Voltage instability impacts power system transfer limits and its reliability. This paper presents an approach to determine a voltage control scheme based on the Model Predictive Control (MPC) theory. MPC is used to develop an optimal control strategy, consisting of a sequence of amounts of the shunt capacitors to switch. The resulting control strategy prevents voltage instability and maintains a desired amount of post-transient voltage stability margin (an index of system security). The objective of optimization is to minimize a weighted sum of the cumulative voltage deviations and the cumulative cost of capacitive controls. The effect of the capacitive control on voltage behavior is computed by means of trajectory sensitivity. The sensitivity of voltage stability margin with respect to the capacitive control is used to construct a security constraint for post-fault operation in the MPC formulation. The efficacy of the proposed approach is illustrated through applications to the 39-bus New England system for preventing voltage collapse.