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(IJCNS) International Journal of Computer and Network Security,Vol. XXX, No. XXX, 2009

Performance Comparison of Different Voltage Regulation Methods

Proposed for the Speed control of Capacitor-run Induction Motors

K.Samidurai1, K.Thanushkodi2

1KarpagamCollege of Engineering, Coimbatore

swami_la@ yahoo.co.in

2Akshaya College of Engineering & Technology, Coimbatorethanush123gmail.com

Abstract: This paper systematically investigates and compares

the performance characteristics of variable-speed, single-phase

capacitor-run fan motor using different voltage regulation

methods namely triac based voltage regulator, single pulse width

modulated (SPWM) ac chopper, and electronic transformer based

voltage regulator. It is found that the electronic transformer

based voltage regulator scheme has superior operating and

performance characteristics as compared to the other schemes.

Experimental results show that apart from improvement in

performance with respect to power factor and total harmonic

distortion (THD) an appreciable amount of energy saving is also

obtained in the electronic transformer based scheme.

Keywords: capacitor-run induction motor, ac choppers, triac

based voltage regulators, electronic transformer based voltage

regulators.

1. IntroductionThe motor used for domestic fans is a capacitor-run single-

phase induction motor with squirrel cage rotor. The rotor

resistance in these motors is higher and is therefore, quite

suitable for wide range of speed control using stator voltage

control [1]. The commonly employed method of speed

control in domestic fan motors is the use of a variable

resistance in series with the stator of the motor. As this

scheme is cheaper, it is popular even today. However, this is

an inefficient method of speed control due to the power loss

in the series resistance. In the triac based schemes, the triac

is inserted either between the a.c mains and the fan motor or

in series with the main winding. The triac based schemes are

simple, reliable, cost effective and superior in power savings

[2-5]. However, it suffers from various drawbacks such as

increased harmonic content and poor power factor, especially

at lower output voltages. The ac chopper essentially consists

of two switches. In general, one is connected in series with

the motor and the other one across the motor as shown in

Fig.1 In this paper, an alternative method of connecting

switches in series and across the main winding of the motor

is also proposed. In this case, the auxiliary winding of the

motor is fed from the supply directly as shown in Fig.2.

When SPWM is used, a series switch is closed, keeping the

parallel switch open; the motor terminal voltage is

symmetrical about the /2 axis and variable speed is

achieved by changing the pulse width.

The Electronic transformer based scheme proposed in this

paper has several advantages over the other schemes

mentioned above. The circuit diagram for the experimental

set up of this scheme is shown in Fig.3.

1

1 AC Supply

Auxiliarywindin

g

Mainwinding

Rotor

(i)

Current

drawn by

motor

(i)

Current

drawn by

motor

(ii)Voltage

across

motor

terminals

(ii)

Voltage

across

motor

terminals

Fig. 5.

Comparis

on of

current

and

voltage

waveform

s of

Electronic

transform

er and

triac

based

schemes

.

200V/div

(a )

Fig.1. Conventional PWM based ac chopper scheme.

1 AC Supply

Auxiliarywind

ing

Mainwinding

Rotor

Fig.2. Proposed PWM based ac chopper scheme

I/M

S3

S1

S2

S4

L

C2

a

F

i

g

1

E

q

ui

v

al

e

n

t

ci

r

c

u

it

o

ft

h

e

m

o

t

o

r

b

C1

Vo

Vi

Fig.3. Circuit diagram of the proposed scheme


2/5


The electronic transformer is making use of an amplitude

modulation and phase shifting technique for achieving a

variable output voltage and hence the speed of the fan motor

can be controlled.

An isolated high frequency link AC/AC converter is termed

as an electronic transformer. The electronic transformer has

size and cost advantages over a conventional transformer

because of high frequency operation of the magnetic core.

Low cost and easy availability of ferrite core material has

helped the implementation of high frequency link power

transformation [6-9].

The use of electronic transformer for speed control of single-

phase induction motor results in improved power factor,

energy saving, reduction in THD, improved efficiency and

improved power quality as compared to the other schemes

listed above. Experimental results are presented to validate

the proposed scheme.

2. Capacitor run Induction Motor Modeling

2.1 Equivalent circuit

The equivalent circuit of the capacitor - run motor based on

double field revolving theory is shown in Fig.4.Where a is

the turns ratio of the auxiliary to main winding, Rlm, Xlm are

the resistance and leakage reactance of the main winding(), Rla, Xla are the resistance and leakage reactance of the

auxiliary winding, Rc, Xc are the equivalent series

resistance and reactance of the capacitor (), Rf, Xf are the

forward equivalent series resistance and leakage reactance of

the rotor referred to the main winding (), Rb, Xb are the

backward equivalent series resistance and leakage reactance

of the rotor referred to the main winding (), I m, Ia, I are the

main, auxiliary and motor currents, respectively (A), Efm, Ebm

are the self-induced voltages in the main winding by its

forward and backward fluxes, respectively (V), aEfm, aEbm are

the mutually induced voltages in the auxiliary winding by the

forward and backward fluxes of the main winding,

respectively (V), Efa , Eba are the self-induced voltages in the

auxiliary winding by its forward and backward fluxes,

respectively (V), Efa / a, Eba / a, are the mutually induced

voltages in the main winding by the forward and backward

fluxes of the auxiliary winding, respectively (V).

