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International Journal of Trend in Scientific 
Research and Development (IJTSRD) 



International Open Access Journal 
ISSN No: 2456 - 6470 | www.ijtsrd.com | Volume - 2 | Issue - 2 


♦ 

♦ 


A DC-DC Converter with High Voltage Gain and 
Two Input Boost Stages for Solar Applications 


K HimaVani 

Department of EEE, Amrita Sai Institute of Science & 
Technology, Paritala, Krishna District, 

Andhra Pradesh, India 


ABSTRACT 

An efficient dc boost converter with two input boost 
stages and high voltage gain is proposed for solar 
applications. The suggested topologies can be used as 
multiport converters and draw continuous current 
from two input sources. Continuous current can also 
be drawn from a single source in an interleaved 
manner. This can be used in solar farms. The 
proposed converters can easily achieve a gain of 20 
while benefiting from a continuous input current. 
Such a converter can individually link a PV panel to a 
400-V dc bus. This proposed work is carried out using 
MATLAB/Simulink platform. 

Keywords: Photovoltaic, MPPT, Voltage Multiplier, 
Fuel Cells 

I. INTRODUCTION 

WITH the increased penetration of renewable energy 
sources and energy storage, high-voltage-gain dc-dc 
power electronic converters find increased 
applications in green energy systems. They can be 
used to interface low voltage sources like fuel cells, 
photovoltaic (PV) panels, batteries, etc., to the 400-V 
bus in a dc microgrid system (see Fig. 1) [1]—[3]. 
They also find applications in different types of 
electronic equipment such as high-intensity-discharge 
lamps for automobile headlamps, servo-motor drives, 
X-ray power generators, computer periphery power 
supplies, and uninterruptible power supplies [4], To 
achieve high voltage gains, classical boost and buck- 
boost converters require large switch duty ratios. The 


Ch Chinna Veeraiah 

Department of EEE, Amrita Sai Institute of Science & 
Technology, Paritala, Krishna District, 

Andhra Pradesh, India 


maximum voltage gain that can be achieved is 
constrained by the parasitic resistive components in 
the circuit and the efficiency is drastically reduced for 
large duty ratios. Also, larger ripples on the high input 
current and output voltage would further degrade the 
efficiency of the converter [5]. 



Fig. 1. High-voltage-gain dc-dc converter in 
dc microgrid system. 

Typically high-frequency transformers or coupled 
inductors are used to achieve high-voltage conversion 
ratios [6]—[15]. The transformer design is complicated 
and the leakage inductances increase for achieving 
larger gains, as it requires higher number of winding 
turns. This leads to voltage spikes across the switches 
and voltage clamping techniques are required to limit 
voltage stresses on the switches. To achieve high- 
voltage conversion ratios, a new family of high- 
voltage-gain dc-dc power electronic converters has 
been introduced. This converter can be used to draw 
power from two dc sources as a multiport converter 
[16], [17].They draw continuous input current from 
both the input sources with low current ripple which 
is required in many applications, e.g., solar. In 


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International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470 


conventional approaches, as the output voltage of PV 
panel is low, several panels are connected in series 
when connecting the PV array to the 400-V dc bus 
through conventional step-up converters. This results 
in reduced system reliability which can be addressed 
by connecting high-voltage-gain converter to each 
individual PV panel. Similar converters with 
interleaved boost input have been proposed earlier 
using the Cockcroft-Walton (CW) voltage multiplier 
(VM) [18], [19]. Current fed converters are superior 
in comparison to the voltage fed counterparts as they 
have lower input current ripple [19]. The demerit with 
the CW-based converters is that the output impedance 
increases rapidly with the number of multiplying 
stages [20], 

1“ 2’" 3 "' 4* 

Stage Stage Stage Stage 


Fig. 2. Proposed high-voltage-gain dc-dc converter 
with four VM stages. 

I. MODES OF OPERATION OF CONVERTER 

The proposed converter is inspired from a Dickson 
charge pump [20]. Diode-capacitor VM stages are 
integrated with two boost stages at input. To help the 
boost stage VM stages are used achieve a higher 
overall voltage gain. The voltage conversion ratio 
depends on the number of VM stages and the switch 
duty ratios of the input boost stages. Fig. 2 shows the 
proposed converter with four VM stages. For better 
understanding, the converter operation with four 
multiplier stages has been explained here. For normal 
operation of the proposed converter, there should be 
some overlapping time when both the switches are 
ON and also one of the switches should be ON at any 
given time (see Fig. 3). Therefore, the converter has 
three modes of operation. The proposed converter can 
operate when the switch duty ratios are small and 
there is no overlap time between the conduction of the 
switches. However, this mode of operation is not of 
interest as it leads to smaller voltage gains. 

