Power amplifiers based on power electronic converters have become one of the ideal physical interfaces for grid voltage simulation due to their flexibility and ease of control. Addressing the drawbacks of existing power amplifier control methods, which can amplify frequency deviations, cause filter circuit parameter drifts, and make it difficult to simulate high-frequency harmonics, an ultra-wideband control strategy for harmonic power amplifiers with mixed feed-in adaptive compensation is proposed. This strategy aims to accurately reproduce wideband voltage signals while balancing dynamic and steady-state performance. Next, a multivariable mixed feed-in loop is designed to compensate for the transient characteristics of the system. In the time domain, an adaptive method considering parameter drifts is derived using the Lyapunov function to compensate for uncertainties in filter parameters. The limitations of digital implementation in mixed adaptive compensation are thoroughly analyzed and overcome. The performance enhancement of the proposed method as a repeated embedded control is discussed. Finally, a prototype is built, and simulations and experiments are conducted to verify the dynamic performance and steady-state accuracy of the proposed strategy. The results indicate that compared to existing controls, the proposed method offers faster dynamic response, higher steady-state accuracy, and a wider range of harmonic frequency tracking. It can achieve rapid and error-free tracking of ultra-wideband reference voltages.