How to solve this differential Equation?

current equation
i1(t) = (1/Cinv)(Vo'(t))
i21(t) = (1/CL)(Vc'(t))
i22(t) = Kn(Vcon-Vc(t)-Vth)(Vo(t)Vc(t))-0.5(Vo(t)-Vc(t))^2

Id=i1(t)+i21(t)
i21(t)=i22(t)

these are detailed relation of equations