Abstract:The control and protection device, as the key equipment to realize rapid protection in the operation and fault of flexible DC system,, needs to be fully tested before being put into operation. The existing method is based on a real-time simulation platform for controller-in-the-loop testing. However, this test method cannot simulate the physical structure of the sub-module in detail because the modular multilevel converter (MMC) sub-module adopts an equivalent modeling method, so it cannot effectively detect the failure of the sub-module. Simulation affects the comprehensive verification of the valve control function. In order to solve the above problems, this paper proposes a sub-module fault simulation technology, which is to add a fault simulation device to the existing test method, which can realize the sub-module fault simulation and make up for the defects of the existing test method. Finally, the joint test results in the laboratory prove its correctness and validity.