Electric Motor Performance Improvement Using Auxiliary Windings and Capacitance Injection

Transcription

1 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection 2 Nicolae DV Tshwane University of Technology South Africa 1 Introuction Generally, some electric machines such as inuction machines an synchronous reluctance motors require reactive power for operation While the reactive power require by a synchronous machine can be taken from the power source or supplie by the machine itself by ajustment of the fiel current, the power factor of an inuction machine is always lagging an set by external quantities (ie, the loa an terminal voltage) Poor power factor aversely affects the istribution system an a cost penalty is frequently levie for excessive VAr consumption Power factor is typically improve by installation of capacitor banks parallel to the motor If the capacitor bank is fixe (ie that it can compensate power factor only for a fixe loa), when the loa is variable, then the compensation is lost Some authors (El-Sharkawi et al, 1984, Fuchs an Hanna, 2002) introuce the capacitors using thyristor/triac controllers; by ajusting the firing angle, the capacitance introuce in parallel with the motor becomes variable an thus compensating the power factor for any loa Other works (Suciu et al, 2000) consier the inuction motor as an RL loa an power factor is improve by inserting a variable capacitor (through a brige converter) which is ajuste for unity accoring with the loa For the above methos, the capacitive injection is irectly into the supply Another metho conceive for slip ring inuction motor was to inject capacitive reactive power irect into the rotor circuit (Reinert an Parsley, 1995; Suciu, et al 2002) The injection of reactive power can be one through auxiliary winings magnetically couple with the main winings (E Muljai et al 1989; Tamrakan an Malik, 1999; Mearametla et al 1992; Umans, an H L Hess, 1983; Jimoh an Nicolae, 2006, 2007) This compensating metho has also been applie with goo results not only for inuction motors but also for a synchronous reluctance motor (Ogunjuyigbe et al 2010) 2 Metho escription 21 Physical solution The metho escribe in this chapter makes use of two three-phase stator winings One set, the main wining (star or elta), is connecte irectly to the source The other set of winings - auxiliary, is only magnetically couple to the main wining All winings have the same shape an pitch, but may have ifferent turn numbers an wire sizes; usually smaller in orer to be accommoate in the slots together with the stator The winings are wwwintechopencom

2 26 Electric Machines an Drives arrange in slots such that there is no phase shift between the two winings Figure 1 shows a possible arrangement of the winings for a four pole inuction machine -C -C -Z +B -Z +B +Y +Y +B +Y -A -X -C -Z +A +A +X +X +A -B +X -B -Y -Y -Y -B +C +Z +C +Z -A -X +Z +C -A -X -X -A +C +Z -X -A +Z +C +Z +C -Y -B -B -Y -Y +X -B +A +X +A +X +A -Z -C -X -A +Y +B +Y +Y +B -Z +B -Z -C -C Fig 1 High Power factor inuction machines-winings arrangement 22 Auxiliary winings connections As mention above, the main wining can have elta or star connection Figure 2 shows the main wining connecte in star an the auxiliary winings connecte in generic (a), star (b) an elta (c) to the capacitor bank via a static switch Figure 3 shows a simpler way to inject capacitive reactive power In this metho, the auxiliary winings are in single phase connection with the apparent avantage of using only one capacitor an static switch 23 Variable Capacitors In orer to achieve a compensation for various loaing of the machine, the compensating capacitor shoul be able to be varie This capability is obtaine through connecting a fixe capacitor via a static switch The static switch can be achieve using thyristors or IGBTs in biirectional configuration wwwintechopencom

3 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection 27 Va Ia * * Vx Vb Ib * * Vy Rotor Vc Ic * * Vz Static Switch C (a) V a V b V c C z V a C x V x V y C x C y (b) V z C z V z V x V c V y (c) C y V b Fig 2 Auxiliary winings: a) generic connection; b) star connection; c) elta connection Va Ia Vx Vb Ib Rotor Vy Ic Vc Vz Va Iax Static Switch C Fig 3 Auxiliary winings: single phase connection wwwintechopencom

