  Traditional optimal power flow (OPF) describes the system performance only in
a single snapshot while the resulting decisions are applied to an entire time
period. Therefore, how well the selected snapshot can represent the entire time
period is crucial for the effectiveness of OPF. In this paper, period OPF is
proposed with a given time period that partitioned into consecutive linear time
intervals, in which bus voltages and branch powers are linear mappings of time.
The optimality and operational limits in each time interval are precisely
represented by its median and two end snapshots, through which the system
performance of OPF model is significantly improved. Simulation case studies on
a modified IEEE 118-bus system have demonstrated the simplicity and
effectiveness of the proposed model.
