Voltage balance and harmonic reduction for axial field permanent magnet synchronous generator with concentrated winding

Axial field permanent magnet machines are gaining wider acceptance day after day due to their advantages over the corresponding radial field machines. Concentrated winding are the choice whenever the simple manufacturing and the low-cost maintenance are the main concerns. The designer of such machine has the freedom to choose any number of coils and magnets. The first part of the paper introduces definite guidelines that help the designer choose a proper combination between number of magnets and number of concentrated coils to get balanced multi-phase voltage waveforms which is a must for a multi-phase generator. The second part of the paper investigates the harmonic reduction of the generator output voltage waveform. The main concern is given to the coil design to achieve that goal by selecting a proper coil span for a certain pole pitch. The paper proposes derived equations to calculate the minimum and maximum allowed values of the coil span to help the designer select a proper value. The double-rotor single-ironless-stator construction is taken as a model to develop the proposed equations and guidelines. Three-dimensional finite element method (3D-FEM) is used to simulate the output voltage of the studied generators. The effectiveness of the proposed equations and guidelines is validated using both 3D-FEM and experimental results.