Adaptive Motor Load Control Method for Shipboard Microgrid Frequency Regulation

Shipboard microgrid requires responsive resources to mitigate frequency fluctuations caused by load changes, but the responses from generators or energy storage usually incur a high cost. Alternatively, since motor drives comprise a significant portion of load, they manifest potentials for frequency regulation from the demand side. However, the existing demand response framework lacks the active control of variable speed drives (VSDs) for full use of motor load power reserve. This article proposes an adaptive motor load control for VSD. The strategy synergizes the dual inertia resources in motor loads, including dc-link capacitors and rotating machines to reduce the frequency deviation. A model predictive control (MPC) mechanism is presented to calculate the optimized reference value of dc voltage and motor speed, enhancing the frequency response capabilities while ensuring a controllable operating trajectory for VSD. Without additional energy storage systems (ESSs), the VSD actively realizes a coordinated control between frequency and speed regulation. In addition, the tuning of weighting factors in the control strategy, covering two operational modes, is discussed and quantitatively assessed. The capability of the proposed system to suppress grid frequency fluctuations is demonstrated through RT-LAB hardware-in-loop experiments and laboratory-scale power platform.