en51 vector control of induction machines

7/31/2019 En51 Vector Control of Induction Machines

1/3N 51 - May 2006 - CEDRAT - CEDRAT TECHNOLOGIES - MAGSOFT Corp.

SOFTWARE>> - 3 -

TThe two requirements of theactive torque and rotor fluxgeneration induction machine

can be performed by the vectorcontrol method using flux, speedand currents regulators.This paper analyses direct vectorcontrol using two induction machinemodels. In the first, the inductionmachine is represented in thecontrol scheme by its circuit modeli.e. the equivalent design withconstant resistance and inductancevalues. The simulations using

this circuit model of the machineare performed using the Matlab/Simulink platform. The secondanalysis, based on the field model ofthe induction machine, is a couplingbetween the regulation system andthe finite element model of themachine. This connection is possibledue to the Flux software-Matlab/Simulink coupling

Control Scheme

The main components of thedirect vector control scheme in thefigure below are: the PWM inverter(PWM2), the current-angularvelocity estimator for the rotor flux(Rotor flux estimator), two blocksfor the axis transformations (ABC-DQ and DQ-ABC), regulatorsfor the flux, angular velocity andstator current components isd andisq (PI_flux, PI_speed, PI_isd,PI_isq).The principle of the direct vectorcontrol is to estimate the amplitudeand the position of the rotor fluxvector with respect to the fixed

reference system (, ).The amplitude and the position ofthe rotor flux are estimated using acurrent-angular velocity estimator.

Comparison Between Field and CircuitModels of Induction Machine Direct

Vector Control.P. DEACONESCU, V. FIRETEANU - Politehnica University of Bucharest.

Field model of theinduction machine

The numerical analysis refers to a2 pole, 3-phase induction machinecharacterized by a rated power of7.5 kW, rated voltage 380 V andrated frequency 50 Hz.The e l e c t romagne t i c f i e l dcomputation domain in figure 2represents half of the inductionmachine cross section. In the figurebelow, the corresponding Simulinkblock that reflects the finite element

field model of the induction machineis called Coupling with Flux2d V8VS.

Results of numericalsimulations

The results of the motor start-upwith and without load correspondingto the two mode l s o f theinduction machine are presentedcomparatively below. Firstly, theparameters of the four regulatorsin Table 1 are presented.

The flux and angular velocityreference values are set to 1.6 Wb,respectively 100 rad/s. Time step is

set to 1e-4 s.

Application 1:Direct vector control of

transient no-load start-up

The figures below present theresults of the no-load start-upregime of the induction machinefor the field and circuit models. Therotor flux module shows almost thesame variation in both models.The i

sdcomponent of the stator

current in the mobile coordinate

system (d, q), has approximatelythe same variation in both models,because the rotor flux modulecontrols this component.

The steady state values of theangular velocity, 110 rad/s in thefield model, figure 4, and 103rad/s in the circuit model, figure 5,are similar, but the steady state isreached 3 times faster in the circuitmodel.

Figure 1: Control scheme of the induction machine.Figure 3: Equivalent electric scheme of the induction machine

and the corresponding Simulink block.

Circuit model of the

induction machine

For the circuit model of theinduction machine, the blockCoupling with Flux2d V8 VS infigure 1 is replaced with the electricequivalent circuit in figure 3, fromthe SymPowerSystems Toolbox ofSimulink. The parameters of the

equivalent scheme have constantvalues, irrespective of time, currentand voltage and relative rotor-stator position.

Flux regulator Angular velocity

regulator

isd

regulator i sq

regulator

Kp

2000 8 105 105

Ki

2500 3 105 105

Table 1: The parameters of the regulators.

Figure 2: Electro-magnetic field

computation domainand the correspondingSimulink block.

(continued on page 4)



SOFTWARE>> - 4 -

Comparison Between Field and Circuit

Models of Induction Machine...(continued)P. DEACONESCU, V. FIRETEANU - Politehnica University of Bucharest (Romania).

