A Robust Three-Degree-of-Freedom Digital Current Controller for High-Speed PMSM Drives With <i>LC</i> Filter

Most current controllers for motor drive systems with inductor-capacitor (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i>) filter achieve two-degree-of-freedom (2DOF) functions, where one degree ensures reference tracking and the other provided by active damping for resonance suppression. However, disturbance rejection is often overlooked, causing a certain amount of current ripple that degrades performance in high-speed motor operation. To address this limitation, this article proposes a robust 3DOF current controller that simultaneously achieves high dynamics, resonant suppression and disturbance rejection functions without the need for a high-order observer and extra sensors. Furthermore, a frequency-domain analysis and parameter design approach are provided to guide digital implementation with high parameter robustness. Finally, the efficacy, superiority and robustness of the proposed method are substantiated through comprehensive experiments on a 30-kW high-speed motor bench with speed up to 90 kr/min.