As fuel cell systems evolve towards the higher power outputs, higher requirements are imposed on air supply capacity and compressor driving power. At present, the power of a single-stack fuel cell system has exceeded 350 kW, which further raises the control requirements of air compressors operating under high-power, high-speed, and wide-speed-range conditions. However, the conventional motor control strategies suffer from the reduced speed estimation accuracy, insufficient system robustness, and degraded steady-state performance under the high-speed operation conditions. To address these issues, a motor controller of high-speed, high-power fuel cell air compressors is designed and developed, and an adaptive sliding mode observer with the novel wide-speed-range is proposed. Based on the traditional sliding mode observer structure, a wide-speed-range saturation function with variable boundary layer is introduced. On one hand, its piecewise regulation characteristics enable the smooth switching, effectively suppresses chattering and improving the speed estimation accuracy. On the other hand, its variable boundary layer allows the dynamic adjustment according to motor speed and estimation error, thereby enhancing the steady-state performance under high-speed conditions. As a result, the proposed method effectively improves the speed estimation accuracy under the high-speed operation and enhances the steady-state performance. The controller employs the silicon carbide power modules to construct a three-phase inverter with a maximum output power of 80 kW and a maximum speed of 80 000 r/min, which can meet the air supply requirements of 200~500 kW fuel cell systems. A high-speed air compressor experimental platform is constructed and compared with the traditional sliding mode observer algorithm. The results show that the controller can achieve stable and reliable motor drive, whose speed fluctuation range is significantly reduced under the high-speed operating conditions. The speed fluctuation at 80 000 r/min is decreased from ±150 r/min to ±90 r/min with a reduction rate of approximately 40%, which significantly improves the speed stability and estimation accuracy, thus verifying the effectiveness of the proposed method.