ABSTRACT: Brushless dc motors have only decades of history.They have been gaining attention from variousindustrial and household appliancemanufacturers because of its high efficiency, highpower density and low maintenance cost, silentoperation, compact form, and reliability. Thisproject describes the procedure of deriving a easymodel for the brush less dc motor with 120-degreeinverter system and its validation in theMATLAB/Simulink platform.

INTRODUCTION permanent magnet brushless dc motors are widely used in many

applications such as motors, sensors, actuators.

Permanent magnet motors with trapezoidal back EMF andsinusoidal back EMF have several advantages over other motortypes.

Most notably, (compared to dc motors) they are lowermaintenance due to the elimination of the mechanicalcommutator and they have a high-power density which makesthem ideal for high torque- to weight ratio applications.

Compared to induction machines, they have lower inertiaallowing for faster dynamic response to reference commands.Also, they are more efficient due to the permanent magnetswhich results in virtually zero rotor losses.

APPLICATIONS OF PMBLDCPermanent magnet brushless dc (PMBLDC)motors could become serious competitorsto the induction motor for servoapplications.

The PMBLDC motor is becoming popular invarious applications because of its highefficiency, high power factor, high torque,simple control and lower maintenance.

PROBLEM WITH THE PMBLDCThe major disadvantage with permanentmagnet motors is their higher cost andrelatively higher complexity introduced bythe power electronic converter used to drivethem.

The added complexity is evident in thedevelopment of a torque/speed regulator

PROPOSED CONCEPT

This project describes theprocedure of deriving a easymodel for the brush less dcmotor with 120-degree invertersystem which is overcome thedrawbacks of PMBLDC.

PMBLDC Motor Drive System

DESCRIPTION OF THE DRIVE SYSTEM The complete drive system is shown in aboveFigure.

It can be categorized into BLDC motor, Inverter, Current Controller, Speed Controller, reference current generator. Each block is modeled separately and integratedtogether.

Analysis Of BLDC Motor Drive System BLDC motor can be realized mathematically in twoways:-

abc phase variable model

And d-q axis model.

In a BLDC motor, the trapezoidal back EMF impliesthat the mutual inductance between stator and rotor isnon sinusoidal, thus transforming to d-q axis does notprovide any particular advantage, and so abc phasevariable model is preferred.

In the present model, the motor is assumed to be starconnected with isolated neutral.

ANALYSIS ASSUMPTIONSThe motor is not saturated.

Stator resistances of all the windingsare equal and self and mutualinductances are constant.

Power semiconductor devices in theinverter are ideal.

back-EMF generating Block as function of rotor angle

Closed-Loop Controller The BLDC motor is fed by a three phase MOSFET basedinverter. The PWM gating signals for firing the powersemiconductor devices in the inverter is injected from ahysteresis current controller which is required to maintainthe current constant within the 60interval of one electricalrevolution of the rotor.

It regulates the actual current within the hysteresis bandaround the reference currents. The reference currents aregenerated by a reference current generator dependingupon the steady state operating mode.

Cont……………. The reference currents are of quasi –square wave.They are developed in phase with the back-emf inmotoring mode and out of phase in braking mode.The magnitude of the reference current is calculatedfrom the reference torque.

The reference torque is obtained by limiting theoutput of the PI controller. The PI controller processeson the speed error signal (i.e. the differencebetweenthe reference speed and actual speed) and outputstothe limiter to produce the reference torque. Theactual speed is sensed back to the speed controllerand processed on to minimize the error in trackingthe reference speed.

Inverter Modeling The inverter supplies the input voltage for thethree phases of the BLDC motor.

It comprises of two power semiconductor deviceson each phase leg Appropriate pairs of FET’s(<1to<6 ) are driven based on the hall sensorsinput.

Three phases are commutated for every 60. Assensors are the direct feedback of the rotorposition, synchronization between stator androtor flux is achieved

Three phase inverter

CONCLUSION The non-linear simulation model of the BLDC motor drivesystem with PI control based on MATLAB/Simulinkplatform is presented.

The control structure has an inner current closed-loop andan outer speed loop to govern the current. The speedcontroller regulates the rotor movement by varying thefrequency of the pulse based on signal feedback from theHall sensors.

The simulation is used to predict the behavior of actualsystem. These predicted results can be used to determinethe range of parameters of controller while designing thesystem.

References [1] Vinatha U, Swetha Pola, “Simulation o f FourQuadrants Operation & Speed Control of BLDCMotor on MATLAB / SIMULINK”TECON 2008-2008IEEE region 10 conference.

[2] TJ.E. Miller, 'Brushless Permanent Magnet andReluctance Motor Drives.' Oxford SciencePublication, UK, 1989.

[3] RKrishnan, Electric Motor Drives: Modeling,Analysis, and Control,Prentice-Hall, Upper SaddleRiver, NJ, 2001.