EJC_ACWLDS_201306 (1).pdf

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Contents lists available at SciVerse ScienceDirect

journal homepage: www.elsev

European Journal

tional Conference on Power Electronics, Machines and Drives (PEMD) held in April

European Journal of Control () indirectly controlled [8,26,30,28]. It uses hysteresis-based control,1 http://encyclopedia2.thefreedictionary.com/Power+System+Load.[1,7,10,14,15,17,19,20,27].(3) Direct torque (and ux) control: The torque (and stator ux) are

directly controlled via selecting appropriate inverter voltagespace vectors through a look-up table but the frequency is

0947-3580/$ - see front matter & 2013 European Control Association. Published by Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.ejcon.2013.05.013

2010 in Brighton, UK and at the 20th International Symposium on PowerElectronics, Electrical Drives, Automation and Motion (SPEEDAM) held in June2010 in Pisa, Italy.

n Tel.: +44 114 22 25630; fax: +44 114 22 25683.E-mail addresses: [email protected], [email protected] controlled via hysteresis-band PWM, which makes thesystem analysis difcult [3,9,11,16,22]. A lot of patches have beenSome preliminary results of this work were presented at the 5th IET Interna-frequency sinusoidal power supply from a constant DC powersource. The control variables are voltage and frequency whilemaintaining their ratio constant to provide (almost) constant

to DC drives. The drawbacks of vector control are: (i) theestimation and eld orientation are dependent on motormeters, which change in reality (e.g. with temperature); (icontroller is very complicated and (iii) the inverter isadvancement of power electronics, digital signal processing (DSP),etc., the technology of VSD for AC motors is matured and AC driveshave replaced DC drives in many application areas. There are mainlythree approaches developed for AC drives [4,6,12]:

(1) V/f control: The idea is to generate a variable-voltagevariable-

oriented (aligned) in the direction of the rotor ux and iq isperpendicular to it, then the control of id and iq is decoupled, asin the case of DC motors. The frequency is not directly controlledas in the scalar control but indirectly controlled; the torque iscontrolled indirectly via controlling the current. The advantage ofvector control is that it provides good performance that is similaras home appliances, robots, pumpindustrial processes and, recently, renthe main driving force in industryreliability, low cost and low mainteincrease productivity and improve quality in many applications, such (2) Vector control: The idea is to control AC motors in a way similar1. Introduction

Motors consume the majority ofconsumed by asynchronous electric mnous electric motors.1 Variable speedwith inverters, are hence widely use cite this article as: Q.-C. Zhong, ,pean Journal of Control (2013), http:ity, of which 5070% isand 310% by synchro-s (VSD), often equippedadays to save energy,

s, automotive, railway,energy. AC motors are

se of their small size,[4,5,12,18]. Due to the

ux. It is widely used in open-loop drives, where the require-ment of performance, e.g. speed accuracy and response, is nothigh and/or the controller needs to be simple [25]. This is alsocalled scalar control because only the amplitude of the voltageis controlled. It is possible to add feedback, e.g. speed, torqueand/or ux, to improve the performance [2,24].

to controlling separately excited DC motors, after introducingsome transformations. The three phase currents are convertedinto d, q current components id and iq, which correspond to theeld and armature currents of DC motors, respectively. If id isDept. of Automatic Control and Systems Engineering, The University of Shefeld, Shefe

a r t i c l e i n f o

Article history:Received 13 May 2013Accepted 13 May 2013Recommended by Alessandro Astol

Keywords:Variable speed drivesWard Leonard drive systemsAC machinesSynchronvertersInverters that mimic synchronous

a b s t r a c t

In this paper, the problemcompletely new viewpointthat generates a variable-physical, extension of theAs a result, AC drives candrives and the introductiomotor is easier to be handControl strategies, with aexperimental results are p

& 2013Ward Leonard drive systems: RevisitAC machines$

nAC Ward Leonard drive system//dx.doi.org/10.1016/j.ejcon.201ional Ward Leonard drive systems for DC machines to AC machines.rded as generator-motor systems, which facilitate the analysis of ACer special functions because a system consisting of a generator and an the conventional AC drive that consists of an inverter and a motor.out a speed sensor, are proposed to implement this idea and theto demonstrate the feasibility.

an Control Association. Published by Elsevier Ltd. All rights reserved.ageventthe four-quadrant operation

, UK

olling the speed of AC machines in four quadrants is revisited from aon the idea of powering an AC machine with a synchronous generatorvariable-frequency supply. This is a natural, mathematical, but not

ier.com/locate/ejconof Controls: Revisiting the four-quadrant operation of AC machines,3.05.013i

which generates ux and torque ripples, and the switchingfrequency is not constant. It also needs motor parameters toestimate the torque (and stator ux) [13,23,29]. Again, thehysteresis-based control makes system analysis very difcult.

