Three-Phase Squirrel-Cage Induction Motor Drive Analysis .
University of South AustraliaSchool of Electrical and Information EngineeringThree-Phase Squirrel-Cage Induction MotorDrive Analysis Using LabVIEWTMA Thesis Submitted in Partial Fulfilment of the Requirementfor the Award of the Degree of Master Engineering (ElectricalPower Engineering)July 2006
ABSTRACTThis thesis will present three-phase squirrel-cage induction motor drive simulators usingthe graphical-language (G-language) of LabVIEWTM. Either abc or quadrature, direct andzero (qdO) machine models will be used in conjunction with sinusoidal and non-sinusoidalsupplies. Non-sinusoidal supplies will include three types of voltage source inverters(VSIs), namely, 1) six-step inverter with 180 conduction angle, 2) six-step inverter with120 conduction angle and 3) sinusoidal pulse-width-modulated (PWM) inverter. Twoseparate simulators are developed; one for the supply of the motor from a sinusoidalvoltage source, the other h m various types of non-sinusoidal voltage source. Themathematical models of the induction machine used in [l] have been adopted for theimplementation. Those mathematical models are in the form of differential equations andare solved using Runge Kutta 4fi order method. The performance of induction machinedrive is then presented into a set of output graphs. These output graphs permit the analysisof stator and rotor currents, stator and rotor flux linkages, electromagnetic torque, rotorspeed and torque-speed chamcteristics. LabVlEWTM has been chosen as the platform ofthis project because it is a flexible programming language combined with built-in toolsdesigned specifically for test, measurement and control.
CHAPTER 1Introduction1 .Evolution of Electrical Drive TechnologyThe technology of electrical drive has begun almost two centuries ago [I]. The history ofelectrical motor started when Hans Christian Oersted discovered the magnetic effect of anelectric current in 1820.In the following year, Michael Faraday discovered theelectromagnetic rotation and built the first primitive direct current P C ) motor. Faradaywent on to discover electromagnetic induction in 1831, but it was not until 1883 that Teslainvented the alternating current (AC) asynchronous motor [2].Currently, the main types of electric motors are still the same, DC, AC asynchronous andsynchronous, are all based on Oersted, Faraday and Tesla's theories. Historically, DCmotor, with its mechanical commutator and brushes, was the undisputed choice inindustrial application, primarily due to its inherent ability to provide independent torqueand speed control. AC asynchronous motor, also named induction motor, though veryrugged and easier to construct, their torque and speed control are more complicated.Induction motors are perhaps the most widely used of all electric motors. They offerreasonable asynchronous performance [3]: a manageable torque-speed curve, stableoperation under load and generally satisfactory efficiency.On an application where dynamic control is not an issue, the control requirement of the ACmachine drive has been done using constant voltshertz (V/f) technique. However, throughthe advancements of induction motor modelling, power electronic devices andmicroprocessors, the development of high performance AC drives has become a reality [4].Since that, two types of high performance AC drive, field oriented and direct torque controldrives have found a place in various applications that previously have been dominated andreserved for DC motors and drive systems.
