Controller design by frequency-weighted approximation-the multivariable case

The method presented offers an effective and time saving tool for multivariable controller design. The relation between controller complexity and achievable closed-loop system behaviour remains transparent in the design process. In some cases with largely different bandwidths of the diagonal elements of the plant, the described technique tends to achieve the goal of decoupling better than the approximation of the desired transient responses. This is caused by the weighting which in these cases assumes larger values over a broad frequency range for the off-diagonal elements. This can be prevented by the introduction of an additional factor in the weighting to influence the ratio of diagonal to off-diagonal weighting