JP7523735B2 - Power System - Google Patents

Description

The present invention relates to a power supply system.

Conventionally, the system shown in Patent Document 1 has been considered as a power supply system that uses a common distributed power source to achieve both uninterruptible power supply functionality and load leveling functionality while satisfying FRT requirements.

The power supply system of Patent Document 1 is configured by providing an open/close switch and an impedance element connected in parallel to the open/close switch between the commercial power grid and the important load, and providing a distributed power source on the important load side of the open/close switch. Also, a disconnection switch is provided on the commercial power grid side of the open/close switch.

When an instantaneous voltage drop or frequency fluctuation occurs in the commercial power grid, as shown in Figure 6(a), the voltage drop or frequency fluctuation is detected and the open/close switch is opened, connecting the commercial power grid to the distributed power source via the impedance element, and the distributed power source continues to operate, including with reverse power flow (FRT operation).

On the other hand, when a power outage occurs in the commercial power grid, as shown in Figure 6(a), it recognizes it as an instantaneous voltage drop for a certain period of time (for example, 2 seconds) and performs FRT operation, then recognizes it as a power outage and opens the parallel-off switch, allowing the distributed power source to operate independently.

Patent No. 6338131

However, in the case of the above power supply system, during an extended power outage, the system will operate autonomously using only distributed power sources, which can lead to unstable power supply to important loads. In addition, when the distributed power source is a grid-connected type cogeneration system, it is assumed that city gas will be supplied, so there is a risk that the gas supply will be cut off due to a disaster, and it is difficult to say that this system contributes to improving BCP (business continuity planning) or power resilience in the event of a disaster.

The present invention was made to solve the above problems, and its main objective is to improve the stability of power supply to important loads during a power outage in a power supply system that satisfies the FRT requirements while simultaneously achieving uninterruptible power supply and load leveling functions using a common distributed power source.

That is, the power supply system according to the present invention is a power supply system provided between a commercial power system and an important load, and supplies power to the important load, and further includes a distributed power source connected to a power line for supplying power from the commercial power system to the important load, an open/close switch provided on the power line closer to the commercial power system than the distributed power source and opening and closing the power line, an impedance element connected in parallel to the open/close switch on the power line, an emergency power source provided on the power line closer to the important load than the open/close switch, a disconnection switch provided on the power line closer to the commercial power system than the open/close switch, and a disconnection switch provided on the power line closer to the commercial power system than the distributed power source, The system includes a system-side voltage detection unit that detects the voltage on the commercial power system side of the switch, a system abnormality detection unit that detects at least an instantaneous voltage drop, a frequency fluctuation, and a power outage from the voltage detected by the system-side voltage detection unit, and a control unit that controls the power supply by the distributed power source and the emergency power source. When an instantaneous voltage drop or frequency fluctuation is detected by the system abnormality detection unit, the control unit opens the open/close switch, and the distributed power source continues to operate including reverse power flow with the distributed power source and the commercial power system connected via the impedance element. When a power outage is detected by the system abnormality detection unit, the control unit opens the parallel-off switch, operates the distributed power source independently, and then starts up the emergency power source.

In such a power supply system, when an instantaneous voltage drop or frequency fluctuation is detected by the system abnormality detection unit, the open/close switch is opened, and the distributed power supply continues operation including reverse power flow with the distributed power supply and the commercial power system connected via the impedance element, so that the FRT requirements of the distributed power supply are satisfied while the uninterruptible power supply function and the load leveling function are both achieved using a common distributed power supply. Here, since it is only necessary to provide a parallel circuit unit of the impedance element and the open/close switch on the power line, the circuit configuration of the device can be simplified, and since a current flows through the open/close switch during normal operation, loss occurring in the impedance element such as a reactor can be eliminated.
In addition, when a power outage is detected by the system abnormality detection unit, the parallel-off switch is opened, and the distributed power source is operated independently before the emergency power source is started, so that the emergency power source can be used to supply power to important loads, improving the stability of power supply to important loads during a power outage. Furthermore, supplying power to important loads using the emergency power source during a power outage can also contribute to BCP (business continuity plan) and improved power resilience in the event of a disaster.

