Lecture_4 Field Weakening of Permanent Magnet Motors - Some New Possibilities

transcript

WEMPEC

Field Weakening of

Permanent Magnet Motors -

Some New Possibilities

T. A. Lipo

Prof. Emeritus

University of Wisconsin

Madison Wisconsin

WEMPEC

Outline

• Brief Review of Field Weakening of PM Motors

• Field Weakening by Modification of the Motor Design

• Field Weakening by Modification of the Stator Circuit

• Issues and Opportunities

WEMPEC

Outline

WEMPEC

Two major classes of PM synchronous

machines

Relatively low inductance Relatively high inductance

WEMPEC

dq model of a wound field synchronous

machine

WEMPEC

dq equivalent circuits for a PM machine in the

synchronously-rotating reference frame

Magnet acts as a

current source

WEMPEC

dq equivalent circuits for a PM machine in the

synchronously-rotating frame – steady state

WEMPEC

Reduced circuit during steady state

WEMPEC

Steady state – final result

WEMPEC

Vector diagram with lagging power factor at

the air gap – stator d-flux magnetizing

WEMPEC

Vector diagram assuming leading power factor

at the air gap – stator d-flux demagnetizing

WEMPEC

Traction Application Torque vs. Speed Curve

Trated

Torque

Prated

= Trated

Rotor Speed max

(CPSR)

Constant Power Range

HighSpeedRegime

ConstantTorque

WEMPEC

Phasor Diagram for the constant torque

range for Non-salient PM machine

WEMPEC

Phasor diagrams for constant power range with

increasing wE with constant VS and IS when EI > ISXS

WEMPEC

Phasor diagrams for increasing wE with constant VS

and IS when EI < ISXS for Xs = 1.1 and EI = 0.8

WEMPEC

Phasor diagrams for increasing we with

constant Vs & Is when EI = IsXs

WEMPEC

Power for increasing e with constant

VS and IS

WEMPEC

d–axis current for increasing speed with

constant Vs and Is

WEMPEC

Phasor Diagrams for Increasing wE with constant

VS and IS when EI=IS(XS+ XEXT)

WEMPEC

Field Weakening - The Problem

• The ratio of EI/Xs determines the maximum extent of

the field weakening range

• When Irated = EI/Xs the maximum power can be

extracted for all speeds

• Maximum power can be derived by designing the motor

with a proper value of Xs or by somehow achieving

a variable EI

• Well designed machines typically have a minimum

amount of copper and iron leading to a machine in

which Xs is to small to achieve the optimum EI/Xs

• Problem can be solved by reducing EI but at the cost

of enlarging the machine

• What to do??

WEMPEC

Solutions

• Modify the stator winding design (i.e. increase Xs)

Increase leakage by creating deeper stator slots

Increase leakage by running on non-fundamental

component space harmonic (i.e. fractional slot wdg.)

• Modify the stator or rotor of machine to vary EI

Stator Modifications

Rotor Modifications

Mechanical Modifications

• Modify the external circuit powering the PM machine

WEMPEC

Outline

WEMPEC

The CPPM Machine (Tapia-Lipo 2002)

WEMPEC

Operating Modes of the CCPM

WEMPEC

SynPM Machine (Luo-Lipo 2000)

WEMPEC

Dual Rotor Machine (Naoe-Fukami 2001)

WEMPEC

DSPM Machine (Chau-Jiang-Wang, 2003)

WEMPEC

Rotor Magnet Adjustment (Zhou et.al. 2010)

WEMPEC

Rotating Iron Segment (Shibukawa 2006)

WEMPEC

Axial Flux Machine with Stator/Rotor Rotation

(Caricchi et.al. 2001&2006)

WEMPEC

Axial Air Gap Adjustment (Nakai et.al.)

WEMPEC

Flux Barrier Adjustment (Baoquan,

Chunyan, & Shukang-2005)

WEMPEC

Outline

WEMPEC

CcomVdc

INV1 INV2

Solution#1 Open Winding Machine Drive

WEMPEC

Field weakening of surface magnet PM machine

The concept presented in Lecture #2 can also

be applied to a PM machine

• Adjust the bridge effective reactance to be capacitive

and thus provide unity power factor as viewed

from the machine terminals below rated speed

• Adjust the bridge effective reactance to provide

a d-axis inductive reactance to allow field weakening

to occur above rated speed

WEMPEC

Flux Weakening

Decoupling

Current Reg

a' b' c'

