Improved Nonlinear Robust Controller for STATCOM Based on System Immersion and Manifold Invariant Methodology

The problem of designing an improved nonlinear robust controller is addressed adopting three perspectives for static synchronous compensator (STATCOM) system in the presence of time-delay, uncertainty parameter and external disturbances. At first, in order to reduce high degree coupling between system state variables and estimation errors, uncertain parameter is estimated by using the system immersion and manifold invariant (I&I) control which can ensure that the estimation errors converge to zero without using certainty equivalence principle. Secondly, since STATCOM system in practice almost contains time-delay nonlinearity and external disturbances, backstepping sliding mode control are adopted to design the control law recursively. At last, to solve the problem of robustness cannot be guaranteed before the motion orbit reaches sliding mode surface. The dissipation inequalities with external disturbances are constructed in each subsystem, which can ensure that nonlinear robust controller has a good stability and strong robustness in real time. Compared with adaptive backstepping sliding mode and adaptive backstepping, the contrastive simulations result show that the time of reaching steady state is shortened by at least 31%, and the oscillation amplitudes of transient responses are reduced by nearly half.