Security assessment of electricity-gas-heat integrated energy systems based on the vulnerability index

Integrated energy systems (IES) realize the coupling of different energy flows and help to improve energy efficiency and increase renewable energy consumption. However, due to the coupling effect, variation of operation parameters in one energy flow can be propagated to other ones through the coupling equipment, which results in complex security problems of IES. Here, we propose a security assessment method based on the vulnerability index (VI) for electricity-gas-heat IES. The vulnerability index combines the current values of state variables, operation limits, and sensitivity factors between state variables and control variables simultaneously. Current values are obtained by the solution of the steady-state IES model by the decomposed Newton-Raphson method. Sensitivity factors are derived based on the Jacobian matrix in the IES model. VI matrixes for IES with different control modes are formulated and deduced. The vulnerable state variables and the key control variables are identified based on the VI matrixes. A case study is conducted to validate the proposed method. Vulnerable state variables and key control variables are identified by the absolute value of vulnerability index with the upward and downward adjustment of control variables. These results are verified by energy flow calculations, which show that vulnerable state variables and key control variables derived by vulnerability index are more accurate than those identified by sensitivity factors. In the situations of determining electricity based on heat and determining heat based on electricity, the method proposed herein is 1.73 and 22.45 times faster than energy flow calculations respectively.