The invention relates to a speed controller comprising: a rectifier module (12) for generating a direct voltage on a power bus (10, 11) from an alternating voltage available on an electrical power-supply network (A); a bus capacitor (Cb) connected between a positive line and a negative line of the power bus; and an inverter module (13) powered by the power bus and controlled to deliver an alternating voltage to an electrical load (2); a protection device (14) for protecting the controller against overcurrents linked with voltage variations on the electrical power-supply network (A).