A novel double dynamic voltage feedforward control strategy for improved current limiting in droop controlled grid-connected inverters during LVRT

Grid-connected inverters with LCL filters require active damping to mitigate system resonance, typically achieved via inductor or capacitor current feedback loops. While inductor current feedback is favoured for its inherent current-limiting capability, capacitor current feedback provides a more inductive output impedance, enabling classic droop control with smaller physical inductors, improved transient response, and reduced total harmonic distortion (THD). This paper proposes a novel current-limiting strategy during low-voltage ride-through (LVRT) for inverters utilising capacitor current feedback, thereby enhancing inverter performance. The strategy introduces double dynamic voltage feedforward (DDVFF), ensuring a rapid response to grid voltage sags and effectively diminishing the current overshoot. A small signal model is developed to analyse stability and aid the controller design. The controller performance is validated through detailed simulations and experimental testing on a 100 kW commercial inverter. The proposed controller reduced current overshoot by 64.5% in response to a 70% symmetrical voltage sag. Moreover, using capacitor current feedback resulted in a rise time that is 78.6% faster compared to inductor current feedback.