Research On Harmonic Control Method Based On Shunt Active Power Filter

In recent years,the large-scale application of power electronic devices has caused more and more serious harmonic pollution problems,posing new challenges to ensuring the quality of grid voltage.In this paper,by investigating the power quality of a certain company,it is found that its electric welding machine is the main source of harmonics.It is proposed that the electric welding machine is used as the load,combined with the complex and unstable harmonics of the electric welding machine,and the parallel active power filter(APF)is used.To suppress harmonic devices.This article mainly focuses on the in-depth research on the detection technology and control technology of parallel APF.Firstly,this paper introduces the harm of harmonics and the scheme of suppressing harmonics,and explains the research status of APF algorithm and products.The working principle of shunt APF is analyzed,and the state equation of its main circuit is deduced.Combined with the characteristics of harmonic current generated by the welding machine,the parameters of each component of the parallel APF and the size of the DC side reference voltage are designed.In the aspect of harmonic current detection,the hardware circuit construction of ip-iq detection algorithm phase-locked loop and sine and cosine generator is complex,and it is found that when the voltage distortion occurs,due to the existence of this module,the extracted fundamental active current will be biased.In this paper,the sine and cosine signals of voltage are obtained by direct formula derivation,and the fundamental current processed by the improved ip-iq detection algorithm is processed by wavelet transform.A simulation model of the improved harmonic detection technology is built to verify its effectiveness.Secondly,SVPWM hysteresis control method is used to track the instruction current.According to the instruction current,the size of the reference voltage is deduced,and the regional relationship between the reference voltage and the error current in the spatial coordinate system is used to judge the conduction sequence of the APF main circuit switch device according to the logic,and finally the tracking current is obtained.The method combines the advantages of the hysteresis control,such as fast response speed,high precision and low switching frequency of space vector control,and the simulation comparison with the triangular wave control and hysteresis control shows that the tracking error and stability time of the method are the least.The DC side voltage control is analyzed,and compared with the traditional PI control,the fuzzy self-adaptive PI control is proposed.Fuzzy toolbox parameters are set,and simulation analysis is done by Simulink.Compared with traditional PI control,overshoot is reduced by 3.587%.Finally,the simulation model of the overall parallel APF is built in Matlab/Simulink,and the load is the welding machine model at work.When the voltage is symmetrical and the distortion occurs,the simulation comparison shows that the harmonic content is below 5%,which meets the national standard and verifies the effectiveness of the scheme.