Research Of FFT Algorithm For Detecting Electric Harmonic Based On Window Function And Interpolation

With the rapid development of the power electronic technology, all kinds of electric power electronic system is used more extensively, the power grid affected by what will produce a large amount of harmful harmonic.When passing a certain limition, the elrctric harmonic will seriously affect the steadiness of the electrical equipment. So the harmonic treament is particularly urgent, the essential problem is to detect the accurate paramenters of the power harmonic.This article compares and analyses the advantages and disadvantages of some commonly detecting power harmonic method, in allusion to the FFT method used directly to deal with the harmonic singal, which has the phenomenon of frequency spectrum leak and the effect of the picket fence, this article puts forward the blackman window and the peronas twin interpolation algorithm combining FFT. At the same time, the polynomial approximation method based on this algorithm is also employed to obtain some correctional formulas for the frequency, the amplitude and the phase. The Matlab simulation show that,with using the algorithm, the frequency,amplitude and the phase of every harmonic detection is obviously improved.Combined with the algorithm mentioned above, The harmonic detection system is designed by this subject. The harmonic detection system is used the method of comboning the hardware and software to design. The hardware of the system depends on Field Programmable Gate Array as the core, with current and the voltage transformer circuit, fight aliasing filter circuit, wave transform circuit, front regulate circuit of A/D inputing circuit, interface of A/D and FSM of FPGA circuit, liquid crystal display circuit and power circuit. etc around. The software of the system depends on NiosⅡcpu as the core, with phase locked loop of DPLL module, the controlling module of A/D sampling, FIFO module, ROM added window module and FFT module. etc around. The technology of System on Programmable Chip is used in the design of the the harmonic detection system. The function of some hardware logic circuit, some software module and NiosⅡcpu can be designed in the FPGA. By this way, this system can meet the optimal balance of the speed, all kinds of process work parallelly, high speed, easily to expand and work stabilized. etc.After the experiment and simulation test of the system, the experimental results verify the feasibility of this design. This system can effectively detect the frequency and amplitude of the harmonic, satisfy the harmonic detection actual requirements, which has a certain practical value. In addition, this article also analysis the results of the experiment and the origin of the error.