A. Mode-I 

In this mode, both the switches SI andS2 are ON. 
Both the inductors are charged from input sources 


Vinl andVin2. The current in both the inductors rise 
linearly. The 


J K 

Model 

Modi-II 

Model 

1 

ModHH 

f 






r 





DJ, 

k 



r 

i t 

j 

1 

[ 

w 


t 




r 


DJ, 













t 


Fig. 3. Switching signals for the input boost stage 
for the proposed converter 


+ v £ , - 



Fig. 4. Mode-I of operation for the proposed 
converter with four VM stages. 

+ vl\ - 



Fig. 5. Mode-II of operation for the proposed 
converter with four VM stages. 

VM capacitor voltages remain unchanged and the 
output diode D ou t is reverse biased (see Fig. 4); thus, 
the load is supplied by the output capacitor C ou t- 

B. Mode-II 

In this mode, the switch S1 is OFF and S2 is ON (see 
Fig. 5). All the odd numbered diodes are forward 
biased and the inductor currentILl flows through the 





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International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470 


VM capacitors charging the odd numbered capacitors 
(Cl,C3,...)and discharging the even numbered 
capacitors(C2,C4, However, if the number of VM 
stages is even, then the output diode is forward biased 
charging the output capacitor and supplying the load. 


inductorL2, one can write the capacitor voltages (see 
Fig. 6) in terms of lower boost switching node voltage 

V C 2 - Vci = V C 4 - V C 3 = (3) 



Fig. 6. Mode-Ill of operation for the proposed 
converter with four VM stages. 

According to, case considered here, since there are 
four VM stages, the output diode in forward biased. 

C. Mode-Ill 

In this mode, switch SI is ON and S2 is OFF (see Fig. 
6). Now, the even numbered diodes are forward 
biased and the inductor current Il 2 flows through the 
VM capacitors charging the even numbered capacitors 
and discharging the odd numbered capacitor. 
However, if the number of VM stages is even, then 
the output diode is reverse biased and the load is 
supplied by the output capacitor. 


III. VOLTAGE GAIN OF THE CONVERTER 

The charge is transferred progressively from input to 
the output by charging the VM stage capacitors. For 
the converter with four stages of VM (see Fig. 2), the 
voltage gain can derived from the volt-sec balance of 
the boost inductors. For LI, one can write 

<»Ll)=0. (1) 


Therefore, from Fig. 5, it can observed that the 
capacitor voltages can be written in terms of upper 
boost switching node voltage as 


Vci = Vc 3 — Vc 2 = Vont 


Vc 4 = 


Mm 

a-*) 


( 2 ) 


When dlis switching duty cycle forSl. Similarly, 
from the volt-sec balance of the lower leg boost 


Where d2 is the switching duty cycle for S2. From (2) 
and (3), the capacitor voltages for the proposed 
converter with four VM stages can be derived 


v,„ 

(1-rfl 


# Stage Stage Stage Stage 



Fig. 7. Proposed converter with N number of VM 

stages. 

x r Mill . Mil2 

VC2 ~ (1-4) + (l-d 2 ) 

T x _ 2 Mill Mn2 

(TT*j + (TT*) 


2 Mill . 2 Mn 2 

(I o^dTy 


(4) 


The output voltage is derived from (2), which is given 

by 


Vc* + 


Mnl 


3Vj, t l 2Vj n2 
(1-di) (1 -d 2 y 


Similar analysis can be extended to a converter with 
N number of VM stages (see Fig. 7). Thus, the VM 
stage capacitor voltages are given by 


V Cn 


V Cn 


( n + \ \ Mnl f n— 1 \ Fjn2 

^ 2 ) (1 -d,) ^ 2 ) (1 -d 2 ) 

if n is odd & n < N, 

/U\ Vinl , /U\ Vin2 

\2/ (1 -di) + V2/ (1 -d 2 ) 

if n is even & n < N. (6) 


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International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470 


The output voltage equation of the converter with N 
number of VM stages depends on whether N is odd or 
even and is given by 


T„, 


Tout 


Vcn + tt^tt if N is odd 

(1 ~<k) 

(N+l\ Vim / N + l\ V ia2 
\ 2 J(l-di) + V 2 J(l-d 2 ) 

Vcn + N if N is even 

(1 — c?i) 


(7) 


