Distortion-Free Saturators for Power Converters Under Unbalanced Conditions

Voltage controlled voltage source converters (VCVSC) and current controlled voltage source converters (CCVSC) have gained importance within distributed power generation systems and equipment for power quality improvement. The control action is susceptible to fall in saturation under disturbance transients or in case of poor control tuning. The use of existing saturation techniques for vector variables, such as three-phase voltage and current, distorts the reference waveforms under unbalanced conditions regardless the used reference frames--stationary (αβ-axis) or synchronous (dq-axis). These harmonics are quite detrimental for the electric grid and reduce the efficiency. This paper presents a distortion-free saturation methodology with two versions and analyzes the performance in function of the control structure (VCVSC and CCVSC) and the saturation point within the control loop. The experimental results prove the advantages of using the proposed saturators.