A harmonic analysis algorithm based on synchronous sampling

The harmonic pollution has become a more and more serious problem because of the large-scale application of nonlinear electrical loads in power systems. It is known to all that fast Fourier transformation (FFT) is an effective method for power signal harmonic analysis, but aliasing effect, picket fence effect, spectrum leakage and spectrum disturbance make it suffer from inevitable limitation. In this paper, to solve the above problems of FFT, an all-digital synchronous sampling algorithm for high-precision harmonic analysis is proposed, which is suitable for the implementation of very large scale integration (VLSI). The main idea of this algorithm is to make the decimation ratio of the decimation filter of a oversampling analog-to-digital converter(OSADC) dynamically associate with the fundamental frequency of the power signals, which is irregularly fluctuant but can be real-time tracked by the frequency estimation algorithm, designed in this paper. As a result, the average sampling frequency of the decimation filter output can change with the input signal frequency. Compared with the software synchronous sampling and asynchronous sampling methods, the proposed algorithm can be implemented more easily and needs much less hardware costs.

I. Introduction

Energy metering data is the tripartite settlement basis of power generators, transmission and distribution companies and electricity customers. Related papers have proved that energy metering can't be measured by simple algebra sum, which is used for traditional electronic digital measurement. It is necessary to measure the fundamental and harmonic energy power respectively and thus achieve the scientific management of electricity [1]. Currently the widely adopted energy measurement algorithms in the academic and business circles are fast Fourier transform(FFT) [2], [3], neural network [4], [5] and wavelet packet transform [6], [7], where the realization cost of FFT is relatively low, making it most widely used for application. However, in practical applications, the fluctuation of grid frequency will lead non-synchronous sampling of fundamental signal, which causes leakage of the spectrum, affects the accuracy of measurement of the fundamental and harmonic energy. So FFT needs windowed interpolation algorithm or synchronous sampling algorithm to ensure the accuracy.