Study On Control Strategy Of Single Boost PFC Converter In Vitual Dq Mode

Boost PFC converters are widely used in small and medium power circuits to solve the harmonic pollution problem caused by power electronic devices.In achieving the functions of PFC circuit,existing control strategies are generally built in the quasi-steady state of the system.In this way,the steady-state deviation appears when tracking the input current,further influencing THD and power factor of the system.Based on this reason,the dc working points of Boost PFC converter system in virtual dq mode are established through coordinate transformation method in this thesis.Meanwhile the control strategies of the system in the virtual dq mode are explored.The main contents and research results are as follows:(1)The dc working point model of Boost PFC converter in the virtual dq mode is proposed,and the controller based on the average current method is designed.In the quasi-steady state mode,the parameters of the controller are designed by establishing the system small signal model near the quasi-steady state working point.Due to the constant change of the working point,the designed PI controller cannot achieve tracking the reference current without static error.Therefore,the dc working points are established through coordinate transformation method.Meanwhile the parameters of the controller are designed according to the model of system in the virtual dq mode.Then,the PI controller can achieve tracking the reference current without static error.Simulation and experimental comparison of the design results in the above two modes show that the average current control method in the virtual dq mode has better effect on THD and PF.(2)From the perspective of system dynamic and steady state performance,the Lyapunov control method in the virtual dq mode is proposed in this thesis.Linearization controller based on the system small signal model can only has good control performance near the working point in theory.When a wide range of load change appears,the stability of the system is difficult to guarantee.In this thesis,the current loop control equations of the system are derived on the basis of the Lyapunov-energy-function convergence theorem,so as to ensure the global stability of the system with a wide range of load changes.In the design of the outer voltage loop,power feedforward is introduced to avoid the effect of the low-bandwidth voltage loop on the system transient performance.(3)The design method of the system inductor current observer is explored.In order to reduce the detection variables of the system,inductor current observer is introduced into the control loop.In the observer’s design from existing literature,integral element is used to reconstruct load information.In this way the observer cannot accurately reflect dynamic change process of inductor current when the load step change,thus affect the transient performance of the system.In view of this,the idea of this thesis is to establish the observer structure containing the load current.And the Lyapunov theorem is used to design the observer parameters.The simulation and experimental results show that the designed observer can accurately reflect the information of the inductor current in the process of dynamic state and steady state.