Topology And Control Strategy Of Auxiliary Power Supply System For Electric Multiple Units

It is difficult to achieve lightweight to Electric Multiple Units(EMU)trains owing to the use of large-capacity power frequency transformers and the under-optimization of system topology in the auxiliary power supply system adopted by EMU.In order to solve this problem,taking EMU train auxiliary power supply system as the research object,this paper realized the lightweight of the auxiliary power supply system by optimizing the main circuit topology and control technology.Meanwhile,the performance of emergency power supply in the auxiliary power supply system is enhanced.This paper studies the main circuit topology and control strategy of the auxiliary power supply system and completes the following works:Combined with the topology of the auxiliary power supply system for CRH2,CRH3 and CRH5 EMUs,this paper makes comparison the advantages of AC-DC-AC auxiliary power supply system and DC-AC auxiliary power supply system,which has two different working pattern,inversion-reduction voltage and reduction voltage inversion,from three aspects,power supply mode,current collection method and grade number of power conversion.A new auxiliary power supply system topology is proposed by absorbing the advantages of various types of auxiliary power supply systems and overcoming their shortcomings.The main circuit structure scheme is composed of a bilateral three-level half-bridge DC-DC converter,a threephase inverter with three-level diode clamped structure,and a charger using three-level halfbridge in primary side and H-bridge in secondary side.An optimized control strategy based on the minimum current RMS is proposed in DCDC converter.After analyzing the principle and power transmission characteristics of the converter,the functional relationship between duty cycle and phase-shift angle in the primary and secondary voltage is derived under the condition that the current RMS is minimum.At the same time,the modulation strategy to duty cycle and phase-shift angle in H-bridge and threelevel half-bridge structure is studied.Finally,a simulation model was built on the MATLAB/Simulink platform to verify the feasibility of DC-DC converter control strategy and modulation strategy.A dual-loop decoupling control strategy for three-phase auxiliary inverter based on output voltage and current feedforward is studied.Firstly,t the complex frequency domain model in the dq coordinate system is deduced from the state equation of the inverter and then the dualloop decoupling control strategy is proposed.For the three-level diode clamp structure,the hardware circuit voltage balancing strategy and the SVPWM modulation algorithm are studied so as to solve the three-phase inverter neutral point offset problem with three-level diode clamped structure.Moreover,the three-phase LC filter parameters are also designed.Finally,a simulation model is built on the MATLAB/Simulink platform to verify the dual-loop decoupling control strategy,the feasibility of two voltage balance control strategy,and the rationality of filter parameter design.As for the charger,according to the analysis of the characteristics to the battery and its fast charging strategy,the step like constant current control strategy is studied.The simulation model is established on the MATLAB/Simulink platform to verify the feasibility of the control strategy.The start scheme in auxiliary power supply system,including system startup circuit,converter soft start,and state machine,is designed,according to the above research.The feasibility of the system startup design is verified by the auxiliary power supply system simulation model established on MATLAB/Simulink platform.What’s more,the feasibility of the AC/DC bus carrying capacity and the emergency power supply scheme for the energy storage device are verified.On the basis of the theoretical research and simulation verification,a low-power experimental system composed of DC-DC converters,auxiliary inverters and chargers is built.The control strategy algorithm of the DC-DC converter,auxiliary inverter and charger and the control core of the state machine are designed based on FPGA.The experimental verification of the system start-up plan,DC current bus with load,emergency power supply by energy storage device and the various control strategy for the related converters are accomplished.