Performance Analysis of Flux-Modulating Consequent Pole Motors

This paper proposes a novel variable-flux permanent magnet (PM) motor, named the “flux-modulating consequent pole motor (FCM),” and investigates its performance through finite element analysis (FEA) and experiments. The proposed FCM is a combination of a flux-modulating (FM) motor and a consequent-pole PM motor. The torque of the FCM can be generated from both the FM and PM motors without causing unbalanced magnetic forces (UMFs). Using 16- and 20-pole analysis models, we examined the torque, efficiency, and power factor of the FCM. We revealed that the magnet torque depends on the value of the winding factor and that the values of both the winding factor and field current determine the efficiency and power factor under variable-speed operation. We also present experimental results on a 20-pole prototype machine of the FCM to verify the operation principle in addition to the validity of the FEA simulations.

I. Introduction

Permanent magnet (PM) motors have been widely used for applications that require high torque and high power. However, because a negative d-axis current injection is employed to achieve high-speed operation, copper and iron losses increase. To address these issues, this paper proposes a novel flux-modulating consequent pole motor (FCM) that is a combination of a flux-modulating (FM) motor and a consequent-pole permanent magnet PM motor. The proposed FCM is shown in Fig. 1. The stator of the FCM comprises an armature winding (W_a) and field winding (W_f). The W_a is shared with both the FM and PM motors. The rotor of the FCM contains PM poles and iron poles, and the stator field magnetic flux modulated by the iron poles results in magnetic poles in the FM motor. In the FCM, unbalanced magnetic forces (UMFs) may occur even when there is no rotor eccentricity. These UMFs are greatly affected by the pole combinations of the FM and PM motors. The UMFs cause undesired vibration and noise, and thus accelerate bearing wear. Moreover, in the FCM, the torque cannot be generated from both the PM and FM motors depending on the pole combinations. Some studies [1]–[3] on motors have used a similar configuration to the FCM. However, they have not indicated a generalized pole combination by which UMFs do not occur and torque can be generated from both the FM and PM motors. In [4], our research group showed appropriate pole combinations of the FCM and revealed that the winding factors of the FM and PM motors affect the open-circuit flux linkage and flux-regulation capability. However, important characteristics, such as torque, efficiency, and power factor, have not been investigated. Fig. 1.

Proposed fcm.