Power supply system with uninterruptible power supply function and load leveling function

Provided is a power supply system comprising: distributed energy resources (2) connected to a power line (L1) for feeding power from a commercial power system (10) to an important load (30); a switch (3) provided in the power line (L1) for opening and closing the power line (L1); an impedance element (4) connected in parallel to the switch (3) in the power line (L1); a voltage detection unit (5) for detecting a voltage on the commercial power system (10) side with respect to the switch (3); and a control unit (6) for releasing, when a voltage detected by the voltage detection unit (5) becomes equal to or lower than a set point, the switch (3) such that the distributed energy resources (2) and the commercial power system (10) are connected through the impedance element (4), and the distributed energy resources (2) continue operation including reverse power flow.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 application of the International PCT application serial no. PCT/JP2018/031601, filed on Aug. 27, 2018, which claims the priority benefits of Japan Patent Application No. 2017-169664, filed on Sep. 4, 2017. The entirety of the abovementioned patent application is hereby incorporated by reference herein and made a part of this specification.

TECHNICAL FIELD

The disclosure relates to a power supply system.

BACKGROUND ART

A power supply system may be classified as an uninterruptible power supply system that is disconnected from a commercial power system to compensate for an important load and a distributed power supply system that realizes load leveling such as peak-cut/peak-shift by charging or discharging a storage battery, at the time of service interruption or momentary power interruption.

With recent improvement in performance of a storage battery, it is conceivable that an uninterruptible power supply function and a load leveling function both be performed in a storage battery system with a large capacity (of a class with a capacity of 500 kW or more). For example, as described in Patent Literature 1, a secondary battery system that can perform both an uninterruptible power supply function and a load leveling function is conceivable. This system is disconnected to supply electric power to an important load at the time of service interruption or momentary power interruption.

Use of distributed power supplies which are connected to a commercial power system has increased, and when such distributed power supplies are simultaneously disconnected at the time of momentary power interruption, there is a likelihood that maintenance of the voltage or frequency of the commercial power system as a whole will be greatly affected. Accordingly, there is demand for continuous operation of such distributed power supplies without disconnection from a commercial power system even at the time of momentary power interruption (fault-ride-through (FRT) requirements).

However, in the above-mentioned power supply system, since disconnection is performed at the time of momentary power interruption, FRT requirements may not be able to be satisfied. As disclosed in Patent Literature 2, it is conceivable that a storage battery for uninterruptible power supply and a storage battery for load leveling be used for a power supply system to construct a system that performs these functions individually, but costs and sizes thereof increase.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Therefore, the disclosure has been invented to solve the above-mentioned problems and a main objective thereof is to provide a novel power supply system that can perform both an uninterruptible power supply function and a load leveling function in types of continuous commercial power supply using a common distributed power supply while satisfying FRT requirements.

Solution to Problem

That is, a power supply system according to the disclosure is a power supply system that is provided between a commercial power system and an important load and supplies electric power to the important load, the power supply system including: a distributed power supply that is connected to a power line for supplying electric power from the commercial power system to the important load; a changeover switch that is provided closer to the commercial power system than to the distributed power supply in the power line and opens and closes the power line; an impedance element that is connected in parallel to the changeover switch in the power line; a system-side voltage detecting unit that detects a voltage of a part closer to the commercial power system than to the changeover switch; and a control unit that opens the changeover switch and connects the distributed power supply and the commercial power system via the impedance element when a voltage detected by the system-side voltage detecting unit becomes equal to or lower than a predetermined set value, wherein the distributed power supply continues to perform an operation including a reverse power flow in a state in which the distributed power supply and the commercial power system are connected via the impedance element.

In this power supply system, since the changeover switch is provided closer to the commercial power system than to the distributed power supply in the power line, the impedance element is connected in parallel to the changeover switch, and the changeover switch is opened when the voltage of the commercial power system side becomes equal to or less than the set value, consumer-side equipment is connected to the commercial power system via the impedance element even at the time of momentary power interruption. Accordingly, it is possible to prevent a voltage drop in the important load at the time of momentary power interruption while satisfying the FRT requirements of the distributed power supply. As a result, it is possible to provide a novel power supply system that can perform both an uninterruptible power supply function and a load leveling function using a common distributed power supply while satisfying FRT requirements.

