A grid voltage perturbations based bidirectional impedance uniform control for grid-connected DC/AC converter

For bidirectional grid-connected DC/AC converters, the power flow variation substantially alters the system stability, and especially severs under heavy load. Towards this problem, this paper proposes a novel impedance uniform control method to eliminate the stability degradation under power flow variations, which is achieved by reshaping the converter negative incremental impedance to resistive in the stability fragile mode. The d-axis voltage perturbation is extracted to dynamically modify the active power current reference. Hence, the system bidirectional damping performance can be simultaneously improved by this dedicated design. Without switching control modes or sacrificing dynamic performance, the grid-connected converter system can maintain satisfied stability under bidirectional power flow variations. Finally, the effectiveness of the proposed control method has been validated by both simulations and experiments. For bidirectional grid-connected DC/AC converters in power dispatching mode, power flow variations shift converter impedance feature, resulting in the non-uniformed stability performance. A impedance uniform control method based on voltage perturbation is proposed, which can maintain satisfactory stability under bidirectional power flow variation.image