Stage 1 Prese

7/28/2019 Stage 1 Prese

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Vikrant MoreAkshay Mhalgi

Akshat Khanna


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Introduction

International Energy Agency (IEA) in its 2009report had mentioned that fossil fuel basedtransportation is the second largest source ofcarbon dioxide emission.

Several vehicle manufacturers haveintroduced hybrid electric vehicles forexample the Honda FCX, Toyota Prius, NissanLeaf.

The true potential of electric vehicles wasunleashed with the introduction of Tesla

Roadster, which offered significantly highermileage and performance comparable tocurrent gasoline versions in the market.

The Indian Government plans to pump in Rs23,000 crore for infrastructure, subsidies, car

finance for hybrids over the next eight years.

Nissan Leaf

Toyota Prius

Honda CR-Z


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Induction Motor vs. PMSM

In a typical driving cycle over a wide speed range, theinduction machine turns out to be more efficient ascompared to a permanent magnet machine which is moreefficient only at its peak efficiency operating point.


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Induction Motor vs. PMSM

China holds monopoly (97%production) over the rare earthmaterial Neodymium, the cost ofwhich has quadrupled over thepast few years.

Compared to the IPM, an IM motorcan tolerate a wide range oftemperatures. Consider thefollowing case - Providingadequate cooling for the ToyotaPrius's permanent magnet motor

adds significantly to the vehicle'sweight. An induction motor, bycontrast, can be cooled passively,thereby reducing weight.

Toyota Prius Cooling system


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Scalar control methods provide satisfactory steady stateperformance but poor dynamic response.

Vector Control : Both magnitude and phase of controlvariables are controlled. The aim of vector control is to

get the response from a induction motor similar to thatof a separately excited DC motor.

The machine control is considered in a synchronouslyrotating reference frame.

Sinusoidal quantities appear as dc quantities in steadystate.

With vector control, ids is analogous to field current & iqsto armature current of a dc machine and areorthogonal.

Induction Motor Speed Control


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d-q Model

Vector control drives are based on the dynamicd-q model of the machine.

In dynamic model, coupling coefficients

between stator & rotor phases vary with rotorposition. Such an analysis is complex.

Using Parks transformation, we refer statorvariables to a synchronously rotating referenceframe fixed in the rotor thereby eliminatingvarying magnetic reluctances .

For vector control drives, we transform threephase stationary reference frame into two phasestationary frame and then transform these into arotating reference frame.


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Direct versus Indirect Vector

Control Direct vector control

Also called feedback method, the flux vector is

obtained by means of direct flux measurement ofestimation.

Direct flux measurement is achieved using Hall Effectsensor.

The sensors need to be fixed in the stator slots and

add to the manufacturing cost of new motor.

Problems such as drift because of temperature, poorflux sensing at lower speed also persist.


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Direct versus Indirect Vector

Control Indirect vector control

The rotor flux vector position is computed from the

speed feedback signal of the motor. The difference between the reference speed and

the rotor speed is fed to the controller.

The controller computes the slip speed that onaddition to feedback motor speed provides the

speed of rotor flux vector from which the angle ofinclination of the rotor flux is computed.


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Rotor Flux Oriented Control

Rotor flux oriented will be used insteadof stator flux oriented control.

It does not require a de-coupler asrequired by stator flux control.

The dynamic response offered byrotor flux oriented control is better.

In, rotor flux oriented control, we willoperate the motor in the fieldweakening region (above basespeed).


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In stator flux orientation, ds is a function of both, ids and iqs ,as shown in the equation below-

Thus, there is a coupling effect and we need a decoupler.

Whereas, in rotor flux orientation,

It can be seen that, flux is only a function of ids and wedont require a decoupler.


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Indirect Vector Control

In indirect vector controlmethod, the unit vector signalsare fed in feed forwardmanner.

The synchronously rotating axis

de-qe is rotating ahead of thedr-qraxis by positive slip anglecorresponding to slipfrequency.

we=wr+wsl. This gives us the

value of

e upon integration


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Sense Speed& compare withreference.

GenerateTorque and Fluxreference

Generateids* fromFlux

reference

Estimate rotor flux

from reference ids

Generateiqs* fromTorquereference

SenseStatorcurrents &apply abc-dq

transformations

Calculate efor vectorrotation

Perform Vector Rotation(for orthogonality) anddq-abc transformation

Compare generatedcurrents with reference

in current controller

GenerateGate pulses

for inverter


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Use of PI Controller

In the indirect vector control implementation, to getthe reference torque we need to use a PI Controller.

Speed controller is required to keep the reference

speed equal to the actual speed, and provide gooddynamic response during transients.

Advantages of a PI controller are, it providesfeedback, eliminates steady state error, increases thedamping factor and reduces maximum overshoot.

Input is speed reference and output is given tohysteresis band controller, which gives torque asoutput.


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Estimator Equations

Iqs Estimator

Flux Estimator

Ids Estimator

Slip Frequency calculation

Theta

iqs* =


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Future Course

PI Tuning for Torque reference and developing currentcontrollers.

Calculate specifications for inverter.

Implement model on dspace.

Run algorithm on induction motor.


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Field Weakening Mode

Induction motor used isoperated above its basespeed, to get the requiredtorque-speed characteristics.

To achieve that, we operate itin the field weakening mode.

In the field weakening mode,the field flux is weakened toincrease the speed.


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THANK YOU

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