International Journal of Scientific & Engineering Research Volume 4, Issue 1, January-2013 1

ISSN 2229-5518

PWM Soft Switched DC–DC Converter with

Coupled Inductor

R.Kavin, B.Jayamanikandan, R.Rameshkumar, S.Sudarsan

Abstract- In this paper, pulse width modulation soft switched DC-DC converter without high voltage & current stress is described. This converter does not require any extra switch to achieve soft switching, which considerably simplifies the control circuit. In this proposed converter, the switch is turned on under zero-current and is turned-off at almost zero-voltage condition. In this converter , it is desirable to control the output voltage by pulse width modulation because of its simplicity and constant frequency. The circuit is simulated using PSPICE and the output voltage is obtained as 100V for 50V input.

Index Terms—Pulse width modulation (PW M), soft single switched (SSS), zero current switching (ZCS), zero voltage switching (ZVS).

1. INTRODUCTION

——————————  ——————————

Unlike the resonant converters, soft-switched converters

usually utilize the resonance in a controlled manner. Resonance is

hen conventional PWM power converters are operated in a switched mode operation, the power switches have to cut

off the load current within the turn-on and turn-off times under the hard switching conditions. hard switching refers to the stressful switching behavior of the power electronic devices During the turn-on and turn-off processes, the power device has to withstand high voltage and current simultaneously, resulting in high switching losses and stress. Dissipative passive snubber

allowed to occur just before and during the turn-on and turn-off processes so as to create ZVS and ZCS conditions. Other than that, they behave just like conventional PWM converters. Quasi resonant converters do not have any extra switch to provide soft switching conditions however they must be controlled by the

are usually added to the power circuits so that the dv

& di of

variation of switching frequency [1]. zero voltage transition, zero

the power devices could be reduced, and the switching loss and stress be diverted to the passive snubber circuits. However, the switching loss is proportional to the switching frequency, thus limiting the maximum switching frequency of the power converters. The stray inductive and capacitive components in the power circuits and power devices still cause considerable transient effects, which in turn give rise to electromagnetic interference problems. These soft-switched converters have switching waveforms similar to those of conventional PWM converters except that the rising and falling edges of the waveforms are ‘smoothed’ with no transient spikes as shown in Fig 1.

Fig. 1. Rising & falling edges of soft switched converters.

current transition, and active clamped converters are PWM

controlled but require at least two switches, which increases the complexity of power and control circuits[2]-[9].

PWM soft single switched converters usually have large no of passive elements, which makes the converter implementation difficult [10]-[14], [16]. The lossless passive snubber circuit introduced in [15] is simple and easy to implement. However, in this converter, a soft switching condition is not achieved for the switch turnoff instant. Furthermore in [16], an additional diode is added in main power path, which would further increase the conduction losses.

In this paper, PWM SSS converters without any substantial increase in voltage and current stresses is presented Furthermore, in this converter, the number of additional components is not high. The switch in converter is turned on under zero current switching and is turned off at almost zero voltage switching condition. The converter main diode turns on under ZVS condition and turns off under zero voltage zero current switching condition. Furthermore, an auxiliary diode turns on under ZVS condition.

With simple modifications, many customized control integrated control circuits designed for conventional converters can be employed for soft-switched converters. Because the switching loss and stress have been reduced, soft-switched converter can be operated at the very high frequency (typically 500 kHz to a few Mega-Hertz). Soft-switching converters also provide an effective

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solution to suppress EMI and have been applied to dc-dc, ac-dc and dc-ac converters.

(4)
This mode ends when the Cr voltage reaches zero. The duration of this mode, change in time (∆t2)

2. CIRCUIT DESCRIPTION AND OPERATION

Fig 2 PW M boost converter

The circuit configuration of PWM soft switched DC- DC converter with coupled inductors is shown in figure 2.1 the circuit components including Lr1, Lr2, D1 & Cr are added to the conventional boost converter. It is assumed that Lf & Cf are large enough so that they can be replaced by a current source(Iin) and a voltage source(V0).

Mode 1 [t0−t1]: At to switch is turned on under ZCS condition due to series inductor Lr1.

The inductor current is represented as Ilr1(t)

(1) At t1, Ilr1 reaches Iin therefore, the duration of this mode is Change in time is represented as(∆t1)

(2)

Fig 3 Mode 1 Operation

Mode 2 [t1−t2]: At t1, the Lr1 current has reached Iin, and the diode Do current has reached zero. Thus, the diode Do turnoff is under ZCS. Lr1 starts to resonate withCr. The resonant capacitor voltage

(5)

Fig 4 Mode 2 Operation

Mode 3 [t2−t3]: When Vcr reaches zero, diode D1 starts to conduct under ZVS condition. This mode ends when the switch is turned

off. The duration of this mode, the change in time is represented as (∆t3)

(6) Where D is switch duty cycle & Ts is switching period.

Fig 5 Mode3 Operation

Mode 4 [t3−t4]:By turning switch off, the ampere turn of Lr1 is transferred to Lr2 now Lr2 ampere turn is sum of its previous ampere turn plus the Lr1ampereturn.

