sourabh jain, shailendra sharma and r.s. mandloi …iret.co.in/docs/volume 2/issue1/5 improved power...

Sourabh Jain, Shailendra Sharma and R.S. Mandloi 35

International Journal of Emerging Trends in Electrical and Electronics (IJETEE) Vol. 2, Issue. 1, April-2013.

Improved Power Quality AC Drive Feeding Induction Motor

Sourabh Jain, Shailendra Sharma and R.S. Mandloi

Abstract: This paper deals with the power quality enhancement of induction motor drive used to operate in vector controlled mode. The improved power quality AC drive consists of voltage source converter (VSC), voltage source inverter (VSI) and an intermediate DC bus supported with capacitors. The performance of improved power quality AC drive is demonstrated on developed simulation model. The obtained result verifies performance of improved power quality AC drive in all four quadrants. Keywords: PWM Rectifier, Indirect Vector Control Drive, Unit template (UTT), Regenerative operation

NOMENCLATURE Rr Rotor resistance(referred to rotor side ) Lr Rotor leakage Inductance Lm Magnetizing Inductance ids Magnetizing component of stator current iqs Torque component of stator current idr d-axis rotor current iqr q-axis rotor current 푖∗ Reference magnetizing component of stator

current 푖∗ Reference Torque component of stator current Ψ d-axis rotor flux linkage Ψ q-axis rotor flux linkage 훹 Rotor flux 휔 Rotor frequency (rad/s) 휔 Electrical frequency (rad/s) 휔 Slip frequency (rad/s) 휔 Rotor mechanical speed 휔 Reference Speed 휔 Base Speed 휃 Rotor angle 휃 Angle of synchronously rotating frame 휃 Slip angle Vref Reference voltage VDC Intermediate DC voltage Vabc Three Phase Supply Voltage Ua Ub Uc Unit template of Phase a,b,c Ia, Ib, Ic Three phase stator current

I. INTRODUCTION The squirrel cage induction motor is most versatile in

industry due to its less maintenance, cheap in cost and rugged in construction [1]. Due to its constant speed characteristics, it is not inherently considered as suitable choice for applications which needs variable speed operation [2]. There have been many control techniques reported in literature which facilitates variable speed operation namely V/f control, vector control and direct torque control (DTC) [3]. The V/f control technique allows the induction motor to deliver its rated torque at speed up to its rated speed, beyond the rated speed, its torque capability is declined [4]. However with this control technique the performance under transient condition is inferior. Vector control technique allows a squirrel-cage induction motor to drive with high dynamic performance. It provides a decoupling of two components of stator current: one producing the airgap flux and the other producing the torque. Therefore, it allows independent control of torque and flux, which is similar to a separately excited dc machine [3]. In Indirect vector control, field angle has been obtained by using rotor position measurement and partial estimation of machine parameters [2]. The magnitude and phase of the stator currents has been controlled in such a way that flux and torque components of current remain decoupled under dynamic and static conditions [3]. Moreover in many applications such as conveyors, trolleys, electric vehicles, locomotives, traction etc. it is required to achieve fast dynamic response in all four quadrant namely forward motoring, forward braking, reverse motoring and reverse braking. In commercial available drives mostly diode bridge rectifier has been used to convert AC into constant voltage DC which creates problem such as ‘poor power factor’, ‘highly discontinuous current’, ‘injection of harmonics into AC mains’ and ‘fluctuations of dc link voltage’ [5]. This paper deals with a four quadrant improved power quality induction motor drive using a voltage source inverter (VSI) and a voltage source converter (VSC) with intermediate DC link.

Sourabh Jain, Shailendra Sharma and R.S. Mandloi are with Department of Electrical engineering, SGSITS, Indore, M.P., India, Emails: [email protected], [email protected], [email protected]



Fig.1 Block Diagram of IFOC induction motor drive

II. SYSTEM CONFIGURATION The system under consideration is shown in Fig.1.The

insulated gate bipolar transistor (IGBT) based VSI is controlled using the indirect vector control. It also consists of three phase VSC. The VSC and VSI shares common DC link. The intermediate point of each-leg of a VSC is connected to input supply through an interface inductor. A star connected high pass filter is used at VSC terminals to absorb switching ripples. Similarly midpoint of each leg of the VSI is connected to star connected three-phase induction motor. Parameters of proposed system are given at appendix 1 2.

