Mitigating a transient response of a series stacked AC-DC converter

Generator operating at a limited speed range is essential for improving mechanical to electrical conversion efficiency in many high-power conversion systems, such as wind turbines and future ship turbine-generator systems. To meet the power quality requirements while supporting the variable speed operation, ac-dc conversion is required as the interface between the generators and a dc power grid. Therefore, high-efficiency ac-dc conversion is crucial to improve the overall conversion efficiency. An ac-dc conversion architecture integrating power electronics to a multi-port permanent-magnet synchronous generator was proposed for higher ac-dc conversion efficiency and higher system reliability. This architecture series stacks passive rectifiers and one active rectifier to generate a constant dc bus. Each of the rectifiers is powered by one three-phase port from the generator. The efficiency and reliability improvements come from the use of passive rectifiers to process a portion of the total power. A simulation model and a laboratory prototype were built to illustrate the feasibility of the proposed architecture. However, the prototype still has unsatisfactory dynamic performance. The dc bus voltage under a generator speed change still contains unwanted oscillation in the transient response. This thesis focuses on resolving the problem by two methods: (i) study the oscillation mechanism by investigating a realistic generator model and implementing a ramp command in speed change; (ii) achieve a better transient response of the dc bus voltage profile under the changes by appropriately improving the dc bus voltage controller on the experimental setup.Ope