(7) At t4, Vcr reaches Vo, the maximum voltage across the switch
(8)

The resonant inductor current is mentioned as
(3)

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Fig 6 Mode 4 Operation

Mode 5 [t4−t5]:This mode begins when the Cr voltage reaches Vo & the diode Do turns on under ZVS condition. At the beginning of this mode, Lr2 current is represented as Ilr2(t)

3. SIMULATION CIRCUIT& RESULTS

1 2

180uH

MUR460

1 2

(9) At t5,theLr2 current reaches zero, and the Diode D1 turns off
under ZCS. The change in time

10uH

90uH

10n

100u R1

(10)

V1 = 0

V2 = 20

TD = 0

TR = 1n TF = 1n PW = 5u

PER = 10u

IRF840

MUR460

Fig 9 Simulation Circuit

The design of the simulation circuit involves the selection of Cr, Lr1, and n. Cr provides the ZVS condition for the switch turnoff instant.

Fig 7 Mode 5 Operation

Mode 6 [t5−t6]: In this mode Iin freewheels through the diode Do, & the current through inductors remains zero. Voltage across the capacitor stays at Vo. The duration of this mode, the change in time is represented as (∆t6)

(12)
where tf is the switch current fall time, Isw is the switch current before turnoff, and Vsw is the switch voltage after turnoff.

Cr is considered much larger than Cr,min to guarantee soft switching. Lr1 provides ZCS condition for the switch turnon instant.

(11)

Fig 8 Mode 6 Operation

(13)

where tr is the switch current rise time. Lr1 is considered much larger than Lr,min to guarantee soft switching. As n increases, the switch voltage stress in fourth mode and freewheeling current in third mode decrease. However, this will result in a higher voltage stress of diode D1 and limits the maximum duty cycle of the converter. Thus, soft switching condition at very light load current can be omitted, and a large value for n can be selected.
The additional current and voltage stresses of a switch can be reduced to a small amount, by choosing large values of Zr and n. However, large values of Zr and n limit the converter maximum duty cycle and soft switching. The designed values for Lr1, Cr1, and n are 18uH, 10nF and 3, respectively. Furthermore, the Lf and Cf values are 180uH and 100uF, respectively. IRF840 is selected for the converter switch, and MUR460 is chosen for diodes Do and D1. The PWM boost converter is simulated at 50v input voltage and 100v output voltage.
The converter operates at 100 kHz and an output power
of 120W.

3.1 Voltage waveform across load

100V

80V

60V

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4. CONCLUSION

Fig 10 Voltage waveform across load

Output voltage across load was obtained as 100V for a dc input of
50V.

3.2 Voltage & Current Waveform across main switch

In this paper, a new PWM SSS boost converter without high voltage and current stresses has been described. This converter does not require any extra switch to achieve soft switching, which considerably simplifies the control circuit. In this prototype a input voltage of about 50 V is given in which the output observed in the load side was about 100V. Different types of loads can be used for this analysis in which the inductive loads give a perfect response for the output. The output ripples gets reduced thus pertaining a perfect output waveforms.

REFERENCES

3.3A

2.0A

0A SEL>>

200

-200

ID(M1)

4.44000ms 4.44500ms 4.45000ms 4.45500ms 4.46000ms 4.46500ms 4.46933ms

V(L1:2,0) ID(M1)

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Fig 11 Voltage & current waveform across main switch.

Main switch is turned on under ZCS condition due to series inductor Lr1 and turned off at almost ZVS. When voltage across main switch starts to fall from 100V to 0V at the same time switch current starts to rise from 0A to 3A.

3.3 Voltage & Current Waveform across Main Diode

5.0A

2.5A

0A SEL>>

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4.365ms 4.370ms 4.375ms 4.380ms 4.385ms 4.390ms 4.393ms

V(D1:2,L3:2)

Time

Figure3.4 Voltage & current waveform across main diode
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and two derived structures,” IEEE Trans. Power Electron., vol. 19, no.

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AUTHOR PROFILE:

R.Kavin was born in Erode on May 7, 1986. He is graduated in 2007 from K.S.R. College of Technology, Tiruchengode and post graduated in 2010 at Sri Venkateswara College of Engineering, Chennai. He is currently working as Assistant professor in the department of EEE at Excel College of Engineering and Technology, komarapalayam. His research interest

involves in Power electronics, Control systems. Email ID:

kavin882@gmail.com

B.Jayamanikandan was born in Erode on April 3,

1986. He is graduated in 2007 from Sri Ramakrishna

Institute of Technology, Coimbatore and post graduated in 2012 at Anna University of technology, Coimbatore. He is currently working as Assistant professor in the department of EEE at Excel College of Engineering and Technology, komarapalayam from

June 2012. His research interest involves in converters, Renewable energy power generation. He has published more than 3 papers in international journals. Email ID: naresh03@gmail.com

R.Rameshkumar was born in the year of 1984, at Salem. He is graduated in 2006 from P.B College of Engineering, Chennai. Currently he is Pursuing his M.E (PED) in Excel College of Engineering & Technology at komarapalayam.

S.Sudarsan was born in karur on November 21, 1985. He is graduated in 2009 from Anna University chennai. He also received M.E degree in Power Electronics and drives during 2012 from Anna University, Chennai. He is currently working as an Assistant professor at V.S.B Engineering College, Karur. His area of interest involves in Power

Electronics, BLDC Drives, inverter, Renewable energy power generation.