Optimal Commutation Law for Three-Phase Surface-Mounted Permanent Magnet Linear Synchronous Motors

Sinusoidal commutation of phase currents leads to force ripple, if the motor back-EMFs differ from ideal case. Force ripple reduces the tracking performance significantly, if no compensation methods are applied. This paper presents a method to optimize the commutation in order to prevent force ripple. No assumptions of periodicity, symmetry, shape or balance of the motor back-EMFs are made. The proposed commutation law considers nonidealities of motor and amplifier. It is based on non-parametric force functions, which are identified in a proposed procedure. The optimal commutated currents produce minimal winding losses and therefore maximize imize motor efficiency. The commutation law is valid for any velocity and any desired thrust force. In this research, three-phase synchronous motors with surface-mounted magnets are considered. Experiments are performed with a linear motor, but the results are also valid for rotating motors.