This paper introduces an adaptive fuzzy PI controller (AFPIC) for a flexible AC transmission system (FACTS) based dynamic power filter (DPF) to be used in wave energy conversion systems. The new FACTS device stabilizes the DC-common bus voltage, reduces quality of power troubles, and enhances energy utilization by acting as a bus quantity enhancer (BQE). The design and realization of the proposed FACTS-based DPF and efficient control schemes are fully studied. To validate the efficiency of the proposed BQE FACTS device, a digital simulation model and a laboratory test system are developed in the MATLAB/Simulink/Simpower software environment for comparison. Various experimental test models of the proposed BQE system and dynamic error-based controller structures have been utilized to verify the simulation results. It has been shown that the utilization of the proposed AFPIC with the novel BQE device and multivariable error driven control strategy is very effective to eliminate stochastic wave influences on voltage on the load side and load variations on the source side by decreasing voltage sag and swells. The effectiveness of the BQE is also tested by applying error energy-based performance indices ISE, IAE, and ITAE.