Modelling and Speed Control of Permanent Magnet Brushless DC Motor using PID

Author Name(s): Sonali Rangari, Gunwanti Shende, Preeti Kapoor
Author Email: rangaris@rknec.edu

Abstract

Trapezoidal flux distributed Permanent Magnet Brushless DC motor (PM-BLDC) has several advantages as compared to conventional DC and AC motor such as high speed, low weight-to-power ratio, high speed, electronic control, and low maintenance. The PM-BLDC motor also known as electronically commutated motor. Day by day usage of PMBLDC motor is increasing, so it is necessary to implement the control technique to control the motor performance parameter like torque, speed. This paper presents a modelling and speed control of three phase PM-BLDC motor. Modelling of PM-BLDC is derived with circuit equation and developed in MATLAB/Simulink model. The speed control strategy is tested on PM-BLDC motor and their performance is evaluated. This paper also shows that by using close loop strategy it is possible to control speed, torque, and rotor angle theta as per requirement.

Introduction

Permanent Magnet Brushless Motors has two types namely Permanent Magnet Synchronous Motor (PMSM) with a flux distribution is sinusoidal, and Permanent Magnet Brushless DC motor (PM-BLDC) with trapezoidal flux distribution. The PM-BLDC motor has a number of advantages over induction motors and brushed dc motors. There is less energy wastage in permanent magnet DC motor, hence the efficiency is very high. These motors have highly reliable with light weight, high torque handling capability, less maintenance and less noise. Due to mentioned advantages the motors are used in various applications such as HVAC, automotive, electronic, medical industries and electric vehicles PM-BLDC motor has trapezoidal back EMF, because of the non-sinusoidal dispersal of the self and mutual inductances in the middle of stator and rotor. There is no specific advantage in conversion of the ‘a-b-c’ equations of the PM-BLDC to the d-q form. Hence the solution of the original ‘a-b-c’ equations is proposed for the PM-BLDC motor [1]. The PM-BLDC motor can be categorized as an electronically commuted motor. With the help of rotor position electronically commutation is performed for PM-BLDC motor. As the rotor position changes simultaneously the polarity of the stator winding is also changed. This is performed by semiconductor switches which are to be switched in synchronization with the rotor position; this operation of motor improves its operating speed and area of applications. Due to rotation of rotor voltage is induced in the stator winding known as back-EMF of PMBLDC motor. So ideally, torque is primarily influenced by back-EMF of PM-BLDC motor. But practically the torque ripple exist mainly due to imperfection of back EMF, ripple of current and phase current commutation and the imperfection EMF is occurred due to the magnet size and shape of the PM-BLDC motor.This paper shows the modelling of PM-BLDC motor based on a-b-c equations of the PM-BLDC motor.

Conclusion

This paper presents the modelling and performance of three phase PM-BLDC motor at variable load condition. From the results it is found that this controller can very well work for variable speed and variable torque. It can be concluded that by using close loop strategy it is possible to control speed, torque, and rotor angle theta. The motor performance i.e. DC voltage, back EMF and stator current, speed and torque vary proportionally with desired performance. The Torque handling capacity of PM-BLDC motor is high. For the desire operation and control, use of PID controller is suitable for medium power drive system. The modelling method can be extended to any number of phases

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