**Volume 4, Issue 1, 2017 **

103
*Available online at www.ijiere.com*

**International Journal of Innovative and Emerging **

**Research in Engineering **

### e-ISSN: 2394 - 3343 p-ISSN: 2394 - 5494

** Analysis of ZVS DC-DC Converter with Voltage Multiplier **

**Circuit for High Voltage Gain **

### Mrs.B.Kiruthiga

1_{, Dr.R.NarmathaBanu}

2
1_{Assistant Professor, Department of EEE , Velammal College of Engineering and Technology, Madurai. }
2 _{Professor, Department of EEE, Velammal College of Engineering and Technology, Madurai. }

**ABSTRACT: **

**This paper presents the simulation and analysis of zero voltage switching (ZVS) dc-dc converters with voltage **
**multiplier circuit for achieving high voltage gain with continuous input current. Also, the proposed converter **
**is able to provide high power density and efficiency. The reverse recovery problem of diode is also alleviated **
**with the use of the leakage inductance. Complete design equations are specified and discussed for the **
**proposed converter. To enhance voltage gain, voltage multiplier circuit i.e., voltage doubler circuit is **
**incorporated. The circuit is simulated using versatile PSIM software and the results are discussed. **
**Performance of the proposed converter with voltage doubler circuit is simulated with the design parameters **
**at 108 kHz switching frequency. **

**Keywords: Boost converter, zero voltage switching, coupled inductor, reverse recovery, high voltage gain, **
**voltage doubler. **

**I. INTRODUCTION **

DC-DC converters are used whenever DC electrical power is to be changed from one voltage level to another. They can be step up or down using a transformer. Mostly these are power electronic converters that can operate with semiconductor switches like MOSFETs and IGBTs. These switches are required to turn on and off periodically and they provide a regulated and isolated with wide output voltage for various applications. A Dc-Dc converter with a high voltage gain is used for many applications, such as lamp ballasts for automobile headlamps, fuel-cell energy conversion systems, solar-cell energy conversion systems, and battery backup systems for uninterruptible power supplies [1]-[6]. In dc–dc converters with high voltage gain, there are several requirements such as high voltage gain [2]-[6], low reverse-recovery loss [7], [8], soft switching characteristic [16], low-voltage stress across the switches, electrical isolation, continuous input current, and high efficiency [9], [10]. In order to meet these requirements, various topologies are introduced.

In [11], a step-up converter based on a charge pump and coupled inductor is suggested. Also the circuit is together with a passive voltage clamping circuit. Here the primary inductor is magnetized under double the input voltage, thereby causing the input current to be reduced and hence the efficiency to be improved at light load. Its voltage gain is around 10 but its efficiency is not high enough due to the switching loss.

In [12], a high step-up converter with coupled inductors is suggested to provide high voltage gain and a continuous input current. However, its operating frequency is limited due to the hard commutation of switches. The converters suggested in [13]–[15] have a similar drawback. Their switching frequencies are limited due to the hard-switching operation. Because hard-switching loss in hard hard-switching is proportional to hard-switching frequency.

In order to increase the efficiency and power density, soft switching technique is required in dc–dc converters. In [17], zero voltage and zero current switching full-bridge converters with secondary resonance is proposed. Here the leakage inductance of the transformer is utilized as the resonant inductor. The efficiency at full load is high. But the Operations with wide range of load and duty cycle can’t be performed.

In [18], ZVT-ZCT-PWM boost converter equipped with the snubber cell is proposed. Snubber cell is developed in order to increase the power density and the efficiency in Pulse Width Modulation (PWM) converters. High efficiency, high power density, quick transition response, ease of control, reduces the EMI noise. But the reverse recovery problem of diode is not alleviated. In [16]–[18], various soft-switching techniques are suggested.

**Volume 4, Issue 1, 2017 **

104 reverse-recovery problem of the output diodes is significantly alleviated due to the leakage inductance of the transformer. Therefore, the proposed converter provides high power density and high efficiency. Also, the voltages across the switches are clamped as the dc-link voltage. The circuit of the proposed converter has been implemented with design values and simulated with switching frequency of 108 KHz.

