Electrical Drives Ppt

ELECTRICAL DRIVES: An Application of Power Electronics Dr. Nik Rumzi Nik Idris, (Senior Member IEEE)

Department of Energy Conversion, Universiti Teknologi Malaysia Skudai, JOHOR

CONTENTS Power Electronic Systems Modern Electrical Drive Systems

Power Electronic Converters in Electrical Drives :: DC and AC Drives Modeling and Control of Electrical Drives :: Current controlled Converters :: Modeling of Power Converters :: Scalar control of IM

Power Electronic Systems What is Power Electronics ? A field of Electrical Engineering that deals with the application of power semiconductor devices for the control and conversion of electric power

Input Source - AC - DC - unregulated

Reference

sensors Power Electronics Converters

Load

Output - AC - DC

Controller

POWER ELECTRONIC CONVERTERS – the heart of power a power electronics system

Power Electronic Systems Why Power Electronics ? Power semiconductor devices

Power switches

isw ON or OFF +

vsw − =0 isw = 0

Ploss = vsw× isw = 0 + Losses ideally ZERO !

vsw −

Power Electronic Systems Why Power Electronics ? Power semiconductor devices

-

A

K

K

K

ia

Power switches

-

G

G

Vak

Vak

Vak

+

+

+ A

ia

A

ia

Power Electronic Systems Why Power Electronics ? Power semiconductor devices

Power switches

D

iD

C

ic

+

+ VDS

G

-

G

VCE -

S E

Power Electronic Systems Why Power Electronics ? Passive elements +

VL

-

iL

High frequency transformer

+

+

V1

V2

-

-

Inductor

+ iC

VC

-

Power Electronic Systems Why Power Electronics ? sensors

Input Source - AC - DC - unregulated

Reference

Power Electronics Converters

IDEALLY LOSSLESS Load !

Output - AC - DC

Controller

Power Electronic Systems Why Power Electronics ? Other factors: • Improvements in power semiconductors fabrication •

Power Integrated Module (PIM), Intelligent Power Modules (IPM)

• Decline cost in power semiconductor • Advancement in semiconductor fabrication •

ASICs

•

Faster and cheaper to implement complex algorithm

•

FPGA

•

DSPs

Power Electronic Systems Some Applications of Power Electronics : Typically used in systems requiring efficient control and conversion of electric energy: Domestic and Commercial Applications Industrial Applications Telecommunications Transportation Generation, Transmission and Distribution of electrical energy Power rating of < 1 W (portable equipment) Tens or hundreds Watts (Power supplies for computers /office equipment) kW to MW : drives

Hundreds of MW in DC transmission system (HVDC)

Modern Electrical Drive Systems •

About 50% of electrical energy used for drives

•

Can be either used for fixed speed or variable speed •

•

75% - constant speed, 25% variable speed (expanding)

Variable speed drives typically used PEC to supply the motors DC motors (brushed) SRM BLDC

AC motors - IM - PMSM

Modern Electrical Drive Systems Classic Electrical Drive for Variable Speed Application :

•

Bulky

•

Inefficient

•

inflexible

Modern Electrical Drive Systems Typical Modern Electric Drive Systems Electric Motor

Power Electronic Converters Electric Energy - Unregulated -

POWER IN

Electric Energy - Regulated -

Power Electronic Converters

Moto r

feedback

Reference

Controller

Electric Energy

Mechanical Energy

Load

Modern Electrical Drive Systems Example on VSD application Variable Speed Drives

Constant speed valve Supply

motor

pump

Power out Power In

Power loss Mainly in valve

Modern Electrical Drive Systems Example on VSD application Variable Speed Drives

Constant speed valve Supply

motor

Supply

pump

PEC

Power out Power In

motor

pump

Power out Power In

Power loss Mainly in valve

Power loss

Modern Electrical Drive Systems Example on VSD application Variable Speed Drives

Constant speed valve Supply

motor

Supply

pump

PEC

Power out Power In

motor

pump

Power out Power In

Power loss Mainly in valve

Power loss

Modern Electrical Drive Systems Example on VSD application Electric motor consumes more than half of electrical energy in the US

