Abstract: For the testing and fault diagnosis requirements of power conversion system of 35 kV three-phase cascaded H bridge. A back-to-back H bridge is chose as the basic test unit. Using multi winding transformers to ensure the independence of each DC power supply, battery cluster function is simulated by low voltage side H-bridge. Designing a energy saving test platform for power conversion system based on three-phase cascaded H bridge considering system parameters. Low voltage side H-bridge is controlled by PWM and cascaded H bridge is controlled by PQ decoupling. The designed testing platform without battery cluster is practicability through simulation and dynamic experiments, provided safety support for the first grid connected operation of cascaded inverters with real batteries.