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Paper

On

“ DESIGN OF NOVEL CONTROL SCHEME FORFOUR-SWITCH THREE PHASE INVERTER FED

PERMANENT MAGNET BRUSHLESS DC MOTOR

DRIVE ”

Submitted in the partial fulfillment of the requirements for the Degree of

Master of Technology in Electrical Engineering (Industrial Drives & Control)

Rashtra Sant Tukadoji Maharaj Nagpur University, Nagpur

Under the supervision of

Prof. K. RAMSHA (Superviser I)

Prof. M.A. GAIDHANE (Superviser II)

Submitted by:

Mr. SWAPNIL W. KHUBALKAR

Department of Electrical Engineering

PRIYADARSHINI COLLEGE OF ENGINEERING, NAGPUR

2011-2012



DESIGN OF NOVEL CONTROL SCHEME FOR FOUR-SWITCH THREEPHASE INVERTER FED PERMANENT MAGNET BRUSHLESS DC

MOTOR DRIVEMr. SWAPNIL W. KHUBALKARPRIYADARSHINI COLLEGE OF ENGINEERING, NAGPURDepartment of Electrical Engineering(M.tech)2011-2012

ABSTRACT

This project proposes a macro-model to simulate ofFour-Switch, Three-Phase Inverter (FSTPI) PM Brushless DC(PMBLDC) motor drive using switching functions. Theproposed model uses inverter switching functions instead ofactual circuits, and capable to show the whole steady state andtransient performance of the drive. An entire BLDC motordrive including power conversion unit, BLDC motor, current

and speed control system will investigate. The proposed modelwill simulate with the help of Matlab/Simulink software. Usingthis concept, it is possible to show the detailed electricalvariables, such as phase current, line and phase voltages anddiode an switch currents. Due to problems caused ofeliminating two power switches, Direct Phase Current (DPC)control method is carried out .

INTRODUCTION

Permanent Magnet Brushless DC(PMBLDC) motors are being used in automotive andhousehold applications due to their greater powerdensity, ease of construction. Moreover, for some

applications it is important to reduce themanufacturing cost of the PMBLDC motor drive.Cost reduction of PMBLDC motor drive is obtained

by reducing the number of power switches and alsoeliminating of the sensors. On the other hand,Prediction of an electric motor performance isnecessary for the evaluation characteristics of motordesigns and motor modeling.

STATE OF THE ART:

Simulation design is a preferred method inmotor designing compared to building motor

prototypes that is more costly and needs longer time.Available simulation softwares for electronic circuitsor dynamic systems can be classified into two maincategories: (1) circuit simulation programs such asPSpice (2) equation solver programs such as Matlab.These programs are not designed specifically for

power electronic systems so that the users have todevelop their own models to fulfill their needs. In this

project, the well-known modeling based onfunctional switching concept will be used to model

the whole of a four-switch PMBLDC motor drive andis implemented in Simulink software.

LITERATURE SURVEY:

A. Simulation of PMBLDC Motor WithSinusoidal Excitation Using Trapezoidal ControlStrategy ,The work reported concern with thesimulation of a sensor controlled PMBLDC motor forTrapezoidal and Sinusoidal excitations. For bothtypes of excitations Trapezoidal current controlstrategy is adapted. The simulated model is used tostudy the variation of speed, torque and current forvarious loads. A comparative study has been madefor both types of excitations.[1]B. Modelling and Simulation of Closed LoopControlled Buck Converter Fed Pmbldc DriveSystem , Permanent Magnet Brushless DC Motor(PMBLDC) is one of the best electrical drives thathas increasing popularity, due to their highefficiency, reliability, good dynamic response andvery low maintenance. This makes the interest ofmodeling an ideal PMBLDC motor and it’sassociated Drive System in simple and lucid manner.In this paper the drive system is proposed with a buckconverter topology. It has the advantages of reducedswitching losses, low inductor power loss, reducedripple by using a pi-filter, which in turn makes theDC link voltage to be stable[2]C. A simplified functional model for 3-phasevoltage source Inverter using switching functionconcept , In this paper, a functional model forvoltage-source inverter (VSI) using switching

function concept is studied and the actualimplementation of the model is proposed with thehelp of MATLAB Simulink. The switching functionconcept is a powerful tool in understanding andoptimizing the performance of the static powerconverters / Inverters[3]



RESEARCH OBJECTIVE:

In this research work , the primary aim todevelop model based on functional switchingconcept which shall be used to model the whole of afour-switch BLDC motor drive and is implemented in

Simulink software. Using this concept, it is alsoaimed to show he detailed electrical variables, suchas phase current, line and phase voltages and diodeand switch currents.