As a control mode for transitioning from the distributed power source to an emergency power source after the distributed power source is operated independently (independent operation mode), the control unit may start up the emergency power source, and then connect the distributed power source in a synchronized state to the emergency power source as a base power source, and gradually transition the load sharing for the important load from the distributed power source to the emergency power source.

As an operation method after the transition to independent operation using the emergency power source is completed, it is preferable that the control unit supplies power to the important loads using the emergency power source alone after the independent operation of the emergency power source is completed, or supplies power to the important loads using a combination of the emergency power source and the distributed power source.

The power supply system according to the present invention is a power supply system provided between a commercial power system and an important load, and supplies power to the important load, and further includes a distributed power source connected to a power line for supplying power from the commercial power system to the important load, an open/close switch provided on the power line closer to the commercial power system than the distributed power source and opening and closing the power line, an impedance element connected in parallel to the open/close switch on the power line, an emergency power source provided on the power line closer to the commercial power system than the open/close switch, a changeover switch provided on the power line closer to the commercial power system than the open/close switch and switching the power source connected to the important load from the commercial power system to the emergency power source, and a disconnection switch provided on the power line closer to the commercial power system than the distributed power source, The system includes a system-side voltage detection unit that detects the voltage on the commercial power system side of the open/close switch, a system abnormality detection unit that detects at least an instantaneous voltage drop, a frequency fluctuation, and a power outage from the voltage detected by the system-side voltage detection unit, and a control unit that controls the power supply by the distributed power source and the emergency power source. When an instantaneous voltage drop or frequency fluctuation is detected by the system abnormality detection unit, the control unit opens the open/close switch, and the distributed power source continues to operate including reverse power flow with the distributed power source and the commercial power system connected via the impedance element. When a power outage is detected by the system abnormality detection unit, the control unit switches the power source supplying power to the important load to the emergency power source by the changeover switch, and starts up the emergency power source after operating the distributed power source independently.

In such a power supply system, when an instantaneous voltage drop or frequency fluctuation is detected by the system abnormality detection unit, the open/close switch is opened, and the distributed power supply continues operation including reverse power flow with the distributed power supply and the commercial power system connected via the impedance element, so that the FRT requirements of the distributed power supply are satisfied while the uninterruptible power supply function and the load leveling function are both achieved using a common distributed power supply. Here, since it is only necessary to provide a parallel circuit unit of the impedance element and the open/close switch on the power line, the circuit configuration of the device can be simplified, and since a current flows through the open/close switch during normal operation, loss occurring in the impedance element such as a reactor can be eliminated.
In addition, when a power outage is detected by the system abnormality detection unit, the power source connected to the important load is switched to the emergency power source by the changeover switch, and the emergency power source is started after the distributed power source is operated independently, so that the important load can be supplied with power using the emergency power source, and the stability of the power supply to the important load during a power outage can be improved. Furthermore, supplying power to the important load using the emergency power source during a power outage can also contribute to BCP (business continuity plan) and improvement of power resilience against disasters.

As a control mode for transitioning from the distributed power source to an emergency power source after the distributed power source is operated independently (independent operation mode), the control unit may start up the emergency power source, and then connect the distributed power source in a synchronized state to the emergency power source as a base power source, and gradually transition the load sharing for the important load from the distributed power source to the emergency power source.

In this power supply system, when the control unit detects a short circuit on the important load side after the emergency power supply has completed independent operation, it is desirable to open the open/close switch and connect the emergency power supply and the important load via the impedance element to suppress overcurrent flowing from the emergency power supply to the short circuit point.

The present invention, configured in this way, can improve the stability of power supply to important loads during a power outage in a power supply system that satisfies the FRT requirements while simultaneously achieving uninterruptible power supply functionality and load leveling functionality using a common distributed power source.

1 is a schematic diagram showing a configuration of a power supply system according to a first embodiment; FIG. 2 is a diagram illustrating an operation state of the power supply system according to the first embodiment. FIG. 13 is a schematic diagram showing the configuration of a power supply system according to a second embodiment. FIG. 11 is a diagram illustrating an operation state of the power supply system according to the second embodiment. FIG. 11 is a schematic diagram showing a state when a short circuit occurs in the second embodiment. 1A and 1B are diagrams illustrating an operation state of a conventional power supply system during a voltage sag and frequency fluctuation and during a power outage.

