JP2016119820A - Autonomous operation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an autonomous operation system capable of stably and continuously operating a system by protecting a storage battery by appropriately controlling a charge/discharge current of the storage battery.SOLUTION: The autonomous operation system comprises: a storage battery system formed from a power conditioner 3 and a storage battery 2; a control device 5 for the storage battery system; a power generation facility capable of charging the storage battery 2; and a load facility. The power conditioner 3 includes: a PQ detection part 20 for detecting an effective/ineffective power component of a bus bar 51; a frequency adjuster 21 for adjusting an output frequency command in response to the effective power component in accordance with droop characteristics; and a frequency control part 11 for correcting the output frequency command in accordance with a frequency correction command. Further, the power conditioner includes: a DC current detector 40 for detecting a DC current of the storage battery 2; and a PI adjustment part 29b and a limiter 30b for limiting an upper limit value of the frequency correction command of a polarity to reduce the output frequency command to 0 when a DC current detection value exceeds a charge current protection level.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a storage battery system having a power conversion device and a storage battery capable of forward / reverse conversion, a power generation facility for charging the storage battery system, and a load fed by the storage battery system disconnected from the system at the time of a power failure of the power system. And a self-sustained operation system including the equipment.

FIG. 6 is an overall configuration diagram of the self-sustaining operation control device described in Patent Document 1.
6, 50 is a bus connected to the power system, 80, 80,... Are distributed power sources connected to the bus 50 via inverters 70, 70,..., 90, 90,. This is a control device that controls the inverters 70, 70,... Based on the current. In addition, 100, 100,... Are loads fed from the distributed power sources 80, 80,... Via the bus 50, and 60 is used for cooperative operation of the inverters 70, 70,. Are output to the control devices 90, 90,...
Here, the distributed power sources 80, 80,... Are constituted by power generation facilities using natural energy such as solar power generation devices and wind power generation devices, or DC power supply facilities such as storage batteries.

  FIG. 7 shows a configuration of the control device 90 in FIG. This control device 90 includes an amplitude detector 91, a PQ detector (active power component / reactive power component detector) 92, proportional controllers 93a to 93d, a voltage command calculator 94, a PWM controller 95, and a phase difference detector 96. , An integrator 97 and the like.

In the control device 90, the amplitude detection unit 91 detects the reference amplitude V _ref of the output voltage of the inverter 70, the reactive current (reactive power) component of the bus 50 output from the PQ detection unit 92 via the proportional control unit 93a, and the amplitude detection unit 91. The deviation from the amplitude of the generated bus voltage is amplified by the proportional control unit 93 b and input to the voltage command calculation unit 94.
Further, the difference between the phase of the bus voltage and the phase angle command θ is detected by the phase difference detection unit 96 and amplified by the proportional control unit 93d. Furthermore, the deviation between the active current (active power) component output from the PQ detection unit 92 and the output command value from the cooperative control device 60 is amplified by the proportional control unit 93c. Then, the reference frequency f _ref of the output voltage of the inverter 70 and the outputs of the proportional control units 93c and 93d are added and input to the integrator 97, and the phase angle command θ is calculated.

  The voltage command calculation unit 94 calculates an output voltage command of the inverter 70 based on the amplitude command and the phase angle command θ output from the proportional control unit 93b, and performs PWM control of the inverter 70 via the PWM control unit 95. Thus, the DC power of the distributed power source 80 is converted into AC power and supplied from the bus 50 to the load 100.

  In the self-sustained operation control apparatus shown in FIGS. 6 and 7, the inverters 70, 70,... Flow into the load 100 from the inverters 70, 70,. Is controlled according to a droop characteristic (slope characteristic) that decreases the amplitude of the output voltage as the reactive power increases, and decreases the frequency of the output voltage as the active power flowing from the inverters 70, 70,. It is carried out. Further, the cooperative control device 60 calculates the total amount of the load 100 to generate output command values of the inverters 70, 70,..., And gives these output command values to the control devices 90, 90,. ,... Are operated in parallel to control the independent operation of the distributed power sources 80, 80,.

JP 2007-1224797 A (paragraphs [0012] to [0028], [0042] to [0053], FIGS. 1 to 5 etc.)

