Implementation of a direct torque controller using a three-level inverter for an electric vehicle application.

摘要

The University of Canterbury has been involved in the research and development ofelectric vehicles since 1974. These electric vehicles use induction motors that aredesigned with a low inductance such that they can run at high speed and therefore have ahigh power to weight ratio. The inverter switching can cause high current ripple due tothe low inductance of these motors. A three-level inverter has been previously developedfor electric vehicle applications that produces an improved voltage waveform andtherefore has reduced current distortion.This thesis describes the development of an induction motor torque controller for a three-levelinverter in an electric vehicle application. Four different induction motor torquecontrol schemes are considered. These are field oriented control, direct torque control(DTC), minimal torque ripple DTC, and DTC using space vector modulation. All four ofthe control schemes are simulated using MATLAB and Simulink, and DTC using spacevector modulation is chosen based on the simulation results. DTC using space vectormodulation is shown to have the low steady-state torque ripple, flux ripple, and currentdistortion that is characteristic of space vector modulation and the fast transientperformance that is characteristic of direct torque control. The implementation of DTCusing space vector modulation that is used is described in detail.DTC using space vector modulation is implemented on a custom-built embeddedcontroller based on a TMS320VC33 DSP and a XC4020XLA FPGA. Theimplementation of the control algorithms and a number of supporting softwarecomponents are also described.The implemented torque controller is tested against a 15hp, 400Hz, 200V inductionmotor. Results are presented that show the performance of the torque controller and thethree-level space vector modulator. The three-level space vector modulator is shown toproduce less current distortion at low modulation indices. The torque produced by thecontroller during steady-state operation differs from the reference torque, but this error isrelatively constant over the range of speeds that are tested. The estimated response tostep-changes in the torque and flux references are shown to be almost instantaneous.