JP7490166B1 - Control device and control method - Google Patents

Abstract

A control device that controls an inverter that converts a DC voltage from a storage battery into an AC voltage, comprising a VSG control unit that controls the frequency of the AC voltage so that it has a virtual inertial force, and a Qv control unit that controls the amplitude of the AC voltage so that the difference between a command value and an actual measured value of reactive power is reduced, and the Qv control unit determines a control amount for the amplitude of the AC voltage in accordance with the relationship between the frequency band of a Qv control system that controls so as to reduce the difference, and the frequency band of the VSG control system controlled by the VSG control unit.

Description

The present disclosure relates to a control device and a control method for controlling an inverter provided in a power source.

In a power system that supplies AC power from a power source to a load, the output voltage and frequency are controlled to be maintained regardless of the supply and demand situation. When the amount of AC power introduced into the power system from renewable energy sources increases compared to synchronous generators, the supply and demand balance is more likely to change suddenly, and the stability of the power system tends to decrease. As a countermeasure to this, a technology called virtual synchronous generator (VSG) control is known (for example, Patent Document 1). In VSG control, the power system is stabilized by giving an inverter installed in the power source a pseudo inertial force that a synchronous generator has.

JP 2016-93103 A

However, in a power supply system consisting of multiple distributed power sources, Qv control is often performed to suppress the reactive power Q circulating between each of the distributed power sources. In Qv control, the amplitude Vv of the AC voltage output from the inverter is controlled so that the reactive power Q output from the inverter approaches a command value. On the other hand, in VSG control, the frequency fv of the AC voltage output from the inverter is controlled so that the active power P output from the inverter approaches a command value. Here, there is a close relationship between the frequency fv, the amplitude Vv, and the apparent power S (power equivalent to the square root of the sum of the square of the active power P and the square of the reactive power Q), and when either the frequency fv or the amplitude Vv is manipulated, it affects both the active power P and the reactive power Q. For this reason, there was a risk that the VSG control and the Qv control would interfere with each other, making it difficult to properly control the inverter.

The present disclosure has been made to solve the above problems, and its purpose is to provide a control device and control method that can appropriately control an inverter even when both VSG control and Qv control are implemented.

In order to solve the above problems, one aspect of the present disclosure is a control device that controls an inverter that converts a DC voltage from a storage battery into an AC voltage, and includes a VSG control unit that controls the frequency of the AC voltage so that it has a virtual inertial force, and a Qv control unit that controls the amplitude of the AC voltage so that the difference between a command value and an actual measured value of reactive power is reduced, and the Qv control unit determines the control amount of the amplitude of the AC voltage depending on the relationship between the frequency band of a Qv control system that controls to reduce the difference and the frequency band of the VSG control system controlled by the VSG control unit.

In order to solve the above problems, one aspect of the present disclosure is a control method performed by a control device that controls an inverter that converts a DC voltage from a storage battery into an AC voltage, in which a VSG control unit controls the frequency of the AC voltage so that it has a virtual inertial force, a Qv control unit controls the amplitude of the AC voltage so that the difference between a command value and an actual measured value in reactive power is reduced, and the Qv control unit determines the control amount of the amplitude of the AC voltage depending on the relationship between the frequency band of a Qv control system that controls to reduce the difference and the frequency band of a VSG control system controlled by the VSG control unit.

According to the present disclosure, the inverter can be appropriately controlled even when both VSG control and Qv control are implemented.

FIG. 1 is a diagram illustrating a configuration example of a microgrid according to a first embodiment of the present disclosure. 4 is a diagram for explaining control performed by a control device C according to the first embodiment. FIG. 4 is a diagram for explaining control performed by a control device C according to the first embodiment. FIG. FIG. 4 is a diagram for explaining Qv control according to the first embodiment. FIG. 4 is a diagram for explaining Qv control according to the first embodiment. FIG. 4 is a diagram for explaining Qv control according to the first embodiment. FIG. 4 is a diagram for explaining Qv control according to the first embodiment. FIG. 11 is a diagram illustrating a configuration example of a microgrid according to a second embodiment. FIG. 11 is a diagram for explaining control performed by a control device C according to a second embodiment. 13 is a diagram for explaining the control performed by a control device C according to a first modified example of the second embodiment. FIG. FIG. 13 is a diagram illustrating a configuration example of a microgrid according to a second modification of the second embodiment. FIG. 2 is a diagram for explaining the relationship between a control device C and an inverter controller according to the first embodiment. FIG. 11 is a diagram for explaining the relationship between a control device C and an inverter controller according to a second embodiment.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiment, and may be modified as desired within the scope of the technical concept of the present disclosure.

First Embodiment
Fig. 1 is a diagram showing an example of the configuration of a microgrid in embodiment 1. As shown in Fig. 1, the microgrid 1 includes a power generation facility 2, a plurality of power receiving and distributing facilities 4, a plurality of storage batteries 5, a power transmission and distribution network 6, and a storage battery control system 10. The components in the microgrid 1 are connected to each other by the power transmission and distribution network 6.

The power generation facility 2 may be, for example, a wind power plant, a solar cell, a hydroelectric power plant, etc. Other types of power generation facility 2 may also be used. Furthermore, multiple types of power generation facility 2 may be used in combination.

The microgrid 1 is configured to charge and discharge the multiple storage batteries 5 according to the power supply and demand situation. For example, when the demand for power is low, the multiple storage batteries 5 are charged using the power generated by the power generation equipment 2. When the demand for power is high, the power generated by the power generation equipment 2 and the power of the multiple storage batteries 5 are combined and output to the power system. Alternatively, the combined power may be supplied to a load in the microgrid 1. In this embodiment, the microgrid 1 constitutes an autonomous power system that independently generates and consumes power.