However, for example, when the load suddenly increases, the inverter that is operated in accordance with the frequency command such that the output power becomes larger than the other inverters will share a large amount of output power. There is a possibility that the storage battery becomes overdischarged and the storage battery voltage becomes insufficient.
On the other hand, when the load suddenly becomes lighter, the inverter that has been operated in accordance with the frequency command such that the input power becomes larger than the other inverters will share a lot of input power, and the distributed power source 80 There is a risk that the storage battery will be overcharged and the storage battery voltage will be excessive.
When such a situation occurs, there is a problem that it is difficult to operate the system stably and continuously.

  Then, the solution subject of this invention is providing the self-sustained operation system which controlled the charging / discharging electric current of a storage battery appropriately, protected a storage battery, and enabled the stable and continuous driving | operation of the system.

In order to solve the above-mentioned problem, the invention according to claim 1 controls a power storage device including a power conversion device capable of forward / reverse conversion and a storage battery connected to a DC side of the power conversion device, and the power conversion device. A storage battery system control device, a power generation facility connected to the alternating current side of the power conversion device and capable of charging the storage battery via the power conversion device, and a connection point between the storage battery system and the power generation facility via a bus Connected load equipment, and
In a state where the storage battery system is disconnected from the power system, the storage battery system is a self-sustaining operation system that supplies power to the load by discharging the storage battery via the power converter and the bus,
The power converter is
Means for detecting an active power component / reactive power component of the bus; means for adjusting an output frequency command according to the active power component based on a droop characteristic; and means for correcting the output frequency command with a frequency correction command; In a self-sustaining operation system with
DC current detection means for detecting the DC current of the storage battery;
Charging current comparison means for comparing a direct current detection value by the direct current detection means and a charging current protection level of the storage location;
Means for limiting the upper limit value of the frequency correction command having a polarity to lower the output frequency command to 0 when the detected direct current value exceeds the charge current protection level.

The invention according to claim 2 is the self-sustaining operation system according to claim 1,
A discharge current comparing means for comparing the DC current detection value with the discharge current protection level of the storage battery; and a polarity for increasing the output frequency command when the DC current detection value exceeds the discharge current protection level. And means for limiting the lower limit value of the frequency correction command to 0.

The invention according to claim 3 is a storage battery system comprising a power conversion device capable of forward / reverse conversion and a storage battery connected to a DC side of the power conversion device, a storage battery system control device for controlling the power conversion device, and the power A power generation facility connected to the alternating current side of the conversion device and capable of charging the storage battery via the power conversion device; a load facility connected via a busbar to a connection point between the storage battery system and the power generation facility; Have
In a state where the storage battery system is disconnected from the power system, the storage battery system is a self-sustaining operation system that supplies power to the load by discharging the storage battery via the power converter and the bus,
The power converter is
Means for detecting an active power component / reactive power component of the bus; means for adjusting an output frequency command according to the active power component based on a droop characteristic; and means for correcting the output frequency command with a frequency correction command; In a self-sustaining operation system with
DC voltage detection means for detecting the DC voltage of the storage battery;
Overvoltage comparison means for comparing a DC voltage detection value by the DC voltage detection means with an overvoltage protection level of the storage location;
Means for limiting the upper limit value of the frequency correction command having a polarity to lower the output frequency command to 0 when the detected DC voltage value exceeds the overvoltage protection level.

The invention according to claim 4 is the self-sustaining operation system according to claim 3,
Undervoltage comparison means for comparing the DC voltage detection value with the undervoltage protection level of the storage battery, and a polarity for increasing the output frequency command when the DC voltage detection value exceeds the undervoltage protection level. And means for limiting the lower limit value of the frequency correction command to 0.

The invention according to claim 5 is the self-sustaining operation system according to any one of claims 1 to 4, wherein a plurality of the storage battery systems are connected in parallel.
According to a sixth aspect of the present invention, in the self-sustained operation system according to the fifth aspect, the frequency correction command is provided with an offset in accordance with the state of charge of the storage places respectively provided in the plurality of storage battery systems. It is characterized by that.

  According to the present invention, the storage battery is protected from an overcharged state or an overdischarged state by appropriately controlling the charging / discharging current of the storage battery using the droop characteristic of the power conditioner, and the autonomous operation system can be stably and continuously performed. It is possible to drive.