These three schemes have been further advanced for a long periodwith the development of related technologies in e.g. control theoryand microelectronics. They are suitable for different applicationsbecause of their different characteristics [4,12,21]. The vector

verter concept of operating inverters to mimic synchronousgenerators [3335]. Ideally, if the motor has the same pole numberas the generator and there was no loss, the torque of the generatorwould be the same as the torque of the motor. Hence, the torque ofthe motor could be controlled via controlling the torque entering thesynchronous generator.

3. Model of a synchronous generator

The model of synchronous generators is very well documentedin many textbooks and other literature. Here, some changes aremade to the model developed in [34], assuming that the uxestablished in the stator by the eld windings is sinusoidal

Co

V/VeDiAC

speed speed

Q.-C. Zhong / European Journal of Control () 2

PlEuntrol type Frequency control Torque control Flux control

f control Direct None Nonector control Indirect Indirect Directrect torque control Indirect Direct DirectWLDS Direct Direct Open-loopcontrol and direct torque (and ux) control provide very goodperformance but the control algorithms involve several transfor-mations and are very complicated. What is worse is that look-uptables are used in the direct torque (and ux) control, whichmakes the analytical analysis of the system very difcult. The highorder of the resulting complete system from these approaches alsomeans that the system stability is difcult to guarantee. V/f controlis simple but the performance needs to be improved. Hence, asimple high-performance AC drive that facilitates the analyticalanalysis of the system is desirable.

From the viewpoint of control system design, the AC motor issimply the load to an inverter. The main control objective of adrive is to regulate the speed and the torque to obtain fast andgood response and the change of the motor parameters (includingthe load) should not impose a major problem to the system. Suchan attempt is made in this paper, following the concept ofoperating inverters to mimic synchronous generators [3335]and motivated by the conventional Ward Leonard drive systems(WLDS). The physical interpretation of this is that the AC motor ispowered by a synchronous generator (SG) driven by a variable-speed prime mover. The synchronous generator and the primemover are then replaced by an inverter that behaves as asynchronous generator. The torque and speed of the AC motorare then controlled via controlling the torque and frequency of thesynchronous generator. The resulting control scheme is verysimple as it does not involve vector transformations nor theestimation of ux. No complicated concepts, e.g. vector controland eld orientation, are needed and the scheme is very easy tounderstand. This also unies the drive for synchronous motors(SM) and induction motors (IM). In the proposed scheme, theattention of how to design AC drives has shifted from motor-oriented to inverter-oriented. This has led to an extremely simplecontroller. It can also be treated as the proposed AC drive ispowered by a synchronous generator while the vector-controlledAC drives are powered by a DC generator with some transforma-tions. Another important advantage is that the complete systemcan be described by the analytic mathematical models of thegenerator and the motor, which facilitate the analytical analysis ofthe system. The comparison of the different types of VSDs is givenin Table 1.

The rest of the paper is organised as follows. The concept of theDCWard Leonard drive systems is reviewed and then extended to ACmachines in Section 2. The mathematical model of synchronousgenerators is described in Section 3 and a control scheme is proposedin Section 4 to implement the concept. Experimental results areshown in Section 6 and conclusions are made in Section 7.

Table 1Comparison of control types for AC VSDs.ease cite this article as: Q.-C. Zhong, , AC Ward Leonard drive syropean Journal of Control (2013), http://dx.doi.org/10.1016/j.ejcon.2. Ward Leonard drive systems

Induction motors, particularly those of the squirrel-cage type,have been the principal workhorse for long time. However, until thebeginning of 1970s, they had been operated in the constant-voltageconstant-frequency (CVCF) uncontrolled mode, which is still verycommon nowadays. VSDs were dominated by DC motors in theWard Leonard arrangement. Ward Leonard drive systems, alsoknown as Ward Leonard Control, were widely used DC motor speedcontrol systems introduced by Harry Ward Leonard in 1891. A WardLeonard drive system, as shown in Fig. 1, consists of a motor (primemover) and a generator with shafts coupled together. The motor,which turns at a constant speed, may be AC or DC powered. Thegenerator is a DC generator, with eld windings and armaturewindings. The eld windings are supplied with a variable DC sourceto produce a variable output voltage in the armature windings, whichis usually used to power a second DC motor that drives the load.