First Embodiment
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a power supply system according to the present invention will
As shown in FIG. 1 , the power supply system 100 of this embodiment is provided between a commercial power system 10 and important loads 30, and performs a function as an uninterruptible power supply system that supplies power to the important loads 30 in the event of an abnormality in the commercial power system 10 (uninterruptible power supply function), and a function as a distributed power supply system that levels the load by providing forward and reverse power flows to the commercial power system 10 (load leveling function).

Here, the commercial power system 10 is the power supply network of a power company (electricity supplier), and includes power plants, a power transmission system, and a power distribution system. Furthermore, the important loads 20 are loads that should provide a stable supply of power even during system abnormalities such as power outages and voltage drops. Although there is only one important load in FIG. 1, there may be multiple important loads.

Specifically, the power supply system 100 includes a distributed power source 2, an open/close switch 3 that connects the distributed power source 2 and the important load 30 to the commercial power grid 10, an impedance element 4 connected in parallel to the open/close switch 3, an emergency power source 5 provided on the important load 30 side of the open/close switch, a disconnection switch 6 provided on the commercial power grid 10 side of the open/close switch, a grid side voltage detection unit 7 that detects the voltage on the commercial power grid 10 side of the open/close switch 3, a grid abnormality detection unit 8 that detects at least an instantaneous voltage drop, a frequency fluctuation, and a power outage from the detected voltage of the grid side voltage detection unit 7, and a control unit 9 that controls the power supply from the distributed power source 2 and the emergency power source 5.

The distributed power source 2 is connected to a power line L1 for supplying power from the commercial power system 10 to the important load 30. The distributed power source 2 is connected to the commercial power system 10, and may be, for example, a power source having a DC power generation facility 21a such as a solar power generation facility or a fuel cell and a power conversion device 22, a power storage device (power storage device) 21b such as a secondary battery (storage battery) and a power conversion device 22, a power generation facility (not shown) that rectifies the electric energy output in AC such as a wind power generation facility or a micro gas turbine to DC and is connected to the system using a power conversion device, or an AC power generation facility 21c such as a synchronous generator or an induction generator. The power supply system 100 is equipped with at least the power storage device 21b, and may also be equipped with any of the above-mentioned distributed power sources 2.

The open/close switch 3 is provided on the power line L1 closer to the commercial power system 10 than the connection point of the distributed power source 2 and opens and closes the power line L1. For example, a semiconductor switch or a hybrid switch that combines a semiconductor switch and a mechanical switch and allows high-speed switching can be used. For example, when a semiconductor switch is used, the switching time can be reduced to 2 ms or less, and the power can be cut off regardless of the zero point. Furthermore, when a hybrid switch is used, the switching time can be reduced to 2 ms or less, and not only can the power be cut off regardless of the zero point, but the current loss can be reduced to zero. The open/close switch 3 is controlled by the control unit 9.

The impedance element 4 is connected in parallel to the open/close switch 3 in the power line L1, and in this embodiment is a current-limiting reactor.

The emergency power supply 5 is provided on the power line L1 closer to the important load 30 than the open/close switch 3, and is, for example, an emergency generator such as a diesel engine emergency generator or a gas turbine emergency generator.

The parallel-off switch 6 is provided on the power line L1 closer to the commercial power system 10 than the distributed power source 2, and is, for example, a mechanical switch. The parallel-off switch 6 is controlled to open and close by the control unit 9. In this embodiment, a power source side voltage detection unit 11 is provided on the power line L1 closer to the distributed power source 2 than the parallel-off switch 6.

The system-side voltage detection unit 7 detects the voltage on the commercial power system 10 side of the open/close switch 3 in the power line L1 via a voltage transformer. Specifically, the system-side voltage detection unit 7 is connected to the commercial power system 10 side of the parallel circuit consisting of the open/close switch 3 and the impedance element 4 via a voltage transformer.

