Sub-module component developed in CBuilder for MMC control and protection test in RTDS

Abstract

Modular multilevel converter (MMC) is one of the most promising direct-current (DC) transmission modules. To establish a flexible sub-module model in RTDS for evaluating the protection and control devices is important and useful for the fast development of MMC-HVDC technology. A component for the sub-module, rtds_SM, is proposed in this paper, which is developed by CBuilder in RTDS to provide a flexible and available model to test the control and protection devices for MMC system. First, the rtds_SM component, considering the bypass switch branch, is established by using CBuilder in RTDS. It has seven inputs and two outputs, which can response to various operation states under various conditions. The information of the capacitor voltage balancing is calculated in the component and output as a variable. Second, the memory usage and the simulation precision of the proposed model are analyzed in detail. It is suitable for the simulation in RTDS if the carrier frequency is smaller than 1.2kHz. Third, the steady states and transient states are tested for the rtds_SM proposed in this paper. Numerical results show that it meets the requirements for various operating conditions. The proposed component has been successfully used to test the controller and protection devices designed by Xian XD Power Systems Co., Ltd. for a practical MMC system in China.