Improved Active Disturbance Rejection Sliding-Mode Speed Control of a Marine Steam Turbine Generator for MVDC Power Systems

In marine medium-voltage direct-current (MVDC) power systems, load variations can disturb the power balance of steam turbine generator sets and cause shaft-speed deviations. This study develops an active disturbance rejection control–sliding-mode control (ADRC-SMC) strategy for turbine speed regulation while accounting for steam-volume dynamics and nonlinear electro-hydraulic actuator constraints. A nonlinear governing-system model incorporating rotor power balance, steam-volume dynamics, actuator deadband, position saturation, and rate limits is established and transformed into a second-order control-oriented ADRC form. A linear extended state observer (LESO) estimates the system states and total disturbance, while a smooth nonlinear speed-error sliding surface, a smooth power reaching term, and a leakage-type smooth super-twisting-like dynamic compensator are introduced to suppress residual disturbances after a LESO compensation. Composite Lyapunov analysis establishes uniform ultimate boundedness under bounded disturbance variation and asymptotic convergence when the total disturbance becomes time-invariant. Under a 50% rated-load increase, the proposed ADRC-SMC reduces the maximum speed undershoot and settling time by 21.36% and 61.46%, respectively, compared with linear active disturbance rejection control (LADRC). Under 100% load rejection, the maximum speed overshoot is reduced by 6.45% compared with LADRC and by 24.08% compared with baseline ADRC-SMC. Multistep-load simulations further confirm stable speed recovery under successive load changes.