To proceed for the work it is planned to doanalysis of the system first to go for modeling in thenext steps. It can be elaborated as follows:

a) ANALYSIS OF FSTPI-BLDC MOTOR DRIVE.b) MODELING OF FSTPI-BLDC MOTOR DRIVE

BASED ON SWITCHING FUNCTION CONCEPT:Modeling of the system may involve to develop the

following model blocks:1. BLDC Motor Block.2. Current Control Block.3. Power Inverter Block.4. Speed Control Block.5. Switch and Diode Current calculator Block

c) SIMULATION OF FSTPI-BLDC MOTOR DRIVE.d) The work then can be finalize by reviewing the

results as per aim & objective decided.

PROJECT SCHEME METHODOLOGY:

Block diagram of switching function concept modeling fora four- switch pmbldc motor drive

Proposed block diagram for the systemcan be look as:

CONSTRUCTION

Fig. Disassembled view of a brushless dc motor

Figure. BLDC motor Transverse section

Fig. – Phase back-EMF, current and position Hall effectsensors waveforms of a three-phase BLDC motor

Above Fig. shows trapezoidal back-EMF, current

waveforms and position Hall Effect sensor signals ofa three-phase BLDC motor. To drive the motor withmaximum and constant torque, the phase currentsshould be synchronized with the corresponding phase

back-EMF voltages. Moreover, at each mode onlytwo phases are conducting and another phase isinactive. However, in a four-switch inverter, thegeneration of 120° conducting current waveforms isinherently difficult due to its limited voltage vectors .In order to use the four-switch inverter topology for athree-phase BLDC motor, Direct Phase Current(DPC) control method that was developed by B.K.Lee is employed . With employing this method, thecurrents of phases A and B in two modes 2 and 5 arecontrolled independently. Therefore, the back- EMFvoltage of phase C does not disturb the phase currentsas shown in Fig below.



(a)Mode1and2

(b) Mode 3 and 4

(c) Mode 5 and 6

Fig. – Current flow during two different modes in a four-switch (FSTPI) BLDC motor drive

MODELING OF FSTPI-BLDC MOTORDRIVE BASED ON SWITCHINGFUNCTION CONCEPTA. BLD C M otor Bl ock

The model of a BLDC consisting of three phases isexplained by means of equations, since there is noneutral used, the sum of the three phase currents mustadd upto zero, i.e.,

ia+ib+ic = 0ia+ib = - ic

Considering all the three phases following equationsare used to model the two pole three phase BLDCmotor.The PMBLDCM is represented in the form of a set ofdifferential equations given as,

where p is a differential operator (d/dt), i a, i b, ic arethree-phase currents , λ a, λ b, λ c are flux linkages and

ean, e bn, ecn are phase to neutral back emfs ofPMBLDCM, in respective phases, R is resistance ofmotor windings/phase.

If the permanent magnet inducing the rotor field iosin the shape of an arc, it requires that the inductances

be independent of the rotor position, hence:La = L b = L c = L s

Considering the symmetry of the above matrix in

addition to independence w.r.t the rotor position:Lab = L ba = L bc = L cb = L ca = L ac = MAbove equation reduces to:

From above two equations we get:

Rearranging the equations, we have obtainedequations in a form suitable for simulation.PMBLDC motor with new power converter topologyis given by Krishnan and Shiyoung (1997). Fourswitch three phase brushless motor for low costcommercial applications is given by Lee (2003).The flux linkages are represented as,

where L is self-inductance/phase, M is mutualinductance of motor winding/phase.The inputs of PMBLDC motor block are terminal

phase voltages and load torque. This block containsfour parts including back- EMF generator, currentcalculation, torque calculation and speed and positiondetermination. Back-EMF is a function of the rotor

position ( θ r ) having the amplitude of E=Ke× ώ m,that Ke is back-EMF constant and ώ m is themechanical speed of rotor. Based on the rotor



position; for example back-EMF of phase A can beexpressed as:

Back-EMF phase voltage can be implemented byusing of look-up table functions in Simulink.The phase currents can be obtained by revising of thedifferential equations as the following:

Therefore, the electromagnetic torque (T e) is obtainedfrom:

Where, Z P is the number of pole pairs. Electricalspeed of the rotor ( r ) is determined from thefollowing motion differential equation:

That T L , J and B are load torque, inertial momentand friction constant respectively. Rotor position inelectrical degree can be calculated from integration ofthe speed as:

θo is the initial position of the rotor. Hall effect position signals referring to Fig. can be obtainedusing function capabilities of Simulink as follows:

u(1) is the position of rotor.

