An Improved DC Voltage Droop Control for Interconnection of Wind Farms by VSC-MTDC

: Two VSC-MTDC control strategies with different combinations of controllers are proposed to eliminate transient fluctuations in the DC voltage stability, resulting from a power imbalance in a VSC-MTDC connected to wind farms. First, an analysis is performed of a topological model of a VSC converter station and a VSC-MTDC, as well as of a mathematical model of a wind turbine. Then, the principles and characteristics of DC voltage slope control, constant active power control, and inner loop current control used in the VSC-MTDC are introduced. Finally, the PSCAD/EMTDC platform is used to establish an electromagnetic transient model of a wind farm connected to a parallel three-terminal VSC-HVDC. An analysis is performed for three cases of single-phase grounding faults on the rectifier and inverter sides of a converter station and of the withdrawal of the converter station on the rectifier side. Next, the fault response characteristics of VSC-MTDC are compared and analyzed. The simulation results verify the effectiveness of the two control strategies, both of which enable the system to maintain DC voltage stability and active power balance in the event of a fault. Background: The use of a VSC-MTDC to connect wind power to the grid has attracted considerable attention in recent years. A suitable VSC-MTDC control method can enable the stable operation of a power grid. Objective: The study aims to eliminate transient fluctuations in the DC voltage stability resulting from a power imbalance in a VSC-MTDC connected to a wind farm. Method: First, the topological structure and a model of a three-terminal VSC-HVDC system connected to wind farms are studied. Second, an analysis is performed of the outer loop DC voltage slope control, constant active power control and inner loop current control of the converter station of a VSC-MTDC. Two different control strategies are proposed for the parallel three-terminal VSC-HVDC system: the first is DC voltage slope control for the rectifier station and constant active power control for the inverter station, and the second is DC voltage slope control for the inverter station and constant active power for the rectifier station. Finally, a parallel three-terminal VSC-HVDC model is built based on the PSCAD/EMTDC platform and used to verify the accuracy and effectiveness of the proposed control strategy. Results: The results of simulation analysis of the faults on the rectifier and inverter sides of the system show that both strategies can restore the system to the stable operation. The effectiveness of the proposed control strategy is thus verified. Conclusion: The control strategy proposed in this paper provides a technical reference for designing a VSC-MTDC system for wind farms.

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Impact of Primary Frequency Control of Offshore HVDC Grids on Interarea Modes of Power Systems

Energies ◽

10.3390/en12203879 ◽

2019 ◽

Vol 12 (20) ◽

pp. 3879 ◽

Cited By ~ 2

Author(s):

Ali Bidadfar ◽

Oscar Saborío-Romano ◽

Vladislav Akhmatov ◽

Nicolaos A. Cutululis ◽

Poul E. Sørensen

Keyword(s):

Power Systems ◽

Frequency Control ◽

Wind Farms ◽

Offshore Wind ◽

Offshore Wind Farms ◽

Dc Voltage ◽

Simultaneous Use ◽

Primary Frequency ◽

Primary Frequency Control ◽

The Impact

Offshore high-voltage DC (HVDC) grids are developing as a technically reliable and economical solution to transfer more offshore wind power to onshore power systems. It is also foreseen that the offshore HVDC grids pave the way for offshore wind participation in power systems’ balancing process through frequency support. The primary frequency control mechanism in an HVDC grid can be either centralized using communication links between HVDC terminals or decentralized by the simultaneous use of DC voltage and frequency droop controls. This paper investigates the impact of both types of primary frequency control of offshore HVDC grids on onshore power system dynamics. Parametric presentation of power systems’ electro-mechanical dynamics and HVDC controls is developed to analytically prove that the primary frequency control can improve the damping of interarea modes of onshore power systems. The key findings of the paper include showing that the simultaneous use of frequency and DC voltage droop controls on onshore converters results in an autonomous share of damping torque between onshore power systems even without any participation of offshore wind farms in the frequency control. It is also found that the resulting damping from the frequency control of offshore HVDC is not always reliable as it can be nullified by the power limits of HVDC converters or wind farms. Therefore, using power oscillation damping control in parallel with frequency control is suggested. The analytical findings are verified by simulations on a three-terminal offshore HVDC grid.