1 is an overall configuration diagram of a self-sustained operation system according to an embodiment of the present invention. It is a block diagram which shows 1st Example of the power conditioner in FIG. It is a block diagram which shows 2nd Example of the power conditioner in FIG. It is a figure which shows the droop characteristic of a power conditioner. It is a figure which shows the droop characteristic of a plurality of power conditioners. It is a whole block diagram of the independent operation control apparatus which concerns on a prior art. It is a block diagram which shows the structure of the principal part in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of a self-sustaining operation system according to this embodiment. In FIG. 1, 1a is a storage battery system comprising a storage battery 2a and a power conditioner 3a, 1b is a storage battery system comprising a storage battery 2b and a power conditioner 3b, and 1c is a storage battery system comprising a storage battery 2c and a power conditioner 3c. . These storage battery systems 1a, 1b, and 1c supply AC power to a load facility 7 to be described later by parallel operation, and the number thereof is not limited to the illustrated example.

  The power conditioners 3a, 3b, 3c function as power converters capable of forward / reverse conversion for charging / discharging the storage batteries 2a, 2b, 2c, and are controlled by the storage battery system control device 5, respectively. The storage battery system control device 5 generates a frequency correction command and an AC voltage correction command, which will be described later, based on measured values such as the DC voltage and DC current (charge / discharge current) of the storage batteries 2a, 2b, 2c, and the power conditioners 3a, Means for transmitting to 3b and 3 are provided.

The power conditioners 3a, 3b, 3c are collectively connected to the bus 50 via the transformers 4a, 4b, 4c, and the bus 50 is connected to the power system 9 via the interconnection transformer 4g and the system breaker 8. ing.
A power generation facility 6 composed of a natural energy power generation device such as a solar power generation device 6a or a wind power generation device 6b is connected to the bus 50 via transformers 4d and 4e. The type of the natural energy power generation apparatus is not limited to the above example, but generally has a characteristic that the output fluctuates.
The load facility 7 is connected to the bus 50 via a transformer 4f.

  In the above configuration, when the storage battery 2a, 2b, 2c is charged via the power conditioners 3a, 3b, 3c with the generated power of the power generation facility 6, and the system breaker 8 is cut off due to a power failure of the power system 9, etc. By discharging the storage batteries 2a, 2b, 2c through the power conditioners 3a, 3b, 3c, AC power can be supplied to the load facility 7 via the bus 50.

Next, FIG. 2 is a block diagram showing a first embodiment of the power conditioners 3a, 3b, 3c.
2, 2 is a storage battery corresponding to reference numerals 2a, 2b and 2c in FIG. 1, 3 is a power conditioner corresponding to 3a, 3b and 3c, and 4 is a transformer corresponding to 4a, 4b and 4c. ing.

  The DC voltage of the storage battery 2 is detected by a DC voltage detector 43 and input to the storage battery system control device 5. The storage battery system control device 5 generates a frequency correction command and sends it to the frequency control unit 11 via the frequency correction command limiter 13 </ b> A, and also generates an AC voltage correction command and sends it to the voltage control unit 12.

  The frequency correction command limiting unit 13A operates such that the current deviation becomes zero, and the adder / subtractor 28f as discharge current comparison means for obtaining a current deviation from the DC current detection value by the DC current detector 40 and the discharge current protection level. A PI (Proportional Plus Integral) regulator 29a, a limiter 30a for limiting the lower limit of its output to 0, and an adder / subtracter as a charging current comparison means for obtaining a current deviation from the DC current detection value and the charging current protection level 28g, a PI controller 29b that operates so that the current deviation becomes zero, a limiter 30b that limits the upper limit value of its output to 0, and a limiter 31 that limits the frequency correction command by the outputs of the limiters 30a and 30b. It is equipped with.

Further, the alternating current of the bus 51 detected by the alternating current detector 41 is input to the PQ detection unit (active power component / reactive power component detection unit) 20 in the droop control unit 10. The PQ detector 20 decomposes the alternating current of the bus 51 into an active current component I _d and a reactive current component I _q , converts the active current component I _d into the frequency adjuster 21, and converts the reactive current component I _q into the AC voltage adjuster 22. To send.