III. CONTROL SCHEME A. VSI Control

The VSI is controlled using indirect field orientation control (IFOC), which is also known as flux feed-forward control. Block diagram of IFOC technique shows in Fig.2. IFOC is derived from dynamic equation of induction motor, unit vector signals are generated in feed forward manner. The stator phase current serves as input, hence the stator dynamics can be neglected. The rotor equation containing flux linkage as a variable given as

푅 푖 +푑훹푑푡

+ 휔 훹 = 0 (1)

푅 푖 +푑Ψ푑푡

− 휔 Ψ = 0 (2)

Where 휔 = 휔 − 휔 The rotor flux linkage equation as, Ψ = 퐿 푖 + 퐿 푖 (3)

Ψ = 퐿 푖 + 퐿 푖 (4)

Eq. (3)-(4) can be rearranged as,

푖 =1퐿

Ψ −퐿퐿

푖 (5)

푖 =1퐿

Ψ −퐿퐿

푖 (6)

The rotor current equations can be obtained by putting Eq.(5)-(6) in eq. (1)-(2) as 푅퐿

Ψ −퐿퐿


− 휔 Ψ = 0 (7)

푅퐿

Ψ −퐿퐿


− 휔 Ψ = 0 (8)

For decoupling control Ψ = 0 푑Ψ푑푡

= 0 So that the total rotor flux Ψr is directed on de-axis 퐿푅푑훹푑푡

+ 훹 = 퐿 푖 (9)

From the q-axis current components and slip gain, the slip speed relation is obtained as:

퐾 =휔∗

푖∗=퐿 푅훹 퐿

,휔 =퐿 푅훹 퐿

푖 = 퐾 푖 (10)

The slip speed, together with the feedback rotor speed, is integrated to obtain the stator reference flux linkage space vector position

휃 = 휔 푑푡 = (휔 + 휔 )푑푡 = 휃 + 휃 (11)

The actual rotor speed and sensed rotor speed is compared. Speed error acts as input to proportional integral (PI) controller, which provides a torque controlling current component 푖∗ of the stator current. This current component is used to regulate the torque along with the slip speed. The output of the PI controller is given as:

푖∗ = 푘 Δ휔 + 푘 Δ휔 푑푡 (12)

Similarly the flux producing current component 푖∗ , is obtained from the stator flux linkage reference value and given by the following equation,

퐾∗ =휔휔

Ψ∗

with 푖∗ = kΨ∗

푖∗ = k휔휔

Ψ∗

(13)

if 0 ≤ 휔 ≤ 휔

otherwise 휔 > 휔



The flux reference is constant till the reference rotor speed below its rated speed, but if motor runs above rated speed, flux weakening essential.

Fig.2 Block diagram of control of VSI B. Control of VSC

The block diagram of control algorithm used for a front end VSC is shown in Fig.3. The control scheme ensures constant DC bus voltage and unity power factor at supply sides even under change in load. The reference DC link voltage (Vref) is compared with the actual DC link voltage and error voltage is proceed through a PI controller, the voltage controller output is multiplied by the in phase unit template of each phase. These reference currents are compared with sensed currents and the error signals are used as input to a PWM modulator which provides pulses for the VSC [10]. The amplitude of phase voltage is obtained as,

푉 = 23

(푉 + 푉 + 푉 ) (14)

The in-phase template are derived as

푈 = 푉푉

,푈 = 푉푉

,푈 = 푉푉

(15)

222

32

cba VVV

Fig.3 Block diagram of control of VSC

IV. MATLAB-BASED SIMULATION The improved power quality AC drive for induction

motor is modeled in MATLAB using Power System Blockset. Fig. 4 depicts the setup used to estimate the performance of the AC drive with proposed control scheme through simulation. The source block connected with a three-phase voltage source active rectifier block. Three leg IGBTs based VSC, capacitive filter and input side inductive filter used as an active rectifier. The performance of the drive is controlled by IFOC controlled VSI. Effectiveness of proposed system improved by VSC at supply sides.

Fig.4 Simulation model of IFOC control induction motor drive

V. SIMUALTION RESULTS Results are obtained on developed simulation model to

demonstrate the performance in the steady state and transient condition shown in Figs.4 to 6. The parameters used in simulation are given appendix 1 2. A. Performance of System During Starting mode Fig.5 shows the simulation results during motoring condition without load applied. At start, rated current is observed to accelerate the motor. After that current is settled. At time 350ms, a 25N-m load is applied on motor. The dc link feedback controller acts to keep dc link voltage at its reference value. B. Performance of System on Braking mode

Till during time, 0 to 500ms AC drive runs in motoring mode, the fundamental input current is in phase with supply voltage. After this time interval, braking is applied on motor. During this time VSC DC link current (Idc-recti) is divided into two components i.e. capacitor current (Idc-capa) and output current (Idc- o/p) which fed into VSC. The observed results are shown in Fig.6. C. Regenerative Braking mode At time t4=1.0 sec. the motor reference speed should be negative. Rotor rotates at opposite direction. Small fluctuation is found in DC link voltage. After time t =1.32 sec. The reference speed is changed negative to zero and



regenerative braking is applied on motor. In this mode, supply currents are fed to the source, variations in currents are shown in Fig.7. VSC currents are observed negative.

Zero speed tracking error is achieved during steady-state conditions and with reference speedvariation.

Fig.5 Simulation results: Motoring mode



Fig.6 Simulation results: Braking mode

Fig.7 Simulation results: plugging and regenerative braking

VI. CONCLUSION

An improved power quality induction motor drive has been modeled and simulated. A three leg voltage source converter (VSC) and a voltage source inverter (VSI) has been used to develop four quadrant induction motor drive. An indirect vector control has been used for controlling a VSI. A unit

template algorithm has been developed for control of VSC. The performance of developed AC drive has been demonstrated under starting, motoring and braking modes and it is found satisfactory.

