Electric spring for power quality improvement

In this paper, we discuss the principles of operating the electric spring (ES) as a reactive power compensator and as a power factor corrector. The theory on electric springs with capacitors for voltage stabilization is reviewed to present a general idea on the behavior of ES. Further discussion focuses on the principle of ES with batteries to cover its eight possible operating modes and their usefulness in providing line current regulation. An input current control scheme is designed for ES with batteries to validate its capability in power factor correction. A low-voltage single-phase power system with different types of loads has been built for verifying the feasibility of proposed theory of ES with batteries. Experimental results show that the ES is capable of performing the eight operating modes when changing the power consumption of the non-critical load, and that with the proposed input current control, the ES can achieve power factor correction for both RL and RC loads.