Using and enhancing the cogging torque of PM machines in valve positioning applications

Abstract

In this study, it is aimed to use the cogging torque of permanent magnet (PM) machines for providing the load torque in the valve positioning applications. The policy is to use the machine cogging torque to overcome the load torque at the steady-state condition (fixed valve position). Therefore, there is no excitation, and no armature Joule losses at the steady-state condition and consequently lower thermal stress for the machine. To have a more compact actuator, it is tried to increase the machine cogging torque. Two well-known types of PM machines, i.e. surface-mounted PM (SPM) and flux-switching PM (FSPM) machines are studied to be applied in this application. Some techniques such as applying auxiliary slots and PM segmentation (for the SPM machine) and two-part rotor topology (for both SPM and FSPM machines) are proposed to increase the machine cogging torque. The impact of each technique on the developed cogging torque is studied by means of finite element analysis. Finally, the SPM and FSPM machines are compared together in the terms of the torque density. The validity of the proposed concept of providing the load torque by the cogging torque is investigated by experimental tests.