ApplyingClosingPhase-AngleControlTechniqueinBounce ... · AC PM contactor is commanded by an electronic control unit (ECU). For a satisfactory ECU controlled actuator, two sets of

Hindawi Publishing CorporationActive and Passive Electronic ComponentsVolume 2009, Article ID 609298, 12 pagesdoi:10.1155/2009/609298

Research Article

Applying Closing Phase-Angle Control Technique in BounceReduction of AC Permanent Magnet Contactor

Chieh-Tsung Chi

Department of Electrical Engineering, Chienkuo Technology University, No. 1, Chieh Shou N. Road, Changhua City, Taiwan

Correspondence should be addressed to Chieh-Tsung Chi, [email protected]

Received 9 August 2008; Revised 14 February 2009; Accepted 14 May 2009

Recommended by Ashok Goel

A new low-cost electronic control circuit actuator is proposed for minimizing the bouncing times of an AC permanent magnet(PM) contactor after two contacts closing. The proposed new actuator overcomes the bouncing problem of an uncontrollablerestrictions imposed by previously conventional AC electromagnetic (EM) contactor based on the minimization of kinetic energyprior to two contacts impact. By choosing the closing phase angle of coil voltage on purpose, the bouncing problems of the movablecontact during the closing process are then overcome. The using life of contacts is then prolonged and their operating reliabilityis improved as well. In order to validate the feasibility and effectiveness of the proposed method here, several simulation andexperimental procedures were performed on a prototype of AC PM contactor in the laboratory. Testing results actually showedthat bouncing problem of contactor’s contacts during the closing process was to be controlled by using the proposed technology.

Copyright © 2009 Chieh-Tsung Chi. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Contactors have an essential place in the field of electricaldevices; they are used when insulation between the controland power parts is needed. The process of the contact bounceafter the movable contacts first touch the fixed contacts couldbe repeated several times before they reach a permanentstate of contact. Contactors bouncing phenomenon duringthe closing process is commonly an undesirable event [1].Especially, the lifespan and reliability of contactor dependupon the ability of their contacts to diffuse the acing heatproduced during closing and opening operations [2, 3].

Several critical disadvantages are often to be foundin conventional electromagnetic (EM) contactor, that con-sumes much more energy to hold armature, produces noiseat lower voltage, its coil is easy to be burnt due to continualworking state, and removes the abnormal dropouts resultsfrom power line disturbances like voltage sag events. In therecent years, to overcome above-mentioned disadvantagesof conventional AC EM contactor [4], a new AC contactorwith a permanent magnet actuator (abbreviated AC PMcontactor) has been successfully developed. It has attractedmore and more attention by many researchers [5, 6].

According to the basic collision theory [7], it is impossi-ble that their interface can be maintained in closing statuswhen two finite bodies under initially different velocitiescollide. Much work has been carried out for this undesir-able phenomenon. However, all explored methods almosthighlighted on minimizing the moving kinetic energy ofcontacts before collision or maximizing the dissipating rateof arc heat after collision [3]. To depress the making speed ofcontact prior to contacts impact, an intelligent AC contactorsmodel capable of switching on at the best closing phase ispresented and improved its lifespan effectively [8]. Shortly,several approaches based on intelligent algorithms were usedto determine the best closing phase angle of coil voltagefor different applications [9–11]. Even though many studiesregarding to the contact-bounce control of conventional ACEM contactor operated in the closing process have beenpublished, however, little attention has been paid to controlthe closing contact bounce related to AC PM contactor [4–6]. Figure 1(a) shows the standard controlling mechanism ofa conventional AC EM contactor. When SW is closed, theAC EM contactor is applied to an AC voltage source andthe current flows through the coil. In addition, Figure 1(b)shows the typical system configuration of a new proposed

2 Active and Passive Electronic Components

SW

AC voltagesource

AC electromagnetic(EM) contactor

(a)

SW

AC voltagesource

Electroniccontrol unit

(ECU)

AC permanentmagnet (PM)

contactor

(b)

Figure 1: Sketch the structure of an (a) AC EM contactor; (b) AC PM contactor.

Permanent magnet

Mechanical systemElectrical system

a

b

c

d

x

u(t) m

Magnetic energy-conversion system

Electroniccontrol

unit(ECU)

Geometricalcentral line

φ

F f

Fmag

x0

N1

N2i1

i2

r1

r2

+

−

Figure 2: System configuration of AC PM contactor.

AC PM contactor. Note that an electronic control unit isincluded and connected with an AC voltage source andAC PM contactor coil in series. As a result of permanent-magnet force forced on armature, not only the fast transitionresult is achieved during the closing process, but also littleenergy is consumed during the holding process. Moreover,the objective of this paper is to present a controlling methodfor minimizing the kinetic energy of movable contacts basedon purposely choosing the closing phase angle of coil voltageof AC PM contactor. Therefore, the lifespan and operatingreliability are hoped to be then obtained simultaneously.