Since a parallel circuit part including the impedance element and the changeover switch has only to be provided in the power line, it is possible to simplify a circuit configuration of the device. Since a current flows in the changeover switch at the time of normal operation, it is possible to prevent a loss from being generated in the impedance element such as a reactor.

The FRT requirements include continuous operation with frequency variation in addition to continuous operation with a voltage drop as described above. When the distributed power supply continues to operate in a state in which the changeover switch is closed in the power supply system having the above-mentioned configuration, the distributed power supply continues to perform operation to follow the frequency variation of the commercial power system and the frequency of a voltage and a current to the important load varies. Here, when the frequency tolerance of the important load is less than the frequency range of the FRT requirements, the important load is detached.

Accordingly, the power supply system may further include a frequency variation detecting unit that detects a frequency variation of a part closer to the commercial power system side than to the changeover switch, and, when a frequency tolerance of the important load or the distributed power supply is not within a predetermined set range, the control unit may open the changeover switch and connect the distributed power supply and the commercial power system via the impedance element when the frequency variation detected by the frequency variation detecting unit is equal to or greater than the frequency tolerance and is included in the predetermined set range.

The frequency tolerance is an allowable frequency variation range in which the important load or the distributed power supply can operate. The predetermined set range is a frequency range of the FRT requirements. When the frequency variation is a stepwise increase, for example, the set range is a range (50 Hz to 50.8 Hz, 60 Hz to 61.0 Hz) from a normal frequency (50 Hz or 60 Hz) to a predetermined varied value (50.8 Hz or 61.0 Hz). When the frequency variation is a ramp-like increase or decrease, the set range is a range with a predetermined rate of variation (±2 Hz/sec) from the normal frequency (50 Hz or 60 Hz) and a range up to an upper-limit set value or a lower-limit set value with a predetermined variation.

At this time, the distributed power supply may continue to perform an operation including a reverse power flow within the frequency tolerance range in a state in which the distributed power supply and the commercial power system are connected via the impedance element.

With this configuration, it is possible to prevent detachment of the important load while satisfying the FRT requirements of the distributed power supply for a frequency variation. Specifically, when the distributed power supply is connected to the commercial power system via the impedance element and continues to perform operation in a state in which the voltage of the distributed power supply side is less than a frequency limit in the frequency tolerance, the frequency and phase thereof are different from those of the voltage of the commercial power system side. On the other hand, by curbing a cross current due to such a potential difference and a voltage variation based thereon using the impedance element, it is possible to stabilize the voltage and current to the important load in a state in which the voltage of the important load side is maintained at less than the frequency limit.

As a specific operating aspect of the distributed power supply, the distributed power supply may continue to perform an operation including a reverse power flow within the smaller frequency tolerance range of the important load and the distributed power supply in a state in which the distributed power supply and the commercial power system are connected via the impedance element.

The power supply system may further include a disconnection switch that is provided closer to the commercial power system than to the distributed power supply in the power line, the control unit may open the disconnection switch when the voltage detected by the system-side voltage detecting unit satisfies a predetermined disconnection condition, and the distributed power supply may supply electric power to the important load to enter a self-operation mode in a state in which the disconnection switch is open.

The power supply system may further include a power-supply-side voltage detecting unit that detects a voltage of a part closer to the distributed power supply than to the disconnection switch in the power line, and the control unit may turn on the disconnection switch when the voltage detected by the system-side voltage detecting unit satisfies the predetermined disconnection condition and the voltage detected by the system-side voltage detecting unit and the voltage detected by the power-supply-side voltage detecting unit satisfy a synchronism detection condition. Here, the predetermined synchronism detection condition is a condition that the magnitude, frequency, and phase of the voltage detected by the system-side voltage detecting unit match the magnitude, frequency, and phase of the voltage detected by the power-supply-side voltage detecting unit.

In addition, the power supply system may further include: a system-connection protection device that is provided closer to the commercial power system than to the disconnection switch in the power line; and a power-supply-side voltage detecting unit that detects a voltage of a part closer to the distributed power supply than to the disconnection switch in the power line, and the control unit may turn on the disconnection switch when the system-connection protection device is deactivated and the voltage detected by the system-side voltage detecting unit and the voltage detected by the power-supply-side voltage detecting unit satisfy a synchronism detection condition.

