Large-scale and regionally intensive introductions of renewable energy sources (RES) requires greater control capacity from frequency control generators (FCGs). To solve this problem, cross-regional operation, which integrates multiple control areas, is widely studied. However, this involves more complicated power flow, due to the wider control area. Thus, a transmission system operator should adjust output of FCGs to compensate for RES fluctuations, considering system indices and power system constraints in various power flow conditions such as day or night. We have proposed a multi-objective optimizing method for FCG dispatches to compensate for RES fluctuations in one case in the daytime. A simulation was needed, under various load and RES output conditions, to evaluate the validity of the method. In this study, a simulation is conducted, using a power system model base on the power system of East Japan under seven power flow conditions. The results support the validity of the proposed method for determining a dispatch, considering multiple system indices in all cases.