2. Principle of Operation

2.1. Mathematical Model. As shown in Figure 2, the structureof an AC PM contactor is composed of three subsystems:electric system, magnetic energy-conversion system, andmechanical system. The magnetic energy-conversion systemincludes the basic mechanism of a conventional AC EMcontactor; in addition, an external permanent magnet is alsoarranged on armature. This permanent magnet is generallymade of Nd-Fe-B material; so that its volume is small. Toreduce energy loss, all iron cores in the magnetic circuit aremade of the ferromagnetic material. Figure 2 depicts that theAC PM contactor is commanded by an electronic controlunit (ECU). For a satisfactory ECU controlled actuator, twosets of exciting coils, such as closing coil N1 and openingcoil N2 are together equipped with the stationary E-type iron

core. The closing coil is driven during the making course,while the opening coil is driven during the breaking course.

During the closing process, the closing coil will beenergized by a full-wave rectified AC voltage source, theequivalent circuit as shown in Figure 3(a). The resultantmagnetic force imposed upon the armature within this pro-cess is the electromagnetic force combined with permanent-magnet force. Therefore, the transition time is generallyshorter than conventional AC EM contactor. By employingKirchhoff ’s voltage law (KVL) to the equivalent electriccircuit of AC PM contactor, the voltage equation can berepresented as shown below

u∗(t) = i1r1 + dλ1dt

=∣∣∣

√2Urms sin(ωt)

∣∣∣, (1)

where

u∗(t): full-wave rectified AC sinusoidal voltage source andits frequency is twice the original applied AC sinu-soidal voltage source u(t);

Urms: root-mean-square value of the applied AC voltagesource;

r1: resistance of the closing coil;

i1: current flows through the closing coil;

λ1: flux linkage produced on the closing coil, it can berepresented as λ1 = L1(x)i1.

Active and Passive Electronic Components 3

Closing coili1

r1

L1

+

−

u∗(t)= √2Urms sin(wt)nπ ≤ wt ≤ (n + 1)πn = 0, 1, 2, · · ·

(a)

Opening coilCi2

r2

L2

+

−Vco

(b)

Figure 3: The equivalent electric circuit of AC PM contactor: (a) during the closing and holding process; (b) during the opening process.

Because the flux that flows in the magnetic circuit cannotbe changed instantaneously, it must be a constant valueduring the closing process. Substituting the representation oflinkage flux λ1 = L1(x)i1 into (1) and yields

u∗(t) = i1R′ + L1(x)di1dt

, (2)

where the generalized resistor is assumed to be defined asR′ = r1 + (vdL1)/dx. As can be seen in (2), the simplifiedvoltage equation of contactor’s electric system is merely afirst-order differential equation. If the initial coil current isset to be zero, that is i1(0) = 0, the complete response of coilcurrent in (2) can be obtained and shown as follows:

i1(t) = −Vm|Z| sin(

θ − φ)e−t/τ + Vm|Z| sin(

wt + θ − φ), (3)

where Vm =√

2Urms is the amplitude of AC sinusoidalexcitation. The first term in (3) is a transient part whilethe second term is a steady-state part. The time constant

τ is L1/R′, the impedance |Z| is√

(R′)2 + w2L21, and thepower factor angle φ is tan−1(wL1/R′), respectively. It isevident that the coil current i1(t) includes a dc offset whenthe circuit is being energized at a point of the sinusoidalwave other than at θ = φ, and this dc-offset componentdecays exponentially at a rate equal to L1/R′ time constantof the electric portion of AC PM contactor. In addition, asshown in Figure 3(b), a negative electromagnetic force willbe produced to overcome the holding force of the permanentmagnet when the opening coil is energized by a breakingvoltage across the capacitor C.

2.2. Equivalent Magnetic Circuit Analysis. The geometryand equivalent magnetic circuit of the developed AC PMcontactor is shown in Figure 4. Clearly, the consideredmagnetic mechanism of the AC PM contactor is sym-metrical. Therefore, the magnetic circuit analysis can bethen easily simplified. Compared with the conventional ACEM contactor, an additional permanent magnet should bearranged on the fixed E-type core. By applying the magnetic

circuit analysis technique, the magnetic equations of AC PMcontactor can be written below

(R1 + Rx1 +R3 +Rx3 +R4)φ3−(R3 +Rx3)φ2 =N1i1 +Fmag

−(R3 + Rx3)φ3 + (R2 + Rx2 + R3 + Rx3)φ2 = i2,(4)

where the reluctances in each part of magnetic circuit are firstcalculated respectively by using reluctance principle. Theyare expressed as follows:

R1 = l1 + l′1 + l3

u0urA1, R2 = l22u0urA2

, R3 = l22u0urA3

Rx1 = x + eu0A1

, Rx2 = x2u0A2, Rx3 = x2u0A3

, R4 = l′3

u0urA1.