4 28 Electric Machines an Drives 231 Thyristor-base variable capacitor Figure 4 shows the use of thyristor to accomplish a variable capacitor The inuctor L r is introuce to reuce limit the surge current; it is relatively small an oes not affect the overall capacitive behaviour Th 2 C Th 1 L r Fig 4 Variable capacitor using biirectional thyristor The equivalent capacitance epens on the elay angle Due to the phase angle control, the evice introuces harmonic currents 232 IGBT-base variable capacitor The above rawback can be aress using IGBTs in biirectional configuration (Figure 5) an a switching frequency higher then operational frequency (50 Hz) Fig 5 IGBT in biirectional topology Figure 6 shows a configuration to achieve a variable capacitor using two biirectional static switches The main capacitor C 1 is introuce in the auxiliary wining circuit, via a biirectional switch Sw 1, for a perio of time epening on the uty cycle ( ) of the switching frequency; in this time the biirectional switch Sw 2 is OFF When Sw 1 is OFF, the capacitor is ischarge The reactor L r limits the capacitive surge current without affecting the capacitive behaviour I x Sw 1 V x L r C 2 C 1 Sw 2 Fig 6 Variable capacitor using two IGBTs in biirectional topology wwwintechopencom

5 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection 29 The capacitor C 2, much smaller than C 1 is connecte to mitigate the voltage spikes uring switching off the main capacitor Thus, the equivalent capacitor can be written as: C eq =δ C 1+C 2 (1) 233 Variable capacitor H-topology Figure 7 shows a single-phase H topology to achieve a variable capacitor This configuration using H-brige biirectional topology obtains a higher equivalent capacitance for the same fixe one as reference In this configuration, the reactor L r has the same purpose of limiting the surge capacitive current, while C 2 also of small value mitigates the voltage spikes The equivalent capacitance coul be express as: C C =C + (2) 2δ-1 1 eq 2 2 ( ) It can be notice that the equivalent capacitance coul increase significant when the uty cycle approaches 50 % In practice, the switches are not ieal an there is no infinite increase of the equivalent capacitance V x I x C 2 Sw1 Sw2 L r Sw3 Sw4 Fig 7 Variable capacitor using H-brige biirectional topology C 1 I x I y I z C Fig 8 Variable capacitor using three-phase H-brige topology wwwintechopencom

6 30 Electric Machines an Drives Another solution to achieve a variable capacitance, or rather to generate a capacitive current was propose using a three-phase H topology as PWM inverter (E Muljai, et al 1989; Tamrakan an Malik, 1999) as presente in Figure 8 The converter injects capacitive reactive power into auxiliary winings an thus improving the power factor of the motor 3 Mathematical moel The machine is treate as having two three-phase winings an the voltages equations system can be written as: where [V abcs ]=[R 1][I abc ]+ [λ abc ] t 0=[R 2][I xyz]+ [λ xyz]+vcxyz t 0=[R r ][I abcr ]+ [λ abcr ] t (3) (2) (5) T V abc= Va Vb Vc (6) T I abcs= Ia Ib Ic ; T λ abc= λa λb λc (7) ra 0 0 rx 0 0 [R 1]= 0 rb 0 [R 2]= 0 ry r c 0 0 r z Note that inices 1 refer to the main wining an 2 to the auxiliary wining (8) λ L abcs abc Labcsxyz L abcsr I abcs λ xyz= Lxyzabcs Lxyz Lxyzabcr Ixyz λ abcr Labcrs Labcrxyz L abcr I abcr The inuctances in eq (9) are time epenent, an this make the equation ifficult an time consuming to solve In orer to obtain constant parameters, the voltage equations (3-5) are then transforme to the rotor reference frame To achieve this, the equations are multiplie with an appropriate transformation matrix K(θ) to obtain: (9) [K(θ)][V abcs ]=[R 1][K(θ)][I abcs ]+ [K(θ)][λ abcs ] t 0=[R 2][K(θ)][I xyzs ]+ [K(θ)][λ xyzs]+ Kθ V cxyzs t (10) (11) wwwintechopencom

