Research On Double Loop Predictive Control Strategy Applied In Single Phase Voltage Source Inverter

Compared to analog control,digital control is reprogrammable,presenting better noise immunity,low susceptibility to age and environmental factors.Among all the digital control methods,predictive control strategy,which is based on the discrete model,is widely used because of its easy modelling,outstanding steady and dynamic performance.However,delay and susceptibility to system parameters limit the development of predictive control.How to work out the problems of delay and weak robustness become the research hotspots.Furthermore,nearly all the methods proposed recently are concentrated on inner loop control,while digital PID control is still used in out loop control.The performance of the system both depends on inner loop control but also out loop control.As a result,how to combine both inner loop control and out loop control becomes the key to improve the performance of the system.Firstly in this paper,digital control methods in common use are introduced,and both advantages and disadvantages are analyzed for predictive control.Accordingly,it also lists different solutions to the shortcomings of predictive control.With the investigations that out loop control only adopts PI control,the great significance of applying deadbeat control into out loop control is proposed.Secondly,by studying the single phase voltage source inverter,this paper also analyzes the working mode of the single phase voltage source inverter and caculates the discrete model of the inverter.According to basic principle of deadbeat control,the control law of double loop predictive control is deduced.Moreover,steady-state error,bandwidth and output impedance are compared between double loop predictive control and out loop PI control-inner loop predictive control,and the results reveal that applying deadbeat control into out loop control can effectively reduce steady-state error,output impedance and improve dynamic response ability.Thirdly,instability of double loop predictive control is analyzed by cooperating time delay.In order to promise the stability of the proposed control strategy,different error correction are creatively introduced into the double loop predictive control law for improving stability.In addition,for avoiding the complicated selection process of error coefficient,dynamic error coefficient are proposed based on Lyapunov stability principle.In order to combine the fast dynamic response of optimal switching state model predictive control,switched predictive control is introduced into the inner loop control.Finally,the power circuit,control circuit,the sampling and adjusting circuit,the driving circuit for the single phase voltage source inverter are designed,and the whole experimental platform is built.In order to verify the feasibility of the proposed control algorithm,the steady state performance for both out loop PI-inner loop predictive control algorithm and the proposed control algorithms under different load conditions,the dynamic performance and the related experiments of robustness under resistive load are carried out.The results present the effectiveness and superiority of the proposed double loop predictive control algorithm.