The microgrid 1 may be connected to a power system including a load via a power transmission and distribution network 6. In this case, a switch (not shown) may be provided between the microgrid 1 and the power system. The switch can be switched between a closed state and an open state. When the switch is in the open state, the microgrid 1 is disconnected from the power system, and the microgrid 1 constitutes an independent power system. When the switch is in the closed state, the microgrid 1 is connected to the power system 3.

Each storage battery 5 may be, for example, a lithium ion battery, a NAS battery, a redox flow battery, etc. Other types of storage batteries 5 may also be used.

The battery control system 10 comprises an integrated controller 11 and multiple PCSs (Power Conditioning Systems) 12.

The integrated controller 11 manages multiple PCSs 12. The integrated controller 11 controls the battery control system 10. The integrated controller 11 may be configured as, for example, a Community Energy Management System (CEMS), an Aria Energy Management System (AEMS), a Building and Energy Management System (BEMS), or the like. The integrated controller 11 has a calculation unit, a communication unit, and the like. The calculation unit is a CPU or the like, and performs calculations to realize the functions of the integrated controller 11 described above. The communication unit communicates with each PCS 12 wirelessly or via wire. For example, the communication unit transmits command values generated by the calculation unit, such as a command value Pref for active power P and a command value Qref for reactive power Q, to each PCS 12.

PCS12 is configured as a distributed power source incorporating an inverter INV that controls the charging and discharging of the storage battery 5. PCS12 has a control device C that controls the inverter INV, and a communication device T that communicates with the integrated controller 11. In this embodiment, each PCS12 performs GFL (Grid Following) control according to command values notified from the integrated controller 11, such as a command value Pref for active power P and a command value Qref for reactive power Q, which will be described later, and causes the storage battery 5 corresponding to the PCS12 to function as a voltage source.

Figure 2 is a diagram for explaining the control performed by the control device C according to the first embodiment. Figure 2 shows a schematic diagram of an inverter INV controlled by the control device C, and a load or other inverter INV, which is a destination connected to this inverter INV via a line impedance L. In the following description, the load or other inverter INV, which is a destination, may be referred to simply as a "destination."

As shown in Figure 2, the relationship between the output voltage v1 of the AC power output from the inverter INV, the line impedance L, the current i flowing through the line impedance L, and the output voltage v2 of the AC power output from the connection destination is given by the following equation (1).

where fv is the frequency of the AC voltage output from the inverter INV. fo is the frequency of the AC voltage output from the connection destination. θo is the phase difference between the active power P and the reactive power Q.

In addition, in this embodiment, the output power may refer to a power flow. That is, the power received by the inverter INV from a load, another inverter INV, or the power grid E as a connected destination may be treated as negative output power, and may be treated as the output power supplied to the load, another inverter INV, or the power grid E as a connected destination.

In equation (1), if the difference between frequency fv and frequency fo is Δf, the relationship in equation (1) becomes the following equation (2-1). Solving equation (2-1) for current i gives the following equations (2-2) to (2-4).

Using equation (2-4), the apparent power S output from the inverter INV is given by the following equation (3-1). Here, P is the active power output from the inverter INV. Q is the reactive power output from the inverter INV. From equation (3-1), the active power P can be expressed as in equation (3-2). Furthermore, from equation (3-2), the reactive power Q can be expressed as in equation (3-3).

In VSG control, the frequency fv of the AC voltage output from the inverter INV is adjusted to give the PCS 12 a pseudo inertial force of a synchronous generator, thereby stabilizing the power system. When the frequency fv fluctuates due to VSG control, active power P and reactive power Q are generated according to the relationship between the amplitude Vo, frequency fo, and phase difference θo at the connected destination. Similarly, active power P and reactive power Q are generated when another inverter INV connected to the inverter INV has VSG control.

When reactive power Q occurs, the output of reactive power Q can be suppressed by adjusting the amplitude Vv of the AC voltage output from the inverter INV through Qv control.

However, as shown in equation (3-2), the active power P includes as parameters both the amplitude Vv and the frequency fv of the AC voltage output from the inverter INV. Also, as shown in equation (3-3), the reactive power Q includes as parameters both the amplitude Vv and the frequency fv of the AC voltage output from the inverter INV.

For this reason, when VSG control varies the frequency fv so that the active power P approaches the command value Pref, the reactive power Q varies with the variation in frequency fv. On the other hand, when Qv control varies the amplitude Vv so that the reactive power Q approaches the command value Qref, the active power P varies with the variation in amplitude Vv. In this way, there is a risk of control interference occurring between VSG control and Qv control.

As a measure to avoid such a situation where control interference occurs, it is possible to perform control to reduce the control amount of the amplitude Vv by the Qv control. In this case, for example, the amount of fluctuation in the amplitude is multiplied by a relatively small gain, for example, a gain (gain) equivalent to a real number greater than 0 (zero) and less than 1, such as 0.3, to control so that the fluctuation of the amplitude Vv is suppressed. However, if the gain of the amplitude Vv by the Qv control is lowered and made small, the effect of suppressing the reactive power Q becomes small. When the effect of suppressing the reactive power Q is small, particularly in a battery control system 10 having multiple inverters INV that perform VSG control, the reactive power Q will be circulated between the inverters INV, resulting in unnecessary power loss.

In response to such problems, the present embodiment takes measures by focusing on the fact that VSG control suppresses sudden changes in output power due to fluctuations in power generation and load fluctuations. Specifically, in the present embodiment, the amplitude Vv is less likely to fluctuate due to Qv control in the relatively high frequency band that is the subject of control in VSG control.

More specifically, in this embodiment, in Qv control, two gains are provided: a high-band gain that is applied to a high frequency band that is likely to interfere with VSG control, and a low-band gain that is applied to a low frequency band that is unlikely to interfere with VSG control. For example, the high-band gain is set to a smaller value than the low-band gain.

