Risks of parametric resonance exist between interphase power controller（IPC）and the associated power grid. Existing approaches to avoid this phenomenon tend to reduce the range of parameters in IPC. To reveal the mechanism of parametric resonance between IPC and the associated power grid，theπ-type equivalent circuits of IPC are established. The reason of parametric resonance between IPC and the associated power grid is the parameters ofπ-type equivalent circuit and energy storage components in the associated power grid satisfying the resonance conditions. Because the three impedance parameters ofπ-type are10times larger than the equivalent parameters of energy storage components in the associated power grid，the risks of parametric resonance can be greatly reduced. Finally，the single-machine system with IPC15is set up，and the simulation results prove the correctness of the conclusions of the proposed parameter selection measures.