Advanced optimization methods for fractional slot concentrated windings

Usage of fractional slot concentrated windings (FSCWs) in electrical machines offers several advantages due to their simplicity and compactness. However, the magnetic field of FSCWs has more space harmonics, including sub-harmonics that lead to undesirable effects. High rotor losses, noise, vibrations and thermal problems are the main drawbacks caused by FSCWs. These disadvantages limit the suitability of this winding type for some applications. In order to improve winding performances, several methods and techniques have recently been developed and analysed. This paper provides an update of latest research activities in terms of optimization of FSCW machines. These include efforts to reduce only sub-harmonics, to simultaneously reduce sub- and high harmonics or to use a higher harmonic for rotor excitation in current-excited synchronous machines. Simplest and most effective methods are considered, and their functionalities are explained briefly. Moreover, the effectiveness of said optimization methods is shown by simulation and experimental results, obtained from various optimized FSCW machines.