Research On Key Control Techniques And Performance Optimization Of Traction Drive System For EMUs

Control techniques of traction drive system, as one of the key techniques of electric multiple units (EMUs), is directly related to operation safety and stability of EMUs. Supported by National Key Technologies R&D Program for the "12th Five-year Plan"—"Research on Hybrid EMU Key Technology and Typical Equipment Development", this dissertation focuses on several key technologies for improving the performance of traction drive system. Control technologies including beat-less control, optimal flux control and pulse width modulation are deeply investigated in theory and experiment. The main achievements are described as below.A beat-less control scheme is proposed for rotor field oriented control system by analyzing the beat phenomenon in the qualitative and quantitative method based on motor impedance characteristics and frequency-domain model. Digital implementation of beat-less control is investigated in detail. The traditional ripple voltage sampling method is optimized to obtain accurate ripple component. Eight discretization methods are applied to discretize the beat-less controller. The optimum discrete method for the beat-less controller is obtained by comparing the discrete precision, control performance and digital implementation in detail. As a result, beat phenomenon is significantly inhibited.The optimum control strategy of motor flux is investigated. A loss model of traction motor under synchronous rotating frame is analyzed by considering iron losses in the equivalent circuit of motor. With this loss model, the reference value of motor flux is optimized. As a result, the low efficiency problem of traditional method under light load condition is improved. A state observer considering iron loss is designed. The adaptive estimation of stator resistance and iron-loss resistance is achieved through the adaptive law based on stability analysis, so that the parameters sensitivity problem of the algorithm is solved. The accuracy and stability of the observer is ensured by closed-loop pole configuration and improved discrete method under low sampling frequency. The impact of iron losses on vector control performance is also analyzed and improved. Two modulation techniques in common use are analyzed and improved in order to adapt the requirement of high power and low frequency feature of EMU traction inverter system. Traditional over-modulation algorithm is improved based on basic bus clamping strategy, the harmonic characteristics of the traditional method are improved, and low-frequency fluctuation phenomenon is solved. A hybrid pulse width modulation strategy on the basis of current harmonic optimization is proposed, by considering the solution of CHMPWM angles and the influence of different angle distributions on its performance. A comparison between CHMPWM and SHEPWM is carried out by considering current harmonics and torque pulsation. By use of FPGA design, the hybrid PWM modulation strategy is implemented. As a result, a smooth transition between different modulation methods is achieved, and the harmonics feature of motor current in medium and high frequency region is improved.An entirely independent EMU traction inverter system is realized.A large amount of functional experiments are carried out through the power-fed test platform. The feasibility and effectiveness of the EMU inverter control technologies above are verified one by one.