15-01-2013, 03:36 PM
Speed control of Brushless DC motor with DSP controller using Matlab
Speed control of Brushless DC motor.pdf (Size: 754.51 KB / Downloads: 134)
INTRODUCTION
The Brushless DC (BLDC) motor is rapidly gaining popularity by its utilization in various industries, such as appliances, automotive, aerospace, consumer, medical, industrial automation equipment and instrumentation. As the name implies, the BLDC motors do not use brushes for commutation; instead they are electronically commuted.. BLDC motors have many advantages over brushed DC motors and induction motors, a few of these are: [1]
a. Better speed Vs torque characteristics
b. High dynamic response
c. High efficiency
d. Long operating life
e. Noiseless operation
Before now, several simulation models have been proposed for the analysis of BLDC motors drives. In this paper we propose a simulation model of a BLDC motor without using a controller, whose characteristics are compared with a model with Integral and Proportional controller. In this model the trapezoidal back EMF waveforms are modeled as a function of rotor position and the switching function concept is adopted to model the Voltage source inverter (VSI). This in turn results in obtaining the detailed voltage and current waveforms of the inverter. Therefore, it can be expected that the developed simulation model can be an easy-to-design tool for the development of BLDC motor drives including control algorithms and topological variations with reduced computation time. II.
CONSTRUCTION AND OPERATING PRINCIPLE
The BLDC motor is also referred to as an electronically commuted motor and, as there are no brushes on the rotor the commutation is performed electronically depending on the rotor position. The stator phase windings are inserted in the slots or can be wound as one coil on the magnetic pole. Figure 1 shows the basic configuration of BLDC motor with converter circuit.
In DC Commutator motor, the current polarity is reversed by the commutator and the brushes, but in the brushless DC motor, the polarity reversal is performed by semiconductor switches which are to be switched in synchronization with the rotor position. Besides the higher reliability, the missing commutator brings another advantage. The commutator is also a limiting factor in the maximal speed of the DC motor. Therefore the BLDC motor can be employed in applications requiring high speed. Replacement of a DC motor by a BLDC motor place higher demands on control algorithm and control circuit. Firstly, the BLDC motor is usually considered as a three phase system. Thus, it has to be powered by a three phase power supply. Next, the rotor position must be known at certain angles, in order to align the applied voltage with the back-EMF. The alignment between the back-EMF and commutation events is very important. In this condition the motor behaves as a DC motor and runs at the best working point. But the drawbacks of the BLDC motor caused by necessity of power converter and rotor position measurement are balanced by excellent performance and reliability, and also by the ever-falling prices of power components and control circuits.
Fig.1: Configuration of BLDC motor with converter circuit
G Prasad, Venkateswara Reddy M, Dr. P V N Prasad, Dr. G Tulasi Ram Das / International Journal of
Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
III. MATHEMATICAL MODEL OF THE BLDC MOTOR
Modeling of a BLDC motor can be developed in the similar manner as a three-phase synchronous machine. Since there is a permanent magnet mounted on the rotor, some dynamic characteristics are different. Flux linkage from the rotor depends upon the magnet material. Therefore, saturation of magnetic flux linkage is typical for this kind of motors. As any typical three-phase motors, one structure of the BLDC motor is fed by a three-phase voltage source. The source is not necessarily to be sinusoidal. Square wave or other wave-shape can be applied as long as the peak voltage does not exceed the maximum voltage limit of the motor. Similarly, the model of the armature winding for the BLDC motor is expressed as follows: