High-Bandwidth Sensorless Control of Synchronous Reluctance Machines in the Low- and Zero-Speed Range

Two aspects of sensorless control of synchronous reluctance machines (SynRMs) in the low-speed and zero-speed range are gaining more and more importance: how to achieve a high control bandwidth and how to lower the test current amplitude to minimize audible noise and high-frequency (HF) losses. A high control bandwidth can be realized by a square-wave-shaped voltage injection (SWSVI). This article presents a new approach, controlling the current ripple generated by the SWSVI constant and simultaneously maintaining a minimum required HF test current amplitude. The proposed solution is optimized for the highly nonlinear machine behavior of SynRMs combined with a standard industrial inverter using regular current sampling. A new low-noise current demodulation by a Kalman filter and its empiric tuning is presented. The prediction step of the filter compensates for the dead time of the control algorithm. Experimental results confirm the excellent performance. Compared to the conventional binomial filter, only half of the test signal amplitude is required. The mean square error of the current demodulation was reduced by 90%.