Design Of Shunt Active Power Filter Based On Repetitive Control

ABSTRACT:The wide use of power electronic device to the power system brings a lot ofharmonic and reactive power. The reactive power and harmonic endanger thesafe operation of electric power systems, and increased the cost of power generation. There are two ways to eliminate the current harmonics and reactive power in power grid mainly in two ways.1) Set the passive filter, this kind of device is mainly composed of L and C two kinds of passive components, by adjusting the the proportion of L and C, produce resonance point similar to harmonic current frequency (Generally lower than the resonant frequency,to prevent the amplification of harmonic current), so that the impedance of the filter circuit is far less than the superior power system at the frequency of harmonic current. This kind of passive filter mainly have the following characteristics:which can only filters some or some fixed frequency harmonic, huge volume, high loss;2) Set the active power filter (APF). APF can realize fast compensation for harmonics and reactive current. APF overcomes the shortcomings of the passive filters, which can not only realize graded compensation and total compensation of harmonics, but also can suppress the harmonic current resonance. At present, the theory of APF has become mature.The main factors influencing the accuracy of APF compensation has two aspects:one is how to extract harmonic reference current signal accurately,another is how to accurately track the command signal. Harmonic extraction algorithm can be divided into two categories, one is how to extract harmonic reference current signal in the frequency domain, another is how to extract harmonic reference current signal in time domain. FFT is commonly used in frequency domain and the instantaneous reactive power theory and the FBD method is commonly used intime domain.Tracking control method of the instruction current mainly have PI control and PID control,which can not track APF command current signal without static error (harmonics signal).The only method to reduce the error is to increase the parameter of P, which will endanger the stability of the system and increases the current harmonic. Proportional resonant control and repetitive control developed recently can track the harmonic instruction signals without static error. Modulation method of power electronic devices are mainly SPWM and SVPWM. SPWM is simple and easy to implement, but the utilization of the DC capacitor voltage rate is very low. SVPWM modulation method is easy to realize the digital control, the output waveform quality is good, the switching loss is relatively small,and utilization of the DC capacitor voltage rate is high.This paper taking three-phase APF as object, establishes the mathematicalmodel of two level APF and analyses the working principle of APF.This paper studies the ip-iq harmonic detection method,p-q harmonic detection method and the FBD method.of various algorithms are compared and analyzed, and finally selected harmonic detection method based on FBD. Through the comparison of various algorithms, and finally selected harmonic detection method based on FBD. The current inner loop uses the composite control method, which can track harmonic reference signal without static error.This paper uses MATLAB/SIMULINK to build the simulation model of two level APF, and uses S-Function to design FBD current harmonic current detection program, current tracking control program based on the composite control algorithm and two level SVPWM modulation program.based on the simulation results, verify the accuracy of harmonic detection method, the effectiveness of repetitive control. The simulation results verify the accuracy of the harmonic detection method and the effectiveness of repetitive control. Finally, in order to verifies the effectiveness of the control algorithm, a prototype of380V/50KVA APF is designed, the experimental results verify the correctness of the above algorithm.