Optimized Reactive Power Capability of Wind Power Plants with Tap-Changing Transformers
Abstract : With the recent advancements in power electronics for wind turbines (WTs) and increasing penetration of wind energy, wind power plants (WPP) have become necessary contributors of reactive power support for the bulk power system. Balancing reactive power support with individual WT operating requirements in a cost-effective manner is a challenge for WPP designers. In this paper, we present a methodology to optimize the WPP reactive power capability as seen from the point of common coupling (PCC), accounting for steady-state operating capabilities of the WPP equipment. Thus, the proposed methodology determines the configuration of the tap-changing transformers within the WPP that maximizes the amount of reactive power the WPP can either consume or inject to the network, considering uncertain levels of wind power generation and voltage magnitudes at the PCC. The optimized reactive power capability (ORPC) problem is initially formulated as a mixed-integer nonlinear programming (MINLP) model. Then, a set of efficient linearization techniques are used to obtain a mixed-integer linear programming (MILP) model that can be solved via off-the-shelf mathematical programming solvers. Results demonstrate that the proposed MILP model is a scalable, flexible and accurate method to maximize the reactive power capability of WPP.
? It considered discrete controllers, scenarios, probability of each scenario, operation mode, electrical and operation limits, all in a unique integrated MILP model.
? This proposed MILP model can be solved using existing off-the-shelf convex optimization solvers, achieving the following benefits: (a) Obtain a tap-setting of the WT and main transformers for the operation of a WPP, according to the type of case study; (b) Convergence to optimality is guaranteed by MILP commercial solvers; and (c) A scalable, flexible and accurate MILP model with a low computational burden.
? A novel, scalable, flexible, and accurate method to solve the RPC problem, with a low computational burden for large WPPs.
? This article deals with reactive power reserve and support from wind power plants (WPP).
? The reactive power reserves conventionally provided by exciter of synchronous generator reduces when replaced by WPPs. This can cause voltage stability issues.
? This issue is further pronounced in weak grids where WPPs are connected to the grid through long lines.
? The need for analysis of reactive power support from WPP is especially essential when the grid is in a stressed condition.
? Using this equivalent WPP collection system model, reactive power capability of any type of WPP can be obtained because the equivalencing method can be applied to any type of WPP
• In this paper, we present a methodology to optimize the WPP’s reactive power capability as seen from the point of common coupling (PCC).
• To this end, the proposed methodology determines the configuration of the tap-changing transformers within the WPP that maximizes the amount of reactive power the WPP can either consume or inject into the network, considering uncertain levels of wind power generation and voltage magnitude at the PCC.
• A novel scalable, flexible and accurate MILP model for solving the ORPC problem, considering NLTC/OLTC transformers and shunt capacitor banks, scenarios, probability of each scenario, operation mode, electrical and operation limits, all in a unique integrated proposed MILP model.
? This method is used as the base case for comparison of results in this study.
? Though this method provides accurate an WPP reactive power capability, the disadvantages of this method are: (i) Many parameters required, (ii) can have high computation time for large WPPs, and (iii) when simulating large power systems with numerous WPP, including detailed model of each WPP may not be efficient.
? It can be therefore concluded that using the proposed model, the WPP reactive power capability is accurately determined using a reduced number of parameters.
? Thus, a fast and efficient calculation of reactive power availability compared to the reactive power capability of the WPP detailed model can be obtained.
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