Sensorless Control Design of High-Speed Electric Drives in Discrete-Time Domain for Mild-Hybrid Turboprop Aircraft Applications

High-speed permanent magnet synchronous machine (PMSM) sensorless control design is not without challenges, especially when the ratio of power electronic modulation frequency to the electrical fundamental frequency (M-F ratio) is relatively low. The model reference adaptive system (MRAS) is a mature sensorless control method and has been widely used in industrial drives. There, an observer is commonly used to estimate rotor speed and angle using machine voltages and currents. The estimated angle is then further implemented for voltage and current frame transformations. Thus, the MRAS sensorless control is indeed a strong-coupled, multivariable, and nonlinear system. This article proposes a detailed MRAS sensorless control system design method in the discrete-time domain for high-speed drives with relatively low M-F ratio with good system stability confidence. A detailed discrete local-linearized small-signal model is developed, and the state-space evolution matrix of the current closed-loop system has been derived. The system stability can be defined and analyzed with its maximum eigenvalue, and the controller design is to make sure that the maximum eigenvalue is falling within the stable region. This proposed design method has been validated on a dual three-phase PMSM by simulation and experiment results with selected stable design points.