Detection Method of Grid Voltage Sag for Offshore Wind Power Converter

When the offshore wind converters are connected to the grid by high voltage direct current, the voltage sag will lead to the disconnection of wind turbines. Therefore, the research of low voltage ride through (LVRT) is increasingly important, whose premise is to detect the grid voltage amplitude quickly and accurately. Firstly, this paper briefly concludes several traditional methods of detecting voltage sag, among which dq transformation based on synchronous rotating frame (SRF) is more suitable for offshore wind power converter due to its accuracy and timeliness. This paper then introduces the principle of dq transformation based SRF phase locked loop (SRF-PLL) as well as its improvement scheme in detail, compares and analyzes the characteristics of delayed signal cancelation (DSC), double second-order generalized integrator (DSOGI) and adaptive notch filter (ANF). Finally, an idea of selecting and improving the traditional method of detecting voltage sag is proposed. This paper distinguishes the differences between the existing traditional detection methods and the improved dq transformations, and provides an idea for selecting and improving the detection method of grid voltage sag suitable for LVRT of offshore wind power converters.