Advantageous Effects of Invention

According to the disclosure having the above-mentioned configurations, it is possible to provide a novel power supply system that can perform both a function of a uninterruptible power supply system and a function of a distributed power supply using a common distributed power supply while satisfying FRT requirements.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment of a power supply system according to the disclosure will be described with reference to the accompanying drawings.

As illustrated inFIG. 1, a power supply system100according to an embodiment is provided between a commercial power system10and an important load30and serves to perform a function of an uninterruptible power supply system (an uninterruptible power supply function) that supplies electric power to the important load30when an abnormality occurs in the commercial power system10and a function of a distributed power supply system (a load leveling function) that levels a load by causing electric power to flow forward and reversely with respect to a commercial power system.

Here, the commercial power system10is a power supply network of an electric power company (an electric operator) and includes a power plant, a power transmission system, and a power distribution system. The important load30is a load to which electric power is to be stably supplied even at the time of system abnormality such as service interruption or momentary power interruption and the number of important load is one inFIG. 1but may be two or more.

Specifically, the power supply system100includes a distributed power supply2, a changeover switch3that connects the commercial power system10, the distributed power supply2, and the important load30, an impedance element4that is connected in parallel to the changeover switch3, a system-side voltage detecting unit5that detects a voltage of a part closer to the commercial power system10than to the changeover switch3, and a control unit6that opens the changeover switch3when a voltage detected by the system-side voltage detecting unit5becomes equal to or lower than a set value.

The distributed power supply2is connected to a power line L1that is used to supply power from the commercial power system10to the important load30. The distributed power supply2is connected to the commercial power system10and is, for example, a distributed power supply including a DC power generation facility21asuch as a photovoltaic cell or a fuel cell and a power conversion device22, a distributed power supply including a power storage device (a power storage device)21bsuch as a secondary battery (a storage battery) and a power conversion device22, a power generation facility (not illustrated) that rectifies electric energy output as AC power from a wind power generator, a micro gas turbine, or the like into DC power and is connected to the system using a power conversion device, or an AC power generation facility21csuch as a synchronous generator or an induction generator. The power supply system100includes at least one power storage device21band may additionally include one distributed power supply2described above.

The changeover switch3is provided closer to the commercial power system10than to a connection point of the distributed power supply2in the power line L1and serves to open and close the power line L1, and, for example, a changeover switch that can be rapidly switched such as a semiconductor switch or a hybrid switch in which a semiconductor switch and a mechanical switch are combined can be used. For example, when a semiconductor switch is used, a switching time can be set to be equal to or less than 2 ms and the changeover switch can be shut off regardless of a zero point. When a hybrid switch is used, the switching time can be set to be equal to or less than 2 ms, the changeover switch can be shut off regardless of a zero point, and a power-supply loss can be made to be zero. Opening and closing of the changeover switch3is controlled by the control unit6.

The impedance element4is connected in parallel to the changeover switch3in the power line L1and is a current-limiting reactor in this embodiment.

The system-side voltage detecting unit5serves to detect a voltage on a part closer to the commercial power system10than to the changeover switch3in the power line L1using a voltage transformer. Specifically, the system-side voltage detecting unit5is connected to a part closer to the commercial power system10than to a parallel circuit including the changeover switch3and the impedance element4via the voltage transformer.

The control unit6serves to compare the voltage detected by the system-side voltage detecting unit5with a predetermined set value and to output a control signal to the changeover switch3to open the changeover switch3when the detected voltage is equal to or lower than the set value. The set value in this embodiment is a voltage value for detecting momentary power interruption. By allowing the control unit6to open the changeover switch3in this way, the commercial power system10, the distributed power supply2, and the important load30are connected to each other via the impedance element4. In this state, the distributed power supply continues to perform an operation including a reverse power flow.

The operation of the power supply system100according to this embodiment (at the time of normal operation and at the time of momentary power interruption) will be described below.

At the time of normal operation of the power supply system100, as illustrated inFIG. 2, the changeover switch3is closed, and the distributed power supply2and the important load30are connected to the commercial power system10via the changeover switch3. The reactor4is connected in parallel to the changeover switch3, but since an impedance of the changeover switch3is smaller than an impedance of the reactor4, the commercial power system10, the distributed power supply2, and the important load30give and take power via the changeover switch3side. Peak-cut/peak-shift can be realized by a reverse power flow due to the distributed power supply2.

