Theory and Operation of a Four-quadrant Switched Reluctance Motor Drive With a Single Controllable Switch-The Lowest Cost Four-quadrant Brushless Motor Driv

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 4, JULY/AUGUST 2005 1047

Theory and Operation of a Four-Quadrant SwitchedReluctance Motor Drive With a Single Controllable

Switch—The Lowest Cost Four-QuadrantBrushless Motor Drive

R. Krishnan, Fellow, IEEE, Sung-Yeul Park, Student Member, IEEE, and Keunsoo Ha, Student Member, IEEE

Abstract—Low-cost motor drives are being sought forhigh-volume energy-efficient home appliances. Key to the re-alization of such low-cost motor drives is the reduction of thepower electronic converter to the barest in terms of its compo-nents, particularly the active devices, finding the motor with theleast complexity for manufacturing and a controller that canextract the desired performance from the machine and convertercombination. These and other factors such as self-starting, speedcontrol over a wide range, and, most of all, the crowning as-pect of four-quadrant operation with a bare minimum numberof controllable switches remain as formidable challenges forlow-cost motor drive realization. An innovative four-quadrantswitched reluctance motor (SRM) drive with only one controllableswitch is realized in this paper, for the first time, in the opinionof the authors. The motor drive is realized using a two-phasemachine and a single controllable switch converter. The theoryand operation of the proposed four-quadrant SRM drive withthe proposed control algorithm for its realization are described.The motor drive is modeled, simulated, and analyzed to verify itsfeasibility for self-starting, speed control, and for four-quadrantoperation, and the simulation results are presented. Experimentalresults confirm the validity of the proposed control algorithm forfour-quadrant control of the SRM drive. The focus of the paperis mainly directed toward the control algorithm for realizing thefour-quadrant operation of the two-phase SRM drive with a singlecontrollable switch converter.

Index Terms—Motor drives control, power electronics, switchedreluctance motor (SRM) drives.

I. PROPOSED MOTOR DRIVE FOR FOUR-QUADRANT OPERATION

FEDERAL regulations for some appliances in regard tomandates on higher efficiency of the system to start with

have come into force and it is expected that they will alsospread to other categories of appliances. One way efficiencycan be increased is by introducing variable-speed operationof the motor. Variable-speed operation increases the part load

Paper IPCSD-05-023, presented at the 2004 Industry Applications SocietyAnnual Meeting, Seattle, WA, October 3–7, and approved for publication inthe IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Industrial DrivesCommittee of the IEEE Industry Applications Society. Manuscript submittedfor review September 1, 2004 and released for publication April 15, 2005. Thiswork was supported by The Center for Innovative Technology, Reston, VA,through the efforts of Panaphase Technologies.

The authors are with the Center for Rapid Transit Systems, The Bradley De-partment of Electrical and Computer Engineering, Virginia Polytechnic Instituteand State University, Blacksburg, VA 24061 USA (e-mail: [email protected]; [email protected]; [email protected]).

Digital Object Identifier 10.1109/TIA.2005.851019

efficiency as well as delivering higher efficiency over theentire speed range and, hence, the interest in variable-speedmotor drives for applications that have traditionally remainedconstant speed or with a few set speeds in home appliances.While a variable-speed universal motor drive may becomeacceptable in some appliances, the industry wants to moveaway from brush and commutator-based machines for reasonsof reliability, safety, longevity of operation, acoustic noise, andoverload capability for longer durations. Hence, the search fora simpler and lower cost four-quadrant brushless motor drivehas intensified with the prospective oncoming variable speedapplications in home appliances and hand tools contributed toby both federal regulations and competition among appliancemanufacturers to introduce newer features and enhance systemefficiency.

