Harmonic components based protection strategy for inverter-interfaced AC microgrid

摘要

In the inverter-interfaced AC microgrid (IIAM), when a short-circuit fault occurs at the distribution line, the output fault current of inverter is commonly limited to two times over its rated current due to the limited overcurrent capacity of power electronic device. Therefore, the conventional overcurrent protection principle cannot be applied to IIAM. Aiming at addressing this issue, a new protection method based on the low harmonics components is proposed in this paper. Through injecting a certain proportion of fifth harmonics to the fault current, the protection device can detect the fault according to the low harmonics components extracted by the digital relay (DR). This scheme does not rely on the large fault current. Therefore, some limitations of the traditional overcurrent protection are avoided. The corresponding experiments were carried out with two 10kVA parallel-connected inverters supply system, and the results proved the feasibility of this approach.