S.D. Sudhoff Fall 2005 - Purdue University

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EE595S: Class Lecture NotesChapter 15: Brushless DC Motor Drives

S.D. Sudhoff

Fall 2005

Fall 2005 EE595S Electric Drive Systems 2

15.1 Architecture

Fall 2005 EE595S Electric Drive Systems 3

15.2 Topology

Fall 2005 EE595S Electric Drive Systems 4

15.3 Equivalence of VSI Schemesto Idealized Source

• 180 VSI• Duty Cycle Modulation• Sine-Triangle Modulation• Sine-Triangle Modulation (with 3rd)• Space-Vector Modulation

Fall 2005 EE595S Electric Drive Systems 5

180 VSI Operation

Fall 2005 EE595S Electric Drive Systems 6

180 VSI Operation

Fall 2005 EE595S Electric Drive Systems 7

180 VSI Operation

Fall 2005 EE595S Electric Drive Systems 8

180 VSI Operation

• Comparing the two figures(15.3-1)

• Now recall(15.3-2)

(15.3-3)

hrc φθθ +=

dccqs vv π

2=

0=cdsv

Fall 2005 EE595S Electric Drive Systems 9

180 VSI Operation

• Using the frame-to-frame transformation(15.3-4)(15.3-5)

• Thus(15.3-6)(15.3-7)

hdcrqs vv φπ cos2=

hdcrds vv φπ sin2−=

dcs vvπ2

21

=

hv φφ =

Fall 2005 EE595S Electric Drive Systems 10

180 VSI Operation

Fall 2005 EE595S Electric Drive Systems 11

Duty Cycle Modulation

• In this case(15.3-8)(15.3-9)

• Thus(15.3-10)(15.3-11)

• So(15.3-12)

(15.3-7)

dccqs vdv π

2=

0=cdsv

hdcrqs vdv φπ cos2=

hdcrds vdv φπ sin2−=

dcs vdvπ2

21

=

hv φφ =

Fall 2005 EE595S Electric Drive Systems 12

Duty Cycle Modulation

Fall 2005 EE595S Electric Drive Systems 13

Sine-Triangle Modulation

• In this case, converter angle calculated as(15.3-13)

• Now recall

(15.3-14)

(15.3-15)

(15.3-16)

vrc φθθ +=

⎪⎩

⎪⎨⎧

>

≤<=

1)(

102

21

ddfv

dvdv

dc

dccqs

π

0=cdsv

( ) 11arccos21)( 4121

21 >⎟

⎠⎞

⎜⎝⎛

⎟⎠⎞

⎜⎝⎛−+−= d

dddf d π

Fall 2005 EE595S Electric Drive Systems 14

Sine-Triangle Modulation

• Converting to the rotor reference frame

(15.3-17)

• (15.3-18)

⎪⎩

⎪⎨⎧

>

≤=

1cos)(

1cos2

21

ddfv

ddvv

vdc

vdcrqs φ

φ

π

⎪⎩

⎪⎨⎧

>−

≤−=

1sin)(

1sin2

21

ddfv

ddvv

vdc

vdcrds φ

φ

π

Fall 2005 EE595S Electric Drive Systems 15

Sine-Triangle Modulation

Fall 2005 EE595S Electric Drive Systems 16

Sine Triangle Modulationwith 3rd Harmonic Injection

• Following our earlier work, we will have(15.3-19)(15.3-20)

3/20cos21 ≤≤= dvdv vdc

rqs φ

3/20sin21 ≤≤−= dvdv vdc

rds φ

Fall 2005 EE595S Electric Drive Systems 17

Space Vector Modulation

• In this case we have

(15.3-21)

(15.3-22)

(15.3-23)

⎪⎪⎩

⎪⎪⎨

<

=3/

3

3/

**

*

**

dcspkspk

rqsdc

dcspkrqs

rqs vv

v

vv

vvv

v

⎪⎪⎩

⎪⎪⎨

<

=3/

3

3/

**

*

**

dcspkspk

rdsdc

dcspkrds

rds vv

v

vv

vvv

v

( ) ( )2*2** rds

rqsspk vvv +=

Fall 2005 EE595S Electric Drive Systems 18

Modulation Summary

• For all VSI strategies, we have(15.3-24)(15.3-25)