Here, the frequency adjuster 21 has a droop characteristic as shown in FIG. That is, the frequency regulator 21 lowers the case where the polarity of the active current component I _d is positive (the frequency of the AC voltage of the bus 51) the output frequency of the power conditioner 3 in (if battery 2 is discharged) a negative frequency command df outputs the frequency control unit 11 in order, if the polarity of the active current component I _d is negative (if the battery 2 is being charged), raising the output frequency of the power conditioner 3 Therefore, a positive frequency command df is output to the frequency control unit 11.

Further, the AC voltage regulator 22 has the same droop characteristic, and when the reactive current component _Iq has a positive polarity (when the current is in a delayed phase), the output terminal voltage of the power conditioner 3 ( When the negative voltage command is output to the voltage control unit 12 to reduce the AC voltage of the bus 51 and the reactive current component _Iq is negative (when the current is in lead phase), the power conditioner 3 A positive voltage command is output to the voltage control unit 12 in order to increase the output terminal voltage.

  Due to the droop characteristics of the frequency regulator 21 and the AC voltage regulator 22 as described above, the storage battery systems 1a, 1b, 1c including the power conditioners 3a, 3b, 3c can each independently share the active power. It has become.

The frequency command df output from the frequency adjuster 21 is added to the reference frequency f ₀ (for example, 50 [Hz] or 60 [Hz]) by the adder / subtractor 28a in the frequency control unit 11, and the addition result is added / subtracted. The frequency correction command via the limiter 31 is added by the device 28b.
The output of the adder / subtractor 28b is input to a VCO (Voltage Controlled Oscillator) 24, and the VCO 24 generates a sine wave signal based on the input frequency.

The voltage command output from the AC voltage regulator 22 is added to the reference voltage v ₀ by the adder / subtractor 28 c in the voltage controller 12, and the addition result is the AC from the storage battery system controller 5 in the adder / subtractor 28 d. It is added to the voltage correction command.
On the other hand, the AC voltage of the bus 51 detected by the AC voltage detector 42 is input to the maximum value calculator 23, and the AC voltage maximum value is calculated and input to the adder / subtractor 28 e in the voltage controller 12. The adder / subtractor 28e obtains a voltage deviation between the output of the adder / subtractor 28d and the AC voltage maximum value and sends it to an AVR (Automatic Voltage Regulator) 25. The AVR 25 sets the voltage deviation to zero. The amplitude of the alternating waveform is calculated, and this amplitude is output to the voltage command calculation unit 26.

The voltage command calculation unit 26 calculates a voltage command having a predetermined frequency and amplitude based on the outputs of the VCO 24 and AVR 25 and outputs the voltage command to a PWM (Pulse Width Modulation) control unit 27.
For example, the PWM control unit 27 compares the voltage command with the carrier to generate a drive signal, and sends the drive signal to the semiconductor switching element of the power conversion unit 3x. The power conversion unit 3x can convert DC power and AC power to each other, performs power conversion by turning on and off the semiconductor switching element, and charges and discharges the storage battery 2.

Next, the operation of the first embodiment will be described.
For example, the power conditioners 3a, 3b, and 3c of the storage battery systems 1a, 1b, and 1c are connected to a constant voltage in a no-load state in which the generated power of the power generation facility 6 in FIG. When the constant frequency control is performed, the output terminal current of the storage batteries 2a, 2b, 2c becomes zero. At this time, since the power conditioners 3a, 3b, and 3c are operated according to the droop characteristic of FIG. 4, the frequency of the bus 51 in FIG. 2 is maintained at the reference frequency f ₀ (for example, 50 [Hz]), and the voltage of the bus 51 It is maintained at the reference voltage v _0.

In this state, when output (only active power is output at a power factor of 1) is generated from the power generation facility 6, the output is all used for charging the storage batteries 2a, 2b, 2c. Thus, the power conditioner 3a, 3b, the polarity of the active current component _{I d} of the output end of 3c become negative (charged) by droop characteristic of FIG. 4, the power conditioner 3a, 3b, 3c is autonomously output The effective current is adjusted between the storage battery systems 1a, 1b, and 1c by increasing the frequency, and the active power (charge amount of the storage batteries 2a, 2b, and 2c) is equally shared.

