Transient response assessment of vector PI current controllers in renewable energy applications

Grid codes force generation units based on renewable sources to act similarly to conventional power plants: when a fault is detected, they must remain connected and support the grid. To fulfill these requirements, the transient response of the current controllers is critical. This paper applies a recently proposed methodology which assesses and optimizes the transient response of proportional-resonant controllers (PR) to a different type of linear regulators: the vector proportional-integral (VPI) controllers. This methodology is based on the study of the error signal roots: both reference tracking and disturbance rejection abilities should be considered for proper gain tuning. This work proves that VPI controllers lead to longer settling times and bigger overshoot than PR controllers for high sampling frequencies. However, as the sampling frequency decreases, the transient response of both controllers presents more similarities. A three-phase voltage source converter prototype has been implemented. Experimental results provide a direct comparison between the transient behavior of VPI and PR controllers in different conditions: a +90° phase-angle jump in the current reference and a `type C´ voltage sag at the point of common coupling.