Applying power margin tracking droop control to flexible operation in multi-terminal DC collector systems of renewable generation

Abstract

An emerging multi-terminal looped DC (MTDC) collector system is now advocated for collecting and transferring large-scale renewable generation. However, it remains an open question as to improving the cooperative control capability of looped converter stations for flexible and robust response to renewable grid-connection fluctuation. This paper addresses this problem with a novel Power Margin Tracking (PMT) droop control and its corresponding system-level control strategy from the perspective of optimal dispatch of the power system. By introducing a power margin correction factor into the droop coefficient, the converter station can make self-adaptive regulations according to its actual available power margin. For operation verification, a multi-period optimal operation model and a four-terminal simulation model is built to provide optimal control parameters and real-time operation states of converter stations, where the power flow model of the looped MTDC grid with renewables generation is considered. The case results prove that the proposed control strategy can improve the cooperative operation capability of multiple converter stations, mitigating grid-connected power fluctuation. It can effectively reduce the DC voltage deviation to enhance the operation stability of the MTDC grid. The operational robustness of the proposed control strategy under 'N - 1' fault cases is verified as well.