Study on maximum torque generation for sensorless controlled brushless DC motor with trapezoidal back EMF. 指導教授 ： 王明賢. 學 生 ： 楊政達 . 南台科大電機系 . OUTLINE. Abstract Introduction Generation torque analysis of brushless DC motor
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Study on maximum torque generation for sensorless controlled brushless DC motor with trapezoidal back EMF
指導教授：王明賢
學 生：楊政達
南台科大電機系
The sensorless controlled brushless DC motor with trapezoidal back EMF has been studied. Since the detected position information on the sensorless rotor has some uncertainty, the brushless DC motor cannot be driven with a maximum torque.
To investigate the nature of torque in the sensorless controlled brushless DC motor, the torque characteristics as a function of commutation delay (or commutation timing error) have been analysed. It shows that the generation torque is influenced by the commutation delay and has a single maximum point. This maximum point is changed by the rotating speed and load conditions.
An iterative learning algorithm and a fuzzy logic controller areemployed to drive the brushless DC motor with maximum torque.
Permanent magnet brushless DC motors are appealing candidates for many high performance applications because of their attractive characteristics in such key categories as power density, torque-to-inertia ratio, power efficiency, robustness and reliability
The motor drive system requires a rotor position sensor to provide the proper commutation sequence. The position sensors such as resolvers, absolute position encorders and Hall sensors increase the cost and size of the motor.
The position detectionalgorithm using back EMF is a practical method for aposition sensorless controlled brushless DC motor.
The rotor position detection errors can be divided into the error deviation and group delay (average error). The error deviation increases the torque pulsation since it causes commutation imbalances. The group delay influences the average torque because it makes the commutation delay.
The results show that the commutation imbalances can be regulated and the firing angle is well adjusted to the position of the maximum torque in any case. It is well demonstrated from these results that the proposed control scheme provides the desirable performance of a sensorless controlled brushless DC motor.
2.1 System description and model equation
The generation torque and the phase currents in a brushless DC motor with trapezoidal back EMF are strongly influenced by the rotor position detection error since it cannot commutate the phase current at an optimal point.
As illustrated in this Figure, it is assumed that three stator phases occupy consecutive nonoverlapping 60°(elec.) phase belts along the stator airgap surface.
2.1 System description and model equation
Axial view of brushless motor including model for magnet radial flux density distribution
Generation torque analysis of brushless DC motor
2.1.1 Back EMF:
2.1.1 Back EMF:
2.1.2 BLDC motor drive system and model
2.1.2 BLDC motor drive system and model
2.2 Generation torque analysis
2.2.1 Typical commutation:
2.2.1 Typical commutation:
2.2.2 Lead commutation:
2.2.2 Lead commutation:
2.2.3 Lag commutation:
2.2.3 Lag commutation:
2.3 Torque–current ratio
2.3 Torque–current ratio
2.3 Torque–current ratio
Piecewise linear model of phase current
2.3 Torque–current ratio
2.3 Torque–current ratio