Abstract—This paper presents a new scheme for coordination between ULTC and STATCOM. Both devices are commonly used to control the voltage and reactive power in network. The STATCOM, unlike ULTC is characterized by its fast response so capable of dynamic voltage control and also providing reactive power in emergency situations. If the control action of these two devices is not coordinated, the STATCOM will quickly response to reactive power demand due to its higher operating speed. Therefore, the capacity of STATCOM will be fully utilized and so cannot have much contribution in emergency situations. In this paper, by making some modifications in the control system of STATCOM and creating a variable reference voltage, a new and simple scheme is produced to coordinate STATCOM and ULTC. Based on the proposed scheme the capacity of STATCOM is reduced hence some compensation margins provided for control purposes in emergency situations. The main advantage of the presented method is that only the STATCOM control system is modified to some extent but that of the ULTC is left unchanged. The simulation results demonstrate the accuracy and ability of the proposed method.

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