Many solutions have been proposed for low-cost motordrives and most of them revolve around the use of single-phaseswitched reluctance motor (SRM) with parking permanentmagnets on the stator and two-switch-based asymmetric con-verter, or two-phase SRM with three-switch-based converterand single-phase permanent-magnet brushless dc motor driveswith four-controllable-switch-based converter, to mention afew [1], and other variations in the literature too numerous tomention here. Use of single-phase and three-phase inductionmotors with four-controllable-switch-based inverters has beenattempted. Many of these solutions, though providing highlydesirable performance, are yet to be embraced as their cost isas yet unacceptable in the appliance industries. The factors thatare widely cited in the industry for not embracing the formerlyproposed solutions are many. Some of these factors are givenbelow, and these served as a compass for the authors to steeraway from these concerns in seeking solutions to the lowcost motor drives in the competitive segment of the applianceindustries.

1) The cost of the machine is higher in almost all cases otherthan the single-phase SRM.

2) The lowest cost machine, which is a single-phase SRM,is not truly low cost as it involves permanent magnetsfor parking the rotor at a desirable position for starting,adding not only to the cost but complexity in manufac-turing.

3) The cost of the converter and inverter has come downsignificantly but not to the level where it can compete

0093-9994/$20.00 © 2005 IEEE

1048 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 4, JULY/AUGUST 2005

with a one-controllable-switch universal motor drive forone-quadrant application in many low-performance vari-able-speed applications.

4) A two-controllable-switch-based converter (which seemsto have gained some traction) is still expensive as com-pared to a one-controllable-switch-based brush dc or acuniversal motor drive system with limited one-quadrantvariable-speed application.

5) Though the proposed brushless and commutatorless so-lutions as compared to brush-type machines in appliancesare welcome, being brushless alone is not the determiningfactor in the selection of a motor or a motor drive in thelow-cost applications which is a key fact of life in this in-dustry segment.

6) In high-speed ( 20 000 r/min) motor drives, the per-manent-magnet brushless machines are believed not toprovide low-cost solutions even though there may be aslight efficiency advantage in these machines, if not athigh speeds, but certainly at low and medium speeds.In appliances, higher efficiency is desirable but cost-ef-fective and high-efficiency solutions are much moredesirable and acceptable is a fact to be noted (as a fewpoint difference in percent efficiency is not a significantfactor).

7) Inmanyinstances, four-quadrantdriveoperationisnotnec-essary but will be an important feature for future productdevelopment of appliances. Some of the proposed conven-tionalthree-phaseortwo-phaseacandSRMdrivessolutionsthough provide a four-quadrant operation, the cost associ-ated with the converter/inverter is high.

Anchored with these industry inputs, the authors have identi-fied the following common features of low-cost motor drivesrequired for high-volume applications:

1) brushless motor (can be ac or permanent-magnet brush-less dc or SRMs);

2) high-speed operational capability;3) high-efficiency operability over a wide speed range;4) four-quadrant operational capability;5) minimum number of controllable switches (preferably

less than two) to reduce the cost of power electroniccircuit as well as to minimize the cost of the attendantcircuits such as gate drives and logic power supplies andalso to minimize the volume of heat sinks;

6) rotor position sensor-free operation;7) smallest footprint for controller and converter layout to

reduce the volume, weight, and cost of the power elec-tronics and controller.

To address these issues to the fullest possible level, somesolutions have already been proposed even though they havenot come into the literature. A single-controllable-switch-basedbrushless motor drive solution is highly desirable for many ofthe low-cost applications and such a set of solutions existed[2], [3] prior to this publication for SRM drive systems. One ofthe variations can be found in [4]. A number of single-quadrantSRM drives with single-switch power converter topologieshave been under research and development for more thanfour years at Virginia Polytechnic Institute and State Uni-