A natural analogy is to replace the DC generator with a synchro-nous generator and the DC motor with an AC machine (an inductionmotor or a synchronous motor); see Fig. 2(a). This conguration iscalled AC Ward Leonard drive systems [31,32]. It is worth noting thatthe physical implementation of an AC Ward Leonard drive system isof limited use, as described below. The prime mover in a DC WLDSmaintains a constant speed and the ux of the generator is variable;the prime mover in an AC WLDS needs to have a variable speed (sothat the frequency of the output can be varied) and the ux of thegenerator is constant. The output of the generator (voltage) in a DCWLDS is varied via controlling the eld voltage and the output of thegenerator (voltage and frequency) in an AC WLDS is varied viacontrolling the speed of the prime mover. If the speed of the primemover could be varied, it could have been used to drive the loadstraight-away and hence there is no need to have a physical ACWLDS. Instead of having a physical synchronous generator that isdriven by a variable-speed prime mover, an inverter that captures themain dynamics of the physical system (the synchronous generator,the variable-speed prime-mover and its controller), as shown inFig. 2(b), can be used to power the motor, following the synchron-

Controllable field Fixed field

Fig. 1. Conventional (DC) Ward Leonard drive systems.Constant Variable

Primemover

Load and that the stator winding resistance and inductance are zero.

stems: Revisiting the four-quadrant operation of AC machines,2013.05.013i

The saturation effect of the machine is introduced by limiting thevoltage to the rated value, as shown in Fig. 3. When the eldcurrent If is constant, the generated voltage e ea eb ecT is

e _ ~sin 1

where is the electrical rotor position (hence _ is the electricalangular speed), is the amplitude of the mutual ux linkagebetween the stator winding and the rotor winding, and ~sin isthe vector sin sin 2=3 sin 4=3T : In fact, is alsothe ratio of the generated voltage (amplitude) to the speed(angular) and Mf If , where Mf is the maximum mutualinductance between the stator winding and the rotor winding.

The mechanical dynamics of the machine is governed by

J TmTeDp _ ;

where J is the moment of inertia of all parts rotating with the rotor,Dp is the damping factor, Tm is the mechanical torque applied tothe synchronous generator by the prime mover and Te is theelectromagnetic torque given by

Te pi; ~sin : 2

Here, p is the number of pole pairs per phase, i ia ib icT is thestate current vector and ; denotes the conventional innerproduct. It is worth noting that if i I0 ~sin then

Te pI0 ~sin ; ~sin 32pI0 cos ;

which is a constant DC value. This is a very important property,

unit, a speed controller and a current feed-forward controller, asshown in Fig. 4. In order to speed up the system response and to

Variablespeed

Variablespeed

Fixed field

SM/IM Load

SG Primemover

Variablespeed

Variablespeed

Fixed field

SM/IM Load

SG Primemover VDC

Inverter

Fig. 2. AC Ward Leonard drive systems. (a) Natural implementation. (b) Proposedimplementation.

Fig. 3. Mathematical model of a synchronous generator.

Q.-C. Zhong / European Journal of Control () 3Fig. 4. Control structure for AC WLDS with a spee

Please cite this article as: Q.-C. Zhong, , AC Ward Leonard drive syEuropean Journal of Control (2013), http://dx.doi.org/10.1016/j.ejcon.minimise the number of tuning parameters, it is advantageousto choose the inertia of the generator to be J0 (i.e., zero inertia).

_ _ _from which a simple control strategy can be designed to regulatethe speed of the AC machine.

4. Control scheme with a speed sensor

4.1. Control structure

As explained before, the idea of the AC Ward Leonard drive systemis to power the AC motor with a synchronous generator, driven by avariable-speed prime mover that is implemented via an inverter.Hence, the focus of the control system is to control the generatorinstead of the motor. The mechanical torque Tm applied to thegenerator can be easily generated by a speed controller (governor),e.g. a PI controller, that compares the actual speed _ f with thereference speed _r . If the motor is synchronous, then the actual speedcan be directly taken from the generator without a speed sensor as themotor runs at the synchronous speed _ . If the motor is inductive, thenthe actual speed (mechanical) can be measured from the motor and itshould be converted to the electrical speed via multiplying it with thenumber of pole pairs p. Usually this involves a low-pass lter to reducethe measurement noise. Another aspect could be easily taken intoaccount is the voltage drop on the stator winding of the motor,particularly, when the speed is low. It can be compensated via a feed-forward path containing the stator winding resistance Rs from currenti to the generated voltage e. Thus, the resulting complete controllerconsists of a synchronous generator model, a speed measurementd sensor. r , f and are all electrical speed.

stems: Revisiting the four-quadrant operation of AC machines,2013.05.013i

torque Te (regarded as a disturbance) to the speed _ is

HT s 4ss 1Dp2s 12

;

which means that any step change in the (load) torque does not cause

C W

Fig. 6. An experimental AC drive.

