Planning and Scheduling Methods for Multiple Clean Energy HVDC Transmission System Considering Short Circuit Ratio

Due to the fact that China's clean energy-rich areas are mostly far away from load centers, large-scale clean energy needs to be consumed through high-voltage direct current transmission. However, the transient overvoltage problems restrict the transmission capacity and renewable energy accommodation. Therefore, this paper takes the short circuit ratio (SCR) as the indicator of voltage support strength and constructs the link between the transient overvoltage and SCR. In order to realize the SCR constraint can be expressed explicitly to be embedded in the planning model. Firstly, we separately study the effects of hydropower units and renewable energy units on the system impedance under different operation situations. Then we derive the relationship between the output of the two types of units and the SCR through Thevenin's theorem and superposition theorem, which can be formed the SCR constraint. Finally, an integrated planning and operation model is constructed to achieve the coordinated optimization of planning and scheduling schemes. Finally, the proposed model is applied to the modified IEEE39 nodes system. It is demonstrated that the SCR can be increased by 19.5% through reasonably adjusting the starting state of the hydropower units and other operating methods. Furthermore, the renewable energy units under this operation method can avoid off-grid because the transient voltage rise is less than the off-grid threshold.