| With the development and utilization of new energy sources and the rapid development of intelligent control systems,switching converters have been widely used in various industries.In the field of new energy vehicles,the direct current of the power battery is converted into variable frequency alternating current for driving the electric motor;in the field of wind turbines,the variable frequency wind power is converted into a fixed frequency alternating current to thousands of households;in the field of automotive applications,through the direct current voltage The conversion(DC-DC)meets the needs of the control system.The rapid development of the application field puts forward higher requirements on the working efficiency,accuracy,stability and applicability of the switching converter.Switching converters are composed of non-linear components such as switching tubes,inductors and capacitors,which cause chaos in the working process,and the generation of chaos will seriously affect the working performance of the switching converter.Therefore,the research on the chaotic generation mechanism and control strategy of the switching converter is an urgent problem to be solved.This thesis intends to study the switchingconverter from the following aspects:Firstly,the switching converter circuit was analyzed based on chaos theory to verify the nonlinear characteristics existing in the switching converter circuit.Discuss the root trajectory and the analysis method of the Bode diagram in the nonlinear system,and analyze the characteristics of various control strategies.Secondly,a typical step-down DC-DC converter is selected for analysis.The simulation model is built based on typical parameters.The analysis method in the field of automatic control is introduced into the switching converter system.The root trajectory and the Bode diagram are used to determine the stability of the system.The function obtains the position of the zero pole,the trend and the interval of the Bode diagram,discusses whether the stability meets the requirements,and adjusts the PID parameters according to the stability criterion,selects the input and output subset range,determines the fuzzy inference function and design control rules,and completes the blur.The PID controller is designed and tested for control effects.Thirdly,chaos theory is applied to the study of nonlinear circuit characteristics of switching converters.The characteristics of voltage-controlled buck converters are analyzed.The topology structure and device parameter selection methods in two working modes are described.The Simulink simulation model is built.The phase diagram is used to analyze the influence of the parameters on the working state of the circuit.The time domain waveform diagram is used to explain the transformation of the working state of the circuit.One of the chaotic generation mechanisms of the switching converter is due to the charging current.When it is too large,it causes the output voltage to rise too fast.Finally,the traditional PID and fuzzy PID control model is built for the Buck DC-DC converter,and the PID parameters are further adjusted according to the actual simulation results.The control effects are tested separately.The performance difference between the traditional PID and the fuzzy PID control is compared.The fuzzy PID is determined by quantitative analysis.It has the advantages of fast adjustment,good robustness,no overshoot and convenient use,which can effectively improve the performance of the switching converter system. |
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