Abstract
Latest unified power flow controller (UPFC) projects adopt novel device structures to meet the requirements of practical applications. Developing power flow calculation methods for these new UPFC structures is of great significance for the design and operation of related projects. To address this issue, this paper deduces an equivalent model of the general structure UPFC, and presents the modified power mismatch equations and Jacobian matrix of the system. Then, three power flow calculation methods suitable for the novel structure UPFC are proposed based on the Newton–Raphson algorithm. The main difference between the three methods is the processing method of UPFC equivalent power injections and the Jacobian matrix. The characteristics of these methods are compared by case studies. Results demonstrate the effectiveness of the three methods for different UPFC structures, and it is found that the improved method, which considers the impact of the Jacobian matrix modifications in UPFC equivalent power injections, can realize power flow calculation in existing calculation programs, and improve the convergence characteristics.
Highlights
Flexible AC transmission systems (FACTS) are a collection of power electronic-based controllers [1,2], including the static var compensator (SVC), static synchronous compensator (STATCOM), static synchronous series compensator (SSSC), unified power flow controller (UPFC), etc
Using the power mismatch equations and the Jacobian matrix given above, the power flow of the power systems with novel structure UPFC can be solved by the Newton–Raphson algorithm
This paper deduces a decoupled UPFC model based on the general structure UPFC
Summary
Flexible AC transmission systems (FACTS) are a collection of power electronic-based controllers [1,2], including the static var compensator (SVC), static synchronous compensator (STATCOM), static synchronous series compensator (SSSC), unified power flow controller (UPFC), etc. Different from the early projects, the latest projects present the following characteristics in terms of the UPFC device structure: (1) As most of the 110 kV and above power grids in China adopt double-circuit lines, the UPFC series side may contain two converters that control the power flows of the double-circuit lines separately, in order to improve the overall transmission capacity; (2) In view of the low demand for reactive power in urban high-voltage grids, the UPFC shunt-side bus can be changed from the original bus to a lower voltage bus to save occupation and investment These novel UPFC structures have been practically applied because of their technical and economic advantages, and provide important references for further applications of.
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