Key Technologies Of Medium Voltage Power System Of Electric Propulsion Ship

With the development of marine power technology,marine elecrtic propulsion system has become a research hotspot.When used in ship with complex operation condition,the electric propulsion system has greater efficiency,more maneuverability,higher automation,higher reliability,lower vibration and noise than diesel engine propulsion system.But the power system is hard to design because the ship power stations have large capacities and too many frequency converters are used.The main problems include high short circuit current,difficult type selection for circuit breaker and harmonic pollution.This thesis researches the key techniques of medium voltage power system of electric propulsion ship taking power systems of projects of polar class heavy transport deck carrier vessel for examples.Research results can be used in design process of similar projects.The main research contents are as follows:First,the harmonics impacts on power system of electric propulsion ship are studied.The paper analyzes the degree of harm caused by different harmonic sources in system.The propulsion frequency converters are the main sources.This paper compares different harmonic suppression schemes and determines that multi-pulse rectification scheme is most suitable for marine electric propulsion system,and uses ETAP software to calculate harmonic of marine medium-voltage electric propulsion system.Secondly,the neutral grounding modes of ship power system are studied.Three grounding modes of isolated neutral point,neutral point grounding by Arc suppression coil and neutral point grounding by resistance are analyzed in detail.The paper confirms that neutral grounding through high resistance is suitable for medium voltage power system of electric propulsion ship.The resistance value of the neutral point earthing resistance cabinet and the setting value of the earthing protection parameters of the generator are determined according to the real ship parameters of polar class heavy transport deck carrier vessel.Finally,the short-circuit current calculation and protection coordination design method of MV Power System are studied.The short circuit current of the polar class heavy transport deck carrier vessel is calculated by using the ETAP software,and the selection of the electric generator,bus bar,transformer and load switch is determined,the protection coordination between the upper and lower switches in power system is analyzed by ETAP.