A Unified Approach to Dynamic Modeling of High Switching Frequency PWM Converters

This dissertation will present the development of a unified approach for dynamic modeling of the PWM and soft-switching power converters. Dynamic modeling of non-linear power converters is very important for the design and stability of their closed loop control. While the use of equivalent circuits is often preferred due to simulation efficiency issues, no unified and widely applicable method for the formulation of these equivalents exists. A review of conventional modeling technique via the method of state-space averaging will be carried out. Complete development of the averaged, equivalent circuit models for the nonlinear power switch/diode combination in modem power converters via the Vorperian method will also be given. After highlighting the limitation\u27s of the Vorperian approach, a more widely applicable approach will be developed. This approach will capitalize on the notion that the derivative of the average of a time varying parameter is equal to the average of the derivative of that parameter. First, the development will show the formulation of the dc modeling equations, then show how these modeling equations are implemented using PSPICE\u27s Analog Behavioral Modeling capability. Next, the validation of the models produced will be presented via comparison to actual circuit simulation and experimental results. The unified approach presented has several advantages over conventional techniques. The unified approach is applicable to virtually any type of converter and is not restricted by topological issues. It is easily derived by a methodical approach, it simulates accurately and quickly, and it produces models that can work equally well in CCM and DCM. Model results agree well with other averaged models and the actual circuit. In addition, the approach will be expanded to include non-ideal effects such as conduction loss for both CCM and DCM operational modes. It will also be applied to the more complicated class of soft-switching topologies. The purpose of the research is to develop a methodology that makes more effective use of computer simulation tools during power converter prototype development. Although, predictions about converter operation are often very good when using this unified method, it should not be considered a substitute for actual circuit simulation or bench top prototyping which often reveal subtle issues not evident from average modeling. The following work will show that the types of computer-based analysis used in the design approach are the necessary and prudent first steps in the design process