Table 2Parameters of the motor.

Parameters Values Parameters Values

Rs 0:17 Rated frequency 128 Hzp 2 Rated speed 3621 rpmRated voltage (line-to-line) 30 VRMS Rated torque 0.528 Nm

Q.-C. Zhong / European Journal of Control () 4This also reduces the system order by one, which helps improvesystem stability.

It is worth noting that the of the generator is always keptconstant. When the speed of the generator exceeds the rated speed,the generated voltage is bounded by the rated voltage so that theinsulation of the motor is not damaged (the voltage boost due to thecurrent feed-forward path should not exceed the margin allowed,which is normally the case). It should be pointed out that p, and Rsshould be chosen the same as those of the motor.

The output u of the controller, which is the sum of the generatedvoltage and the compensated voltage drop on the motor statorwinding, can be passed though a three-phase inverter, after appro-priate scaling according to the DC-link voltage, to power the AC motor.The switches in the inverter are operated so that the average values ofthe inverter output over a switching period should be equal to u,which can be achieved by many known pulse-width-modulation(PWM) techniques. Because of the inherent low-pass ltering effectof the motor, it may not necessary to connect LC lters to improve thetotal harmonic distortion.

4.2. System analysis and selection of parameters

In order to simplify the analysis, assume that the speed feedbackis taken from _ , i.e., _ f 1=s 1 _ . The torque Te can be regardedas a disturbance to simplify the analysis. The transfer function fromthe speed reference _r to the speed _ , assuming zero load, is then

H _ s KPs KIs 1

Dps2 Dp KPs KI:

_ _ _

Fig. 5. Control structure for AFor a step change of r , the speed jumps by KP=Dpr , which isnormally regarded as aggressive, and then settles down. In order toavoid this, take KP0. Hence

H _ s KIs 1

Dps2 Dps KI:

This is a second order system and the poles are

s1;2 17

14KI=Dp

p2

:

If KI is chosen as

KI Dp4

;

then the two poles are s1;2 1=2 and

H _ s s 1

2s 12:

This would leave enough margin for the controller to cope withuncertainties and parameter variations. The transfer function from

Please cite this article as: Q.-C. Zhong, , AC Ward Leonard drive syEuropean Journal of Control (2013), http://dx.doi.org/10.1016/j.ejcon.LDS without a speed sensor.a static error in the speed _ . If there is a step change Te in the torque,the speed jumps by 1=DpTe and then recovers. Hence, in order toreduce the impact of the load on the speed, Dp should not be too small.

The speed response is directly related to the time constant ofthe low-pass lter used in the speed measurement unit. Thesmaller the time constant, the faster the system response.

The above analysis is approximate because the loop involvingthe motor that affects Te is not fully considered and the speedfeedback is not exactly taken from the motor. However, it doesoffer some insightful understanding to the system and, in princi-ple, reects the system dynamics as can be seen from theexperimental results to be shown in the next section. It is worthnoting that, although the above design leads to a non-oscillatoryresponse, the closed-loop system in real implementation could beoscillatory because of the reasons mentioned above.

The four-quadrant operation of AC machines comes automati-cally with the proposed AC WLDS. There is no need to add anyextra effort or device; the change of the sign of the speed referencechanges the direction of the motor rotation. A positive frequency

stems: Revisiting the four-quadrant operation of AC machines,2013.05.013i

Fig. 8. Reversal at high-speed with a load. (a) Speed. (b) Torque of the generator. (c) Current. (d) Voltage.

Fig. 7. Reversal at high-speed without a load. (a) Speed. (b) Torque of the generator. (c) Current. (d) Voltage.

Q.-C. Zhong / European Journal of Control () 5

Q.-C. Zhong / European Journal of Control () 6(spefreqof tneg

Iconis dcho

(1)

(2)

(3)

5.

5.1.

Ispeto tconsynspee

PlEued) reference leads to a positive speed and a negativeuency (speed) reference leads to a negative speed. A changehe frequency from negative to positive, or from positive toative, leads to the reversal of the motor rotation.n summary, the speed response is determined by the timestant of the speed measurement unit and the torque responseetermined by Dp. The parameters of the controller can besen as follows:

Choose p, and Rs the same as, or close to, those of the motorand choose J0.Determine the time constant to meet the requirement of thespeed response (also the requirement of the measurementnoise) and Dp to meet the requirement of the torque response.Choose KP0 and KI Dp=4.

