Design And Current Control Strategy Of LCL-filter Based On Shunt Active Power Filter

How to provide consumers with safe, reliable, high-quality economic power isthe main problem facing the power system. Reactive power compensation andharmonic suppression is one of the key technologies to achieve this goal. Activepower filter (APF) is a new type device for reactive power and harmonic dynamicalcompensation. L filter is used as traditional output filter of APF, it’s used to restrainharmonic which is near switching frequency, but the attenuation ability is limited.The filtering effect of the LCL filter is superior to L-filter, but the parameters ofdesign and current control strategy is more complex.This paper makes a research on the single L-filter of the active power filter.Based on the tracking of command current for compensation current andrequirements of inhibitting harmonic in switching frequency, it gives a designprogram of single L-filter. By the simulation of compensation characteristics itverifies the fact that the output filter designed by this method has a goodcompensation characteristics and it can effectively inhibit the high frequencyharmonic. However, there are also some limitations.The expressions of relationship between the ratio of grid side inductance toinverter side inductance、damp resistance and system loss, resonant frequency,harmonic current attenuation ratio of LCL filter is derived. The parameters trend ofimproving filtering performance of the system is discussed. Based on the trend,the design formula of inverter side inductance, grid side inductance,filtercapacitance, damp resistance is given. The simulation results and experimentalresults verify that by adopting the proposed method, the switching frequencyharmonics is suppressed effectively and the system side total harmonic distortion isreduced.It puts forward higher requirements for control system design to use LCL filter.Considering the problem of phase diversity, this paper proposes an control strategybased on the inverter side current closed-loop control and capacitor currentfeed-forward, it makes a summation of command current and low frequencycomponent which is output of capacitive current going through low-pass filter, anduses closed-loop control of the inverter side of the current negative feedback.analyze the improved strategy of steady-state error of compensation harmonic andcommand current, attenuation ability around switching frequency, bode diagram androot locus. Made a comprehensive evaluation of the improved strategy. The simulation shows effectiveness of the improved strategy presented in this paper.