In this brief two sliding mode control alternatives to regulate the stator voltage amplitude for a stand-alone wound rotor synchronous generator are presented. Both controllers use the stator voltage -component error in the sliding surface. In a first case an outer proportional-integral (PI) loop controller is added to provide the proper d-voltage component reference. The second approach consists in extending the dynamic system to include the integral term as state variable and to modify the former sliding surface by adding this new state. Finally, both simulations and experimental results validates the proposed algorithms.