Abstract
Increasing offshore wind farms are rapidly installed and planned. However, this will pose a bottle neck challenge for long-distance transmission as well as inherent variation of their generating power outputs to the existing AC grid. VSC-HVDC links could be an effective and flexible method for this issue. With the growing use of voltage source converter high-voltage direct current (VSC-HVDC) technology, the hybrid VSC-HVDC and AC system will be a next-generation transmission network. This paper analyzes the contribution of the multi VSC-HVDC system on the AC voltage stability of the hybrid system. A key contribution of this research is proposing a novel adaptive control approach of the VSC-HVDC as a so-called dynamic reactive power booster to enhance the voltage stability of the AC system. The core idea is that the novel control system is automatically providing a reactive current based on dynamic frequency of the AC system to maximal AC voltage support. Based on the analysis, an adaptive control method applied to the multi VSC-HVDC system is proposed to realize maximum capacity of VSC for reactive power according to the change of the system frequency during severe faults of the AC grid. A representative hybrid AC-DC network based on Germany is developed. Detailed modeling of the hybrid AC-DC network and its proposed control is derived in PSCAD software. PSCAD simulation results and analysis verify the effective performance of this novel adaptive control of VSC-HVDC for voltage support. Thanks to this control scheme, the hybrid AC-DC network can avoid circumstances that lead to voltage instability.
Highlights
VSC-HVDC technology is a promising solution for integration of future offshore wind farms into the existing AC system and an attractive bulk power transmission structure in the next-generation networks [1]
An adaptive control method applied to the multi VSC-HVDC system is proposed to realize maximum capacity of VSC for reactive power according to the change of the system frequency during severe faults of the AC grid
Vt,abc and Vsabc are the AC voltages at the terminal and PCC respectively, iL,abc are the current flowing to the AC network, ron denotes the switch on-state resistance of VSC, while R and L are resistance and inductance at AC side of VSC, and ρ is the output of phase-locked loop (PLL)
Summary
VSC-HVDC technology is a promising solution for integration of future offshore wind farms into the existing AC system and an attractive bulk power transmission structure in the next-generation networks [1]. An adaptive control method of the VSC-HVDC networks is proposed to enhance the voltage support by automatically adjusting the reactive current limits while ensuring not to worsen the frequency of the system according to the dynamics conditions of the system. This results in the maximum utilization of the VSC capability for reactive power support.
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