New Compensators for Non-Minimum Phase Systems

Non-minimum phase systems are relevant class of dynamic systems with unstable internal dynamics. For such systems, even though the complementary external dynamics are stabilized by state-feedback control, internal states may still converge slowly or even diverge. Focusing on linear systems, transfer functions of non-minimum phase systems show zeros in the positive complex half-plane. It is known that if there is an odd number of real-valued positive zeros in the transfer function, then the associated step response shows at least one undershoot which is more pronounced the more such zero is closer to the imaginary axis. This performance impairment cannot be easily counteracted by classical compensators as unstable pole/zero cancellation would internally destabilize the entire control loop. Thus, customary controller designs accept a lower performance. In past common research, the involved PIs found a feasible pole/zero cancellation technique that compensates some fractional-order minimum phase components of the numerator polynomial. Such action will still render the control loop internally stable. Since this approach is entirely novel, there is a number of open questions that shall be addressed and answered in the solicited project. The main scope of the collaborative research encompasses the analysis of system dynamics, the compensator design for the non-minimum phase systems, and its application in case studies. In order to reach the individual project targets, the project will implement several practical measures and further strengthen the academic relationship between the research groups at UiA in Norway and TU-Ilmenau in Germany. Synergies expected from the complementary cooperative research will increase visibility of both groups on national level and within the international communities of control and systems engineering. It will also contribute to an enhanced education quality of the master and doctoral students, and postdoc experience at both institutions.