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PMAC Motor Design and VFD control Agenda

• Basic AC Induction motor design • Motor Technologies • PMAC Motors • Controlling PMAC motor with VFDs

AC Induction Motor Parts

Rotor Fan Blades Rotor Bar

End Rings

Stator Frame

Stator Windings & Magnetism

C2

A1 B2

C3

A2

B3

C4

A3 B4

C1

A4

B1

N

S

N

S

+

- -

N S N S

AC induction motors do not require commutation

The Stator winding applies magnetism to the Rotor energizing the rotor to create North and

South poles on the rotor causing it to turn.

How Rotor Current Is Generated

The North & South pole values applied to the stator windings on the previous page & shown above generate magnetic lines of flux that induce a voltage onto the rotor windings. The induced polarity on the rotor would be the opposite polarity of the stator winding. The strength of the induced polarity is proportional to the current

flow through “or magnetic lines of flux in” the stator windings.

Rotor Field Created by Induced Current Flow in Rotor Conductors

Rotating Magnetic Field of Stator

Rotor Field Created By Induced Current Flow In Rotor Conductors

S N

Motor Technologies

DC Motor AC Motor

PM DC Wound

Series Shunt

Compound

Asynchronous

Synchronous (Conventional)

Single Phase Polyphase

BLDC

PMAC / PMSM

Synchronous Reluctance

Line Start PM

Stepper

Universal Motor

Servo

Servo

• Shaded pole • Split phase

• Capacitor start • Permanent split

capacitor • Capacitor start –

capacitor run

Wound rotor

Squirrel cage

Synchronous

Switched Reluctance

Present capability

Future capability

PMAC vs. AC Induction Design & Construction

AC Induction • Die cast rotor • AC Line or VFD power • Low power density • Narrow air gap • Varying # poles within frame size

PMAC • Permanent Magnet rotor • VFD power only • High power density • Wider air gap • Fixed pole count within frame size

PMAC vs. AC Induction Performance

AC Induction • NEMA Premium (IE3) efficiency • Steep efficiency curve • Normal NEMA/IEC frame sizes • Asynchronous (typical 3% slip)

PMAC • Ultra Efficient (IE4+) efficiency • Flat efficiency curve • 2-3 frame size reduction • Synchronous (0% slip) • Inherent braking • Excellent dynamic performance • High system Power Factor

Unique Terminology

Back EMF Reluctance Torque

Inductance Saliency

Demagnetization Magnetic Torque

Ripple Torque Cogging

Generated voltage from rotation of a PM motor Created when the rotor tries to align itself to the lowest energy state Resistance to a change in current, causing current to lag voltage Difference between inductance values of the “D” and “Q” axes Loss of magnetic properties due to high temperature or current Torque generated from magnetic interaction (magnet/field) Non-uniform angular velocity; “jerkiness” during rotation Detent felt when manually rotating a PM motor from alternating N & S

Unique Terminology

Radial Flux Axial Flux

IPM SPM

Commutation Electromotive Force

Magnetomotive Force Pull-Out Torque

Magnetic flux is perpendicular to shaft (a.k.a. “Sausage”)

Magnetic flux is in line with the shaft (a.k.a. “Pancake”)

Interior Permanent Magnet topology; magnets embedded in rotor

Surface Permanent Magnet topology; magnets on O.D. of rotor

Process of energizing winding to facilitate interaction with magnet

Driving force (“motive”)1 which produces voltage

Driving force (“motive”)2 which produces magnetic flux

Torque required to pull motor out of synchronism with stator field

1 In PM circuits, the source is magnetic energy from the rotor 2 In PM circuits, the source is electrical current from the stator

PMAC Technology Overview

Two Winding Types • Distributed (induction) • Concentrated

Magnet Materials • Ferrite • High Energy (Rare Earth Magnet)

Neodymium Iron Boron (NdFeB) Samarium Cobalt (SmCo)

Stator Designs • Optimized # slots • Standard materials • Standard processes

Two Rotor Types • Surface mount (SPM) • Interior mount (IPM) • Optimized pole count

The term "salient" refers to visible, or exposed, or sticking out. So a "salient pole motor" is one in which exposes the N and S poles to the rotor.

