A Novel Universal Grid Voltage Sag Detection Algorithm

Low voltage rid through (LVRT) requires a wind turbine controller to be able to provide rapid response to any power grid voltage sag, which in turn demands a rapid and accurate detection technique of power grid voltage sag. Different voltage sag detection methods have been proposed, such as peak voltage detection, root mean square (RMS) detection, Fourier Transform, conventional DQ transform and its modified versions, such as matrix method and alpha beta transform. Peak voltage detection and RMS method demand at least half a cycle for the voltage sag depth information to become available, and for a three-phase power grid, they need three separate modules for the three-phase grid voltage sag detection, which is undesirable. Fourier transform can return accurate steady-state voltage information of the supply phases, however it can take up to one cycle for the voltage sag depth information to be measured accurately. Conventional DQ transform is only suitable for three-phase symmetrical voltage sag, and its modified versions are generally too complex and slow. This paper proposes a novel DQ transform solution for fast and accurate detection of any single phase, two-phase or three-phase symmetrical and asymmetrical voltage sag. This novel DQ transform algorithm is simpler and more universal than other techniques proposed by other researchers and/or used in the industry.