T(θ)-1

Lq_com

Ld_com

Limiter iq*

vb1*vc1*

iaibic

vq_com*

vd_com*

vcom* vq2*

va2*vb2*vc2*

Vector Rotator

Field weakening of surface magnet PM machine-

Control block diagram

WEMPEC DP - 37

Simulation results – below base speed

0.1 0.15 0.2 0.25 0.3 0.35 0.4-100

time/s

•INV1 supply real voltage

•INV2 supplies imaginary voltage

WEMPEC DP - 38

Simulation results – flux weakening

single inverter drive open-winding drive

Load: 20 Nm

Speed command: 100 rad/s

0.1 0.15 0.2 0.25 0.3 0.35 0.4-80

time/s

0.1 0.15 0.2 0.25 0.3 0.35 0.4-80

time/s

WEMPEC DP - 39

Simulation results – flux weakening

0 0.1 0.2 0.3 0.4 0.50

time/s

/rad/s

single inverter drive open-winding drive

Load: 20 Nm

Speed command: 100 rad/s

0 0.1 0.2 0.3 0.4 0.50

time/s

/rad/s

WEMPEC

Rotor speed for ramp speed command

Dual converter:

Single converter:

Speed reference :

(Mech rad/s)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

t(sec)

WEMPEC

d- and q-axis currents during ramp speed increase

Dual converter:

Single converter:

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8-30

t(sec)

WEMPEC

Field weakening of surface magnet PM machine

Dual converter:

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80

t(sec)

WEMPEC

Dual converter:

Single converter:

Speed reference:

0 0.1 0.2 0.3 0.4 0.5 0.60

t(sec)

Rotor speed for step change in speed command

WEMPEC DP - 46

Harmonics of open-winding drive

•Effective doubled switching frequency compared to

traditional open-winding drive

•The voltage reference assigned to the two inverters

are not 180 degrees apart

va1va2

regular INV2 compensation

WEMPEC DP - 47

Harmonics of open-winding drive

0 0.005 0.01 0.015

0 0.5 1 1.5 2

0 0.005 0.01 0.015

0 0.5 1 1.5 2

Single drive Open-winding 180 deg shift Open-winding 90 deg shift

m = 0.5

Vdc = 1

THD = 0.6574

m1 = 0.5, m2 = 0.5

Vdc1 = 0.5, Vdc2 = 0.5

Phase shift = 180 deg

THD = 0.3747

m1 = 0.5, m2 = 0.5

Vdc1 = 0.5, Vdc2 = 0.5

Phase shift = 90 deg

THD = 0.7696

WEMPEC DP - 48

Harmonics of open-winding drive as function of

phase shift

80 100 120 140 160 180

phase shift

open-winding drive

single drive

80 100 120 140 160 1800.2

phase shift

open-winding drive

single drive

M = 0.5 < = 0.6

Vdc = 1

THD = 0.6574

M1 = 0.5, M2 = 0.5

Vdc1 = 0.5, Vdc2 = 0.5

Vdc = 1

THD = 0.5631

M1 = 0.5, M2 = 0.5

Vdc1 = 0.5, Vdc2 = 0.5

WEMPEC DP - 49

Harmonics of open-winding drive THD as

function of modulation index M

0 0.2 0.4 0.6 0.8 10

open-winding

single drive

0 0.2 0.4 0.6 0.8 10

open-winding

single drive

180 degree phase shift 90 degree phase shift

WEMPEC

Adjustable Power Factor PM Machine

Features:

• Effective field weakening of a PM machine can be achieved

for any design (buried or surface magnet)

• Power factor control to unity power factor can be

achieved below rated speed

• Concept can be extended to PM machines operating

from the utility grid

• Concept can also be extended to PM generators

Issues:

• Rating of the auxiliary power converter

WEMPEC

Solution #2 Field weakening by winding switching

Stator winding currents of phase a1 and a2

WEMPEC

Normal operation – current directed into the dots

Thyristors turned on creating neutral

WEMPEC

Thyristors turned off reversing the current in phase a2,b2,c3

High speed operation – current reversed in half of the

three stator windings

WEMPEC

Standard lap winding – q = 2 slots/pole/phase

WEMPEC

Currents reversed in half the windings

WEMPEC

Phasor diagram for operation at 2 pu speed

before the switching event

WEMPEC

Phasor diagram for operation at 2 pu speed

after the switching event

WEMPEC

Currents as a function of speed in constant power region

WEMPEC

Outline

WEMPEC

Issues and oppurtinities

• Rating of the inv2 inverter (variable impedance inverter

• Transients involved in changing inv2 controller from

and equivalent capacitor to an equivalent inductor

• What is the best winding switching strategy to extend

constant horsepower the highest?

• How do we design a concentric winding to accomplish

field weakening concept keeping the inverter ratings

equal?

• How serious are the losses resulting from the switched

winding strategy?

• Can the winding switching concept be extended to

fractional slot windings?

WEMPEC

Thank You for Attending!

Thanks to my student Di Pan

WEMPEC

Lecture_4 Field Weakening of Permanent Magnet Motors - Some New Possibilities

Documents