Abstract
The coastal urban multi-terminal DC (CU-MTDC) is a prospective solution for enhancing the power supply security of the coastal urban power (CUP) grid and integrating the large-scale offshore wind farm. However, the large DC disturbances may significantly impact the CUP power supply security. The existing DC unbalanced power distribution methods are difficult to be applied in the CU-MTDC because of the complicated optimization process and the expansion of the influence range of a DC fault. To solve the above problems, this paper proposes a coordinated control strategy of CU-MTDC under abnormal conditions. First, calculation principles for the active power reference of center coastal urban power (CCUP) grid converters are proposed. Second, a DC unbalanced power coordinated distribution strategy under abnormal conditions is used based on the dynamic priority control to ensure power supply security of the critical AC lines. Third, the controller parameters of CCUP grid converters are calculated. Through a simple control process, the number of the regulation converters is dynamically scheduled according to the DC unbalanced power. The DC fault influence range on the urban power grid can be limited in a sufficiently small area. Simulation verified the effectiveness of the proposed control strategy.
Highlights
With the rapidly increasing urban power load, the security of coastal urban power (CUP) supply is facing challenges [1] because of the shortage of transmission corridors and limitation of short circuit capacity [2,3]
High voltage direct current based on voltage source converter (VSC-HVDC) technology is recognized as an advanced approach for efficient and stable operation in future CUP grid [2], due to their high transmission capability [6,7], the flexibility of power dispatch and no short circuit current limitation et al [2,8]
The five-terminal coastal urban multi-terminal DC (CU-MTDC) and interconnected CUP grid shown in Figure 7 are studied in PSCAD/EMTDC to verify the feasibility of the proposed coordinated control strategy under abnormal conditions
Summary
With the rapidly increasing urban power load, the security of coastal urban power (CUP) supply is facing challenges [1] because of the shortage of transmission corridors and limitation of short circuit capacity [2,3]. On the basis of the [10], the detailed control strategy of a back-to-back VSC-HVDC interconnected two load areas of the urban power grid is proposed in [11]. Compared with the research on urban MTDC, considering the influence of the AC system, the coordinated operation mode and control strategy of MTDC in large power systems have been extensively studied, which can be used for reference. Due to the large-scale power grid and too many optimization factors, this kind of method cannot be applied in real-time control because of the complicated calculation process. The influence range of DC faults on the urban power grid can be limited in a sufficiently small area; the parameter design of controllers is proposed to cooperate with the distribution strategy, which is very friendly to practical engineering realization.
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