Abstract The static synchronous compensator (STATCOM) is one of the recently developed converter-based flexible AC transmission systems (FACTS) controllers. Usually the reactive output of a STATCOM is regulated to maintain the desired AC voltage at the bus, to which a STATCOM is connected. This paper describes a multi-control functional model of a STATCOM for power system steady-state operations. Nine control functions of a STATCOM are presented. An innovative implementation of the current control function of a STATCOM is proposed to circumvent the multiple-solution problem of the current control. The innovative reactive power flow and apparent power control functions of a STATCOM are also proposed. Furthermore, a comprehensive strategy for the enforcement of multiple violated constraints associated with a STATCOM is proposed. Numerical examples on the IEEE 30-bus system, IEEE 118-bus system and IEEE 300-bus system are used to illustrate the multi-control functional model of a STATCOM.