DRAFT: NONLINEAR CONTROLLER DESIGN WITH BANDWIDTH CONSIDERATION FOR A NOVEL COMPRESSED AIR ENERGY STORAGE SYSTEM

To achieve both accumulator pressure regulation and gen-erator power tracking for a Compressed Air Energy Storage (CAES) system, a nonlinear controller designed base on an en-ergy based Lyapunov function. The control inputs for the storage system are the pump/motor displacements inside the hydraulic transformer and the liquid piston air compressor/expander. While the pump/motor inside the liquid piston has a low band-width, the other pump/motor inside the hydraulic transformer has a relatively higher bandwidth. On the other hand, the pneu-matic energy storage path of open accumulator has high en-ergy density, whereas the hydraulic path is more power dense. The nonlinear controller is then modified based on these proper-ties. In the proposed approach, the control effort is distributed between the two pump/motors based on their bandwidths: Hy-draulic transformer reacts to high frequency events, while the liquid piston air compressor/expander perform a steady stor-age/regeneration task. As the result, liquid piston air compres-sor/expander will loosely maintain the accumulator pressure ra-tio, while the pump/motor in hydraulic transformer precisely tracks the desired generator power. This control scheme also allows the accumulator to function as a damper for the storage system by absorbing power disturbances from the hydraulic path generated due to wind gusts