As a result, in Qv control, it is possible to suppress fluctuations in amplitude Vv by applying a high-band gain in high frequency bands that are prone to interference with VSG control. On the other hand, in Qv control, it is possible to suppress reactive power Q by applying a low-band gain in low frequency bands that are unlikely to interfere with VSG control. Therefore, it is possible to achieve both avoidance of control interference and suppression of wasteful power generation due to circulation of reactive power Q.

Figure 3 is a diagram for explaining the control performed by the control device C according to the first embodiment. The "controlled object" shown in Figure 3 corresponds to the connection destination in Figure 2, and is the inverter controller that controls the inverter INV, the inverter INV, the inverter output filter, and the power system connected via the inverter INV. The inverter controller here is a device that sets the amplitude and frequency of the AC voltage output by the inverter INV to the inverter INV. In addition, the power system connected via the inverter INV is, for example, another PCS 12 as a connection destination, wiring and loads between the other PCS 12, etc. Depending on the relationship with the power system connected via the inverter INV, the control device C controls the amplitude Vv and frequency fv of the AC voltage output from the inverter INV.

As shown in FIG. 3, the control device C includes, for example, control blocks B11, B12, B13, a zero order hold ZOH, an adder, and a subtractor.

The control device C receives as input the command value Pref and the command value Qref, which are the command values for the active power P and the reactive power Q, respectively, notified by the integrated controller 11. The control device C also receives as input the actual measured value Pmeasure and the actual measured value Qmeasure, which are the measured values for the active power P and the reactive power Q, respectively, from the inverter INV. The actual measured value Qmeasure and the actual measured value Pmeasure are measured, for example, by a measuring device attached to the power line to which power is supplied.

The control device C uses a subtractor to calculate the deviation dQ of the reactive power Q. The deviation dQ is the difference between the command value Qref and the actual measured value Qmeasure. The control device C uses a subtractor to subtract the signal value obtained by performing a zero-order hold ZOH on the actual measured value Qmeasure from the command value Qref, and outputs the resultant difference value as the deviation dQ to the control block B11.

Control block B11 performs Qv control. Control block B11 is an example of a "Qv control unit." In the example shown in this figure, control block B11 is described as "two-stage gain." In addition, a closed-loop control system that can be expressed by the transfer function of the output/input from control block B11, which corresponds to the "Qv control unit," to the controlled object may be described as a "Qv control system."

The control block B11 calculates the amplitude deviation so that the deviation dQ approaches zero. The control block B calculates the amplitude deviation so that the deviation dQ approaches zero by performing feedback control such as PI control. The amplitude deviation here is the difference between the amplitude Vv of the AC voltage output by the inverter INV to the controlled object and the rated voltage Vm.

Here, the gain applied to the amplitude deviation when the control block B11 performs Qv control will be explained using Figures 4 to 7. Figures 4 to 7 are diagrams for explaining the Qv control according to the first embodiment.

Figure 4 shows a schematic diagram of frequency characteristics L1 to L3 of the gain applied to Qv control. The horizontal axis of Figure 4 is frequency F, and the vertical axis is gain Gain. Frequency characteristic L1 is an example of the frequency characteristic of the gain applied to the amplitude deviation in conventional Qv control. Frequency characteristic L2 is the frequency characteristic of the gain applied to the amplitude deviation in this embodiment. Frequency characteristic L3 is another example of the frequency characteristic of the gain applied to the amplitude deviation in conventional Qv control.

The frequency characteristic L1 shows the characteristics when a relatively large gain is set as a uniform value independent of the frequency band as the gain applied to the amplitude deviation in Qv control, and the reactive power Q is suppressed. In this case, in the high frequency band, the control by Qv control and the VSG control interfere with each other, making it difficult for the inverter INV to be appropriately controlled.

The frequency characteristic L3 shows the characteristics when a relatively small gain is set as a uniform value independent of the frequency band as the gain applied to the amplitude deviation in Qv control, and the operation is performed such that the reactive power Q is hardly suppressed. In this case, the interference between the control by Qv control and the VSG control can be suppressed, but the reactive power Q cannot be suppressed, so that unnecessary power is consumed.

In contrast, in the high frequency band that is prone to interference with VSG control, the frequency characteristic L2 operates by applying a relatively small high band gain. This makes it possible to suppress fluctuations in the amplitude Vv. On the other hand, in the low frequency band that is unlikely to interfere with VSG control, the frequency characteristic L2 operates by applying a relatively large low band gain. This makes it possible to suppress reactive power Q. Therefore, it is possible to achieve both avoidance of control interference and suppression of unnecessary power generation.

Figure 5 shows a block diagram illustrating an example of the configuration of control block B11. As shown in Figure 5, control block B11 can be expressed, for example, with the numerator and denominator being functions of an Nth order system, where N is any natural number. In the example shown in this figure, a case will be described in which control block B11 is configured with a first order function.

The control block B11 includes, for example, a multiplier, a first frequency characteristic adjuster, and a second frequency characteristic adjuster. The multiplier is a multiplier that multiplies by K, where K is the gain of the amplitude deviation. The first frequency characteristic adjuster is a frequency characteristic adjuster that applies a transfer function {1/(1+sTa)}. The second frequency characteristic adjuster is a frequency characteristic adjuster that applies a transfer function (1+sTb). Ta and Tb are time constants. s is a Laplace operator.

The control block B11 multiplies the deviation dQ by the gain K of the amplitude deviation, and outputs the product obtained by applying the transfer function {1/(1+sTa)} and the transfer function (1+sTb) to the product as the amplitude deviation. This allows the control block B11 to output the value obtained by applying the transfer function {K·(1+sTb)/(1+sTa)} to the deviation dQ as the amplitude deviation.

Here, if the low-band gain is to be made larger than the high-band gain, the time constant Tb must be made smaller than the time constant Ta.

In addition, it is desirable to set the time constants Ta and Tb to be large enough so as not to affect the characteristics of control systems other than the Qv control system, i.e., VSG control and governor control by control block B13.