versity, Blacksburg. Power electronics and controller werepacked within 3 in 3 in 1.5 in with standard off-the-shelfcomponents for a 1-hp motor drive, though versions underdevelopment are expected to have a volume reduction of 50%in the packaging. While such packaging may be of criticalimportance in commercial and industrial applications, thiswill not be pursued in detail, as imparting four-quadrant op-erational capability with this converter-based drive systemis considered much more important. It is highly significantas it bestows for the first time a four-quadrant operation ona brushless motor drive with only a one-controllable-switchconverter. This alters the current state of art, as there is no othermotor drive which can have a four-quadrant operation withthat bare minimum of controllable-switch-based converter. Forthe first time, such a development points to the realization ofthe lowest cost brushless motor drive that may be ideal formany applications. Some of these applications have eludedintroduction of variable-speed and four-quadrant operation dueto the higher cost of the total motor drive package. Note thata conventional four-quadrant SRM drive requires a minimumof two or more controllable switches and, as well, so do brushdc and ac universal motor drives. Therefore, the key aspect offour-quadrant operability with a wide variable-speed controlwill be the focus of this paper. It is believed with this fullyfour-quadrant and variable-speed operation incorporated inthe single-controllable-switch-based SRM drive, a low-costbrushless variable-speed motor drive has been realized for thefirst time in the literature.

A two-phase SRM, one-controllable-switch converter, and adigital signal processor (DSP) controller are the building blocksof the low-costmotordriveconsidered in thispaper.Theproposedcontrol algorithms for starting, four-quadrant operation andvariable-speed control of an SRM drive with single controllableswitch are the key to the realization of the low-cost motor drive.The proposed system is modeled, simulated, and analyzed forvalidating the proposed control algorithms. Experimental resultsfromalaboratoryprototypeconfirmthefeasibilityoftheproposedlow-cost motor drive four-quadrant control and operation.

Thispaper isorganizedasfollows.SectionIIdescribes thecon-sidered SRM and its features, and also the converter and its opera-tionwith theSRM.Section IIIgives the realizationofself-startingof the motor drive without parking magnets. Section IV detailsthe control algorithm for the realization of a four-quadrant motordrive. Based on these developments, the complete drive system,its modeling, simulation, andanalysis arepresented in Sections Vand VI. Experimental results are presented both for self-startingand for four-quadrant operation in Section VII. Conclusions aredrawn and presented in Section VIII.

II. CONSIDERED MACHINE AND POWER CONVERTER

Rationale for the selection of the electric machine and adescription of the one-controllable-switch-based converter aregiven in this section.

A. Machine

The machine selection was based on factors such as the fol-lowing [1], [10]:

KRISHNAN et al.: THEORY AND OPERATION OF A FOUR-QUADRANT SRM DRIVE 1049

1) free of brush and commutator;2) easier manufacturability (and that, too, anywhere around

the world, and this factor excludes permanent-magnetbrushless dc machines);

3) preferably no permanent magnets on the rotor or statorto reduce manufacturing complexity (this excludes allpermanent-magnet machines including brushless dc ma-chines);

4) operability at speeds up to 40 000 r/min;5) lowest cost (eliminates almost all other machines other

than SRMs);6) operational capability with unidirectional current (this

eliminates induction and synchronous reluctance ma-chines).

Given these factors, the choice narrows to switched reluctancemachines. With a minimum of winding insertion operation, atwo-phase SRM with concentric windings is considered forfurther study. The machine is a two-phase SRM with one phaseforming the main phase and the other forming an auxiliaryphase. The torque is mainly extracted from the operation of themain phase. The auxiliary phase is intended for commutationof current in the main phase winding. Note that the auxiliarywinding also lends itself to sensing the rotor position by mon-itoring its current and flux linkages or by other variables andmeans. A number of opportunities which open up with thiskind of two-phase machines are to be noted. The number ofturns in the main and auxiliary windings need not be equal toeach other and, as well, their wire sizes also need not be equal.The only requirement of the machine is that the phase windingsmust be spatially (phase) shifted from each other. As the focusof the paper is neither on design of such machines nor on therequirement to optimize the drive system performance, furthertreatment of the machine is not given for lack of space. Themachine used in this study is described with its characteristicsin [4]. Equally other types of machines such as those givenin [5]–[8] may also be sufficient for the proposed motor drivesystem. While the constructional details and cost may varybetween these machines to some extent, a number of featuresdesirable in low-cost machines are preserved.