2.2 Mathematical model

The steady state mathematical model of the motor consists of

the set of equations which govern its steady state operation

under all operating conditions. From Fig.4, the following

equations can be written.

V = Zlm Im + Efm + Ebm jEfa /a + jEba /a (1)

V = ( Zla + Zc ) Ia + Efa + Eba + ja Efm - jaEbm (2)

Where:

Efm = Zf Im = Im ( Rf + jXf ) (3)

Ebm = Zb Im = Im ( Rb + jXb) (4)

Efa = a2 Zf

Ia = a2 Ia( Rf + jXf ) (5)

Eba = a2 Zb Ia = a

2 Ia ( Rb + jXb) (6)

Substituting from Equations (3) (6) into Equations (1) and

(2) yields:

V = ( Zlm + Zf + Zb ) Im - ja ( Zf - Zb ) I (7)

V = ja ( Zf - Zb ) Im + ( Zla + Zc + a2 ( Zf + Zb ) ) Ia

(8)

The solution of Equations (7) and (8) gives the main and

auxiliary winding currents under any operating conditions.

Hence, the total motor current is obtained as:

I = Im + Ia (9)

The net amount of power transferred across the air gap (P g) is

obtained as:

Pg = ( Im2 + a2 Ia

2 ) ( Rf - Rb ) + 2a Im Ia ( Rf + Rb ) sin ( a m )

(10)

Where m and a are the phase angles of the main and

auxiliary winding currents, respectively.

The electromechanical torque developed ( Tmd ) is:

Tmd = Pg / s (11)

Where s is the synchronous speed (rad/s). The mechanical

power developed (Pmd ) is given by:

Pmd = ( 1 S ) Pg (12)

Where S is the per unit slip. The output power ( Po ) is:

Po = Pmd Prot (13)

Where Prot is the rotational losses.

The two voltage equations (7) and (8) constitute the

steady state mathematical model of the capacitor - run motor.

The solution of these equations under any operating pointgives the main and auxiliary winding currents. Hence, all the

performance characteristics of the motor at the particular

2


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load point can be calculated. It should be noted that

particular load point means a given value for the applied

voltage and motor speed [5].

3. Results and analysis

A 230 V, 1350 r/min and 60 W rated typical

domestic fan motor is taken for analysis. For performance

comparison, the waveforms of voltage across the motor

terminals and the current drawn by the motor for schemes

listed above are recorded. Fig.5 shows the voltage and

current waveforms of different voltage regulation methods

recorded at a fan speed of 1115 r/min. In the case of triac

based regulators and PWM ac choppers with two different

configurations shown in Fig.1 and 2 there is discontinuity

in the motor current and an appreciable amount of

distortion in the motor terminal voltage is observed. In the

proposed electronic transformer based scheme, as voltage

and current waveforms are sinusoidal, there is an

improvement in input power factor and efficiency,

reduction in THD is observed.

Subsequently certain steady-state characteristics

are plotted as shown in Fig.6 using the values measured at

different speeds. These characteristics include input power

drawn, input power factor, source current, THD and

harmonic spectrum of motor terminal voltage. The

characteristic curves clearly demonstrate the best

performance of the proposed electronic transformer based

scheme as compared to the other schemes. From the

characteristics curves, it is seen that the electronic

transformer based scheme exhibits improved power saving

and better input power factor when compared to other

schemes over the entire speed range. Also it is observed

that in the other schemes, increased copper loss due to the

harmonic currents reduces the overall efficiency of the

motor. At higher speeds, the THD of motor terminal

voltage is high with triac and ac chopper based scheme;

hence the efficiency of the motor with the proposed

electronic scheme remains higher over the entire range of

speed.

3

Fig.4. Equivalent circuit of the motor

Xc

Rc

Rla

Xla

a2Rb

a2Rf

a2Xf

a2Xb

Rlm

Im

V

Ia

Rf

I

Xlm

Xf

-jEfa/a

Rb

Xb

+jEba

/a

Ef

m

Ebm

Efa

Eba

0 [V]

0[A]

10ms/div

i

ii 200V/div

300mA/div

(a) Electronic transformer regulator

(i) Current drawn by motor

(i) Current drawn by motor

(ii) Voltage across motor terminals

(ii) Voltage across

motor terminals

Fig. 5. Comparison of current and voltage

waveforms of Electronic transformer and triac

based schemes

.

0[A]

0 [V]

300mA/div

200V/div

ii

i

5ms/div(b) Triac regulator

(c) Conventional SPWM ac chopper

20ms/div

0[V]

1000mA/div0[A]

200/div


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Fig.5. Comparison of measured waveforms of different

voltage regulation schemes at 1115 r/min.

