Speed Sensorless Control for Four-Switch Three-Phase Brushless DC Motor

This dissertation proposes a novel asymmetric pulse width modulation (PWM) scheme for four-switch three-phase (FSTP) brushless dc (BLDC) motor drives. This PWM scheme not only achieves the BLDC motor using FSTP inverter, but also does not need any current sensor and complex algorithm, so it can make the lowest manufacture cost of the inverter. Furthermore, this dissertation proposes a novel commutation control for the FSTP BLDC motor drive without position sensor. This sensorless control detects the crossing point of two floating voltages, and estimates the commutation timing. This sensorless control only needs two voltage sensors, so it not only reduces the cost of position sensors, but also increases the reliability of whole system.
When the BLDC motor drive uses Hall sensors as position sensors, sampling rates of the rotor speed will change with the rotor speed of BLDC motors. The fuzzy PI controller presented in this dissertation includes three fuzzy logics and three PI controllers. When the speed of BLDC motors changes, fuzzy logics will give PI controllers suitable speed errors to achieve robust control. The fuzzy logic of the fuzzy PI controller presented in this dissertation is based on the rotor speed, and therefore the controller reduces the complex of fuzzy logics and is easy to be implemented.
Finally, we implement our novel asymmetric PWM scheme and novel sensorless control in DSP (Digital Signal Processor) which is designed by Texas Instruments, TI, incorporated and FPGA (Field Programmable Gate Array) which is designed by Xilinx to prove that the sensorless control does not need complex calculation, and can be implemented in very low cost controller.