Comparative performance analysis of field-oriented control and direct torque control for a fractional-slot concentrated winding interior permanent magnet synchronous machine

This paper presents performance analysis of a fractional-slot, concentrated, non-overlapping winding Interior Permanent Magnet (IPM) Synchronous Machines under two commonly used control strategies: rotor field oriented control (RFOC); and Direct Torque Control (DTC). Application of concentrated winding to IPM machine is gaining attention from research community because of its advantages such as high-power density, high efficiency, short end-turns, wider flux-weakening capability, fault tolerance, robust rotor, and presence of additional reluctance torque component. The major disadvantage of concentrated winding is non-sinusoidal magnetomotive force (MMF. However, using appropriate combination of slots and poles, sinusoidal EMF and low cogging torque can be achieved despite presence of MMF harmonics. A 14-pole/ 18-slot, double layer concentrated winding IPM machine had been designed and constructed at the University of New South Wales. Above mentioned two control schemes were applied to this constructed prototype machine. The performances of the two control schemes are compared in terms of torque and current ripple, transient responses for the step variations of speed and load under maximum torque per ampere and field weakening regions. Both RFOC and DTC are based on the dq model of the machine which assumes sinusoidal variation of MMF. The experimental result of the concentrated winding IPM machine indicates that the conventional dq model starts to deteriorate in the field-weakening region resulting in a steady-state error between estimated flux and measured flux. This paper attempts to investigate the sources of this error and causes of deterioration of the dq model. This work is a preliminary investigation for the possible improvement in the control schemes of the concentrated winding IPM machine.