It is seen that there is a saving in power of the order of 8-10

W with a single unit of electronic transformer operated

motor of rating 60 watts. The use of a large number of such

motors with the proposed electronic transformer based

scheme in domestic and small-scale industries will result in

reasonable saving in energy over a period of time. Though

the proposed scheme is little expensive, it is advisable to go

by the scheme as the power saving over a period of time is

quite large. The quality of the power supply is improved with

the proposed scheme as it reduces the THD of the system.

4. Conclusion

The performance of different voltage regulation

schemes used for speed control of capacitor-run induction

motors is discussed. Experimental results show that the

electronic transformer based scheme proposed in this paper,

has an edge over the triac and ac chopper based schemes.

Apart from improvement in performance with respect to

power factor and total harmonic distortion an appreciable

amount of energy saving is also obtained in the electronic

transformer based scheme. Even though the saving in input

power is only a few watts with a single motor, the use of a

large number of capacitor-run fans in domestic and small-

scale industries will result in increased energy saving over a

period of time.

References

[1]. Paice DA. Induction motor speed control by stator

voltage control. IEEE Trans Power Appl Syst 1968; 87(2):

pp.585-91.

[2]. Cattermole DE, Davis RM, Wallace AK. The design

optimization of a split phase fan motors with triac

voltage (speed) control. IEEE Trans Power Appl Syst

1975; 94(3): pp.778-85.

[3]. Cattermole DE, Davis RM. Triac voltage (speed) control

for improved performance of split-phase fan motors. IEEE

Trans Power Appl Syst 1975; 94(3): pp.786-91.

4

(d) Proposed SPWM ac chopper

20ms/div

0[V]

0[A]

200V//div

1000mA/div

(a)

(b)

(c)

Fig.6. Performance characteristics


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[4]. Donald W. Novotny, and A. Frederick Fath. The

Analysis of Induction Machines Controlled by Series

Connected Semiconductor Switches. IEEE Trans power

App Syst 1968; 87(2): 597-605.

[5]. Hamid.M.B Metwally. New method for speed control of

single phase induction motor with improved motor

performance. Energy conversion & Management. 42(2001):

pp. 941-50.

[6]. Koosuke Harada, Fumimasa Anan, Kiyomi Yamasaki,

Masahito Jinno,Yasuhiro Kawata and Tetsuya Nakashima et

al. Intelligent Transformer , IEEE Proc PESC 23- 27 June

1996, vol.2, pp.1337-41.

[7]. H. Krishnaswami and V. Ramanarayanan. Control of

high frequency AC link electronic transformer. IEE Proc:

Electr. Power Appl., May 2005 ; pp.509-16.

[8]. W.G.Hurley. Optimizing Core and Winding Design in

High Frequency Transformers. IEEE Proc CIEP 14-17

October 1996: pp. 2-13.

[9]. G.Saravana Ilango,K.Samidurai, M.Roykumar and

K.Thanushkodi. Energy Efficient power electronic controller

for a capacitor-run induction Motor. Energy

conversion & Management, 50(2009): pp.2152 2157.

K. Samidurai received his B.E degree in

Electrical & Electronics Engineering from

Bharathiar University, Coimbatore, India in

1992 and M. Tech degree in Power Systems from National

Institue of Technology, nng and theM.Sc (Enggree from

Madras University, Chennai, India in 1972 and 1976

respectively, and the PhD degree in Electrical & Electronics

Engineering from Bharathiar University, Coimbatore, India

in 1991.He is currently the Principal of Akshaya College of

Engineering& Dr. K. Thanushkodi received his B.E degree

in Electrical & Engineering and the M.Sc (Engg) degree

from Madras University, Chennai, India in 1972 and 1976

respectively, and the PhD degree in Electrical & Electronics

Engineering from Bharathiar University, Coimbatore, India

in 1991.He is currently the Principal of Akshaya College of

Engineering& Technology, Coimbatore, India. His research

interests include computer modeling and simulation,

computer networking, power systems and power electronics.

Tiruchirapalli, India in 2005. Since 2005,

he has been Assistant Professor in

Department of Electrical & Electronics

Engineering, Karpagam College of Engineering, Coimbatore,

India. His research interests are in the areas of power quality

(PQ), energy conservation and power electronics. He is

currently working towards his PhD degree at Anna

University, Chennai, India.

Dr. K. Thanushkodi received his B.E

degree in Electrical & Engineering and the

M.Sc (Engg) degree from Madras

University, Chennai, India in 1972 and

1976 respectively, and the PhD degree in

Electrical & Electronics Engineering from Bharathiar

University, Coimbatore, India in 1991.He is currently the

Principal of Akshaya College of Engineering& Technology,

Coimbatore, India. His research interests include computer

modeling and simulation, computer networking, power

systems and power electronics.

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