In the control described above, the output frequency of the power conditioners 3a, 3b, and 3c increases, so the frequency of the bus 50 (51) also increases. However, the storage battery system controller 5 shows the frequency of the increased bus 50 in the figure. measured by measuring means not, as the frequency is maintained at the reference frequency f _0, to produce a three frequency correction command to the power conditioner 3a, 3b, 3c.
The three frequency correction commands are negative and all have the same value, and these frequency correction commands are simultaneously transmitted to the frequency control unit 11 of the power conditioners 3a, 3b, and 3c via the limiter 31 of the frequency correction command limiting unit 13A. As a result, the output frequency of the adder / subtractor 28b is lowered. Therefore, the power conditioner 3a, 3b, the output frequency of the 3c is gradually decreased at the same time, while maintaining the distribution ratio of the effective current (charge amount), it reduces the frequency of the bus 50, eventually settling to the reference frequency f ₀ To do.

In the frequency correction command limiting unit 13A, when the DC current detection value of the storage battery 2 exceeds the charging current protection level, the upper limit value of the polarity frequency correction command for reducing the frequency of the bus 50 is set to 0 by the limiter 30b. By limiting, the charging current of the storage battery 2 is prevented from becoming excessive.
On the other hand, when the DC current detection value exceeds the discharge current protection level, the limit value 30a limits the lower limit value of the polarity frequency correction command for increasing the frequency of the bus 50 to 0 by the limiter 30a. Is prevented from becoming excessive.

  Here, the storage battery system control device 5 weights the three frequency correction commands to be transmitted to the power conditioners 3a, 3b, and 3c in accordance with the SOC (State of Charge) of the storage batteries 2a, 2b, and 2c, respectively. ing.

That is, by sending a frequency correction command weighted to the positive polarity side to the power conditioner corresponding to the storage battery having a high SOC, the droop characteristic has a positive polarity like the “discharge machine characteristic” in FIG. Have an offset. The power conditioner to which a positive polarity offset is given by this droop characteristic is controlled to increase the amount of discharge from the storage battery at the time of discharging and to decrease the amount of charge to the storage battery at the time of charging.
Conversely, by sending a frequency correction command weighted to the negative polarity side to a power conditioner corresponding to a low SOC storage battery, the droop characteristic has a negative polarity as shown in “Charging machine characteristics” in FIG. Have an offset of. The power conditioner to which the negative polarity offset is given by this droop characteristic is controlled so as to reduce the amount of discharge from the storage battery at the time of discharging and to increase the amount of charge to the storage battery at the time of charging.

Next, FIG. 3 is a block diagram showing a second embodiment of the power conditioners 3a, 3b, 3c.
In the second embodiment, the DC current detector 40 in the first embodiment of FIG. 2 is deleted, and a part of the function of the frequency correction command limiting unit 13B is different from the first embodiment. Other configurations and functions are the same as those in the first embodiment.

That is, the DC voltage of the storage battery 2 detected by the DC voltage detector 43 and the storage battery undervoltage protection level are input to the adder / subtractor 28f as the undervoltage comparison means in the frequency correction command limiter 13B by the illustrated symbols. The DC voltage and the storage battery overvoltage protection level are input to the adder / subtractor 28g serving as the overvoltage comparison means with the illustrated symbols.
According to the second embodiment, when the DC voltage detected value exceeds the storage battery overvoltage protection level, the limit value 30b limits the upper limit value of the polarity frequency correction command for reducing the frequency of the bus 50 to 0. , To prevent the storage battery voltage from becoming excessive (overcharge state), and conversely, when the detected DC voltage exceeds the storage battery undervoltage protection level, the frequency correction of the polarity to increase the frequency of the bus 50 By limiting the lower limit value of the command to 0 by the limiter 30a, it is possible to prevent the storage battery voltage from becoming insufficient (becomes an overdischarge state).

  As described above, according to the power conditioner according to the first embodiment or the second embodiment, the effective current of the bus is controlled by limiting the frequency correction command according to the DC current or the DC voltage of the storage battery 2. Meanwhile, the overcharge protection and the overdischarge protection of the storage battery 2 can be performed.

  INDUSTRIAL APPLICABILITY The present invention includes a plurality of storage battery systems that are charged by various power generation facilities and can be operated in parallel, and can be used as a system that powers load equipment by operating these storage battery systems independently.