For example, a method of determining the time constants Ta and Tb and the gain K of the amplitude deviation, which are the control parameters for performing the Qv control of this embodiment, can be considered to determine the control parameters through three stages, from the first stage to the third stage. In the first stage, the time constant Tb is determined. In the second stage, a low-band gain is determined, which corresponds to the gain K of the amplitude deviation related to the convergence value when the gain is converged in the low frequency band. In the third stage, (K·Tb/Ta) is determined, which corresponds to the high-band gain related to stability in the high frequency band. The time constant Ta is indirectly determined in the third stage.

Figure 6 shows the gain characteristic, which is the frequency characteristic of the gain applied to the amplitude deviation in the Qv control of this embodiment. The horizontal axis of Figure 6 is the angular frequency ω, and the vertical axis is the gain G. In Figure 6, the solid line shows the frequency characteristic of the Qv control (two-stage gain) of this embodiment. The dashed line shows the frequency characteristic of the gain K of the amplitude deviation. The dashed line shows the frequency characteristic of the transfer function {1/(1+sTa)} corresponding to the first frequency characteristic adjuster. The two-dot chain line shows the frequency characteristic of the transfer function (1+sTb) corresponding to the second frequency characteristic adjuster.

In the example of Figure 6, the gain K of the amplitude deviation as a control parameter is "2". This means that it is amplified by approximately 6 [dB] from before amplification. Furthermore, the time constant Ta is 0.1 [sec]. This is the time constant corresponding to the cutoff frequency at which the gain G attenuates by approximately 3 [dB] in the frequency characteristic of the transfer function {1/(1+sTa)}. Furthermore, the time constant Tb is 0.01 [sec]. This is the time constant corresponding to the frequency at which the gain G increases by approximately 3 [dB] in the frequency characteristic of the transfer function (1+sTb).

The relationship between the transfer function and the frequency characteristic can be obtained by replacing the Laplace operator s in the transfer function with the complex number jω corresponding to a sine wave. Specifically, as shown in formula (4-1), in the transfer function {K · (1 + sTb) / (1 + sTa)} in which the Laplace operator s in the transfer function {K · (1 + jωTb) / (1 + jωTa)} is replaced with the complex number jω, the limit value when the angular frequency ω approaches 0 as shown in formula (4-2) corresponds to the low-band gain. In the example of this figure, the low-band gain is the gain K of the amplitude deviation. Also, as shown in formula (4-3), in the transfer function {K · (1 + jωTb) / (1 + jωTa)}, the limit value when the angular frequency ω approaches infinity ∞ corresponds to the high-band gain. In the example of this figure, the high-band gain is (K · Tb / Ta). That is, in the gain characteristic shown in the example of this figure, the gain of the amplitude deviation is K, which is a low-band gain, in the low frequency band, and is (K·Tb/Ta), which is a high-band gain, in the high frequency band. In the example of this figure, the gain difference between the low-band gain and the high-band gain is about 20 dB.

7 shows the phase characteristic of the gain applied to the amplitude deviation in the Qv control of this embodiment. FIG. 7 shows the phase characteristic of the transfer function having the gain characteristic shown in FIG. 6. The horizontal axis of FIG. 7 is the angular frequency ω, and the vertical axis is the phase ∠G. In FIG. 7, the solid line shows the phase characteristic of the Qv control (two-stage gain) of this embodiment. The dashed line shows the phase characteristic of the gain K of the amplitude deviation. The dashed line shows the phase characteristic of the transfer function {1/(1+sTa)} corresponding to the first integrator. The dashed line shows the phase characteristic of the transfer function (1+sTb) corresponding to the second integrator. In the example of FIG. 7, the Qv control (two-stage gain) of this embodiment causes a delay of up to about 50 [deg.]. As described above, the control parameters must be set so that the Qv control system expressed by the zero-order hold ZOH and the transfer function of the controlled object does not become unstable, in addition to the control block B11. As a method for determining the stability of the Qv control system, general control theories such as Nyquist's stability determination method can be used.

Returning to the explanation of Figure 3, in the control device C, the amplitude deviation calculated by the control block B11 is subjected to a zero-order hold ZOH, the rated voltage Vm is added to the amplitude deviation subjected to the zero-order hold ZOH, and the added value is output as the amplitude Vv.

As shown in the lower part of Figure 3, the control device C controls the frequency fv based on the active power P. The control device C uses a subtractor to calculate a subtractor output difference value by subtracting the governor output value from the command value Pref of the active power P, and outputs the calculated subtractor output difference value to the control block B12. The governor output value here is the output value from the control block B13. The control block B13 is a functional block that performs control simulating a governor (governor) for keeping the rotational speed of a synchronous generator constant.

Control block B12 performs VSG control. Control block B12 is an example of a "VSG control unit." A closed-loop control system that can be expressed by a transfer function of output/input from control block B12, which corresponds to the "VSG control unit," to the controlled object may be referred to as a "VSG control system." Control block B12 calculates a deviation dP of active power P. The deviation dP is the difference between the subtractor output difference value and the actual measurement value Pmeasure. Control block B12 uses the subtractor to subtract the signal value obtained by performing zero-order hold ZOH on the actual measurement value Pmeasure from the subtractor output difference value, and sets the resulting difference value as the deviation dP.

The control block B12 calculates the frequency deviation df based on the deviation dP. When calculating the deviation df, the control block B12 applies a transfer function corresponding to the braking parameter D and the inertia parameter M to simulate the inertial force of a synchronous generator. Specifically, the control block B12 divides the deviation dP by the braking parameter D, applies the transfer function {1/(1+sM/D)} to the divided value, and outputs the result as the frequency deviation df. The control block B12 outputs the sum of the signal value obtained by performing zero-order hold ZOH on the frequency deviation df and the rated frequency fn as the frequency fv. The control block B12 also outputs the frequency deviation df to the control block B13.