7 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection 31 0=[R r][k(θ r)][i abcr]+ [K(θ r)][λ abcr] t When these equations are expane, after substantial matrix manipulations, it resolves to: (12) where an V qo1 = R s1 I qo1 + λ q01 + λ ϖ qo1 t 0= R 2 I qo2 + λ q02 + ϖ λ qo2 + Vc q02 t 0= R r I qor + λ q0r + ϖ r λ qo1 t ϖ=ω ; ϖ r = ( ω ωr) (13) (14) (15) (16) 1 Vc qo2 = I q02 t+ ϖ Vc (17) q02 C Neglecting the 0 sequence since we initially are assuming a balance system, the expression for the stator an rotor flux linkages, resolves into the matrix: λ L +L 0 L +L 0 L 0 I q1 ls1 m lm m m q1 λ 1 0 L I ls1+lm 0 L lm+lm 0 Lm 1 λ q2 L lm +Lm 0 L ls2+lm 0 Lm 0 I q2 = λ 0 L 2 lm +Lm 0 L ls2+lm 0 Lm I 2 λ L qr m 0 Lm 0 L lsr+lm 0 Iqr λ 0 L 0 L 0 L +L I r m m lsr m r (18) 4 Equivalent moel 41 Symmetrical loae auxiliary winings When each phase of the auxiliary winings is loae with equal capacitors (C), eventually star connecte, the entire circuit is having a symmetrical behaviour an the equivalent circuit is very simple as shown in Figure 9 I 1 R 1 L l1 L lm L lr R 2 L l2 V 1 C L m R r/s Fig 9 Equivalent circuit for symmetrical loaing auxiliary wining wwwintechopencom

8 32 Electric Machines an Drives This equivalent circuit has two branches, each having separate resistance (R 1 main an R 2 - auxiliary) an leakage reactance (L l1 main an L l2 auxiliary) together with a common mutual leakage inuctance L lm, which occurs ue to the fact that the two set of winings occupy the same slots an therefore mutually couple by their leakage flux The mutual inuctance that occurs between main wining an rotor is represente by L m Other parameters of the equivalent circuit are: main wining resistance R 1, auxiliary wining resistance R 2, main wining leakage reactance L 1, auxiliary wining leakage inuctance L 2 ; mutual leakage inuctance L lm, rotor leakage inuctance L lr ; an the rotor resistance R r an s is the slip In this analysis there is no nee to refer the auxiliary wining quantities to the main wining, because the two sets of winings are woun for the same number of turns with a transformation ratio of one The above equivalent circuit helps us to etermine the input impeance seen from the supply an the conition for unity power factor Z =R +jx + in 1 l1 ( RR-XX ) +j( XR+XR ) ( R+R ) +jx+x ( ) Where: R 1 an jx l1 are the components of the main wining (per-phase impeance), X 2 is the equivalent reactance of the auxiliary wining incluing the compensating capacitor, R 2 is the resistance (per-phase) of the auxiliary wining, R 3 an X 3 are the equivalent resistance an reactance of the paralleling the rotor branch with magnetizing branch: The conition for unity power factor is: 1 X= 2 -Xl2 ωc { ( ) ( )} (19) (20) X 3=Im jx lm+ R r/s +jx lr // jxm (21) { ( ) ( )} R 3=Re R r/s +jx lr // jxm (22) Which, after some mathematical manipulation can be written as: With: Im{ Z in} = 0 (23) 2 X 2+ X 2+ =0 (24) =X 3+X l1 (25) =-R 2R 3+ ( R 1+R 2) R 3+2X3X l1 (26) ( ) ( ) 2 2 =-X 3 R2R 3- R 2+R 3 R 2 +Xl1 R 2+R 3 +X 3 (27) wwwintechopencom

9 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection 33 The equation (24) together with relations (25) to (27) prouces two solutions, which means for a given slip (s) there are two values for the capacitor satisfying the conition for unity power factor The practical/recommene value is the high X 2 or small C connecte to the auxiliary wining in orer to have a small current through it 42 Asymmetrical loae auxiliary winings If the auxiliary winings are connecte as single-phase configuration, then the system has an asymmetrical behaviour This connection is obtaine by connecting in series the three auxiliary winings an thus we can write: I x = I y = I z = I X Using this conition of current in the expansion that results to equations (3) (18) it can be written: I 2 = I q2 = 0, thus the resulting expression from this can be represente in a -q-0 equivalent circuit of Figure 10 shown below I 1 R 1 L ωλ q1 l1 L lm (ω-ω r)λ qr L lr V 1 R 2 V 2=0 L l2 L m R r (a) I q1 R 1 L ωλ 1 l1 L lm (ω-ω r)λ r L lr V q1 R 2 V q2=0 L l2 L m R r (b) I 01 R 1 L l1 L l2 R 2 V 01 L lm V 02 C eq (c) Fig 10 The -q-0 equivalent circuit: a) equivalent circuit; b) q equivalent circuit; c) 0 equivalent circuit wwwintechopencom

