Study On ISOP Modular Converter Applied To High And Wide Input Voltage Range

Modularized power converter can be applied to high-voltage high-power situation by serializing conventional power electronic converters.ISOP(Input-Series-Output-Parallel)modularized power supply is a kind of modular power supply with serial input and paralleled output,which can be used to realize the conversion from high voltage small current to low voltage large current.In order to allocate the input voltage and power equally for each module to avoid the damage that caused by the high voltage or large current,it's necessary to adopt a certain control strategy.In this thesis,the ISOP voltage sharing control strategy is studied based on the two-switch flyback converter.The working process of the two-switch flyback converter operating in DCM mode during a switching period is analyzed in this thesis as a basis for the design of the main circuit and the selection of the devices.The relation between the duty ratio and dc gain of the flyback converter proves that the variation range of the dc gain is wider than that of other converters,which is suitable for wide i nput.In this design,the two-switch flyback converter is selected,for its switch only takes half of the input voltage compared with the single-switch flyback converter,,which reduces the cost and is more suitable for high voltage situations.The small-signal model of the two-switch flyback converter is established in the second part of the thesis and the transfer function is deduced for the closed-loop design of the circuit.This paper chooses the peak current control as the control strategy,which has higher dynamic response speed than voltage control,and has a relatively simple structure.And then the design is verified through simulation.Next part of the thesis analyzes three commonly used ISOP voltage sharing control strategies by theory and simulation to select a control strategy suitable for wide voltage input applications.Through the analysis,it can be seen that the three-loop control strategy can achieve accurate voltage sharing and can avoid the effect caused by the difference between the the sub-modules' parameters.But on the other hand,it has low reliability,complex control loop and the isolation problem,which is caused by the sample circuit on the high voltage side.The wire-less control strategy,based on the output voltage upturning characteristic,has high reliability and can operate redundantly,but the output voltage will change with the input voltage to a certain extent,which is not suitable for wide input applications.Compared to them,the same duty cycle control strategy has a simple structure and has no dedicated voltage sharing control loop,but the voltage sharing is inaccurate,the reliability is low,and the dynamic response is slow.In order to improve its reliability,it's better to use the same duty cycle control with the mechanism to automatically choose a master modular.This paper eventually chooses the same master-slave duty cycle control for experiments.The final part of the thesis designs the main transformer,the drive and control circuit to build an experimental platform.Through experiment,it's proved that when the circuit parameters are not significantly different,the same duty cycle control with automatic master-slave selection mechanism has good steady-state voltage-sharing characteristics within a certain input voltage range,which verifies the feasibility of the scheme.