Analysis & Study On Modeling Of DC-DC Switching Converter

Modeling analysis DC-DC switching converters is the key step to study, analyze and design switching power supplies. Difference between the traditional ideal model and the actual nonideal converter is a problem that cannot be ignored to model switching converters. In order to solve the problem, this dissertation is devoted to study on modeling and analyzing DC-DC switching converter. The research results are helpful to optimize behavior and improve design efficiency of switching power supplies. On the basis of the current situation and developing trend of modeling methods of DC-DC switching converters discussed, a circuit averaging method is put forward to model nonideal basic converters operating in the continuous conduction mode (CCM). The method is exemplified by modeling nonideal buck converter and nonideal boost converter operating in CCM, the modeling procedures are illustrated concretely, simulation analysis and experiment verification are performed, corresponding CCM PWM-switch models are obtained. The equivalent circuit models of nonideal buck-boost converter operating in CCM are derived. Steady-state and dynamic small-signal analysis are discussed based on the derived models. Parasitic components existed in actual converters are included into the derived models, which are intuitive and of clear physical meaning. Therefore, the derived models carry practical value. The circuit averaging modeling method of nonideal converters operating in the discontinuous conduction mode (DCM) is presented. Both parasitic components and current ripples are included into equivalent circuit models of DCM converters. At the first time, this dissertation succeeds in deriving large-signal averaging circuit models, DC circuit models, small-signal equivalent circuit models corresponding to nonideal buck converter and nonideal boost converter operating in DCM. Based upon these models, the steady-state analysis is performed, transfer functions are obtained, small-signal characteristics of buck and boost converter are studied in detail with simulation and theory analysis. The small-signal characteristics in DCM are compared with their small-signal characteristics in critical CCM and CCM. Large-signal averaging models of nonideal buck as well as boost converter operating in CCM and DCM are combined respectively. The CCM-DCM mode boundaries for the buck and boost converters are determined. The circuit averaging methods to model half-bridge transformer-isolated converter with consideration of conduction losses, transformer-leakage inductance, both conduction losses and transformer-leakage inductance are studied. Transfer functions are derived. Effects of the converter parameters on transfer functions, the steady-state and small-signal characteristics of the converter are discussed, and the corresponding simulation is performed. State-space averaging method is first employed to derive the quiescent dc and small-signal ac equations of half-bridge converter including transformer-leakage inductance. The results are identical with those derived using circuit averaging method. A circuit averaging method of deriving circuit models including parasitic components and current ripples of CCM converters is introduced. Dynamic large-signal, DC, and small-signal circuit models including parasitic resistances and current ripples of nonideal synchronous rectifier buck converter operating in CCM are established. Closed-loop modeling of nonideal synchronous rectifier buck converter for voltage-mode control is studied. Transfer functions are obtained. Effects of parasitic components on control loop design of the converter are explored. Systematic simulation analysis is performed. All the results show that it is necessary to include parasitic components of converters into equivalent models.