The system abnormality detection unit 8 compares the detected voltage detected by the system side voltage detection unit 7 with a predetermined setpoint, and detects an instantaneous voltage drop if the detected voltage is equal to or lower than the setpoint. The system abnormality detection unit 8 also detects frequency fluctuations (frequency up (OF), frequency down (UF)) from the detected voltage detected by the system side voltage detection unit 7. The frequency fluctuations are, for example, step up or ramp up/down. The system abnormality detection unit 8 also detects a power outage from the detected voltage detected by the system side voltage detection unit 7. In addition to instantaneous voltage drops, frequency fluctuations, and power outages, the system abnormality detection unit 8 may also detect at least one of voltage up, phase fluctuations, voltage imbalance, harmonic abnormalities, or flicker.

When the system abnormality detection unit 8 detects an instantaneous voltage drop or frequency fluctuation, the control unit 9 opens the open/close switch 3. Then, the commercial power system 10 is connected to the distributed power source 2 and the important load 30 via the impedance element 4, and operation including reverse power flow from the distributed power source 2 is continued. When the system abnormality detection unit 8 detects that the system abnormality has been restored, the control unit 9 closes the open/close switch 3.

In addition, as shown in FIG. 2, when a power outage is detected by the system abnormality detection unit 8, the control unit 9 opens the parallel-off switch 6 and causes the distributed power source 2 to operate independently.

Specifically, the control unit 9 opens the parallel-off switch 6 when the voltage detected by the grid-side voltage detection unit 7 satisfies a predetermined parallel-off condition. Here, the predetermined parallel-off condition is that the duration of the voltage drop in the grid voltage (the state in which the detected voltage is equal to or lower than the set value) is equal to or longer than a predetermined value (longer than the duration of the momentary sag). In other words, until the predetermined parallel-off condition is met, the control unit 9 recognizes it as an instantaneous voltage drop, opens the open/close switch 3, and the distributed generation 2 performs FRT operation. Then, when the predetermined parallel-off condition is met, the control unit 9 opens the parallel-off switch,
With the parallel-off switch 6 open, the distributed power source 2 enters an isolated operation mode and supplies power to the important load 30. In this way, the distributed power source 2 goes from normal grid-connected operation to FRT operation and then enters isolated operation. Note that when the parallel-off switch 6 is opened, the open-close switch 3 has already been opened, so that the overcurrent caused by opening the parallel-off switch 6 is suppressed by the impedance element 4.

The control unit 9 then starts the emergency power supply 5 after the distributed power supply 2 has been put into independent operation. After the emergency power supply 5 has been started, the distributed power supply 2 is connected in a synchronized state with the emergency power supply 5 as a base power supply, and the load sharing for the important load 30 is gradually transferred from the distributed power supply 2 to the emergency power supply 5. Here, the control unit 9 may operate in such a way that, after the emergency power supply 5 has completed its independent operation, the emergency power supply 5 alone supplies power to the important load 30, or the emergency power supply 5 and the distributed power supply 2 in combination supply power to the important load 30 so that the output of the emergency power supply 5 does not suddenly change.

The control unit 9 turns on the parallel-off switch 6 when the voltage detected by the grid-side voltage detection unit 7 eliminates the predetermined parallel-off condition, and the voltage detected by the grid-side voltage detection unit 7 and the voltage detected by the power supply-side voltage detection unit 11 satisfy the synchronization test condition.

Effects of the First Embodiment
According to the power supply system 100 of this embodiment configured as described above, when an instantaneous voltage drop or frequency fluctuation is detected by the system anomaly detection unit 8, the open/close switch 3 is opened, and the distributed power source 2 continues operation including reverse power flow in a state in which the distributed power source 2 and the commercial power system 10 are connected via the impedance element 4, so that it is possible to achieve both an uninterruptible power supply function and a load leveling function using the common distributed power source 2 while satisfying the FRT requirements of the distributed power source 2. Here, since it is only necessary to provide a parallel circuit unit of the impedance element 4 and the open/close switch 3 on the power line L1, the circuit configuration of the device can be simplified, and since a current flows through the open/close switch 3 during normal operation, it is possible to eliminate loss occurring in the impedance element 4 such as a reactor.
Furthermore, when a power outage is detected by the system abnormality detection unit 8, the parallel-off switch 6 is opened, the distributed power sources 2 are operated independently, and then the emergency power source 5 is started, so that the important loads 30 can be supplied with power using the emergency power source 5, and the stability of the power supply to the important loads 30 can be improved during a power outage. Furthermore, supplying power to the important loads 30 using the emergency power source 5 during a power outage can also contribute to a business continuity plan (BCP) for disasters and improved power resilience.

