- 2014 IEEE. In this paper, we propose a rectangular representation of FACTS devices such as the Phase Shift Transformer (PST) and the Unified Power Flow Controller (UPFC) in AC optimal power flow problems. This is motivated by the increasing need to incorporate FACTS devices in real-time operations to provide economic and technical benefits to the system. As a first step towards utilizing new control capabilities enabled by devices such as voltage source converters, we propose a rectangular representation of these devices in the AC optimal power flow problem. The rectangular representation of ACOPF has received increasing attraction due to faster convergence compared with conventional polar representation. In this paper, voltage actor FACTS devices such as PST and UPFC are modeled and incorporated in the rectangular ACOPF. The efficacy of the proposed formulation is shown via numerical examples on the IEEE 14 bus system.