The Research Of Current Source Multilevel Converters

The maneuverability is the ability of changing the orientation of the vessel quickly when it receives orders, and it is an important judging criterion of the battle performance of a vessel. At the same time, a vessel's maneuverability is related to the electric driving system closely. Multilevel current source inverter (CSI) is widely used in the high-power supplying fields, because of its advantages of controlling the output current more directly and conveniently, faster dynamic response and the convenience of feedback brake in motor driving. Therefore, there will be much space in the development and research of multilevel current source inverter used in motor driving system of the vessels.Multilevel converter is actually a power amplifier which consists of hardware based on the circuit topologies and software based on the control strategies. Multilevel converter technology has been mainly focused on the voltage source inverters (VSI) by now, and very few literatures research on current source inverters. With the development of the superconducting magnetic energy storage technology, superconductors can be used as higher efficient energy storage elements; the multilevel current source inverters will be heavy attractive in high power applications due to their advantages. The main contents of this thesis are as follows.At first, the thesis reminds the history of the driving equipment used in the vessels. The vessels' driver is developed from steam turbine and diesel engine to electric power. Then, this thesis introduces the developing actuality and topologies of high-power inverter. A new kind of single-phase 5-level current source inverter topology based on the POD-PWM technique is discussed in this thesis. Consisting of fewer transistors and current sharing inductors, the structure of this type of inverter is very simple. The POD-PWM technique is applied to the topology, and the control strategies of the new type of single-phase five-level CSI topology in open loop control system and in closed-loop control system are discussed respectively. There is bigger current fluctuation in the sharing inductor and it can not ensure the current equalization with the open-loop control. However, with the closed-loop control, it can ensure the current equalization and the harmonic components can be largely reduced. This single phase CSI topology is verified by the simulation results.A type of three-phase 5-level CSI topology and POD-PWM technique is presented here. The new multilevel CSI synthesize current wave with several levels of sharing inductor currents. The structure of the new inverter is very simple. The current balance of sharing inductors can be achieved without closed-loop control. Three-phase five-level CSI topology principle is analyzed, and the switching control strategy is also presented and the proper switching sequence is given also. The proposition is validated by simulation.The single-phase 5-level and three-phase 5-level topology of the current source inverters can be developed into 7-level and more higher levels. The harmonic components can be reduced with the increasing of the current levels.