CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 application of the International PCT application serial no. PCT/JP2019/024661, filed on Jun. 21, 2019, which claims the priority benefits of Japan Patent Application No. 2018-141122, filed on Jul. 27, 2018. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The disclosure relates to a power supply system.

Description of Related Art

In recent years, due to the high performance of a storage battery, especially in a large-capacity (500 kW capacity class or higher) storage battery system, realization of both an uninterruptible power supply function and a load leveling function is being considered. For example, as shown in Patent Document 1, a secondary battery system achieving both an uninterruptible power supply function and a load leveling function has been considered. This system is configured to supply power to an important load through disconnection with respect to a power failure or an instantaneous voltage drop.

However, as distributed power supplies interconnected with commercial power systems increase, if these distributed power supplies are disconnected all at once at the time of an instantaneous voltage drop, it may have a great impact on the maintenance of the voltage and the frequency of the entire commercial power system. For this reason, it is required to continuously operate the distributed power supplies without disconnecting them from the commercial power system even at the time of an instantaneous voltage drop (i.e., fault ride through (FRT) requirements).

RELATED ART

Patent Document(s)

Patent Document 1: Japanese Patent No. 3402886

SUMMARY

Problems to be Solved

On the other hand, the inventor of the present application, in a manner as shown in Patent Document 1, continues the development of a power supply system having a configuration in which an opening/closing switch is provided on a commercial power system side of a distributed power supply on a power line, and meanwhile, an impedance element is connected in parallel to the opening/closing switch. In this power supply system, at the time of a system abnormality, the opening/closing switch is opened to connect the distributed power supply with the commercial power system via the impedance element. Herein, a generator, a power storage device, a solar power generation device, and the like may be used as the distributed power supply.

However, in the above power supply system, when an important load fluctuates at the time of a system abnormality, due to the inertial force of the generator, the generator cannot catch up with the fluctuation and thus drops out. In addition, when a solar power generation device is connected as a distributed power supply, the generator will drop out for the same reason due to output fluctuation of the solar power generation device. As a result, there is an issue that it is difficult to stably supply power to an important load at the time of a system abnormality.

Therefore, the disclosure has been made to solve the above issues, and its main objective is to stably supply power to an important load even at the time of a system abnormality while satisfying the FRT requirements.

Means for Solving the Problems

Namely, a power supply system of the disclosure includes a distributed power supply, an opening/closing switch, an impedance element, a system abnormality detection part, and a switch control part. The distributed power supply is connected to a power line for supplying power to an important load from a commercial power system. The opening/closing switch is provided on a commercial power system side of the distributed power supply on the power line. The impedance element is connected in parallel to the opening/closing switch on the power line. The system abnormality detection part detects an abnormality of the commercial power system. The switch control part opens the opening/closing switch and connects the distributed power supply and the commercial power system via the impedance element when an abnormality of the commercial power system is detected. In a state where the distributed power supply and the commercial power system are connected via the impedance element, the distributed power supply continues an operation including a reverse power flow. The distributed power supply includes a rotary power generation device connected to the power line and an energy storage device connected to the power line. The energy storage device includes an energy storage part, a bi-directional power converter, and a convertor control part. The bi-directional power converter performs charging and discharging of the energy storage part. The convertor control part controls the bi-directional power converter to perform an operation simulating an inertial force of the rotary power generation device.

With such a power supply system, the opening/closing switch is provided on the commercial power system side of the distributed power supply on the power line, and meanwhile, the impedance element is connected in parallel to the opening/closing switch, and the opening/closing switch is opened when an abnormality of the commercial power system is detected. Therefore, at the time of a system abnormality, the distributed power supply becomes interconnected with the commercial power system via the impedance element. Accordingly, while satisfying the FRT requirements of the distributed power supply, it is possible to prevent a voltage drop to the important load at the time of a system abnormality. As a result, while satisfying the FRT requirements, it is possible to achieve both the uninterruptible power supply function and the load leveling function by using the common distributed power supply Herein, since it is only necessary to provide a parallel circuit part of the impedance element and the opening/closing switch on the power line, the circuit configuration of the device can be simplified, and meanwhile, since the current flows through the opening/closing switch at the time of normal operation, the loss caused in the impedance element such as a reactor can be eliminated.

In particular, in the disclosure, in the energy storage device used as the distributed power supply, since the bi-directional power converter of the energy storage device is controlled to perform an operation simulating the inertial force of the rotary power generation device, the inertial force of the rotary power generation device can be compensated for. Therefore, it is possible to prevent the generator from dropping out with respect to the fluctuation of the important load. As a result, it is possible to stably supply power to the important load even at the time of a system abnormality.

It may be considered that the distributed power supply has a solar power generation device including a solar power generation panel and a power converter. In that case, the factors for the dropout of the rotary power generation device include not only the fluctuation of the important load but also the output fluctuation of the solar power generation device. In the disclosure, since the energy storage device performs an operation simulating the inertial force of the rotary power generation device, even when the output of the solar power generation device fluctuates, it is possible to stably supply power to the important load.

It is desired that the converter control part performs current control on the bi-directional power converter when the commercial power system is normal, and performs voltage control on the bi-directional power converter when the commercial power system is abnormal. On the other hand, if the converter control part constantly performs voltage control on the bi-directional power converter, it is possible to stably supply power to the important load even when the operation of the rotary power generation device is stopped.

Effects

According to the disclosure configured in this manner, while satisfying the FRT requirements, it is possible to stably supply power to an important load even at the time of a system abnormality.