Control scheme without a speed sensor

Control structure

f the motor is synchronous, then there is no need to have aed sensor because the speed of synchronous motor convergeshe speed _ of the generator, which is internally available in thetroller for feedback. Even for induction motors, _ is thechronous speed and can be used to reect the actual motord (the difference is the slip). In this case, Dp can be chosen as 0.

Fig. 9. Reversal at low-speed without a load. (a) Speed.

ease cite this article as: Q.-C. Zhong, , AC Ward Leonard drive syropean Journal of Control (2013), http://dx.doi.org/10.1016/j.ejcon.The slip of an induction motor can be compensated to some extent aswell. It is well known that the speed drop _s is in proportion to thetorque over a wide speed range, i.e.

_s KTTe:

This can be obtained from the torquespeed characteristics of themotor. For synchronous motors, KT0. This load (torque) effect can becompensated via adding KTTe to the speed reference _r . The resultingspeed-sensorless control scheme for ACmachines is shown in Fig. 5. Itconsists of the model of a synchronous generator, a speed controller, aload-effect compensator and a current feed-forward controller, whichis a feed-forward path containing the stator winding resistance Rsfrom current i to the generated voltage e. This scheme is applicable forboth synchronous (with KT0) and induction motors. For synchro-nous motors, it provides zero-static-error speed control; for inductionmotors, there is normally a small static error depending on thecompensation accuracy of the load (torque) effect. The accuracy canbe improved via using a two-dimensional table to determine KTaccording to the torquespeed characteristics of the motor, taking intoaccount both the synchronous speed and the torque.

5.2. System analysis and selection of parameters

In order to simplify the exposition below, consider the casewhen the motor is synchronous, i.e., KT0. The transfer function

(b) Torque of the generator. (c) Current. (d) Voltage.

stems: Revisiting the four-quadrant operation of AC machines,2013.05.013i

Q.-C. Zhong / European Journal of Control () 7from the speed reference _r to the speed _ , assuming zero load, is

H _ s KPs KI

Js2 KPs KIand the transfer function from torque Te (regarded as a distur-bance) to the speed _ is

HT s s

Js2 KPs KI:

The system is of second order and the poles are

s1;2 17

14KIJ=K2P

q

2J=KP:

Increasing KI tends to make the system response oscillatory. Dene J=KP , i.e., KP J=. If KI is chosen as

KI KP4

J42

;

then the two poles are s1;2 1=2. Under this set of parameters

H _ s 4s 1

2s 12;

HT s 42s

J2s 12:

The speed response can be tuned by changing and the torqueresponse can be tuned by changing J.

Fig. 10. Reversal at low-speed with a load. (a) Speed. (b) T

Please cite this article as: Q.-C. Zhong, , AC Ward Leonard drive syEuropean Journal of Control (2013), http://dx.doi.org/10.1016/j.ejcon.(1)

(2)

(3)(4)

6.

sysboatroltionto tTheconbi-d

6.1.

wh

orqu

stem201In summary, the control parameters can be chosen as follows:

Choose p, and Rs the same as, or close to, those of the motorand choose Dp0.Determine the time constant to meet the requirement of thespeed response and J to meet the requirement of the torqueresponse.Choose KP J= and KI KP=4.Choose KT according to the torquespeed characteristics of themotor (KT0 for synchronous motors).

Experimental results

The proposed AC WLDS was veried on an experimentaltem, as shown in Fig. 6. The system consists of an inverter, ard consisting of current sensors, a dSPACE DS1104 R&D con-ler board equipped with ControlDesk software, and an induc-motor. The motor parameters are given in Table 2. Accordinghe parameters, it can be found that 0:0305 and KT86.82.inverter has the capability to generate PWM voltages from astant 42 V DC voltage source and the motor is equipped with airectional encoder with 1000 lines for speed measurement.

Case 1: with a speed sensor for feedback

The control parameters were chosen as 0:1 s and Dp0.08,ich results in KI0.2. Many experiments were carried out to

e of the generator. (c) Current. (d) Voltage.

s: Revisiting the four-quadrant operation of AC machines,3.05.013i

Fig. 12. Reversal at high-speed without a load (without a speed sensor). (a) Speed. (b) Torque of the generator. (c) Current. (d) Voltage.

Fig. 11. Reversal at an extremely low speed without a load. (a) Speed. (b) Torque of the generator. (c) Current. (d) Voltage.

Q.-C. Zhong / European Journal of Control () 8

test the performance of the system and some of the results areshown here.