(5)

The reluctance in each part of magnetic circuit is generally afunction of the average length of individual magnetic circuit.Analog to the total resistance in the electrical circuit, thetotal reluctance R(x) in the magnetic circuit can be obtainedby using the similar calculating procedures. Shortly, theequivalent inductance value L(x) across the coil can also bederived by the following formulas

L(x) = N2

R(x), (6)

where N is the number of windings of coil. The relationship

among flux φ, flux density⇀B and cross-sectional area of iron

core is given by

φ =∫⇀B ·d

⇀S=

⇀B ·

⇀S , (7)

where⇀B and

⇀S are the vector quantities whose magnitude is

B and S, respectively.

2.3. Determination of Electromagnetic Force. The electromag-netic force Fe (not magnetic force Fmag) is a function ofcoil current and armature displacement. If the armaturedisplacement is held at a constant, then the variation ofmechanical energy is equivalent to zero. The stored magnetic


l3

A2 A3

l′3A1

l1

l′1

N1

el2

x

A12

(a)

Rx3R3R4

R1

φ3

φ2

+Fmag

i2+

R2 Rx2

Rx1

N1 × i1+

(b)

Figure 4: Developed AC PM contactor, (a) sketch of the geometry and (b) equivalent magnetic circuit.

coenergy in the magnetic energy-conversion system can beexpressed as [12]

W ′c (λ, i) =∫ λ

0

ζ

L(x)dζ

= λ2

2L(x),

(8)

where ζ is the dummy variable of integration. Since therelationship between coil current and flux linkage is given byi(λ, x) = λ/L(x), the electromagnetic force is the derivativeof the stored magnetic coenergy. The electromagnetic forceis the derivative of the stored magnetic coenergy. Thus,

Fe = ∂W′c (λ, i)∂x

= ∂∂x

[∫

v

(∫ H

0

⇀B ·d

⇀H

)

dv

]

= 12i2∂L(x)∂x

.

(9)

According to [6], in fact, no matter how the permanentmagnet is arranged on armature or the fixed iron coreof magnetic circuit, the effect of the permanent-magnetforce upon armature is near to equal. The resultant forceimposed upon armature includes gravitational force, frictionforce, and magnetic force. Figure 2 shows that the normalline of installation platform is commonly parallel with thegeometrical central line of contactor mechanism and leadsto the gravitational force component that almost does notinfluence on the resultant force. Therefore, the final resultantforce can be simplified and expressed as shown below

F = Fmag − F f , (10)

where Fmag is the magnetic force which consists of elec-tromagnetic force and permanent-magnet force during theclosing and opening processes, however, it merely includes

the holding force of permanent magnet during holdingprocess. F f only represents the spring antiforce. The equationgoverning the motion of armature can be directly formulatedfrom Newton’s law of motion as shown below

Fmag − F f = md2x

dt2, (11)

where m is the mass of armature. Based on work-energytheorem in physics [7], the resultant mechanical work doneby armature can be presented as follows:

Wm = −∫ x0

xFmagdx

=∫ v

v0mvdv

= 12mv2 − 1

2mv20 = ΔEk,

(12)

where the initial velocity of armature v0 is zero since thearmature is stationary at opening position, the final kineticenergy of armature or movable contacts Ek = (mv2)/2 iscompletely determined by the final velocity of armature vbefore two contacts impact.

3. Theoretical Analysis ofClosing Contact Bounce

By Newton’s third law, the changing rate of a systemmomentum varies proportionally with the resultant forceimposed upon the system and is in the direction of thatforce. It follows that the vector change in momentum ofeither system, in any time interval, is equal in magnitudeand opposite in direction to the vector change in momentumof the other. The net change in momentum of the system istherefore zero. That is,

∑

Pf =∑

Pi, (13)


x

y

Fixed contact

Movablecontact

v1x

m1

m2

v2x

(a)

v′1x

v′2x

(b)

Figure 5: The sketch of movable contact and fixed contact (a)before collision (b) after collision.

where Pi and Pf are stand for the linear momentum ofmovable contact before and after two contacts impact,respectively. Since the linear momentum of movable contactis conservative, it is to be held a constant value before andafter two contacts impact. Currently, the contact system ofcontactor can be viewed as consisting of two parts, a movablecontact and fixed contact. The mass of movable contact is m1and its initial moving velocity is v1x.In contrast, the mass offixed contact is m2 and its initial velocity v2x is zero, that is,stationary. If the movable contact is collided with the fixedcontact along with a straight line, the final velocities of thesecontacts can be written as follows:

m1v′1x + m2v

′2x = m1v1x. (14)

