Advanced Electrical Drives_unit1

8/12/2019 Advanced Electrical Drives_unit1

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ADVANCED ELECTRICAL DRIVES

UNIT-I

Prepared by

A.VENKADESANAP/EEE,SRM UNIVERSITY


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Introduction

A Motor with Power Electronics converter

forms a open loop drive.

A Motor with Power Electronics converter and

controller forms a closed loop drive.


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Introduction-Closed Loop Electrical

Drives


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Types of Electrical Drives

DC Motor Drives

AC Motor Drives

Special Motor Drives


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DC Motor Drives

Advantages

The control of DC Motor is simple.

Disadvantages

It is costlier

The dc motor requires regular maintenance


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AC Motor Drives

The AC motor in particular induction motor is

the workhouse of power industries.

The construction of IM is simple and requires

less maintenance.

Hence, induction motor drives are most

popularly used for variable speed control

applications.


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Converters for AC motor drives

AC voltage controllers - variable voltagecontrol

Cyclo-converters - Variable Frequency Control

Inverters V/F Control


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Types of Inverter

Three Phase six switch inverters

Three Phase four switch inverters

Multilevel Inverters Matrix Converters

Soft Switched based Inverters


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Modeling of Inverters

Modeling of inverter assumes importance for

effective analysis and control.


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Types of Modeling - Inverters

Switching function model

Average Model


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Switching Function for Inverters

The switching function modeling of inverters is

a powerful tool in understanding the

operation of inverters and for designing of

controllers.

The inverters are modeled using the switching

states.


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Switching States

The number of switching states depends on

the total number of legs present in the

inverter.

The states can be calculated using the formula

2k , where K is the number of legs.

6 switch 3 leg inverter three phase inverter23=8.


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Switching model of Three Phase Six

Switch Converter

1-denotes leg, 2-denotes switch number


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Switching Constraints

Switching Constraints (no two Switches on the

same leg should be on)

S11

+S12

=1; S21

+S22

=1; S21

+S22

=1


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Definition of Switching States

Leg A Leg B Leg C

S11 S12 Vao S21 S22 Vbo S31 S32 Vco

1 0 Vdc 1 0 Vdc 1 0 Vdc

0 1 0 0 1 0 0 1 0


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Switching States

StatesOn State

SwitchesSa Sb Sc Vao Vbo Vco Vab Vbc Vca Van Vbn Vcn

I S12S22S32 0 0 0 0 0 0 0 0 0 0 0 0

II S11S22S32 1 0 0 Vdc 0 0 Vdc 0 -Vdc 2/3Vdc -1/3Vdc -1/3Vdc

III S11S21S32 1 1 0 Vdc Vdc 0 0 Vdc -Vdc 1/3Vdc 1/3Vdc -2/3Vdc

IV S12S21S32 0 1 0 0 Vdc 0 -Vdc Vdc 0 -1/3Vdc 2/3Vdc -1/3Vdc

V S12S21S31 0 1 1 0 Vdc Vdc -Vdc 0 Vdc -2/3Vdc 1/3Vdc 1/3Vdc

VI S12S22S31 0 0 1 0 0 Vdc 0 -Vdc Vdc -1/3Vdc -1/3Vdc 2/3Vdc

VII S11S22S31 1 0 1 Vdc 0 Vdc Vdc -Vdc 0 1/3Vdc -2/3Vdc 1/3Vdc

VIII S11S21S31 1 1 1 Vdc Vdc Vdc 0 0 0 0 0 0


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Equivalent Circuit Indicating Vnobetween the two neutral point

Three Phase Inverter Three Phase Star Connected Load


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Derivation of Voltages across Load

Vao=Van+Vno----------------(1)

Vbo=Vbn+Vno ---------------(2)

Vco=Vcn+Vno----------------(3) Adding (1)+(2)+(3) and in balanced Three

phase system, Van+Vbn+Vcn=0;

Vao+Vbo+Vco=3Vno

(4)3

ao bo cono

V V VV


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Derivation of Voltages across the

Load

Sub in Vno in (1), (2), (3)

12

31

23

1 23

an ao bo co

bn bo ao co

cn co ao bo

V V V V

V V V V

V V V V


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Voltages across the Load in terms

of Switching Function

12

31

23

1 23

an ao a bo b co c

bn bo b ao a co c

cn co c ao a bo b

V V S V S V S

V V S V S V S

V V S V S V S


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Modeling of Three Phase Inverter

using MATLAB

Sinusoidal unipolar PWM schemes are used.

Vdc=717V

Switching Frequency=10KHz


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Modeling of Single Phase Inverter.

Assignment-I


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Assignment II

Realize the three phase inverter as a switching

model. Simulate the same using MATLAB in

such a way that the magnitude of the

fundamental component of line to line voltageshould be 3005%V. Assume switching

frequency as 15KHz. Use Sinusoidal unipolar

Switching scheme.


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Modeling of Induction Machine

Similar to inverter modeling, induction motor

can be modeled using mathematical

equations.