Fixed speed

Variable speed

Improvements in energy utilization in electric motors give large impact to the overall energy consumption HOW ? Replacing fixed speed drives with variable speed drives Using the high efficiency motors Improves the existing power converter–based drive systems

Modern Electrical Drive Systems Overview of AC and DC drives

DC drives: Electrical drives that use DC motors as the prime mover Regular maintenance, heavy, expensive, speed limit Easy control, decouple control of torque and flux AC drives: Electrical drives that use AC motors as the prime mover Less maintenance, light, less expensive, high speed Coupling between torque and flux – variable spatial angle between rotor and stator flux

Modern Electrical Drive Systems Overview of AC and DC drives Before semiconductor devices were introduced ( Vtri Vc < Vtri



t

t  Ttri

q dt

t on  Ttri

ton

Vdc

1 dTtri Va   Vdc dt  dVdc Ttri 0 0

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters d

0.5

vc -Vtri Vtri

vc

-Vtri

For vc = -Vtri  d = 0

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters d

0.5

vc

-Vtri

-Vtri Vtri

vc Vtri

For vc = -Vtri  d = 0 For vc = 0 

d = 0.5

For vc = Vtri 

d=1

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters d

0.5

-Vtri

-Vtri

vc

Vtri

Vtri

vc

1 d  0. 5  vc 2Vtri For vc = -Vtri  d = 0 For vc = 0 

d = 0.5

For vc = Vtri 

d=1

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Thus relation between vc and Va is obtained as:

Va  0.5Vdc 

Vdc vc 2Vtri

Introducing perturbation in vc and Va and separating DC and AC components:

DC:

Vdc Va  0.5Vdc  vc 2Vtri

AC:

Vdc ~ ~ va  vc 2Vtri

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Taking Laplace Transform on the AC, the transfer function is obtained as:

v a ( s) Vdc  v c ( s) 2Vtri

vc(s)

Vdc 2 Vtri

va(s)

DC motor

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Bipolar switching scheme Vdc

-Vdc

q vtri

vc

2vtri

+

Vdc

vA

Vdc + VAB

0

-

−

vc

Vdc vB

0

q

Vdc

v d A  0.5  c 2Vtri VA  0.5Vdc 

Vdc vc 2Vtri

v dB  1 - d A  0.5 - c 2Vtri VB  0.5Vdc -

Vdc vc 2Vtri

vAB -Vdc

VA - VB  VAB 

Vdc vc Vtri

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Bipolar switching scheme

v a ( s) Vdc  v c ( s) Vtri

vc(s)

Vdc Vtri

va(s)

DC motor

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Vdc

Unipolar switching scheme

vc

Leg b Vtri

-vc

+

vtri

Vdc

qa

vc

−

vA Leg a

vtri

d A  0.5 

vB

qb

-vc

vc 2Vtri

VA  0.5Vdc 

Vdc vc 2Vtri

dB  0.5  VB  0.5Vdc -

- vc 2Vtri Vdc vc 2Vtri

vAB

VA - VB  VAB 

The same average value we’ve seen for bipolar !

Vdc vc Vtri

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Unipolar switching scheme

v a ( s) Vdc  v c ( s) Vtri

vc(s)

Vdc Vtri

va(s)

DC motor

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters DC motor – separately excited or permanent magnet

di a v t  ia R a  L a  ea dt Te = kt ia

Te  Tl  J

dm dt

e e = kt 

Extract the dc and ac components by introducing small perturbations in Vt, ia, ea, Te, TL and m ac components ~ d i ~ ~ v t  ia R a  L a a  ~ ea dt

~ ~ Te  k E ( ia )

dc components Vt  Ia R a  Ea Te  k EIa

~ ~) ee  k E (

Ee  k E 

~) d( ~ ~ ~ Te  TL  B  J dt

Te  TL  B()

