 Open Access
 Total Downloads : 489
 Authors : Meera Khalid, Sreeraj T S
 Paper ID : IJERTV3IS070538
 Volume & Issue : Volume 03, Issue 07 (July 2014)
 Published (First Online): 15072014
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Design And Implementation of a Battery Charger With Soft Switching Technique
Sreeraj T S

Tech Research Scholar Electrical and Electronics engineering
Govt. Engineering College,Idukki
Ms Meera khalid Assistant Professor
Dept.of Electrical and Engineering and Technology
Govt. Engineering College, Idukki
AbstractA new soft switching technique with zero current switching is developed for a battery charger circuit with buck converter.The proposed new circuit is obtained by placing an auxillary circuit in series with the resonant capacitor which significantly decrease the switching losses in the power switches.the new battery charger with a buck converter has many advantages like simple structure,simple control,low cost,light weight,high efficiency etc.The operating principle and the design aspects of the charger circuit are analysed.The required values of the resonant inductance nad resonant capacitance are calculated from the characteristic curve and functions derived from the required circuit.A charger circuit is designed for a 3.7V 1020mAh lithium ion battery and the simulation is done in matlab.
Index TermsBuck converter,Zero current Switching,soft switching,battery charger.

INTRODUCTION
Rechargeable batteries are widely used in our day to day life which include mobile phones,laptops,cameras,digital clock,UPS etc.The batteries used in these devices require a charging circuit.The life and the charging process of the battery depends on the type of the charging circuit.Linear power regulators which are used in the conventional charging schemes can handle only low power levels and moreover they have a low efficiency and low power density.The recent trend is the development of pulse width modulation (PWM) in the dcdc converter for the charging process where semiconductor power switches are used.The switches in this mode operates in a switch mode where a whole of the load current is turned on and off during each switching session.The switch mode operation results in high switching losses and stress.The efficiency of the switch mode system lies in the incrementation of the frequency but this adversely affects the switching loss and the magnetic interference.To remove the above mentioned shortcomings soft switching technique is used.Zero voltage switching (ZVS) and zero current switching (ZCS) are the commonly used methods.The above mentioned techniques results in either zero voltage or zero current across the switch.ZCS eliminates the turn on losses and decrease turn off losses by slowing down the increase in voltage resulting in lowering of the overlap between the voltage and current.But it is required to have a large resonant capacitor for efficient lowering of the switching loss.In ZCS the switch current is forced to zero
before the switch voltage rise.For high efficiency applications the ZCS are generally used.
The converters are required to have a high operating frequency so as to reduce the size of the passive components and also to achieve high power density.The traditional ZCS converter operates with constant on time control and it need to operate in a large switching range,making filter design perfect.The primary feature of the proposed ZCS PWM converter is the addition of an auxillary switch in the traditional circuit.The resonance condition of the new converter is powered by the the auxillary switch which makes the resoance condition and temporarly stops for time that can be controlled there by removing the weakness of fixed conduction or cut off time in a normal quasiresonant converter.
A new high efficiency battery charger with ZCS buck converter is analysed and designed which has a simple structure,low switching losses and high efficiency.
Following the introduction the circuit configuration is discussed in section II,section III describes the operating principle,normalized voltage gain is discussed in IV,design and simulation is discussed in section V and conclusion in VI.

CIRCUIT CONFIGURATION

Resonant converters are used for the soft switching implementation in the charger circuit due to their simple operation and low switching losses.Fig.1 shows the circuit of a ZCS converter which has an extra resonant tank circuit consist of resonant inductor Lr,resonant capacitor Cr and diode Dm.This additional LC tank circuit is placed in the converter to make a zero current situation for the swithc to turn off.The inductor Lr is used to limit the di/dt of the switch and is connected in series to the power switch S.The capacitor Cr is placed as an auxillary energy transfer element.Dm is the freewheeling diode.Inductor Lf and capacitor Cf are used as a low pass filter circuit which filter high frequency ripple signal and provides a stable source for charging.Diode Df prevents the flow of energy from battery to the circuit.The elements Lr and Cr represents a series resoanant circuit where the oscillations are started by the turning off of the diode Dm.Here the soft switching technique is implemented in both the switch and the diode.
Fig.1 Battery charger circuit using ZCS converter
In the ZCS resoannt converter,when the switch S is turned on the inductor starts to oscillate with the capacitor in resonance condition.The resonance inductor makes the current to zero there by making the main switch turned off with ZCS condition.The turn on time of the main switch is decided by the resonant time of the resonant inductor and resonant capacitor.It operates in fixed on time control and the output is asjusted by changing the off time of the switch.the control produces harmonics at unpredictable frequencies and this makes the design of filter difficult.
To mitigate the aforesaid porblems a new ZCS converter is being proposed.Here an auxillary switch is inserted in series with the resonant capacitor.The main and the auxillary switch can be operated in synchrony with out any isolation devices as shown in Fig.2
Fig.2 Battery charger circuit using proposed ZCS converter
III OPERATING PRINCIPLE
For analysis purpose the output inductor is assumed to be a large to be considered as a current source Io .The circuit parameters are defined below
1)Resonant inductor Lr 2)resonant capacitor Cr

