Research On Control And Protection Of Resonant DC Converter Applied To Electric Locomotive

In recent years,China’s rail transit has developed rapidly,and the auxiliary power supply system of electric locomotives has been widely studied.In order to meet the development of high frequency,miniaturization and high power density of the auxiliary power supply system,this paper proposes a resonant switched capacitor converter(RSCC)based on silicon carbide devices(Si C)to be used in auxiliary converters’ DC link to achieve high-efficiency voltage conversion.The RSCC transfers energy through the series resonant tanks.This paper first analyzes the basic principles of RSCC under open loop control,and studies the output characteristics of pulse width modulation(PWM)control and phase shift control in view of the input and output voltage fluctuations caused by complex working conditions during the operation of electric locomotives.Then emphatically analyzes the implementation principle and load conditions of soft switching under phase shift control,and in order to improve the problem of the small load range of RSCC soft switching,a frequency optimization control is proposed to achieve efficiency improvement in a wide load range.In addition,a detailed analysis of the resonant characteristics after voltage adjustment is carried out,and the resonant characteristics under different operating conditions are improved through optimized control.This paper also adopts a feedforward control strategy to improve the dynamic characteristics of RSCC.The protection design of the auxiliary power supply system of electric locomotives is the key to its stable operation.This paper mainly studies the soft start and fault protection of RSCC.Firstly,the RSCC soft-start current stress is analyzed,and a soft-start control strategy is adopted to reduce current stress.then the feasibility of the fault blocking strategy and the influence of digital delay are analyzed.The output characteristics under different short-circuit protection control strategies are studied and compared,and a combined control is proposed to realize the dynamic performance of short-circuit protection.In order to achieve high-voltage and high-power testing,this paper adopts a cascaded RSCC system with energy feedback(CREF).CREF realizes the increase and control of the test voltage through the step-up RSCC prototype;the tested RSCC prototype adopts current closed-loop control to adjust the power of the cascade system.In this way,the experiment of the tested RSCC under the rated voltage and rated power is realized,and energy feedback and more energy-saving high-power test conditions are realized.Finally,simulation and experimental platforms are built to verify the correctness and feasibility of the above control strategy and protection strategy.