Control block B13 simulates governor-like behavior. Control block B13 applies transfer function {K/(1+sT)} to frequency deviation df to calculate the governor output value. T indicates the governor time constant. Governor time constant T is a time constant equivalent to integral time. Here, K indicates the governor gain. Control block B13 feeds back the calculated governor output value.

As described above, the control device C according to the first embodiment is a control device that controls the inverter INV that converts the DC voltage from the storage battery 5 into an AC voltage. The control device C includes a control block B12 (VSG control unit) and a control block B11 (Qv control unit). The control block B12 (VSG control unit) controls the frequency of the AC voltage so that it has a virtual inertial force. The control block B11 (Qv control unit) controls the amplitude of the AC voltage so that the difference between the command value Qref and the actual measurement value Qmeasure in the reactive power Q is reduced. The control block B11 (Qv control unit) determines the control amount of the amplitude of the AC voltage, for example, the value of the gain to be multiplied by the amplitude deviation, according to the relationship between the frequency band of the Qv control system that controls so that the difference between the command value and the actual measurement value in the reactive power is reduced, and the frequency band of the VSG control system controlled by the VSG control unit. As a result, the control device C according to the first embodiment can change the amount of fluctuation of the amplitude Vv by Qv control between a frequency band controlled by VSG control and a frequency band not controlled by VSG control. For example, it is possible to reduce the amount of fluctuation of the amplitude Vv in a frequency band controlled by the VSG control system to avoid control interference, and to increase the amount of fluctuation of the amplitude Vv in a frequency band not controlled by the VSG control system to suppress the generation of reactive power Q. Therefore, even when both VSG control and Qv control are implemented, the inverter can be appropriately controlled.

In addition, in the control device C according to the first embodiment, the control block B11 (Qv control unit) has a high-band gain (first gain) and a low-band gain (second gain). The high-band gain (first gain) is a gain intended to mitigate interference between the Qv control system and the VSG control system. The low-band gain (second gain) is a gain intended to reduce the steady-state deviation of the difference. The difference is the difference between the command value Qref and the actual measured value Qmeasure in the reactive power Q. The high-band gain (first gain) is a value smaller than the low-band gain (second gain). This allows the control device C according to the first embodiment to achieve gain adjustment according to the frequency band, that is, a two-stage gain. In the frequency band (relatively high frequency band) to be controlled in the VSG control, it is possible to control so that the amplitude Vv is less likely to fluctuate due to the Qv control and does not interfere with the VSG control. In addition, in a frequency band (a relatively low frequency band) that is not subject to control in VSG control, the amplitude Vv by Qv control can be varied so as to suppress the generation of wasteful power due to the circulation of reactive power Q.

In addition, in the control device C according to the first embodiment, the control block B11 (Qv control unit) calculates the amplitude deviation amount so that the difference between the command value Qref and the measured value Qmeasure in the reactive power Q is reduced. The control block B11 (Qv control unit) applies the transfer function {K·(1+sTb)/(1+sTa)} to the calculated amplitude deviation amount, thereby calculating a control amount obtained by multiplying the amplitude deviation amount by a high-band gain (first gain) or a low-band gain (second gain), which is a gain corresponding to the frequency band of the Qv control system, as a fluctuation amount for fluctuating the amplitude Vv. The transfer function {K·(1+sTb)/(1+sTa)} is a function in which the time constants Ta and Tb are set so that the amplification amount is reduced in the frequency band of the VSG control unit system. As a result, in the control device C of the first embodiment, a two-stage gain can be realized by passing the signal corresponding to the amplitude deviation amount through a filter that blocks signals in the frequency band that is the subject of control in the VSG control, and it is possible to control the circulation of reactive power Q so that suppression is less likely to occur in the frequency band that is the subject of control in the VSG control (relatively high frequency band) so as not to interfere with the VSG control, and in the frequency band that is the subject of control in the VSG control (relatively low frequency band).

Second Embodiment
Here, a second embodiment will be described. This embodiment differs from the above-described embodiment in that the command value Qref of the reactive power Q is not notified from the integrated controller 11.

For example, assume that the command value of Qref is fixed at 0 (zero) and the amount of reactive power Q required by the power system such as other PCS 12, wiring, and loads that are the control targets is Qa (actual measured value Qmeasure). In this case, the amplitude Vv calculated by Qv control is always an amplitude value greater than the rated voltage Vm.

Here, in the battery control system 10, if there is a PCS 12 equipped with the same Qv control as above, the multiple PCSs 12 are controlled so that each of them outputs an amplitude Vv greater than the rated voltage Vm. This changes the amplitude Vv of the AC voltage output in each PCS 12, and the actual measured value Qmeasure of the reactive power Q measured in each PCS 12 changes every time the amplitude Vv changes, and the amplitude Vv calculated by the other PCSs 12 changes in conjunction with each change in the actual measured value Qmeasure. Such a chain of changes is likely to cause the battery control system 10 to be inappropriately controlled, so it is better to avoid it. In order to avoid the chain of changes, for example, it is possible to take measures such as lowering and reducing the gain to reduce the amount of fluctuation in the amplitude Vv due to the Qv control. However, in this case, the variation in the load end voltage becomes large.

To address this issue, in this embodiment, the control device C calculates a command value Qref for the reactive power Q. The control device C sets the reactive power Qa (actual measured value Qmeasure) required by the power system to be controlled in advance as the command value Qref, and calculates the amplitude Vv.

In the battery control system 10, when a PCS 12 having the same Qv control as described above is present, the multiple PCSs 12 are controlled so that each outputs an amplitude Vv that is as close as possible to the rated voltage Vm. This reduces the amount of fluctuation in the amplitude Vv in the AC power output by each PCS 12, and suppresses a chain of changes. For example, even if measures are taken to reduce the gain and reduce the amount of fluctuation in the amplitude Vv due to the Qv control, the variation in the load end voltage can be improved.