**II. SWITCHED MODE POWER SUPPLY **

Power supply is a broad term but this chapter is restricted to discussion of circuits that generate a fixed or controllable magnitude dc voltage from the available form of input voltage. Integrated-circuit (IC) chips used in the electronic circuits need standard dc voltage of fixed magnitude. Many of these circuits need well regulated dc supply for their proper operation. In majority of the cases the required voltages are of magnitudes varying between -18 to +18 volts. Some equipment may need multiple output power supplies.For example, in a Personal Computer one may need 3.3 volt, ±5 volt and ±12 volt power supplies. The digital ICs may need 3.3volt supply and the hard disk drive or the floppy driver may need ±5 and ±12 volts supplies [22]. The individual output voltages from the multiple output power supply may have different current ratings and different voltage regulation requirements. There are two broad categories of power supplies: Linear regulated power supply and switched mode power supply (SMPS).

The switched mode power supply converts the available unregulated ac or dc input voltage to a regulated dc output voltage. However in case of SMPS with input supply drawn from the ac mains, the input voltage is first rectified and filtered using a capacitor at the rectifier output. The unregulated dc voltage across the capacitor is then fed to a high frequency dc to dc converter. Most of the dc to dc converters used in SMPS circuits have an intermediate high frequency ac conversion stage to facilitate the use of a high frequency transformer for voltage scaling and isolation. The high frequency transformer used in a SMPS circuit is much smaller in size and weight compared to the low frequency transformer of the linear power supply circuit.

The ‘Switched Mode Power Supply’ owes its name to the dc to dc switching converter for conversion from unregulated dc input voltage to regulated dc output voltage. The switch employed is turned ‘ON’ and ‘OFF’ (referred as switching) at a high frequency. During ‘ON’ mode the switch is in saturation mode with negligible voltage drop across the collector and emitter terminals of the switch where as in ‘OFF’ mode the switch is in cut-off mode with negligible current through the collector and emitter terminals. On the contrary the voltage-regulating switch, in a linear regulator circuit, always remains in the active region.

Switched mode power supplies can be classified according to the circuit topology. The most important distinction is between isolated converters and non-isolated ones. The isolated converter of SMPS such as buck converter, boost converter, buck boost converter, cuk converter, etc… The non isolated converter such as flyback converter, forward converter, push pulls converter, etc… the flyback type of converter is used in the proposed converter.

**III. VOLTAGE DOUBLER CIRCUIT **

A Voltage Multiplier Circuit is a special type of rectifier circuit which produces a DC output voltage which is many times greater than its AC input voltage. Although it is usual to use a transformer to increase the voltage, sometimes a suitable step-up transformer or a specially insulated transformer required for high voltage applications may not be available. One alternative approach is to use a voltage multiplier circuit.

Voltage multiplier circuits are constructed from series combinations of rectifier diodes and capacitors that give a DC output equal to some multiple of the peak voltage value of the AC input voltage. By adding a second diode and capacitor to the output of the simple half-wave rectifier, we can increase its output voltage.

Voltage multipliers may be classified as voltage doublers, triplers, quadruplers, etc. The classification depends on the ratio of the output voltage to the input voltage. here the voltage doubler rectifier is used. the voltage doubler rectifier doubles the given input voltage. in other words, double the peak voltage value because the diodes and the capacitors function together to effectively double the voltage. The Voltage Doubler circuit shown in Fig. 1. consists of only two diodes, two capacitors and an oscillating input voltage.

Fig. 1 Voltage doubler circuit

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**IV. PROPOSED CONVERTER **

The Zero voltage switching DC-DC converter employing voltage doubler circuit is shown in Fig. 2. It consists of a ZVS boost converter stage and a ZVS voltage doubler converter stage. The ZVS boost converter stage provides a continuous input current and ZVS operation of the power switches. The ZVS voltage doubler converter stage provides a high voltage gain. Since single power processing stage can be a more efficient and cost-effective solution, both stages are merged and share power switches to increase the system efficiency and simplify the structure. Since both stages have the ZVS function, ZVS operation of the power switches can be obtained with wider load variation. Moreover, due to the ZVS function of the boost converter stage, the design of the half bridge converter stage can be focused on high voltage gain. Therefore, high voltage gain is easily obtained. ZVS operation of the power switches reduces the switching loss during the switching transition and improves the overall efficiency.

The ZVS boost converter stage consists of a coupled inductor Lc, the lower switch Q1, the upper switch Q2, the auxiliary diode Da, and the dc-link capacitor Cdc. The diodes DQ1 and DQ2 represent the intrinsic body diodes of Q1 and Q2. The capacitors CQ1 and CQ2 are the parasitic output capacitances of Q1 and Q2. The coupled inductor Lc is modeled as the magnetizing inductance Lm1, the leakage inductance Lk1, and the ideal transformer that has a turn ratio of 1:n1 (n1 = Ns1/Np1). The ZVS voltage doubler converter stage consists of a transformer T, the switches Q1 and Q2, the output diodes Do1 and Do2, the dc blocking capacitors CB1 and CB2, and the output capacitor Co . The transformer T is modeled as the magnetizing inductance Lm2, the leakage inductance Lk2, and the ideal transformer that has a turn ratio of 1:n2 (n2 = Ns2/Np2).

