Sensorless Control for a Nonsinusoidal Seven-Phase Surface-Mounted PM Machine

This article addresses the position sensorless control of a seven-phase surface-mounted permanent magnet (SPM) machine with highly nonsinusoidal back electromotive force (emf), which is termed biharmonic as fundamental and third harmonic are of the same order. The control is implemented through a vector decomposition of the seven-phase machine into three magnetically independent virtual machines, each of them been controlled in its own rotating frame. Three electromotive force methods to evaluate the rotor position can thus be achieved and the method will be all the robust as the current of the relative virtual machine is null. Since the rated control aims at producing the torque from the first and the third harmonics, the fifth harmonic of the back emf is used to estimated the position. Simulation and experimental tests show the real possibility of this approach. In particular, an original and specific startup procedure is developed, that is based on the sequential use of different virtual machines.