Multivariable virtual reference feedback tuning for non-minimum phase plants

When applying model reference control to a non-minimum phase (NMP) plant, it is important to include the NMP (transmission) zero(s) in the reference model, otherwise the controller will tend to cancel out these zeros, often causing loss of internal stability. In data-driven (DD) control it is not possible to conceive a priori a reference model with the NMP zero(s) because no model of the plant is available; accordingly, DD design methods tend to fail in NMP plants. For single-input-single-output plants, this problem has been solved by using a flexible reference model in a DD design. This letter presents an extension of that method for multi-input-multi-output plants.