This study presents the analysis of debates on the future super grid in China. The rapid increase of power demands and the uneven distribution of energy bases and load demands in China require bulk-capacity long-distance power transmission. Two candidate solutions are thus proposed, that is, the ultra-high-voltage ac (UHVAC) synchronous power grid and the extra high-voltage ac (EHVAC) asynchronous super power grid. The debates on the above two power grids are first reviewed. The two candidate power grids are then compared in detail in terms of security, economic and environmental aspects. Finally, this study provides a suggestion for the construction of UHV synchronous power grid in China as well as the future research direction. The research, discussion and conclusion related to UHVAC and EHVAC transmissions in China are expected to provide useful references for power system planning in other countries and to promote the development of the global power industry.
Focused on the challenges raised by the largescale integration of renewable energy resources and the urgent goal of energy saving, a novel control scheme for the unified power flow controller (UPFC) series converter is proposed to achieve line loss reduction and security enhancement in distribution systems with a high penetration of renewable energy. Firstly, the line loss minimum conditions of a general distribution system with loop configurations are deduced. Secondly, security constraints including the permissible voltage range, the line loading limits and the UPFC ratings are considered. System security enhancement with the least increase in line loss is tackled by solving a much reduced optimal power flow (OPF) problem. The computational task of the OPF problem is reduced by deducing the security-constrained line loss minimum conditions and removing the equality constraints. Thirdly, a hybrid control scheme is proposed. Line loss minimization is achieved through a dynamic controller, while an OPF calculator is integrated to generate corrective action for the dynamic controller when the security constraints are violated. The validity of the proposed control strategies is verified in a modified IEEE 33 bus test system.
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