Direct Seamless Transfer Strategy by Limiting Voltage Drop of Interface Filter in Energy Storage Equipment of Microgrid

Microgrids should go into islanding operations to supply power for local critical loads in the event of grid faults. During the operation of the microgrid, the voltage of the point of common coupling (PCC) can be maintained within a certain range by energy storage equipment (ESE). In this article, a direct seamless transfer strategy is developed based on the design of the power and inductor parameters of the three-phase converter in the ESE. When unintentional islanding occurs, the amplitude and frequency of the PCC voltage is affected by the output voltage of the converter, the rated power of the converter, and the voltage drop across the inductor. To ensure the value of the amplitude and frequency of the PCC voltage within the prescribed range, limiters are added to the modulation waves to realize the direct seamless transfer strategy. By analyzing the vector diagram of voltage and current vectors for different loads, the power requirement of the ESE and the voltage drop across the inductor in the converter are obtained. Finally, the design of the limiters' parameters, analysis of inductor ripple current, and influence of nonlinear load on the PCC voltage are presented for the proposed control strategy.