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This paper presents a simple, robust controller for use in speed control of an internal combustion engine for series- hybrid electric vehicle applications. Particular reference is made to the stability of the rectified DC link voltage under load disturbance and potentially inaccurate system models. In the system under consideration, the primary power source is a 4-cylinder normally aspirated gasoline internal combustion engine, which is mechanically coupled to a three-phase permanent magnet AC generator. The generated AC voltage is subsequently rectified to supply a lead-acid battery, and permanent magnet traction motors via three-phase full bridge power electronic inverters. Two complementary performance objectives exist. Firstly to maintain the internal combustion engine at its optimal operating point, and secondly to supply a stable 42 V supply to the traction drive inverters. Achievement of these goals minimises the transient energy storage requirements at the DC link, with a consequent reduction in both weight and cost. These objectives imply constant velocity operation of the internal combustion engine under external load disturbances and changes in both operating conditions and vehicle speed set-points. An electronically operated throttle allows closed loop engine velocity control. System time-delays and non-linearities render closed loop control design extremely problematic. A model based controller is designed and shown to be robust in controlling the DC link voltage, resulting in well-conditioned operation of the hybrid vehicle.