Figure 5 shows the sketch of the movable contact andfixed contact before and after two contacts impact. The totalkinetic energy of contact system should be maintained at aconstant value due to the conservative principle. In otherwords, the initial total kinetic energy value of contact systemis equivalent to the one of final total kinetic energy value.Therefore, it can be represented by

12m1(

v′1x)2 +

12m2(

v′2x)2 = 1

2m1v

21x. (15)

From the expressions of linear momentum and kineticenergy indicated in (14) and (15), respectively, we cancalculate the final velocities of both movable contact andfixed contact after two contacts impact be which can givenas follows:

v′2x =2m1

m1 + m2v1x (16)

v′1x =m1 −m2m1 + m2

v1x. (17)

The fixed contact is always arranged on the fixedmechanical frame of the contactor and as a result assumingm1 � m2 is reasonable. Because the fixed contact is alwaysstationary after two contacts impact, the final velocity offixed contact depicted in (17) equals zero. In contrast, thefinal velocity of movable contact is equal in magnitude andopposite in direction of initial velocity. This means that thelinear momentum produced by movable contact will act onthe contact spring system with a linear momentum m1v′1x.Thus, the stretched and compressed actions of contact springcan be repeated for many times before attaining permanent

state, that is, contact bounce. As we known, the contactbounce mainly depends on three influencing factors, suchas the characteristic of contact spring which is not allowedto change for a existing products, the current flows throughthe contact which is also not controllable as long as it islower than rating value, and controlling the moving velocityof movable contact prior to the impact. Obviously, the lastmethod is more feasible than other approaches, and it is easyto be achieved by using controlling approach.

4. Electronic Control Unit

4.1. Control Strategy. As we know, if an AC PM contactoris operated in the closing process, the armature is notonly forced by an uncontrollable permanent-magnet force,but also forced by a controllable electromagnetic force.Therefore, the desired dynamic resultant magnetic forcevalue imposed upon armature will be derived by controllingthe one of independent variable of contactor, such as coilcurrent. However, the coil current is a function of the closingphase angle of applied AC sinusoidal voltage source. In otherwords, if we carefully select a proper closing phase angle ofAC sinusoidal voltage source, an anticipated value of coilcurrent will be obtained and leads to the desired value ofresultant magnetic force. This result can also be obtainedfrom those representations shown in (3), (9), and (11).

4.2. Implementation of Control Circuit. Figure 6 shows acomplete electronic control circuit for the control of pro-posed AC PM contactor, it is referred to as an electroniccontrol unit (ECU) here. The operation process of ECU isdetermined by the value of applied coil voltage. The ECU iscomposed of several simple digital and analog components.Therefore, the manufacturing cost of ECU is inexpensive.The ECU is also designed for controlling the closing con-tact bounce, improving robustness, and monitoring otherdynamic behaviors of AC PM contactor. The remainder ofthis section will be used to describe the operation of the ECUgradually. Each functional block shown in Figure 6 will bedescribed in a separate paragraph.

(1) Rectifier Circuit. The input portion of the ECU isequipped with a full-wave bridge rectifier operating from anAC sinusoidal voltage source u(t) as indicated in Figure 6. Itis responsible for converting the AC sinusoidal voltage sourceto a dc pulsating voltage u∗(t), as denoted in Figure 3. Therectified AC voltage source u∗(t) has the same amplitudeas u(t). However, the frequency of u∗(t) is two times u(t).A metal-oxide varistor (MOV) (it is included in ECU, butit is not drawn in Figure 6) is connected with the input offull-wave bridge rectifier in parallel to prevent a suddenlyproduced higher transient over-voltage in applied AC voltagesource from damaging the ECU.

(2) Coil Voltage and Current Detectors. Part G in Figure 6depicts that the designed coil voltage detector includes tworesistors, R19 and R21. It is connected with the full-waverectified AC voltage source in parallel. First, the sampled coil


A B

C

D

E

F

CGH

I

J

Relay

R24

R5

R1

R3

R6R7

C4

C2

C1+

C1

C5

C3

J1C2+

U51 2

2738495

1

VDDVCC

VEEGND

T1IN

R1INR2IN

T1OUT

R1OUTR2OUT

T2OUTT2IN

16

1411

10

7

138

6

6

15

912

1011

345

Q4U4

U215U1

U3

R2

C6Y1

P4

CR1

R19U7C

Q8

P5

P3

D1

K1

D2

C8Q7

U7B U7A

C9R23

R18

GND

R17

R22

R20

MOS1

MO

S2

Relay

Rel

ay

R21

+

+

+

+

+

u(t)

u (t)

