A Resonant Converter With Modular Rectifier Structure

The massive use of fossil energy over the past decades leads to its shortage as well as severe environmental pollution,the development of renewable energy is considered as an effective solution to alleviate this problem,which is vital to the sustainable development of society.In order to ensure the stable operation of power grid when renewable energies are integrated into power grid,DC power grid emerges as the times require.DC transformer is used to connect different voltage levels of DC power grids and it is the core equipment in DC power grids.This paper focuses on low to medium DC voltage energy conversion,and studies the topology and control of a converter with wide output voltage range,By introducing the idea of modular multilevel into the resonant converter,this paper proposes a Resonant converter with Modular Rectifier structure(RMR).In order to analyze the Mode of RMR convenient,only one submodule in the upper arm and lower arm of the rectifier side is considered.According to different working situations,it can be divided into three Modes,and the advantages and disadvantages of the three Modes are analyzed.An optimal Mode is adopted and the adopted Mode can realize zero-voltage switching(ZVS)of switches in primary side and zero-current switching(ZCS)of rectified diodes in secondary side.In this optimal Mode,the gain characteristics of the converter is obtained by using trajectory analysis.A voltage control strategy is proposed by adjusting the switching frequency of the converter and the pulse width of the switches in secondary side to achieve higher operating efficiency based on this Mode.An 800W with one submodule RMR prototype is constructed to demonstrate the principle,the efficiency under voltage gain of 1,1.25,and 1.5 are measured.The efficiency of all operating conditions is higher than 93%,the peak efficiency is 96.8%.Furthermore,this paper studies multi-module RMR.The voltage balancing of submodule capacitor is essential for stable operation of RMR.Firstly,the relationship between the width of gate signals and the charge of the submodule is analyzed,and a voltage balancing algorithm based on the capacitor voltage sequence of the submodules is proposed accordingly.An 8kW RMR prototype with 4 SiC power devices submodules in each arm is built,the effectiveness of the voltage balancing algorithm is verified under the experimental conditions of 300V input and 800V?1200V output,and the efficiency under voltage gain of 1,1.25,and 1.5 are measured.The efficiency of all tested conditions is higher than 92.5%,the peak efficiency is also up to 96.8%.