Variable polarity LMS feedback based on displacement nulling to compensate unbalance of magnetic bearing

In consideration of the decrease of high-speed motor magnetic rotor displacement accuracy generated by unbalance vibration, a LMS feedback algorithm based on the principle of displacement nulling was proposed. The generalized dynamic stiffness of the system was improved by online identifying the same-frequency component in displacment signal and adding feedback to achieve unbalance compensation. In addition, the stability of close loop system was analyzed by use of generalized root locus; meanwhile, to cross over the critical frequency and achieve the displacement compensation within the whole speed range, a variable polarity strategy was raised. The experiment results demonstrate the method can suppress the displacement same-frequency vibration effectively within the whole speed range.