- Secondary voltage controls, as a non-cost voltage control, are often conducted by utilities as the first option to solve voltage violations. Utilities like PJM and MISO manually coordinate secondary voltage controls aiming at regulating voltage profile and avoiding the use of potentially costly controls, such as transmission loading relief or load shedding. The speed of secondary voltage control devices ranges from three up to 15 minutes, depending on the control mode (either automatic or manual). Increasing voltage stability has not (in the past) been considered as a control objective. In this paper, a novel decentralized secondary voltage control system is designed to automatically generate optimal control decisions meeting different control objectives (such as maximum stability margin, minimum controls and losses). The proposed system aims at providing fast and coordinated secondary voltage control decisions in the time range from several seconds to a few minutes. Comparative studies are performed between the proposed system and existing secondary voltage control approaches applied in utilities. 2012 IEEE.