Abstract
Continuous commutation failures (CFs) are serious malfunctions in line-commutated converter high-voltage direct current (HVDC) systems that cause the continuous and rapid sag of transmitted power and may threaten the stability of AC systems. The conventional emergency control strategies of AC systems exhibit difficulty in responding quickly and accurately. After suffering from continuous CFs, the forced blocking of direct current (DC) converter to prevent AC system instability might also cause other adverse effects. This study proposes a ride-through control method to improve the endurance capability of AC systems against continuous CFs. An active power output model of inverter station under continuous CFs is built, while considering the process and mechanism of CFs. The impact of continuous DC power sag on the stability of sending-end system is analyzed through a four-area AC/DC equivalent model. A rolling calculation model for the power angle and acceleration area variations of the sending-end system during continuous CFs is established on the basis of model predictive control theory. A calculation method for the emergency power control reference is obtained by using the aforementioned models. Lastly, a ride-through control method for continuous CFs is developed by utilizing the emergency control of adjacent HVDC link. Simulation results show that the proposed control method can improve the endurance capability of an AC system to continuous CFs and reduce blocking risk in an HVDC link.
Highlights
With the rapid development of large-capacity high-voltage direct current (HVDC) transmission technology and the accelerating construction of HVDC projects, hybrid AC/DC power grids are rapidly developing [1,2]
If the stability of an AC system can be guaranteed by an emergency control strategy during continuous commutation failures (CFs), the risk of DC blocking caused by continuous CFs can be reduced
Continuous CFs typically occur during the recovery process, and the maximum transmitted power during CF recovery is determined by the magnitude of AC fault voltage reduction and DC
Summary
With the rapid development of large-capacity high-voltage direct current (HVDC) transmission technology and the accelerating construction of HVDC projects, hybrid AC/DC power grids are rapidly developing [1,2]. Energies 2019, 12, 4183 such as setting a delay time when reclosing a device or implementing generator tripping from the sending-end grid, were proposed in [7,8] to improve the stability of an AC grid. In consideration of the fast power control capability of a DC system [11], a DC power compensation modulation method that is implemented after CF recovery was proposed in [12]; this method can reduce tripped generator capacity in a sending-end system. If the stability of an AC system can be guaranteed by an emergency control strategy during continuous CFs, the risk of DC blocking caused by continuous CFs can be reduced. A ride-through control method for continuous CFs is developed through the emergency control of adjacent HVDC, case studies are performed in MATLAB/SIMULINK to verify the effectiveness of the proposed control method
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