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters DC motor – separately excited or permanent magnet Perform Laplace Transformation on ac components ~ d i ~ ~ v t  ia R a  L a a  ~ ea dt

Vt(s) = Ia(s)Ra + LasIa + Ea(s)

~ ~ Te  k E ( ia )

Te(s) = kEIa(s)

~ ~) ee  k E (

Ea(s) = kE(s)

~) d( ~ ~ ~ Te  TL  B  J dt

Te(s) = TL(s) + B(s) + sJ(s)

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters DC motor – separately excited or permanent magnet Tl (s)

Va (s) + -

1 R a  sL a

Ia (s)

kT

-

Te (s)

1 B  sJ

+

kE

(s )

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters q

vtri Torque controller

Tc

+

+

Vdc –

−

q

kt

DC motor Tl (s)

Converter

Te (s)

Torque controller

+ -

Vdc Vtri,peak

Ia (s) 1 R a  sL a

Va (s)

+

kT

-

Te (s)

+

-

kE

1 B  sJ

(s )

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Closed-loop speed control – an example Design procedure in cascade control structure

•

Inner loop (current or torque loop) the fastest – largest bandwidth

•

The outer most loop (position loop) the slowest – smallest bandwidth

•

Design starts from torque loop proceed towards outer loops

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Closed-loop speed control – an example OBJECTIVES:

•

Fast response – large bandwidth

•

Minimum overshoot good phase margin (>65o)

•

BODE PLOTS

Zero steady state error – very large DC gain

METHOD

•

Obtain linear small signal model

•

Design controllers based on linear small signal model

•

Perform large signal simulation for controllers verification

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Closed-loop speed control – an example

Ra = 2 W

La = 5.2 mH

B = 1 x10–4 kg.m2/sec

J = 152 x 10–6 kg.m2

ke = 0.1 V/(rad/s)

kt = 0.1 Nm/A

Vd = 60 V

Vtri = 5 V

fs = 33 kHz • PI controllers

• Switching signals from comparison of vc and triangular waveform

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Torque controller design Open-loop gain Bode Diagram From: Input Point To: Output Point 150

kpT= 90 Magnitude (dB)

100

compensated

kiT= 18000

50

0

-50 90

Phase (deg)

45

0

compensated -45

-90 -2

10

-1

10

0

10

1

10

2

10

Frequency (rad/sec)

3

10

4

10

5

10

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Speed controller design

*

+ –

T* Speed controller

Torque loop

1

T

1 B  sJ



Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters Speed controller design Open-loop gain Bode Diagram From: Input Point To: Output Point 150

kps= 0.2 Magnitude (dB)

100

kis= 0.14

50

compensated

0

-50 0

Phase (deg)

-45

-90 -135

compensated

-180 -2

10

-1

10

0

10

1

10

Frequency (Hz)

2

10

3

10

4

10

Modeling and Control of Electrical Drives Modeling of the Power Converters: DC drives with SM Converters

Large Signal Simulation results 40 20

Speed

0 -20 -40

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

2 1

Torque 0 -1 -2

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

INDUCTION MOTOR DRIVES

Scalar Control

Const. V/Hz

Vector Control

is=f(r)

FOC

Rotor Flux

Stator Flux

DTC

Circular Flux

Hexagon Flux

DTC SVM

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

Control of induction machine based on steady-state model (per phase SS equivalent circuit):

Rs

Is

Llr’

Lls

+ Vs –

Lm

+ Eag

Im

Ir ’

–

Rr’/s

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Te Pull out Torque (Tmax)

Te

TL

Trated

s

Intersection point (Te=TL) determines the steady –state speed

sm

rated rotors

r

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

Given a load T– characteristic, the steady-state speed can be changed by altering the T– of the motor:

Pole changing Synchronous speed change with no. of poles Discrete step change in speed

Variable voltage (amplitude), variable frequency (Constant V/Hz) Using power electronics converter Operated at low slip frequency

