AC sampling represents developing direction in the measurement of electric power parameters and grid harmonics analysis. Synch-sampling is an ideal AC sampling method, it may appear deviation (sampling synchronous deviation ) because of the limitation of minimum timing unit of timer and variety of signal frequence. Synchronous deviation caused by limitation of the timer has already been studied by numerous scholars, however, Synch-sampling in the instance of signal cycle instability has been less discussed.This paper proposed a novel algorithm - Matrix Series Method based on real-time sampling and related correcting error when cycle signal is instable.The theory of real-time and best Synch-sampling can be summed up for three points: (1) Sampling time is calculated real-timely by using the last cycle value. (2) N points can be sampled in one signal cycle each time; (3) The error between real sampling point and ideal Synch-sampling point is no more than minimum timing unit of timer.Although synchronous deviation of real-timely synchronous sample is very small, synchronous deviation still exists. Synchronous deviation can lead to spectrum analysis error directly. Course of reducing error with specific algorithm harmonics analysis is called frequency spectrum correcting in the situation when the synchronous deviation exists. This paper proposed a novel frequency spectrum method- Matrix Series Method. Matrix Series Method can be summarized for three steps:(1) Initiative vector of harmonics series are formed by using formula DFT basedon the obtained N sampling points and N sampling values.(2) Gain Matrix G is calculated by using N sampling points.(3) Accurate harmonics coefficient vector is calculated by frequency spectrumcorrecting formula based on the obtained matrix G and vectorThe crucial frequency spectrum correcting formula is deduced from Matrix Inversion Theorem and Matrix series of DFT, it has only addition and multiplication operation of matrix series, the more iterative times are,the higher precision is. The main advantages of Matrix Series Method are simpler algorithm, higher precision and more real-time. The effectiveness of Matrix Series Method is shown by the simulation results.An electric parameter monitoring instrument (experimental equipment) based on PSoC (Programmable System on Chip)is also studied, Synch-sampling method and Matrix Series Method are realized theorily in this instrument.

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