Aggregated-Impedance-Based Stability Analysis for a Parallel-Converter System Considering the Coupling Effect of Voltage Feedforward Control and Reactive Power Injection

In this article, the sequence impedance of a single converter is separated into a fixed impedance term and an output power dependent term. Then, an aggregated impedance model of identical parallel converters is established to evaluate the stability performance. It is found that the internal power allocation among parallel converters has no impact on the system stability. Further analysis has indicated that the total reactive power injection and the type of voltage feedforward control have highly coupled impact on the system stability. Specifically, increasing the reactive power can always help to stabilize the system when no voltage feedforward loop or voltage feedforward with a low-pass filter is adopted. However, when the direct point of common coupling (PCC) voltage feedforward control is applied to converters, reactive power injection within a certain range can improve system stability. Comprehensive verification results are provided to validate the correctness of conclusion and the reactive power injection approach.