Variable voltage (amplitude), frequency fixed E.g. using transformer or triac Slip becomes high as voltage reduced – low efficiency

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

Variable voltage, fixed frequency e.g. 3–phase squirrel cage IM

600

Torque

V = 460 V

Rs= 0.25 W

500

Rr=0.2 W Lr = Ls = 0.5/(2*pi*50)

400

Lm=30/(2*pi*50) f = 50Hz

300

Lower speed  slip higher Low efficiency at low speed

200

100

0

p=4

0

20

40

60

80 w (rad/s)

100

120

140

160

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant V/Hz

To maintain V/Hz constant Approximates constant air-gap flux when Eag is large

+ V

+ Eag

_

_

 ag = constant

Eag = k f ag



E ag f



V f

Speed is adjusted by varying f - maintaining V/f constant to avoid flux saturation

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant V/Hz 900 800 50Hz

700 30Hz

Torque

600 500 10Hz 400 300 200 100 0

0

20

40

60

80

100

120

140

160

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant V/Hz Vs Vrated

frated

f

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant V/Hz

Rectifier

3-phase supply

VSI

IM

C

f Ramp

s*

+

V

Pulse Width Modulator

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant V/Hz

In1 Out 1

Subsystem isd Va

isq

Out1

ird speed

0.41147 Step

Slider Gain 1

In 1

Rate Limiter

Out2

Vb

Vd

Scope

irq Out3

Constant V /Hz

Vq Vc

Te

speed

Induction Machine

To Workspace 1 torque To Workspace

Simulink blocks for Constant V/Hz Control

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant V/Hz 200 100

Speed

0 -100 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

400 200

Torque

0 -200 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200 100

Stator phase current

0 -100 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

Problems with open-loop constant V/f

At low speed, voltage drop across stator impedance is significant compared to airgap voltage - poor torque capability at low speed

Solution: 1. Boost voltage at low speed 2. Maintain Im constant – constant ag

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

700

600

50Hz

A low speed, flux falls below the rated value

Torque

500

400

30Hz

300 10Hz 200

100

0

0

20

40

60

80

100

120

140

160

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives With compensation (Is,ratedRs) 700

• Torque deteriorate at low frequency – hence compensation commonly performed at low frequency

600

Torque

500

400

• In order to truly compensate need to measure stator current – seldom performed

300

200

100

0

0

20

40

60

80

100

120

140

160

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

With voltage boost at low frequency Vrated

Linear offset

Boost

Non-linear offset – varies with Is frated

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Problems with open-loop constant V/f Poor speed regulation

Solution:

1. Compesate slip 2. Closed-loop control

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives

Rectifier

3-phase supply

VSI

IM

C

f Ramp

s*

+

+ +

Slip speed calculator

Vdc

Idc

V +

Vboost

Pulse Width Modulator

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives A better solution : maintain ag constant. How? ag, constant → Eag/f , constant → Im, constant (rated)

Rs

Is

Controlled to maintain Im at rated Lls Llr’ Ir ’

+

+ Vs –

Lm maintain at rated

Im

Eag –

Rr’/s

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant air-gap flux 900 800 50Hz

700 30Hz

Torque

600 500 10Hz 400 300 200 100 0

0

20

40

60

80

100

120

140

160

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant air-gap flux Im 

Im 

Im 

j L lr 

Rr s

Is

R j (L lr  L m )  r s j L r 

Rr s

   R j  r L r  r s  1  r  jslip Tr  1    jslip  r Tr  1  1  r 

Is

Is ,

   jslip  r Tr  1  1  r  Is  Im , jslip Tr  1 • Current is controlled using currentcontrolled VSI • Dependent on rotor parameters – sensitive to parameter variation

Modeling and Control of Electrical Drives Modeling of the Power Converters: IM drives Constant air-gap flux 3-phase supply

VSI

Rectifier

IM

C

Current controller

*

+

PI

-

slip +

r +

|Is|

s

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