5.Speed Control OfPMBLDC Motor Using MATLABSimulink and Effects of Load

8/13/2019 5.Speed Control OfPMBLDC Motor Using MATLABSimulink and Effects of Load

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International Conference on Mechanical and Electrical Technolog (ICMET

Sp Conol oPBLDC oo sing ATLAB/Silin n cs o Lon Ini Cngs

V M VthjuResearch Scholar, Department of EEE,

Anna University, Chennai, IDIA,600 025,([email protected]).

MthuProfessor, Department of EEE

SSN College of Engineering, Kalavakkam,IDIA,603 110, ([email protected])

UdhykumAssistant Professor, Deparment of EEE,

Anna Universi, Chennai, IDIA, 600 025,([email protected]).

:Modeling and simulation of electromechanical

systems with machine drives are essential steps at thedesign stage of such systems. This paper describes the

procedure of deriving a model for the brush less dcmotor with 120-degree inverter system and its validation

in the MATLAB/Simulink platform. The discussion

arrives at a closed-loop speed control, in which PI

algorithm is adopted and the position-pulse

determination is done through current control for astandard trapezoidal BLDC motors. The simulation

results for BLDC motor drive systems conrm thevalidity of the proposed method.

Keywords: PMBLDC Motor, simulation and modeling,speed control.

I. INTRODUCTION

Recently, permanent magnet brushless dc motors(PMBLDCM) are widely used in many applications such asmotors, sensors, actuators, etc []. Permaent magnet motors

with trapezoidal back E and sinusoidal back EMF haveseveral advantages over other motor pes. Most notably,(compaed to dc motors) they are lower maintenance due to

the elimination of the mechanical commutator and they havea high-power densi which makes them ideal for high

torque-to weight ratio applications [2]. Compared toinduction machines, they have lower ineria allowing forfaster dynamic response to reference commads. Also, theyare more ecient due to the permanent magnets whichresults in virually zero rotor losses [3]. Permanent magnetbrushless dc (PMBLDC) motors could become seriouscompetitors to the induction motor for servo applications.The PLDC motor is becoming popula in vaiousapplications because of its high eciency, high power factor,high torque, simple control and lower maintenance [4]. Themajor disadvantage with permanent magnet motors is theirhigher cost and relatively higher complexi introduced bythe power electronic converter used to drive them. The addedcomplexi is evident in the development of a torque/speedregulator [5]. The magnetization directions and intensities

98-1-4244-8102-6/10/$26.00 C 2010 IEEE 54

are analyzed using nite element analysis with a detailedmagnetization procedure for ferrite bonded magnets used ininner-rotor pe BLDC motors [6]. The eect of statorresistace on average-value modeling of electromechanicalsystems consisting of BLDC motor and 120-deee invertersystems, including commutation current has been presented[7]. is shown that the model becomes more accurate bothin time and equency domains for the motors with largestator resistance (small electrical time constat of the stator

winding) pically operate with small commutation angle.Bhim sing, B P singh and Jain have proposed a digitalspeed controller for BLDCM ad implemented in a digitalsignal processor [8]. Later in 1998 peter vas has developedscheme to extract the rotor position ad the speed of BLDCmotor by Extended Kalman Filter (EKF) [9]. Jadric andB. Terzic have successlly adapted te Hall Eect sensor tosense the rotor position for eve 60 degree electrical [10].

Due to the extensive use of modeling and simulation adthe heavy reliance on their accuracy, both simulation speedand model accuracy are ve important. For the purposes ofstabili aalysis and controller design, it is oen desirable toinvestigate the large-signal trasients and small-signalcharacteristics of the system. Simulation studies are alsooen performed many times to achieve the required designgoals. In this study, the nonline simulation model of theBLDC motors drive system with proporional-integral (PI)control based on MATLAB/Simulink platform is presented.The simulated results in terms of elecomagnetic torque androtor speed are given.

II. NAATIVE OF PMBLDCM DRIVE

Fig.1 shows the pical BLDC motor controlled by ainverer. Typical Hall-sensor-conolled BLDC motors, suchas the one considered in this paper, is ve common. Theinverer converts a dc source voltage into 3-phase ac voltages

with equency corresponding to the rotor position and speed.This paper focuses on pical Hall-sensor controlled VSIdriven BLDC motors, where the inverer operates using 120-degree commutation method. Rotor position is sensed byHall Eect sensors embedded into the stator which gives the


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Inteational Conference on Mechanical and Electrical Technolog (ICMET

sequence of phases. Whenever the rotor magnetic poles passnear the Hall sensors, they give a high/low signal, indicatingthe N or S pole is passing nea the sensors. The three Hallsensors, , m ad are used to detect the rotor position.To rotate the BLDC motor, the stator windings should beenergized in a sequence. Based on the combination of these

three Hall sensor signals, the exact sequence of commutationcan be determined

ABH

bs-x

sFigure 1. BLC Motor controlled by the inerer

A. Closed Loop Control

Fig.2 describes the basic building blocks of thePLDCM drive system. The drive consists of speedcontroller, reference current generator, pulse widthmodulation (PWM) current controller, position sensor, themotor ad a IGBT based voltage source inverer (CC-VSI).The speed of the motor is compared with its reference valueand the speed error is processed in PI speed conoller. Theoutput of this controller is considered as the reference torque.

A limit is put on the speed controller output depending onpermissible maximum winding currents. The referencecurrent generator block generates the three phase reference

currents (i*, i*, ic*) using the limited pea currentmagnitude decided by the controller and the position sensor.The PWM current controller regulates the winding currents(i, i, i) within the small band aound the reference

currents(i*, i*, i*)' The motor currents are compaed withthe reference currents and the switching commands aegenerated to drive the power switches.