SIX switch Inverter BlockUntil now, the reduced part converters have been applied mainly to ac induction motor drivesHowever, these days, the BLDC motor is attractingmuch interest, due to its high efficiency, high powerfactor, high torque, simple control, and lowermaintenance. Thus, we have been investigating the

possibility of the reduced part converter for BLDC

motor drives with advanced control techniques.Consequently, we found that one switch leg (twoswitches) in the conventional six-switch converter, asshown in Fig. 1, is redundant to drive a three-phaseBLDC motor. It results in the possibility of the four-switch configuration instead of the six switches, asshown in Fig. 2.

Fig. 1. Conventional six-switch three-phase BLDC motor drivesystems.

Fig. 2. Proposed four-switch converter topology for three-phase BLDC motor.

MODELING OF POWER INVERTER

BLOCK.

Power Inverter BlockThis block generates the terminal phase voltages ofBLDC motor using developed switching functions D a

and D b. Terminal phase voltage v xn is obtained as:

v xn = e x ; i x = 0

v xo −v no ; i x ≠0

where v xo and v no are the terminal voltage of phase xand star point of the motor respectively that must becalculated. Equation means that, when the phase

current is zero (silent phase), the terminal voltage isequal to phase back- EMF voltage. To obtain voltagevno, equation can be revised as:

vv

0=

0 00 00 0

+ − 0 00 − 00 0 −

+ +

vvv



Therefore, the voltage v no in each mode is asfollowing:

Moreover, the terminal voltages v ao and v bo areobtained as:

v =v

2. D

v =v

2. D

that V dc is the voltage across of DC-bus.

Simulink implementation

RESULT

Fig. graph of speed vs. time

REFERENCES:

[1] R. Somanatham , P. V. N. Prasad , A. D.Rajkumar ;”Simulation of PMBLDC Motor WithSinusoidal Excitation Using Trapezoidal ControlStrategy ” (ICIEA 2006) 0-7803-9514-X/06[2] S. Prakash , R. Dhanasekaran , Syed Ammal ;“Modelling and Simulation of Closed LoopControlled Buck Converter Fed Pmbldc Drive

System” Research Journal of Applied Sciences,Engineering and Technology 3(4): 284-289, 2011ISSN: 2040-7467[3] B. K. Lee , M. Ehsani ;”A simplified functionalmodel for 3-phase voltage source Inverter usingswitching function concept “ 0-7803-5735-3/1999[4] A. Halvaei Niasar, A. Vahedi, H. Moghbelli;“Analysis and Control of Commutation TorqueRipple in Four-Switch, Three-Phase Brushless DCMotor Drive”, Proceeding of the 2006 IEEEInternational Conference on Industrial Technology(ICIT06), pp.239-246, India.[5] A. Halvaei Niasar, H. Moghbeli, A. Vahedi;

"Modeling and Simulation Methods for Brushless DCMotor Drives", Proceeding of the First InternationalConference on Modeling, Simulation and AppliedOptimization (ICMSAO'05), pp.05- 6/05-6, February2005, Sharjah, U.A.E.[6] B.K. Lee, T.H. Kim, M. Ehsani; “On thefeasibility of four switch three-phase BLDC motordrives for low cost commercial applications:topology and control”, IEEE Transactions on PowerElectronics, Vol. 18, No. 1, pp. 164- 172, January2003.[7] B.K. Lee and M. Ehsani; “Advanced BLDCMotor Drive for Low Cost and High PerformancePropulsion System in Electric and Hybrid Vehicles”,2001 IEEE International Electric Machines andDrives Conference, 2001, Cambridge, MA, June2001, pp. 246-251.[8] B. K. Lee and M. Ehsani; “A simplifiedfunctional model for 3-phase voltage-source inverterusing switching function concept”, in Conf. Rec.

IEEE-IECON, pp. 462-467, 1999.[9] L. Salazar, G. Joos; “PSPICE Simulation ofThree-Phase inverters by Means of switchingFunctions”, IEEE Trans. On Power Electronics, Vol.9, No. 1,pp. 35-42 January 1994.[10] P. Pillay, R. Krishnan; “Modeling, simulation,and analysis of permanent-magnet motor drives. II:The Brushless DC Motor Drive”, IEEE Transactionson Industry Applications, vol. 25, No. 2, March/April1989, pp. 274-279.[11] A. Halvaei Niasar, H.Moghbelli, and A.Vahedi,”Sensorless control of a four -switch, three-

phase brushless DC motor drive”,presented at the

Iranian Conf. Electr. Eng. (ICEE 2007), May, IranTelecommun. Res. Center (ITRC), Tehran, Iran.[12] Sanjeev Singh , Bhim Singh , “A VoltageControlled Adjustable Speed PMBLDCM Driveusing A Single-Stage PFC Half- Bridge Converter”, 978-1-4244-4783-1/January 2010

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