Modeling and Robust Control of Linear Direct-Drive Motors


The high precision position control of linear direct-drive motors requires the modeling of the system including the friction nonlinearity, reluctant and cogging forces together with the model parameter uncertainties. Besides, the model parameters may change in different operation points. In order to obtain a stable and high performance control system several robust control methods will be considered:

1. A discrete-time identified model is considered as the nominal model. All nonlinearities and parameter variations are considered as model uncertainties and disturbances in the frequency domain. Then a robust controller is designed based on the principe of loop shaping.

2. Several models are identified in different operating points then a robust multimodel approach is used to stabilize all models. Another approach is to use different controller for each model.

3. Each problem is locally treated. It means that the friction nonlinearity is compensated with feed forward or adaptive control. The cogging and reluctant forces which are position dependent are compensated using the ILC approach or a look-up table. Finally, the variation of the load inertia is compensated with a robust controller with respect to parametric uncertainty.