Research On DC/DC Converter Modeling And Control Methods Based On U Model

At present,most of the modeling methods of DC/DC converters were based on approximate equivalent and linearization methods to obtain linear time-invariant models,then the linear control theory was used to design DC/DC converters.However,DC/DC converter was a time-varying and non-linear system,using linear time-invariant model as a mathematical model can not accurately describe the dynamic behavior of circuit cycle and period.Using input and output data of the system to directly establish a non-linear time-varying model is a widely used method at present.NARMAX model was a widely used discrete non-linear model.It can effectively describe a large class of non-linear systems.However,because of its complex structure and numerous parameters,it was difficult to design controllers based on this model.The U model was a polynomial function of time-varying parameters of a class of non-linear objects.It was convenient to design the non-linear control system with the method of linear control system design.In view of this,this paper introduced the concept of U model,using U model to establish the mathematical model of DC/DC converter,and the identification method and control method of U model parameters of DC/DC converter were studied.The main contents of this paper are as follows:(1)This paper analyzed the advantages and disadvantages of NARMAX model,the NARMAX model of DC/DC converter was established,and deduced the U model of DC/DC converter based on NARMAX model.The U model is solved by Newton-Raphson iteration algorithm.Aiming at the problem that the denominator of Newton-Raphson iteration algorithm may be zero,the improved algorithm was introduced.(2)This paper identifed the parameters of its U model.In the process of parameter identification of U model,a weighted recursive least squares algorithm of dynamic forgetting factor was proposed,which used single neuron PID algorithm to complete the dynamic change of forgetting factor.Taking the Buck converter as an example,the proposed method is compared with the conventional weighted recursive least squares algorithm with constant forgetting factor.The results show that the dynamic forgetting factor weighted recursive least squares algorithm based on single neuron PID control can better describe the input-output relationship of Buck converter when the duty cycle changes.That is,the proposed algorithm has higher identification sensitivity when the system parameters change rapidly and higher identification accuracy when the parameters change slowly.(3)A fuzzy PID control algorithm based on U-model of DC/DC converter was proposed.The adaptive function was realized by adjusting the parameters of the PID on-line.The actual object input was obtained by using the output of the controller and Newton-Raphson iterative algorithm.Taking Buck converter as an example,the effect of this controller was compared with that of conventional PID controller.The simulation results show that the fuzzy PID controller based on U model can effectively reduce the adjustment time and overshoot,and has better control effect on DC/DC converter.At last,An experimental platform based on dSPACE real-time simulation system is built to verify the effectiveness of the U-model fuzzy-PID control algorithm.