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Comparing AC Dynamic Transients Propagated Through VSC HVDC Connection With Master–Slave Control Versus DC Voltage Droop Control

IEEE Transactions on Sustainable Energy ◽

10.1109/tste.2017.2781237 ◽

2018 ◽

Vol 9 (3) ◽

pp. 1285-1297 ◽

Cited By ~ 7

Author(s):

Wenjuan Du ◽

Qiang Fu ◽

Haifeng Wang

Keyword(s):

Droop Control ◽

Dc Voltage ◽

Control Versus

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Implementation of DC voltage controllers on enhancing the stability of multi-terminal DC grids

International Journal of Electrical and Computer Engineering (IJECE) ◽

10.11591/ijece.v11i3.pp1894-1904 ◽

2021 ◽

Vol 11 (3) ◽

pp. 1894

Author(s):

Moussa Belgacem ◽

Mohamed Khatir ◽

Mohammed Abdeldjalil Djehaf ◽

Sid Ahmed Zidi ◽

Riyadh Bouddou

Keyword(s):

Control Strategies ◽

Voltage Control ◽

Wind Farms ◽

Voltage Regulation ◽

Green Energy ◽

Offshore Wind ◽

Dc Voltage ◽

Dc Voltage Control ◽

Simulation Results ◽

The Stability

Because of the increasing penetration of intermittent green energy resources like offshore wind farms, solar photovoltaic, the multi-terminal DC grid using VSC technology is considered a promising solution for interconnecting these future energies. To improve the stability of the multi-terminal direct current (MTDC) network, DC voltage control strategies based on voltage margin and voltage droop technique have been developed and investigated in this article. These two control strategies are implemented in the proposed model, a ±400 kV meshed multi-terminal MTDC network based on VSC technology with four terminals during the outage converter. The simulation results include the comparison and analysis of both techniques under the outage converter equipped with constant DC voltage control, then the outage converter equipped with constant active power control. The simulation results confirm that the DC voltage droop technique has a better dynamic performance of power sharing and DC voltage regulation.

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Demonstration of Converter Control Interactions in MMC-HVDC Systems

Electronics ◽

10.3390/electronics11020175 ◽

2022 ◽

Vol 11 (2) ◽

pp. 175

Author(s):

Jinlei Chen ◽

Sheng Wang ◽

Carlos E. Ugalde-Loo ◽

Wenlong Ming ◽

Oluwole D. Adeuyi ◽

...

Keyword(s):

Power Control ◽

Current Control ◽

Operating Conditions ◽

The Other ◽

Constant Current ◽

Droop Control ◽

Dc Voltage ◽

Control Scheme ◽

Point To Point ◽

Dc Current

Although the control of modular multi-level converters (MMCs) in high-voltage direct-current (HVDC) networks has become a mature subject these days, the potential for adverse interactions between different converter controls remains an under-researched challenge attracting the attention from both academia and industry. Even for point-to-point HVDC links (i.e., simple HVDC systems), converter control interactions may result in the shifting of system operating voltages, increased power losses, and unintended power imbalances at converter stations. To bridge this research gap, the risk of multiple cross-over of control characteristics of MMCs is assessed in this paper through mathematical analysis, computational simulation, and experimental validation. Specifically, the following point-to-point HVDC link configurations are examined: (1) one MMC station equipped with a current versus voltage droop control and the other station equipped with a constant power control; and (2) one MMC station equipped with a power versus voltage droop control and the other station equipped with a constant current control. Design guidelines for droop coefficients are provided to prevent adverse control interactions. A 60-kW MMC test-rig is used to experimentally verify the impact of multiple crossing of control characteristics of the DC system configurations, with results verified through software simulation in MATLAB/Simulink using an open access toolbox. Results show that in operating conditions of 650 V and 50 A (DC voltage and DC current), drifts of 7.7% in the DC voltage and of 10% in the DC current occur due to adverse control interactions under the current versus voltage droop and power control scheme. Similarly, drifts of 7.7% both in the DC voltage and power occur under the power versus voltage droop and current control scheme.

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