1.2DC DrivesDC drives are used extensively in variable-speed drives because of their variablecharacteristics. DC motors can provide a high starting torque and it is also possible toobtain speed control over a wide range. Also, the methods of speed control are normallysimpler and less expensive than those of AC motors [5].In DC motor, the magnetic field is created by the current through the field winding in thestator. This field is always at right angles to the field created by the armature winding.This condition, known as field orientation, is needed to generate maximum torque. Thecommutator-brush assembly in the DC motor has ensures that this condition will bemaintained regardless of the rotor position. Once field orientation is achieved, the DCmotor's torque can be controlled directly by only varying the armature current and bykeeping the magnetising current constant. The torque response is fast since it can bechanged instantaneously by controlling the current supplied by the source [6].However, the main drawback of the DC motor is the uses of brushes and commutators havereduced the reliability of the DC motor. Since brushes and commutators will wear down,regular servicing is could not be avoided. Due to commutators, DC motors are not suitablefor very high speed applications and require more maintenance than do AC motors 15-71.13AC DrivesThe evolution of AC drive technology has been partly driven by the desire to emulate theperformance of the DC drive, such as fast torque response and speed accuracy, whilemaintaining the advantages offered by the standard AC induction motor which is robust,simple in design, low cost, light and compact. Rashid [5]has outlined several advantagesof AC drives which are lightweight, inexpensive and have low maintenance compared toDC drives.For variable-speed applications, AC motors require power converters and AC voltagecontrollers in order to control fhquency, voltage and current. These power controllers,
which are relatively complex and more expensive, require advanced feedback controltechniques such as model reference, adaptive control, sliding mode control and fieldoriented control. However, the advantages of AC drives outweigh the disadvantages.There are two types of AC drives namely, synchronous motor drives and induction motordrives [5,8].1.3.1 Synchronous motor drivesA brief explanation about synchronous motors is available in [5]. Synchronous motorshave a polyphase winding on the stator, also known as armature, and a field windingcarrying DC current on the rotor. There are two magnetomotive forces (MMF) involved;one due to the field current and the other due to the armature current. The resultant MMFproduces the torque. The armature is identical to the stator of induction motors, but there isno induction in the rotor.A synchronous motor is a constant-speed machine and always rotates with zero slip at thesynchronous speed, which depends on the frequency and the number of poles.Asynchronous motor can be operated as a motor or generator. The power factor (PF) can becontrolled by varying the field current.With cycloconverters and inverters, theapplications of synchronous motors in variable-speed drives are widening.1.3.2 Induction motor drivesThe three-phase induction motor is the work-horse of modem industry. Three-phaseinduction motors are commonly used in adjustable-speed drives and they have three-phasestator and rotor windings. There are two common types of induction machines, namely,squirrel-cage and wound-rotor.Squirrel-cage induction motors have a cylindrical rotor with short-circuited rotor windingswith the voltage supplied to stator windings. The rotor does not have a brush andcommutator but consists of conducting bars that are placed into the rotor slots. These barsare shorted by the shorting rings [I].
contrast, tne wound-rotor mduction motors have wye-connecied rotor wmdmgs. inaddition to the voltage that is applied to the stator windings, the phase voltages can besupplied to the rotor wmdrngs uslng brushes and slip nngs.inus, torque-speedcharacteristic could be shaped [I].However, wound-rotor induchon motors have not 6een wdely used because fheirefficiencyand maximal angular velocity are lower compared to squirrel-cage. On the otherhand, squml-cage mduchon motors have been tremendously used in hgh-performanceelectric drives and electromechanical systems. Therefore, in the case of the simulatordeveloped by the author and presented in this thesis, onfy three-phase squirrel-cageinduction motor drive will be presented.1.4Power Electronic DevicesPower electronic circuits are principally concerned with processing energy. They convertelectrical energy from the form supplied by a source to the form required by a load. Theseconversions are permitted by the switching characteristics of the power devices. Thepower electronics circuits can be classified into four types [9, 101:(i)AC-DC convertersAn AC-DC converter in which energy flows from the AC network to the DCnetwork is called a rectifier.(ii) DC-DC convertersThe DC-DC converter takes the DC output of the AC-DC converter andtransforms it to the different DC voltages required by the electronics. Inrelatively high power applications, such as traction, the DC-DC converter isknown as a chopper.
(iii) AC-AC convertersThis converter is used to obtain a variable AC output voltage fiom a fixed ACsource. This type of converter is also known as AC voltage controller.(iv) DC-AC convertersDC-AC converters are also known as inverter. The function of an inverter is tochange a DC input voltage to a symmetrical AC output voltage of desiredmagnitude and frequency. The output voltage could be fixed or variable at afixed or variable frequency. Inverters can be broadly classified either as voltagesource inverters (VSIs) or current-source inverters (CSIs),LabVIEWTM has been used as the platform in this project. LabVIEWTMis a moderngraphical programming language that is especially useful for controlling equipments andinstruments such as those used in research laboratories. Furthermore, LabVIEWTM is ascientific and engineering rapid application development environment specialized towardsdata acquisition, electronic measurement and control applications [l 11. LabVTEWTM canbe used to handle data acquisition in easier way compared to text based programminglanguage. It is known that fully functional data acquisition program can be created in just90 seconds [121.LabVIEWTM programs are called virtual instruments (Ws) [13]. Basically, there are threemain parts of a VI which are the b n t panel, the block diagram and the icon. The mainpurposes of the fiont panel are to get the input values and to view the outputs fkom the VIblock diagram. Each front panel has an accompanying block diagram. The block diagramcan be assumed as source code. Finally, the function of the icon is to turn a VI into anobject that can be used in the block diagrams of other VIs as if it were a subroutine.
