Research On Control Strategy Of Modular Resonant Converter

As an important part of the power conversion,the DC-DC converter has been widely used in various fields.Higher requirements on the voltage level and power level of the DCDC converter were purposed because of the development of laser technology,radar technology,electrostatic precipitator technology,etc.In the high-voltage power supply,the secondary winding of the transformer has a large number of turns,and the distributed capacitance and leakage inductance cannot be ignored.The LCC resonant converter can effectively utilize these distributed parameters,so the LCC converter is suitable for highvoltage and high-power applications.However,in addition to the difficulty in manufacturing technology of high-frequency transformers and controlling the distribution parameters,the large switching losses and low speeds of the high-power semiconductor switching devices and other factors also lead to the difficulty in increasing the voltage level and power level of a single converter.The modular technology has the advantages of simple design of the unit module converter,easy expansion of the module and can effectively reduce the voltage and current stress of the semiconductor switching devices and improve the system reliability,so it is the best way to solve the difficulties of the high voltage and high power converter.In this paper,the theory and control strategy of the input-parallel output-series(IPOS)modular system based on LCC resonant converter are studied for high-voltage and high-power applications.In this paper,firstly,the working state and the implementation of soft switch of the fullbridge LCC resonant converter under the control of variable frequency or variable frequency and duty cycle are analyzed.A mathematical model of the LCC converter operating in discontinuous mode under the control of variable frequency or variable frequency and duty cycle is established.According to its mathematical model,the variable frequency control strategy and the variable frequency variable duty cycle control strategy are used to adjust the voltage of the master module and the slave module of the system.Secondly,the theory and characteristics of the multi-module IPOS converter system are analyzed.To ensure the normal operation of the system,it is necessary to ensure the balance of the current on the input side and the voltage on the output side of each module,and the relationship between the input current sharing and the output voltage sharing of the IPOS system is established.The control strategy of IPOS system is proposed: multi-module system adopts interleaving control method to reduce ripple;the output voltage of each module in the system needs equalization control.As long as the output side of the IPOS system is equalized,the natural current sharing on the input side can be realized.The IPOS system uses constant voltage control as a constant voltage source.The system output constant voltage and the intermodule voltage equalization can be realized by adjusting the output voltages of the mster module and the slave module.Finally,based on the system control strategy proposed in this paper,the system simulation model and experimental prototype are built.The validity of the system interleaving control and the correctness of the voltage regulation strategy of the master and slave modules are verified by model simulation.The tests verify the correctness of theoretical analysis and simulation results.In addition,under the control strategy proposed in this paper,the IPOS system can operate stably whether light load or full load under the conditions of equalizing voltage control,output constant voltage control and interleaving control,and it can fast reach a steady state when disturbed.