Sensorless Control with Indirect Field Oriented Speed Estimation for Seven-Phase Induction Machines

Multiphase machines offer more degrees of freedom than conventional three-phase machines. Thus, a multiphase drive can control multiple spatial harmonics independently of each other. With the torque generation in the 1 stvector space, this paper proposes to inject currents in the 3rd vector space for the speed estimation thus realizing a sensorless control scheme. At lower mechanical speeds, the back-EMF decreases and becomes more difficult to estimate as the signal-to-noise ratio decreases. Injecting a slip increases the stator frequency, which in turn allows a better estimation of the back electromotive force. An experiment showing a start from standstill conditions demonstrates the proposed control.