21

C7R15

R13

Q2

Q3

Q32N3904

Q3

Pin36

MOS2MOS1

_computer5 V _computer5 V

_computer5 V

_computer5 V

C1−

C2−

R8

R9

R10

R11

R12

R14

R16

Q6

Q5

U6

5 V

5 V

5 V

5 V

5 V

5 V5 V

5 V

5 V

5 V

5 V5 V

5 V

V15 V

Pin26

Pin36

VB

VB

Pin26

161533

34353637383940

234567

1314

1

1231

VDDVSSVSS

MCLR/VPP

OSC2/CLKOUTOSC1/CLKIN

RA5/AN4/SSRA4/T0CKIRA3/AN3/VREF+RA2/AN2/VREF

VDD

RE2/CS/AN7RE1/WR/AN6RE0/RD/AN5

RD7/PSP7

RD5/PSP5RD4/PSP4RD3/PSP3RD2/PSP2RD1/PSP1RD0/PSP0

RC7/RX/DTRC6/TX/CK

RC4/SDI/SDARC3/SCK/SCL

RC2/CCP1RC1/T1OSI/CCP2

RC0/T1OSO/T1CKI

RC5/SDO

RD6/PSP6

PICI6F877-04/P

171823242526

1920212227282930

89

10

1132

∗

−

−

−

−

+

−

21

21

43

5

21

−RA1/AN1RA0/AN0

RB7/PGDRB6/PGCRB5

RB2RB1RB0/INT

RB4RB3/PGM

Figure 6: It shows the schematic diagram of a microcontroller-based ECU.

voltage is amplified by a unity amplifier to increase the loadimpedance, and then is sampled and fed to microcontroller.In addition, a coil current detector, which consists of aresistor R22, is connected with the coil in series. Theresistance of R22 should be as small as possible to avoidaffecting the coil current value; hence, it is designed to onlyhave 20 mΩ. The voltage across R22 is proportional to thecoil current. Therefore, the voltage across R22 is sampled andjustified by microcontroller through two amplifying stages,as the part F shown in Figure 6, the coil current value is theneasy to be calculated by using Ohm’s law.

(3) Making Signal Generator and Driver. After the voltagevalue of the dc supply is stable, the coil voltage begins tobe read and justified by microcontroller. If the sampled coilvoltage attains the desired minimum closing voltage valueof AC PM contactor, microcontroller begins producing amaking signal according to the setting of closing phase angleof AC voltage source shown in part J of Figure 6, which isa logical high signal over a period of closing time, to closethe contactor. In general, the logical making signal should befirst amplified by a voltage amplifier, as shown in the part B in

Figure 6, and then used to conduct the power MOSFET Q7.After the closing process has been completed, this makingsignal will disappear immediately.

(4) Breaking Signal Generator and Driver. Normally, theelectrolytic capacitor C8 should be charged to the amplitudeof AC voltage source before opening process starts, thatis,√

2Urms, this is also called a breaking voltage. If thecoil voltage value is lower than the maximum releasingvoltage of the AC PM contactor, microcontroller begins togenerate a logical breaking signal and amplified to drivepower MOSFET Q8 on for performing the opening process.

(5) Serial-Port Interface. To provide field and remote con-trolling capability with the ECU, there is a serial-portcommunication interface also included in the ECU, as shownin part D in Figure 6. Integrated circuit U5 is combined withits interface circuit to form a signal converter from RS-232level to logical type or vice versa. Moreover, a photo-coupleris installed between microcontroller and series port interfacefor increasing the operating safety of ECU.


u(1)/u(2)

fai/L(x)

In1

1/mv x

In1

In1

In2

Signal

Out1

Out1

Out2

Out1

Out1

Shading coil

Spring force

PM force

f(u)

f(u)

Ru

[ , voltage]

0.5

x

dL/dx

dL/dx

×

×

+

++

−

1s

+

−

1s

1s

N∗N/R(x)

t1

Figure 7: It shows the complete simulation model.

5. Simulation and ExperimentalResults and Discussions

For convenient conducting of the relevant experiments, anexperimental contactor prototype has been established inour laboratory. This contactor prototype is allowed to besupplied to a rated rms voltage 220 V of AC voltage source.The capacity contactor contact is 5.5 KW and its nominalvalue of the coil current is 24 A. The number of windings is3750 turns, the resistance across two coils’ terminals is 285Ω,and the mass of armature is 0.115 Kg. The contact’s gap is4 mm, while the air gap between the armature and fixed ironcore is about 6 mm. A permanent magnet is arranged on thecentral leg of armature.

5.1. Model Setup and Verification of Feasibility. The dynamicsimulation model of the AC PM contactor, which was imple-mented by Matlab/Simulink software, had been establishedby using the governing equivalent electrical and mechanicalequations. Figure 7 shows the completed simulation modelof AC PM model.

