Harmonics reduction in high-efficiency operation of double-conversion UPS

UPS are used to protect critical loads, and double-conversion is often the preferred choice. While providing optimum protection, this topology offers limited efficiency. Some double-conversion UPS feature a high-efficiency (ECO) mode, with the load normally fed via the bypass path. In this operating mode, load current harmonics may be let through towards the utility, and may induce a high load on the neutral conductor. In this context, this paper discusses Advanced ECO Mode topologies that reduce neutral current and mitigate harmonics resulting from non-linear or unbalanced load.