Research On Isolated Boost Converter And Flyback Inverter

The main research contents of this dissertation have two parts: isolated boost converter and flyback inverter.Isolated boost converter has advantages of high frequency electrical isolation, multi-output solutions, lower input ripple current and high reliability for the short circuit of load, etc. It is attractive in applications such as high voltage multiple outputs with isolation requirement, single stage power factor correction and bi-directional DC/DC converters. This paper comprehensively summarizes the typical topologies of isolated Boost converter family, and classifies existing topologies into several categories. The characteristic of those topologies are analyzed in detail. A novel isolated interleaving two-transistor forward boost converter is proposed in this paper. This converter has less voltage stress of power switches, and no transformer magnetic deviation. In all interleaving two-transistor forward switches, zero voltage switching can be obtained which can apparently improve the power density.However the isolated boost converters need to resolve two problems. 1) The transformer leakage inductance will cause surge voltage across the switches. Two clamp circuits are combined to solve this problem: LCD clamp circuit, in which the voltage across clamp capacitor is no reverse; flyback clamp circuit, which consists of an additional flyback winding coupled with the boost inductor and a diode connected to the output terminal.2) The low output voltage causes the control loop to call for maximum duty cycle and a large surge of input current when converter starts up, thus damaging the converter. The peak current mode PWM controller can limit the duty cycle. Flyback can deliver the stored energy in primary side to the output side during power switch off period. These two methods can alleviate the inrush current. This paper research voltage and current close-loop control Flyback converter and isolated Boost converter with peak current mode PWM controller. The start process of Flyback converter is divided into three stages: inrush current, current regulating and voltage regulating stages. The start process of isolated boost converter is divided into three stages: Flyback work, Buck work and Boost work. Isolated boost converter inrush current occur during Flyback work.A flyback inverter is studied in this paper which consists of two bi-directional...