B. Power Converter

The power converter chosen to work with the two machinephase windings is shown in Fig. 1. This is only one of the single-controllable-switch-based converter topologies [2]. The powerconverter obtains its dc link either from a single-phase (as shownin figure) or from a three-phase ac through appropriate rectifiersand an electrolytic capacitor. The machine-side converter con-sists of a controllable switch Q , two diodes D and D , and acapacitor C . The main winding is controlled with the control-lable switch directly. When it is turned on (mode 1), the mainwinding is applied with the dc-link voltage. If there is current inthe auxiliary winding, then it goes to charge the dc-link capac-itor C , and closes the path through the capacitor C . When Qis turned off, (mode 2) a path for the current is provided throughdiode D and capacitor C and also through auxiliary windingand D . Note that the capacitor C is very small compared tothe dc-link filter capacitor C almost by a factor of 100–200.During the turn-off of the controllable switch, it is seen that the

Fig. 1. Considered motor and power converter schematic for four-quadrantoperation.

capacitor gets charged or the current is circulated through theauxiliary winding and during both operations, the main windingis involved. From this, it is seen that the current in the auxiliarywinding is also controlled by the controllable switch indirectly.Alternately, one can perceive D and C as a snubber circuit fortransferring energy from the main winding during turn-off in-stants of current control and commutation and also as an energysource to force current through the auxiliary winding. More onthe converter operation, analysis, and design will be publishedin the near future [3]. Diode D is optional it may be noted andif it is used it need not be a fast acting type. With this, the circuitbecomes very compact and it is believed that it has the lowestnumber of elements compared to other circuits in the literature.

III. SELF-STARTING

The single-switch converter creates a challenge in starting theSRM. As the dc link is energized, note that the current flowingin the main winding attracts the rotor poles to align with themain stator poles. At this position, there is no torque productioncapability for the main winding even if current is built in to themain phase winding. As for the auxiliary winding, it requiresa current to produce a torque. This current can come from theauxiliary (or snubber or auxiliary) capacitor C when the maincurrent decays and the auxiliary capacitor has enough chargeto initiate a current closing the current path through the dc-linkcapacitor C . If the auxiliary current is insufficient to producea significant torque to move the rotor from its aligned positionwith the main stator poles, then other options are built in forself-starting. They are described in the following paragraph.

Key to the success of the four-quadrant operation of the con-sidered motor drive is the ability to start at all rotor positionsin both directions. In order to start reliably, a starting scheme isproposed in this paper. When the rotor poles are aligned to themain stator poles, a start gate pulse signal of certain durationis applied to the controllable switch. At this time, the rotor is atstandstill. This results in turn-on of the switch for a desirable du-ration until the current is equal to a nominal or preset value andthen the switch is turned off. That provides a charge to the aux-iliary capacitor C , as well as forcing a current in the auxiliarywinding. Thereby, the energy in the main winding is transferredto the auxiliary winding and/or auxiliary capacitor due to theflow of current from the main winding to the auxiliary winding


and to the capacitor depending on the charge state of the capac-itor. This results in the auxiliary winding producing a torque.That torque may be enough to move the rotor poles away fromtheir aligned position with the main stator poles. When the mainwinding current decays, note that the auxiliary capacitor sup-plies the auxiliary winding with the current, resulting in somepositive torque production by the auxiliary phase winding.

However, the starting problem will persist if the rotor polesalign with the stator main poles exactly and the starting torqueproduced by the auxiliary winding is insufficient to turn the rotorpoles away from the aligned position with the main poles. In thatcase, multiple turn-on and turn-off of the controllable switchbuilds a larger current in the main winding and, also, the auxil-iary winding, resulting in starting of the machine. The numberof multiple turn-on and turn-off signals is determined by manyfactors including the thermal capability of the machine as wellas by the way the two machine phases are arranged spatially withrespect to each other or how the rotor is constructed so that thereis an overlap of torque characteristics of phase windings overthe rotor position. Invariably, all these factors are influenced bythe intended application and its starting torque requirement. It iscritical to ensure that the desired direction of rotation is enforcedquickly when single-pulse or multiple-pulse starting is applied,so that the rotor does not traverse noticeably over a significantangular distance in the unintended direction.