10 34 Electric Machines an Drives The particularity of connecting the auxiliary winings in a single phase wining creates an asymmetrical situation which brings about the relevance of the zero sequence The power factor of the machine coul be efine by the argument of Z a, which is V a /I a An this is expresse as: V V +V a q1 01 Z= a = Ia I q1+i01 (28) (Z 01+Z lm) V 01(C)=(-jωC+Z 02) I 02 Z lm (29) As can be observe from the equations (28) an (29), the power factor of the machine epens on C an thus it can be brought to unity by means of ajusting the equivalent capacitance It shoul be also notice that the asymmetrical behaviour of the auxiliary winings connecte as single-phase configuration has got a significant raw-back namely creating torque ripple This isavantage shoul not be overseen by the simplicity of the physical solution Given this, further in this, we will consier only the symmetrical loaing of the auxiliary wining 5 Concept valiation For the valiation of this concept of improving performances of the inuction motor injecting capacitive reactive power via auxiliary winings, a stanar 4 kw, 380V, 50Hz, 4 pole, 36 slots with frame size DZ113A inuction motor have been use The stator was rewoun with two full-pitches, single layer winings (see Figure 1)The main winings elta connecte have same number of turns like in the original motor but the size of the wire has been reuce to accommoate the auxiliary winings The auxiliary winings were connecte in elta in orer to reuce current through them For this stuy, the auxiliary winings have the same number of turns as main winings The rotor is unchange Table 1 shows the parameters of the moifie motor uner test obtaine using the IEEE test proceure The mutual leakage inuctance X lm is very small compare to the other reactance s (E Muljai et al, 1989) Description of ata Values Main Wining Rate Voltage 380 V Auxiliary Wining Rate Voltage 380V Number of poles 4 Magnetizing Reactance (X m ) 3786 Ω Main wining phase resistance (R 1 ) 433 Ω Auxiliary wining phase resistance (R 2 ) 181 Ω Main wining leakage reactance (X l1 ) 697 Ω Auxiliary wining leakage reactance(x l2 ) 697 Ω Rotor resistance (R r ) 135 Ω Rotor leakage reactance (X lr ) 197 Ω Full loa main wining current 86 A Table 1 Specific parameters of the inuction motor uner test wwwintechopencom

11 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection 35 Firstly, the motor was teste without compensation; the results are presente in Table 2 I L (A) T L (Nm) P(W) S(VA) PF Slip RPM Table 2 Experimental ata for the motor uner test 51 Simulation results Base on Matlab platform, a simulation moel has been built (Figure 11) The parameters from Table 1 have been use for Matlab moel after elta-star transformation The rotor resistor was simulate using a variable resistor epening on slip The moel was run firstly to show the capability of ajusting the power factor via the static switch + i - Continuous pow ergui 0 t Clock R1 Xl1 Xl2 R2 Main Auxiliary v Va + - Ia Xm 0056 s Xr 0 Control C V In1 Conn2 Conn1 Rr/s Ieal Switch g 1 I Active & Reactive Power PQ m 2 Lr Q P (Variable Resistor) Fig 11 Basic simulation moel 511 Thyristor-base variable capacitor One of the first solutions to introuce a variable capacitor was to use an ac-ieal switch base on two thyristors anti-parallel connecte The test was one using a 100 µf an a elay angle of 45 0 for a slip of (no loa) This results in a reuction of reactive power rawn by the motor from 1193 VAr to 46 VAr The main rawback of this switching solution is the strong istorting currents introuce as coul be seen in Figure 12 As coul be notice, both currents main an auxiliary are very much istorte Obviously, the power factor compensation is accompanie with egraing of all other performances of the motor wwwintechopencom

12 36 Electric Machines an Drives Relative amplitue (V, A) va (t) ia (t)* ix (t)* Time (sec) Fig 12 Electric parameters (v a, i a an i x ) for compensate moel using thyristor-base variable capacitor 512 IGBT-base variable capacitor The other solution teste to obtaining variable capacitor was that of Figure 6 The values for the two capacitors were chosen as: C 1 = 100 µf an C 2 = 1 µf The valiation simulation was one for a slip of s = 00026; the switching frequency was 1 khz an then the uty cycle manually ajuste Figure 13 shows the main an auxiliary currents towar supply voltage for a uty cycle of 40 % (Fig13 a) an 80% (Fig13 a) v a Relative amplitue (V, A) a v a i a *10 i x *10 Relative amplitue (V, A) b i a *10 i x * Time (sec) Time (sec) Fig 13 Main an auxiliary currents for s = 00026, 1 khz an: a) = 40 %; b) = 80 % As can be notice a uty cycle of 40 % oes ajust the shift between the main current an voltage marginally increasing the power factor from 015 to 032 lagging When the uty cycle was increase to 80%, then the main current arrive in phase with the voltage It can also be notice a relative high ripple especially for low uty cycle Figure 14 shows the same simulation conitions, but now the switching frequency was raise to 4 khz As can be notice the ripple has been reuce significant The other methos of proucing variable capacitive reactive power, meaning the H-brige topologies require a more complex control system an are not aresse in this stuy wwwintechopencom

