Study Of Active Power Filter By Improved Repetitive Control

Numerous nonlinear loads result in grid current or grid voltage distortion with development of power electronics technology, and the grid power quality is affected seriously. The distorted current and distorted voltage includes numerous harmonic, which reduce the efficiency of energy production and power transmission, also influence the users. What is more, the accidents and malfunctions occur more and more because of the harmonic pollution. Eliminated the harmonic pollution and created"green power grid"has become the problem that power technology workers must solve now.As the equipment can eliminates the harmonic dynamically and effectively, active power filter—APF has become the research focus in recent years. The compensative effect of the APF depends on how to make the compensating current tracking the reference current better and reduce the tracing error. The error between compensating current and reference current is periodic, wherefore the control effect using traditional PI is not ideal enough, and what is more, too large closed loop gain will cause the system instability. The internal mold of repetitive controller includes mathematic model describing the error signal, thus the steady state error of system can be eliminated completely at the fundamental frequency and its integral multiple frequency of the error signal. Then the low-pass filter is introduced to the system to improve the stability.Through the analysis of stability and steady-state behavior of the traditional repetitive controller, finding that low-pass filter affects the steady-state behavior of the system. Although increasing corner frequency of the low-pass filter can improve steady-state control accuracy, too large corner frequency may cause the system instability. To solve these problems, an improved repetitive controller is proposed in this dissertation. First given the selection criteria of corner frequency, derived the relationship among delayτd, corner frequencyωcand period of power supplyτ, then design steps of parameters of the improved repetitive controller is proposed. Simulation results show that the improved repetitive control algorithm not only maintains the system stability, but enhances steady-state control accuracy of the system effectively and superior to traditional PI control algorithm and repetitive control algorithm. In this dissertation, a single phase APF experimental facility was developed based on TMS320LF2812 and FSAM30SH60A. Firstly the hardware and software of the system is introduced respectively, and then the realization of control algorithm and flowchart are proposed. Experimental results show that the APF based on improved repetitive control can eliminate harmonic and compensate reactive power effectively.