In this embodiment, VSG control is performed in each PCS 12, and measures are taken to gradually converge to an ideal state in which the difference Δf in the frequency of the AC voltage output from each PCS 12 approaches 0 (zero). Specifically, in this embodiment, assuming that the difference Δf in the frequency of the AC voltage output from each PCS 12 has become 0 (zero), the command value Qref is calculated so that the reactive power Q is suppressed. By calculating the command value Qref in this way, it is possible to prepare in advance so that the reactive power Q is effectively suppressed when the control by the VSG control in each PCS 12 converges to an ideal state.

Below, the configuration for calculating the command value Qref for the microgrid 1 of this embodiment will be explained using Figures 8 and 9. Below, configurations that differ from the above-mentioned embodiment will be mainly explained, and configurations similar to those in the above-mentioned embodiment will be given the same reference numerals and their explanation will be omitted.

Figure 8 is a diagram showing an example of the configuration of a microgrid according to the second embodiment. As shown in Figure 8, the microgrid 1 includes an integrated controller 11a. The integrated controller 11a notifies each PCS 12 of a command value Pref for active power P, but does not notify the command value Qref for reactive power Q.

Figure 9 is a diagram showing an example of the configuration of a microgrid according to the second embodiment. As shown in Figure 9, the control device C includes a control block B14 (reactive power command setting unit). The control block B14 (reactive power command setting unit) calculates a command value Qref for reactive power Q based on the actual measured value Pmeasure and the actual measured value Qmeasure, which are the actual measured values of active power P and reactive power Q, respectively. Below, a method in which the control block B14 (reactive power command setting unit) calculates the command value Qref for reactive power Q will be described.

First, control block B14 assumes that the difference Δf between frequency fv and frequency fo is 0 (zero) as shown in equation (5-1), and calculates active power P as shown in equation (5-2) and reactive power Q as shown in equation (5-3). Equation (5-2) can be calculated by substituting 0 (zero) for the difference Δf in equation (3-2). Equation (5-3) can be calculated by substituting 0 (zero) for the difference Δf in equation (3-3).

Next, the control block B14 estimates the phase difference θo between the active power and the reactive power using equations (5-2) and (5-3). For example, the control block B14 expresses the apparent power S in a vector expression using complex numbers as shown in equation (5-4) using equations (5-2) and (5-3). By solving equation (5-4) for the amplitude Vo, the vector expression of the amplitude Vo is calculated as shown in equations (5-5) and (5-6). Then, the scalar value of the amplitude Vo can be obtained using equation (5-6) as shown in equation (5-7). Furthermore, the scalar value of the phase difference θo can be obtained using equation (5-6) as shown in equation (5-8).

When the amplitude Vo can be measured using a measuring instrument, the control block B14 estimates the line impedance L based on the measured value of the amplitude Vo. The rated voltage Vm may also be adjusted so that the amplitude Vo falls within a specified range. The control block B14 calculates a command value Qref based on the value obtained by substituting the line impedance L for the phase difference θo shown in equation (5-7) such that the reactive power Q is suppressed as the difference Δf approaches 0 (zero).

If the amplitude Vo cannot be measured, the control block B14 sets the line impedance L using a preset value or a representative value. The control block B14 calculates the command value Qref of the reactive power Q based on the value obtained by substituting the line impedance L for the phase difference θo shown in equation (5-7).

The control block B14 may apply a low-pass filter to the estimated value of the phase difference θo to remove frequency change components corresponding to noise, and use the resulting value as the phase difference θo to calculate the command value Qref of the reactive power Q.

As described above, the control device C according to the second embodiment further includes a control block B14 (reactive power command setting unit). The control block B14 (reactive power command setting unit) calculates the command value Qref of the reactive power Q using the actual measurement value Pmeasure and the actual measurement value Qmeasure. The control block B14 (reactive power command setting unit) calculates the command value Qref on the assumption that the frequency difference Δf between the power system as the connection destination, for example, the other PCS12, the wiring and the load between the other PCS12, and the power system as the connection destination, for example, the other PCS12, the wiring, the load, etc., is zero. As a result, in the control device C according to the second embodiment, as the frequency difference Δf of the AC voltage output from each PCS12 gradually approaches the ideal state approaching 0 (zero), it is possible to calculate a command value Qref such that the reactive power Q is suppressed, and to output the amplitude Vv based on the calculated command value Qref. Therefore, it is possible to control the amplitude so that the reactive power Q is suppressed.

In the second embodiment, the control block B14 (reactive power command setting unit) calculates the line impedance L to the connection point based on the amplitude Vo at the connection point with the power grid to which it is connected, calculates the phase difference θo based on the calculated line impedance L, and calculates the command value Qref based on the phase difference θo. As a result, the control device C according to the second embodiment has the same effects as those described above.

<Modification 1 of the second embodiment>
Here, a first modified example of the second embodiment will be described. In this modified example, the gain is not set according to the frequency band in the Qv control, but a uniform gain is set independent of the frequency band as in the conventional case.

Figure 10 is a diagram for explaining the control performed by the control device C according to the second embodiment. As shown in Figure 10, in this modified example, the control block B11 performs conventional Qv control. The control block B11 of this modified example calculates an amplitude deviation so that the deviation dQ, which is the difference between the command value Qref and the actual measured value Qmeasure in the reactive power Q, approaches 0 (zero), and outputs a value obtained by multiplying the calculated amplitude deviation by a uniform gain G regardless of whether the frequency corresponding to the time series change in the amplitude deviation is high or low.

