Variable speed generating unit for vehicle on-board applications

Variable speed operation has been proposed in literature as a solution to efficiency and pollution problems for diesel generating units, as well to improve efficiency and power conversion in rotating systems for renewable energy sources. In general, different topologies of prime-movers, like internal combustion engines, wind turbines and hydro turbines, etc. can be used to move an electric generator at variable speed. In variable speed generating systems, the electric output frequency is disengaged from the mover speed through a power electronic converter. This paper deals with a newly-conceived variable speed generating unit to be used in on-board vehicle applications. The control structure is discussed and experimentally verified by means of a 40kW rated power converter prototype. It is shown that the proposed voltage control allows simplifying the overall control configuration and fast compensation of load unbalances. Further to that, a complete current limiting strategy is described and tested under different load conditions.