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Figure 2. PMBLDC motor drie system

The PI controller is widely used in indust due to itsease in design and simple structure. The rotor speed (n) is

compared with the reference speed n)* and the resultingerror is estimated at the n sampling instat as:

()

The new value of torque reference is given by

Tn Tn K K (2)Where, (n) is the speed error of previous interval,

and (n) is the speed error of te working interval. K adK ae the gains of proportional and integral controllersrespectively. By using Ziegler Nichols method the K and K

values are determined [].

B. Reference Current Generator

The magnitude of the reference current (*) is determined by

using reference torque (T*) and the back emf constant (K);

* *

= [2]. Depending on the rotor position, theKb

reference current generator block generates three-phase

reference currents (i*, i*, i*) considering the value of

reference current magnitude as *, * and zero. Thereference current generation is explained in the Table..

Table .Rotor position signal Vs reference current

Rotor Position Signal Reference Currents

r * * *

_ 60 * * 0

60 - 20 * 0 *

20 -80 0 * *80 - 240 * * 0

240 - 300 * 0 *300 - 360 0 * *


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C PWM Current ControerThe PWM current controller contributes to the generation

of the switching signals for the inverer switches. The

switching logic is formulated as given below.If i < (i) switch 1 ON and switch 4 OFF

If i> (i) switch 1 OFF and switch 4 ON

If i < (i) switch 3 ON and switch 6 OFF

If i> (i) switch 3 OFF and switch 6 ON

If i < (i) switch 5 ON and switch 2 OFF

If i> (i ) switch 5 OFF and switch 2 ON

III. MODELING

A. BackEMFThe phase back emf in the PLDC motor is trapezoidal

in nature and also a nction of the speed () and rotorposition angle () as shown in Fig.3.

Figure 3. Components of back E

The normalized nction of back emfs is shown in Fig.5.From this, the phase back emf e can be expressed as

f O) = E

fa (O)=6E/11-Or-E

f O) =-E

f O) = 6E / O,r 2 E

0< < 12012 0< O< 180 (3)

180< O< 300

300< O< 360

Where, E=Kb(r ad e can be described b E andnormalized back emf nction f) [ea = E fa (Or)] The back emf nctions of other two phases (e and e) canalso be determined in similar wa using E and thenormalized back emf nction f() and f().

IV. PMBLDC MOTOR AND INVERTER

The PLDC motor is modeled in the 3-phase abcame. The general volt-ampere equation for the circuitshown in the Fig can be expressed as:

545

Va eVb =Rib Ab ebc =Ric+pc+ec

(4)

(5)

(6)

Where, V V ad V are phase voltages and ma bedened as:

Vdc

Figure 4. nerter circuit with PMBLDCM drie

o o

Vbn= VbO- VnO'and

o o o.

(7)

Where V, V, V and V are three phase and neutralvoltages with respect to the zero reference potential at themid-point of dc link (0) shown in the Fig. R is the

resistance per phase of the stator winding, p is the timedierential operator, and e, ad e are phase to neutralback emfs. The , and are total ux linkage of phase

windings a, b and c respectivel. Their values can beexpressed as:

Aa LSia - M(ib + iJ (8)Ab Lsib - Ma + U (9)

(10)

Where, L and M e self and mutual inductancesrespectivel.

The PLDC motor has no neutral connection andhence this results in,

ia+

ib+

ic 0 (11)Substituting (11) in (8) (9) and (10) the ux linkages areobtained.

Ls Ls d Ls

(12)

B substituting (12) in volt-ampere relations (4)-(6) andrearranging these equations in a current derivative ofstatespace form, gives,

lI L s Va - - e a lILs Vb - - b

(13)

(14)


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as

pic= lI(Ls+M)(Vcn-Ric-ecn) (15)

The developed electromagnetic torque may be expressed

T w, (16)Where, '/ is the rotor speed in electrical rad/sec.

Substituting the back emfs in normalized form, thedeveloped torque is given by

T = K {f 8 f8 f8} (17)The mechaical equation of motion in speed derivative

form can be expressed as:

w, (P / T TL Bw/ J (18)Where, P is the number of poles, T is the load torque

in N-m, B is the ictional coecient in Nm/rad, and '1 isthe moment of inertia in kg_m

The derivative of the rotor position 9r) in state spaceform is expressed as:

O, w, (19)The potential of the neutral point with respect to the zero

potential (v) is required to be interpreted properly to avoidthe imbalance in applied phase voltages.This can be obtained by substituting (7) in (4) to (6) andadding them together to give

3 (20)Ls M

Substituting (11) in (20) results in

VaO + o + vo -3o (ean +ebn +ecn) o [VaO + o + vo - (ean +ebn +ec]/3 (21)The set of dierential equations viz. (13),(14), (15), (18)and (19) denes te developed model in terms of the

variables i, i, i, n and 9r for the independent vaiable, time.

V. SIMULATION SULTS this work the drive model with PI speed conoller isdeveloped and simulated in order to validate the model andthe designed controller. For conducting the studies andaalysis, this paper considers a pical industrial BLDCmotor (Arrow Precision Motor Co., LTD) with importancespecications: 2hp, 500rpm, 4 poles (Refer Appendix).Fig.5-2 shows simulated results.

$.dy $, Cn'

Figure 5. Stator phase currents

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Back l r the BLD m

n 1 jEb E

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5.Speed Control OfPMBLDC Motor Using MATLABSimulink and Effects of Load