Position and Speed Control of BLDC Motor using Hall Sensor

Position and Speed Control of BLDC Motor using Hall Sensor

Anisha C. G

Department of Electrical and Electronics Engineering, Sree Buddha College of Engineering,

Alapuzha, Kerala, India

Abhilasha Parthan Department of electrical and Electronic engineering Sree Buddha College of

Engineering, Alapuzha, Kerala, India

AbstractPermanent magnet brushless DC motor (PMBLDC) find wide applications in industries due to their high power density, high torque, little or no torque ripple, compact size, and precise position control. However, ripple-free precision control of brushless motors required precision position measurement. It cab be difficult to mount encoders directly to the shafts of these motors, and for precision position control, a sensorless configuration may be inappropriate. We propose a method of measuring rotor position using analog Hall Effect sensors to measure the magnetic field of the rotor magnets to create a computationally simple motor control scheme. Based on the rotor position, the power devices are commutated sequentially every 60 degrees. To achieve desired level of performance the PM motors requires PI-speed controller. The simulation of the proposed method was done using MATLAB software package in SIMULINK environment.

Index TermsBrushless dc motor (BLDC), Closed loop control, Hall Effect sensor.

1. INTRODUCTION

   The permanent magnet brushless DC (PMBLDC) motor is rapidly gaining popularity by its utilization in various industries, such as appliances, automotive, areospace, consumer, medical, industrial automation equipment and instrumentation [1]. As the name implies, the PMBLDC motors do not use brushes for commutation instead of they are electronically commutated. The principle of a PMBLDC motor is similar to that of a conventional DC motor but has better characteristics and performance as compared to the other motors. Using a PMBLDC is more advantageous as it reduces mechanical losses, has high efficiency, noiseless operation and improved speed-torque characteristics [2]. The major disadvantage of BLDC motor is their higer cost and relatively greater degree of complexity introduced by the power electronics converter [3]. The speed of the motor is directly proportional to the applied voltage across the winding.

   A BLDC motor has a rotor with permanent magnets and a stator with windings. The brushes and commutator have been eliminated and the windings are connected to the control electronics energize the winding with particular sequence of switching pulses [4]. The energized stator winding leads the rotor magnet, and switches just as the rotor aligns with the stator [5].

   This paper propose a simulation model with a PI controller, which is responsible to generate PWM pulses to inverter

   switching using hall sensor. The organization of this paper is as follows. Section II describes operation principle of BLDC motor. Section III describes proposed control scheme. Section IV presents the simulation results of the proposed method and section V presents the conclusion.

2. OPERATION OF BLDC

   A permanent magnet AC motor, which has a trapezoidal back EMF, is reffered to as brushless DC motor (BLDC) [6]. The BLDC drive system is based on the feedback of rotor system at fixed points for commutation of the phase current [7]. The BLDC motor requires quasi-rectangle shaped currents fed into the machine. Alternatively, the voltage may be applied to the motor every 120°, with current limit to hold the current within motor capabilities [8]. Because the phase current are excited in synchronism with the constant part of the back EMF, constant torque is generated. The electromagnetic torque of the BLDC motor is related to the product of phase, back EMF and current. The back emf in each phase is trapezoidal in shape and is displaced by 120 electrical degrees with respect to each other in three phase machine [9]. A rectangle current pulse is injected into each phase so that current coincides with the back EMF waveform. Hence the motor develops an almost constant torque. Figure: 1 shows the equivalent circuit of BLDC motor and inverter topology.

   Figure:1 Equivalent circuit of BLDC and inverter topology

   Assuming that stator resistance and inductance of all winding are equal, the voltage equations of BLDC motor can be expressed as

   Va ia

   ia ea Vn

   d

   Using a proportional and integral gain the error is amplified.

   V R i L

   i e V

   (1)

   The magnitude of error determines the duty ratio and

   b b

   Vc ic

   dt b b n

   ic ec Vn

   according to that output voltage of inverter varies and speed of motor is controlled.

   Where Vx, ix and ex (x=a, b, c) denote the terminal voltage, the phase current and the phase back EMF. R is the stator resistance and L is the stator inductance. Vn is the neutral voltage of Y-connection motor. The electromagnetic torque equation is given by

   1

   IV SIMULATION RESULTS

   The proposed control scheme is simulated in MATLAB/SIMULINK software. The motor parameters used for simulation is shown in Table.1. The informative results are

   Te eaia ebib ecic

   m

   (2)

   displayed in the following figures.

   TABLE 1

   BLDC motor parameter

   Where Te is the electromagnetic torque and m

   is the speed.

   Parameters	Values
   Voltage	500V
   No. of poles	2
   Torque constant	0.1 Nm/A
   Maximum speed	3500 rpm
   Resistance	2.8 ohm
   Inductance	8.5 mH
   Flux linkages	0.175

   Parameters	Values
   Voltage	500V
   No. of poles	2
   Torque constant	0.1 Nm/A
   Maximum speed	3500 rpm
   Resistance	2.8 ohm
   Inductance	8.5 mH
   Flux linkages	0.175

   Figure: 2 show the phase current and commutation sequence using hall sensor.

   Figure: 2 Phase current and commutation sequence

3. PROPOSED CONTROL SCHEME

The BLDC motor is used in electromechanical actuator in the real time applications. The electromechanical actuator should be controlled in closed loop where only speed loop is closed in this application. PI controller is used as a speed controller for recovering the actual motor speed to the reference. The reference and measured speed are the inputs to the controller. The contolled signal of PI-controller is fed to the six step inverter which is connected to the BLDC motor. The hall sensor sense the rotor position and corresponding gate signal is generated to switch the inverter. The block diagram of the control scheme is shown in figure. 3.

Figure: 4 Stator and electromotive force

m

ref

BLDCM

PI

PI

INVERTER

INVERTER

CONTROLLER

HALL SENSOR

HALL SENSOR

GATE SIGNAL

Figure: 3 closed loop control scheme

Figure: 5 Electromotive torque

V. CONCLUSTION

The proposed method of measuring rotor position using aalog hall effect sensor provide the portion of information need to synchronize the motor excitation with rotor position inorder to produce constant torque. It detects the change in magnetic field. The rotor magnets are used as trigger the hall sensors. The simulation of PI controller using MATLAB/SIMULINK to control the speed of flexible BLDC motor proves that the desired speed is attained with shorter response time. The characteristic of motor is obtained and the analysis reveals that is capable of controlling the motor drive over wide speed range.

Figure: 6 Rotor speed

Figure: 7 Line to line voltage

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