• Where

(15.3-26)

vdcrqs mvv φcos=

vdcrds mvv φsin−=

( )( )⎪

⎪⎪⎪⎪⎪

⎪⎪⎪⎪⎪⎪

≥−

≤−

=

ο

3/vvs

3/vvvv

dd

ddf

dd

d

m

dc*spk

dc*spk

dc

spk

modulationvectorpace3

1

modulationvectorspace

)3/2( modulation harmonic-third

1) (modulation triangle-sine)(

1)( modulation triangle-sine

modulation cycle-duty

modulation source- voltage180

*21

221

2

2

π

π

π

Fall 2005 EE595S Electric Drive Systems 19

Modulation Summary

• Note, for space vector modulation(15.3-27))( ** r

dsrqsv jvvangle −=φ

Fall 2005 EE595S Electric Drive Systems 20

15.4 Average-Value Analysis of VSI Drives

• Average-value rectifier model(15.4-1)

• Where(15.4-2)

(15.4-3)

(15.4-4)

rrrrror iplirvv −−= αcos

rectifierphasesingle rectifierphase three

2

22

330

⎪⎩

⎪⎨⎧

=E

Evr

π

π

rectifierphase single rectifierphase three

2

3

⎪⎩

⎪⎨⎧

=ceu

ceur L

Lr

ω

ω

π

π

rectifierphase single rectifierphase three2

⎩⎨⎧

=c

cr L

Ll

Fall 2005 EE595S Electric Drive Systems 21

Working Out the Details…

Fall 2005 EE595S Electric Drive Systems 22

Final Average Value Model

• Nonlinear Average Value Model (NLAM)

(15.4-21)( )

⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢⎢

−−+−

−−

+

⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢⎢

⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢

′−

−−

−−

−−−

=

⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢⎢

))((sin

cos00

)sin(coscos

000000000000

00000

00000000000000000000

2231

2

1

1

23

01

1222

3

'

1

11

11

1

Lr

dsr

qsqdP

JP

rqsrL

LvdcL

rdsrL

LvdcL

rdsv

rqsvC

mrL

r

rds

rqs

st

st

dc

r

mJP

Lr

q

mLr

C

LLr

L

CC

LLr

r

rds

rqs

st

st

dc

r

TiiLLimv

imv

iiv

iivivi

Liivivi

p

d

q

d

q

d

q

dc

rl

d

s

q

s

st

stst

st

st

dcdc

rlrl

rl

ωφ

ωφ

φφα

ωλ

λ

ω

Fall 2005 EE595S Electric Drive Systems 23

NLAM Startup PredictionFigure 15.6-2

Fall 2005 EE595S Electric Drive Systems 24

Detailed Startup PredictionFigure 15.6-1

Fall 2005 EE595S Electric Drive Systems 25

Steady-State Performance of VSI Drives

• For Steady State Conditions(15.5-1)

• From Our Earlier Work(15.4-14)

• Thus(15.5-2)

• The Steady-State Stabilizing Current is Zero So

(15.5-3)

rrldcr IrVv −−= αcos0 0

)sincos(23

vrdsv

rqsdc iimi φφ −=

)sincos(0 23

vrdsv

rqsstr IImII φφ −−−=

)sincos(0 23

vrdsv

rqsr IImI φφ −−=

Fall 2005 EE595S Electric Drive Systems 26

Steady-State Performance of VSI Drives

• Combining (15.5-3) with (15.5-1) yields(15.5-4)

• From the Machine Voltage Equations(15.5-5)(15.5-6)

)sincos(cos 23

0 vrdsv

rqsrlrdc IImrvV φφα −−=

mrrdsdr

rqssvdc ILIrmV λωωφ ′−−−= cos0

rqsqr

rdssvdc ILIrmV ωφ +−−= sin0

Fall 2005 EE595S Electric Drive Systems 27

Steady-State Performance of VSI Drives

• Solving (15.5-5) and (15.5-6) for the Currents

(15.5-7)

(15.5-8)

qdrs

vdcdrmrvdcsrqs

LLrmVLmVrI 22

sin)cos(ω

φωλωφ+

+′−=

qdrs

vdcsmrvdcqrrds LLr

mVrmVLI 22

sin)cos(

ω

φλωφω

+

−′−=

Fall 2005 EE595S Electric Drive Systems 28

Steady-State Performance of VSI Drives

• Substitution of (15.5-7) and (15.5-8) into (15.5-4) and Solving Yields

(15.5-9)