The objective of the thesis is to build user friendly simulators in order to analyse theitransient behaviour and steady-state performance of a three-phase squirrel-cage inductionmotor drive. The simulators are also to serve as a teaching and learning aid in electricalmachine courses.1.7Structure of the ThesisThe work presented in this thesis is organised in five main chapters. These five chaptersare structured as follows:Chapter 1 reviews the evolution of electrical drive technology. A brief description aboutLabVIEWMis also discussed.Chapter 2 describes the dynamic modeling of three-phase squirrel-cage induction motorsusing abc and quadrature, direct and zero (qdO) quantities as well as non-sinusoiddsupplies from voltage source inverters (VSIs).Chapter 3 covers a general description of the design of the VI in order to associate themodelling of induction motor with graphic programming of the VI.Chapter 4 discusses performance analysis of electrical drives with different configurationsusing the simulators designed,Finally, Chapter 5 gives the conclusions of the thesis and the suggestion for further work asan extension of this study.All the block diagrams of the simulators are shown in Appendices.
CHAPTER 2Three-Phase Squirrel-Cage Induction Motor Drive2.1IntroductionThis chapter presents an overview of the principle of three-phase squirrel-cage inductionmotor drive. First, the model and the related equations of three-phase induction machineare described and presented in both abc and quadrature, direct and zero (qdO) machinemodels. Then the operation principles of six-step and pulsed-width-modulated (PWM)inverters are discussed.2.2Dynamic Model of Induction MachineThe steady state model of induction motor, which is represented by a steady equivalentcircuit shown in Figure 2.1 [5], describes only a steady state behavior of the inductionmotor. It was used when steady state analyses, such as efficiency, losses, steady statetorque, currents and fluxes are need to be evaluated. Designing the machine drives basedon this model will only produced a drive that normally has a poor transient performance[14]. When machine drives for high performance application need to be designed, a modelthat can describe the transient as well as the steady state behavior of the induction machineis needed. Therefore, by using the dynamic model, the transient behavior of the inductionmotor, which can not be analysed using steady state equivalent model, can be predicted andstudied.
Figure 2.1: Per-phase steady state equivalent circuit of induction motor [5]In developing the dynamic model of the induction motor, a few assumptions are made [2,151. These assumptions will only simplify the analysis and at the same time will not affectthe validity of the develop model.(i)The induction machine is considered as symmetrical two poles, three phasewindings.(ii)The winding on the stator is symmetrically distributed such that the spatialmagnetomotive force (MMF) produced is sinusoidal.(iii)The surface windings have negligible depth. The core is assumed to haveinfinite permeability.Hysteresis, eddy current and slotting effects can beneglected.The cross section of the machine with the above assumption is shown in Figure 2.2 [I].The magnetic axes of the stator is represented by ar, bs and cs while magnetic axes of therotor is represented by ar, br and cr. The angle between the rotor and stator axis isindicated by 8,. The mathematical model of three-phase induction machines using machinevariables has been derived in detail in [I].
bs magneticmas-? is/b e 2.2: Cross-section of elementary symmetrical three-phase induction motor [I]22.1abc machine model'This section develops the mathematical model of three-phase induction motors usingmachine variables. The goal is to find a set of dierential equations to map the dynamicsof induction machines in order to perform a thorough analysis of the transient behavior andsteady-state performance.Figure 23: Three-phase symmetrical induction motor [I]1The mathematical models presented here are adopted from [I]. All rotor parameters are referred tothe stator.
