Abstract
In China, a growing number of regional power grids are interconnected by the line-commutated converter based high voltage direct current (LCC-HVDC) tie-line, forming a large-scale interconnected power grid. As the operation and control of the interconnected power grid are undertaken by multiple control centers, there is a demand for a distributed alternating current (AC)/direct current (DC) power flow algorithm. In this paper, a distributed power flow algorithm considering the LCC-HVDC tie-line is implemented based on the existing work of the author. The paper proposed some technologies to implement the algorithm. In the fixed-point iteration scheme of this paper, the combined boundary bus states are used to calculate the power flow of the DC system, thus the coordination of discrete state variables of the DC system is avoided. Also, the idea that converting the DC tie-line to an AC line is proposed to calculate the extended WARD equivalent of the external network of subsystems. Moreover, the unbalanced power distribution method is improved to make it more in line with the practical situation. Tests were carried out on the IEEE 118-bus system and an interconnected power grid constructed by six IEEE 118-bus systems, the correctness and effectiveness of the algorithm were proved.
Highlights
The simultaneous calculation executed in the integrated network model in existing energy management systems (EMSs) may present challenges when the concerned network consists of different types of systems operated by different entities
The detailed equipment models were maintained by each control center, and graphics platforms could be shared through the web or scalable vector graphics (SVG) if allowed by the market environment, so other advanced applications of local EMS can perform an accurate calculation based on the whole network bus model obtained from the distributed power flow calculation of [1]
Like the distributed optimal power flow, the distributed state estimation can be solved by the distributed optimization techniques, such as constructing an alternative solution mode based on the Lagrange multiplier method [6] or using alternating-direction method of multipliers (ADMM) to solve the state estimation problem [7]
Summary
The simultaneous calculation executed in the integrated network model in existing energy management systems (EMSs) may present challenges when the concerned network consists of different types of systems operated by different entities (independent system operators, transmission system operators, or utilities). Like the distributed optimal power flow, the distributed state estimation can be solved by the distributed optimization techniques, such as constructing an alternative solution mode based on the Lagrange multiplier method [6] or using ADMM to solve the state estimation problem [7] The convergence of this category of algorithms is not very ideal. The reasonable design makes the distributed computing achieve reliable convergence and get correct results without coordinating the discrete state variables The contents of this part: Modeling and power flow calculation method of AC/DC system (Section II), modeling method of the subsystem (Section III), construction of fixed-point iteration scheme (Section IV, part A and B). According to the sequential algorithm, the AC system and the DC system calculate the power flow alternately and exchange the boundary variables until the exchange variables no longer change
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