(N + 2\ Vim (N\ Vjn 2 

V 2 J(l-d t ) \ 2 J (1 — d 2 )' 


( 8 ) 


For N=l, if one combines the topology depicted in 
Fig. 7 with its alternative (see Fig. 8), then the 
resulting converter in Fig. 9 is similar to the 
multiphase converter introduced in [22], When both 
topologies with N number of VM stages are 
combined, the finalised converter is shown in Fig. 10. 
When N is odd, then from (7) and (10), the voltage 
gain of the combined topology is given by 


T out 


/N + l\ Vmi ( N + 1 \ T„2 

V 2 Jil-dt) \ 2 J(l-d 2 ) 

if N is odd. (12) 


When converter operates in an interleaved manner 
with single input source, ifdlandd2 are choosen to be 
an identical, i.e.,dl =d2 =d, then the output voltage is 
given by 

Vou, = <iV+l)-^. (9) 



Fig. 8. Alternative to the proposed converter with 
N number of VM stages. 

In [21], an interleaved boost power factor corrected 
converter with voltage-doubler characteristics is 
introduced. It is worth noting that there is an 
alternative to the proposed converter (see Fig. 8) 
where diodeDl of the first VM stage is connected to 
the lower boost switching node and capacitorCl is 
connected to the upper boost switching node 
(compare with Fig. 7). The output voltage equation 
for this alternative topology is given by 


Tout 


Tout 


(N + 1\ Tim /JV + l\ Tn2 

V 2 ) (1 -d i ) + \ 2 J(l-d 2 ) 

if AT is odd (10) 

(N\ Tui / V + 2 \ Tu2 

V 2 / (1 — d\) + \ 2 ) (1 -d 2 ) 

if AT is even. (11) 


In this case, the original topology and its alternative 
each process half of the output power. In other words, 
the average currents ofDoutlandDout2are equal. 
When N is even, the output voltage of the combined 
topology would be either (8) or (11) and will be 
dictated by the topology that provides a higher output 
voltage. Both legs (see Fig. 10) would compete with 
each other and only one of the output diodes 
(DoutlandDout2) would process the entire power 
while the other will be reverse biased. When Nis 
even, putting the converters in parallel only makes 
sense if there is only one source used and dl =d2. 



Fig. 9. Combined topology with single VM stage. 






Fig. 10. Combined topology with Number of 
VM stages. 


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International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470 


output voltage to be 

V out = (N + 1)-^- if AT is even. (13) 

(1 -d) 

For the combined topology with a single input source 
and identical duty ratiosdlandd2, i.e.,dl =d2 =d, both 
the boost stages will always have symmetrical 
inductor and switch currents irrespective of the 
number of VM stages. 



Fig 13. Output Voltage of the Converter. 


IV. SIMULATION RESULTS 


The proposed dc-dc high gain with two input stages 
for pv systems performance is studied in 
MATLAB/SIMULINK platform. The fig 11 shows 
the simulated circuit of dc-dc high gain converter and 
control circuit. The continuous current of two input 
inductors are shown in fig 12, the output voltage of 
converter in fig 13. The performance of proposed 
converter is also analyzed by using it in photovoltaic 
systems. It is observed that the gain of the converter 
attains 20. The simulation diagrams of photovoltaic 
panel and the output current and voltage are also 
presented. 


□ 




Fig 11. Simulation diagram of DC-DC High Gain 
Converter 




Fig 14. Simulation diagram of the proposed 
converter in grid connected PV system. 



Fig 15. Simulation diagram of DC-DC High Gain 
Proposed Converter 



Fig 12. Two Input Inductor continuous currents 
and voltage across Dout. 


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International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470 



Fig 16&17. Modeling of PV panel 



Fig 18. Grid voltage and grid current, 
v. CONCLUSION 

In this paper, a family of novel high-voltage-gain dc- 
dc converters with two boost stages at the input for 
photovoltaic applications has been proposed. The 
proposed converter is based on diode-capacitor VM 
stages and the voltage gain is increased by increasing 
the number of VM stages. Power can be drawn from 
two input sources like a multiport converter in an 
interleaved manner when connected to single source. 
One of the advantages of the proposed converter is 
that since it is a multiport converter with high voltage 
gain, it has the flexibility to be connected to 
independent sources while allowing power sharing, 
MPPT algorithms, etc., to be implemented 
independently at each input port. Furthermore, an 
alternative topology of the proposed converter has 
been presented and combining them both would result 
in a new converter topology. The proposed converter 
can be used for solar applications where each panel 
can be individually linked to the 400-V dc bus. 

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