Amplitude Error Based Frequency Deviation Detection for Grid Voltage Parameters Tracking

In this work, for the estimation of three-phase utility voltage parameters, a pseudo open-loop synchronization technique (OLST) with nominal-frequency tuned guaranteed stable sliding discrete Fourier transform (GSDFT) as pre-filter is presented. When the utility frequency is off-nominal, due to asynchronous sampling, amplitude and phase errors are introduced in the in-phase and quadrature components of GSDFT output. Mathematically it is shown that there exists a relationship between the ratio of peak value of Sine and Cosine components of GSDFT output and frequency deviation. Based on this finding, an algorithm is developed to detect the input signal frequency deviation from the nominal frequency. Subsequently, with curve fit technique, amplitude and phase errors are compensated. With a test case comprising of simultaneous change in amplitude, phase and frequency, harmonic and dc offset distortion, the real-time performance of the proposed OLST is proven.