• Caution: This Expression Only Valid if DC Current (15.5-14) Is Positive

vqdrrlsrlqdrs

vqrvsmrrlrqdrsdc

mLLrrrmLLr

LrmrvLLrV

φωω

φωφλωαω

2sin)(

)sincos(cos)(2

432

2322

23

022

−+++

−′++=

Fall 2005 EE595S Electric Drive Systems 29

Steady-State Performance of VSI Drives

• Suppose the DC Current from (15.5-14) is Negative

This Can’t HappenThus

• (15.5-10)

Substitution of (15.5-7) and (15.5-8) Into (15.5-10) Yields

• (15.5-11)

0sincos =− vrdsv

rqs II φφ

)2sin)((

)sincos(

210

vqdrs

vqrvsmrIdc LLrm

LrV dc φω

φωφλω

−+

−′==

Fall 2005 EE595S Electric Drive Systems 30

Steady-State Performance of VSI Drives

• Solution Algorithm1. Calculate DC Voltage Using (15.5-9)2. Calculate QD Currents Using (15.5-7); (15.5-

8)3. Calculate DC Current Using (15.5-14)4. If DC Current >= 0, Goto 75. Calculate DC Voltage Using (15.5-11)6. Goto 27. Done

Fall 2005 EE595S Electric Drive Systems 31

Steady-State Performance of VSI Drives

Fall 2005 EE595S Electric Drive Systems 32

15.6 Transient Performance of VSI Drives

• Linearizing (15.4-21) We Have

(15.6-1)

[ ]

( ) ( )

⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢

∆∆∆∆∆

⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢

−−

+

⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢⎢

∆∆

∆∆∆∆∆

⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢

−−+′

−+−

−−−−

−−

−−

−−

=∆∆∆∆∆∆∆

+−

L

v

ro

JP

vLmv

vLv

vLmv

vLv

Ciim

Cii

LLv

r

rds

rqs

st

st

dc

r

rqsqdJ

PrdsqdmJ

P

rqsL

LLr

rLL

vLm

LrdsL

LrL

LLr

vLm

Cst

LstLstr

Lst

vCm

vCm

CC

LLr

Tr

rds

rqsststdcr

T

mv

iivivi

iLLiLL

i

i

iivivip

d

dc

d

dc

q

dc

q

dc

dc

rdsv

rqsv

dc

rdsv

rqsv

rlrl

r

d

q

d

s

d

q

d

q

m

q

d

q

d

q

s

q

stdcdcdcdc

rlrl

rl

φ

α

φφ

φφ

ωλ

ωφ

ωφ

φφ

ω

φφφφ

α

λ

cos

0000

0cossin00

0sincos000000000000000

000

0)())((0000

00sin0

00cos0

0000000000

0sincos00

00000

12

00

00

)cos(sin23)sin(cos

23

cos

012

223

012

223

000

000

1

11

023

02311

1

000

000

000000000

00

0

0

00

Fall 2005 EE595S Electric Drive Systems 33

Transient Performance of VSI Drives

• In (15.6-1), Note that(15.6-2)xxx ∆+= 0

Fall 2005 EE595S Electric Drive Systems 34

Predictions of Linearized ModelStartup

Fall 2005 EE595S Electric Drive Systems 35

Predictions of Detailed ModelStartup

Fall 2005 EE595S Electric Drive Systems 36

Predictions of Linearized ModelStep Change in Duty Cycle

Fall 2005 EE595S Electric Drive Systems 37

Predictions of Detailed ModelStep Change in Duty Cycle

Fall 2005 EE595S Electric Drive Systems 38

15.8 Case Study: VSI Based Speed Control

• Parameters

• Design ObjectivesLoad is InertialNo Steady-State ErrorPhase Margin of 60o at Nominal Speed of 200 rad/s(mechanical)

E 85.5 V

euω 377 rad/s

cL 5 mH

dcL 5 mH

dcC 1000 Fµ

J 5 mN!m!s2

sr 2.98Ω

qL 11.4 mH

dL 11.4 mH

mλ ′ 0.156 Vs

P 4

Fall 2005 EE595S Electric Drive Systems 39

Control Law

• Mathematically

(15.8-1)∫ −+−= ∗∗ dtKd rmrmK

rmrm )()( ωωωω τ

Fall 2005 EE595S Electric Drive Systems 40

Starting Point: Open Loop Frequency Response

• ObserveGain Margin is InfinitePhase Margin is 20o

Fall 2005 EE595S Electric Drive Systems 41

Selection of τ

• Integral Feedback Will Decrease Phase By 90o at Frequencies Less Than 1/(2πτ)

