This document summarizes a research paper on modelling a high step-up DC-DC converter for photovoltaic modules. The converter uses a coupled inductor to achieve high voltage gain from a low PV panel output voltage. It operates in both continuous conduction mode and discontinuous conduction mode. Simulation results show the output voltage is regulated at 150V with a photovoltaic array input. The converter has benefits of high efficiency, reduced component stress, and isolation of the PV panel during non-operation for safety.

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MODELLING OF HIGH STEP UP DC-DC CONVERTER
FOR PHOTOVOLTAIC MODULES
ANU R1
, RESHMILA .S2
1
M.Tech Scholar: Dept. of EEE,Sree Narayana Gurukulam College of Engineering, Kolenchery, India
2
Associate professor – Dept. of EEE, Sree Narayana Gurukulam College of Engineering, Kolenchery, India
ABSTRACT
Photovoltaic (PV) power-generation systems are becoming increasingly important and prevalent in
distribution generation systems. A high voltage gain converter is essential for the module’s grid connection through a dc–
ac inverter or for battery charging for standalone PV system. This paper consists of a high gain dc-dc boost converter
which can be used to boost the output from a PV module. During non operating conditions the switch can isolate PV
panel from load, enhancing safety. A coupled inductor is used to get high step up ratio. The leakage inductor energy of
the coupled inductor is recycled to the load efficiently. Thus the converter has less switching stresses and has a high
efficiency performance.
Keywords: AC Module,Coupled Inductor,High Step Up Voltage Gain.
1. INTRODUCTION
Solar energy is one of the commonly used renewable sources. Photovoltaic systems can be effectively used for
distributed generation. PV technology exploits the most abundant source of free power from the Sun and has the potential
to meet almost all of mankind’s energy needs. Power from the PV can either connected to grid through an inverter or can
be used for battery charging. The output voltage from a PV panel is usually small. So for a PV modules grid connection
or for standalone application a DC-DC boost converter is needed.
The DC-DC converters requires large step up conversion from low voltage of the panel to the voltage level of
applications. The transformerless switched capacitor type converters [1] can obtain higher voltage gain than conventional
boost converter by increasing the turns ratio of the coupled inductor.
The soft-switched continuous-conduction mode (CCM) boost converters are suitable for high voltage and high-
power applications has the following features: ZVS turn-on of the active switches in CCM, negligible diode reverse
recovery due to ZCS turn-off of the diodes, greatly reduced components voltage ratings, reduced energy volumes of
passive components due to interleaving effect [2]. The soft switching of the converters will improve the converter
efficiency [3].
In order to achieve low volume and high efficiency, multiphase interleaved converters can be used for the
DC/DC converters. The inductors represent a main part concerning the converter volume. Coupled inductors can reduce
the volume and increase the efficiency [4].
The step-up ratio of the conventional boost converter can be raised by using a coupled inductor. In order to
achieve high voltage gain without extreme duty cycle of switch three-winding coupled inductor is used. The circulating
current phenomenon and switch surge voltage production are avoided since the leakage inductor energy is released to the
output terminal [5].
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A new high step-up dc–dc converter is designed for regulating the dc interface between various micro sources and a dc–
ac inverter to electricity grid. The converter achieves high step-up voltage gain with appropriate duty ratio and low
voltage stress on the power switch [6].
A new high gain converter using coupled inductor is proposed. High gain is obtained by increasing turns ratio of
coupled inductor. Here also the leakage inductor energy is recycled to the load and hence switching stress is reduced.
Size and weight of the converter is reduced, number of components is less and also complexity of the circuit is less.
2. CIRCUIT DESCRIPTION AND OPERATING PRINCIPLES OF THE HIGH STEP UP DC-DC
CONVERTER
The circuit configuration of the proposed converter is shown in Fig. 1. The converter includes a coupled
inductor T1and a floating active switch S1. N1 and N2 are respectively the primary and secondary windings of the coupled
inductor. The capacitor C1 and diode D1 receives energy from N1. The secondary winding of N2 is connected to capacitor
C2 and diode D2. D3 is the rectifier diode which is connected to the output capacitor C3.
Fig. 1: Proposed circuit of high step up DC-DC converter
The simplified circuit of the proposed converter is shown in Fig. 2. T1, the coupled inductor represented as a
magnetizing inductor Lm, primary and secondary leakage inductors Lk1 and Lk2, and an ideal transformer. The following
assumptions are made to simplify the circuit analysis.
1) All components except the leakage inductance of coupled inductor T1, are ideal. The on-state resistance RDS (ON) and
parasitic capacitance of the main switch S1 are neglected.
2) The capacitors C1 ~ C3 should be sufficiently large such that the voltage across them are constant.
3) The equivalent series resistance of C1 ~ C2 and parasitic capacitance of T1 are neglected.
4) The turns ratio of the coupled inductor N2/N1 is denoted by n.
Fig. 2: Simplified circuit model of high step up DC-DC converter
The operating modes are described as follows.

