Study On The Converter Of Urban Rail Vehicles Based On The Piecewise Improved Direct Torque Control

With the acceleration of the process of urbanization, the circumstance of traffic is becoming increasingly serious. As a focused developing traffic facilities, urban rail transit is serving to ease the pressure of city traffic issues. Because of the dependence on importing urban rail vehicle traction drive control systems, this paper carried out a research on traction of urban rail vehicles based on direct torque control.In this paper, the working mechanism of urban rail vehicle converter and the operation timing of main electrical had been illustrated explicitly, the position of voltage space vector obtained from the calculation and the analyzing of8kinds of switch states of inverter. Author also constructed a mathematical model of asynchronous traction motor and analyzed the influence of voltage space vector on stator flux and torque. Aiming at eliminates the existence of the DC deviation error of pure integrator, the paper proposes an improved cutoff frequency adaptive integrator to observing the stator flux linkage. Through the comparative analysis of hexagon stator flux trace and circular flux trace which illustrates a fact that in the low speed the circular flux torque ripples much more minor while the switching loss is lower in the high speed by choosing hexagon stator flux trace, the author proposes an improved direct torque piecewise control method. Dual norms based on speed and flux linkage locus has been proposed in order to solve the smooth transition of two control modes.The paper simulated both the hexagon flux track control and circular flux track control by using Matlab/simulink. And also established the improved direct torque segmentation control simulation model, detailed analysis shows that the model integrator can effectively suppress the DC and DC offset error. The improved transition mode control strategy can actualize the smooth transition between the two kinds of control methods.