• We Will Select Breakpoint Frequency at 0.01 Hz for τ of 16 s

Fall 2005 EE595S Electric Drive Systems 42

Compensated Frequency Response

Fall 2005 EE595S Electric Drive Systems 43

Selection of K

• Select K to Achieve Phase Margin of 60o

• Thus, We Choose K=0.25 (-12 dB)

Fall 2005 EE595S Electric Drive Systems 44

Compensated Frequency Response

Fall 2005 EE595S Electric Drive Systems 45

Time-Domain Response

Fall 2005 EE595S Electric Drive Systems 46

Critique of Design

• Drive Becomes Quite Overmodulated• Bandwidth is Not Nearly 100 Hz• Significant Overcurrent (Rated is 2.6 A,

rms)• The Speed is not 200 rad/s At End of Study

Fall 2005 EE595S Electric Drive Systems 47

15.9 Current-Regulated Drives

• Current Based Inverter Current RegulationAdvantages

• Torque Control Bandwidth• Robustness w.r.t. Machine Parameters• Robust w.r.t. Faults• Control design with lower order system

Disadvantage• Switching Frequency Cannot Be Directly Controlled

Fall 2005 EE595S Electric Drive Systems 48

Hysteresis Current-Regulated Drive

Fall 2005 EE595S Electric Drive Systems 49

Performance of HysteresisControlled Drive

Fall 2005 EE595S Electric Drive Systems 50

Voltage Source Based Current Regulation

• AdvantagesControlled Switching FrequencyCan Offer Excellent Waveform Quality

• DisadvantageLower Control Bandwidth

Fall 2005 EE595S Electric Drive Systems 51

Sine Triangle Current Regulator

Fall 2005 EE595S Electric Drive Systems 52

Example 15B

• Suppose We Utilize

(15.B-1)

(15.B-2)

• Place Poles At s=-200, s=-1000

)()( rqs

rqs

ipm

rdsssr

rqs ii

sKKiLv −⎟

⎠⎞

⎜⎝⎛ ++′+= ∗∗ λω

)( rds

rds

ip

rqsssr

rds ii

sKKiLv −⎟

⎠⎞

⎜⎝⎛ ++−= ∗∗ ω

Fall 2005 EE595S Electric Drive Systems 53

Example 15B

• Results(15B-4)(15B-5)

sKi /2280Ω=

Ω= 7.10pK

Fall 2005 EE595S Electric Drive Systems 54

Performance During Step Change In Current

Fall 2005 EE595S Electric Drive Systems 55

15.10 Voltage Limitations of Current-Source Inverter Drives

• Lets Assume(15.10-1)(15.10-2)

• Then(15.10-3)

(15.10-4)

∗= rqs

rqs ii

∗= rds

rds ii

mrrdsdr

rqss

rqs iLirv λωω ′++= **

** rqsqr

rdss

rds iLirv ω−=

Fall 2005 EE595S Electric Drive Systems 56

15.10 Voltage Limitations of Current-Source Inverter Drives

• Recall That(15.10-5)

• Thus(15.10-6)

• Also Recall(15.10-7) (w/o Harmonics)

(15.10-8) (w Harmonics)

( ) ( )22

21 r

dsrqss vvv +=

22 )()(2

1 ∗∗∗∗ −+′++= rqsqr

rdssrm

rdsdr

rqsss iLiriLirv ωωλω

dcs vv6

1=

dcs vvπ2

=

Fall 2005 EE595S Electric Drive Systems 57

Response to Step Decrease in DC Voltage

Fall 2005 EE595S Electric Drive Systems 58

15.11 Current Command Synthesis(Non-Salient Machines)

• Recall (15.11-1)

• Thus(15.11-2)(15.11-3)

• Advantages

• But..

rqsm

Pe iT λ′= 22

3

∗′

∗ = ePrqs Ti

mλ12

32

0=∗rdsi

Fall 2005 EE595S Electric Drive Systems 59

15.11 Current Command Synthesis(Non-Salient Machines)

• Voltage Requirement(15.11-4)

• If Not Enough Voltage

(15.11-5)

(15.11-6)• This is Referred to as Flux Weakening• Warning:

