Resilient DC Voltage Control for Islanded Wind Farms Integration Using Cascaded Hybrid HVDC System

Abstract

To integrate large-scale islanded onshore wind power with different sizes, this paper proposes an integration system based on the cascaded hybrid HVDC transmission system, which consists of LCC and several MMCs in series connection at the DC side of the rectifier. A large-scale wind farm is connected with one LCC and one MMC while several small-scale wind farms are connected with MMCs directly. Owing to the hierarchical integration arrangement, the operating flexibility can be improved with reduced capacity and the number of step-up interfacing transformers. A resilient DC voltage control is proposed for the integration system to adaptively redistribute power among the converters during wind power fluctuations. Firstly, the topology and operating characteristics of the wind power integration system are introduced. Then, a resilient DC voltage control is proposed to ensure stable operation during wind power curtailments. Finally, a simulation model of the hybrid cascaded HVDC transmission system is built in PSCAD/EMTDC to verify the effectiveness. The research results show that the system provides a new option for long-distance transmission of large-scale islanded wind power.

A Strategy for Optimal and Selective Utilization of Multiple Interline DC Power Flow Controllers in VSC-HVDC Grids

“…Future voltage source converter (VSC)-based high-voltage direct current (HVDC) grids interconnecting offshore wind farms (OWFs) and onshore AC networks will have several HVDC lines and buses. Hence, the secure, flexible, and optimal operation of those HVDC grids will be a challenge due to the existence of numerous line current distribution possibilities for a given pattern of offshore wind power generation and onshore power generation/consumption [1][2][3][4]. The further expansion of existing VSC-HVDC grids (e.g., the connection of new OWFs, onshore VSCs, or HVDC lines) and especially the occurrence of HVDC line contingencies (e.g., outages of some HVDC lines in the context of the N-1 security criterion) might lead to bottlenecks in HVDC lines, which should be addressed.…”

A strategy for optimal and selective utilization of multiple interline DC power flow controllers in VSC-HVDC grids

“…Future voltage source converter (VSC)-based high-voltage direct current (HVDC) grids interconnecting offshore wind farms (OWFs) and onshore AC networks will have several HVDC lines and buses. Hence, the secure, flexible, and optimal operation of those HVDC grids will be a challenge due to the existence of numerous line current distribution possibilities for a given pattern of offshore wind power generation and onshore power generation/consumption [1][2][3][4]. The further expansion of existing VSC-HVDC grids (e.g., the connection of new OWFs, onshore VSCs, or HVDC lines) and especially the occurrence of HVDC line contingencies (e.g., outages of some HVDC lines in the context of the N-1 security criterion) might lead to bottlenecks in HVDC lines, which should be addressed.…”

Flex-LCC: A New Grid-Forming HVDC Rectifier for Collecting Large-Scale Renewable Energy

“…Hybrid valves in [9], [10], [11], [12], [13], and [14] can also be used to integrate large-scale islanded or weak-grid-supported RESs. However, in [9], the high dc voltage also exists in the HBMMC part because of the parallel connection at the dc side.…”

“…In [12] and [13], the HBMMC is used to increase the dc voltage and power carrying of the SCH valve further. Recently, a sending-end station based on the SCH valve has been analyzed in [14] to integrate multiple islanded onshore RESs, drawing on China's Baihetan project [15]. However, in [9], [10], [12], [13], and [14] and in the Baihetan project, the LCC part use its firing angle to achieve the power control, resulting in several challenges for the SCH valve when used to integrate large-scale islanded or weak-grid-supported RESs.…”