In theory, all the dynamic behavior of AC PM contactorcould be characterized directly by two independent variables,such as the displacement of armature and coil current.Figures 8(a) and 8(b) show all time-varying waveforms of thearmature displacement and coil current during the closing,holding and opening processes obtained by simulationmodel while was matched with those ones by contactorprototype well. Observing the simulated coil-current curveduring the closing process, as shown in Figure 8(b), a largercoil-current difference was produced between the measuredcoil current and the simulated coil current from t = 0.04seconds to t = 0.055 seconds. This was mainly causedby some small mechanical friction forces of contactor tobe ignored. When the operating state of AC PM contactor

had entered into holding process, we could see that the coilcurrent was near to zero as the applied AC voltage source wasremoved. Only a little input electrical energy will be absorbedby the ECU. This is the reason why the AC PM contactor hasan outstanding energy-saving performance than the otherelectromagnetic contactors. Figures 8(e) and 8(f) showedthe displacement of armature and coil current of AC PMcontactor during the opening process. The coil current firstproduced by a maximum negative peak value was used togenerate a sufficient electromagnetic force for overcomingthe holding force produced by permanent magnet. Shortly,the current flowing through the opening coil was thenattenuated exponentially to zero because the disengagementof contacts had been completed. To reduce the opening arcsproduced between movable contacts and fixed contacts, thetotal opening time duration of AC PM contactor should becontrolled as little as possible.

5.2. Implementation of Moving Velocity Control of Armature.As mentioned above, in addition to the fact that basicmechanism of AC PM contactor must be equipped with apermanent magnet on armature, an ECU is also needed andused to control the operation of contactor under differentoperating processes. Figures 9(a) and 9(b) show the typicaltiming sequences of AC PM contactor that is operatedin the closing process and opening processes, respectively.Figure 9(c) demonstrates an incorporated control flow chartof microcontroller. Note that these functions of microcon-troller have already been built in ECU. Figure 9(a) depictsthat microcontroller should first sample the zero crossingpoint of AC applied voltage source. A closing phase angle ofthe AC PM contactor was selected. Namely, AC PM contactorwas assumed to be triggered by pin RB1 of microcontrollerat point B and operated in the closing process. The closingperiod of the AC PM contactor was maintained by t2 time.


0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Time (s)

0

1

2

3

4

5

6

7

8×10−3

Dis

plac

emen

t(m

)

(a)

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Time (s)

−0.20

0.2

0.4

0.6

0.8

1

1.2

1.4

Coi

lcu

rren

t(A

)

(b)

0.1 0.15 0.2 0.25

Time (s)

0

1

2

3

4

5

6

7

8×10−3

Dis

plac

emen

t(m

)

(c)

0.1 0.15 0.2 0.25

Time (s)

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2C

oilc

urr

ent

(A)

(d)

0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

Time (s)

0

1

2

3

4

5

6

7

8×10−3

Dis

plac

emen

t(m

)

ExperimentSimulation

(e)

0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

Time (s)

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

Coi

lcu

rren

t(A

)

ExperimentSimulation

(f)

Figure 8: Time-varying waveforms of both armature displacement and coil current during the (a) closing process, (b) holding process, and(c) opening process.


(a)

(b)

t

t

V

V

RB1

RA1

A

B

t1

t2

t

t

t

V

V

RB2

V

RB3

RA1

SW off

t3

t4

Start

Initialize

Enable A/Dmodule

Read coil voltage and current

Read coil voltage and current

Delay

RB = 1

RB2 = 1

RB3 = 1

RB = 0 End

Yes

Yes Yes

No

No NoClosing processstarts?

Opening processstarts?

Zero cross point? t3

Delayt4

Delayt2

Delayt1

(c)

1 ms

Figure 9: For AC PM contactor (a) command sequences during the closing process (b) command sequences during the opening process,and (c) flow chart of microcontroller software.

During the opening process, the zero AC voltage sourcewas made sure, and then 1 milliseconds time delay wasset for advancing to check whether the opening processof AC PM contactor was actually produced. The pin RB2of microcontroller became logical high level and delayedfor t3 time if yes. Similarly, the high logical signal inpin RB3 of microcontroller was generated for assisting theECU to complete the opening process of AC PM contactorsafely.