In the field model, saturationis taken into account and therotor flux follows the non-linearmagnetic curve of the materials.Since the direct vector controlmethod requires a constant rotorflux, the operation of the fluxregulator is slowed down, and, thusthe dynamic regime of the angularvelocity is slower compared to thecircuit model.In the circuit model, the computationof rotor flux uses the equivalentscheme with constant values of

parameters and the saturation isnot taken into account.

The angular velocity controls thevariation of the torque and of theisq component of the stator current.Thus, the isq component falls to zerowhen angular velocity reaches thereference value.The magnetic torque increasesuntil the rotor flux reaches thereference value; then, the magnetictorque stabilises, (17 Nm in thefield model, figure 6, and 22 Nm,in the circuit model, figure 7) untilthe angular velocity reaches thereference value. The differencebetween the mean values of themagnetic torque obtained by thetwo models is explained by thevariation in the magnetic state ofthe induction machine.

Application 2:Direct vector control oftransient start-up with

load

The second direct vector controlapplication refers to the start-upof the motor with load. The loadtorque is applied at t = 0 s havinga value of 10 Nm. The results ofthe start-up with load regime of theinduction machine for the field andcircuit model are presented in thefigures below.

Again, there are insignificantdifferences between the timevariation of the isd component inthe models.

By studying the numerical resultsin figures 8 and 4 we note thatthe dynamic regime with load is2.5 times slower than the no-loadregime.

(continued on page 5)

Figure 4: Time variation of angular velocity(field model).

Figure 5: Time variation of angular velocity(circuit model).

Figure 7: Electromagnetic torque variation(circuit model).

Figure 6: Electromagnetic torque variation(field model).

Figure 9: Time variation of angular velocity(circuit model).

Figure 8: Time variation of angular velocity(field model).



SOFTWARE>> - 5 -

Comparison Between Field and Circuit

Models of Induction Machine...(continued)P. DEACONESCU, V. FIRETEANU - Politehnica University of Bucharest (Romania).

The steady state mean value of theisq component, figures 10 and 11,after the angular velocity reachesthe reference value, is higher inthe field model than in the circuitmodel.

Conclusions

This paper brings new contributionsto the study of the direct vectorcontrol scheme of the inductionmachine by using a Flux - Matlab/Simulink coupling.The field model takes into accountthe specific electromagneticphenomena of the induction machinesuch as armature slotting, magneticnonlinearity of laminations and slipdependent equivalent rotor circuitparameters. Thus this model ismuch more realistic for the studyof dynamic behaviour of the squirrelcage induction machine than thecircuit model in which the equivalentparameters of the electric scheme,resistances and inductances areconstant, irrespective of themachines operating conditions.Vector control algorithm performancedepends on the magnetic stateo f the induc t ion mach ine . Figure 10: Component isq of the stator

current (field model).

Figure 11: Component isq of the statorcurrent (circuit model).

A variation of the magnetic stateleads to fluctuations and deviationsin all mechanical and electricalquantities. As a result, we observethat the dynamic regime of angularvelocity, torque and stator currentsis slower in the field model comparedto the circuit model and theirnumerical values are different. Thedynamic regime of motor start-upwith load is slower than in the caseof no-load start-up.In variable-speed AC drives that usevoltage fed inverters, controlling the

voltage amplitude and frequencyoutput of the inverter feeding the

AC motor is essential for torque andspeed control of the machine. Usingthe direct vector control scheme,the stator currents can be controlledand kept constant to a referencevalue without producing substantialJoule losses. The chosen referencevalue of the angular velocity istwo times smaller than the ratedangular velocity in order to verifythe capacity of the control schemeto function at different angularvelocities.

Jobs at CEDRAT !!

Want to live in Grenobles mountains and

work in an high tech and continuously

growing company?

CEDRAT will open jobs both in the Sales team and inthe Application team by the end of the summer.Check regularly our website and apply [email protected].

en51 vector control of induction machines

Documents