A Voltage Sag Detection Method Based on Variable Step Difference

The quick and accurate detection of voltage sag is the premise of fast compensation, but under the condition of frequency offset, the phase jump angle is hard to be detected precisely by the software phase locked loop. Based on αβ-dq transform, a detection method by utilizing variable-step difference is proposed to generate αβ components of voltage in this paper. By using instantaneous sample values of the constant 50Hz sine and cosine signals to form αβ-dq transform matrix, Voltage amplitude and phase jump angle can be calculated, which avoids the measurement error in phase jump angle caused by phase lock holding. The detecting characteristics for such influence factors as harmonics, noise and frequency offset are analyzed in detail by using modified methods. Theoretical analysis and simulation results show that the improved method based on variable\|step difference has such advantages as easy realization mode and less calculation amount, which can meet the requirement of real-time and accuracy by regulating detecting sample interval without needing of synchronous phase clocking.