Microprocessor-based phase tracking system for digital power metering

The paper presents the analysis and design of the low pass filter system of the phase tracking system for digital power metering. Three algorithms, sinusoidal signal phase tracking (SSPT), non-sinusoidal signal phase tracking (NSSPT) and filter-based phase tracking (FBPT), are designed for the implementation of digital power metering based on DSP in hardware and based on numerical differentiation and central Lagrange interpolation with 7 points in software. The FBPT algorithm based system employs a low pass filter to filter the high order harmonics of non-sinusoidal signals, and the FBPT algorithm is realized in the same steps as that of the SSPT algorithm. Using the SSPT and FBPT algorithms, the phase angle of the power system is estimated to an accuracy of 0.001% over 0-360° in at most a half cycle. Some examples are given to illustrate the proposed algorithms in Matlab.