A seamless transfer algorithm based on active frequency detection with feedforward control method in distributed generation system

Abstract

This paper proposes a control strategy for grid-interactive Power Conditioning System (PCS) with feedforward control method based on active frequency detection. PCS should supply the power to critical loads continuously regardless of grid condition. Hence, PCS detects grid condition fast and transfers between two operation modes smoothly. In addition, it also important to detect its operating condition accurately for safety. In most of cases, PCS can detect its operation mode. However, when PCS operates in Non-Detection Zone (NDZ) condition, power gap between PCS and load is almost same, it cannot detect its operation mode precisely. Hence, other technique is needed to escape NDZ condition. This paper proposes using an active frequency method to get out of NDZ condition and a feedforward control to detect grid condition rapidly for seamless transfer. Controllers are composed of a current controller with a feedforward voltage controller. Each of the controllers checks power components independently, Hence, it helps restore the load voltage quickly when grid fault occurs. In NDZ condition, active frequency method helps PCS escape this condition. Proposed seamless transfer control strategy is verified by the experimental results.