Research On DC/DC Converter Based On Predictive Functional Control

With the large number of applications of DC/DC converters,the requirements for their dynamic performance are increasingly strict,in addition to the strict requirements on their steady-state performance.The small signal model is used in the traditional control method to design the controller parameters.The DC/DC converter designed by this way has good steady-state performance near the operating point.However,when large signal changes such as load variation occur,the dynamic performance is difficult to meet the requirements.Therefore,it is of important theoretical and engineering value to improve the dynamic performance of DC/DC converters by appropriate methods.DC/DC converters are strongly nonlinear systems and it is difficult to obtain accurate mathematical models.Therefore,in this thesis,the predictive functional control(PFC)algorithm with low computational complexity and low requirement for model accuracy is applied to the fixed-frequency DC/DC converters,effectively avoiding the difficulties of accurately modeling and reducing the adverse effects caused by load variation and model mismatch.So,the dynamic performance of the DC/DC converter is increased.The main contents of this thesis are as follows:(1)Introduce the basic principles of PFC algorithm,deduce the expression of control variable in the form of discrete state-space equation,analyze the closed-loop stability of PFC controlled system theoretically,and verify theoretical analysis through first-order and second-order system simulation.(2)Aiming at the characteristics of single Buck converter,a PFC method is proposed which uses the voltage and current real sample values to calculate the model predicted values.The correction error is corrected by adding feedback correction coefficients,and the explicit expression of duty cycle is derived.The effectiveness of the PFC method is verified by Matlab software simulation.(3)Combining the characteristics of the parallel Buck converter and the master-slave control strategy,a cascade control method for inner-loop PI controller and outer-loop PFC controller is proposed.The inner-loop PI controller and Buck converter are modeled as a generalized process,and the explicit expression of the current inner-loop reference value is deduced.The effectiveness of the PFC-PI cascade control method is verified by Matlab software simulation..(4)Set up single Buck converter and parallel Buck converter experiment platforms with FPGA as the controllers,give the specific implementation steps of the closed-loop PI,PFC and PFC-PI control method,and use the schematic and Verilog HDL language programming methods to design these three controllers.Through the single and parallel Buck converter experiments,the effectiveness of the proposed PFC and PFC-PI control method are proved.The experimental results also show that the PFC and PFC-PI control method have better dynamic performance than the double closed-loop PI control method when the load is changed.