Research On Harmonic Detection And Current Compensation Strategy Of Four-bridge Active Filter

People cannot live without electricity power nowadays from our daily life to the industrial production.A great deal of non-linear loads has been connected to the power grid,which has greatly reduced the electricity quality.Especially,the problems of harmonic current and three-phase imbalance in the three-phase four-wire system grow more and more prominent.Three-phase four-leg active power filters can be directly connected to the source of harmonic current in parallel,which can effectively reduce the harmonic current from the source plunged into the power grid.At the same time,it can also play the role of reactive power compensation.I have studied two key technologies in this paper: harmonic current detection algolrithm and compensating current regulation.Accurate and timely harmonic current extraction algorithm is the premise to ideal compensation performance of active power filter.Based on the study of FBD harmonic current check algorithm and the generalized integrator harmonic detection algorithm,in this paper,I introduce the method of the combination of the two.This combination is to extract the electric voltage positive sequent flow phase information of the fundamental wave using generalized integrator firstly and then to extract the fundamental wave flow and the harmonic current using the FBD power theory.The simulation results show that the proposed algorithm can improve the phase delay of the FBD algorithm in the load mutation.In time,no error compensation current control strategy is an important guarantee for the active power filter to achieve the desired effect.In this paper,an improved internal model of repetitive controller is introduced,which will be used in the compensation current control process of four-leg active power filter.I have deduced the parameter of the internal repetitive controller.Software simulation results show that the method can effectively solve the problem of the critical steady state of the original repetitive control strategy.When the power network has frequency fluctuation,the method cannot compensate the harmonic current effectively.To solve this problem,I have introduced FIR filter to improve the internal model of repetitive controller and have designed the FIR filter parameter.Performance analysis and software simulation show that the repetitive –control electric compensation strategy of this internal FIR filter can have a good compensation performance even when power grid frequency fluctuates.This has improved the adjustability in the case of frequency fluctuation based on the repetitive–control electric compensation strategy.In addition,I have carried out a general design of the three-phase four-leg active power filter experimental platform to validate the effectiveness of harmonic detection algorithm and electric current compensation regulation.