A New Control Technique for Achieving Wide Constant Power SpeedOperation with an Interior PM Alternator Machine

Jackson Wai Thomas M. Jahns

University of Wisconsin-Madison1415 Engineering Drive

Madison, WI 53706Ph: 608-265-3821Fax: 608-262-5559

E-Mail: waij@cae.wisc.edu

University of Wisconsin-Madison1415 Engineering Drive

Madison, WI 53706Ph: 608-262-5702Fax: 608-262-5559

E-Mail: jahns@engr.wisc.edu

Abstract-A new flux weakening control algorithm ispresented for achieving wide constant power operation withan interior permanent magnet (IPM) synchronous machineoperating as an alternator. The algorithm is designed toinitiate flux weakening only when necessary by recognizing thethreshold conditions for current regulator saturation, makingthe algorithm inherently adaptive to changes in the inverterbus voltage. A 6kW 42V automotive integratedstarter/alternator (ISA) using a direct-drive IPM machineserves as the target application for this development.Simulation results show that the new algorithm is capable ofdelivering very good static and dynamic bus regulationcharacteristics over a 10:1 engine operating speed range.Tests are presently under way to confirm these performancepredictions using a prototype IPM starter/alternator system.

Keywords: Permanent magnet machines, AC motor drives,road vehicle power systems, power control, synchronousgenerators

I. INTRODUCTION

With proper design, an interior permanent magnet (IPM)synchronous machine can achieve constant power operationover a wide speed range in both the motoring andgenerating regimes [1]. As a result, IPM machines areattracting increasing attention for a variety of applicationsranging from electric vehicle propulsion [2] to machinetools [3].

While the design of an IPM machine for extended speedoperation poses several technical challenges, the success ofthe complete drive system depends on the availability of anappropriate control algorithm that can extract the fullperformance capabilities from the machine. In particular,special flux weakening control techniques are necessary toachieve constant power operation over a wide speed range.Previous work reported in the literature has generallyfocused on extended speed range applications for the IPMmachine operating as a motor [4-6]. This paper presents anew control algorithm designed to extract near-constantpower from an IPM machine over a wide speed range whenit is operating as an alternator.

The application that has motivated this work is a direct-drive integrated starter/alternator (ISA) for an automotivevehicle [7]. The development of many new electrically-

S/A rotoracts as

flywheel

Torque converterinside rotor hub Flywheel, alternator, starter, pulley, &

possibly a belt eliminated

New Parts Eliminated Parts

Fig. 1 Integrated starter/alternator (ISA) configuration.

powered accessories combined with wide interest in mildhybrid concepts using electric machines for low speedacceleration has drawn significant attention to ISA systems[8]. As illustrated in Fig. 1, the new ISA replaces theconventional engine flywheel and is driven directly by theengine crankshaft without gearing. The machine isdesigned to operate as both the engine starter and alternator,replacing the two separate machines that perform thesefunctions in conventional vehicles, along with theirassociated pulleys, belts, and gears.

Performance specifications developed in consultation withseveral automotive manufacturers call for the ISA to supply150Nm of starting torque at low speeds. In addition, theISA must deliver 42V power to the automotive accessoriesover a 10:1 speed range extending from 4KW at 600rpm to6KW at 6000rpm. It is this latter requirement thatmotivated selection of the IPM machine for furtherdevelopment as an attractive candidate for this application.

Significant progress has been made towards development ofan IPM machine that is capable of meeting thesechallenging application requirements [9]. This effort hasculminated in construction of a prototype version of a 12-pole IPM machine designed for this direct-drive ISAapplication. Figure 2 shows the stator and rotor of thismachine, illustrating its use of two magnet cavities per polewith saturating magnetic bridges that link the iron polepieces into unitary rotor laminations.

0-7803-7116-X/01/$10.00 (C) 2001 IEEE

807

Fig. 2 Rotor and stator assemblies of prototype 6 kW IPMmachine for ISA application.