characteristic impedance Zo= (Lr/Cr)1/2

resonant angular frequency wo=1/(LrCr)1/2 5)switching period Ts
6)resonant frequency fr=wo/2 7)switching frequency fs
Some of the assumptions made for the analysis are, 1)semiconductor used are ideal
2)no forward voltage drop during turn on 3)no leakage current during turn off

no resistance for the resonant inductor and capacitor

filter inductance Lo and filter capacitance Co are larger than the resonant inductor Lr and resonant capacitor Cr
Fig.3 Waveform of the proposed charger
Fig.4 shows the equivalent circuit of the proposed converter
The total operating modes of the converter are divided into six modes in one switching cycle.The operating principle are discussed below
Mode I
Mode II
Mode III
Mode VI
Fig.5 Circuit representation of the converter for various operating modes. (a) Mode I. (b) Mode II. (c) Mode III. (d) Mode IV. (e) Mode V. (f) Mode VI
Mode I (tott1):The main switch Sm and auxillary switch Sa are in off condition and the diode Dm is in on condition.Current through Dm is equal to the charging current Io.Gate signal is applied to the main switch during the starting of this mode.The inductor current iLr rises linarly during this mode.Current thrugh Dm is the difference between ilr and Io.This mode ends when Dm turns off.The governing equations are
vDS(t)=0 (1)
Vs=vLr
=L
r
(2)
iL (t)= (tto) (3)
r
vCr(t)=0 vDm(t)=0
i (t)=I – (tt )
(4)
(5)
Dm 0 o
(6)
Mode IV
vDm(t)=0 iSa(t)=0
t1 is the time interval between t1 and t2
(7)
(8)
t1=t1t0=
0
(9)
Mode II (t1tt2):In this mode the diode Dm becomes reverse biased and turned off.The main switch remains on and iLr=I0 at t=t1. iLrI0 current passes from Dm to Da,the body diode of the auxillary switch Sa.The current pass through resonant capacitor Cr which makes a resonant conditon with the resonant inductor Lr.The circuit parameters are given below.
vDS(t)=0
i (t)= (tt )
(10)
Mode V
Sa 0 0 1
(11)
i (t)=I + (tt )
v (t)= 0 +v
(t)
Lr 0
0 0 1
(12)
Cr
4 Cr
(25)
V (t)= 1 ( t )d
v (t)= 0 + V 1 + cos
(
) (26)
cr
1 0 0 1
Cr 4
0 4 3
=Vs 1 cos 0 ( 1)
(13)
vCr(t)= vDm(t) (26)
i (t)= – (tt ) (27)
V (t)=Vs 1 cos ( )
Sa 0 0 4
dm 0 1
t =t t = 1 + cos (
)
(14)
Maximum resonant inductor current iLr(t) occurs at t'max
5 5 4
0
0 4 3
(28)
Peak capacitor voltage occurs at t=t2
Wo(t2t1)=
When iLr(t)=I0 peak capacitor voltage is 2Vs The operating time in this mode is given by
t =t t =
Mode VI (t5tt0+Ts):At the time t=t5,the charging current is commutated from the resonant capacitor to the diode Dm with soft switching.The auxillary switch is turned off with soft switching technique.This mode is the off state of the
converter and the duration can be controlled by the gate
2 2 1
0
(15)
signal of the main switch.
V
(t)=V
The interval ends when current through diode Da is reduced to zero.
ds s
(29)
I (t)=I
Mode III (t2tt3):Main switch is in on condition and load current Io flows through Sm and the voltage across Cr is
Dm 0
The time interval is given by
(30)
clamped at 2Vs.
ILr(t)=I0
(16)
t6=Ts[t5+t4+t3+t2+t1]
(31)
VCr(t)=2Vs
(17)
Vdm(t)=Vs
IV) NORMALIZED VOLTAGE GAIN
Vda(t)=Vs
(18)
(19)
The normalized voltage gain is found out by equalizing the energy supplied Ea and the energy absorbed by the battery
Time interval for this mode and mode I are assumed to be same
E0.The equation is given by
E +0
(32)
s= 0
t3=t3t2= 0
mode IV (t tt ):At the time t=t
(20)
the auxillary switch S is
The normalized voltage is obtained by equating the time interval equations (9),(15),(20),(25),(28),(31) discussed above.
=V I 10 + 2 1 + 3 2 + 4 3 + (5
3 4 3
a s 0 2
turned on with ZCS.A reverse resonance condition is generated.At the end of this mode the main switch Sm is
turned off with ZCS.The charactersitics governing equations
4) (33)
Energy absorbed by the battery over one switching cycle is,
are as follows
E = +0 =
(34)
0 0 0 0
0 0
vDS(t)=0
(21)
Equating the input and output expressions,
0 = 1 10 + 2 1 + 3 2 + 4 3 +
i (t)= (tt )
2
Sa 0 0 3
(22)
(5 4) (35)
i (t)=I – (tt )
Normalized voltage gain,
Lr 0 0 0 3
3 1
V (t)= 1 ( t )d+2V
(22)
M=fs
20
+
20
+
2 0
sin1
+ 0 1 +
cr
3
0 0 3 s
cos sin1 (36)
=V 1 + cos 0 ( 3)
Vdm(t)=Vs 1 + cos 0 ( 3)
Time interval of this mode is
(23)
(24)
Let sin1 =
The equation is simplified to
M=f = 3 + + + 1 + cos (37)
4=t t = 1
sin 00 (25)
s 2
4 3 0
Mode V (t3tt4):In this mode the main switch is in off condition and the charging current flows through the switch.The resonant capacitor is in discharging mode and this mode comes to an end when voltage vcr falls to zero at t=t5.
Normalized voltage gain 
M=0 
Normalized load 
Q= 0 0 
Charging current 
I = 0 0 0 
Normalized switching frequency 
F = ns 0 
Table.1 Performance Parameters
V) DESIGN AND SIMULATION
Fig 6. Simulink Model
For the experiment purpose a 3.7V1020mAh lithium ion battery is used.The circuit parameters of the charger circuit were fixed.
1)Input voltage Vs=12V 2)Output voltgae V0=5V 3)Switching frequency fs=18kHz 4)Time period Ts=50Âµsec 5)Output current I0=1A

