Tique Crespo Kendall Connection Live
Tique Crespo
Kendall Connection Live
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