PERMANENT MAGNET SYNCHRONOUS MOTORSIN INNER- AND OUTER-ROTOR CONFIGURATIONS

FOR TRACTION APPLICATIONS

Univ.Prof. Dr. Manfred SchrödlInstitute of Energy Systems and Electrical Drives

University of Technology, Vienna

Presentation at A3PS conference„ECO-MOBILITY“

Austria Center Vienna, Nov. 15th, 2011

Contents

1. Introduction2. Most important properties of the presented PMSM

traction drives3. Possible geometrical motor configurations4. Control of the PMSM – Sensorless approach5. Example 1: 500 Nm outer rotor PMSM for wheel drives6. Example 2: 100 Nm outer rotor PMSM for light vehicles7. Example 3: 200 Nm inner rotor PMSM for drive trains8. Example 4: 3.000 Nm railway traction drive9. Conclusion and outlook

Introduction

Permanent magnet synchronous motors (PMSMs) for tractionapplications in different geometrical construction are presented, especially:

Outer rotor configuration (e.g. for direct integration into wheels)Inner rotor configuration (e.g. for combination with gear-boxes)

The presented motors have been built up and tested at Vienna University of Technology.

The geometrical structures and the control concepts based on sensorless control (INFORM® method and EMF model) are shown.

Measurements of important properties are given.

Most important propertiesof the presented drives

High torque per volumePermanent short circuit is admissibleSensorless control up to double rated torque from standstillUsing INFORM® methodConcentrated windings – Advantages in production and isolationRobust construction – large air gap, no mechanical sensorsLarge field-weakening range - constant power range is possibleApplication in gearless direct drivesHigh efficiency – up to 95 %

Possible geometricalmotor configurations

Inner rotor configuration(e.g. for combination with gear-boxes)

Outer rotor configuration(e.g. for dirctly integrated wheel drives)

Disc rotor configuration(e.g. for small moment of inertia)Not treated in the presentation

PMSMs with air gap magnetsand buried magnets

Inner rotor configurations

Buried magnets(enabling fluxconcentration)

Air gap magnets(protectionagainst corrosionnecessary)

Outer rotor configurations

PMSM inner rotors (examples)

Air gap magnets (left)Buried magnets withoutflux concentration(middle) (industry)

Inner rotor withflux-concentratingburied magnets(by TU Vienna)

PMSM outer rotor applications (examples)

Starter/Generator or mild hybrid application (ZF Sachs)

Gearless directdrive for tramapplications

PMSM tooth coils(examples)

2 variants:a) Each tooth has a coilb) Each second tooth has a coil(industry examples)

Stators of outer rotor PM motors (upperpictures – PMs by TU Vienna)

Stator of inner rotor PM (left picture, constructed and built up by TU Vienna)

Classical strategy: Position-sensor-based current control (which is closely related to torque-control), maybe with superimposed speed-control

Disadvantage: Expensive and place-consuming position sensor + cabling necessary

Control of the PMSM –Sensorless approach

Presented newstrategy:

INFORM® method forlow speed and standstill

combined with EMF method for high speed

„INdirect Flux detection by On-line Reactance Measurement“

Control of the PMSM –Sensorless approach

INFORM® method

Basic idea:Measuring the current change vector due to a voltage test vector (lower figure)This signal is position-dependent.3 different test directions are possible (right)

(POS1)

y

inverse INFORM-Reaktanz(Richtung der Stromänderung)

yPOS 1 o

INFO

RM-A

chse

POS 2POS 3

(POS3)

Δy

(POS2)

Richtung des angelegten

INFORM

symbolischerRotor

Spannungsraum-zeigers

INFORM

Control of the PMSM –Sensorless approach - INFORM® method

Measurement of the characteristic INFORM curve

(POS1)

y

inverse INFORM-Reaktanz(Richtung der Stromänderung)

yPOS 1 o

INFO

RM-A

chse

POS 2POS 3

(POS3)

Δy

(POS2)

Richtung des angelegten

INFORM

symbolischerRotor

Spannungsraum-zeigers

INFORM

CharacteristicINFORM curve

theoretical

measured at rated current(300Nm)

measured at 3x rated current(500Nm)

Sensorless Control of the PMSM –Combining INFORM® method,

EMF model and mechanical observer

EMF model isalways active. INFORM stabilizesEMF model at lowspeed. Mechanicalobserver issynchronized byINFORM and/or EMF model.

Main goals of the motor:

Outer rotor construction – high torque per volume ratioSensorless control possible up to 3x rated currentLarge air gap – easy mechanical assemblyConcentrated windings – simple productionHigh efficiency (small rotor losses)

Example 1: 500 Nm Outer Rotor PMSM for wheel drives

Data of presentedPMSM

reference voltage 325 V (peak)

reference current (continuous current) 56.6 A (peak)

continuous output power 15 kW

continuous / peak torque 310 / 500 Nm

reference speed 673 rpm

per unit resistance at 120 °C 0.036

number of pole pairs 15

number of teeth 36

short-circuit current 43.6 A (peak)

air gap diameter 34 cm

length of active iron 5 cm

Torque production

The torque depending on current magnitude was measured on a test stand.

Load motor (600 Nm) Torque measurement PMSM

Produced torque (including reluctancetorque) over current magnitude:

300 Nm at rated current500 Nm at 3x rated current

Efficiency measurements

The efficiency was measured in the speed / torque plane using a high-quality power measuring system.

Machine torque over rotor speed with efficiency and hyperbolic power-isolinesBlue lines: Achievable range in the torque/speed plane at rated and 3xrated current

14 kW isoline

Short-circuit currents over machine speed (ωfinal= 16 %), Ch1: is,d,sc Ch2: is,q,scCh3: ti (35Nm/div.), is,d,sc|ω→∞≈0.78

Flux-parallel currentcomponent (yellow):

Flux-normal currentcomponent (blue): .

,

,,22,,

,,22

,2

,,

qsdss

sPMscqs

qsdss

qsPMscds

llrri

llrl

i

ωωψ

ωψω

+−

=

+

−=

Short circuit behaviour(Linear Speed change from 0 to 16% of rated speed)

Torque ( ) .,,,,, qsdsqsdsqsPM iilli −+=ψ (red)

78% of ratedcurrent

100 Nm

If PMSM rotor cannot be decoupled from the drive train -> Short circuitmust be admissible for permanent operation.Possible reasons: winding fault (short circuit) orInverter fault (short circuit is „safe condition“)

Thermal behaviour

The PMSM was air-cooled (natural cooling).

The temperature rise at 70 % and 100 % of reference current is shown. The temperature behaviour can be modeled by a time constant of 25 min.

70% rated current

100% rated current

Dynamic behaviour of implemented sensorless

INFORM/EMF controlThe following picture shows a PMSM step response

Sensorless controlled speed step from standstill to 30% of rated speed(coupled with load machine – high moment of inertia).

Estimated (green) and real (red) rotor position

Torque-producing current isqup to 220% of rated current(Torque up to 430 Nm)

Reference speed

Actual speed

Speed step is performed within 160 ms

Two variants of stator slots have been tested at same rotor geometryOuter rotor construction – direct integration into wheel (see figure)Sensorless control possible up to 3x rated currentLarge air gap – easy mechanical assemblyConcentrated windings – simple production

Example 2: 100 Nm Outer Rotor PMSM for light wheel drives

reference DC link voltage 48 V

Continuous / peak output power 3/6 kW / motor

continuous / peak torque per motor 100 / 200 Nm

reference speed 600 rpm

Constant torque range 0-300 rpm

Constant power range 300-600 rpm

number of teeth 18 or 36

Number of poles 24

short-circuit / continous current ratio <1

PMSM with 24 rotor polesand 36 stator teeth

PMSM with 24 rotor polesand 18 stator teeth

Example 2: 100 Nm Outer Rotor PMSM for light wheel drives –

Integration into wheelWheel motors at laboratory test stands(left figures)

Integration of wheel motors into light vehicle (golf caddy)

A high-performance inner rotor motor forelectric / hybrid vehicles was developedand tested at TU Vienna.Large air gap – easy mechanical assemblyConcentrated windings – simple productionLiquid cooling necessary

Example 3: 200 Nm Inner Rotor PMSM for drive trains

Reference motor voltage 250 V (rms)

Reference motor current 220 A (rms)

Reference power 90 kW

Reference/maximum speed 3500 /8000 rpm

Motor diameter 250 mm

CAD construction (left) and realised PMSM at TU Vienna test stand (right)

The stator ist liquid-cooled and fitted with tooth-coil windings.The rotor has buried permanent magnets in flux-concentrating arrangement.The short-circuit current is smaller than the nominal current.

Example 3: 200 Nm Inner Rotor PMSM for drive trains – stator

and rotor construction

Figure: Stator and rotor of the PM inner rotor motor

Example 4: 3000 Nm Railway traction drive

TU Vienna supportedconstruction, buildingup of 3000 Nm / 1.000 rpm outer rotorprototypes and lab test stand

Upper figure: Industrial bogie withclassical induction motors

Left figure: Construction of innovative PM drive (1.. Bearing, 2..Rotor with buried permanent magnets, 3..Stator,4.. Housing, 5..wheel, 6.. Shaft)

Left: StatorRight: Rotor

Right figure shows assembly of stator and rotor (in vertical position)

Lower figure shows test stand with1000 Nm / 4000 rpmDC drive, gear box 1:4 and PMSM under test (4000 Nm, 1000 rpm)

Example 4 (continued):3000 Nm Outer Rotor PMSM traction drive

Assembly and testing at TU Vienna

Example 4 (continued):3000 Nm Outer Rotor PMSM traction driveMeasurements during sensorless control

Upper figure: speed/torque-curve forcyclic testing of the motor(acceleration at ratedtorque, drive in field-weakening range, breakingand standstill .. Repeatedcontinuously)

Lower figure: The curveshows sensor-based and sensorless control up to 4000 Nm, almost samebehaviour. Furthermore, the characteristic INFORM curves up to 3xrated current are shown.

Load motor (600 Nm) Torque measurement PMSMProduced torque (including reluctancetorque) over current magnitude:

300 Nm at rated current500 Nm at 3x rated current

Example 4 (continued):3000 Nm Outer Rotor PMSM – Efficiency and

energy consumption during standard test cyclecompared to induction motor

Efficiency plots of PM motor/generator (left) and induction motor/generator (lower right)Including operating points along the test cycle(medium right curve) and correspondingenergy consumption (upper right table)

Conclusion and outlook

Permanent magnet synchronous machines in inner and outer rotorconfiguration for electric traction have been presented.

The most important properties have been discussed.

Sensorless control up to overload even at standstill has been shown.

All drives have high efficiency (up to 95 %)

Some examples between 100 and 3.000 Nm have been built up at TU Vienna.

Thank you for your attention!

Manfred Schrödl, Institute of Energy Systems and Electrical Drives

Vienna University of Technology

Manfred.schroedl@tuwien.ac.at