Speed Control of Four-Switch Three-Phase Brushless DC Motor without Position Sensors
Date Issued
2008
Date
2008
Author(s)
Wang, Tzu-Chien
Abstract
This thesis proves the practicability of the low cost structure using a four-switch three-phase inverter without position sensors, and proposes a novel fuzzy PI control theory. Besides theory computation, the thesis also presents complete experimental results in proof of the theory. Decreasing the cost of the actuators is a tendency in the future. This thesis applies a novel asymmetric pulse width modulation (PWM) scheme and uses the structure of four-switch three-phase (FSTP) brushless dc (BLDC) motor drives to reduce the cost. This PWM scheme not only achieves the BLDC motor using FSTP inverter, but also does not require any current sensor and complex algorithm, so the lowest manufacture cost of the inverter could be achieved. First, this thesis applies a novel commutation control for the FSTP BLDC motor drive without using position sensors. This sensorless control detects the crossing point of two floating voltages, and estimates the appropriate commutation timing. It only requires two voltage sensors to reduce the cost of position sensors and increases the reliability of whole system. Furthermore, this technique reduces the numbers of power switches and doesn’t require any position sensor. When the brushless dc motor runs with or without Hall sensors, the frequency of the position signals depends on the rotor speed. Considering this phenomenon, the fuzzy PI controller including three fuzzy logics and three PI controllers is designed in this thesis. If the speed of BLDC motor varies, the fuzzy PI controller will trigger the defined PI controllers depending on the rotor speed and sum the weighted output of each PI controllers. Then it delivers the command to the inverter in order to modulate the duty cycle. This kind of fuzzy PI controller provides higher flexibility of design, and a more robust goal is accomplished. The fuzzy logic of the fuzzy PI controller designed in this thesis is based on the rotor speed, and therefore the controller reduces the complex of fuzzy logics and is easy to be implemented. Finally, the whole algorithm is implemented in a DSP. This thesis focuses on distinct sampling methods, and the experimental results with distinct conditions are compared and discussed.
Subjects
four-switch three-phase inverter
brushless dc motor
senseless control
digital signal processing
fuzzy control
variable sampling
Type
thesis
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