A new method for three-phase voltage detection and protection based on reference frame transformation

A distributed power generation system is required to cease to energize the grid within a specified clearing time at the detection of an abnormal grid voltage. Traditionally, three-phase grid voltage protection is achieved by calculating and monitoring the rms values of grid voltages from the instantaneous voltage data. This requires continuously accumulating the sampled voltage data over one or more cycles before an rms value is calculated, which not only demands lengthy computations but also causes a time delay in response to a voltage fault. In this paper, a new method for three-phase grid voltage detection and protection based on reference frame transformation is proposed, analyzed and implemented on a 30 kW three-phase grid-connected inverter. By calculating and monitoring the instantaneous magnitude of the grid voltage vector in the synchronous d-q reference frame, the proposed method has an immediate response for grid voltage faults. The simulation and laboratory tests on the inverter have verified that the new method is simple and accurate, and offers a fast dynamic performance.