Second Embodiment
Next, a second embodiment of a power supply system according to the present invention will be described with reference to the drawings.

As shown in FIG. 3, the power supply system 100 of this embodiment differs from the first embodiment in the connection position of the emergency power supply 5. In other words, the emergency power supply 5 is provided on the power line L1 closer to the commercial power system 10 than the open/close switch 3.

The power supply system 100 also has a changeover switch 12 that is provided on the power line L1 closer to the commercial power system than the open/close switch 3 and switches the power supply connected to the important load 30 from the commercial power system 10 to the emergency power supply 5. The changeover switch 12 is controlled by the control unit 9.

The control unit 9 opens the open/close switch 3 when the system abnormality detection unit 8 detects an instantaneous voltage drop or frequency fluctuation. The control unit 9 then connects the commercial power system 10 to the distributed power source 2 and the important load 30 via the impedance element 4, and continues operation including reverse power flow from the distributed power source 2. When the system abnormality detection unit 8 detects that the system abnormality has been restored, the control unit 9 closes the open/close switch 3.

In addition, as shown in FIG. 4, when a power outage is detected by the system abnormality detection unit 8, the control unit 9 switches the power source connected to the important load 30 to the emergency power source 5 by the changeover switch 12 and operates the distributed power source 2 independently.

Specifically, the control unit 9 switches the changeover switch 12 to the emergency power source 5 when the voltage detected by the grid side voltage detection unit 7 satisfies a predetermined disconnection condition. Here, the predetermined disconnection condition is that the duration of the voltage drop of the grid voltage (the state in which the detected voltage is equal to or lower than the set value) is equal to or greater than a predetermined value (longer than the duration of the momentary drop). In other words, until the predetermined disconnection condition is met, the control unit 9 recognizes it as an instantaneous voltage drop, opens the open/close switch 3, and the distributed power source 2 performs FRT operation. Then, when the predetermined disconnection condition is met, the control unit 9 switches the changeover switch 12 to the emergency power source 5, and with the changeover switch 12 switched to the emergency power source 5, the distributed power source 2 enters an independent operation mode and supplies power to the important load 30. In this way, the distributed power source 2 switches from normal grid-connected operation to FRT operation and then enters independent operation. Note that when the disconnection switch 6 is opened, the open/close switch 3 has already been released, so the overcurrent caused by the opening of the disconnection switch 6 is suppressed by the impedance element 4.

The control unit 9 then starts the emergency power supply 5 after the distributed power supply 2 has been put into independent operation. The control unit 9 also closes the open/close switch 3 at the timing of starting the emergency power supply 5. After the emergency power supply 5 has been started, the distributed power supply 2 is connected in a synchronized state with the emergency power supply 5 as a base power supply, and the load sharing for the important load 30 is gradually transferred from the distributed power supply 2 to the emergency power supply 5. Here, the control unit 9 may operate in such a way that, after the emergency power supply 5 has completed its independent operation, the emergency power supply 5 alone supplies power to the important load 30, or the emergency power supply 5 and the distributed power supply 2 in combination supply power to the important load 30 so that the output of the emergency power supply 5 does not suddenly change.

Furthermore, as shown in FIG. 5, if the control unit 9 detects a short circuit on the important load 30 side after the emergency power supply 5 has completed its independent operation (during the emergency power supply 5's independent operation), it opens the open/close switch 3 and connects the emergency power supply 5 and the important load 30 via the impedance element 4, thereby suppressing the overcurrent flowing from the emergency power supply 5 to the short circuit point.

The control unit 9 turns on the parallel-off switch 6 when the voltage detected by the grid-side voltage detection unit 7 eliminates the predetermined parallel-off condition, and the voltage detected by the grid-side voltage detection unit 7 and the voltage detected by the power supply-side voltage detection unit 11 satisfy the synchronization test condition.

