## 1 Introduction  
Unmanned aerial vehicles (UAVs) are increasingly being used for civilian purposes such as logistics, transportation, traffic relations, and security. Recently, their application range has been expanding; UAVs, initially operated only for military uses, have started to be used for various purposes such as aerial photography and pesticide application. The application range of UAVs will expand because they do not entail inherent safety risks and high expenses compared to a much larger, manned aircraft. In recent years, China has emerged as a leader in the commercial UAV market, along with technology powerhouses such as the United States and Europe [1, 2, 3]. The technology for creating a UAV motor with high power output and high efficiency has emerged to enlarge the size of the UAV platform, because the weight of the UAV increases owing to the use of various functions of the UAV platform. Therefore, most UAV motors adopt permanent-magnet synchronous motors, in which surface permanent magnet motors are most commonly used. Electric motors for operating UAVs significantly affect flight performance. The flight distance, efficiency, torque, vibration, maximum speed, and acceleration forces are determined or changed depending on the drive motor. An interior permanent-magnet (IPM) synchronous motor has a structure in which a permanent magnet is embedded in the rotor. An IPM synchronous motor has the advantage of being able to obtain a large torque per unit volume because it has both an alignment torque owing to a permanent magnet, and a reluctance torque owing to the difference in the \(d\)-\(q\)-axis magnetic resistance. In addition, there is a substantial difference in the \(d\)-\(q\)-axis inductance distribution inside the rotor because the magnetic properties of the embedded permanent magnet are similar to those of a void. The rotor can have a wide range of variable-speed driving characteristics through field weakening control in proportion to the saliency ratio. Therefore, torque can be augmented because of the advantages of high output power and high-speed operation by securing high power density, wide speed range, and mechanical stiffness, which are the characteristics of an IPM motor. Accordingly, the study aimed to design and analyze UAV motors with the IPM method based on the hypothesis that high-power results can be obtained when these are used in UAV motors. Furthermore, we plan to design a method to minimize rotational interference from external foreign substances by developing a hermetic design. A self-oil cooling-type low heat generation structure supplementing the vulnerability of a hermetic structure to heat generation was designed and is proposed [4; 5; 6]. Demand for a low heat generation design that can improve flight duration and reliability increases as the output power of the UAV motor increases with the design of the IPM synchronous motor. The self-heating increases as the output power per unit weight of the motor increases, which is directly related to the increase in the internal temperature. This adversely affects the overall performance because it causes internal thermal deterioration and reduces the lifetime. Various cooling methods, such as installing a coolant channel within the housing or directly spraying cooling oil into the motor, have been studied to improve the internal temperature environment of the motor. However, the size and installation of the motor are limited, because this approach requires an additional device to cool the motor. Cooling technology, which is the core technology of heat dissipation design, is closely associated with high efficiency, miniaturization, high performance, and motor durability. Meanwhile, cooling methods for effectively discharging or distributing the generated heat can be classified into three types according to the fluid used.