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Dynamic Control Strategy and Fault Protection for Microgrids with High Renewable Energy

Dehua Zheng

Microgrid is a group of interconnected loads and distributed energy resources (including microturbines, diesel generators, energy storage, renewable resources, and all other kinds of distributed energy resources) at distribution level with defined electrical boundaries that has black start capacity and can operate in island mode and/or grid-connected mode. Because of the uncertainty, intermittent, and discontinuity of the renewable resources, transient disturbance and dynamic disturbance exist in the microgrid. For the fault current is small in the system and the microgrid has very little inertia, the disturbance control and fault protection of microgrids are more difficult than the ones of traditional grids.

The most challenging part of protection and dynamic control of microgrids is figuring out whether a fault or disturbance is occurring in the system. In the microgrid, there may appear transient characteristics similar to the transient and dynamic disturbance at the initial faults. If there is a fault, the transient disturbance control should be used to prevent the system from collapsing and make sure the right breakers should be tripped. But if there are transient and dynamic disturbances, even the initial characteristics of the transient and dynamic are very similar to the fault ones, the breakers should not be tripped. So that Mr. Zheng has been leading his team to propose and develop the dynamic disturbance control, transient disturbance control and fault protection technologies, and they all have been well applied in practical projects.

The main innovations are as follows:

(1) Relying on the dynamic disturbance control technology of the energy storage system, it can achieve safe and stable operation under the condition of high permeability of renewable energy, and can support 100% consumption of renewable energy generation in microgrid system.

(2) Through real-time load and power generation monitoring, analysis and control technology, relying on power and energy storage energy to effectively suppress transient disturbances and dynamic disturbances, respectively, to achieve unplanned seamless switching from grid connected mode to island mode or vice versa (time less than 10 milliseconds), Improve the safe and stable operation level of the system.

(3) Based on the Park transformation and the fault identification technology of branch current and voltage harmonic rapid changing rate, the precise positioning and fast isolation of the fault components of the microgrid are realized.

(4) Based on the power and load side comprehensive treatment technology, the total harmonic distortion rate (THD) of voltage and current is less than 3% when operating on an island.

The microgrid dynamic disturbance control technology, transient disturbance control technology and fault protection technology have been evaluated by domestic and foreign experts as reaching the international leading level.