Effects of the Second Embodiment
According to the power supply system 100 of this embodiment configured as described above, when an instantaneous voltage drop or frequency fluctuation is detected by the system anomaly detection unit 8, the open/close switch 3 is opened, and the distributed power source 2 continues operation including reverse power flow in a state in which the distributed power source 2 and the commercial power system 10 are connected via the impedance element 4, so that it is possible to achieve both an uninterruptible power supply function and a load leveling function using the common distributed power source 2 while satisfying the FRT requirements of the distributed power source 2. Here, since it is only necessary to provide a parallel circuit unit of the impedance element 4 and the open/close switch 3 on the power line L1, the circuit configuration of the device can be simplified, and since a current flows through the open/close switch 3 during normal operation, it is possible to eliminate loss occurring in the impedance element 4 such as a reactor.
Furthermore, when a power outage is detected by the system abnormality detection unit 8, the changeover switch 12 switches the power source connected to the important load 30 to the emergency power source 5, and the emergency power source 5 is started after the distributed power sources 2 are operated independently, so that the important load 30 can be supplied with power using the emergency power source 5, and the stability of power supply to the important load 30 can be improved during a power outage. Furthermore, supplying power to the important load 30 using the emergency power source 5 during a power outage can also contribute to a business continuity plan (BCP) for disasters and improved power resilience.

<Other Modified Embodiments>
The present invention is not limited to the above-described embodiment.

For example, the impedance element 4 may be a capacitor, or a combination of a reactor, a resistor, or a capacitor.

Furthermore, the grid-side voltage detection unit of the above embodiment may be provided in the grid-connection protection device. Examples of grid-connection protection devices specified in the grid-connection regulations include an overvoltage relay (OVR), an undervoltage relay (UVR), a directional short circuit relay (DSR), a ground fault overvoltage relay (OVGR), an overfrequency relay (OFR), an underfrequency relay (UFR), a transfer cutoff device, and the like. In this case, the control unit may open the disconnection switch when any one of the interconnection protection devices is activated. In addition, the control unit may also turn on the disconnection switch when all of the grid-connection protection devices are in an inoperative state and the detection voltage of the grid-side voltage detection unit and the detection voltage of the power supply-side voltage detection unit satisfy the synchronization test condition. With this configuration, since the voltage detection unit provided in the interconnection protection device is used, there is no need to provide a separate grid-side voltage detection unit, and the device configuration can be simplified.

In addition, the power supply voltage detection unit in the above embodiment is provided between the parallel-off switch and the open/close switch, but may be substituted with a function for measuring the voltage at the grid connection point of the distributed power supply.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the invention.

Reference Signs List 100: Power supply system 10: Commercial power system 30: Important load L1: Power line 2: Distributed power source 3: Open/close switch 4: Impedance element 5: Emergency power source 6: Parallel-off switch 7: System-side voltage detection unit 8: System abnormality detection unit 9: Control unit

Claims (3)

A power supply system provided between a commercial power system and a critical load, for supplying power to the critical load, comprising:
A distributed power source connected to a power line for supplying power from the commercial power system to the critical load;
an open/close switch that is provided on the power line closer to the commercial power system than the distributed power source and opens and closes the power line;
an impedance element connected in parallel to the open/close switch in the power line;
An emergency power supply provided on the power line on the important load side of the open/close switch;
a parallel-off switch provided on the power line closer to the commercial power system than the open/close switch ;
a system-side voltage detection unit that detects a voltage on the commercial power system side of the open/close switch;
A system abnormality detection unit that detects at least an instantaneous voltage drop, a frequency fluctuation, and a power outage from the detection voltage of the system side voltage detection unit;
A control unit that controls power supply by the distributed power sources and the emergency power sources,
when an instantaneous voltage drop or a frequency fluctuation is detected by the system abnormality detection unit, the control unit opens the open/close switch, and causes the distributed power source to continue operation including reverse power flow in a state in which the distributed power source and the commercial power system are connected via the impedance element,
When a power outage is detected by the system abnormality detection unit, the control unit opens the parallel-off switch, operates the distributed power sources independently, and then starts up the emergency power sources. The power supply system according to claim 1, wherein the control unit, after starting the emergency power supply, connects the distributed power supplies in a synchronized state with the emergency power supply as a base power supply, and gradually shifts the load sharing of the important load from the distributed power supplies to the emergency power supply. The power supply system according to claim 2, wherein the control unit supplies power to the important loads from the emergency power supply alone after the emergency power supply has completed its independent operation, or supplies power to the important loads from a combination of the emergency power supply and the distributed power supply.