1a, 1b, 1c: Storage battery systems 2, 2a, 2b, 2c: Storage batteries 3, 3a, 3b, 3c: Power conditioner 3x: Power converters 4, 4a, 4b, 4c, 4d, 4e, 4f, 4g: Transformers 5: Storage battery system control device 6: Power generation facility 6a: Solar power generation device 6b: Wind power generation device 7: Load facility 8: System breaker 9: Power system 10: Droop control unit 11: Frequency control unit 12: Voltage control unit 13A , 13B: Frequency correction command limiting unit 20: PQ detection unit (active current / reactive current detection unit)
21: Frequency regulator 22: AC voltage regulator 23: Maximum value calculator 24: VCO (Voltage Controlled Oscillator)
25: AVR (Automatic Voltage Regulator)
26: Voltage command calculation unit 27: PWM (Pulse Width Modulation) control units 28a, 28b, 28c, 28d, 28e, 28f, 28g: Adder / subtractors 29a, 29b: PI (Proportional Plus Integral) regulators 30a, 30b, 31: Limiter 40: DC current detector 41: AC current detector 42: AC voltage detector 43: DC voltage detector 50, 51: Bus

Claims (6)

A storage battery system comprising a power conversion device capable of forward / reverse conversion and a storage battery connected to the DC side of the power conversion device, a storage battery system control device for controlling the power conversion device, and an AC side of the power conversion device And a power generation facility capable of charging the storage battery via the power converter, and a load facility connected via a busbar to a connection point between the storage battery system and the power generation facility,
In a state where the storage battery system is disconnected from the power system, the storage battery system is a self-sustaining operation system that supplies power to the load by discharging the storage battery via the power converter and the bus,
The power converter is
Means for detecting an active power component / reactive power component of the bus; means for adjusting an output frequency command according to the active power component based on a droop characteristic; and means for correcting the output frequency command with a frequency correction command; In a self-sustaining operation system with
DC current detection means for detecting the DC current of the storage battery;
Charging current comparison means for comparing a direct current detection value by the direct current detection means and a charging current protection level of the storage location;
Means for limiting the upper limit value of the frequency correction command having a polarity to reduce the output frequency command to 0 when the DC current detection value exceeds the charging current protection level;
A self-sustaining operation system characterized by comprising In the self-sustaining operation system according to claim 1,
A discharge current comparison means for comparing the DC current detection value and the discharge current protection level of the storage location;
Means for limiting a lower limit value of the frequency correction command having a polarity to increase the output frequency command to 0 when the DC current detection value exceeds the discharge current protection level;
A self-supporting operation system characterized by further comprising: A storage battery system comprising a power conversion device capable of forward / reverse conversion and a storage battery connected to the DC side of the power conversion device, a storage battery system control device for controlling the power conversion device, and an AC side of the power conversion device And a power generation facility capable of charging the storage battery via the power converter, and a load facility connected via a busbar to a connection point between the storage battery system and the power generation facility,
In a state where the storage battery system is disconnected from the power system, the storage battery system is a self-sustaining operation system that supplies power to the load by discharging the storage battery via the power converter and the bus,
The power converter is
Means for detecting an active power component / reactive power component of the bus; means for adjusting an output frequency command according to the active power component based on a droop characteristic; and means for correcting the output frequency command with a frequency correction command; In a self-sustaining operation system with
DC voltage detection means for detecting the DC voltage of the storage battery;
Overvoltage comparison means for comparing a DC voltage detection value by the DC voltage detection means with an overvoltage protection level of the storage location;
Means for limiting the upper limit value of the frequency correction command having a polarity to lower the output frequency command to 0 when the DC voltage detection value exceeds the overvoltage protection level;
A self-sustaining operation system characterized by comprising In the self-sustained operation system according to claim 3,
Undervoltage comparison means for comparing the DC voltage detection value with the undervoltage protection level of the storage location;
Means for limiting a lower limit value of the frequency correction command having a polarity to increase the output frequency command to 0 when the DC voltage detection value exceeds the undervoltage protection level;
A self-supporting operation system characterized by further comprising: In the self-sustained operation system according to any one of claims 1 to 4,
A self-sustaining operation system, wherein a plurality of the storage battery systems are connected in parallel. In the self-sustaining operation system according to claim 5,
An independent operation system characterized in that an offset is given to the frequency correction command in accordance with the state of charge of a storage battery provided in each of the plurality of storage battery systems.

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