Analysis of Voltage Support Mechanism for Asymmetrical Short-Circuit Faults in Power Electronics-Based Systems

With the large-scale integration of renewable energy generation equipment, the transient voltage characteristics of power systems have undergone significant changes. Due to the limited overcurrent capability, renewable energy generation devices have weak transient voltage support. Traditional vector control methods, based on the dq rotating reference frame of individual converters, operate within their respective reference frames and fail to effectively coordinate the overcurrent capabilities of multiple devices. During an asymmetric short-circuit fault, renewable energy devices also control the negative-sequence current, absorbing the negative-sequence current from the AC system to suppress the negative-sequence voltage. In contrast, traditional synchronous generators do not have the ability to control negative-sequence currents. This paper takes a typical single-phase ground fault as an example. It uses the symmetrical components method and composite sequence network. The paper derives the voltage at the renewable energy grid connection point. It also provides expressions and vector relationships for the positive- and negative-sequence components, which are expressed in terms of the positive- and negative-sequence currents. The paper also analyzes the impact of the magnitude and phase of positive- and negative-sequence currents on voltage imbalance and low-voltage ride-through performance, and proposes a new current distribution strategy.