IV. FOUR-QUADRANT CONTROL AND OPERATION OF THE

CONSIDERED SRM DRIVE

A large amount of literature [1], [11]–[14] exists on four-quadrant control of conventional SRM drives with high degreeof freedom in the machine converter , and none exists for SRMdrives with a single-controllable-switch power converter. Thisis due to the absence of the converter itself on the scene so far.Significant features peculiar to this converter are limited directcurrent control of the main phase and its heavy dependence onthe auxiliary phase winding and auxiliary capacitor state. Like-wise, the auxiliary winding current control is dependent on theduty cycle of the controllable switch, motor speed and load,and state of the auxiliary capacitor. These constraints have tobe managed very tightly in order to implement a four-quadrantvariable-speed operation in this motor drive. It is discussed inthis section.

A. Clockwise (CW) Motoring and Regeneration

In order to achieve motoring in the forward direction, for ex-ample, the CW direction, the stator winding should be excitedwhen the rotor is moving from the unaligned to the aligned posi-tion. Assuming that the rotor poles reach the unaligned position(almost in alignment with the auxiliary stator poles) of the mainphase winding and such a position is detected, the main phasewinding is energized. When the rotor poles have reached nearhe aligned position with the main poles, the current in the mainphase is turned off. The machine spins then, for example, in theCW direction and, during this time, the main winding is ener-gized as the rotor poles move from the auxiliary stator poles tothe main stator poles. The regenerative braking, on the contrary,is achieved by excitation of the stator windings when the rotor

moves from the aligned position toward the unaligned position.During this time, the kinetic energy in the machine is transferredto the dc-link source via the auxiliary winding. Note that the ma-chine is still in the CW direction of rotation but its speed rapidlydecreases toward standstill.

B. Counter Clockwise (CCW) Direction Motoring andRegeneration

When the speed reversal command is obtained, the controlgoes into the CW regeneration mode as explained in the para-graph above. That brings the rotor to the standstill position. In-stead of waiting for the absolute standstill position, continuousenergization of the main phase is attempted during the time rotorpoles move from aligned to unaligned rotor positions. This notonly slows the rotor to standstill rapidly but also provides an op-portunity for reversal if the rotor poles come to a stop betweenthe main and auxiliary poles. Therefore, there is the necessity fordetermining the instant when the rotor of the machine is ideallypositioned for reversal. Hall-effect sensors are used to ascertainthe rotor position and speed and they are located at the mainwinding and auxiliary winding. From the Hall sensor outputs,it is determined whether the machine has reversed its direction.Crucial to this is finding the aligned rotor position of the rotorpoles with the auxiliary poles. This is the ideal moment for en-ergizing the main stator phase so that the machine can start mo-toring in the CCW direction.

1) Delay Time: After sensing the unaligned position, thepulsewidth-modulation (PWM) signal is cleared and a reversalstart pulse can be implemented. Sufficient time for the reversalstart pulse, which may be named the delay time, is requireddue to the fact that the rotor does not move from its alignedposition with the stator main poles as it does not produce anytorque at this detent position. Best position to insert the startpulse for reverse rotation is when the rotor poles are in betweenthe main stator poles and the auxiliary stator poles. The way toget the rotor in to such a position is achieved by the proceduredescribed below.

The start pulse for reverse rotation consists of one turn-onswitch signal and one turn-off switch signal. When the turn-onsignal is given to the controllable switch, current flows into themain winding. During turn-off of the controllable switch, cur-rent in the main winding flows into the auxiliary winding aftercharging the capacitor to a value equal to the dc-link voltage.When the controllable switch is again turned on, the current inthe auxiliary winding goes to the dc-link source, resulting inits prolongation. With the increase of auxiliary current by thisprocess of charging and discharging from the main winding,the rotor starts moving from its aligned position. The energyin the capacitor will increase the current through the auxiliarywinding, thus producing a torque moving the rotor poles towardthe stator auxiliary pole pair and eventually aligning the rotorwith the auxiliary poles and enabling rotation in the CCW di-rection of rotation.

