Interior type permanent magnet synchronous motors (IPMSMs) have been widely used for various applications because of their high efficiency and high power density. It is well known that the flux weakening control of an IPMSM can extend the operating range by reducing the back-EMF and producing reluctance torque. An IPMSM, however, experiences a large harmonic iron loss in the stator teeth caused by the distorted flux density. In particular, the harmonic eddy current loss significantly increases in the high speed region under flux weakening control. This paper describes a novel motor-drive system that includes an individual multi-phase drive in order to control the current and voltage in each armature winding. The proposed system can be expected to achieve high efficiency driving, a wide operating range, fail-safety and so on. Furthermore, the proposed method gives the distorted flux density distribution a sinusoidal waveform, because the individual control can observe and regulate the instantaneous flux linkage in each stator tooth, although the motor consists of a full-pitch distributed winding. Therefore, the proposed drive can suppress the harmonic iron loss under the flux weakening operation. Simulation and experimental results show that the proposed method can achieve an extensive reduction in the total iron loss in particular in the high speed region.
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