Abstract— This paper presents a proposed Horse Herd Optimization (HHO) technique for tuning a PI controller of a Multi-Function Converter (MFC) system. The MFC system consists of the converter and its associated controls. It is used to mitigate harmonic distortion caused by a Variable Speed Drive (VSD) operated in a modified Cigre benchmark 14-bus distribution network. Moreover, the MFC system is used to provide reactive power compensation for achieving unity power factor at the Point of Common Coupling (PCC). First, voltage and current harmonics at all buses are calculated in accordance with the IEEE Std. 519-2022 requirements. Five cases are considered for studying the harmonic distortion mitigation, using the MFC system: (i) no MFC system; (ii) installing an MFC system controlled by a hysteresis controller; (iii) installing an MFC system controlled by a fuzzy logic controller; (iv) installing an MFC system controlled by a PI controller tuned by Particle Swarm Optimization (PSO) method; and (v) installing an MFC system controlled by a PI controller tuned by the HHO method. Second, the reactive power compensation using the MFC system is investigated when switching an RL load at the VSD busbar for achieving unity power factor. Simulation studies are performed based on the MATLAB/Simulink software. The results have shown that the MFC system with the proposed HHO-tuned PI controller provides the most reduction in currents and voltages harmonic distortions compared to the other controllers. The Total Demand Distortion (TDD) of the current is reduced from 25% to 2.7% after installing the MFC system, which indicates a significant reduction of harmonics. Moreover, the MFC system proved to capable for providing the required reactive power to maintain unity power factor at the PCC, even if an additional RL load is added at the same bus.