Research On Harmonic Detection Strategy Based On 100 KHz Switching Frequency SAPF

A large number of non-linear and impulsive loads are used in the power grid,and the proportion of distributed generation is increasing,which cause a lot of power quality problems such as harmonic and reactive currents.Harmonic currents have many harmful effect in the power system,for example,harmonic currents can cause conductor overload,overheating,insulation damage and burn out,affecting the normal operation of electrical equipment.How to suppress harmonics in power grid becomes a very important subject.As an efficient harmonic suppression device,Shunt Active Power Filter(SAPF)has been developed continuously in recent decades.Compared with Si based IGBT SAPF,Si C-based MOSFET SAPF can achieve more precise suppression of harmonic current due to its higher switching frequency and higher control bandwidth,more than this,the power density of SAPF has been further improved.High switching frequency has become a new development trend of SAPF.In order to realize selective harmonic suppression for SAPF controlled by Digital Signal Processor(DSP),a large number of harmonic suppression instructions need to be calculated in each sampling cycle,and the increase of switching frequency will lead to the problem that DSP can not complete all harmonic extraction instructions in a single switching cycle.Therefore,under the limited operation resources of DSP,how to make high switching frequency SAPF achieve better harmonic suppression become very meaningful.This paper presents a mathematical model of SAPF with 100 kHz switching frequency based on ABC three phase stationary coordinate system and DQ rotating coordinate system.The advantages of Recursive Fourier transform(RDFT)used in SAPF are analyzed in detail,and the control system under DQ synchronous rotating coordinate system is given.When RDFT is based on ABC three phase coordinate system for harmonic extraction,due to the shortage of operation resources of DSP at 100 kHz switching frequency,this paper analyzes the error effects of different sampling frequencies on the harmonic extraction of RDFT in time domain and frequency domain through discrete simulation.In order to maximize the utilization of DSP operation resources,Frequency-division decimation strategy of RDFT is proposed,which enables the 100 kHz SAPF to achieve the suppression of 5th to 31 th harmonics.In this paper,according to the characteristic that RDFT has phase compensation,the harmonic suppression effect of SAPF is further improved after adding phase compensation.According to the characteristics of harmonics indifferent coordinate systems,RDFT is used to detect harmonics based on DQ synchronous rotating coordinate system to reduce the calculation amount and realize harmonic suppression within 50 th.Finally,the proposed strategy is verified on a prototype three-phase three-wire shunt active power filter with a capacity of 10 kVA and a switching frequency of 100 kHz.