Research On The Topologies And PWM Control Strategies Of Current Source Multilevel Converters

Multilevel converter is actually a power amplifier which are consisted of hardware based on the topologies and software based on the control strategies.Multilevel converter technology has been mainly used for voltage-source inverters (VSI) by now, very few literatures research on current source inverter (CSI).With the development of the superconducting magnetic energy storage (SMES) technology, superconducting inductors can be used as higher efficiency energy storage elements, the multilevel current source inverters (CSI's) will be very attractive in high power applications due to their advantages such as controlling the output current more directly and conveniently, faster dynamic response, easy regeneration capability, and implicit short-circuit protection. This dissertation research on some relevant technology of multilevel CSI. The content of the dissertation is as follows:A new kind of direct type single-phase 5-level current source inverter topology based on the POD PWM technique is discussed in this paper. Including very few switching valves 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. There is current fluctuation in the sharing inductor and it can not ensure flow equalization with the open-loop control , however, with the closed-loop control , it can ensure flow equalization and the harmonic components are largely reduced. This single-phase CSI topology is verified by the simulation and experimental results.A type of three-phase direct type 5-level CSI topology and PWM technique is presented. The new multilevel CSI's synthesize current wave from several levels of balance inductor currents. The structure of the new inverter is very simple. The current balance of sharing inductors can be achieved without close-loop control. Three-phase five-level CSI topology principle is analyzed ,the switch control strategies is also presented and the proper switching sequence is given .Acompounding PWM technique is applied in the inverter, then, the proposition is verified by the simulation results and experimental results.The direct type single-phase 5-level and three-phase 5-level current source inverter topology can be developed to 7-level and higher level. The harmonic components can be reduced with the increasing of the current level.