An Improved DC Fault Protection Scheme Independent of Boundary Components for MMC Based HVDC Grids

Abstract

For modular multilevel converter (MMC) based DC grids, current-limiting reactors (CLRs) are mainly employed to suppress the fault current and provide boundary effects to detect internal faults. Thus, most existing protection schemes are highly dependent on the larger CLRs to guarantee high selectivity. However, in existing MMC based HVDC projects, the size of CLRs is restrained by the cost, weight, and system stability under normal state. Thus, boundary protections may fail to detect high-resistance faults and pole-to-ground faults under weak boundary conditions. To overcome these shortcomings, this paper proposes a fast and selective DC fault detection scheme independent of boundary components. The propagation characteristics of line-mode backward traveling-waves (TW) are analyzed to identify external and internal faults. The polarities of zero-mode backward TWs are employed to select faulted poles. The directional overcurrent based pilot protection is adopted as a complementary criterion to detect remote faults. The proposed method can be applied in MMC-HVDC systems with small CLRs that cannot provide strong boundary conditions. Besides, the detection speed is fast (less than 1.5ms). Moreover, it is robust to fault resistance and immune to noise. Various simulation results in PSCAD/EMTDC verifies the effectiveness of the proposed scheme.

DC Fault Protection Algorithms of MMC-HVDC Grids: Fault Analysis, Methodologies, Experimental Validations, and Future Trends

“…The sensitivity requires the protection devices to accurately detect any internal faults, regardless of fault types and fault resistances [35], e.g., the pole-to-pole (PTP) and the pole-toground (PTG) faults. Considering the coupling of the faulted and healthy poles, some methods have been proposed to discriminate the faulted poles, e.g., the integration of the change of pole voltages [31], the zero-mode component based methods [36], the morphological gradient based methods [37].…”

“…These non-boundary protection schemes cannot work well for remote faults. Reference [36] introduced the distortion effects of the line-mode backward TWs to identify faults independent of boundary components. Except for [36][93][94], there are no other references concerning single-end protection schemes that independent of boundary elements for the MMC HVDC systems.…”

An Improved DC Line Fault Detection Scheme Using Zone Partition for MTDC Wind Power Integration Systems

“…However, it cannot identify pole-to-pole (PTP) faults. To improve the applicability for different fault types, TW frequency characteristics which are dependent on the fault distances are adopted to identify internal faults in [28]. Whereas, these non-boundary schemes cannot work well for remote faults.…”

“…Whereas, these non-boundary schemes cannot work well for remote faults. Except for [27] [28], there are no other references concerning single-end fault detection schemes that do not rely on CLRs.…”

Research on Multi-Port DC-DC Converter Based on Modular Multilevel Converter and Cascaded H Bridges for MVDC Applications

“…In high-voltage and high-power DC conversion occasions, MMC also has greater advantages. However, in the case of medium-voltage and low-voltage power distribution levels, the structural characteristics of MMC will lead to a great increase in cost and losses [14][15][16][17][18], [20][21][22][23].…”