Influence of Different Fault Ride-Through Strategies of Converter-Interfaced Distributed Generation on Short-Term Voltage Stability

Fault ride-through strategies of converter-interfaced distributed generation units are an important factor, that is to be considered, when evaluating system stability in future power systems with high share of distributed power generation. Two major groups of control strategies exist: control systems based on current injection as required by several European grid codes and voltage controlled inverter strategies. This paper investigates the influence of the fault ride-through strategy on short-term voltage stability following voltage sags in the distribution grid caused by a three phase short circuit in the overlaying transmission network. A control strategy with blocking current mode resulting in zero current output during fault ride-through is taken as reference. Voltage support by means of current injection is considered with two variations: reactive current injection and current injection in both axes based on the grid impedance angle. A hierarchical d/q-voltage control strategy is used as an example for voltage controlled inverter behavior. Comparative analysis using time domain simulations in a one load infinite bus system is performed and fundamental differences between the control strategies are described. Voltage stability is evaluated regarding the maximum possible fault duration, until induction motor stalling and subsequent local voltage collapse occurs. The comparison of the control strategies shows that d/q-voltage control is able to improve short-term voltage stability and is less dependent on the grid impedance and load composition than control based on current injection.