Nowadays, power systems operate near the voltage stability margin because of high load demand. Therefore, the system operator must be aware of the operating system condition in order to use preventive and corrective control actions to avoid the voltage collapse that might occur. In this regard, having a suitable algorithm to determine the time that operator needs to use either preventive or corrective control is essential. Also, it is necessary to obtain suitable models for implementing these control actions. In this paper, based on the load prediction curve of each bus, a new method is proposed to estimate the remaining time that voltage instability will occur. Also, a new algorithm is suggested to select the best control action (preventive or corrective) according to the remaining time until voltage instability and the operating state of the power system. In addition, two models based on voltage stability constrained optimal power flow (VSC-OPF) considering the constraints related to voltage stability index and the remaining time until voltage instability have been proposed for both kinds of control. The effectiveness of the proposed algorithm and models has been tested on IEEE 14-bus and IEEE 57-bus power systems.