| Summary: | The supercapacitor, as a recently developed electrochemical energy storage device, offers extremely high capacitance per unit volume. Due to its unique double-layer structure and electrostatic charge mechanism, the supercapacitor has a much higher power density than the battery, and a much higher energy density than the conventional capacitor. It also benefits from a long cycle life, and wide temperature range. However, limited by a low cell voltage of 2.7V and high equivalent series resistance, the supercapacitor may be inefficient for high power grid level applications. Characteristic analysis of the supercapacitor shows that the efficiency reduces to 54.7% at peak current conditions. Based on supercapacitor modelling studies, two parameter identification methods are proposed, which are realised by a simple experiment, with an acceptable accuracy. A parallel combined supercapacitor and electrolytic capacitor energy storage system is proposed to improve high power application performance, which offers efficiency improvements in excess of 10%. A detailed description of such parallel capacitor systems are included in this thesis, where a design guide is developed to achieve an optimal design in terms of system efficiency, power capability, and volume. The capacitor based energy storage technique is suited to distributed generation applications where low-voltage ride through and grid code compliance are important considerations. A supercapacitor based static synchronous compensator is proposed, which is able to manipulate both active and reactive power exchange with the power system. Steady-state and transient responses are studied based on simulation of a test power system. A system frequency based control algorithm is used for active power control, which has a better stabilised system frequency than with conventional voltage control. The parallel hybrid capacitor technique is employed, which greatly improves the system performance in terms of efficiency, thermally, costs, and volume, compared with a system that only uses supercapacitors.
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