Load Following Ability of a Ship Generating Plant Comprising a Mixed Set of High-Speed and Synchronous Turbo-Generators

A ship power system comprising a mixed set of large line-connected 60 Hz turbo generators and lower-powered high speed electronically-matched permanent magnet turbogenerators is potentially unstable against large, abrupt changes of the load power demand. Concerns include whether the high speed turbine could stall or overspeed. We show that suitable control algorithms can fully protect the high-speed generator. Yet with that protection of the high speed turbine, the stability of the AC-bus voltage and the 60Hz generator frequency become the critical limiting factors. Following rapid increases of load, up to 15 MW/s, the high-speed generator always operates safely because of the control design and the energy stored on the DC bus. System stability is potentially threatened, however, by abrupt decreases of load. Limits on the rate of decrease depend on the initial and final load powers.