Research And Implementation Of Microgrid Protection Scheme

As a new type of grid structure, Micro-grid has advantages in the control and management of distributed generation and reducing the fluctuations of distributed generation. However, due to the existence of distributed generation, micro-grid has featured with two-way flow, small short circuit capacity and short protective action time. These features make the Micro-grid system difficult to protect. Therefor, developing appropriate protection strategies for microgrid can promote the use of micro-grid technology, which is significantly important.In this paper, firstly, commonly used control strategy and current-limitation strategy for the three-phase inverter interfaced distributed generation is analyzed. During the unbalanced Faults, even though the current-limitation of the inner-loop-current control in master control resource in island operated LV microgrid, the peak phase current may still exceed the limit value. Then this paper proposes an improved current-limitation strategy which can ensure the output current of the inverter not exceed its set peak-value even under unbalanced faults. This strategy detects the fault, and then limits the phase current magnitude of the master control resource through changing the reference voltage, and restores the microgrid to its normal operating condition subsequent to fault clearance. Simulation and hardware experiment verify the validity of the proposed strategy. Based on the constraints of the control strategies, the microgrid failure analysis method is also introduced, and the accuracy of the method is verified through simulation results.Microgrid is a system with complex working conditions, and the traditional current mutation algorithm cannot be directly used to protect the microgrid. Through analyzing the traditional characteristics of the current mutation algorithm and combines microgrid’s failure characteristics, this paper proposed low-voltage adaptive current mutation protection, this protection algorithm can acquire the micro-grid operation state before the failure moment, and can adaptively adjust the protection settings, and the simulation results proved the feasibility of the strategyFinally, a microgrid centralization protection scheme based on communications is proposed. According to the characteristics of low voltage micro-grid, from an economic point of view this paper put forward a principle for protection devices installation. In the principle, the electronic circuit breakers is used in combination. The proposed protection scheme, which based on the local information can continue working when the micro-grid communication system is fail.By writing protection program on PZK-36B protection equipment and interface to active distribution network combined with static simulation platform, the protection scheme is verified. Finally, with a typical low-voltage micro-grid model the protection configuration is given,and five scenario simulations verified the feasibility of the protection configuration.