An integrated inverter containing an input LC filter is integral to supplying an AC load to an integrated power system(IPS). But in high-power scenarios, the connection between the inverter and the LC filter may result in significant small-signal stability issues. Furthermore, the control strategies implemented under both dq and abc frameworks increase the difficulty of stability analysis. This paper establishes a unified impedance model for high-power inverters in dq-frame, using a control strategy under the hybrid frame, and discusses the reasons for the instability issues about the inverter. To ascertain the accuracy of the theoretical analysis, the 300kW inverter system is simulated and verified.