Magnetic Saliency

The d-axis is when the rotor is aligned with the poles. It is also the orientation with highest inductance. The q-axis is when the rotor is aligned with the gaps. It has the lowest inductance. It can be shown that reluctance motors work best when you maximize the saliency ratio.

Magnetic Saliency

d-axis inductance, Ld

N

SS

N magnet

steel

Low inductance path

q-axis inductance, Lq

N

SS

N magnet

steel

High inductance path

Iron

Magnet (airgap)

Iron

Higher Inductance Lower Inductance

Fig. A. D-axis flux path Fig. B. Q-axis flux path

No magnets in the flux path.

Magnets in the

flux path.

Describes the relationship between PM motor’s d-axis and q-axis inductance.

Magnetic Saliency

IPM Motors Note: For optimum control, a saliency ratio of 1.2 :1 or greater is usually recommended.

d

q

LL

LL

==>min

max ratiosaliency Ld Lq

SPM Motors

In a Salient PM Synchronous Machine, there is a difference between the SPM and IPM motor rotor d-Axis (main Flux direction) and the rotor q-Axis (main torque producing direction) inductances.

Advantages of IPM: • Higher allowable rotational speed • Enhanced starting performance

Efficiency: PMAC vs. NEMA Premium AC Motor

0.70

0.75

0.80

0.85

0.90

0.95

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Effic

ienc

y

Speed (RPM)

Variable Speed Constant Torque Motor PerformanceEfficiency vs Speed

5 HP, 184T SyMAX PMAC vs NEMA Premium Induction

PM Motor Eff

Ind Motor Eff

91.7% (338 watts loss)

89.5% (438 watts loss)

900

90.6% (387 watts loss)

84.6% (679 watts loss) 23% improvement

43% improvement

IP 43 Protection

Max Guard® Insulation

Natural NEMA Frame

Comprehensive Nameplate

Up to 5000 RPM

Totally Enclosed Non-Ventilated

With or without sensor feedback

48 or 56 frame mounting

Embedded rare earth magnet design

UL and cUL Component Recognition

Torque to 72 lb-in

SyMAX® Commercial Motors

V-Ring “Forsheda” shaft seal (optional)

Natural NEMA Frame

IP 54 Protection (IP55 or 56 optional) Comprehensive Nameplate

Cast Iron Severe Duty Construction

Ultra Efficient™ IE4 levels, Higher than NEMA Premium

Max Guard® Insulation

Terminal Block (optional)

Cast Iron Bearing Caps (ea end)

Precision Balanced Rotor

Grounding Provisions on Frame/Foot

Epoxy interior & exterior paint

Encoder provisions (optional)

TEFC – Standard TENV or TEBC (optional)

SyMAX® Industrial Motors

VFD Drive and PMAC Motor

PM-Capable Drives

PowerFlex-525

PowerFlex 753 and 755

General Drive Considerations

Drives with PM Motor vector algorithms are recommended (PF-755 uses Vector). Some drives with Scalar Mode algorithms can work, with decreased

efficiency. (PF-525 uses Scalar)

IPM control mode (that uses both Ld and Lq values) will provide the highest efficiency.

SPM control mode will run the motor with reasonable efficiency. Carrier Frequency must be greater than 10x the max motor operating frequency. Most drives need to be de-rated when using higher carrier frequencies. The drive’s amp rating should be no more than 2X motor FLA

In order to optimize efficiency of the motor, sometimes experimentation with drive settings is needed.

“Tricking” the drive with incorrect values may or may not work well, depending on the drive and the load you’re trying to run. “Tricking” the drive should be avoided.

Some drives have an “auto-tune” procedure that has the drive determine the parameter settings of the motor.

These values are not always accurate and should be checked before running the motor.

General Drive Considerations

VFD Drive and PMAC motor

Drive settings explained

BEMF Volts/1000rpm

Poles

Volts

Amps

Rated or Base RPM and Hz

R (resistance) Ld (in Henries) Lq (in mili Henries)

PMAC SyMax Motor Nameplate data

R, Ld, and Lq values are phase only not Phase to Phase values