Improved state enumeration method for transmission grids with renewable energy sources in load spaces

The penetration level of renewable energy sources (RESS) in transmission grids makes the operation states complex. So, it is necessary to execute the effective and online state estimation for transmission grids with renewable energy sources to realize the reliable monitoring of the operation state. However, because the state estimation for transmission grids needs to analyze each possible operation state, the evaluation process is time-consuming and cannot meet online applications’ requirements. Therefore, an improved state-enumeration (SE) method is proposed for online reliability evaluation. First, the total amount of load shedding of all operation states is selected as the system reliability index, and a modified linear optimal model for the transmission grid is established by DC power flow equations. Second, the intermediate variables in the SE model are eliminated and the operational constraints are simplified by using the relaxation technique. And then a linear SE model is established in load spaces, which can be easily solved by linear programming. Because the variables in the function and constraints are the same, the computation burden is greatly reduced. Finally, the proposed strategy is tested by using the modified RBTS and IEEE RTS-96 grids, and the simulation results verify its accuracy and efficiency.