Research And Design Of Marine Water-cooled Three-level Inverter

In recent years,China has attached more and more importance to the ocean,and naval cause has developed rapidly,in order to improve power quality and efficiency,three-level inverter in the ship has been widely used.In this paper,the Neutral Point Clamped three-level inverter is used as the research object,among the numerous control methods,the advantages of SVPWM control method which has become one of the hot research are prominent,and this method is easy to implement.In addition,the neutral point potential balance problem of DC side is the inherent problem of NPC type three-level inverter.In this paper,the midpoint potential balance problem is studied from the perspective of the midpoint potential fluctuation.The main work of this paper is as follows:(1)Three kinds of topologies of three-level inverters are compared.for the needs of this design,a Neutral Point Clamped three-level inverter is chosen as the main circuit topology,the topology and working principle of Neutral Point Clamped three-level inverter are studied in detail.And the SVPWM control strategy is described from the reference vector position judgment,the vector synthesis,the vector action order and the action time.(2)The reason and harm of the midpoint potential fluctuation are analyzed,on the basis of existing control methods,a novel method of small vector adjustment coefficient control based on charge conservation is proposed.The closed-loop control is realized by three-phase current and neutral current.(3)The parameters of the main power conversion device of the three-level inverter are calculated,and the main circuit device model is selected according to the calculation result.The SVPWM control strategy and the neutral potential balance control method are simulated to verify the feasibility of the scheme.(4)The main heating devices and heat generation of the inverter are analyzed,the series-parallel heat pipe is chosen as the main structure of the radiator,and the water-cooling system is designed by the heat balance principle,and the thermal equilibrium state of the water cooling system failure and the inverter during the emergency half-load operation are analyzed,The simulation proves the feasibility of the cooling system when the inverter is in emergency half-load operation.