Considerations of non-sinusoidal field distribution in a permanent magnet synchronous motor control

Permanent magnet synchronous motors are often used in variable speed drive applications. In classical controls, flux distributions are supposed sinusoidal with the angular rotor position. The fed currents are sinusoidal to give a desired constant torque. With these assumptions, in the d-q rotating frame bound to the rotor all electrical values are constant. Synchronous motors with interior permanent magnets are often used for their high power-to-weight and torque-to-weight ratios. These motors with flux enhanced arrangement have a nonsinusoidal field distribution and their electrical parameters vary in the d-q frame with the angular position. Consequently usual sinusoidal fed currents produce torque ripple which leads to vibrations and mechanical instabilities. Other inconveniences due to nonsinusoidal field distribution can appear in other drives applications. For example, in control without mechanical sensors, inductances harmonics affect the estimation of position. In this paper, an analysis of the influence of nonsinusoidal field distribution in permanent magnet synchronous motors is made for different controls