Design and analysis of brushless DC machines

The brushless DC drive is now widely used and conventional design methodology determines key dimensions to give the required pole flux and the target torque/speed characteristics. However these analytical procedures give only limited information on saturation, armature reaction, and space/time variation of flux arising from MMF and permeance harmonics. This additional information can be provided by finite element techniques. This paper describes the application of transient magnetic finite element techniques to brushless DC machines involving permanent magnets, magnetic nonlinearity, induced currents, rotor movement and associated inverter circuits. The approach is being used to investigate and aid optimisation of machines under constant current and voltage forced operating conditions. Computed results for static/low speed torque ripple and dynamic current waveforms show close agreement with measured values.