During the closing process, Figure 10 showed that thosecorresponding time-varying forces imposed upon armatureunder different closing phase angles of AC voltage source.The curve showed that when the closing phase angle ofapplied AC voltage source was set to 30 degree, the resultantmagnetic force would be larger than those produced by otherclosing phase angles. The time-varying velocity of armatureof AC PM contactor shown in Figure 10(c) depicted thatmoving velocity or kinetic energy of armature before twocontacts impact was near 0.8 m/s. The total closing timeof contact at 30 degree was obviously shorter than theother cases. Moreover, as those displacement curves ofarmature shown in Figure 10(b), the closing process of AC

PM contactor would be completed within time interval0.01 ∼ 0.012 seconds. However, there is a common andimportant feature occurs after the movable contact of thefirst time touches the fixed contact, the armature would beaccelerated by various accelerations. This result representsthat the linear momentum of movable contact after twocontacts impact would be dissipated by various rates. Thiswas also the reason why the bounce duration of AC PMcontactor was commonly fewer than that of conventional ACEM contactor. As the moving velocity curves of armaturewere simulated over a period of possible closing phase angleand shown in Figure 10(d), they were often higher thanthat in AC EM contactor. These results were generated bythe resultant electromagnetic force. It was produced by theaddition of original electromagnetic force and holding forceof permanent magnet. In addition, the moving velocitycurves of armature also showed that they were a periodicfunction of the closing phase angle of AC voltage source.The AC PM contactor revealed that the period was 180degree. The moving velocity curve produced at closing phaseangle equals 55 degree would lead to a minimum kineticenergy (Ek = (mv2)/2) for AC PM contactor. In contrast,


0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2×10−2

Time (s)

0

5

10

15

20

25

30

35

40

45

50

EM

forc

e(N

)

0 deg30 deg60 deg

90 deg120 deg150 deg

(a)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2×10−2

Time (s)

0

1

2

3

4

5

6

7×10−3

Dis

plac

emen

t(m

)

0 deg30 deg60 deg


(b)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2×10−2

Time (s)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Vel

ocit

y(m

/s)

0 deg30 deg60 deg


(c)

0 20 40 60 80 100 120 140 160 180

Initial phase angle (deg)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Vel

ocit

y(m

/s)

AC PM contactorAC EM contactor

(d)

Figure 10: Time-varying curves of (a) magnetic force, (b) armature displacement, (c) armature velocity, and (d) the angle-varying curve ofmoving velocity.

an optimal closing phase angle of conventional AC EMcontactor also existed at near 0 degree. Of course, thisspecial closing phase angle of applied AC voltage sourcewould also result in minimizing the kinetic energy ofarmature of AC EM contactor during the closing process aswell.

5.3. Assessment of Bouncing Reduction. The designed testingrig had been established and is shown in Figure 11(a). Theeffects of the proposed bounce reduction technique upon theAC PM contactor were carried out on the testing rig by aseries of experiments. One of the three pairs of contact was

connected with a circuit including a dc voltage source E anda fixed resistor Rt, if the voltage Vt across the measuringresistor was set to E the contacts close together; otherwise,the voltage Vt across the measuring resistor would be setto zero voltage. There were three types of voltage source:85%, 100%, and 110% of rated voltage source. They actedas the typical testing voltages of the AC PM contactor in thetesting rig, respectively. Aiming at AC PM contactor and ACEM contactor, ten times of closing sequence were conductedand recorded under each of the three testing voltage. Foreach testing condition, the arithmetic mean of the bouncingtimes of contact was calculated and is shown in Table 1. Some


Fixed contact

Movable contactContact bridge

Link

ECU

Digitalscope

E

AC source

Vt Rt

+

+

−

−

(a)

0 20 40 60 80 100 120 140 160 180

Initial phase angle (deg)

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

Tim

e(m

s)

MinAvgMax

(b)

Figure 11: It shows (a) a testing rig for measuring the bouncing duration of contact after two contacts impact (b) measured results.

important conclusions are made based on the above testingresults.

(1) Comparing bouncing duration of contact of AC PMcontactor with that of AC EM contactor, we can seethat AC PM contactor is better.

(2) For any type of contactor, the bouncing durationwhen a higher value of voltage source was appliedwould be longer than that of when a lower voltagevalue of voltage source was applied.

(3) The difference of bounce reduction percentagebetween AC EM contactor and AC PM contactor wasnear 38%.

(4) If both AC PM contactor and AC EM contactorwere assumed to apply same value of AC voltagesource, generally, the bounce-reduction performanceobtained by former case was often superior to lattercase.

(5) Angle-varying maximum, average, and minimumbounce-duration curves obtained by each testingvalue of the AC voltage source were shown inFigure 11(b). The average bounce-duration curveclearly indicated that a minimum moving veloc-ity of armature would be occurred at near 40degree. Therefore, these experimental results shownin Figure 11(b) are in agreement well with thosesimulation results shown in Figure 10(d).

5.4. Comparison of Energy Saving. Energy-saving character-istic offered by the AC PM contactor is one of its importantadvantages. As listed in Table 2, both AC PM contactor andAC EM contactor are assumed to be operated in the holdingprocess for one year. The total energy is dissipated by AC

Table 1: Comparisons of average bouncing duration of a pair ofcontacts after collision for both AC PM contactor and AC EMcontactor.

