An electrical grid control system includes a plurality of power conversion apparatuses each storing active power relationship information indicating a relationship between an active power control level representing a level of control for active power output to an electrical grid, and a connection point frequency being a frequency at a connection point to the electrical grid; and a control apparatus that repeatedly receives information indicating a system frequency measured in the electrical grid, determines the active power control level based on the system frequency, and transmits the active power control level to the plurality of power conversion apparatuses. Each power conversion apparatus repeatedly measures the connection point frequency, receives the active power control level from the control apparatus, and controls the active power based on the measured connection point frequency, the received active power control level, and the active power relationship information.