Direct Torque Control Algorithm For Three Level Traction Inverter Motor System

Direct torque control is one of the two main control methods in the field of electric traction drive.Compared with vector control technology,it has the characteristics of rapid dynamic response,simple control structure and high robustness.It is more suitable for the field of electric locomotives with extremely high torque response and complicated operating environment.The current high-speed locomotive control method is still the main vector control technology,so the direct torque technology research has great practical significance and economic value.The three-level inverter motor system which is used in the electric traction drive system has been chosen as the research object.Direct torque control algorithm were studied and analyzed in detail.Moreover refer to the data of the high-speed EMU,the feasibility and validity of the algorithm are verified by MATLAB/Simulink and RT-LAB experiment platform.The details are as followsFirstly,the characteristics of the three-level traction inverter are analyzed,and established the mathematical models.The relationship between the midpoint potential and the space voltage vector of the three-level traction inverter is further analyzed,and the realization idea and realization method of the SVPWM modulation algorithm of the three-level inverter are expounded.Then,the characteristics of the direct torque control algorithm are analyzed,and the change rate of output voltage and the balance problem of midpoint potential in the inverter are analyzed.The principle of vector sending in three-level structure inverter-motor system is summarized.Then the scheme of the observer is expounded,and the realization method of the DSC algorithm based on hexagonal flux trajectory is given.Secondly,according to the characteristics of asynchronous traction motor in different speed domain,a full-speed DTC scheme is designed.In order to make the locomotive can start quickly,the reference torque is large at beginning,as the speed increases,the reference torque decreases with a certain trend.When the traction motor speed close to the rated speed and the speed can not be increased,field weakening control is chosen to obtain the ability of increase speed.In the low-speed domain indirect stator-quantities control(ISC)algorithm with a circular flux trajectory is used.The ISC is based on predictive thoughts and SVPWM,the problem of start torque ripple could be avoid,so that the traction motor get better starting performance.To avoid the traditional direct torque algorithm to start torque ripple larger problem,so that traction motor starting more stable.In the medium-speed domain,The DSC algorithm of 18-Angular and 12-Angular flux trajectories.To solve the contradictions of the switching frequency,switching loss and the speed of traction motor.In high-speed domain field weakening control is chosen to expand the traction motor speed range.The problem of torque hopping for switching between different algorithms,the control strategy based on flux linkage and velocity is given.Finally,The hardware-in-the-loop experiment platform with TMS320F28335 DSP controller and RT-LAB.The feasibility and validity of the DTC scheme are verified on the experimental platform.