A Novel Technique to Control the Speed of PM Brushless DC Motor for Electric Bike

Abstract

The work presented in this thesis deals with the simulation, design & development of the buck converter fed PM Brushless DC Drive. Speed of the motor is controlled by varying the D.C. Link voltage of the three phase inverter. Buck converter is used to vary the D.C. Link voltage of the inverter. By varying the duty cycle of the buck converter, output voltage of the buck converter is varied & consequently the speed of the motor is controlled. Simulation of the buck converter & PM Brushless DC Drive is carried out in the PSIM simulation tool. Pulses of the buck converter are generated by comparing triangular wave with that of the signal coming from the accelerator of the bike, which is the variable d.c. voltage. Buck converter is designed with the voltage & current ripples of 1%. Switching frequency considered in this work for the buck converter is 20 kHz. The simulation results of the 3-phase inverter are validated using resistive load as well as the driven motor. For the resistive load, three 120° phase shifted pulses are obtained from three phase transformer. Then these three sine waves are converted into square waves. Dead time between the pulses of the same phase MOSFETs is generated by triggering the Monostable Multivibrator on the positive edge of the input pulses & then by EX-ORING the triggering pulses with the positive edge triggered pulse. Driver I.C. being used for MOSFET is the IR 2110. MOSFETs being used are IRFP 240. Motor is first driven manually & observed the Hall-effect sensors signals, which are 120’ phase shifted. Opto coupler is used to invert the three output signals obtained from the Hall Effect sensors & finally 6-output signals are obtained. To remove the loading of the opto coupler on the Hall-effect sensor signals, Buffer I.C. 4050BC is used. Motor is driven on No-load & speed of the motor obtained at 90% duty cycle. The obtained maximum speed is 340 rpm. Speed is controlled from 200 rpm to 340 rpm by varying duty cycle between 60% to 90%.