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Study On Passive Lossless Soft-Switching PWM Converters

Posted on:2005-10-16Degree:MasterType:Thesis
Country:ChinaCandidate:S J LuoFull Text:PDF
GTID:2132360125465002Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
With the development of semiconductor devices (mainly active switch devices), the switching frequency of PWM (Pulse Width Modulation) converters becomes higher, which makes PWM converters (mainly high-frequency transformers, inductors and capacitors in converters) smaller, and this will benefit design and application of them. What's more, higher switching frequency will reduce the audio-frequency noise and improve dynamic response of PWM converters.However, conventional PWM-conversion is a kind of hard-switching technology. That is to say, active switch device is turned on with non-zero voltage, and turned off with non-zero current. And then, as switching frequency becomes higher, the dissipation of active switch devices will increase quickly, which will lower circuit efficiency, weaken power-processing ability, and increase EMI of PWM converter. In detail, hard-switching PWM converter meets problems in turn-on and turn-off dissipation, turn-off with inductive load, capacitive turn-on, reverse recovery of diodes, and so on.Soft-switching is the main solution to above problems of PWM converter at present. It can be divided into two main types, i.e. active soft-switching and passive soft-switching, and passive soft-switching includes RC snubber and PLSS (Passive Lossless Soft-Switching).This paper studies application of PLSS in PWM power converter. On basis of synthesis and analysis of existing PLSS-PWM converters, this paper presents a PLSS-bridge inverter circuit, and makes theoretical and simulation study of it. In the end, an experiment of this novel PLSS-bridge inverter is made. The main jobs and conclusions as follows:Firstly, a novel PLSS-bridge inverter circuit was proposed, and its operation principle was analyzed. This circuit can realize soft-switching of active switching devices and energy of ZVC feeds back to the load directly, so its operation principle is simple and efficiency is high. This novel PLSS-bridge inverter works with 8 additional passive devices. Judged from existing related research documents, this is one of the PLSS-bridge inverter with least devices.Secondly, operation conditions of this novel PLSS-bridge inverter is analyzed and obtained: with correct power supply, load current, and dead-time, ZVC can be reset, and zero-voltage turn-off of active switchs will be achieved. Otherwise, only zero-currentturn-on of them can be achieved.Thirdly, simulation study of this novel PLSS-bridge inverter is made, and simulation waveforms reveal that all active switches' zero-current turn-on and zero-voltage turn-off can be achieved in correct operation conditions.Fourthly, experiment study of the PLSS-bridge inverter is made based on theoretical and simulation analysis, and experiment results verify the correctness of above theoretical and simulation study.Fifthly, this paper analyzed a PLSS-boost converter. Operation principle and process of the PLSS-boost converter are analyzed and main electrical variables' expressions are derived. These electrical variables' theoretical and simulation waveforms are given, which proves that this PLSS-boost converter can realizes active switch's zero-current turn-on and zero-voltage turn-off, and this converter's control mode won't be influenced.
Keywords/Search Tags:Soft-Switching, Passive Lossless Soft-Switching, PWM Converter, Full-Bridge Inverter
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