由π型模块级联成的简单电网作潮流计算的一种情况：已知始端电压和末端复功率及电网各处参数，利用前推回代法求始端复功率和末端电压(A simple power grid cascaded by PI module is used for power flow calculation: the initial terminal voltage and terminal complex power and the parameters of the grid are known. The forward and backward method is used to calculate the terminal complex power and terminal voltage)