V. DRIVE SYSTEM CONTROL

With the understanding gained over the discussion of theself-starting and four-quadrant control, the drive system control


Fig. 2. Proposed motor drive control system.

schematic is derived as in the following and shown in Fig. 2.The drive system senses current and two discrete rotor posi-tions, spaced 45 apart. A DSP accepts the Hall position signalsand the analog current signal. From the discrete rotor positionsignals, rotor speed is estimated. The analog current signal isfiltered before it is fed to the DSP where it is digitized throughits analog-to-digital converter (ADC).

A startup signal is issued for the machine to activate its speedcommand. Depending on the speed command, which consists ofthemagnitudeanddirection, theoperationalmodecorrespondingto motoring or braking is evaluated. If it is motoring mode, thespeed error is found from the difference of the speed and its com-mandwhichthenisprocessedbythespeedcontroller, in thiscaseaproportional plus integral (PI) controller. Then, the output of thespeed controller forms the current command. The current com-mand is enforced by means of current feedback control having acurrent controller which again is a PI type. The output of the cur-rent controller is a control signal that is proportional to the dutycycle of the controllable switch in the converter. This is updatedfor every carrier period in the PWM control.

If speed command indicates regenerative braking has to beperformed then it takes a different route. If the rotor speed isabove a certain set low speed, only the PI current controller is inforce and nothing is tampered with. If the rotor speed is lowerthan the set low-speed threshold, then the controller gives a re-versal pulse to act upon directly and circumvents the PI currentcontroller during this period. Once the speed is reversed, thenautomatically the controller goes into motoring mode in the op-posite direction and the PI current controller comes into playin dynamically determining and controlling the PWM signalwhich serves as the gate control signal.

The software implementation of the control algorithm isshown in Fig. 3 at macrolevel. With the explanations providedin this and previous sections, this figure becomes self-explana-tory. Note that SSSRM stands for single-switch SRM drivesystem.

A. Four-Quadrant Control Algorithm

The flowchart for four-quadrant control implementation isshown in Fig. 4. The purpose of the quadrant controller is to set


Fig. 3. Flowchart for the software implementation of the proposed drivesystem.

up the PWM sequence with respect to the quadrant commandand to generate the start pulse for reversal. After the rotor speedreaches the desired speed, the starting signal for reversal will beapplied to the power converter. Fig. 4 shows the flowchart forthe four-quadrant control algorithm based on the descriptionsin Sections III–V.

The reason why the controller checks the unaligned positionfor four-quadrant control is to easily obtain a huge negativetorque with short delay. The maximum negative torque can beproduced after the rotor passes the unaligned position (45 ) forthe machine under consideration. PWM off indicates the deac-tivation of the PWM function resulting in no current flow to themain winding. The “delay” is the time duration needed to movethe rotor to the maximum negative torque position.

The detailed flowchart for the DSP execution of the entireproposed scheme is given in Fig. 5 and, in this case, the speedcommand is given for 5000 r/min and the low-speed thresholdis kept at 250 r/min so that reversal is enforced. Similar to theflowchart given in Fig. 3, this flowchart also is self-explanatory.

VI. MODELING, SIMULATION, AND ANALYSIS

OF THE DRIVE SYSTEM

In order to verify the feasibility of the proposed drive system,the drive system was modeled, simulated, and analyzed. Thissection gives a step-by-step derivation of the model of the drivesystem from the algorithmic descriptions in Sections III–V. Thedrive system block diagram for modeling is shown in Fig. 6.

The individual system equations for the motor and speed andcurrent controllers can be written from a standard modelingprocedure well known in the literature and one such is givenin [1] and the same is followed here. The integration of theconverter modes of operation with the machine and controlleris critical. In order to model the converter, the devices areassumed to be ideal even though their voltage drops can be

Fig. 4. Flowchart for software implementation of the four-quadrant controlalgorithm.

incorporated if required. Noting that the voltage drops of thedevices are small compared to the dc-link voltage, they aretreated as ideal devices.

