Nonlinear Modeling Of DC-DC Power Converters Based On PSM Mode And Integration Design

The applications of PWM DC/DC converters are very common in PIC (Power Integrated Circuits).But the efficiency of converters badly decrease at light loads.In order to solve this problem, PSM (Pulse Skip Modulation) DC/DC converters are increasingly adopted in PIC at present.As a new modulation mode, PSM is distinguished from traditional PWM and PFM.It regulates the output voltage and current by adjusting the CFCW (Constant Frequency Constant Width) control pulses number of normally operated and skipped periods. Its distinct advantages are the high efficiency and low EMI, especially at light loads. The study on nonlinear modeling and nonlinear phenomena based on PWM DC/DC converters is very mature. But nonlinear modeling and nonlinear characteristic of PSM converters have not been lucubrated.This dissertation addresses the issues on nonlinear modeling and nonlinear characteristic study of PSM DC/DC converters. Energy model, discrete-time model, averaged model and fuzzy ratiocination model are proposed and built. Finally,a PSM power integrate circuit is fulfilled.The innovative contributions are listed as follows:1. The Energy Model (EM) of power converter is firstly proposed .EM describes the relationship between capacitor energy states and power supply at consecutive clock periods.Therefore,the essence of power converter is disclosed from EM. Based on energy balance, EM of PSM Boost converter and EM of PWM Buck Converter are built respectively.The following three nonlinear researchs are fulfilled from the finished EMs.(1) The capacitor energy locus diagram is depicted from EM of Boost converter when the load R is changed. Therefore, dynamic behaviors of output voltages are quantificationally studied when the dissipative energy of resistor and the stored energy of capacitor are changed.(2) The capacitor energy locus diagram is depicted from EM of Buck converter when K eaof error amplifier is changed.The output voltage bifurcation diagram is derived as well as the position of first bifurcation point from the above EM.Therefore,nonlinear bifurcation and chaos phenomena of PWM DC/DC converters can be studied from EM. (3) For PSM power converter shortcomings that the output voltage ripple is very large and the actual switching frequency is easy to enter into audio range,EM is adopted to optimize PSM controller .2. Discrete-time models are firstly built for PSM converters. Discrete-time model is synchronous switching map,which describes iteration of output voltages at consecutive switching periods. Discrete-time model shows the periodic behavior of PSM power converter and can be used to analyze nonlinear characteristic of PSM power converter.(1) The output voltage movement diagram is depicted from the model when load R or input voltage ui n is changed.The nonlinear characteristics are detailedly analyzed for PSM power converters.Compared the nonlinear characteristics of PSM converters with the bifurcation and chaos phenomena of PWM converters,the differences between them are distinguished.(2) The PSM mode is fulfilled for Boost power converter using FPGA. The validities for models and analytic results are verified by testing actual circuits.3. Averaged models are built to solve small signal modeling for PSM converters.(1) The state-space averaged equations are built for PSM Boost converter. Therefore,dc equivalent circuit model and small-signal ac equivalent circuit model are subsequently derived.(2) The averaged switch model is built for PSM Buck converter.Therefore,dc equivalent circuit model and small-signal equivalent circuit model at low frequency are subsequently derived.4. Based on the interpolation theory of fuzzy controller, fuzzy ratiocination model of fuzzy controller is built to solve the FPSM converters modeling .This dissertation theoretically solved the key problems, i.e., large signal modeling in nonlinear study of PSM DC/DC converters. These models have theoretical values in developing PIC .