The effect of an active rectifier on motor drive system losses

Abstract

This thesis investigated the effect of replacing a passive diode bridge rectifier with an active rectifier in an electric motor system fed by converter and analysed its impacts on system losses and performance. Two converter configurations were developed and compared using MATLAB/Simulink. The first model consisted of a passive diode bridge rectifier connected to a voltage source inverter (VSI), where the inverter output voltage and frequency were regulated using an open-loop volts-per-hertz (U/f) control strategy to control the operation of the induction motor. The second model replaced the passive rectifier stage with an IGBTbased active rectifier while maintaining the same VSI and motor control parameters to provide a fair comparison between both systems. The AFE control system utilized synchronous reference frame control, where the DC-link voltage is regulated through directaxis current control while maintaining improved grid-side current quality. The benchmark used for comparison was a motor test setup. Both the simulation results were compared with those measured from the original motor test setup. The hardware setup motor had a nominal power of 2.2 kW. The performance indicators for the analysis included: the effect of active rectifier on grid side harmonics, effect on the DC ripple, converter losses, effect on the dynamic performance of the motor and effect on the power factor. The results showed that the active front-end converter significantly improved the grid-side performance by reducing harmonic distortion and achieving near-unity power factor compared to the passive diode bridge rectifier. In addition to that, the improved DC-link voltage regulation provided by the active rectifier enhanced motor drive performance by significantly reducing torque and speed ripple under different operating conditions. However, the additional controlled semiconductor devices and high frequency switching operation increased the converter losses. Therefore, the active rectifier provided improved power quality and controllability at the expense of increased converter losses.