Mathematical modelling and control of bearingless brushless direct current machine with motor and generator double modes for flywheel battery

Abstract

The performance of flywheel battery is affected by the vibration and friction of traditional mechanical bearing. A novel kind of bearingless brushless direct current machine (BBLDCM) with the hybrid capabilities of electrical machine and suspension is suitable for flywheel battery which reduces the losses and improves the power quality. The structure and the principle of suspension force in generator are introduced first. Then, the mathematical models of BBLDCM are deduced, especially the mathematical models of suspension force in motor and generator modes. The finite element analysis (FEA) is carried out to prove the validity of the mathematical model and distinguish the difference of mathematical models between the motor mode and the generator mode. Furthermore, the control system of the BBLDCM is established according to the mathematical model deduced above. The simulations of rotation, power generation and suspension are accomplished. Finally, the experiments are carried out through the BBLDCM digital control platform. The results of simulations and experiments show an excellent working performance and a stable suspension of rotor without any mechanical contact of BBLDCM in both motor and generator modes which verify the validity of mathematical models.