Then by the vibration compensation controller, a vibration compensation force is generated, which is used to suppress or eliminate the unbalanced displacement.
Secondly, in the u-v coordinate system, the given signals of unbalanced displacement components are set to zero; then through the closed-loop controls of [u.sub.m] and [v.sub.m], the given signals of vibration compensation force components in the u-v coordinate system, i.e., [F.sub.cu]* and [F.sub.cv]*, are obtained.
Figure 3 shows the schematic diagram of unbalance vibration compensation controller, where [alpha] and [beta] are the measured radial displacements; [u.sub.m] and [v.sub.m] are the unbalanced displacement components in the u-v coordinate system; [F.sub.cu] * and [F.sub.cv]* are the vibration compensation force DC signals in the u-v coordinate system; [F.sub.ca]* and [F.sub.c[beta]]* are the vibration compensation force AC signals in the [alpha]-[beta] coordinate system.
Because the output variables of the BLIM inverse system are current signals, the "force/current" transformation is needed to convert the vibration compensation force to the vibration compensation current.
Replacing [F.sub.[alpha]] and [F.sub.[beta]] in (7) with [F.sub.c[alpha]]* and [F.sub.c[beta]]*, then the analytical formula of vibration compensation current can be derived as follows:
In (25), ([i*.sub.c2m] and [i*.sub.c2t] are the given signals of the vibration compensation current components along the m and t-coordinate axes.
Figure 6 shows the displacement response curves before vibration compensation. From Figure 6, (1) without vibration compensation, under the action of the displacement closed-loop control, the rotor unbalance vibration occurs; the radial displacement components along the [alpha]- and [beta]-coordinate axes present periodic fluctuations
(2) after the BLIM control system enters its steady state, under the combined action of the random displacement controller and the vibration compensation controller, the unbalanced displacement components along the [alpha]- and [beta]-coordinate axes gradually decrease to zero; the rotor axis trajectory almost shrinks to the stator center; the suspension control precision of rotor has been greatly improved