U(s)=(R-L*s)I(s)+E(s),U(s)是u(t)的拉氏变法像函数,I(s)是i(t)的拉氏变法像函数,E(s)是e(t)的拉氏变法像函数,
I(s)=[U(s)-E(s)]/(R-L*s)