6.1.1. Reversal at high-speed without a loadThe reference speed was changed from 3600 rpm to 3600 rpm

at around t0.6 s. The responses (speed, torque, current andvoltage) are shown in Fig. 7. The motor quickly reversed from3600 rpm to 3600 rpm and settled down in about 1.2 s. Therewas a very short period of over-current around 70%; the voltagedropped when the reversal was started and then gradually built upafter the reversal. The phase sequence of the currents was changedat around 0.85 s, which corresponds to the change of the rotatingdirection of the magnetic eld, to enable the reversal.

6.1.2. Reversal at high-speed with a loadThe reference speed was changed from 1800 rpm to 1800 rpm

at around t1 s. The responses are shown in Fig. 8. The motorquickly reversed from 1800 rpm to 1800 rpm in about 1.5 s,which is slightly longer than the case without a load. There wasabout 11% overshoot in the speed and the over current increasedto about 150%.

6.1.3. Reversal at low-speed without a loadThe reference speed was changed from 150 rpm to 150 rpm at

around t0.6 s. The responses are shown in Fig. 9. It took about1.5 s to complete the reversal and settle down. The over-currentwas only about 15% and the speed overshoot was about 6%. Note

that the sequence of the three phase currents/voltages changed ataround t0.8 s.

6.1.4. Reversal at low-speed with a loadThe reference speed was changed from 300 rpm to 300 rpm at

around t2.2 s. The responses are shown in Fig. 10. The motorquickly reversed from 300 rpm to 300 rpm in about 2 s. Therewas a noticeable stop in the middle of the reversal process. Theover current was about 50%.

6.1.5. Reversal at an extremely low speed without a loadThe reference speed was changed from 4.5 rpm to 4.5 rpm at

around t5 s. The responses are shown in Fig. 11. It took about 15 sto complete the reversal and settle down due to the extremely lowspeed. There were some ripples in the measured speed, which wasowing to the error in the measurement unit (the motor actuallyrotated smoothly). The motor speed dropped to 0 quickly butremained standstill for about 12 s, during which the torque increasedalmost linearly, before the torque was accumulated high enough tostart the motor. Once the current gradually increased to a level that isenough to generate the required torque, the motor started rotating.

6.2. Case 2: without a speed sensor for feedback

The control parameters were chosen as 0:1 s and J0.08,which results in KP0.8 and KI2. Many experiments werecarried out and some of the results are shown here.

Q.-C. Zhong / European Journal of Control () 9Fig. 13. Reversal at high-speed with a load (without a speed sensor)

Please cite this article as: Q.-C. Zhong, , AC Ward Leonard drive syEuropean Journal of Control (2013), http://dx.doi.org/10.1016/j.ejcon.. (a) Speed. (b) Torque of the generator. (c) Current. (d) Voltage.

stems: Revisiting the four-quadrant operation of AC machines,2013.05.013i

Transactions on Industrial Electronics 59 (June (2)) (2012) 752761.

[2] R. Ancuti, I. Boldea, G.-D. Andreescu, Sensorless V/f control of high-speed

surface permanent magnet synchronous motor drives with two novel stabilis-ing loops for fast dynamics and robustness, IEE Proceedings of the ElectricPower Applications 4 (March (3)) (2010) 149157.

[3] L. Bascetta, G. Magnani, P. Rocco, A.M. Zanchettin, Performance limitations ineld-oriented control for asynchronous machines with low resolution positionsensing, IEEE Transactions on Control Systems Technology 18 (May (3)) (2010)559573.

[4] I. Boldea, Control issues in adjustable speed drives, IEEE Industrial ElectronicsMagazine 2 (September (3)) (2008) 3250.

[5] B.K. Bose, Variable frequency drives-technology and applications, in: Proceed-ings of the IEEE International Symposium on International Industrial Electro-nics (ISIE), 1993, pp. 118.

[6] B.K. Bose, Modern Power Electronics and AC Drives, Prentice-Hall, EnglewoodCliffs, NJ, 2001.

[7] D. Chatterjee, A novel magnetizing-curve identication and computer storagetechnique for induction machines suitable for online application, IEEE Trans-6.2.1. Reversal at high-speed without a loadThe reference speed was changed from 3600 rpm to 3600 rpm

at around 0.7 s. The responses are shown in Fig. 12. The motorquickly reversed from 3600 rpm to 3600 rpm in about 1.3 s.There was a very short period of over 100% over-current and thespeed overshoot was about 14%. The static error was almost zero.

6.2.2. Reversal at high-speed with a loadThe reference speed was changed from 1800 rpm to 1800 rpm

at around t0.4 s. The responses are shown in Fig. 13. It tookabout 1.6 s to complete the reversal and there was about 200%over-current.

