## 1 Introduction  
Permanent magnet (PM) brushless AC motors are widely used as power sources for vehicles and home appliances. These machines can be categorized as interior PM motors (IPM) and surface-mounted PM motors (SPM), wherein the PMs are attached to the rotor surface. In particular, IPM motors are used in a variety of fields because they can provide a reluctance torque component in addition to the magnet torque component, resulting in an increased torque density when compared with that of SPM motors. This is structurally advantageous for high-speed operation, where it helps in the mitigation of the scattering problems of PMs [1, 2]. In particular, IPM motors using rare earth magnets with a high residual magnetic flux density are applied to energy systems that require high power density and efficiency. However, rare earth magnets are expensive, and their supply is unstable owing to the limited production and strict policies. Therefore, studies to find an alternative to the series of rare earth PMs are being conducted. In particular, ferrite magnets have a low residual magnetic flux density compared with the rare earth magnets, and extensive research is underway pertaining to the use of a ferrite magnet as a rare-earth substitute because of their low price and stable supply [3, 4, 5, 6]. Therefore, studies on a model based on a ferrite magnet providing reluctance torque and on a model based on a consequent-pole (CP) structure to reduce the use of magnets are being studied. The CP structure can reduce the use of PMs. Also, it can be used in areas that require a high output, while having a multipole structure. In addition, it is possible to review the additional performance by changing the slot/pole combination. The vernier permanent magnet (VPM) motor has the advantage of generating a high torque at a low speed [7; 8]. However, because VPM motors require relatively large magnet usage, studies to apply the CP structure are underway. In particular, research is being conducted to improve the back electromotive force (back-EMF) and torque while reducing the use of PMs by mixing the toroidal-winding outer rotor and CP structure with the VPM motor structure [9; 10; 11; 12]. Further, to improve the torque characteristics in flux-weakening operations, research is also being conducted to apply the CP motor (CPM) structure to the rotor structure [13; 14; 15]. There are also studies that have applied the CP PMs and Halbach PM arrays to a linear PM vernier machine [16]. The switched reluctance motor (SRM) has a mechanically robust structure and is low-priced due to the absence of PMs. However, it has the disadvantage of having a relatively low efficiency and high noise and vibration compared with the PM motors. To increase the efficiency of SRMs, research is being conducted to apply the CP structure to the SRM structure, securing a wide speed area and increasing the torque density when a sine wave current is applied and reducing the ripple (DC current application) and magnetic usage [17; 18]. In addition, a study is also underway to apply the CP structure to the transverse-flux motor structure. In particular, the CP structure is applied to the flux-reversal PM motor to reduce the PM usage and torque ripple [19]. The CP structure which is widely used in various fields is basically arranged with the same polarity, and the opposite polarity is composed of iron cores. Therefore, it is difficult to design, and further studies are required to improve the asymmetric waveforms of the back-EMF and the structural noise vibrations. In this study, we propose a novel CP rotor structure of the IPM model used in automotive compressor systems. The proposed CP rotor structure represents a mixture of flared-type rotor and CP rotor assembly structures. The flared-type IPM model adopts a flared structure of C-shape ferrite magnets. In particular, the flared-shape structure can increase the amount of useful magnetic flux. So, the flared-type IPM motor is a form of the concentrated-flux-type IPM motor, thereby improving the power density.