Output impedance mitigation at filter resonance for single and three-phase UPS systems with reduced sensor count

Widespread deployment of Voltage Source Inverters (VSI-s) in high penetration applications like distributed generation, UPS and stand-alone renewable energy conditioning imposes stringent demands on reliability and output voltage regulation. Reported literature offers numerous solutions for output voltage regulation, which includes twin aspects of command tracking and output impedance control. Most of these methods rely on measurement of at least two separate variables per phase, which compromises overall reliability. This paper focuses on output voltage regulation approaches requiring measurement of a single variable, per phase. It is analytically shown that single-loop approaches are inadequate for satisfying both reference tracking and output impedance specifications. Subsequently, two new improvements using a multi-loop approach are proposed and performance of these techniques are predicted analytically. Experimental results are presented to confirm the validity of suggested approaches.