Switching control between three-coil and five-coil modes for six-pole active magnetic bearings

Abstract

Six-pole active magnetic bearings (AMBs) have fewer poles than the more common eight-pole AMBs making it possible for them to be miniaturized and used in the development of small motors. In this paper, we propose a novel control method for the six-pole AMB, which switches between three-coil and five-coil modes. The three-coil mode excites three coils to generate a suspension force and reduce power consumption. In contrast, the five-coil mode excites five coils and can generate a larger maximum force than the three-coil mode. By switching between the two modes, it is possible to realize both an increase in the maximum suspension force and a reduction in power consumption. This paper derives the coil currents in the three- and five-coil modes, and introduces a switching method between them. The proposed method is verified with a test rig, and results show that the proposed method enables stable levitation with a lower current limit compared with the method that uses the three-coil mode alone. Moreover, a start-up procedure with a low current limit is proposed and experimentally verified.

Keywords

• active magnetic bearing
• six-pole stator
• control current
• power consumption
• switching control
• three-coil mode
• five-coil mode
• rotary machinery