Research On Harmonic Detection And Current Control Strategy Of Parallel APF

Since the beginning of the 21st century,the development of power electronics technology is changing with each passing day,a large number of power electronics devices are widely used in industrial and agricultural production and life,making a great contribution to the development of the economy and society,but it also causes serious harmonic pollution to the power grid and affects the normal and stable operation of the power system.Active Power Filter(APF)with its good harmonic compensation performance has become the focus of attention.The key of APF to realize harmonic compensation lies in the detection of harmonic current and the tracking control of instruction current.In this paper,the parallel APF of three-phase three-wire system is taken as the research object,and the above two key technologies are studied.It is the premise for APF to realize harmonic compensation to detect harmonic current accurately in real time.In this paper,this paper focuses on the harmonic current detection method based on instantaneous reactive power theory which is widely used at present.By combining theoretical analysis with simulation,the p-q detection method and i_p-i_q detection method are compared and analyzed in detail under different operating conditions.Among them,when the power grid voltage is distorted or the three-phase asymmetry of p-q detection method,the error of detection results is large,while the detection results of i_p-i_q detection method are basically unaffected by the power grid operation.As the low-pass filter in the traditional i_p-i_q detection method has a long delay and a poor filtering effect,this paper improves it and adopts the integral-mean filter with better filtering effect to replace the traditional low-pass filter.Simulation results show that the improved i_p-i_q detection method has better real-time performance and higher harmonic detection accuracy.In three-phase three-wire system,the traditional hysteresis current control method is only used for single-phase bridge arm.In order to track the instruction current better,this paper combines the traditional hysteresis current tracking control method with the voltage space vector control method,and adopts a voltage space vector hysteresis control method.The region determination method of reference voltage vector is optimized,and the system has a fast dynamic response speed by setting double hysteresis loop.Simulation results show that this method not only has the advantages of high real-time performance of traditional hysteresis current control method,but also can effectively reduce the switching frequency and current tracking errors of the device.On the basis of the above research,the hardware and software circuit design of APF system was completed,and a prototype was successfully developed for experiment.The experimental results show that the parallel APF system designed in this paper can detect the harmonic current accurately,and the harmonic compensation effect is better.