Switching transients are ignored in this modeling as the elec-trical and mechanical time constants are much greater thanthe turn-on time and turn-off time of the devices. With theseassumptions, the converter–machine combination system equa-tions can be derived based on the conduction or nonconductionof the controllable switch given by modes 1 and 2, respectively.Also, these equations are impacted based on the main andauxiliary currents being greater than zero and on the stateof the auxiliary capacitor voltage. The system equations arethen assembled and integrated and solved for the variables ofinterest.

The system equations are derived and given in the following.

Q1 ON

(1)

(2)


Fig. 5. Detailed flowchart for DSP implementation of the proposedfour-quadrant and variable-speed control system.

(3)

(4)

(5)

(6)

(7)

(8)

Q1 OFF

(9)

(10)

(11)

(12)

(13)

where are main phase, auxiliary phase, and aux-iliary capacitor current, respectively, are phaseresistance of the main and auxiliary winding, respec-tively, is the dc-link voltage, is the auxiliary ca-pacitor voltage, are main and auxiliary windingflux linkages, respectively, are main and auxil-iary inductances, respectively, is the auxiliary capac-itor value, and is the rotor position. The load dynamicequation is

(14)

where is the electromagnetic torque obtained frommachine characteristic as a function of and is theload torque, is the rotor speed, is the rotor and loadinertia, and is the friction coefficient of the motor andthe load.

A simulation result showing the four-quadrant operation ofthe motor drive in normalized units is given in Fig. 7.

The machine is assumed to be in the unaligned position andthe starting is smooth. Even when the rotor is put in the alignedposition, the starting was delayed for a few hundred microsec-onds, but the system started smoothly (not given for lack ofspace here). Notice the smooth main phase current and its closefollowing of the reference. The simulation results demonstratethe feasibility of the proposed control algorithms.

VII. PERFORMANCE OF THE PROPOSED MOTOR DRIVE SYSTEM

In order to validate the proposed four-quadrant operationalcontrol of the considered motor drive system, comprehensivesets of experiments were performed. Results relating to self-starting at aligned and midpoint between aligned and alignedpositions, are shown in Figs. 8 and 9, respectively. There ishardly any noticeable difference in the time taken to reach thecommanded 5000 r/min from both the starting positions withthe control.

Fig. 10 shows four-quadrant operation from standstill to5000 r/min and then from there to 5000 r/min reversal and

then back to standstill. The speed and current are well behavedin this four-quadrant operation. Results at speeds higher than5000 r/min have been successfully achieved. Experimentalresults validated the simulation results and the basic controlalgorithms for this SSSRM drive.


Fig. 6. Block diagram of the proposed motor drive system.

Fig. 7. Simulation of the four-quadrant operation of the proposed motor drivesystem in normalized units.

Fig. 8. (a) Multiple pulses for self-starting from standstill at aligned position.(b) PWM signals for motoring operation to 5 000 r/min (scale: motor speed =2000 rpm/div, and time = 200 ms/div).

Fig. 9. Self-starting from standstill at midpoint between aligned and unalignedposition to 5 000 rpm (scale: motor speed = 2000 rpm/div, and time = 200ms/div).

Fig. 10. Four-quadrant speed control performance of the drive system (scale:speed and its command= 5000 r/min/div; current= 10 A/div; time= 5 s/div).

VIII. CONCLUSION

For the first time, a two-phase SRM drive with a single con-trollable switch was presented for four-quadrant operation andcontrol. The proposed system and its control structure for four-quadrant operation is validated with simulation and proven withexperimental work. The invention is believed to be original.The invention is fundamental as it changes the paradigm oflow-cost motor drives. The presented system is considered tobe the lowest cost four-quadrant motor drive system with theself-starting feature. The position-sensorless control has beenincorporated in this motor drive for one-quadrant operation [9].It has immense use in appliance applications.


ACKNOWLEDGMENT

The authors acknowledge with gratitude the following: L.Whelchel, President and CEO of Panaphase Technologies forgranting permission to submit this paper for publication basedon the intellectual property of the company; C. Hudson for hishelp in the development of the power electronics and DSP con-troller package; A Staley for her help on machine details andcharacteristics; and Prof. Holtz for suggestions to improve thepresentation of Figs. 8 and 9.

