( Abstract )
Nowadays, the nonlinear nature of electric loads leads to a strong demand of a high-quality and reliable power source both by the customers and utilities. To address this issue, the uninterruptible power supplies (UPSs) are extensively employed for the critical loads such as communication systems (i.e., data centers), medical support systems, semiconductor manufacturing systems, etc. For improving the power quality using UPS system, it is important to achieve the sinusoidal output voltage waveform with very low total harmonic distortion (THD) regardless of the load types. Typically, the inverter with LC output filter in the UPS system is a suitable solution to fulfill this requirement. The main criteria to evaluate the regulation performance of the UPS inverter output voltage are fast dynamic response, small steady-state error, and low THD. Furthermore, the various load conditions (abrupt load changes, unbalanced load, and nonlinear load) including parameters uncertainties extremely degrade the performance of the UPS inverter. Thus, an appropriate control strategy is desired to sufficiently meet the performance criteria of the UPS systems under any type of electrical loads and uncertainties.