This paper proposes an adaptive fixed-frequency hysteresis band control method for a unified power quality conditioner (UPQC). First, a detailed analysis of the mathematical model and control for UPQC is performed. The series inverter is controlled to compensate for harmonic distortions in the source voltage, thereby maintaining a balanced voltage waveform applied to the load with harmonic distortion within permissible limits. Simultaneously, the shunt inverter is controlled to compensate for the current harmonics generated by nonlinear loads. The reference voltage for compensation is determined based on the distorted source voltage, while the reference harmonic current is derived using the i_p–i_q harmonic detection method. The harmonic mitigation performance of the UPQC is evaluated under two control scenarios. In Scenario 1, a conventional proportional integral (PI) controller is used for DC-link voltage regulation, and traditional hysteresis band controllers are used for both the series and shunt inverters. In Scenario 2, a fuzzy-PI controller is applied for DC-link voltage regulation, along with an adaptive fixed-frequency hysteresis band controller for both the series and shunt inverters. Simulation and experimental results under ideal, sag, swell, unbalanced, and distorted source-voltage conditions demonstrate that Scenario 2 is more effective than Scenario 1 in reducing the total harmonic distortion (THD) of the supply current and the load voltage and in stabilizing the DC-link voltage.