Research On Parallel Compound Control And Delay Suppression Strategy Of HAPF

In recent years,with the call of Green Grid in China,the research and management of harmonic has become an important mission in the field of electrical engineering.As a new generation device of harmonic management,hybrid active power filter(HAPF)plays a dominant role in the realm of harmonic suppression.In this paper,a kind of HAPF system which consists of parallel active power filter(PAPF)and thyristor switched filter(TSF)is proposed as the study object.The problems of stability and time-delay in the operation of HAPF are studied in order to achieve excellent effect both of harmonic compensation and current response speed on the basis of reliable and stable operation of the system.In view of the HAPF topology proposed in this paper,the operation mechanism is analyzed,and the key parameters of the system are rationally designed based on the criterion of resonance suppression.In order to solve the possible problem of parallel resonance in the HAPF system when the parameter of TSF is shifted,the reference signal of damping current is extracted based on self-tuned filter.A compound control of HAPF containing harmonic compensation and resonance suppression can be realized by combing the reference signal of damping current with harmonic current.The harmonic equivalent circuit of HAPF under the compound control is established,and the equivalent control block diagram of the system is deduced.Based on the equivalent circuit and the control block,the effective range of damping coefficient is defined.The analysis shows that the resonance of the system can be effectively suppressed and the harmonic voltage at the PCC will not be magnified in the calculated range of the damping coefficient.By establishing the vector relation of various currents in the system,the inherent delay of steady state in the digital control system is analyzed.It can be seen that the inherent delay has seriously affected the performance of harmonic compensation of HAPF.Therefore,a current control strategy of gray prediction including two steps prediction of instruction current and one step prediction of outputting current is proposed to restrain the delay error of compensation current generated by PAPF.By constructing a GM(1,1)prediction model for the load harmonic current and adding the adjustment loop of predictive error,the negative effects on harmonic compensation caused by the inherent delay can be effectively reduced.Considering that the HAPF has a delay of transient response in compensating harmonic currents when the load current changes suddenly,the characteristics of various low pass filters are analyzed and compared.Eventually,the moving average filter with excellent performance is chosen and improved by increasing the filtering speed in the transient state.The weight function of the filtering speed is designed according to the condition of load current and the transient delay can be shortened which is equivalent to reducing the window size.When the load current is changed,the weight function comes into effect.Then the time-delay of transient response in harmonic detection of HAPF can be reduced under the premise of ensuring the effect of harmonic compensation.The simulation models of the HAPF system and the proposed control strategies are built based on the MATLAB/SIMULINK simulation environment,and the experiment is debugged based on the platform of HAPF prototype in the laboratory.The strategies of the compound control and the suppression of delay in both steady-state and transient-state are effectively verified through the simulation and experiment.The results show that the proposed control strategies can effectively guarantee the stable operation of HAPF and suppress resonance of the system.The accuracy of harmonic compensation and the response speed of compensating current are also greatly improved.