In three-phase three-wire power systems, unified power quality conditioners (UPQCs) compensate for current/voltage fluctuations while enhancing load-side power quality. However, current solutions face three key limitations: (1) limited responsiveness to rapid disturbances, (2) sensitivity to grid variations, and (3) inadequate phase-locked loop (PLL) performance, all of which undermine compensation effectiveness. Traditional proportional-integral (PI) controllers further exacerbate these issues through overshooting during control quantity disturbances. This paper proposes an enhanced finite control set model predictive control (FCS-MPC) system integrated with linear active disturbance rejection control (LADRC) to improve UPQC's anti-disturbance capabilities. The architecture combines a series active power filter (APF)-side voltage compensation module based on FCS-MPC, a shunt APF-side current compensation module based on FCS-MPC, and a LADRC-optimized mixed second/third-order generalized integrator-based PLL (MSTOGI-PLL). Through rigorous MATLAB/Simulink simulations, the proposed UPQC demonstrates superior robustness compared to conventional controllers, achieving 85% voltage sag compensation within 12.5 ms response time. Simulation result validation confirms that the LADRC-enhanced FCS-MPC system significantly improves disturbance rejection, yielding effectively reduced voltage total harmonic distortion (THD) and enhanced post-compensation power quality across various grid anomalies.