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ELECTRIC DRIVES

CONVERTERS IN ELECTRIC DRIVE SYSTEMSMODULE 2

Dr. Nik Rumzi Nik IdrisDept. of Energy Conversion, UTM

2006

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CONVERTERS - Module 2

AC-DC controlled rectifierapproximate modelSIMULINK examples

open-loopclosed-loop

Switch Mode DC-DCconverter2-Q and 4-Q converters

Small signal modelingunipolarbipolar

SIMULINK example

Current-controlled for SMconvertersBridge converter

hysteresisfixed frequency3-phase VSI

hysteresisfixed frequencySVM-based

Assignment 1

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AC-DC controlled rectifier

+

Vo

+

Vo

cos

V2

Vm

o

90o 180o

m

V2

m

V2

90o

m,LLV3

m,LL

V3

cosV3

Vm,LL

o

For steady state continuous current flow

Average voltageover 10ms

Average voltageover 3.33 ms

50Hz1-phase

50Hz3-phase

180

o

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AC-DC controlled rectifier

firing

circuit

controlled

rectifier

+

Va

vc

va(s)vc(s) DC motor

The relation between vc and va is determined by the firing circuit

?

It is desirable to have a linear relation between vc and va

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AC-DC controlled rectifier

linear firing angle control

Input voltageVm

vtvc

0

2 3 4

Sawtooth compared with control signal

Results of comparison to trigger SCRs

Output voltage

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AC-DC controlled rectifier

linear firing angle control

Vm

vtvc

0

2 3 4

vc

ctvv

t

c

v

v

cosV2

Vm

a

t

cm

av

vcos

V2V

A non-linear relation between Va and vc

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AC-DC controlled rectifier

Cosine-wave crossing control

Vm

vsvc

0 2 3 4

Input voltage

Cosine wave compared with vc

Results of comparison trigger SCRs

Output voltage

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AC-DC controlled rectifier

Cosine-wave crossing control

Vm

vsvc

0 2 3 4

Vscos(t)Vscos() = vc

s

c1

v

vcos

cosV2

Vm

a

s

c1

ma

v

v

coscos

V2

Vs

cma

v

vV2

V

A linear relation between vc and Va

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AC-DC controlled rectifier

e.g. cosine wave crossing control

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AC-DC controlled rectifierControl model

Va is the average voltage over one period of the waveform- sampled data system

Delays depending on when the control signal changes normally takenas half of sampling period

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AC-DC controlled rectifierControl model

Va is the average voltage over one period of the waveform- sampled data system

Delays depending on when the control signal changes normally takenas half of sampling period

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AC-DC controlled rectifierControl model

s2

T

HKe)s(G

vc(s) Va(s)

s

m

V

V2K

Single phase, 50Hz

T=10ms

s

m,LL

V

V3K

Three phase, 50Hz

T=3.33ms

Simplified if control bandwidth is reduced to much lower than thesampling frequency

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AC-DC controlled rectifier

SIMULINK EXAMPLES

MATLAB v6.5, SIMULINK v5

SympPowerSystems toolbox

Open-loop control

Closed-loop control

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AC-DC controlled rectifierOpen loop

firing

circuit

controlled

rectifier

+

Va

vc

+

-v

+

-v

+

-v

Voltage Measurement1

+

-v

A

B

C

pulses

+

-

Universal Bridge

acos

Trigonometric

Function

alpha_deg

AB

BC

CA

Block

pulses

Synchronized

6-Pulse Generator

Step1

Step

Series RLC Branch

Scope2

Scope1

Scope

-K-

Gain

+i

-

Current Measurement1

+i

-

Current Measurement

sig

na

l

+ -

Controlled Voltage Source

DC motormodeled with

R-L and Vdc

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+

-v

+

-v

+

-

v

Voltage Measurement1

+

-v

A

B

C

pulses

+

-

Universal Bridge

acos

Trigonometric

Function

alpha_deg

AB

BC

CA

Block

pulses

Synchronized

6-Pulse Generator

Step1

Step

Series RLC Branch

Scope2

Scope1

Scope

-K-

Gain

+i

-

Current Measurement1

+i

-

Current Measurement

sig

na

l

+ -

Controlled Voltage Source

Three-phase AC source

Controlled rectifier

Load

Firing circuitscr_openloop_3phase.mdl

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AC-DC controlled rectifierClosed loop

firing

circuit

current

controllercontrolled

rectifier

+

Va

vciref

+

-v

+

-v

+

-v

+

-v

+

-v

A

B

C

pulses

+

-

Universal Bridge

acos

alpha_deg

AB

BC

CA

Block

pulses

Synchronized

6-Pulse Generator

Step

Signal

Generator

SeriesRLC Branch

Scope2

Scope

PID

PID Controller1

-K-

+i

-

+i

-

signa

l

+ -

5

Constant1

To control the current current-controlled converter

Torque can be controlled Only operates in Q1 and Q4 (single converter topology)

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+

-v

+

-v

+

-v

+-

v

+

-v

A

B

C

pulses

+

-

Universal Bridge

acos

alpha_deg

AB

BC

CA

Block

pulses

Synchronized

6-Pulse Generator

Step

Signal

Generator

Series RLC Branch

Scope2

Scope

PID

PID Controller1

-K-

+i

-

+i

-

sig

na

l

+ -

5

Constant1

closed_loop_unipolar_4q_with_id.mdl

Open-loop system from previous simulation

Closed-loop elements