differential equations for the voltages that is applied to the abc stator and rotor windings,the abc stator and rotor currents, and flux linkages. With rotor parameters are referred tothe stator,where the abc stator and rotor voltages, currents and flux linkages are given in vector form,In Eq.(I), the diagonal matrices of the stator and rotor resistances are expressed as[::I: [::I:rs 0 rs 0 and rr 0 rr 0The flux linkages are found using the corresponding currents in the stator and rotorwindings and self and mutual inductances. The stator and rotor self inductances areL, L, L ,L, L,, L,where LI, and LITare stator and rotor leakage inductances while L, is stator magnetisinginductance. The matrices of self and mutual inductances between the stator windings, L,,and rotor windings, L, are found to be
(4)mutual inductances between the stator and rotor windingsare sinusoidal h c t i o n s o f the rotor angular displacement, 0,. Hence,cos 0,In particular, the analysis o f the stator and rotor magnetically coupled system, which can beaccomplished using Figure 2.3, leads to the following set of equationsFrom Eq. (6),explicit expressions for derivatives of Eq. (1) can be found.
Hence, the following sets o f voltage equations are obtained.di,1ubs rsi, --L,- (Lk2dr( :): L,mOr -dr--d l , l1u, rsie--L,---dib,L,- (L dtd r 22dicr L, m B r -dtdim L,)- ,mdtLP F)di,u, rrim LmcosBr- L,msdr ibr s i n k . - sin(.(Or --- L,cosi, sin B , i,IuW rri, L,(sin O ,( :); -0.1. - ( L , L , ) dim -;) i,sinkr f)Imr(Or--:---L,-1di,2dtdi,dr00s1dibrdt2--L,- (L, iWsin9,dr1di, ( L , L,)---L,- d r 2q)di, L,)--L,dr[ (or -i,sind r 2LWdt ) i,sink ) i sin ).(8)Eq. (8) is rearranged into Cauchy's form and is implemented for performance analysis ofinduction machines.
dtdihII1idldi,dt dimdrdibrdtdim-- dt cosB0rrL,cosCrL,cosArr -10000rL,mAL rL,cosCr L,cosC000jes000iorib,0--I,-r013 ' a,- 1.3 'm(DrLx,osin AL x m o r sin B ,a,- 1 . 3 a, 01.3 ' a,Lt,mrshCLz,msinALxma, sinB-1.3 ' nu a,r0Lzmm r sinBLz,a,sinCLzmw r sinAm rm r1i,rS -0rL,cosAjarrSrL,cosBsSrSr L,cosAsSrL,cosCr0rL,cosBsSr L,cosB-0-r1 . 3m r 0 1L LZnua, sin ALzmer sin B-Lx,mrshCLE,a,rm rsinCLz,a,rsin Brr0- 1 . 3m a, r1 . 3 a, 0-1.3 ' a,1.3 ' a,0Lzmm r sin ALzma r sinC1.3 'ma,rLzmm sin BLzmm sin A- 1 . 3 a, rrsin Cmrm rm rm*
where,'1, ( L LL F / L, L L / 3 , - L L L ,2nuThe expression for the torque developed by induction motor is obtained in order to find thenet torque. The electromagnetic torque for a two poles three-phase induction machine isfound using the expression for coenergy, Wc. In particular,where1 .T1-L/ l)iabcs iibcsLsr(Or)iabcr - i L ( L r - L/rl)ia 2wc T ' a b a & s(1 1)Solving Eq. (10) gives1.2im --IbrI -[im(ib1.2--Irn-Lim) ibS(ibr2-iw) i,(im -iar) ia6,,,1.22-Lim) im(im2 -!-im)]sinor--lbr-ibr)]mserThe equations of motion consist the mechanical parameters namely, moment of inertia, J,friction and damping coefficient, B, and load torque, TL,that describe the circuitrytransient behaviour are given asand
where or is the rotor angular velocity. Substituting Eq. (12) into Eq. (13) gives2.2.2gdO machine model2Lyshevski [ l ] has stated that the quadrature, direct and zero (qdO) machine model can beapplied to reduce the complexity of the resulting diffefential equations that map thedynamics of two-phase induction machines. In order to develop the mathematical model ofthree-phase induction motors in the stationary reference frame, three-phase inductionmachine with quadrature and direct magnetic axes is considered as shown in Figure 2.4 [ l ,141. The real and the imaginary axes of the stator are represented by ds and qs, while d rand qr are the real and the imaginary axis of the rotor.qs magneticFigure 2.4: Cross-section of the two poles, three-phase winding induction motor [1,141-The mathematical models presented here are adopted from [I]. All rotor parameters referred tothe stator in the stationary reference frame.
