Multi-path nonlinear dynamic compensation for rudder roll stabilization

The design of rudder roll stabilizers (RRS) for ships is complicated by yaw-axis coupling, non-minimum phase shift, and the angle and rate limits of the rudder. These saturations tend to limit the available feedback and restrict RRS implementation to vessels with very fast rudders. This paper describes the application of a Nyquist-stable RRS with a multiple feedback path nonlinear dynamic compensator to provide high performance with slower steering mechanisms used on larger vessels. The restrictive sufficient condition of absolute stability is satisfied for angle or rate saturation. Computer simulation results are included to show the efficacy of the approach.