Control of a statcom with supercapacitor energy storage

STATCOM (STATic COMpensator) has been used in electrical power systems as a shunt-connected compensator for voltage support and to improve power quality. Compared with the conventional compensators such as the synchronous condenser and the SVC (Static Var Compensator), the STATCOM has a faster speed of response to deal with dynamic and transient impacts. Although the STATCOM is capable of reactive power support to improve power quality, the ability to support real power is limited due to the insufficient energy storage capability of the conventional DC-link capacitor. Therefore, the application of the STATCOM to improving power system stability has been limited. This thesis proposes a solution to enhance the performance of the STATCOM by adding supercapacitor energy storage to the DC-link of the conventional STATCOM. With the fast charge/discharge characteristics of the supercapacitors, the enhanced STATCOM can absorb and inject real power to the ac power grid virtually instantaneously. The control design of the STATCOM based on a vector control strategy is presented, including the design of an instantaneous reactive power controller based on a small-signal model of the ac power system. The control design of the supercapacitor energy storage system (SCESS) based on small-signal models of the de-to-de converter is documented. The STATCOM and the SCESS are controlled together using a feed-forward control technique. In addition, this thesis also proposes that the enhanced STATCOM can be applied to reduce instability and tripping due to the rate of change of frequency (ROCOF) protection devices caused by large load impacts. The amount of the energy required for the enhanced STATCOM to maintain the stability of the system is also discussed