## 1 Introduction  
LSPMMs are widely used in industrial production, oil field exploration, wind power generation, port lifting, and ship propulsion [1, 2]. The traditional drive system of an induction motor plus a mechanical deceleration mechanism has disadvantages, such as complex structure, leakage of lubricating oil, poor operation reliability, high maintenance cost, and low overall efficiency of the system; thus, this system does not meet the requirements of economic development, energy saving, and environmental protection [3, 4]. The use of direct drive motors to replace traditional drive systems has become the consensus of scholars at home and abroad [5]. In addition, the power factor and efficiency of permanent magnet motors are higher, and permanent magnet motors can maintain good performance over a wide range of load changes [6]. Therefore, LSPMMs are wildly used. However, an LSPMM needs to output a large torque, and it will generate a large electromagnetic torque, resulting in a large magnetic load and copper loss [7]. On the other hand, the lower speed results in less effective self-fan cooling, causing the high-temperature rise of the motor [8]. The higher motor temperature can result in the permanent magnet (PM) undergoing demagnetization and, ultimately, worse motor performance [9]. Hence, for LSPMMs, the suitable temperature is significant for guaranteeing good motor operating conditions. For LSPMMs, most of the literature focuses on motor design and performance optimization. An LSPMM with fractional concentrated winding used in a coal mine conveyor belt system was designed, of which the temperature distribution of different conductor turns and permanent magnet materials are presented in [10]. A new stator cooling structure design was studied to achieve a lower temperature rise, and the results show that the larger magnetic load and lower current density can improve torque density [11]. The U-shaped hybrid pole is proposed to improve motor torque density in [12]. The effects of stator tooth shape on output torque and bearing stress have also been studied, based on a bearingless outer rotor of a permanent magnet synchronous motor [13]. Furthermore, the effects of pole pair number and winding type on motor performance were investigated in [14]; a suitable embrace was found in order to obtain minimum cogging torque in [15]; and the influence of ratio of external diameter to stack length on torque and efficiency was analyzed in [16]. In the electromagnetic design of LSPMMs, the selection of magnetic load and current density has a great influence on electromagnetic performance. Magnetic load mainly affects the rotor core loss, eddy current loss of the PM, and stator core loss. For LSPMMs, eddy current loss of the PM and rotor core loss change very little when the magnetic flux density changes [17; 18]. Therefore, stator core loss is mainly considered when the magnetic load is changing, and the copper loss of the stator winding is mainly considered when the current density is changing [19; 20]. These two losses will affect the efficiency and the temperature characteristics of the motor [21]. In addition, for LSPMMs, due to the different heat dissipation characteristics of the core and winding, even at the same efficiency, different distributions of core loss and winding loss will result in different temperature distributions. However, in the existing literature, the electromagnetic properties are usually designed and optimized for maximum efficiency [22]. When the efficiency is high, the temperature performance of the motor may not be the optimal due to different core loss and winding loss distributions. The temperature characteristics of some LSPMMs are also analyzed based on different cooling schemes [11; 23; 24]. In these analyses, the effects of electromagnetic design parameters, especially the magnetic load and current density on the temperature, are not analyzed and summarized, which makes it difficult for designers to select optimal electromagnetic parameters to achieve better temperature performance.