Impact of control implementations on the output impedance of voltage-sourced converters

This paper analyzes and investigates the effect of the control strategies on the virtual output impedance of Voltage sourced converter system (VSC-based), namely; stationary frame (αβ-frame) control based and rotating frame (dq-frame) control based. The obtained equivalent output impedance is then used to analyze the stability of such a system. It is found that the modeling and implementation has significant impact on the real part of input impedance; wherein with αβ-frame a positive resistance is achieved in all the frequency ranges while in dq-frame a negative resistance at low frequency region appears. However, αβ-frame causes instability issue as the grid impedance increases while dq-frame maintains the stability under the same gird conditions.