International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 03 | Mar -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 2666 A Hybrid DC-DC Converter for Standalone Applications Varun Jo Abu 1 , Sija Gopinathan 2 , Leela Salim 3 1 PG Scholar, Department of Electrical and Electronics Engineering, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India 2 Assistant Professor, Department of Electrical and Electronics Engineering, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India 3 Assistant Professor, Department of Electrical and Electronics Engineering, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - The conventional energy sources available in the world are diminishing every year creating a huge difference between the demanded energy and the available energy. Efficient utilization of the ample renewable energy resources present in the world can be used to cover this extra demand. With the use of this renewable energy sources the levels of pollution and global warming can controlled to a lower level. A significant demerit with the renewable energy sources is their fluctuating nature. Hybridization technique is hence utilized to overcome this problem. This allows two sources to meet the load separately or simultaneously depending on the availability. In this paper a double input single output DC-DC converter is presented for stand-alone systems. The topology operates as a bootstrap circuit by employing the charging switches in case of only one input port powering or one input being short circuited and maintains the expected output voltage making the system fault tolerant. Key Words: Hybrid system, Multi-input converter, Bootstrap operation, Solar panel, Fuel cell 1. INTRODUCTION Rise in the energy demand and limitation in fossil fuels have increased the role of renewable energy resources. Renewable energy sources will have to play a significant role in overcoming these problems. Systems based on petroleum product and fossil fuels will result in environmental pollution and hence global warming. This elevated the need for renewable energy sources which is abundant and environment friendly. Solar energy, wind energy, etc. are capable of supplying energy to meet the power demand. Even though the capital cost and space requirement for such systems are high, the running cost is extremely low. They can be easily utilized in distributed generation, micro grid, stand- alone systems, rural telephony systems etc. The main disadvantage of such a system is its unpredictable and intermittent nature, i.e., the output from these systems will always be fluctuating and doesn’t deliver a constant output. To overcome this challenge, hybrid renewable energy systems were implemented which clubs two or more energy resources to produce a constant output. Hybridization improves the efficiency and life of the system and also brings down the storage requirement. However, by combining these two fluctuating sources, the efficiency and reliability of the system can be refined notably. At the same time, the capital cost and complexity can increase as a result of hybridization. Multi input converters (MIC) have a simpler structure, improved power density and lower cost due to sharing of switches and other components [1]-[3]. Dynamic performance can be improved and complex communication among multiple different sources can be avoided due to the unified power management with centralized control. Thus MIC is appropriate for renewable power systems. Isolated [4]-[6] and non-isolated MIC has been developed for DC-DC conversion. Galvanic isolation is used in isolated MICs, but the disadvantage is the larger number of active switches present in it. Non-isolated converters have the advantages of small size, high power density and more efficiency. Based on buck and/or boost converter structures, various non-isolated topologies were developed. A triple input boost DC-DC converter developed in [7] consists of a photovoltaic source, fuel cell and a battery in a unified structure. A buck voltage source cell parallel connected MIC is presented in [8] which can operate in buck, boost or buck-boost mode, but with only any one of the input ports powering. Two-input series- connected buck DC–DC converters proposed in [9]–[11] have a simple topology and efficient energy utilization. They can deliver power to the load from two power sources simultaneously or individually. The series-connected two- input converter in [10] has one input port connected to a renewable energy source and other to a storage element, used for nanogrid application. Although both individual and simultaneous operations are possible for this converter, when one input source is shut down, the other port takes up the operation and the output voltage will be less than the existing input voltage. This implies that the converter is not able to maintain the expected output voltage in the one port powering case if the expected output voltage is more than either of two input voltages. Due to the randomness and intermittency of renewable energy sources present as inputs, it is necessary for the converter to be loaded with a flexible compensation program for error free individual operation. A circuit topology was designed in [12] which include a combination of a charging switch and a series connected double input converter (SCDIC). In this circuit, the converter operates in bootstrap mode in the case of one port powering and it meets the expected output voltage. The disadvantage with this topology