13 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection v a 300 v a Relative amplitue (V, A) i a *10 i x *10 Relative amplitue (V, A) i a *10 i x * Time (sec) Time (sec) Fig 14 Main an auxiliary currents for s = 00026, 4 khz an: a) = 40 %; b) = 80 % 513 Capacitance versus slip for unity power factor Now, the moel was run for each value of the slip (spee) given in Table 2 The result of these simulations is the capacitance proucing unity power factor (see Table 3) s (n) C Y (µf) I a (A) P a (W) Q a (VAr) S a (VA) (1496) (1491) (1487) (1477) (1468) (1491) Table 3 Simulation results: capacitance versus slip for unity power factor It is interesting to observe that the capacitance proucing unity power factor oes not vary so much as presente in other stuies (E Muljai et al 1989; Tamrakan an Malik, 1999) concerning similar metho of injecting capacitive reactive power Moreover, it coul be foun a fix value of 75 µf which maintain a high power factor irrespective of the loa/slip Table 4 shows the simulation results for the fixe capacitor an variable loa/slip Figure 15 shows the variation of the power factor versus slip an Figure 16 shows the variation of the supply current versus slip for compensate with a fix 75 µf capacitor per phase an uncompensate machine PF wwwintechopencom

14 38 Electric Machines an Drives s C Y I a P a Q a (µf) (A) (W) (VAr) (VA) PF Table 3 Simulation results: capacitance versus slip for unity power factor S a Compensate machine 08 Power Factor Uncompensate machine Fig 15 Power Factor versus slip Slip 9 8 Uncompensate machine Supply current Ia (A) Compensate machine 3 2 Fig 16 Supply current versus slip Slip 52 Experimental valiation After rewining the machine uner test with both sets of winings elta connecte, three ientical capacitors were connecte to the auxiliary Then the compensate motor was loae graually to get the same spees as for the uncompensate motor The testing starte with a capacitance of 25 µf as foun uring the simulation: C Δ = C Y / 3 This i not prouce the results foun via the simulation Then a value of 28 µf was foun to give a relative even power factor of approximate 095 in the entire loaing range (see Table 4) wwwintechopencom

15 Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection 39 Figure 17 shows the phase voltage (v an ) an current (i a ) for the uncompensate (Fig 17a) an compensate (Fig 17b) with slip of It can be observe, the power factor increase from 017 to 0937 which represent 450% improvement for no loa For full loa the improvement in power factor is 29% I L (A) T L (Nm) P(W) S(VA) PF Slip RPM Table 2 Experimental ata for the motor uner test 1) [THS720P]CH1 100 V 2 ms 2) [THS720P]CH2 5 A 2 ms 1) [THS720P]CH1 100 V 5 ms 2) [THS720P]CH2 1 A 5 ms (a) (b) Fig 17 Voltage an current for: a) uncompensate motor; b) compensate motor 6 Comments This stuy prove that irect injecting capacitance reactance through auxiliary wining oes improve the power factor of the inuction motor; it also increases the ratio torque over current What is also very interesting is this metho achieves a flat variation of power factor with respect of loa variation This is a very important improvement given the fact that majority of inuction motors o not work at constant full loa where the classic esign prouces maximum performances However, this metho introuces extra copper losses reucing the overall efficiency an increasing the operation temperature This stuy i not intene to eluciate the full effect of the metho upon the torque especially the existence of the influence prouce by the current flowing through auxiliary winings The only aspect clearly notice was the torque ripple introuce by the singlephase auxiliary wining connection Further more, the same metho was applie to a synchronous reluctance motor (Ogunjuyigbe et al, 2010) The same type of stator wine similarly as above was use with a salient mille rotor obtaine from the corresponing squirrel cage inuction motor The experimental results show an improvement of the power factor from to for the entire loaing range va ia va ia wwwintechopencom

