A Compressed Air Energy Storage (CAES) test-bed has been developed to experimentally demonstrate the energy storage concept proposed in [1] for offshore wind turbines. The design of the testbed has been adapted to the available air compression/expansion technology. The main components of the system consist of an open accumulator, a hydraulic pumpmotor, air compressor/expander, an electrical generator and load, a differential gearbox and a hydraulic control valve. These components are first characterized and then a dynamic model of the system has been developed. The objective is to regulate the output current/voltage of the generator while maintaining a constant accumulator pressure in the presence of input and demand power variations in the system. This is achieved by Proportional-Integrator (PI) control of pumpmotor displacement and field current of the generator. The stability of these controllers has been proved using an energy-based Lyapunov function. Experimental results for storage and regeneration modes have been presented showing excellent performance of the system in response to power disturbances.

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