access icon free Adaptive backstepping droop controller design for multi-terminal high-voltage direct current systems

Wind power is one of the most developed renewable energy resources worldwide. To integrate offshore wind farms to onshore grids, the high-voltage direct current (HVDC) transmission cables interfaced with voltage source converters (VSCs) are considered to be a better solution than conventional approaches. Proper DC voltage indicates successive power transfer. To connect more than one onshore grid, the DC voltage droop control is one of the most popular methods to share the control burden between different terminals. However, the challenges are that small droop gains will cause voltage deviations, while higher droop gain settings will cause large oscillations. This study aims to enhance the performance of the traditional droop controller by considering the DC cable dynamics. Based on the backstepping control concept, DC cables are modelled with a series of capacitors and inductors. The final droop control law is deduced step-by-step from the original remote side. At each step the control error from the previous step is considered. Simulation results show that both the voltage deviations and oscillations can be effectively reduced using the proposed method. Further, power sharing between different terminals can be effectively simplified such that it correlates linearly with the droop gains, thus enabling simple yet accurate system operation and control.

Inspec keywords: wind power plants; control system synthesis; HVDC power convertors; power cables; HVDC power transmission; power transmission control; voltage control

Other keywords: droop gain settings; traditional droop controller design; renewable energy resources; DC cable dynamics; droop control law; control error; adaptive backstepping droop controller design; voltage source converters; wind power; DC voltage; power transfer; power sharing; multiterminal high-voltage direct current systems; VSC; DC voltage droop control; DC grid; system operation; onshore AC grid; capacitors; backstepping control concept; offshore wind farms; HVDC transmission cables; voltage deviation; inductors

Subjects: DC-AC power convertors (invertors); Power cables; Control system analysis and synthesis methods; AC-DC power convertors (rectifiers); Voltage control; Control of electric power systems; Wind power plants; d.c. transmission

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