On the other hand, when a short-circuit accident (for example, a three-phase short circuit) occurs on the commercial power system10side, the voltage of the commercial power system10side decreases. This voltage drop is detected by the system-side voltage detecting unit5. When the voltage detected by the system-side voltage detecting unit5is equal to or lower than the set value, the control unit6opens the changeover switch3.

As illustrated inFIG. 3, when the changeover switch3is opened, the distributed power supply2and the important load30are connected to the commercial power system10via the reactor4. In this state, a current flowing from the distributed power supply2to a short-circuit accident point is limited by the reactor4, an accident current flowing to the short-circuit accident point is curbed and a voltage drop of the important load30is prevented. In this state, the distributed power supply2continues to perform an operation including a reverse power flow and continues to perform power generation and output.

The system-side voltage detecting unit5detects the voltage on the commercial power system10side regardless of opening or closing of the changeover switch3. When the voltage detected by the system-side voltage detecting unit5becomes equal to or higher than a predetermined restored voltage, for example, when a residual voltage of the commercial power system becomes equal to or greater than 80%, the control unit6closes the changeover switch3.

A result of simulation of a compensation operation at the time of momentary power interruption of the power supply system100having the configuration illustrated inFIG. 1is illustrated inFIG. 4.

The result of simulation of a compensation operation represents (a) voltage/current waveforms of the commercial power system side, (b) voltage/current waveforms of a consumer side, and (c) opening/closing of the changeover switch when a voltage drop of 50% is maintained for 0.35 seconds. The voltage/current waveforms of the commercial power system side indicate a voltage and a current which are detected in a part closer to the commercial power system than to the changeover switch in the power line, and the voltage/current waveforms of the consumer side indicate a voltage and a current which are detected in a part closer to the important load than to the distributed power supply in the power line.

From the result of simulation illustrated inFIG. 4, it was ascertained that it is possible to supply constant voltage and current (electric power) to the important load30without disconnecting the distributed power supply2and the important load30from the commercial power system10by opening the changeover switch3at the time of occurrence of momentary power interruption and interposing the impedance element4between the commercial power system10, the distributed power supply2, and the important load30.

With the power supply system100according to this embodiment having the above-mentioned configuration, since the changeover switch3is provided closer to the commercial power system10than to the distributed power supply2in the power line L1, the reactor4is connected in parallel to the changeover switch3, and the changeover switch3is opened when the voltage of the commercial power system10side becomes equal to or lower than the set value, the distributed power supply2and the important load30are connected to the commercial power system10via the reactor4even at the time of occurrence of momentary power interruption. Accordingly, in the power supply system100, since the distributed power supply2and the important load30are not disconnected from the commercial power system10at the time of normal operation and at the time of momentary power interruption, it is possible to prevent a voltage drop in the important load30at the time of momentary power interruption while satisfying the FRT requirements of the distributed power supply2. As a result, it is possible to provide a novel power supply system100that can perform both an uninterruptible power supply function and a load leveling function using a common distributed power supply2while satisfying the FRT requirements.

In addition, since a parallel circuit part including the reactor4and the changeover switch3has only to be provided in the power line L1, it is possible to simplify the circuit configuration of the system100. Since a current flows in the changeover switch3at the time of normal operation, it is possible to prevent a loss which is generated in the reactor4.

Second Embodiment

A second embodiment of the power supply system according to the disclosure will be described below with reference to the accompanying drawings.

The power supply system100according to this embodiment satisfies FRT requirements for a frequency variation in addition to the FRT requirements for a voltage drop in the first embodiment.

Specifically, the power supply system100according to the second embodiment includes a frequency variation detecting unit7that detects a frequency variation in a part closer to the commercial power system10than to the changeover switch3in addition to the configuration according to the first embodiment as illustrated inFIG. 5. The frequency variation detecting unit7serves to detect a frequency variation (a frequency increase (OF) or a frequency decrease (UF)) from the voltage detected by the system-side voltage detecting unit5.

The control unit6controls opening and closing of the changeover switch3on the basis of the frequency variation detected by the frequency variation detecting unit7. This frequency variation is, for example, a stepwise increase or a ramp-like increase or decrease.

The operation of the distributed power supply2along with opening/closing control of the changeover switch3which is performed by the control unit6will be described below with reference toFIGS. 6 and 7.

