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Improving Stability in Shipboard DC Power Systems with Constant Power Loads

By LCDR Adam J. Mills; Robert W. Ashton, Ph.D

The US Navy, over the last two decades, has invested significantly in developing Integrated Power System (IPS) on warships. IPSs present unique challenges to electrical distribution system designers. The inclusion of megawatt energy weapon systems, high-powered radars and increased computation capacity coupled with the planned use of a medium voltage DC (MVDC) architecture result in the ever-greater inclusion of power electronics into the shipboard electrical distribution system. The inverters and converters used to provide tailored voltage and frequency to each load exhibit a constant-power load profile to the MVDC bus. These constant-power loads destabilize the MVDC bus by introducing non-linear negative impedance. Large pulsed loads, such as laser weapon systems or electromagnetic railguns, prevent the use of classical linear controls. Energy storage devices (ESDs), such as batteries or flywheels, coupled to bidirectional DC-DC converters, may be used as controlled sources in addition to generator voltages. This paper introduces a multi-input non-linear adaptive linear quadratic regulator based control algorithm using generator voltage and energy storage device current as control inputs to produce superior MVDC bus voltage regulation in a CPL dominated system while reducing the need for bulk stabilizing capacitance.