Study On Key Technologies Of Input Series Combination Converters Control Strategy

High voltage DC transform has extensive needs in rail transit,aircraft power supply system,flexible DC transmission systems,etc.The high DC voltage poses a significant challenge to the device selection of converter,system isolation and reliability design.Through a number of sub-modules in series,the module series and parallel technology can reduce the voltage stress of each module to solve the problems caused by the high DC voltage.Module series and parallel technology develop towards the direction that building blocks,high reliability and high dynamic response so that the combined system has the good characteristics as a single module system.The key problem of combined system lies in the average stable operation of sub-modules under any operating condition.Therefore,the design needs to ensure that the voltage stress of sub-modules does not exceed the limit under the steady state and dynamic operation modes.To achieve this expectation,the module series and parallel technology focuses on the study of the voltage and current sharing control strategies.The goal of this paper is to improve the output dynamic characteristics and the reliability of the combined system,and shorten the research and development time.The aspects of sub-module topological type selection,the design of voltage and current sharing control strategy and the analysis of parameter mismatch effects are researched in the key technology of the input series DC/DC converters' control strategy.Firstly,aiming at the problem of sub-module topology selection for combined converter with common duty ratio control,an analytical method for the natural voltage sharing stability based on steady-state operating point model is proposed.Then the stability of the three basic types of topology is deduced.The conclusions provide reasonable suggestions for the topology selection of sub-module.Aiming at the poor output characteristics of the combined system in high voltage power supply with high bus voltage,an input voltage sharing control strategy based on peak current control which has good output dynamic characteristics is researched.It can be applied for input series output parallel connection.The advantages of peak current control is combined with voltage sharing technology between modules to make that the combined system still has a good output voltage and input voltage sharing dynamic characteristics when the bus in high voltage,high slope and large span variation.Secondly,aiming at the problems of circuit delay and insulation caused by the high voltage isolation devices in the input voltage sharing control methods for the input series output parallel system with auxiliary source,an output current differential sharing control scheme is proposed.Only the output side current and voltage which have common ground are sampled to calculate,and the accurately output current sharing can be obtained in the input series output parallel system.The isolation devices are omitted in the control circuit which improved the steady voltage sharing characteristics and reliability.In addition,aiming at the insulation problems of input voltage sharing control methods and backup problems of multiple modules for the input series output parallel connection system,an output voltage differential control strategy is proposed.All the sampled state variables are on the output side that the signal isolation problems are solved.The proposed control method has a master-slave structure can be improved to automatic master-slave structure to realize hot plug and backup functions.At the same time the proposed control method still remains the simple circuit structure which is more suitable for multiple modules system.Finally,aiming at the existing sharing control methods exploiting the development combination system has the problems that design difficulty and long development cycle,an input voltage sharing control strategy with paralleled MOSFET is proposed.The existing closed-loop modules are expanded according to the requirements.The constantvoltage modules are connected input series and output series.The constant current modules are connected input series and output parallel.This solution greatly omits the development time of main topology and output voltage control loop combined system.It shorten the development time of combination system at the same time improves the dynamic voltage sharing characteristics at both input and output sides of system.