In this modified example, a command value Qref close to the actual measurement value Qmeasure calculated in the control block B14 in the previous stage is input to the control block B11. Therefore, the deviation dQ becomes close to 0 (zero), and the amplitude deviation does not become a large value. Therefore, even if a conventional Qv control, that is, a Qv control that amplifies with a uniform gain G regardless of the frequency band, is performed, it is possible to suppress control interference with the VSG control. Moreover, the command value Qref is calculated so that the reactive power Q is suppressed in the ideal state in which the difference Δf approaches 0 (zero) by the VSG control. Therefore, the reactive power Q is suppressed in the ideal state in which the VSG control has converged, and it is possible to suppress the reactive power Q and suppress wasteful power consumption while suppressing control interference with the VSG control.

As described above, the control device C according to the first modified example of the second embodiment includes a control block B12 (VSG control unit), a control block B11 (Qv control unit), and a control block B14 (reactive power command setting unit). The control block B12 (VSG control unit) controls the frequency of the AC voltage so that it has a virtual inertial force. The control block B11 (Qv control unit) controls the amplitude of the AC voltage so that the difference between the command value Qref and the actual measurement value Qmeasure in the reactive power Q is small. The control block B14 (reactive power command setting unit) calculates the command value Qref of the reactive power Q. The control block B14 (reactive power command setting unit) uses the actual measurement value Pmeasure of the active power P and the actual measurement value Qmeasure of the reactive power Q to calculate the command value Qref of the reactive power Q assuming that Δf is 0 (zero) at the connection point with the power system of the connection destination connected via the inverter INV. Here, Δf is the difference between the frequency fv of the AC voltage output from the inverter INV and the frequency fo of the AC voltage at the connection point. In other words, the command value Qref is calculated on the assumption that the frequency fv of the AC voltage output from the inverter INV and the frequency fo of the AC voltage at the connection point are the same frequency, and the frequency is in a stable ideal state in the battery control system 10. As a result, in the control device C according to the first modification of the second embodiment, it is assumed that the frequency is controlled to a stable ideal state in the battery control system 10 by the VSG control, and Qv control is performed so that the reactive power Q is suppressed in the ideal state. This makes it possible to suppress wasteful power consumption by suppressing the reactive power Q while suppressing control interference with the VSG control.

<Modification 2 of the second embodiment>
Here, a second modification of the second embodiment will be described. This modification differs from the above-described embodiment in that the integrated controller 11 is not provided.

Figure 11 is a diagram showing an example of the configuration of a microgrid according to the second modification of the second embodiment. As shown in Figure 11, the battery control system 10 includes one PCS 12 and a battery 5. The control device C performs VSG control using a control block B12 (VSG control unit) based on a command value Pref corresponding to an active power P that is predetermined according to the power supply capacity of the battery control system 10 including the battery 5. Similarly to the second embodiment, the control device C also calculates a command value Qref for reactive power Q using a control block B14 (reactive power command setting unit), and performs Qv control using a control block B11 (Qv control unit) based on the calculated command value Qref.

The Qv control by the control block B11 (Qv control unit) may be performed using two-stage gain, or a uniform gain that is independent of the frequency band may be set as in the past. The Qv control using two-stage gain here refers to Qv control that applies a high-band gain to the high frequency band and a low-band gain to the low frequency band depending on the frequency band.

<Variations of the embodiment>
In the above-described embodiment, the battery control system 10 is described by way of example with a configuration including a plurality of PCSs 12. At least one of the plurality of PCSs 12 included in the battery control system 10 may be provided with a control device C that performs VSG control and Qv control with two-stage gain. In the other PCSs 12 among the plurality of PCSs 12 included in the battery control system 10, VSG control may be performed or not performed. In addition, in the other PCSs 12, Qv control may be performed or not performed. When Qv control is performed, Qv control with two-stage gain may be performed, or a uniform gain independent of the frequency band may be set as in the past.

<Relationship between the control device C and the inverter controller>
In the above, the control device C controls the amplitude and frequency of the AC voltage output by the inverter INV to the inverter INV controller as the controlled object, but the present invention is not limited to this. A part or the whole of the control device C may be the inverter INV controller. The relationship between the control device C and the inverter controller will be described with reference to Figs. 12 and 13. Figs. 12 and 13 are diagrams for explaining the relationship between the control device C and the inverter controller.

Figure 12 shows the relationship between the control device C and the inverter controller in the first embodiment. In Figure 12, the range of configurations that can be taken as an inverter controller in the control device C and the controlled object in Figure 3 are shown by the symbols INVC1 to INVC3, respectively.

When the inverter controller is a device having components within the range indicated by the symbol INVC1, the inverter controller has the functions of the control device C of the first embodiment and the function of setting the amplitude and frequency of the AC voltage output by the inverter INV to the inverter INV.

When the inverter controller is a device having components within the range indicated by the symbol INVC2, the control device C is a device that outputs a signal value obtained by performing zero-order hold ZOH on the amplitude deviation calculated by the control block B11 for Qv control, and outputs a signal value obtained by performing zero-order hold ZOH on the frequency deviation df calculated by the control block B12 for VSG control. The inverter controller acquires the amplitude deviation that has been zero-order hold ZOHed from the control device C, and sets the sum of the acquired amplitude deviation and the rated voltage Vm to the inverter INV as the amplitude Vv of the AC voltage output by the inverter INV. The inverter controller also acquires the frequency deviation df that has been zero-order hold ZOHed from the control device C, and sets the sum of the acquired frequency deviation df and the rated frequency fn to the inverter INV as the frequency fv of the AC voltage output by the inverter INV.

When the inverter controller is a device having components within the range indicated by the symbol INVC3, the control device C has the functions of the control device C according to the first embodiment, and outputs a signal value indicating the frequency fv of the amplitude Vv of the AC voltage output by the inverter INV to the inverter controller. The inverter controller acquires a signal value indicating the frequency fv of the amplitude Vv from the control device C, and sets the acquired signal value in the inverter INV as the frequency fv of the AC voltage output by the inverter INV.