7. Conclusions and discussions

The concept of the conventional DC Ward Leonard drivesystems is extended to AC machines. Instead of implementing itphysically, it is implemented mathematically and an inverter iscontrolled to replicate the dynamics of the physical set of avariable-speed prime mover and a synchronous generator. Thisleads to the smooth operation of AC machines in four quadrants.The change of the sign of the frequency set-point leads to thechange of the phase sequence of the current and, furthermore, thechange of the rotational direction. Two control schemes, one witha speed sensor and the other without a speed sensor, are proposedfor the system, which is then validated with the experimentalresults. The main purpose of this paper is to propose and validatethe concept. Some further studies, e.g. the comparison with otherapproaches, detailed analysis of the complete system and theapplication of the strategy, are left for future research.

While it is vital for some applications to achieve the fastestpossible torque response, this may have been aggressively pushedfor some applications where the response speed is not critical. Forthe formal case, it is often achieved via controlling the currentprovided by the inverter, but for the latter case, the speedregulation can be achieved by controlling the voltage providedby the inverter. In other words, AC drives can be classied ascurrent-controlled AC drives and voltage-controlled AC drives.Vector control and direct torque control belong to the current-controlled AC drives while V/f control and the proposed AC WLDSbelong to the voltage-controlled AC drives. Similarly to AC dives,the inverters in smart grid integration can be current-controlled orvoltage-controlled; see [33] for detailed and systematic treatmentof controlling inverters for renewable energy and smart gridintegration.

References

[1] E. Al-Nabi, B. Wu, N.R. Zargari, V. Sood, Input power factor compensation forhigh-power CSC fed PMSM drive using d-axis stator current control, IEEEactions on Industrial Electronics 58 (December (12)) (2011) 53365343.

Please cite this article as: Q.-C. Zhong, , AC Ward Leonard drive syEuropean Journal of Control (2013), http://dx.doi.org/10.1016/j.ejcon.[8] M. Depenbrock, Direct self-control (DSC) of inverter-fed induction machine,IEEE Transactions on Power Electronics 3 (October (4)) (1988) 420429.

[9] K. Gulez, A.A. Adam, H. Pastaci, Torque ripple and EMI noise minimization inPMSM using active lter topology and eld-oriented control, IEEE Transac-tions on Industrial Electronics 55 (January (1)) (2008) 251257.

[10] K. Hatua, A.K. Jain, D. Banerjee, V.T. Ranganathan, Active damping of output LClter resonance for vector-controlled VSI-fed AC motor drives, IEEE Transac-tions on Industrial Electronics 59 (January (1)) (2012) 334342.

[11] A.K. Jain, V.T. Ranganathan, Modeling and eld oriented control of salient polewound eld synchronous machine in stator ux coordinates, IEEE Transac-tions on Industrial Electronics 58 (March (3)) (2011) 960970.

[12] M.P. Kazmierkowski, L.G. Franquelo, J. Rodriguez, M.A. Perez, J.I. Leon, High-performance motor drives, IEEE Industrial Electronics Magazine 5 (September(3)) (2011) 626.

[13] F. Khoucha, S.M. Lagoun, K. Marouani, A. Kheloui, M. El Hachemi Benbouzid,Hybrid cascaded H-bridge multilevel-inverter induction-motor-drive directtorque control for automotive applications, IEEE Transactions on IndustrialElectronics 57 (March (3)) (2010) 892899.

[14] R. Leidhold, Position sensorless control of PM synchronous motors based onzero-sequence carrier injection, IEEE Transactions on Industrial Electronics 58(December (12)) (2011) 53715379.

[15] H. Liu, S. Li, Speed control for PMSM servo system using predictive functionalcontrol and extended state observer, IEEE Transactions on Industrial Electro-nics 59 (February (2)) (2012) 11711183.

[16] M. Mengoni, L. Zarri, A. Tani, G. Serra, D. Casadei, Stator ux vector control ofinduction motor drive in the eld weakening region, IEEE Transactions onPower Electronics 23 (March (2)) (2008) 941949.

[17] M. Mohseni, S.M. Islam, M.A. Masoum, Enhanced hysteresis-based currentregulators in vector control of DFIG wind turbines, IEEE Transactions on PowerElectronics 26 (January (1)) (2011) 223234.

[18] M. Pacas, Sensorless drives in industrial applications, IEEE Industrial Electro-nics Magazine 5 (June (2)) (2011) 1623.

[19] C. Patel, R. Ramchand, K. Sivakumar, A. Das, K. Gopakumar, A rotor uxestimation during zero and active vector periods using current error spacevector from a hysteresis controller for a sensorless vector control of IM drive,IEEE Transactions on Industrial Electronics 58 (June (6)) (2011) 23342344.

