Additional Feedback Loop for Improved Control Robustness

Feedback control is ubiquitous in diverse fields. Most of existing control methods in general have a single feedback loop for each control objective. This paper proposes a new controller structure, which features an additional feedback loop to control the same output. With the additional loop, the robustness of the system can be enhanced. In particular, the influence of external disturbances can be significantly suppressed especially within the control bandwidth. It is also discovered that the addition of the second feedback loop does not necessarily sacrifice the stability and dynamics of the original system. The proposed control technique can be easily combined with various existing control methods by closing an extra loop outside the original one. Straightforward design procedure of the outer loop is also introduced. The implementation of the proposed dual-loop controller is illustrated with a grid-connected single-phase inverter and is verified in simulation.