Applied AC voltage source Average bouncing duration (ms)

(Nominal value equals 220 V) EM contactor PM contactor

85% 1.556 0.832

100% 1.568 1.012

110% 1.620 1.088

Percentage of bounce reduction 38.19%

Table 2: Compare the energy-saving performance of AC EMcontactor with AC PM contactor.

Item EM type PM type

Applied voltage (V) 220 220

Coil current (A) 0.0791 0.0138

Volt-Ampere (VA) 17.402 3.036

Total energy (KWH) 152.44152 26.59536

Fee (NT dollars) 457.32456 79.78608

PM contactor is only 27% of that by AC EM contactor.Moreover, the number of coils equals 2000 turns, which isapproximately half of the currently needed coil windings ofAC EM contactor.

6. Conclusions

An AC PM contactor with ECU controlled actuator ispresented and features energy saving and no noise pollu-tion, and voltage-sag immunity. By arranging a permanentmagnet on armature, all operations of the AC PM contactorare automatically controlled by the ECU. There is no any


operating change for those people who are used to theconventional AC EM contactor. But several key problemsgenerally produced by conventional AC EM contactor arethen overcome. Based on selecting an optimal closing phaseangle of the applied AC voltage source, movable contactof contactor engages with its fixed contact by a minimumkinetic energy. The bouncing duration and energy-savingperformance of the proposed AC PM contactor have beenvalidated through some simulation and experimental tests.The bounce duration after two contacts collision duringthe closing process is then reduced significantly. The energydissipation is saved very obviously. In addition, the lifespanof contactor contacts is prolonged and their operatingreliability is improved as well.

Acknowledgment

This work was supported by the National Science Council(Taiwan) under Grant NSC 97-2622-E-270-002-CC3.

References

[1] X. A. Morera and A. G. Espinosa, “Modeling of contactbounce of ac contactor,” in Proceedings of the 5th InternationalConference on Electrical Machines and Systems, vol. 1, pp. 174–177, Shengyang, China, August 2001.

[2] T. S. Davies, H. Nouri, and F. W. Britton, “Towards thecontrol of contact bounce,” IEEE Transactions on ComponentsPackaging and Manufacturing Technology Part A, vol. 19, no. 3,pp. 353–359, 1996.

[3] J. H. Kiely, H. Nouri, F. Kalvelage, and T. S. Davies, “Develop-ment of an application specific integrated circuit for reductionof contact bounce in three phase contactors,” in Proceedings ofthe 46th IEEE Holm Conference on Electrical Contacts, pp. 120–129, September 2000.

[4] M. Rong, J. Lou, Y. Liu, and J. Li, “Static and dynamic analysisfor contactor with a new type of permanent magnet actuator,”IEICE Transactions on Electronics, vol. E89-C, no. 8, pp. 1210–1216, 2006.

[5] S. Fang and H. Lin, “Magnetic field analysis and control circuitdesign of permanent magnet actuator for AC contactor,” inProceedings of the 8th International Conference on ElectricalMachines and Systems (ICEMS ’05), vol. 1, pp. 280–283, 2005.

[6] S. H. Fang, H. Y. Lin, C. F. Yang, X. P. Liu, and J. A. Guo, “Com-parison evaluation for permanent magnet arrangements of ACpermanent magnet contactor,” in Proceeding of InternationalConference on Electrical Machines and Systems (ICEMS ’07),pp. 939–942, Seoul, Korea, October 2007.

[7] D. Holliday and R. Resnick, Fundamental of Physics, JohnWiley & Sons, Taiwan.

[8] W. Li, J. Lu, H. Guo, W. Li, and X. Su, “AC contactor makingspeed measuring and theoretical analysis,” in Proceedings of the50th IEEE Holm Conference on Electrical Contacts and the 22ndInternational Conference on Electrical Contacts, pp. 403–407,2004.

[9] X. Zhou, L. Zou, and E. Hetzmannseder, “Asynchronousmodular contactor for intelligent motor control applications,”in Proceedings of the 51st IEEE Holm Conference on ElectricalContacts, pp. 55–61, September 2005.

[10] X. Su, J. Lu, B. Gao, G. Liu, and W. Li, “Determination ofthe best closing phase angle for AC contactor based on game

theory,” in Proceedings of the 52nd IEEE Holm Conference onElectrical Contacts, pp. 188–192, Montreal, Canada, July 2006.

[11] Z. Xu and P. Zhang, “Intelligent control technology of ACcontactor,” in Proceedings of the IEEE Power Engineering SocietyTransmission and Distribution Conference, pp. 1–5, April 2005.

[12] A. E. Fitzgerald, C. Kingsley Jr., and S. D. Umans, ElectricMachine, McGraw-Hill, Taiwan, 1983.

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