Abstract
The modular multilevel converter (MMC) with the clamp double submodule (CDSM) performs outstandingly on the handling of DC fault current. As CDSM is composed of multiple switching devices, different operating modes can be produced according to the combination of switching states. Among the effective operating modes, there are inevitably some unexpected modes, which may cause abnormal operation or even failure of the MMC. In order to improve the reliability of MMC, it is necessary to identify all the effective operating modes of CDSM and analyze their trigger conditions. In this article, a novel mode identification method for power converter with multiple switches is used. According to reasonable combination of switching states, the components of CDSM are connected in an orderly manner to obtain all effective operating modes. Based on the operating principle of CDSM, the unexpected modes are further recognized from the effective operating modes, so that the impact of the unexpected modes on the MMC can be obtained. Finally, the recognition and analysis results of the unexpected modes in CDSM is verified by Simulink and Plecs RT Box.
Highlights
In 2003, the concept of modular multilevel converter (MMC) was firstly proposed [1]
The topology of 3-phase MMC is shown in Fig. 1, which is composed of six arms
To prevent the impact of unexpected modes of clamp double submodule (CDSM) on MMC, a novel mode identification method is used in this article
Summary
In 2003, the concept of modular multilevel converter (MMC) was firstly proposed [1]. Due to the distinguish advantages of high modularity [2], small harmonic content [3] and low converter losses [4], MMC has been widely used in high-voltage direct-current (HVDC) system. MMC should have the ability to handle DC fault current and identify the component failures. Among the submodules used in MMC, the clamp double submodule (CDSM) has the ability of handling DC fault current because it can output negative capacitor voltage [6, 7]. Compare with other types of submodule, CDSM can output more voltage levels and is more costeffective, so it has become a popular SM in the MMC system [8, 9]. Xiaofu Fan et al.: Mode Identification and Analysis of Modular Multilevel Converter (November 2019)
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