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Types of induction motor modeling

Steady State Modeling

Dynamic Modeling

Space Vector Model

dq Model

Before going to see about the dq modeling ofinduction motor, it is mandatory to know

about the Reference frame transformation

theory.


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Reference Frame Transformation

The use of reference frame theory can simplify

the analysis of electric machines.

It also provide a powerful tool for the digital

implementation of sophisticated

control schemes for ac drives.


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Reference Frames

Stationary Frame

Synchronous Frame


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Transformation of variables

between the two frames

abc(stationary) ab(stationary)

abc(stationary) dq(Synchronous Frame)


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abc (stationary) to dq

(synchronous)

2 4cos cos cos

3 32

3 2 4-sin -sin -sin3 3

a

d

b

q

c

xx

x

x x

where x represents either current, voltage, or flux linkage, and

is the angular displacement between the a-axis and d-axis of

the three-phase and two-phase reference frames

---------------------------------------------------------------------------------------(4)


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Variables in three-phase (abc) stationary frame

and two-phase (dq) synchronous frame


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(synchronous)

The three-phase variables,xa, xband xc, are in

the stationary reference frame which does not

rotate in space.

The two-phase variables, xdand xq, are in the

synchronous reference frame whose direct (d)

and quadrature (q) axes rotate in space at the

synchronous speed e. e= 2fs.

0

( ) ( )

t

et t dt


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(synchronous) (other formula)

2 2cos cos cos

3 32

3 2 2-sin -sin -sin3 3

a

d

b

q

c

xx

x

x x


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dq (rotatory) to abc (stationary)

cos -sin

2 2

cos - -sin -3 3

4 4cos - -sin -

3 3

a

d

b

q

c

xx

x xx

---------------------------------------------------------------------------------------(5)


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dq (rotatory) to abc (stationary)-

other formula

cos -sin

2 2cos - -sin -

3 3

2 2cos -sin3 3

a

d

b

q

c

x xx

xx


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MATLAB SIMULATION

abc to dq and dq to abc- MATLAB MODEL


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3/2 or 2/3 Stationary

Transformation

With the rotating speed of the two-phase reference frame set at zeroand its d-axis coincident with the a-

axis of the three-phase frame (e=0 and e = 0), both frames arestationary in space.

Sub e= 0 in equation (4) and (5),equation for 3/2 & 2/3 stationaryreference frames are obtained.


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abc (stationary) to ab (stationary)

1 11 - -

2 2 2

3 3 30 -

2 2

s a

d

bsq

c

xx

xxx


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ab (stationary) to abc (stationary)

1 0

1 3-

2 2

1 3- -2 2

a s

d

b s

q

c

xx

xx

x


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MATLAB SIMULATION

3/2 and 2/3 phase stationary. Model


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Problem 1 on Transformation

Find the voltages in two stationary reference frames

Solution
http://localhost/var/www/apps/conversion/tmp/scratch_2/Solution%20on%20problem%201.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_2/Solution%20on%20problem%201.ppt


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Transformation Theory

The transformation is valid only for the

balanced three phase system.

xa+ xb+ xc= 0


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If system is not balanced, what happens to the

equations

Answer is ZERO SEQUENCE COMPONENT

should be incorporated in the equation.

b ( ) d


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(synchronous) with zero sequence

component

2 2cos cos cos

3 3

2 2 2-sin -sin -sin

3 3 3

0.5 0.5 0.5o

d

q

x

x

x

a

b

c

x

x

x

d ( ) b ( i )


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dq (rotatory) to abc (stationary)

with zero sequence component

cos -sin 1

2 2

cos - -sin - 13 3

4 4cos - -sin - 1

3 3

a

b

c

x

xx

d

q

o

x

xx


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dq modeling of induction motor

D i E i l t i it f


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Dynamic Equivalent circuit for q-

axis

D i E i l t i it f d


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Dynamic Equivalent circuit for d-

axis


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Mathematical Equations

Stator side equations

Rotor side equations


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Flux Linkage equations


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Electromagnetic Torque Equations


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Mathematical Equations

S-laplace operator


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Dq Modeling in various frames

Stationary Frame; e=0 (stanley Equations)

Synchronously Rotating Frame; e= s

Rotor Reference Frame; e

= r


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dq modeling in various frames

Various Frames efor the

machine

Angle for

transformation

Stationary 0 0

Synchronous s Theta derived

from

synchronous

speedRotor r Theta derived

from rotor speed


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MATLAB SIMULATION

DQ MODEL IN VARIOUS FRAMES


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How to reduce switching loss

Decrease switching frequency by optimizing

performance.

Discontinuous PWM Techniques

Resonant Inverters


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Types of Resonant Inverters

Load Resonant Inverters

Resonant circuits in the load

Resonant Switch Inverters

Zero Current Switching

Zero Voltage Switching

Resonant dc link inverters

Resonant circuits in between dc input and inverter

Resonant ac link inverters

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