Objectives  To solve the steering control problem of X-rudder submarines under different available rudder surfaces conditions, the rudder control distributor of an X-rudder submarine is designed.

  Methods   A cascade control structure including a main controller and control allocator is adopted in the design of the steering control system. The main controller adopts an existing mature algorithm, and a constrained control allocation algorithm is designed by converting the rudder angle control allocation problem with the rudder angle and rudder speed limit to solve the weighted least square (WLS) problem. The control allocation algorithm is verified through a simulation of turning at certain depths and diving in three operation cases (i.e. quadruple rudder, triple rudder and double rudder).

  Results  Under the given rudder conditions, with the decrease in the steering surface, the difference in the submarine's diving performance is not significant, turning performance is reduced slightly and heeling and rudder angle oscillation tends to be serious.

  Conclusions  The simulation results show that the control allocation algorithm is reasonable and suitable for different rudder configurations.