Back-EMF waveforms and core losses in brushless DC motors

The paper describes a self-consistent set of algorithms applicable to the calculation of the back-EMF waveform of any winding distribution in all the main classes of radial-airgap brushless DC motor, together with the no-load core losses. The algorithms depend on an approximation of the airgap flux-density distribution, and include new methods based on the flux linkage and EMF waveforms of a single-turn coil wound around one tooth. The paper describes the methods used to calculate these waveforms and their application to the calculation of core loss and total winding EMF. The methods are validated using test data from a range of widely different designs, and by finite-element calculations. Because of their speed and physical simplicity, the algorithms are particularly useful in integrated CAD software which simulates the operation of the complete drive system at the same time as building up the motor design from basic dimensions. The structure of the calculations is such that measured or finite-element data can easily be incorporated for checking or calibration purposes.