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[14] G. Suresh, B. Fahimi, K. M. Rahman, M. Ehsani, and I. Panahi, “Four-quadrant sensorless srm drive with high accuracy at all speeds,” in Proc.IEEE APEC’99, 1999, pp. 1226–1231.

R. Krishnan (S’81–M’82–SM’95–F’01) receivedthe Ph.D. degree in electrical engineering fromConcordia University, Montreal, QC, Canada.

He is a Professor of electrical and computer en-gineering at Virginia Polytechnic Institute and StateUniversity (Virgina Tech), Blacksburg. His researchinterests are in electric motor drives and power elec-tronics. He is the author of Electric Motor Drives(Upper Saddle River, NJ: Prentice–Hall, 2001), itsChinese translation (Taipei, Taiwan, R.O.C.: PearsonEducation Taiwan, 2002), Indian Edition (New Delhi,

India: Prentice-Hall of India, 2002 ), and International Edition (Upper SaddleRiver, NJ: Prentice-Hall International, 2001) and Switched Reluctance MotorDrives (Boca Raton, FL: CRC Press, 2003, 2nd ed.), and coeditor (with M. P.Kazmierkowski and F. Blaabjerg) of Control in Power Electronics (New York:Academic, 2002), the latter which won the Best Book Award from the Ministryof Education and Sport, Poland, in 2003. His inventions constituted foundingtechnologies for two startup companies in the U.S. He directs the Center forRapid Transit Systems at Virgina Tech, pursuing unique, safe, high-speed, en-ergy-efficient, and personal electric transit solutions. He has developed and de-livered short courses for industry on vector-controlled induction motor drives(with Prof. J. Holtz and Dr. V. R. Stefanovic), permanent-magnet synchronousand brushless dc motor drives, and switched reluctance motor drives, and is cur-rently developing linear electric motor drives with Prof. I. Boldea.

Prof. Krihnan has been a recipient of three Best Paper Awards from the In-dustrial Drives Committee of the IEEE Industry Applications Society. In addi-tion, he received the First Prize Paper Award from the IEEE TRANSACTIONS ON

INDUSTRY APPLICATIONS. He was awarded the IEEE Industrial Electronics So-ciety’s Dr. Eugene Mittelmann Achievement Award for outstanding technicalcontributions to the field of industrial electronics. He is a Distinguished Lec-turer of the IEEE Industrial Electronics Society. He serves as the Vice President(Publications) and Senior AdCom Member of the IEEE Industrial ElectronicsSociety. He served as the General Chair of the 2003 IEEE Industrial ElectronicsConference.

Sung-Yeul Park (S;05) was born in Seoul, Korea,in 1973. He received the B.S. degree in control andinstrument engineering in 1998 from Hoseo Univer-sity, Asan, Korea, and the M.S. degree in 2004 fromVirginia Polytechnic Institute and State University,Blacksburg, where he is currently working toward thePh.D. degree.

His research interests include power electronics,fuel-cell systems, and microcontroller applicationsystems.

Keunsoo Ha (S’04) was born in Seoul, Korea, in1970. He received the B.S. and M.S. degrees inelectrical and control engineering from Hong-IkUniversity, Seoul, Korea, in 1993 and 1995, respec-tively. He is currently working toward the Ph.D.degree at Virginia Polytechnic Institute and StateUniversity, Blacksburg.

In 1995, he joined the Precision Machinery Re-search Center, Korea Electronics Technology Insti-tute, where he has been a Senior Researcher since2000 and has conducted research on the development

of BLDCM drives for household air conditioners and refrigerator fans and stepmotor controllers for car dashboards and linear motor drivers for machine tools.His research interests include electric motor drives, power electronics, and sen-sorless control.

Documents

Theory and Operation of a Four-quadrant Switched Reluctance Motor Drive With a Single Controllable Switch-The Lowest Cost Four-quadrant Brushless Motor Driv