Hybrid AC/DC hub for integrating onshore wind power and interconnecting onshore and offshore DC networks

Abstract

A hybrid AC/DC hub is proposed in this study, where a modular multilevel converter and a line-commutated converter are paralleled at the AC side to integrate onshore wind power, and connected in series at the DC sides to interconnect two DC networks with different voltages. The hybrid AC/DC hub facilitates wind power integration and DC network interconnection with reduced converter ratings and power losses when compared with the 'conventional' approach using DC-DC converters. To investigate the design requirement and performance of the hybrid AC/DC hub, power flow analysis is assessed to evaluate the converter power rating requirement. To ride through DC faults at either side of the interconnected DC networks, a coordinated DC fault protection for the hybrid AC/DC hub is proposed and studied. Simulation results in PSCAD/EMTDC verify the feasibility and effectiveness of the proposed control and protection of the hybrid AC/DC hub under power flow change, AC and DC fault conditions.

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

“…L jk_1 =L jk -M jk , L jk_0 =L jk +M jk . Equation (3) demonstrates that the couplings between the positive and negative poles can be eliminated by the phase-modal transformation. And the line-mode and zero-mode equivalent circuits can be obtained:…”

“…Due to the intermittent nature of renewable energy resources, they impose new technical challenges for integration into power systems. With the merits of self-commutation, decoupled active and reactive power control and black start capabilities, the modular multilevel converter (MMC) based DC grid technology is widely recognized as a suitable approach for long-distance power transmission [1]- [3]. To utilize the diversity of renewable energy resources across different regions, such as the North Sea in Europe, the inland areas in saizhaoyang@foxmail.com, zhanghaobo9902@foxmail.com, radio.zuo@ foxmail.…”

A Diode-MMC AC/DC Hub for Connecting Offshore Wind Farm and Offshore Production Platform

“…P2p DC faults in DC networks of S 1 and S 2 are considered. If a DC fault occurs on either DC network, the healthy DC side feeds the fault current into the faulty DC side through the MMC due to its direct electrical connection [13,14]. On account of the expensive cost and large volume relative to ACCBs at comparable voltages, high-voltage DC circuit breakers (DCCBs) are not considered in the offshore scheme to interrupt the DC faults [21,22].…”

“…However, the operation control and fault ride-through operation when connecting with an offshore wind farm have not been investigated. A hybrid AC/DC hub composed of the LCC and MMC in series connection has been proposed for onshore wind-power integration and interconnection of two DC networks with different DC voltages [14], but this hub is not suitable for offshore applications due to the large footprint and heavyweight of the LCC, which also needs a strong AC grid for commutation.…”

DC Fault Study of a Point-to-Point HVDC System Integrating Offshore Wind Farm Using High-Temperature Superconductor DC Cables

“…As part of the pathway towards that goal, the UK government aims to have 40 GW of offshore wind farm (OWF) capacity operational by 2030. To achieve this, offshore wind power transmission using modular multilevel converter (MMC) based high-voltage direct current (HVDC) technology will play an important role and has supplanted 2-or 3-level voltage source converter (VSC) as the standard form of HVDC converter adopted by industry [1]- [3]. Up to the time of writing, more than ten MMC-HVDC projects have been commissioned globally to integrate OWFs [4].…”