Normalised switching frequency fns=0.3

Equvalent output impedance R = 0=5
0 0

Characteristics impedance Z = 0=5
0
Fig.8 Trigger signal VG and control signal VGa

Normalized voltage gain M=0=0.42

Resonant frequency f = =60kHz
0

Resonant inductor L = 0 =13.269H
r 0

Resonant capacitor C = 1 =0.53F
r 0 0

Filter inductor L0=100Lr=1.326mH 14)Filter capacitor C0=100Cr=53.1F
The time intervals for various modes were calculated based on the circuit parameters
1)t = 0=1.10575sec
1
2) t = =8.33sec
2 0
3) t = 0=1.10575sec
3
Fig.9 Main switch current and voltage
4
4) = 1
0
sin 00 =1.1396sec
5) t = 1 + cos
(
) =12.719sec
5 0
0 4 3
6) t6=Ts[t5+t4+t3+t2+t1]=25.6sec
Duty cycle of the switches 1)For main switch
D= =0.233
2)For auxillary switch
D =4+5=0.277
a
Fig.10 Freewheeling diode voltage VDm and auxillary switch voltage VDa
Fig.11 Voltage and current waveform of ausillary switch
Fig.12 Freewheeling diode Dm current and voltage waveform

CONCLUSION
This paper deals with a new zero current buck dcdc converter having an auxillary resonating circuit for the battery charger.This is much simpler and cheaper than other circuits having a large number of componentsThe operating principle and analysis for a mobile phone battery is been analysed .

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