Research On Auxiliary Resonant Commutation Inverter With Bidirectional Reset Of Magnetizing Current

Voltage source inverter(VSI)is increasingly being used in all kinds of applications at different power grade.Although the VSI has been developed for decades of years,the demands on higher conversion efficiency and higher power density never stop.By increasing switching frequency the amount of inductance and capacitance can be decreased,and thus increasing the power density.However,in a hard-switching converter,the higher switching frequency results in increased switching losses in power semiconductor devices such as insulated-gate bipolar transistors(IGBTs)and metal-oxide semiconductor field-effect transistors(MOSFETs)and causes highfrequency electromagnetic interference(EMI).The above problems limit the application of switching devices in high frequency.The application of softswitching techniques to inverters can not only realize high switching frequency,miniaturization,and lightweight,but also reduce the electromagnetic interference(EMI)and switching noise.Based on a short review of the current research status of soft-switching inverters,Section Ⅱ presents an auxiliary resonant commutation inverter with bidirectional reset of magnetizing current and modulation strategy.Phase-shift full bridge charges the auxiliary resonant pole inductor through isolating transformer to achieve zero voltage switching(ZVS)of main switches.The zero voltage switching of the all auxiliary switch is realized by storing energy in the magnetizing inductor.Commutation charge phase and magnetization current reset phase are assigned to the positive phase and the negative phase respectively and bidirectional reset of magnetic current is reached.However,after analyzing the working principle,the structure of the circuit topology leads to a complex control strategy and large turn-off loss of the auxiliary switch,which make it unsuitable for practical applications.Therefore,according to these problem,this thesis propose a improved topology in Chapter 3.Simplified the structure and control strategy of the auxiliary circuit.Through the loss analysis of each part,it is concluded that the freewheeling loss of the magnetizing current can be optimized.Therefore,Section Ⅳ propose an improved modulation strategy,which reduced the magnetizing current freewheeling loss and improved efficency.This thesis introduces topological composition,operating principle and divide a switching cycle into multiple operating modes,give the equivalent circuit diagrams of each mode,and calculate the duration of each mode,analyze the resonant circuit of soft-switching inverter in Chapters 3 to 5 and design the component for ZVS guaranty under the modulation strategy before and after improvement.Based on the above analysis,the simulations are given with SIMetrix software and demonstrating the validity and features of the proposed inverter and modulation strategy.In addition,the power loss in each component is analyzed.By comparison the loss results under the control strategy before and after the improvement,it is concluded that the improved modulation strategy effectively reduces the conduction loss of the magnetizing current and improves the efficiency of the inverter.Finally,the proposed soft-switching topology in Chapters 3 and 4 is applied in the 1kW experimental prototype.The experimental results and efficiency test results under these two modulation strategies are presented and show that the proposed soft-switching inverters and two modulation strategies can realize soft-switching of all switches and improve inveter efficiecy.