Design and control of a field intensified interior permanent magnet synchronous machine

Permanent magnet synchronous machines (PMSMs) have been used in various applications owing to the high power density of the magnets. Especially interior permanent magnet synchronous machines (IPMSMs) are attractive in high power density applications since IPMSMs can generate both magnet torque and reluctance torque, and the field weakening control can reduce the output voltage. However, a lot of field weakening current is required to generate a lot of reluctance torque, the carefully magnet design, the thick magnet is used, is needed not to demagnetize the magnet. Hence, the cost of the magnet increases and the operating temperature is limited. In this paper, a field intensified IPMSM (FIIPM) is proposed. The proposed FIIPM has a forward saliency and the positive current on the direct axis is added in order to the magnet to generate a reluctance torque. The technique of adding the positive current contributes the magnet not to demagnetize, and using a thick magnet to protect from the demagnetization is not necessary. This paper shows that IPMSMs are difficult to generate more reluctance torque than magnet torque by using a relationship between saliency and torque ratio. The FIIPM is introduced as a possible design option for high reluctance torque machine. The general characteristics of FIIPMs are analyzed using finite element analysis (FEA).