16 40 Electric Machines an Drives The economic benefits are relate with the savings on eman especially for places where a large number of three-phase inuction motors are use uner variable loaing 7 References M A El-Sharkawi, S S Venkata, T J Williams, an N G Butler, An aaptive Power Factor Controller for Three-Phase Inuction Generators, Paper 84 SM presente at the IEEE/PES Summer Meeting, Seattle, Washington, July 15-20, 1984 Fuchs, EF Hanna, WJ; Measure efficiency improvements of inuction motors with thyristor/triac controllers,, IEEE Transaction on Energy Conversion, Volume 17, Issue 4, Dec 2002 pp Suciu, C; Dafinca, L; Kansara, M; Margineanu, I; Switche capacitor fuzzy control for power factor correction in inuctive circuits, IEEE 31st Annual Power Electronics Specialists Conference, 2000 Vol 2, pp C Suciu, M Kansara, P Holmes an W Szabo, Performance Enhancement of an Inuction Motor by Seconary Impeance Control, IEEE Trans On Energy Conversion, Vol 17, No 2, June 2002 J Reinert, MJ Parsley, Controlling the spee of 8 1 inuction motor by resonating the rotor &wit, in IEEE Transactions on Inustry Applications, Vol 31, No 4, July/August 1995, pp E Muljai, TA Lipo, DW Novotny, "Power Factor Enhancement of Inuction Machines by Means of Soli State Excitation," IEEE Trans on Power Electronics, Vol 4, No 4, pp , Oct 1989 I M Tamrakan an OP Malik, Power Factor Correction of Inuction motors Using PWM Inverter Fe Auxiliary Stator Wining, IEEE Transaction on Energy Conversion, Vol 14, No3, Sept, 1999, pp J B Mearametla, M D Cos, an Baghzouz, Calculations an measurement of unity plus three-phase inuction motor, IEEE Transactions on Energy Conversion, vol 7, no 4, pp , 1992 S D Umans, an H L Hess, Moelling an analysis of a the Wanlass three-phase inuction motor configuration, IEEE Transaction on Power Apparatus an Systems, vol 102, no 9, pp , 1983 R Spée an A Wanllace, Comparative Evaluation Of Power-Factor Improvement Techniques For Squirrel cage Inuction Motors, Inustry Applications Society Annual Meeting, 1990 AA Jimoh an DV Nicolae, Performance Analysis of a Three-Phase Inuction Motor with Capacitance Injection, OPTIM 06, 10 th International Conference on Optimization of Electrical an Electronic Equipments, Brasov, Romania, May 17-20, 2006 DV Nicolae an AA Jimoh, Three-Phase Inuction Motor with Power Electronic Controlle Single-Phase Auxiliary Stator Wining, PESC 07, The 38 th IEEE Power Electronics Specialists Conference, Orlano, USA, June 17-21, 2007 ASO Ogunjuyigbe, AA Jimoh, DV Nicolae an ES Obe, Analysis of Synchronous Reluctance Machine with Magnetically Couple Three Phase Winings an Reactive Power compensation, IET Electric Power Applications, 2010, Vol 4, Iss 4, pp wwwintechopencom

17 Electric Machines an Drives Eite by Dr Miroslav Chomat ISBN Har cover, 262 pages Publisher InTech Publishe online 28, February, 2011 Publishe in print eition February, 2011 The subject of this book is an important an iverse fiel of electric machines an rives The twelve chapters of the book written by renowne authors, both acaemics an practitioners, cover a large part of the fiel of electric machines an rives Various types of electric machines, incluing three-phase an single-phase inuction machines or oubly fe machines, are aresse Most of the chapters focus on moern control methos of inuction-machine rives, such as vector an irect torque control Among others, the book aresses sensorless control techniques, moulation strategies, parameter ientification, artificial intelligence, operation uner harsh or failure conitions, an moelling of electric or magnetic quantities in electric machines Several chapters give an insight into the problem of minimizing losses in electric machines an increasing the overall energy efficiency of electric rives How to reference In orer to correctly reference this scholarly work, feel free to copy an paste the following: Nicolae DV (2011) Electric Motor Performance Improvement Using Auxiliary Winings an Capacitance Injection, Electric Machines an Drives, Dr Miroslav Chomat (E), ISBN: , InTech, Available from: InTech Europe University Campus STeP Ri Slavka Krautzeka 83/A Rijeka, Croatia Phone: +385 (51) Fax: +385 (51) wwwintechopencom InTech China Unit 405, Office Block, Hotel Equatorial Shanghai No65, Yan An Roa (West), Shanghai, , China Phone: Fax: