Frequency consensus control strategy for multi-terminal HVDC transmission system based on disturbance degree

The multi-terminal HVDC (MTDC) grid, which connects asynchronous AC regions, can support frequency regulation. Nevertheless, under diverse disturbance scenarios, in order to enhance the frequency regulation performance of the MTDC, the couplings among the power, frequency, and DC voltage of the converter stations must be taken into account. This paper delves into this issue. To begin with, by considering data such as the frequency regulation capabilities of each region and the DC voltage variation range, we determine the gains with the aim of attaining consistent frequency deviations and an accurate DC voltage when each non-disturbed converter station shares the unbalanced power. Furthermore, a communication-free disturbance identification method is proposed to precisely identify the degree and location of the load disturbance. On this basis, a frequency control strategy is designed. This strategy adjusts the control parameters according to the magnitude of the disturbance, enabling the system to achieve flexible power sharing under different disturbance conditions. Finally, the simulation results show that this strategy can achieve flexible frequency control and improve the stability of the DC voltage.