AbstractThis paper discusses the feasibility of a decentralized voltage control scheme for large‐scale power systems. The algorithm is intended to apply to a reactive normal operating state from an emergency state caused by illcondition and also to keep the operating state away from approaching unstable boundaries in preventive control. The procedure for releasing voltage deviation (over/under voltage) is formulated as a multistage decision process over a certain time interval. The optimization problem is transformed into a two‐point boundary value problem using the discrete maximum principle and is solved easily by using the discrete Riccati equation.For a large‐scale power system, control values must be computed from a large number of state variables, and this inevitably prolongs the slow dynamics with controllers. The centralized control system in a large‐scale system cannot be justified from the economical and technical viewpoints. To resolve the foregoing problems, a decentralized voltage control system incorporating slow voltage dynamics is pr