# Loss Research and Thermal Analysis of BLDC Hollow-Cup Motor Under Reactor Suppression
## 1 Introduction  
BLDC hollow-cup motors are in high demand for unmanned aerial vehicles (UAV), ventilators, and robotic arm applications owing to their high efficiency, low cost, high speed, and other significant characteristics. BLDC hollow-cup motors are different from other types of motors, through which the toothless structure enables the cogging effect of the motor to be suppressed [1][PERSON] However, the small armature inductance of BLDC motors cannot effectively suppress current-time harmonics, which leads to increased core loss, reduced efficiency, and higher operating temperatures [2]. In this study, due to the high speed and the current harmonic of the BLDC motor, the significant loss and over-temperature of the BLDC motor is the urgent problem, leading to the irreversible demagnetization of PMs and even to the failure of the motor. [PERSON] and [PERSON] [3,4] proposed the use of special materials, such as amorphous magnetic materials (AMM) and nanocrystalline magnetic materials (NMM), as core elements for high-speed motors to reduce the core losses. A new type of BLDC motor is investigated in Ref. [5]; its stator and rotor are made of soft magnetic composite (SMC) cores, which reduce eddy current losses and increase motor efficiency. The core loss of the segmented stator core is further reduced by applying a corner radius to each tooth root [6]. The literature [7,8] proposes methods to reduce core losses and cogging torque by optimizing the rotor shape of high-speed permanent magnet synchronous motors (PMSMs). The use of molded transposed windings in PMSMs is described in Ref. [9]. This type of winding reduces the copperloss of the motor, to some extent. [PERSON] et al. investigated the effects of the winding arrangement and core material on iron loss for high-speed switching motor reluctance [10]. [PERSON] and [PERSON]. [PERSON] [11] proposed a split-phase winding method for a HSPMM (high-speed permanent magnet motor) which reduces the rotor eddy current losses. Ref. [12] analyzed the effect of copper shielding on eddy current losses in high-speed PMSMs. Moreover, the current harmonic magnetic field causes eddy current loss in the rotor, and excessive eddy current losses can lead to an increase in temperature. In the study of the effect of time harmonics on electromagnetic losses, Ref. [13] focused on a surface-mounted high-speed PMSM that uses segmented permanent magnets to reduce eddy current losses in the rotor. [PERSON] and [PERSON] [14] designed a high-speed PMSM with closed slots that significantly reduced the 11 th and 13 th harmonics of the air-gap flux density, resulting in a reduction in rotor eddy current losses. [PERSON] and [PERSON] [15] proposed an optimized current switching and harmonic elimination scheme based on 7 th harmonic current injection for trapezoidal BLDC motors to reduce losses and improve efficiency. [PERSON]. [PERSON] et al. proposed the use of Halbach array permanent magnet configurations in brushless DC motors to eliminate reverse electromotive force harmonics and reduce losses [16]. A BLDC motor control scheme is proposed in Ref. [17], where the loss is reduced by current harmony, and its negative effects are minimized. [PERSON] et al. analyzed the additional electromagnetic losses in the motor during inverter power supply [18]. The analyzed results show that the current time harmonic and stator slotting are the main reasons for the increase in electromagnetic losses. In this paper, based on previous research, this study takes a high-speed BLDC motor as the research subject. In order to improve efficiency, it is important to study the loss under reactor suppression by using FEA on the magnetic-thermal coupling. The key innovations in this paper are as follows: by changing the system inductance value and analyzing its effect on motor loss and temperature, a method involving a reactor in series between a BLDC hollow-cup motor and a controller is proposed. Through this method, the core loss and rotor eddy current loss can be effectively suppressed.