Research On Control Strategy For APF Based On Non-harmonic Current Detection

With the widespread access of non-linear power electronic devices in the power grid,the power quality of the power grid has become a hot issue.Active power filter(APF),one of the important ways to improve the power quality of the power grid,has been widely studied and applied because of its excellent compensation performance.At present,the research of active power filter is mostly based on harmonic detection,which needs to detect and extract the harmonic current of load current.This leads the error of harmonic detection into compensation current,which affects the real-time and accuracy of compensation,and reduces the compensation effect of active power filter.However,the control scheme based on non-harmonic current detection for avtive power filter has no harmonic detection and extraction,less current transformer and calculation,high compensation accuracy,and significant control advantages.In this paper,the control methods of non-harmonic current detection have been studied in depth,including:By comparing the similarities and differences between harmonic current detection method and non-harmonic current detection method with control block diagram and mathematical deduction,it is concluded that the two methods have equivalent control effect under certain circumstances.At the same time,the reasons of voltage fluctuation on DC side of APF is analyzed.A fractional order PI controller is introduced to suppress the influence of DC side voltage fluctuation,and the Outaloup rational approximation algorithm of fractional order controller is improved,which enhances the approximation accuracy of the algorithm near the end of the frequency band.The simulation results show that the fractional PI controller can suppress the DC voltage fluctuation and improve the response of the system.A current loop control strategy based on non-harmonic current detection is established.Starting from the control strategy and second order generalized integrator,a current controller named reduced order vector proportional integrator is obtained.The controller not only has the characteristics of high gain at the resonant frequency,but also achieves zero-pole cancellation and eliminates the influence of the control plant on the system.The complexity,stability,anti-interference and control precision of second order generalized integrator,reduced order generalized integrator and reduced order vector proportional integrator in control system are analyzed and compared.The parameter robustness,parameter tuning process,stability and controller implementation of the proposed controller are analyzed.The advantages of using reduced order vector proportional integrator are verified by simulation.Finally,an experimental prototype of APF is built,and the hardware circuit design and software design of the system is given,including the calculation and selection of the parameters of the main circuit,the detection and driving circuit,as well as the software design process.The feasibility and superiority of control scheme based on the non-harmonic current detection are further verified by the experimental results.