22 )()(2

1 ∗∗∗∗ −+′++= rqsssr

rdssrm

rdsssr

rqsss iLiriLirv ωωλω

2

22222 )(2

z

izrvzLi

rqsmrssrssmr

ds

∗∗ +′−+′−=

λωωλ

222ssrs Lrz ω+=

Fall 2005 EE595S Electric Drive Systems 60

15.11 Current Command Synthesis(Salient Machines)

• Recall(15.11-7)

• Thus(15.11-8)

• Also Recall(15.11-9)

))((223 r

dsrqsqd

rqsm

Pe iiLLiT −+′= λ

qdm

rqsqdP

erds LLiLL

Ti−′

−−

= ∗∗ λ1

)(223

22 )()(2

1 ∗∗ += rds

rqss iii

Fall 2005 EE595S Electric Drive Systems 61

15.11 Current Command Synthesis(Salient Machines)

• Strategy: Minimize Fundamental Component of Current

• Why?

Fall 2005 EE595S Electric Drive Systems 62

15.11 Current Command Synthesis(Salient Machines)

• Result

• In this Case, What If Inadequate Voltage

Fall 2005 EE595S Electric Drive Systems 63

15.11 Current Command Synthesis(Salient Machines)

Fall 2005 EE595S Electric Drive Systems 64

15.12 Average-Value Modeling of Current Regulated Drives

• We Begin With(15.12-1)(15.12-2)

• Ignoring Stator Transients(15.12-3)(15.12-4)

• Thus(15.12-5)

*rqs

rqs ii =

∗= rds

rds ii

rmrdsdr

rqss

rqs iLirv ωλω ′++= ∗∗∗

∗∗ −= rqsqr

rdss

rds iLirv ω

])()([ 223 r

qsmrrds

rqsqdr

rds

rqss iiiLLiirP λωω ′+−++= ∗∗∗∗

Fall 2005 EE595S Electric Drive Systems 65

15.12 Average-Value Modeling of Current Regulated Drives

• Since(15.12-6)

• We Have(15.12-7)

• Again Assuming Our Currents Are Equal to Commanded Values

(15.12-8)

dcdc V

Pi =

])()([ 2123 r

qsmrrds

rqsqdr

rds

rqssVdc iiiLLiiri

dcλωω ′+−++= ∗∗∗∗

))((223 ∗∗∗ −+′= r

dsrqsqd

rqsm

Pe iiLLiT λ

Fall 2005 EE595S Electric Drive Systems 66

15.12 Average-Value Modeling of Current Regulated Drives

• Resulting State Model(15.12-9)

⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢

−−+′

′+−++−+

⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢

⎥⎥⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢⎢⎢

−−

−−

=

⎥⎥⎥⎥⎥⎥

⎢⎢⎢⎢⎢⎢

∗∗∗

∗∗∗∗∗

]))(([00

])()([

00000

0000

00

000

000

2231

2

21231

cos

1

11

11

1

0

Lrds

rqsqd

rqsm

PJ

P

rqsmr

rds

rqsqdr

rds

rqssVC

Lv

r

st

st

dc

r

C

LLr

L

CC

LLr

r

st

st

dc

r

TiiLLi

iiiLLiir

vivi

vivi

p

dcdc

rlr

st

ststst

st

dcdc

rlrlrl

λ

λωω

ωω

α

Fall 2005 EE595S Electric Drive Systems 67

15.3 Case Study: Current-Regulated Inverter-Based Seed Control

• Chief Assumption(15.13-1)

• We’ll Use(15.13-2)

• Thus We Obtain

(15.13-3)

∗= ee TT

))(1( 1rmrmspe KT ωωτ −+= ∗∗

τ

τ τ

ωω

JK

JK

JK

rm

rmss

s

++

+=∗ 2

)1(

Fall 2005 EE595S Electric Drive Systems 68

15.3 Case Study: Current-Regulated Inverter-Based Seed Control

• Let Us Place Poles Ats=-5, s=-50

• This YieldsKp=0.257 Nms, τ=0.22 s

• Other Design AspectsUse Sine Triangle Current Regulator From Example 15 B (s=-200, s=-1000)Limit Currents to +/- 3.68 AInject All Current into Q-Axis

Fall 2005 EE595S Electric Drive Systems 69

15.3 Case Study: Current-Regulated Inverter-Based Seed Control

Fall 2005 EE595S Electric Drive Systems 70

15.3 Case Study: Current-Regulated Inverter-Based Seed Control