Quasi-Resonant Control for Harmonic Current Suppression of a Magnetically Suspended Rotor

In the magnetically suspended rotor (MSR) system of the flywheel, harmonic current produced mainly by mass imbalance and sensor runout would cause undesirable harmonic vibration. Resonant control (RSC) is one of the remarkable performance alternatives for rejecting a set of selected frequency components of the periodic disturbance in a control system. Based on the intrinsic relationship between RSC and repetitive control, which is deduced and clarified, this paper proposes a novel quasi-resonant control (QRSC) scheme for a baseline prestable MSR system to suppress the harmonic current. By introducing a damping factor, QRSC achieves a good balance between stability and dynamic performance. With hybrid phase compensation, it provides system absolute stability and expands the stability margin of the MSR system. Further, as the domination of harmonic current, low-order frequency components are suppressed by parallel QRSCs (PQRSC). A stability criterion with rigorous proof for the plug-in PQRSC-controlled MSR system is addressed as well. Experimental results obtained with a magnetically suspended flywheel prototype corroborate the theoretical approach.