Fast and high-precision phase detection of positive phase sequence component by three phase PLL with complex coefficient filter

A power grid connected inverter is operated in synchronized with reference ac voltage at the point of common coupling. The robust phase detection is indispensable for inverter operation in harsh condition. The phase detection system is required to be immune to unbalance and distortion of ac voltage waveform. A complex coefficient filter can discriminate positive and negative frequency component in input signal, which cannot be attained for conventional real coefficient filter. This paper studies the applicability of infinite impulse response digital filter with complex coefficient to a phase detection system by phase locked loop (PLL) for three phase ac system. The frequency characteristics and dynamic response of the filter is assessed, and series connection of band pass and notch filter is evaluated to satisfy both required performance. The phase detection system is implemented in the digital processor hardware and the applicability of the complex coefficient filter is experimentally evaluated.