Proportional–Resonant Controller Based on Virtual Impedance for Harmonic Suppression of ESS-UPS System

A proportional–resonant controller based on the output impedance is proposed for a single-phase full-bridge inverter offering harmonic suppression of uninterruptible power supply with an energy storage system. In order to design the voltage transfer function and output impedance independently, the proposed controller properly places a virtual impedance loop within the output voltage controller, and control gains are selected according to the proposed design rules. To secure a high power quality, the virtual impedance is designed to have low output impedance characteristics in all frequency bands. In addition, some practical issues are analyzed and readily compensated such as parametric error and the performance of output voltage tracking respectively. Mathematical and theoretical analyses are presented to validate the proposed controller, and experiments were conducted to verify its performance.