| 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 presents the application of the duality in deriving multilevel CSI ,especially the direct type CSIs, including following aspects.First this dissertation focus on the basic duality in normal circuits, and generalizes the element duals,structural duals,duals of switchs,magnetic duals. Large circuits can be more easily transformed by first dividing them into subcircuits,then find the duals of each subcircuits by substitution.In the dissertation a full-bridge duality transformation of parallel resonant dc-dc converters is given.A kind of direct type single-phase 5-level current source inverter topology derived from duality transformation is proposed in this paper. The switching strategy that can ensure equal current division among the branches is presented. The POD PWM control and 1/4 cycle strategy is employed to the converter. This inverter is verified by the simulation and experimental results. The waveforms of output current of the inverters are provided.A new type of three-phase direct type multilevel CSI topology is presented. The new multilevel CSI's not derived from the VSI directly, but it's a duality in idea,it synthesize the staircase 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 with a new PWM metod. The proposition is verified by the simulation results and experimental results. The waveforms of output current and current-sharing inductors current of the inverter are provided. |
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