Asymmetric Voltage Sag Detection Method Based on Delay Small Angle Method and Moving Average Filter

As one of the most influential power quality problems, voltage sag seriously threatens the normal operation of modern manufacturing, public service and other industries. The fast and accurate detection of voltage sag events is the first step to control voltage sag. The asymmetric short-circuit fault also introduces negative sequence component when it causes voltage sag, which poses a new challenge to voltage sag detection. The traditional voltage sag detection method based on single synchronous reference frame phase locked loop (SSRF-PLL) and instantaneous dq decomposition can’t detect the power grid voltage with negative sequence and harmonic components accurately and quickly. This paper presents a new method of asymmetric voltage sag detection based on delay small angle method and moving average filter. Firstly, the positive and negative sequence components of asymmetric voltage are separated by delay small-angle method combined with instantaneous symmetric component method, and then the amplitude information of the separated positive and negative sequence components is obtained by instantaneous dq transformation respectively. Finally, the harmonic components are filtered by half-period moving average filter, and the amplitude information of the positive and negative sequence components of fundamental voltage is obtained. The proposed method can detect asymmetrical voltage sags quickly and accurately. The simulation results based on PLECS simulation software prove the feasibility and effectiveness of the proposed method.