Open-circuit fault diagnosis in neutral-point-clamped UPS inverters with no additional sensors

The operating conditions of UPS inverters and the fact that the load is unknown lead to great difficulties in fault diagnosis. This paper proposes the use of a fault diagnosis algorithm based on estimated pole voltage error for UPS inverters based on the 3-level Neutral-Point-Clamped topology. This algorithm is independent from the load and is not affected by unbalanced three-phase operation. This algorithm provides very fast and reliable results and requires no additional sensors or hardware. Simulation results are presented to demonstrate the algorithm´s speed and robustness.