To control a power state of a power system properly according to a communication state. A system for controlling a power system includes a plurality of sensor devices configured to output measurement data; a first control apparatus configured to estimate a first power state of the power system by using the measurement data obtained by the plurality of sensor devices, calculate a first controlled variable according to the estimated first power state, and output the calculated first controlled variable; and at least a second control apparatus configured to execute a predetermined control operation according to either the first controlled variable calculated in the first control apparatus, or a second controlled apparatus calculated in the second control apparatus. When it is not able to obtain part of the measurement data, the first control apparatus estimates the first power state by using predetermined measurement data among the obtained measurement data.