Multivariable feedback design to improve tracking performance on tractor vibration test rig

The multivariable tracking accuracy on an automotive vibration test rig can be improved by extending the current industrial off-line iterative feedforward procedure with a real-time multiple-input-multiple-output (MIMO) feedback controller. This paper shows that for the considered 4×44×4 application, the two most common approaches, namely full MIMO identification and μμ-synthesis on one hand and decentralised control on the other hand fail to design a robust MIMO controller with acceptable performance. Therefore, a control design based on static decoupling is applied. This is a combination of (1) a transformation of the inputs and the outputs to decouple the system, and (2) independent single-input-single-output (SISO) controllers designed for the diagonal elements of the transformed system, using standard SISO identification and H∞H∞-techniques. To optimise the closed-loop performance, a new decoupling algorithm is developed. The new presented algorithm outperforms the existing decoupling algorithms, yielding satisfactory multivariable closed-loop performance.