UPS-Integrated Reactive Power Compensation to Avoid Capacitor Bank Expansion

Abstract

The increasing penetration of nonlinear industrial loads necessitates effective reactive power compensation to maintain voltage stability and operational efficiency of the power system. Although capacitor banks are widely deployed in industrial distribution systems, their discrete control characteristics often fail to mitigate rapid voltage fluctuations. In contrast, dedicated power electronic compensators offer continuously adjustable reactive power. However, their high capital and maintenance costs remain significant obstacles to industrial adoption of these technologies. This study proposes a reactive power compensation dispatch strategy that utilizes the spare inverter capacity inherently available in redundant uninterruptible power supply systems used to protect sensitive industrial equipment. A day-ahead optimization framework based on mixed-integer quadratic constrained programming is developed to coordinate the continuous reactive power provided by these inverters with the discrete switching behavior of conventional capacitor banks. Numerical simulations of a 33-bus distribution system demonstrated that the proposed hybrid strategy significantly enhanced grid performance compared with capacitor only operation, achieving a 38% reduction in voltage deviation and a 17% reduction in total power loss while maintaining the substation power factor near unity. These results confirm that spare inverter capacity within an uninterruptible power supply infrastructure can function as an effective source of reactive power, thereby reducing the need for the expansion of capacitor banks in industrial distribution systems.