An LCC-MMC hybrid cascaded inverter applicable for UHVDC power overhead line transmission and dynamic reactive power self-compensation

Abstract

The LCC-MMC hybrid cascaded inverter (LMHCI) dedicated for hierarchical connection and multi-terminal infeed is proposed in this paper. The receiving terminal of the UHVDC system is formed by the LCC and MMC in hybrid cascaded connection. The system combines the merits of hierarchical connection with asynchronous interconnection, which optimizes the network structure of the receiving system. The topology of the system is introduced in detail. The reactive support of the lower-valve to the upper-valve is analyzed detailly, and the control strategy of both steady state and the reactive power emergency compensation strategy of the system are proposed for different operating conditions. Then the DC fault ride through and restart strategy are proposed. Finally, the LMHCI based UHVDC system is built in PSCAD/EMTDC. The simulation verifies the effectiveness of the emergency compensation strategy, the DC fault clearing strategy and the re-starting strategy. The results indicate that this kind of UHVDC inverter is of the good application prospect in the UHVDC connected to load-intensive receiving power grid.

Keywords

• Hierarchical connection mode
• Line commutated converter
• Modular multilevel converter
• Hybrid HVDC
• Ultra HVDC