As one of the new generation flexible AC transmission systems (FACTS) devices, the interline power flow controller (IPFC) has the significant advantage of simultaneously regulating the power flow of multiple lines. Nevertheless, how to choose the appropriate location for the IPFC converters has not been discussed thoroughly. To solve this problem, this paper proposes a novel location method for IPFC using entropy theory. To clarify IPFC's impact on system power flow, its operation mechanism and control strategies of different types of serial converters are discussed. Subsequently, to clarify the system power flow characteristic suitable for device location analysis, the entropy concept is introduced. In this process, the power flow distribution entropy index is used as an optimization index. Using this index as a foundation, the power flow transfer entropy index is also generated and proposed for the IPFC location determination study. Finally, electromechanical electromagnetic hybrid simulations based on ADPSS are implemented for validation. These are tested in a practical power grid with over 800 nodes. A modular multilevel converter (MMC)-based IPFC electromagnetic model is also established for precise verification. The results show that the proposed method can quickly and efficiently complete optimized IPFC location and support IPFC to determine an optimal adjustment in the N-1 fault cases. Index Terms-Flexible alternative current transmission systems, interline power flow controller, modular multilevel converter, optimized location method, power flow transfer entropy. Ⅰ. INTRODUCTION he modern power system is currently experiencing a rapid surge in electricity demand, resulting in increased pressure on long-distance power transmission, transmission lines approaching their thermal limits, and increased risks of voltage deviation [1], [2]. Consequently, the security and stability of the system's oper-_____________________________________