Combined three-phase inverter is constituted of three signal H-bridge inverters. This topology has several advantages and specially suits for high power application. However, when applying combined configuration into high power application, many new features are found. These new features affect the performance of inverter system in many ways. On the viewpoint of system, these new features must be fully considered. In this paper, these features are discussed in detail. These features, which relate to system capability, model building, controller designing, protecting scheme choosing, are analyzed. Based on the analysis, the design guidelines are given. A 300kW high power inverter system with combined configuration is built. By employing the analysis and guidelines that presented in the paper, the performance, reliability and stability of the inverter system have been enhanced greatly. The further work is also proposed at the end of this paper.