[20] G. Pellegrino, E. Armando, P. Guglielmi, Direct ux eld-oriented control ofIPM drives with variable DC link in the eld-weakening region, IEEE Transac-tions on Industry Applications 45 (September/October (5)) (2009) 16191627.

[21] J. Rodriguez, R.M. Kennel, J.R. Espinoza, M. Trincado, C.A. Silva, C.A. Rojas,High-performance control strategies for electrical drives: an experimentalassessment, IEEE Transactions on Industrial Electronics 59 (February (2))(2012) 812820.

[22] S.-Y. Shao, E. Abdi, F. Barati, R. McMahon, Stator-ux-oriented vector controlfor brushless doubly fed induction generator, IEEE Transactions on IndustrialElectronics 56 (October (10)) (2009) 42204228.

[23] K.-K. Shyu, J.-K. Lin, V.-T. Pham, M.-J. Yang, T.-W. Wang, Global minimumtorque ripple design for direct torque control of induction motor drives, IEEETransactions on Industrial Electronics 57 (September (9)) (2010) 31483156.

[24] M. Suetake, I.N. da Silva, A. Goedtel, Embedded DSP-based compact fuzzysystem and its application for induction-motor V/f speed control, IEEETransactions on Industrial Electronics 58 (March (3)) (2011) 750760.

[25] X.-D. Sun, K.-H. Koh, B.-G. Yu, M. Matsui, Fuzzy-logic-based V/f control of aninduction motor for a DC grid power-leveling system using ywheel energystorage equipment, IEEE Transactions on Industrial Electronics 56 (August (8))(2009) 31613168.

[26] I. Takahashi, T. Noguchi, A new quick-response and high-efciency controlstrategy of an induction motor, IEEE Transactions on Industry Applications 22(September (5)) (1986) 820827.

[27] A. Trentin, P. Zanchetta, C. Gerada, J. Clare, P.W. Wheeler, Optimized commis-sioning method for enhanced vector control of high-power induction motordrives, IEEE Transactions on Industrial Electronics 56 (May 5) (2009)17081717.

[28] S.A. Zaid, O.A. Mahgoub, K.A. El-Metwally, Implementation of a new fast directtorque control algorithm for induction motor drives, IEE Proceedings of theElectric Power Applications 4 (5) (2010) 305313.

[29] Y.-C. Zhang, J.-G. Zhu, Z.-M. Zhao, Wei Xu, D.G. Dorrell, An improved directtorque control for three-level inverter-fed induction motor sensorless drive,IEEE Transactions on Power Electronics, February 2010.

[30] L.-B. Zheng, J.E. Fletcher, B.W. Williams, X.-N. He, A novel direct torque controlscheme for a sensorless ve-phase induction motor drive, IEEE Transactionson Industrial Electronics 58 (February (2)) (2011) 503513.

[31] Q.-C. Zhong, Four-quadrant operation of AC machines powered by invertersthat mimic synchronous generators, in: Proceedings of the 5th IET Interna-tional Conference on Power Electronics, Machines and Drives, 2010.

[32] Q.-C. Zhong, Speed-sensorless AC Ward Leonard drive systems, in: Proceed-ings of the International Symposium on Power Electronics Electrical DrivesAutomation and Motion (SPEEDAM), 2010, pp. 15121517.

[33] Q.-C. Zhong, T. Hornik, Control of Power Inverters in Renewable Energy andSmart Grid Integration, Wiley-IEEE Press, 2013.

[34] Q.-C. Zhong, G. Weiss, Static synchronous generators for distributed genera-tion and renewable energy, in: Proceedings of the IEEE PES Power SystemsConference & Exhibition (PSCE), 2009.

[35] Q.-C. Zhong, G. Weiss, Synchronverters: inverters that mimic synchronousgenerators, IEEE Transactions on Industrial Electronics 58 (April (4)) (2011)Q.-C. Zhong / European Journal of Control () 1012591267.

stems: Revisiting the four-quadrant operation of AC machines,2013.05.013i

AC Ward Leonard drive systems: Revisiting the four-quadrant operation of AC machinesIntroductionWard Leonard drive systemsModel of a synchronous generatorControl scheme with a speed sensorControl structureSystem analysis and selection of parameters

Control scheme without a speed sensorControl structureSystem analysis and selection of parameters

Experimental resultsCase 1: with a speed sensor for feedbackReversal at high-speed without a loadReversal at high-speed with a loadReversal at low-speed without a loadReversal at low-speed with a loadReversal at an extremely low speed without a load

Case 2: without a speed sensor for feedbackReversal at high-speed without a loadReversal at high-speed with a load

Conclusions and discussionsReferences