VII. APPANDIX 1. THREE PHASE INDUCTION MOTOR

PARAMETER Rated Power = 7.5 kW Rs=0.7384Ω Rated voltage = 415V Rr′ = 0.7402Ω Rated current = 14.5A Ls=0.003045H Rated Speed Ns =1450r/min Lr=0.003045H Frequency f = 50Hz Lm = 0.1241H Poles Pair p = 2 J = 0.0343 kg.m2 Friction Factor(F) =0.000503 N.m.s Kp = 6.28 Ki = 0.96

2. VOLTAGE SOURCE CONVERTER(VSC)

PARAMETER Supply Voltage = 415V

Line Impedance Rs= 0.5 Ls= 5mH

Frequency = 50Hz

Filter Rf = 5Ω Cf = 20µF

DC bus capacitance = 7500 µF

Switchs(Sw1 – Sw6) = IGBTs

Kp = 0.36 Ki = 3.2

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International Journal of Emerging Trends in Electrical and Electronics (IJETEE)

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Sourabh Jaintechnology institute vidisha in the year 2008. He has obtained his M.E from Institute of Technology and Sin 2012. He has 2 years experience.area of Power electronicsquality.

Dr. Shailendra Sharma 1972. He received the M.E. degree in engineering with specialization in electronics from the Shri Govindram Seksaria Institute of Technology and Science (SGSITS), Indore, in 2004. He got Ph.D. degree in the Department of Electrical Engineering, Indian Institute of TechnologDelhi. He has five years of industrial experience as an

Erection and Commissioning Engineer with M/s Dhar Textile Mills Ltd., Indore. In 2004, he joined the Department of Electrical Engineering, SGSITS, as an Assistant Professor.electronics, electric drives, power quality, and renewable energy systems. Mr. Sharma is an Associate Member of the Institution of Engineers, India.



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570, May/June 1985. J. Rodríguez, L. Morán, J. Pontt, J. Hernández, L. Silva, C. Silva, and P. Lezana, “High-voltage multilevel converter with regeneration capability,” IEEE Trans. Ind. Electron., vol. 49,

846, Aug. 2002. H. Fujita and H. Akagi, “The unified power quality conditioner: the integration of series- and shunt-active filters,” IEEE Trans. Power Electron.,vol. 13, no. 2, pp. 315–322, Mar.

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Journal of Electric Power Systems and Research, 81, Feb.1994.

Vector Control of AC Machines", Clarendon Press

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Siemens Rev., vol. 34, no. 5, pp. 217–220, 1972. Huang, M.S.; Liaw, C.M. “Improved field weakening control for IFO induction motor” IEEE Transactions on Aerospace And Elecronic Systems, Vol. 39, No. 2 pp. 647-659 April

P. Farmanzadeh, “A robust controller design to stabilize induction motor drive operation using (IFOC) method” in Proc. IEEE PEDSTC, 2012, pp. 218 - 222 E. Etien, C. Chaigne, and N. Bensiali, “On the stability of full

induction motor in regenerating mode,” IEEE Trans. Ind. Electron., vol. 57, no. 5, pp. 1599–1608,

A. V. Ravi Teja and C. Chakraborty, “A novel model reference adaptive controller for estimation of speed and stator

controlled induction motor drives,” in Proc. IEEE ISIE, Bari, Italy, 2010, pp. 1187–1192.

Sourabh Jain has obtained his B.E from Samrat ashok technology institute vidisha in the year 2008. He has obtained his M.E from Shri Govindram Seksaria

Technology and Science (SGSITS), Indore, in 2012. He has 2 years experience. He is working in the

Power electronics, Electric drives and power

Shailendra Sharma was born in Indore, India, in 1972. He received the M.E. degree in electrical engineering with specialization in electronics from the Shri Govindram Seksaria Institute of Technology and Science (SGSITS), Indore, in 2004. He got Ph.D. degree in the Department of Electrical Engineering, Indian Institute of Technology (IIT) Delhi, New

He has five years of industrial experience as an Erection and Commissioning Engineer with M/s Dhar Textile Mills Ltd., Indore. In 2004, he joined the Department of Electrical Engineering,

Professor. His fields of interest include power electronics, electric drives, power quality, and renewable energy systems. Mr. Sharma is an Associate Member of the Institution of Engineers, India.


R.S.Mandloi has obtained his B.E from Govindram Seksaria Institute of Science (SGSITS), Indore, in 2003his M.E from Shri Govindram Seksaria Institute of Technology and Science (SGSITS), Indore, in 2006He has 6 years experience. He is presently working as an Assistant Professor

working in the area of Power electronics, Drives

40

Vol. 2, Issue. 1, April-2013.

has obtained his B.E from Shri Govindram Seksaria Institute of Technology and

cience (SGSITS), Indore, in 2003. He has obtained Shri Govindram Seksaria Institute of

cience (SGSITS), Indore, in 2006. years experience. He is presently working as

Assistant Professor in SGSITS Indore. He is Drives and power quality.

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