II. CONTROL TECHNIQUE PRESENTATION

A. IPM Machine Operating EnvelopeThe principles for achieving wide constant power

operation using IPM synchronous machines have beenestablished in the technical literature [4,10]. The machineequations governing the dynamic operation of the IPMmachine in the rotor dq reference frame are summarizedbelow. Note that the d-axis is aligned with the rotorpermanent magnet flux.

vd = rs id + pλds - ωrλqs (1)

vq = rs iq + pλqs + ωrλds (2)

λds = Lds id + φpm (3)

λqs = Lqs iq (4)

where

id and iq are the d- and q-axis stator currents [A]

vd and vq are the d- and q-axis stator voltages [V]

λds and λqs are the d- and q-axis stator flux linkages [Wb]

Lds and Lqs are the d- and q-axis stator inductances [H](Note that Lqs> Lds in an IPM machine)

φpm is the d-axis permanent magnet flux linkage [Wb]

ωr is the rotor rotation frequency [elec. rad/s]

Magnetic saturation has a significant impact on theoperating characteristics of an IPM machine. Experiencewith the automotive ISA machine [9,11] has indicated thatsaturation can be modeled quite accurately by making Lqs afunction of the q-axis stator current iq while treating Lds as aconstant. Cross-coupling saturation effects [12] betweenthe q- and d-axes are not significant in this machine and arenot included in this model.

Equations (1) and (2) can be rewritten using (3) and (4) pluschain differentiation to reflect the fact that Lqs is a functionof iq:

vd = rs id + Lds pid - ωr Lqs iq s (5)

vq = rs iq + Lqs' piq + ωr( Lds id + φpm) (6)

where

Lqs' = q

qs

iL∂

∂iq + Lqs (7)

Previous work [4,10] has demonstrated the value of the dqcurrent plane for evaluating the extended speed operatingcharacteristics of IPM machines. More specifically, suchplots provide a means of visually depicting the constraintsimposed by the inverter voltage and current limits and theirinteractions. Figure 3 presents the dq current plane plot forthe ISA machine described above whose electricalparameters are provided in the Appendix. The Appendixincludes a numerical expression for Lqs as a function iq thathas been fit to machine's inductance characteristics.

The current limit manifests itself in Fig. 3 as a circle ofamplitude 326A (peak) centered at the origin, while thevoltage limit takes the form of a family of nested ellipses allcentered at the IPM machine's characteristic current value,-φpm/Lds. The radii of the ellipses vary inversely with therotor speed. These ellipses are distorted in the vertical (iq)direction because of Lqs saturation effects, and their longestdiameters exhibit a noticeable counter-clockwise tilt fromthe horizontal (id) axis because of stator resistance effects.At any given speed, the IPM machine can operate at anycombination of iq and id values that falls within theoverlapping area of the current limit circle and the voltagelimit ellipse associated with that speed.

-800 -600 -400 -200 0 200 400 600-600

-400

-200

0

200

400

600

id [A]

iq [A

]

Current LimitCircle

Imax

VoltageEll ipses

Max T/Awithout saturation

Max T/A with Lqssaturation effect

Motoring

Generating

-φφ P M/Lds

ωω r increasing

Generat ing ModeEnvelope Trajectory

Fig. 3 Plot of id-iq current plane for the 6kW IPM machine showingcurrent limit circle, voltage limit ellipses, and current vector

trajectories.

808

Figure 3 identifies the maximum torque-per-Amp currentvector trajectory for the ISA machine in the secondquadrant motoring regime for starting operation, with andwithout the effects of magnetic saturation. The trajectorywithout saturation forms an angle with the negative –id axisthat exceeds 45 degrees, while the angle of thecorresponding trajectory with saturation is less than 45degrees.

During generating operation of the IPM machine at elevatedspeed, the maximum output power point follows theperiphery of the current limit circle towards the negative idaxis as indicated in Fig. 3. This motion is forced by theincreasing speed that progressively shrinks the voltage limitellipse, preventing the machine from operating in thevicinity of the maximum torque-per-Amp trajectory (forgenerating) identified by a dashed line in Fig. 3.

The amplitude of the ISA machine's characteristic current,φpm/Lds (=135A) is less than the inverter current limit(326A). This may seem surprising since optimum extendedspeed operation occurs when the value of φpm/Lds equals theinverter current limit [1]. However, the other ISA systemspecifications, including a limit on the machine’s maximumback-emf amplitude, result in this lower value ofcharacteristic current. Given this situation, the maximumgenerating output power trajectory eventually separatesfrom the current limit circle as the speed increases,following a trajectory that leads to the -φpm/Lds characteristiccurrent point on the negative id axis at infinite speed.

It is important to note that the illustrated generating modetrajectory in Fig. 3 for speeds above the corner pointactually represents an optimistic outer limit for the currentvector locus that can only be approached but never quitereached for an actual current regulated drive. This is truebecause the outer boundary of the voltage ellipse at anyspeed corresponds to six-step voltage operation,representing a condition in which the current regulatorloops are completely saturated. Since the current regulatorloses control of the instantaneous machine phase currentsunder such conditions [4], the current vector commandmust be continually adjusted so that it always resides safelyinside the voltage ellipse. However, it is desirable toapproach the ellipse as closely as possible under heavy loadconditions in order to deliver maximum power from theIPM machine, taking full advantage of the availableinverter dc bus voltage.

With this observation in mind, it is clear that angle betweenthe commanded current vector and the negative d-axis inFig. 3 must be reduced as the shrinking voltage ellipseprogressively intrudes on the current limit circle for speedsabove the corner point. This control action, illustrated inFig. 4, provides the basis for the new generating modecontrol algorithm described in the next section.

IS1

IS2

θ2θ1

- Iq

- Id

Flux Weakening Action

Fig. 4 Plot of current vectors illustrating flux weakening actionduring generating mode operation.

Starter/AlternatorMachine

Shaft AngleTransducer

Te

*

iq

42V

+

-

DC LinkCapacitor

VectorRotator

V d c

Vdc

V dc

T Start(For Starting)

Vdc*

(ForGenerating)

+ -P I

S/AControlModule

id

V qe*

Vd

e*

V qs*

Vd

s*

θθr

V dc

GateSignals

SpaceVector

ModulatorVectorRotator

d/dt

ωω r

θθ r

θθ r

Fig. 5 Block diagram of ISA controller configuration.

B. Controller Configuration

A top-level block diagram of the ISA controller is providedin Fig. 5. This figure includes many of the features thattypically appear in high-performance vector controlconfigurations utilizing synchronous-frame currentregulation. That is, phase current information is combinedwith rotor position feedback to develop measurements ofthe instantaneous id and iq that are fed to the currentregulator imbedded in the block labeled S/A ControlModule. Another input to this module is the torquecommand Te

* that is derived from either the starting torquecommand or the bus voltage regulator, depending on thesystem's operating mode.

The outputs of this module are the voltage commands vde*

and vqe* in the synchronous reference frame. These voltage

commands are then converted back to the stationaryreference frame using a second vector rotator before beingapplied to a space vector modulator. This modulatordevelops the inverter switching commands, making use ofthe measured bus voltage vdc to insure a smooth transitionfrom PWM operation into saturated six-step voltageoperation under all bus voltage conditions [13].

809

Figure 6 shows the detailed structure of the S/A ControlModule that appears as a block in Fig. 5. The controlcomponents enclosed by the inner dashed-line box in thelower half of Fig. 6 are responsible for flux weakeningoperation and are only are activated at elevated speedswhen the current vector approaches the prevailing voltagelimit ellipse at any given speed. Under all other conditions,such as low-speed starting operation, the flux-weakeningcontroller is essentially dormant, having no effect on thecontrol action of the Fig. 6 S/A Control Module. Thecontrol elements lying across the top half of Fig. 7dominate its response under such conditions, as describedbelow.

Starting Operation

The vector control principles for controlling the ISAmachine to deliver high starting torque (up to 150 Nm) as amotor are well established in the literature [14] and will besummarized only briefly here. Since starting modeoperation occurs only at low speeds where the voltage limitellipse is not a factor, the maximum torque-per-Amptrajectory in the second quadrant provides the preferredoperating points for motoring torque production. Themaximum available starting torque from the ISA machineoccurs at the point in the second quadrant where themaximum torque-per-Amp trajectory intersects the currentlimit circle.

The S/A Control Module in Fig. 6 executes this startingmode control by converting a starting torque command Te

*

into the corresponding values of d- and q-axis currentcommands, idm and iqm, using the function blocks f1 and f2and the polar-to-rectangular conversion block. These f-functions are pre-programmed with the maximum torque-per-Amp trajectory that matches the IPM machine'scharacteristics. The two f-functions develop the desiredcurrent vector trajectory in polar coordinates as currentamplitude |I|* and angle θ* commands (see Fig. 5) forconvenient compatibility with the flux weakening controlalgorithm that will be described in the next section. The θ*angle command passes through to the polar-to-rectangularconverter unaffected by the flux weakening controlalgorithm at low speeds during starting.

The upper right side of Fig. 6 represents the stator currentregulator in the synchronous reference frame. There aremany different ways in which such a regulator can beimplemented. The particular implementation shown in Fig.6 applies feedforward decoupling compensation to theoutput voltage commands using the machine's steady-statevoltage relations, so that:

vqss = rs iqm

+ ωr (Lds idm + φPM) (9)

vdss = rs id

m - ωr (Lqs iqm) (10)

PolarTo

Rect

VoltageCompensation

Block

iqm

id

+ -

+

-

+

+

+

+

vdss

vqe*

θθ *'

| I |*T e*

ModulationIndex

Calculator+

-

Mth

ββ ∗∗

Flux WeakeningControl Module

S/AControl

Modlule

AS

vdc

G

G

Integrator

MaximumTorque/Amp Functions

00 << β β ∗∗ << 1 1

idm

iq

∆∆ iq

∆∆ id

vqss

vde*

vqe'

vde'

f2(T)

f1(T)

vqe* vd

e*

θθ∗∗

ωω r

M

Fig. 6 Block diagram of S/A Control Module.

Generating Operation

Development of an effective flux-weakening controlalgorithm provides the key to achieving extended constant-power operation to meet the demanding generating moderequirements of the automotive ISA application. The newalgorithm implemented in this system works by directlyreducing the angle θ of the commanded current vector withrespect to the negative d-axis as illustrated earlier in Fig. 4.

The control elements that implement this flux weakeningaction are enclosed in the sub-block labeled FluxWeakening Control Module in the lower half of Fig. 6.This module executes the current vector angle reduction bymultiplying the angle command θ* from maximum torque-per-Amp function f2 by a scaling factor β* that variesbetween 0 and 1. According to this approach, only theangle of the current vector, and not its amplitude, is directlycontrolled by the flux weakening algorithm. As long as thevalue of β* is 1, the Flux Weakening Control Module exertsno influence on the current vector trajectory defined by themaximum torque-per-Amp trajectory.

The value of β* is determined by how closely the requiredstator voltage approaches the saturated six-step voltagevalue at any instant in time. Since the ISA drive isdesigned for high frequency PWM operation, theinstantaneous PWM modulation index, M, can be used as aconvenient and sensitive indicator of the current regulator’sproximity to total saturation (i.e., M = 1). The modulationindex value can be conveniently calculated using thesynchronous frame dq voltage commands, vqs

e* and vdse*, as

follows:

M =

dc

2*eqs

2*eds

V2)v()v(

π

+(11)

where Vdc is the measured value of the dc link voltage at theconverter input terminals.

810

Any excess value of M above a preset threshold level, Mth(less than but close to 1) is integrated to reduce the value ofβ∗ (0<β∗<1) that scales the current vector command angleaccording to θ*’ = β∗ · θ∗ . This feedback loop achieves thedesired flux weakening action in Fig. 4 by swinging thecurrent vector in towards the negative d-axis in order toretain it within the prevailing voltage ellipse at that timeinstant. By this action, the value of the modulation indexnaturally decreases as the current vector operating pointmoves away from the voltage ellipse boundary, establishinga stable operating point loop in the flux weakening regime.

When the torque command and/or rotor speed dropsufficiently so that flux weakening is no longer required,the feedback loop naturally responds accordingly to reduceits effect on the current vector angle θ. That is, the value ofβ∗ quickly integrates back to 1 when the modulation indexdrops below its threshold value M*. Thus, the feedbackloop becomes passive with no effect on the vector controloperation until flux weakening action is required again.

Use of the measured value of dc link voltage Vdc in themodulation index calculation (11) makes it possible for thecontroller to adapt immediately to any changes in the busvoltage. This feature is important in applications such as anautomotive ISA where the dc bus voltage can be expectedto change significantly depending on the bus loading andthe vehicle battery state of charge. On the other hand, thisvoltage measurement can be replaced by a constant value inapplications where the dc bus voltage is known and wellregulated within a narrow range, eliminating the need forthe bus voltage sensor.

The flux weakening algorithm introduced above is naturallybipolar, working as well for motoring operation as forgenerating where it is primarily needed in the ISAapplication. The resulting motoring torque envelope alongthe voltage ellipse boundary for the IPM machine in thisISA application is shown in Fig. 7. This figure confirmsthat the required 150 Nm for starting will be available atlow speeds during operation on the maximum torque-per-Amp trajectory.

IV. CONTROLLER PERFORMANCE

A. Drive System Simulation

Steady-state and dynamic performance characteristics of thecomplete ISA drive system including the machine, PWMinverter and the controller have been investigated usingcomputer simulation. Matlab/SimulinkTM was chosen as thepreferred simulation software tool for carrying out thisanalysis.

The switching behavior of the inverter is modeled using sixideal switches. The IPM machine is modeled in the dqsynchronous frame using the parameter values found in theAppendix, including the effects of magnetic saturation onLqs as a function of iq. All of the controller functions are

0 1000 2000 3000 4000 5000 60000

20

40

60

80

100

120

140

160

Speed (rpm)

Tor

que

(Nm

)

156 Nm

Fig. 7 Motoring torque envelope for the ISA machine operatingwith a 42V bus.

modeled individually including PWM space vectormodulation and its saturation characteristics as themodulation index M approaches 1. However, controllerquantization and sampling delays have not been included inthis model.

Starting Mode Operation

Simulation results confirm that the ISA drive systemoperates as expected to deliver 150 Nm during low-speedstarting operation. Since the engine is designed to start atspeeds well below 500 rpm, flux weakening operation is notactivated during this operating mode.

Dynamic specifications for the ISA starting mode operationcall for development of full starting torque within 20 ms,based on suggestions from automaker representatives whohave helped to oversee this development effort. Figure 8shows the simulated step torque response of the IPMmachine at standstill using a nominal 42 Vdc bus voltage.The torque response curve predicts that the system responseto such a large-signal step command is very well behaved,with the torque reaching its final value of 150 Nm within 5ms, far less than the 20 ms maximum limit. Once reached,the system holds the steady-state torque very stably at thedesired 150 Nm level as the machine rotor accelerates.

According to draft specifications that have been developedfor the new 42-V bus [15], the bus voltage is allowed totemporarily drop as low as 21 V during starting modeoperation due to the heavy electrical load. Simulation ofstarting mode operation with the bus voltage set at 21 V(see Fig. 9) confirms that the IPM machine retains itscapability of developing the required 150 Nm well withinthe 20 ms dynamic response requirement. The machinecorner speed drops to approximately 400 rev/min underthese low bus voltage conditions (refer to Fig. 7), but thiscorner speed is still sufficiently high to insure fast enginestarting.

811

0 0.005 0.01 0.015 0.02 0.025-20

0

20

40

60

80

100

120

140

160

time [sec]

Tor

que

[Nm

]

Fig. 8 Starting torque step response for 150 Nm command.Vdc = 42V

0 0.005 0.01 0.015 0.02 0.025-20

0

20

40

60

80

100

120

140

160

time [sec]

Tor

que

[Nm

]

Fig. 9 Starting torque step response for 150 Nm command.Vdc = 21V

Generating Mode Operation

Based on the emerging specifications for the new 42-VPowernet [15], the bus voltage should be regulated toremain within a band of voltage between 30 and 50 Vduring normal operation. A simple closed-loop voltageregulator using the measured bus voltage was introducedinto the system during ISA system operation in thegenerating mode, as indicated in Fig. 5.

The Simulink ISA system model has been used to evaluatethe performance capabilities of this generating modecontroller under various operating conditions. Unlike thestarting mode operation described above, system operationas an alternator inevitably exercises the new flux weakeningalgorithm, particularly at higher speeds.

0 0.05 0.1 0.15 0.239.5

40

40.5

41

41.5

42

42.5

t [sec]

Vd

c [

V]

Fig. 10 Generating mode bus voltage response for step loadincrease from 0 to 4kW at 600 rev/min. Note expanded scale and

suppressed zero.

0 0.05 0.1 0.15 0.2-250

-200

-150

-100

-50

0

50

t [sec]

id a

nd

iq

[A

]

iq and iq command

id and id command

0 0.05 0.1 0.15 0.2-250

-200

-150

-100

-50

0

50

t [sec]

id a

nd

iq

[A

]

iq and iq command

id and id command

Fig. 11 Generating mode d- and q-axis current commands andresponses for step load increase from 0 to 4kW at 600 rev/min.

It is assumed that a 42-V battery is connected to the bus tosupply the engine starting power as indicated in Fig. 5. Inaddition, a dc link capacitor is present to absorb the PWMripple current from the switching converter as well as toassist in supporting the bus voltage during transient loading.The battery has been modeled as a voltage source in serieswith a resistance. Parameters for a charged lead-acidbattery were used to maximize the resistive decouplingbetween the battery and the ISA system (see Appendix).

Figures 10 and 11 present the predicted transient responsecharacteristics of the ISA system during generating modeoperation for a sudden step in load from 0 to 4 kW (i.e.,rated load) at 600 rev/min. This represents a worst-casestep load that exceeds any transients expected during

812

0 0.05 0.1 0.15 0.239

39.5

40

40.5

41

41.5

42

42.5

t [sec]

Vd

c [V

]

Fig. 12 Generating mode bus voltage response for step loadincrease from 0 to 6kW at 6000 rev/min.

0 0.05 0.1 0.15 0.2-200

-150

-100

-50

0

50

t [sec]

id a

nd

iq

[A

]

iq and iq command

id and id command

0 0.05 0.1 0.15 0.2-200

-150

-100

-50

0

50

t [sec]

id a

nd

iq

[A

]

iq and iq command

id and id command

Fig. 13 Generating mode d- and q-axis current commands andresponses for step load increase from 0 to 4kW at 600 rev/min.

normal vehicle operation. The bus voltage recovers to 42 Vin approximately 50 ms with a maximum voltage excursionof 2 V, well within the specified limits for normal Powernetoperation (note the expanded scale and suppressed zero inFig. 10). The d- and q-axis currents in Fig. 11 are similarlywell behaved, rising smoothly from 0 to their new steady-state values needed to support the 4 kW load.

Figures 12 and 13 show the corresponding transientresponses for the bus voltage and dq machine currentsduring a worst-case step load from 0 to 6 kW (rated load) atthe maximum operating speed of 6000 rev/min. Althoughthe transient voltage dip is somewhat larger (2.8V) than forthe 4 kW step, the duration of the transient is noticeablyshorter (~15 ms). Here again, all of the transientwaveforms are well behaved. Because of the high speed,the 6kW operating point takes the IPM machine deep intoits flux weakening regime. This is apparent from the post-

-180 -160 -140 -120 -100 -80 -60 -40 -20 0-180

-160

-140

-120

-100

-80

-60

-40

-20

0

id [A]

iq [A

]

Flux Weakening Action Begins

Max T/A2000 rpm @ 6 kW load

3000 rpm @ 6 kW load

6000 rpm @ 6 kW load

Fig. 14 Transient current vector trajectory during steps from 0 to6kW at 2000 rev/min, followed by stepped speed increases to

3000 rev/min and then to 6000 rev/min, all at 6 kW.

transient steady-state current values in Fig. 13, with largenegative values of id compared to iq.

The action of the flux weakening algorithm can be clearlyillustrated by examining the transient trajectory of the statorcurrent vector in the synchronously-rotating dq referenceframe as shown in Fig. 16. In this example, the deliveredoutput power is initially stepped from 0 to 6 kW at 2000rev/min. The speed is subsequently stepped first to 3000rev/min, and, finally, to 6000 rev/min with the output powerheld constant at 6 kW. Each of these steps takes the IPMdeeper into flux weakening operation, apparent in Fig. 14from the clockwise migration of the current vector in thedirection of the negative d-axis.

B. Experimental Verification

A demonstrator version of the ISA system using theprototype IPM synchronous machine shown earlier in Fig. 2has been assembled for purposes of experimentalverification. A block diagram of this equipment is providedin Fig. 15. Since the focus of this verification effort is onthe machine and the controller, the inverter power stage of acommercial industrial drive (excited via a step-downtransformer to generate the 42V dc link) was selected foruse in the ISA drive system. The control algorithm hasbeen implemented using a dSpace 1103 controller,appropriate for this type of rapid prototyping effort. Ahigh-performance four-quadrant induction motor drive isused as the load machine and prime mover during ISAstarter and alternator operation, respectively.

Experimental tests are planned to verify the operatingcharacteristics of the ISA system, including the performanceof the flux weakening control algorithm during generatingmode operation. Results of this testing will be presented atthe conference.

813

Step down Xfrmr

dSpace Controller

ISA Drive

Resistor Load Bank

4-Quad IM

Dyno Drive

230 Vac 3φ

230 Vac 3φ

ISA Machine

IM Dyno Mach

Torque- meter

Fig. 15 Laboratory configuration for ISA system tests.

V. CONCLUSIONS

This paper has presented a new flux weakening algorithmfor an IPM synchronous alternator machine suitable forexciting the machine to deliver constant power over a widespeed range (10:1 or higher). The flux weakeningalgorithm acts to rotate the instantaneous current towardsthe negative d-axis in the synchronously-rotating referenceframe in order to establish and maintain operation withinthe combined constraints imposed by the available voltage,current, and the rotor speed. Advantages of this algorithminclude its ability to automatically adapt to changes in thebus voltage by using the PWM modulation index torecognize the threshold of current regulator saturation.

Simulation results have been presented that demonstrate thedesirable performance characteristics of this algorithm overa wide speed range in conjunction with an automotiveintegrated starter/alternator system designed to deliver 6kWat 6000 rev/min. The results indicate that the fluxweakening algorithm responds rapidly and in a well-behaved manner over a wide range of operating conditions.Experimental tests are presently being conducted to confirmthese predicted results.

APPENDIX

Machine Parameters

Rs = 0.0103 Ω Lds = 64.97µH φPM = 6.3x10-3 Wb

Lqs = C (iqs)B [H] for Lqs < Lqmax; otherwise Lqs = Lqmax

where C = 0.0058, B = -0.605, Lqmax = 305.05µH

Lead-Acid Battery Model(Charged) and dc Link Parameters

Vbat = 38.9 V Rbat = 10 Ω Cbus = 75x10-3 F

ACKNOWLEDGMENTS

The authors gratefully acknowledge the support of the MITConsortium on Advanced Automotive Electrical/ElectronicComponents and Systems and the Wisconsin ElectricMachines and Power Electronics Consortium (WEMPEC).We also thank Dr. Edward Lovelace for his generousconsultation assistance regarding the ISA machine.

REFERENCES

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[15]"Road vehicles – Conditions for electrical and electronicequipment for a 42V powernet – Part 1: General", Draftspecification, WGS/WD 03/2000-1, ISO, Apr 2000.

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