Figure 13 shows the relationship between the control device C and the inverter controller according to the second embodiment. In Figure 13, the range of configurations that can be taken as an inverter controller for the control device C and controlled object in Figure 9 are indicated by the symbols INVC4 to INVC7, respectively.

When the inverter controller is a device having components within the range indicated by the symbol INVC4, the inverter controller has the function of the control device C of the second embodiment and the function of setting the amplitude and frequency of the AC voltage output by the inverter INV to the inverter INV.

In addition, in Figure 13, the range enclosed by the symbol INVC4 includes the input of the command value Pref for active power P, but this does not indicate that the inverter controller has the function of generating and inputting the command value Pref. When the inverter controller is a device that includes the components in the range indicated by the symbol INVC4, it is assumed that the command value Pref is input from outside the inverter controller. For example, the command value Pref is input to the inverter controller from the integrated controller 11.

When the inverter controller is a device having components within the range indicated by the reference symbol INVC5, the inverter controller has the functions of the control device C according to the second embodiment minus the functions of the control block B14, i.e., the functions of the control device C according to the first embodiment. This is similar to the case where the device has components within the range indicated by the reference symbol INVC1 in Figure 12, so a description thereof will be omitted.

When the inverter controller is a device having components within the range indicated by the symbol INVC6, the inverter controller is the same as the case where the inverter controller is a device having components within the range indicated by the symbol INVC2 in Figure 12, and therefore the description thereof is omitted.

When the inverter controller is a device having components within the range indicated by the symbol INVC7, the inverter controller is the same as the case where the inverter controller is a device having components within the range indicated by the symbol INVC3 in Figure 12, and therefore the description thereof is omitted.

The control device C described above has an internal computer system. The process steps of the above-mentioned processing are stored in the form of a program on a computer-readable recording medium, and the computer reads and executes this program to perform the above-mentioned processing. Here, computer-readable recording medium refers to a magnetic disk, magneto-optical disk, CD-ROM, DVD-ROM, semiconductor memory, etc. Also, the computer program may be distributed to a computer via a communication line, and the computer that receives the distribution may execute the program.

1...Microgrid, 2...Power generation equipment, 4...Power distribution equipment, 5...Storage battery, 10...Battery control system, 11...Integrated controller, 12...PCS, C...Control device, INV...Inverter, B11...Control block (Qv control unit), B12...Control block (VSG control unit), B14...Control block (reactive power command setting unit)

Claims (8)

A control device for controlling an inverter that converts a DC voltage from a storage battery into an AC voltage,
a VSG control unit that controls the frequency of the AC voltage so that it has a virtual inertial force;
A Qv control unit that controls the amplitude of the AC voltage so that a difference between a command value and an actual measured value of reactive power becomes small;
Equipped with
The Qv control unit determines a control amount of the amplitude of the AC voltage according to a relationship between a frequency band of a Qv control system that controls so as to reduce the difference and a frequency band of a VSG control system that is controlled by the VSG control unit.
Control device. The Qv control unit includes a first gain which is a high-band gain intended to reduce interference between the Qv control system and the VSG control system, and a second gain which is a low-band gain intended to reduce a steady-state deviation of the difference,
The first gain is smaller than the second gain.
The control device according to claim 1 . The Qv control unit calculates an amplitude deviation amount that reduces the difference, and calculates the control amount by multiplying the amplitude deviation amount by a gain corresponding to a frequency band of the Qv control system by applying a transfer function to the amplitude deviation amount.
The transfer function is a function having a time constant set so that the amount of amplification is small in the frequency band of the VSG control system.
The control device according to claim 2. and a reactive power command setting unit that uses an actual measured value of active power and an actual measured value of reactive power to calculate a command value of reactive power on the assumption that a frequency of an AC voltage output from the inverter at a connection point with a destination power system connected via the inverter is the same as a frequency of an AC voltage at the connection point.
The control device according to claim 1 . the reactive power command setting unit calculates a line impedance to the node based on an amplitude at the node, calculates a phase difference between active power and reactive power based on the calculated line impedance, and calculates a command value for reactive power based on the calculated phase difference;
The control device according to claim 4. A control device for controlling an inverter that converts a DC voltage from a storage battery into an AC voltage,
a VSG control unit that controls the frequency of the AC voltage so that it has a virtual inertial force;
A Qv control unit that controls the amplitude of the AC voltage so that a difference between a command value and an actual measured value of reactive power becomes small;
a reactive power command setting unit that uses an actual measurement value of active power and an actual measurement value of reactive power to calculate a command value of reactive power on the assumption that a frequency of an AC voltage output from the inverter at a node with a destination power grid connected via the inverter is the same as a frequency of an AC voltage at the node;
A control device comprising: A control method performed by a control device that controls an inverter that converts a DC voltage from a storage battery into an AC voltage,
The VSG control unit controls the frequency of the AC voltage so that it has a virtual inertial force,
The Qv control unit controls the amplitude of the AC voltage so that a difference between a command value and an actual measured value of the reactive power becomes small,
The Qv control unit determines a control amount of the amplitude of the AC voltage according to a relationship between a frequency band of a Qv control system that controls so as to reduce the difference and a frequency band of a VSG control system that is controlled by the VSG control unit.
Control methods. A control method performed by a control device that controls an inverter that converts a DC voltage from a storage battery into an AC voltage,
The VSG control unit controls the frequency of the AC voltage so that it has a virtual inertial force,
The Qv control unit controls the amplitude of the AC voltage so that a difference between a command value and an actual measured value of the reactive power becomes small,
a reactive power command setting unit, using an actual measurement value of active power and an actual measurement value of reactive power, calculates a command value of reactive power on the assumption that a frequency of an AC voltage output from the inverter at a connection point with a destination power system connected via the inverter is the same as a frequency of an AC voltage at the connection point;
Control methods.

Images