Development Of Comprehensive Treatment Device For Traction Power Supply System Of Urban Rail Transit

The traction power supply system of urban rail transit mainly adopts 12 or 24 pulse rectifier units,which has the advantages of simple and reliable structure and high efficiency.However,there are three shortcomings: first,the energy can only flow in one-way,and absorbing regenerative braking energy requires adding an energy feedback device or an energy storage device.Second,although the multi-pulse rectifier reduces the harmonic current on the medium voltage network,the harmonic current content in the transformer winding is still very large,which increases the loss of the transformer and reduces the capacity utilization rate and life of the transformer.Third,the leakage reactance of the transformer produces a commutation overlap angle,which causes the DC voltage output of the diode rectifier to decrease with the increase of the load,which increases the loss of the catenary.Based on the above shortcomings,the paper proposes the idea of a comprehensive treatment device in parallel with the diode rectifier: when the train is towing,the comprehensive treatment device treats the harmonics and reactive power generated by the rectifier;when the train is braking,the comprehensive treatment device feeds back the regenerative braking energy through the rectifier transformer to the medium voltage network.The main research work on the main circuit and control system of the comprehensive treatment device is as follows:The main circuit design of comprehensive treatment device.Considering the efficiency and volume of the comprehensive treatment device,the main circuit grid-connected inverter adopts the diode-clamp three-level topology.In order to reduce the circulating current and the symmetry of the circulating current generated by the parallel connection between the comprehensive treatment device and the diode rectifier,the positive and negative poles of the DC side are configured with filter inductors.In order to further reduce the influence of the circulating current,the thyristor with the positive and negative poles of the DC side is turned off during the harmonic and reactive power treatment mode,which can isolate the DC side of the device to block the circulating current.On this basis,the selection of switch tube,the design of filter and supporting capacitor parameters are also completed.The control system design of comprehensive treatment device.In the harmonic and reactive power treatment mode,the current loop is quasi-proportional-integral resonance control(quasi-PIR control)to improve the harmonic compensation accuracy.In the energy feedback mode,the outer voltage loop incorporates power feedforward to improve the dynamic response performance.The hysteresis control algorithm base on variable modulation wave quickly reduces the voltage unbalance at the neutral point.The modulation strategy is the equivalent SVPWM strategy,which has the advantages of small calculation amount and high utilization rate of DC voltage.Finally,using the simulation tool to verify the control system.The hardware and software design of the control system of comprehensive management device.In terms of hardware,the combination of FPGA+ARM is used as the core control,and analog sampling circuits such as voltage and current,digital I/O detection control circuit,and PWM drive circuit are designed.In terms of software,the control system algorithm is written with the ideaof modularization.System experimental verification.A 2k W low-power experimental platform was built,which was mainly composed of transformer,6-pulse rectifier,load resistor,DC power supply and comprehensive treatment device.And systematic experiments were carried out.The experimental results show that in the braking energy feedback mode,the device can stably feedback braking energy,and the AC feedback current THD is only 3.1%.In the harmonic and reactive power treatment mode,the power factor of the transformer valve side is increased from 0.954 to 0.992,the current THD of the valve side is reduced from 23.5% to2.4%,the transformer loss is reduced by 10.4%,and the DC voltage is increased by 3.48%.In addition,the effects of the neutral point voltage balance control algorithm,power feedforward and quasi-PIR control algorithm are also verified by experiments.The system experiment verifies the feasibility of the comprehensive treatment device,and provides certain experience for the follow-up development of high-power prototypes.