(1) When the frequency tolerance of the distributed power supply2and the important load30satisfies a frequency range (a predeteimined set range) of the FRT requirements and the frequency variation of the commercial power system10is within the frequency range of the FRT requirements ((1) inFIG. 6), the control unit6maintains the state in which the changeover switch3is turned on. At this time, the distributed power supply2continues to operate to follow the frequency variation of the commercial power system10((a) ofFIG. 7A).

(2) When the frequency tolerance of at least one of the distributed power supply2and the important load30is not within the frequency range of the FRT requirements and the frequency variation of the commercial power system10is less than the smaller frequency tolerance ((2) inFIG. 6), the control unit6maintains the state in which the changeover switch3is turned on. At this time, the distributed power supply continues to operate to follow the frequency variation of the commercial power system ((a) ofFIG. 7A).

(3) When the frequency tolerance of at least one of the distributed power supply2and the important load30is not within the frequency range of the FRT requirements and the frequency variation of the commercial power system10is equal to or greater than the smaller frequency tolerance and is within the frequency range of the FRT requirements ((3) inFIG. 6), the control unit6opens the changeover switch3. Then, the distributed power supply2and the important load30are connected to the commercial power system10via the reactor4. At this time, when the operation is continuously performed in a state in which the voltage of the distributed power supply2is less than the frequency limit, the frequency and phase thereof are different from those of the system-side voltage. On the other hand, a cross current due to a potential difference and a voltage variation based thereon are curbed by the reactor4, it is possible to stabilize supply of power to the important load30in a state in which the voltage of the important load side is maintained less than the frequency limit ((b) ofFIG. 7B).

The frequency variation detecting unit7detects the frequency variation of the commercial power system10regardless of opening or closing of the changeover switch3, and the control unit6closes the changeover switch3when the frequency variation of the commercial power system10becomes less than the smaller frequency tolerance.

With the power supply system100according to this embodiment having the above-mentioned configuration, it is possible to prevent detachment of the important load while satisfying the FRT requirements of the distributed power supply for the frequency variation as well as to achieve the same advantageous effects as in the first embodiment.

Third Embodiment

A third embodiment of the power supply system according to the disclosure will be described below with reference to the accompanying drawings.

Although not described in the first and second embodiments, in the power supply system100, a disconnection switch8is provided closer to the commercial power system10than to the distributed power supply2in the power line L1as illustrated inFIG. 8. In the power supply system100according to this embodiment, a power-supply-side voltage detecting unit9that detects a voltage of a part closer to the distributed power supply2than to the disconnection switch8in the power line L1is provided.

The disconnection switch8in this embodiment is an on-off switch that disconnects the commercial power system10and the distributed power supply2and is, for example, a mechanical switch. InFIG. 8, the disconnection switch8is provided closer to the commercial power system10than to the changeover switch3, but may be provided closer to the distributed power supply2than to the changeover switch3. Opening and closing of the disconnection switch8is controlled by the control unit6.

When the voltage detected by the system-side voltage detecting unit5satisfies a predetermined disconnection condition, the control unit6opens the disconnection switch8. Here, the predetermined disconnection condition is a condition that a duration time of a voltage drop of the system voltage (a state in which the detected voltage is equal to or less than the set value) is equal to or greater than a predetermined value (a time which is longer than a duration time of momentary power interruption). In a state in which the disconnection switch8is open, the distributed power supply2enters a self-operation mode and supplies electric power to the important load30. Since the changeover switch3is already open, an overcurrent due to opening of the disconnection switch8is curbed by the reactor4.

When the voltage detected by the system-side voltage detecting unit5eliminates the predetermined disconnection condition and the voltage detected by the system-side voltage detecting unit5and the voltage detected by the power-supply-side voltage detecting unit9satisfy a synchronism detection condition, the control unit6turns on the disconnection switch8.

In addition, when a predetermined disconnection condition such as a condition that the frequency variation detected by the frequency variation detecting unit7departs from the frequency range of the FRT requirements is satisfied, the control unit6also opens the disconnection switch8. At this time, the control unit turns on the disconnection switch8when the detected frequency variation is within the normal range.

A series of operations in the power supply system100will be described below with reference toFIGS. 9 and 10. In the following description, the frequency variation is not considered.