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2.1 CCM Operation
The operating principles of continuous conduction mode are described in this section. Fig. 3 shows the typical
waveforms during five operating modes of one switching period.
Fig. 3: Typical waveforms of the converter at CCM operation
The operating modes are described as follows.
Mode 1 [t0, t1]: In this transition interval switch S1 is turned ON so that the magnetizing inductor Lm charges C2 through
T1 continuously. Switch S1 and diode D2 are conducting in this mode. This mode ends when the current through primary
leakage inductor Lk1 equals current through magnetizing inductor Lm.
Mode 2 [t1,t2]: In this interval source Vin is series connected with N2,C1 and C2. This series combination will charge
output capacitor C3 and load R. In this mode magnetizing inductor receives energy from Vin. Switch S1 and diode D3 are
conducting in this mode and this mode ends when switch S1 is turned OFF.
Mode 3 [t2,t3]: In this mode Lk2 charges C3. Only diodes D1 and D3 are conducting during this mode. The stored energy in
Lk1 charges capacitor C1 through diode D1.At the same time energy stored in Lk2 charges output capacitor C3 and load.
This mode ends when current iLk2 decreases to zero.
Mode 4 [t3,t4]: During this transition interval only diodes D1 and D2 are conducting. The energy stored in Lm is releaed to
C1 and C2. The energy that stored in C3 is discharges to the load R. Due to the energy transfer, the current iLk1 and iLm are
decreases. And this mode ends when iLk1 decreases to zero.
Mode 5 [t4,t5]: During this mode only diode D2 is conducting. The magnetising inductor Lm releases its energy to C2.
This mode ends when S1 gets turned ON in the next switching period.
2.2 DCM Operation
The operating principles for discontinuous conduction- mode (DCM) are described in this section. Fig. 4 shows
the typical waveforms of the converter at DCM operation.

4. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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Fig. 4: Typical waveforms of the converter at DCM operation.
The operating modes are described as follows.
Mode 1 [t0, t1]: During this mode of operation switch S1 and diode D3 are conducting. The source Vin charges output
capacitor C3 and load R through N2, C1 and C2. At the same time Lm and Lk1 receives energy from Vin. This mode ends
when S1 is turned OFF.
Mode 2 [t1, t2]: During this interval only diodes D1 and D3 are conducting, and switch S1 is OFF. In this mode energy
stored in Lk2 charges capacitor C3 and energy stored in Lk1 charges capacitor C1 through D1. This mode ends when the
current iLk2 reduces to zero.
Mode 3 [t2, t3]: In this transition interval only diodes D1 and D2 are conducting. The energy stored in coupled inductor T1
charges capacitors C1 and C2. The energy stored in capacitor C3 is discharged to the load. This mode ends when current
through iLk1 becomes zero.
Mode 4 [t3, t4]: During this mode only diode D2 is conducting. In this mode the magnetizing inductor Lm releases its
energy to C2 and stored energy in C3 is discharges to the load R. This transition mode ends when iLm becomes zero.
Mode 5 [t4,t5]: During this switching interval energy stored in C3 is discharged to load R and all active components are
turned OFF. This mode ends when S1 is turned ON for the next switching period.
3. SIMULATION RESULT
Simulation of the high step up DC-DC converter has been done for both open loop and closed loop. A
MATLAB/SIMULINK simulator was used for simulation in order to investigate the operational characteristics of the
system.
3.1 Closed Loop Control
The input to the converter is given from a photovoltaic array. The photovoltaic array is modelled by the series
connection of 72 PV cells. Voltage feedback is used with a constant voltage of 150V as reference voltage. Fig. 5 shows
the simulink model of the converter in the closed loop control. Fig.6 shows the output voltage waveform for a reference
voltage of 150V. From Fig. 6 it is clear that the output voltage settles to a voltage of 150V.

5. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30-31, December, 2014, Ernakulam, India
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Fig. 5: Simulink model of the converter in closed loop control
Fig. 6: Output voltage waveform for a reference voltage of 150V
4. CONCLUSION
The converter has a high gain compared to the conventional boost converter because of the presence of coupled
inductor. Since the energy of the coupled inductor’s leakage inductor has been recycled efficiently to the load, the
voltage stress across the active switch S1 is constrained, which means low ON-state resistance RDS(ON) can be selected. By
coupling the inductor, size and weight of the converter is not so large. The position of the switch of the high gain
converter is different from that of conventional boost converter. The switch is placed in such a way that it can isolate dc
current from the PV panel during non operating condition thus enhancing safety to system technicians.
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ISSN Print : 0976-6545, ISSN Online: 0976-6553.