SUMMARY
The desire for an enhanced power transfer capability and quality of electricity delivered to the customers has led to emergence of Flexible Alternating Current Transmission Systems (FACTS). This work compares power system voltage stability with and without compensation. The compensation is done by optimal placement of Unified Power Flow Controller (UPFC) using Artificial Neural Network (ANN) technique. The algorithm to implement the stabilizing processes employed Newton-Raphson-based load flow equations in MATLAB R2018a environment. The stability of Nigerian 330 kV, 30–bus network was assessed before and after the implementation of UPFC and UPFC-ANN controlled. The results obtained without compensation showed: New Haven, Onitsha, Gombe, Jos, Kano and Calabar with voltage magnitude of 0.9003, 0.9468, 0.6608, 0.8141, 0.8138 and 0.9319 p.u, respectively violated the statutory limit of 0.951.05 p.u and total active power loss was 218.76 MW. With UPFC on bus Calabar, the total active power loss reduced to 200.85 MW, while buses New Haven, Gombe, Jos and Kano produced voltage magnitude of 0.9130, 0.6608, 0.8141 and 0.8138 p.u, respectively, still constrained. ANN based UPFC placement on bus Gombe - the most critical bus with Voltage stability index (VSI) of 0.9252, the voltage magnitude of buses New Haven, Onitsha, Gombe, Jos, Kano and Calabar enhanced to 0.9533, 0.9552, 1.0481, 1.0399, 1.0425 and 1.0081 p.u, respectively and total active power loss reduced by 28.81% compared with 8.19% reduction with UPFC. The study revealed ANN controlled UPFC is suitable and appropriate for improving voltage stability and reducing power loss on power system.