An Adaptive Reclosing Strategy for MMC-HVDC Systems With Hybrid DC Circuit Breakers

Abstract

Modular multilevel converter (MMC) based high voltage direct current transmission (HVDC) is an effective solution for large-scale renewable power integration over long-distance. In the overhead MMC-HVDC systems, the high voltage DC circuit breakers (DCCB) are implemented to interrupt the DC fault current. Subsequent to fault isolation, the DCCBs are required to automatically re-close to restore power transmission quickly. However, when the DCCBs are re-closed to permanent faults, they will be tripped again, resulting in a high requirement of interruption capacity for DCCBs and second overcurrent strikes on the HVDC systems. To overcome the drawbacks of the conventional auto-reclosing scheme, this paper proposes an adaptive reclosing scheme based on the active pulse injection from the converter associated with the coordination control of hybrid DCCBs. The single-end adaptive reclosing scheme as well as the two ends adaptive reclosing scheme dedicated to two-terminal HVDC systems and meshed DC grids are presented respectively. By applying this method, the location of faults can also be achieved in the case of permanent faults. In order to verify the effectiveness of the proposed adaptive reclosing schemes, extensive simulations have been conducted under PSCAD/EMTDC.

A Single-End Protection Scheme for Hybrid MMC HVDC Grids Considering the Impacts of the Active Fault Current-Limiting Control

“…Denote the first negative backward TW from the fault point as V 1 b . The initial backward TW V 1 b will be reflected at the terminal of OHL.…”

“…The initial backward TW V 1 b will be reflected at the terminal of OHL. The reflected TW is forward and denoted as V 1 f . The initial TWs V 1 b and V 1 f can be calculated as [21]:…”

“…Based on equations (5)- (7), the change of the DC line voltage (∆V dc_line ) can be obtained as: (8) As can be seen from equation (8), the DC line voltage V dc_line drops rapidly once TW V 1 b arrives at the terminal of the OHL. Denote the time when the initial backward TW V 1 b arrives at the terminal of OHL as t 1 . With the delay for the voltage derivative measurement, the reference of the DC current I dcref shifts to zero.…”

“…For forward faults (F 12 and F 2 ), equation (6) points out that the magnitude of the voltage derivative of the initial backward TW V 1 b (dV 1 b /dt, it is negative) is larger than that of the initial forward TW V 1 f (dV 1 f /dt, it is negative). Thus, for forward faults, it can be obtained: (20) where min () represents the function that obtains the minimum value.…”

“…With the merits of flexibility and reliability, the modular multilevel converter (MMC) based DC grid using overhead lines transmission is promising to integrate large-scale wind power and solar energy over long-distance [1] [2]. There are two main approaches to construct the DC grid topology: 1) The half-bridge (HB) MMC with large-capacity fast-speed DC circuit breakers (DCCB).…”