(1) At the time of normal operation

In a state in which the changeover switch3and the disconnection switch8are closed, the power supply system100operates in a system connection manner. The reactor4is connected in parallel to the changeover switch3, but since a current flows in the changeover switch3side with a low impedance value, transmission and reception of effective power including a reverse power flow is performed with the commercial power system10((a) ofFIG. 9A).

(2) At the time of occurrence of momentary power interruption

When a system voltage drop (UV) is detected using the voltage detected by the system-side voltage detecting unit5, the control unit6opens the changeover switch3. As a result, the reactor4connected in parallel to the changeover switch3is inserted, electric power is supplied while maintaining a reverse power flow to limit an overcurrent flowing from the distributed power supply2to the commercial power system10, and a voltage drop of the voltage supplied to the important load30is prevented (a uninterruptible power supply (UPS) operation is performed on the important load30) ((b) ofFIG. 9B).

(3) Operation at the time of disconnection and after disconnection due to system voltage drop (which occurs due to system service interruption or the like)

When the voltage detected by the system-side voltage detecting unit5satisfies a predetermined disconnection condition, the control unit6opens the disconnection switch8. As a result, the distributed power supply2is disconnected from the commercial power system10and enters a self-operation mode (an operation mode in which a storage battery is used as a voltage source inFIG. 10A) ((c) ofFIG. 10A). Since the changeover switch3is already opened, the disconnection switch8is opened without an overcurrent.

(4) Operation at the time of health restoration of system (restoration of power)

When the commercial power system is restored to a healthy state by the voltage detected by the system-side voltage detecting unit5, the control unit6turns on the changeover switch3. Thereafter, when the voltage detected by the system-side voltage detecting unit5and the voltage detected by the power-supply-side voltage detecting unit9satisfy a synchronism detection condition (the magnitude, frequency, and phase of the voltage of the distributed power supply2match the magnitude, frequency, and phase of the voltage of the commercial power system10), the control unit6turns on the disconnection switch8. Accordingly, (1) the operation at the time of normal operation described above is restarted ((d) ofFIG. 10B).

Other Modified Examples

The disclosure is not limited to the above-mentioned embodiments.

For example, when the important load30includes a motor30aand a power-factor improvement capacitor30bthat is connected in parallel to the motor30aas illustrated inFIG. 11, it is thought that a resistor is used as the impedance element4. In this case, opening and closing control of the changeover switch3at the time of normal operation and at the time of momentary power interruption is the same as in the above-mentioned embodiments. With this configuration, it is possible to prevent parallel resonance of the reactor and the power-factor improvement capacitor30bwhich is generated when a reactor is used as the impedance element4as well as to achieve the same advantageous effects as in the above-mentioned embodiments. A current flows in the resistor at the time of opening of the changeover switch, but since the time in which the changeover switch3is open is only several seconds, it is not necessary to cope with a thermal loss due to the resistor.

A capacitor may be used as the impedance element4, or a combination of two of a reactor, a resistor, and a capacitor may be used.

The system-side voltage detecting unit in the above-mentioned embodiments may be provided in a system-connection protection device. Examples of the system-connection protection device which is defined in system connection regulations include an overvoltage relay (OVR), an undervoltage relay (UVR), a short-circuit direction relay (DSR), a ground-fault overvoltage relay (OVGR), an overfrequency relay (OFR), an underfrequency relay (UFR), and a transfer interrupting device. In this case, it is conceivable that the control unit opens the disconnection switch when any connection protection instrument operates. When all the system-connection protection devices are deactivated and the voltage detected by the system-side voltage detecting unit and the voltage detected by the power-supply-side voltage detecting unit satisfy the synchronism detection condition, the control unit may turn on the disconnection switch. With this configuration, since the voltage detecting unit included in the connection protection instrument is used, it is not necessary to provide a particular system-side voltage detecting unit and thus to simplify a device configuration.

The power-supply-side voltage detecting unit in the above-mentioned embodiments is provided between the disconnection switch and the changeover switch and may be replaced by a function of measuring a system connection point voltage of the distributed power supply.

In addition, the disclosure is not limited to the above-mentioned embodiments and can be modified in various forms without departing from the gist of the disclosure.

INDUSTRIAL APPLICABILITY

According to the disclosure, it is possible to provide a novel power supply system that can perform both an uninterruptible power supply function and a load leveling function in a continuous commercial power supply type using a common distributed power supply while satisfying FRT requirements.