Abstract
By connecting many wind farms and grids via multi-terminal high-voltage direct current transmission (MT-HVDC), the reserve power of each grid can be shared to balance the power mismatch. Resulting from a shortage of generated power, the frequency nadir and the lowest DC voltage may violate the constraints of continuous operation. Using a trade-off, this paper proposes a new control strategy based on adaptive droop control to make a compromise between DC voltage and grid frequency. By applying the proposed method, the demands from both sides are efficiently met. The proposed method relies on a decentralized approach, avoiding dependence on the communication link. In addition, wind farms are allowable to operate at the optimal power point without using a de-loading strategy. Time-domain simulations are conducted in PSCAD. The improvement in system reliability is proved by comparing with existing methods.
Highlights
High-voltage direct current transmission (HVDC) is a wellknown method of transmitting high power (>500 MW) over long distances
Voltage source converters (VSCs) are becoming popular in HVDC plans owing to bi-directional transmission as well as active and reactive power decoupling control
This paper proposes a method to efficiently re-distribute supporting power during the transient time and maintain both frequency and DC voltage within their limits predefined by the operators of AC and DC grids
Summary
High-voltage direct current transmission (HVDC) is a wellknown method of transmitting high power (>500 MW) over long distances (hundreds of kilometers). Upon a frequency contingency in a specific grid, the connected HVDC terminal quickly mitigates the mismatch using energy from the DC capacitor, which causes DC voltage variation This variation of DC voltage is used as a signal to trigger power support from other synchronous grids. Because the regulation responsibility is shared among many terminals in the DC grid, the DC voltage droop control is preferred due to its high reliability This causes frequency variation in all AC grids since they provide power to the DC system. This paper proposes a method to efficiently re-distribute supporting power during the transient time and maintain both frequency and DC voltage within their limits predefined by the operators of AC and DC grids. The proposed method is validated through simulation and compared with existing methods
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