Fig. 2 Proposed zero voltage switching DC-DC converter

*A. Design methodology *

This section deals with the design aspects of transformer, coupled inductor and capacitor design.
1)* Transformer design*

For flyback converters [21], the transformer is the most important factor that determines the performance such as the efficiency, output regulation and EMI. Contrary to the normal transformer, the flyback transformer is inherently an inductor that provides energy storage, coupling and isolation for the flyback converter. In the general transformer, the current flows in both the primary and secondary winding at the same time. However, in the flyback transformer, the current flows only in the primary winding while the energy in the core is charged and in the secondary winding while the energy in the core is discharged. Usually gap is introduced between the cores to increase the energy storage capacity.

(a) Turns Ratio:

where

Vo is the output voltage Vin is the input voltage D is the duty cycle

(b) Magnetizing Inductance: o 2

in V (1 D) n

V D

2 dc m

in s RF

(V D) L

2P f K

(1)

**Volume 4, Issue 1, 2017 **

106 where

Vdc is the voltage across the dc-link capacitor Pin is the input power

fs is the switching frequency KRF is the ripple factor

(c) Leakage Inductance:

where

Io is the output current Ts is the switching period

2)* Coupled Inductor Design*

Coupled inductor is used to reduce converter volume by using one core instead of two (or more) to improve regulation of multi output converters and steer the ripple current from one winding to another [20]. Mutual inductance occurs when the change in current in one inductor induces a voltage in another nearby inductor [20]. The mutual inductance L12, is also a measure of the coupling between two inductors.

The mutual inductance also has a relationship with the coupling coefficient. The coupling coefficient is always between 1 and 0, and is a convenient way to specify the relationship between a certain orientations of inductors with arbitrary inductance:

where

k is the coupling coefficient and 0 ≤ k ≤ 1 L12 is the mutual inductance

L11 is the self inductance of the primary coil L22 is the self inductance of the secondary coil

(a) Self Inductance:

where

Lk1 is the leakage inductance of the primary side Lk2 is the leakage inductance of the secondary side N1 is the number of turns in primary side

N2 is the number of turns in secondary side

(b) Mutual Inductance:

where

Lm is the magnetizing inductance

* *

* 3) Capacitor design *

The dc-link capacitance of the circuit is determined by

The output capacitance of voltage doubler circuit is given by 2

* 2 in s k

o

(1 (1 2a) ) (n V DT ) L

8I

1

11 k1 12

2 N L L ( )L

N

2

22 k 2 12

1 N

L L ( )L

N 2 12 m 1 N L ( )L

N o dc c DI C

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107
*B. Performance analysis of proposed converter *

** **The following equation (10)-(20) is utilized for analyzing performance of the proposed converter.

(a) Voltage Gain of the Boost Converter Stage

(b) Auxiliary Diode Current

(c) DC-Blocking Capacitor Voltage

(d) Maximum Output Diode Currents

(e) Output Voltage

(f) Output Current

where

As *a* increases, voltage gain get decreases. Therefore optimum value of *a* should be considered. Here *a* is equal to
0.1.

(g) Voltage Gain

From equations (10), (16), (18) and (19), the voltage gain M of the proposed converter is in dc

### V

### V

### 1 D

###

###

1 in s da

ki

### n DV T

### I

### L

###

in cb1 DV V 1 D 2 3cb2 2 in

2 3

### [D d

### (D / (1 D))d ]

### V

### n V

### 1 D d

### d

###

###

###

###

2 in cb2 2 s

do1

k (n V V )d T I

L

2 in cb2 o 2 s do2

k

### (n V

### V

### V )(D d )T

### I

### L

###

###

###

2 3o 2 in

2 3 2 3

[D d (D / (1 D))d ]

V n V

[(D d d )(1 D d d )]

2 3 do1 o (1 D d d )I I

2

3

d a(1D)

(10) (11) (12) (13) (15) (14) (17) (16) (18) (19)

k 2 o

2 in s

8L I 1

a (1 1 )

2 n V DT

(20)

aD
d_{2}

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**V. SIMULATION RESULTS AND DISCUSSIONS **

