Discrete-Time Control of High-Speed Sensorless Electrical Drives

High-speed sensorless electrical drives are gaining a considerable interest in the last years for applications ranging from automotive to aeronautical sector. In modern electrical drives, the control algorithms are commonly implemented in the discrete-time domain. As regards the design of these controllers and position estimation observers, a commonly adopted procedure consists in designing the algorithm in the continuous time and subsequently discretizing the control law. However, the effectiveness of such procedure is guaranteed as long as the fundamental-to-switching frequency ratio remains sufficiently small; whereas, for higher values of that ratio, the performance of the closed loop system progressively worsens leading to the instability. In this paper, the control law is synthetized in the discrete-time domain considering the delay introduced by the position estimation procedure. The digital implementation of a simple position observer is also discussed. A permanent magnet motor has been considered as a case study, even if the presented approach could be easily extended to other types of electrical machines. The effectiveness of the proposed approach is validated by means of simulations and experimental tests.