state of the circuit breaker (11). Therefore, in the open state of the circuit breaker (11), high power factor operation of the power generation system (30) can be assisted.

[0135] Furthermore, the operating conditions required or preferred for the power system (100) differ depending on whether the power system (100) is connected to the power grid (10) due to the closing of the circuit breaker (11) or whether the power system (100) is separated from the power grid (10) due to the opening of the circuit breaker (11).

[0136] In consideration of the above circumstances, a power system (100) according to one aspect of the present disclosure (Aspect 12) is a power system (100) connected to a power grid (10) via a circuit breaker (11), comprising a load device (22) and a power storage system (40), wherein the power storage system (40) includes a power storage device (41) that outputs DC power, a power converter (42) that converts the DC power to AC power, and a control device (45) that controls the power converter (42), wherein the control device (45) makes the numerical values ​​of one or more control parameters applied to the control of the power converter (42) different depending on whether the circuit breaker (11) is closed or open. In the above aspect, when the circuit breaker (11) is in a closed state, the control parameters can be set to numerical values ​​suitable for operating conditions for connection with the power grid (10), and when the circuit breaker (11) is in an open state, the control parameters can be set to numerical values ​​suitable for operating conditions when separated from the power grid (10). Therefore, control parameters can be set so that the frequency converges quickly and stably, for example, immediately after the circuit breaker (11) opens or immediately after load fluctuations while it is open. [Explanation of symbols]

[0137] 100...Power system, 10...Power grid, 11...Circuit breaker, 21...Interconnection point, 22...Load device, 23...Control device, 24...Circuit breaker, 25...Circuit breaker, 30...Power generation system, 31...Prime mover, 32...Power generation device, 33...Transformer, 34...Control device, 40...Energy storage system, 41...Energy storage device, 42...Power converter, 43...Interconnection reactor, 44...Transformer, 45...Control device, 50...Output control unit, 51...Calculation processing unit, 52...Conversion processing unit, 53...Control processing 54... Range limiting unit, 55... Calculation processing unit, 56... Low-pass filter, 57... Rate of change limiting unit, 60... Inertia control unit, 61... Calculation processing unit, 62... Inertia processing unit, 63... Braking processing unit, 70... Voltage control unit, 71... Calculation processing unit, 72... Control processing unit, 73... Calculation processing unit, 80... Reactive power control unit, 81... Reactive power calculation unit, 82... Deviation calculation unit, 83... Deviation suppression unit, 84... Calculation processing unit, 90... Drive processing unit, 91... Synchronization holding unit, 92... Overcurrent suppression unit.

Claims

1. A power system connected to the power grid via a circuit breaker, Load device and Equipped with an energy storage system, The aforementioned energy storage system is A power storage device that outputs DC power, A power conversion device that converts the aforementioned DC power into AC power, Includes a control device for controlling the power converter, The control device is The power system includes a conversion processing unit that converts the frequency deviation between the command value and the set value of the frequency into a change in the output power of the power converter, Among the one or more conversion parameters applied to the conversion by the conversion processing unit, the value of the dead zone parameter that defines the dead zone in the numerical range of the frequency deviation in which the change in the output power is maintained at zero is made different for the closed state and the open state of the circuit breaker. Power system.

2. A power system connected to the power grid via a circuit breaker, Load device and Equipped with an energy storage system, The aforementioned energy storage system is A power storage device that outputs DC power, A power conversion device that converts the aforementioned DC power into AC power, The power converter includes a control device that performs pseudo-inertia control to simulate inertia response, The control device is Includes an inertia control unit for the pseudo-inertia control of the power converter, Of the one or more inertia control parameters applied to the pseudo-inertia control, the numerical value of the braking coefficient, which represents the degree of braking in the pseudo-inertia control, is made different between the closed state and the open state of the circuit breaker. Power system.

3. A power system connected to the power grid via a circuit breaker, Load device and Equipped with an energy storage system, The aforementioned energy storage system is A power storage device that outputs DC power, A power conversion device that converts the aforementioned DC power into AC power, Includes a control device for controlling the power converter, The control device is The power converter includes a voltage control unit for maintaining the output voltage of the power converter at a set value, The value of the control gain applied to the voltage control unit is made different depending on whether the circuit breaker is in a closed or open state. Power system.

4. A power system connected to the power grid via a circuit breaker, Load device and Equipped with an energy storage system, The aforementioned energy storage system is A power storage device that outputs DC power, A power conversion device that converts the aforementioned DC power into AC power, Includes a control device for controlling the power converter, The control device is The power converter includes a deviation suppression unit that integrates the deviation between the set value and the measured value of the reactive power output by the power converter, The value of the integral gain applied to the deviation suppression unit is made different depending on whether the circuit breaker is in a closed or open state. Power system.

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