Active grid-connected and off-grid switching method for cascaded energy storage system

Abstract

The invention relates to an active grid-connected and off-grid switching method for a cascaded energy storage system. The system is characterized in that: when the cascade type energy storage system is switched from a grid-connected state to an off-grid state, the cascade type energy storage system enters an off-grid voltage control loop with the voltage amplitude, phase and angular frequency of a current alternating current power grid adopted as initial values; and when the cascaded energy storage system is switched from the off-grid state to the grid-connected state, the amplitude and phase of the voltage output by the cascaded energy storage system in the off-grid state are adjusted, and when the voltage and the amplitude are synchronous, the cascaded energy storage system is switched to the grid-connected state. According to the grid-connected and off-grid switching method, the problem that local key equipment cannot work normally due to transient (such as 100ms) power failure caused by grid connecting and grid disconnecting of a locking device in the prior art is solved. When droop control and the virtual synchronous machine are adopted to realize grid connection and grid disconnecting in the prior art, a droop coefficient and the rotational inertia of the virtual synchronous machine are difficult to determine, and the system tends to be unstable. With the method of the invention adopted, the above problem can be solved.

Description

Technical field [0001] The present invention relates to a method of switching a network switching method, and more particularly, the active and off-network switching method of a cascading energy storage system. Background technique [0002] As distributed renewable energy and energy storage devices are increasing, the modern power distribution system has brought structure changes. The general photovoltaic power generation or the output voltage of the energy storage device is low, and the high pressure grade grid is required to be connected by a boost transformer. The high-pressure cascading energy storage system is a new type of energy storage converter. Such converters can reach a higher AC side output voltage through the H-bridge, which can be directly connected to 10kV, 35kV high-pressure rating grid directly, thereby increasing the efficiency of converter. [0003] The microgrid mainly based on the cascading system is also facing and related to the network switching. At prese...

AI Technical Summary

Problems solved by technology

Since the response time of the commonly used off-grid switch is about 100ms, it will cause a short power outage during this period, resulting in the failure of the local key load to work normally.

[0004] Most of the existing seamless off-grid switching methods use droop control and virtual synchronous machine, but droop control and virtual synchronous machine control will bring changes in output voltage amplitude and frequency, and the determination and comparison of droop coefficient and virtual synchronous machine moment of inertia Difficult, easy to cause system instability

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