Study On Coal Mine Multi-output Output Intrinsically Safe Two-stage Converter

With the rapid development of the coal industry, more and more electrical equipment isapplied to the coal mine. As the supply core of the electrical equipment, the requirements of safetyperformance becomes very high. Front-end input of primary intrinsically safe power supply isnon-intrinsically safe, so flameproof enclosure of the power supply is essential. The actualexplosion-proof type is flameproof and intrinsically safe, that is output intrinsically safe. Theordinary converter switch suffered large voltage stress becouse of the voltage levels in coal mine.So the current MOSFET is difficult to meet the performance requirements. And the outputintrinsically safe power supply is usually required to output with a variety of grades, such as5V,12V,18V and so on. The paper describes a two-stage converter. The first stage is a three-levelflyback converter which overcomes the disadvantage of big voltage stress existing in ordinaryconverters, and the second stage is a closed loop Buck regulator which solves the problem of poorcross regulation in multi-output converter. So the research on output intrinsically safe two-stageswitching converter with multiple output functions has great practical significance.First, the structure classification of output intrinsically safe switching power supply and itsprotection type are introduced. Through analyzing and comparing its characteristics, the structureand protection type of the output intrinsically safe two-stage converter are selected. The principleof two-stage converter is analyzed. The relation of the operating mode、duty cycle and primaryinductance converter peak current with each parameter of three-level flyback converter is derived.The variation of the operating mode、duty cycle and primary inductance converter peak currentwith input voltage and output current is obtained. The theoretical analysis is proved by simulationcorrectly.Then, the stability of the two-stage converter with multi-output is analyzed. The small-signalmodel of the first-stage and second-stage converter is established to verify the stability of thetwo-stage converter. Combined with measures to improve the safety performance, the new outputintrinsically safe converter is designed, including the main circuit control circuit and output cut-offtype protection circuit. And the design process is described in detail. The performance of prototypeis verified by the experiment.Finally, the energy transfer process of the inductor and capacitor in the second stage Buckconverter is analyzed in the case of normal and abnormal operation. The most dangerous momentof output short-circuit and the maximum output short-circuit discharged energy are gotten.Comparing with the minimum ignition energy, intrinsically safe performance of the converter isevaluated. The validity of the theoretical analysis is verified by the experimental results.