특수목적선박의 하이브리드 전기추진시스템 구축에 관한 연구

Abstract

Since the industrial revolution, global warming has been progressed due to the increase of greenhouse gases(GHGs) by continuous use of fossil fuels. The major natural disasters that have occurred frequently in recent are due to global warming, it is reported that this steady rise of earth average temperature is progressing with increasing greenhouse gases, especially carbon dioxide. IMO(International Maritime Organization) announced the emission regulation of GHGs by each country through the UNFCCC(United Nations Framework Convention on Climate Change), and prepared the counterstep to reduce air pollution by ship. The goal of this counterstep is to reduce GHGs by 30% compared to current levels till 2025. Also, this regulation is expected to further strengthen in the future. In line with this trend, researches on electric propulsion system(EPS) for ships have been proceeding their goals for reducing of air pollution, furthermore, zero emission. The Korean government is also actively investing in research and development on the use of renewable energy and related technologies to reduce GHGs, the main cause of global warming. As a result, great progress has been made in the field of transportation. On land, hybrid electric vehicles(HEV), which use alternating a engine and a electrical motor according to driving conditions, have already been developed and commercialized. Also at sea, the research, development and investment for electrical propulsion ship adopted the hybrid concept is progressing actively. Specially, these hybrid propulsion systems are being actively applied to special purpose ships such as navy warships and patrol & rescue ships. These ships have various operational conditions compared to general ships. These are propelled by a part of propulsion system at low speed or cruise mode, and are propelled by all the power of the ship at emergency or warlike training situations mode. Most of the larger ships over 3,000 tonnage class, which are currently being built, have a hybrid system, that is, CODLAD(COmbined Diesel-eLectric And Diesel). These ships have two propulsion shafting systems each consisting of a diesel engine and a propulsion motor. For example, 3,000 tonnage class patrol & rescue ship was first deployed including korea coast guard and korea navy in 2010. This ship has propulsion systems that are operated flexibly according to the operating situations. That is, this ship can be propelled by two propulsion motors at low speed mode(less than 12 knots), by two diesel engines at cruise speed mode(abt. 15 knots), and by simultaneously connecting these four sets at high speed mode(max. 28 knots). Like this, Because it is possible to effectively divide and operate the large capacity and high horsepower engine, it could was achieved that reducing fuel costs, extending engine life, reducing noise and vibration in the ship, and improving the living environment of the crew. But, the small special purpose boats, such as coast guard boats and environmental monitoring boats engaged in the offshore waters near the land, are equipped with high-speed diesel engines and water-jet propulsion. Since most of these boats are equipped with high speed diesel engine as a main engine, they have a problem that the fuel cost increases due to the incomplete combustion and discharging a large amount of GHGs. In particular, these special purpose boats normally operate at high speed only when entering, departing or emergency. In other words, most of on patrol and surveillance is done at low speed. therefore, it is necessary to solve serious problems such as increase of fuel cost and induction of air pollution. In this paper, I propose one solution to solve these problems. It is a hybrid electric propulsion system(CODOL, COmbined Diesel Or eLectric) consisted of a battery charging system using the PTO(Power Take Off) of main engine and a motor driven propulsion system using this battery. Main components of the hybrid electrical propulsion system(after, H-EPS) are a electrical generation system with efficient electrical power generation performance even in a variable speed condition of a diesel main engine and a charging system that efficient storage performance of the electric energy. The purpose of this study is to examine the performance of H-EPS as follows, and based on this, design the main specifications of H-EPS for small special purpose boats. Firstly, The generator of power generation system for the H-EPS is required to have the highest reliability and stability, despite a isolation at sea and a poor engine room environment, In addition, it should be a compact structure with high output and light in relation to volume. SEIG(Self Excited Induction Generator) and PMSG(Permanent Magnet Synchronous Generator) are selected as the generator of H-EPS, and their output characteristics are compared and analyzed through experiments. These generators are mainly used in new and renewable energy fields because they have efficient generation performance even under the variable speed conditions of prime mover. Secondly, the H-EPS performance greatly depends on the fast charging characteristics into the battery of the electric energy generated from the generator and the highly efficient discharging characteristics of the charged electric energy. For fast charging characteristics, lead acid battery and lithium ion battery are selected as battery. Lead-acid batteries are the most commonly used in ships, and lithium-ion batteries are increasing in use due to their excellent efficiency and other advantages. These two batteries are tested under various conditions and their characteristics are compared and analyzed. And, the induction motor is selected as the propulsion motor which is the main consumption source of electric energy, and its characteristics are analyzed through various discharging experiments. Of course, these results are used as design data for actual H-EPS building. Thirdly, I select a 14m class coast guard boat as the actual target ship, build an H-EPS based on various experimental data derived from the above, and derive numerically the effect of H-EPS.