Computer simulations, which predict the performance of the designed converter system, are carried out by utilizing the PSIM [23] computer simulation package program. PSIM is simulation software specifically designed for power electronics and motor drives. With fast simulation and friendly user interface, PSIM provides a powerful simulation environment for power electronics, analog and digital control, magnetic and motor drive system studies. The input voltage Vin is 24V and the output voltage Vo is 380 V. The switching frequency fs is 108 kHz. According to the design parameters given in Section IV, the circuit parameters can be selected. The turns ratio of transformer is n1/n2 = 1/6. The magnetizing inductance and leakage inductance of transformer are 474 μH and 170 μH respectively. The dc link capacitor Cdc is 470 μF. The self inductance L11, L22 and mutual inductance L12 are 800 μH, 235 μH and 400 μH respectively. The dc-blocking capacitors CB1 and CB2 are 6.6 μF and 2.2 μF, respectively. The aluminium electrolytic capacitor 47 μF /450 V are used as the output capacitor Co

The circuit diagram for Zero voltage switching DC-DC converter using voltage doubler circuit in PSIM is shown in Fig. 3.

Fig. 3 Simulation of ZVS DC-DC converter with high voltage gain

The simulation result of zero voltage switching DC-DC converter using voltage doubler circuit is shown in Fig. 4 - 6.

Fig. 4 Experimental waveforms for output voltage and output current

The zero voltage condition is obtained by using resonant capacitor. If the upper switch Q2 is turned OFF. Then, the capacitor CQ2 starts to be charged and the voltage VQ2 across Q2 increases toward Vdc. Simultaneously, the capacitor CQ1 is discharged and the voltage VQ1 across Q1 decreases toward zero. With an assumption that the output capacitances CQ1 and CQ2 of the switches are very small and all the inductor currents are not changed. When the voltage VQ1 across the lower switch Q1 becomes zero, then the body diode DQ1 is turned ON. Then, the gate signal for Q1 is applied. Since the current has already flown through the body diode DQ1 and the voltage vQ1 is maintained as zero before the switch Q1 is turned ON, the zero-voltage turn-ON of Q1 is achieved. Similarly the zero voltage condition is achieved for both the switches.

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Fig. 5 Experimental waveforms for Switch Q1

Fig. 6 Experimental waveforms for Switch Q2

To check the correctness of design values, simulation results have also been given. The theoretical values are calculated from the equations (10) to (20). The comparison of theoretical and simulated values of Zero voltage switching DC-DC converter using voltage doubler circuit is shown in the Table 1.

TABLE I- COMPARISON OF RESULTS

**PARAMETER ** **THEORETICAL VALUE ** **SIMULATION **

**VALUE **

Vo 378.7 V 380 V

Io 0.254 A 0.2535 A

Ida 2.285 A 2.15 A

Vcb1 61.72 V 61.2 V

Vcb2 256 V 256 V

Ido1 1.56 A 1.46 A

Ido2 0.746 A 0.68 A

Vdc 85 V 85.5 V

**Volume 4, Issue 1, 2017 **

110 From the above table, it is clear that the simulation value of the proposed converter is nearly equal to the theoretical value. The voltage gain obtained from the proposed converter is nearly equal to 16. Therefore high voltage gain is obtained. Also, the proposed converter presents a higher efficiency when compared to the non isolated boost converter with a coupled inductor [8]. The efficiency of the proposed converter is 93.3% and for the non isolated boost converter with a coupled inductor [8], it is only 92%.

**VI.CONCLUSION **

A ZVS DC–DC converter with high voltage gain has been suggested. It can achieve ZVS turn-ON of two power switches while maintaining continuous conduction mode. Also the reverse-recovery problem of the diode is alleviated with the use of the leakage inductance. Near equal values are obtained with simulation when compared with theoretical values and the proposed converter is providing enhanced voltage gain. Based on the output power rating obtained through simulation, it is expected that, the proposed converter may also provide high power density.

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[13]C. T. Pan and C. M. Lai, “A high-efficiency high step-up converter with low switch voltage stress for fuel-cell system applications,” IEEE Transactions on Industrial Electronics, Vol. 57, No. 6, pp. 1998–2006, June 2010. [14]S.K. Chang chien, T. J. Liang, J. F. Chen, and L. S. Yang, “Novel high step-up DC-DC converter for fuel cell

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111 [21]N. Mohan, T. M. Undeland and W. P. Robbins, “Power Electronics: Converters, Application and Design,” 3rd

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