Under the light of energy function method, angle instability and voltage instability can be thought as different unstable mode, and be distinguished from each other by characteristic of UEP.

• 在能量函数法的思想下，功角稳定和电压稳定的关系可以通过不稳定平衡点模式来研究，并由不稳定平衡点模式的不同而区分出两者。