In the most general case, the model is developed in the arbitrary reference hme, and theframe angular velocity, a, is not specified. Since stationary reference frame model isapplied in this thesis, thus, the angular velocity is later to be assigned to zero, w 0.To transform the machine abc stator and rotor voltages, c u m t s and flux linkages to theqdO axis components, the following transformations are used.where the Park transformation matrix for stator and rotor, K, and K, are given as23K s - sin8 sin111andIn the stationary reference h e , one assigns o 0, and thus, 8 0. Therefore, the matrixthat needs to be applied in the stationary reference h m e is found as
COS Kssine .sink-5.1 f11[.) iRl -in) o1From Eq. (116), stator voltages in qd0 model are found to beL3331and can be simplified as211 --u,3 (t) - T U * (t)u, ( 0 -u,3 (I)1Uds ( 0 --ubs&1(t) - t ( ,45(f)The diffe ntialequations for the voltages from Eq. (1) can be transformed to qdOquantities by taking note the inverse Park transformation matrices,K;' and K;'Multiplying left and right sides of Eq. (21) by Y, and K, will finally results the voltageequations for stator and rotor circuits in the arbitrary reference frame,
The expressions fo
Three-Phase Squirrel-Cage Induction Motor Drive 2.1 Introduction This chapter presents an overview of the principle of three-phase squirrel-cage induction motor drive. First, the model and the related equations of three-phase induction machine are described and presented in both abc and
3.0 Dynamic Modeling of three phase squirrel cage Induction Motor for Speed Torque Analysis The dynamic modeling of three phase squirrel cage induction motor is done by using a simulink designed model for three phase induction motor fed by PWM inverter. Table IV: Parameters Description Table of three phase Squirrel Cage Induction Motor I L (Amp)
the supplier's works. Squirrel-cage and slip-ring motors in mechanical/electrical modifications: Three-phase motors for use aboard ships, squirrel-cage type 0.09 - 490 kW Three-phase motors to IEC/DIN, squirrel-cage type 0.06 - 500 kW Three-phase motors, squirrel-cage type 2.2 - 315 kW Three-phase brake motors 0.12 .
induction motor is more rugged and work more efficiently compared to wound-rotor induction motor. If supply voltage and frequency are constant, then a squirrel-cage induction motor runs at a constant speed which makes it suitable for use in constant speed drive [1, 2]. Several standard designs of squirrel-cage induction motors are
operating manual three-phase squirrel cage induction motors service instruction manual for squirrel - cage induction motor type s(k,l)g 56 80 a,b s(k,l)h 56 80 a,b (2)sie(k,l) 80-2a,4b www.elektropol-cantoni.com iso 9001 2013a-en rev 0 operating manual
Investigation of Broken Rotor Bar Faults in Three-Phase Squirrel-Cage Induction Motors 479 im s ii B Ñ Dn E 2BLv2 L 2 60 (1) where B im is the amplitude of the fundamental component and theith harmonic component,Eiis the effective value of voltage induce d by the fundamental air-gap flux and the ith harmonic air-gap flux,Dis the inner diameter of the stator core,nsis the
3.1 3-phase AC Induction Motor Drives The AC induction motor is a workhorse with adjustable speed drive systems. The most popular type is the 3-phase, squirrel-cage AC induction motor. It is a maintenance-free, less noisy and efficient motor. The stator is supplied by a balanced 3-phase AC power source. The synchronous speed ns of the motor is .
Chapter 1. Energy in the Wind Stream 1 1.1. Basic calculations 1 1.2. The Betz limit 2 1.3. Wind turbines' power characteristics 5 1.4. Exercises 9 Chapter 2. Squirrel-Cage Induction Generators 10 2.1. Analyzing the equivalent circuit 10 2.2. Wind energy conversion with squirrel-cage induction machines 17 2.3. Exercises 22 Chapter 3.
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