Abstract
This paper proposed a probabilistic load flow technique of AC/VSC-MTDC (Alternate Current/Voltage Source Control-Multiple Terminal Direct Current) hybrid grids based on an improved stochastic response surface method. The applied traditional stochastic response surface method is inherent with the capability to tackle correlated normal variables; however, the accuracy is poor in the case of correlated diverse distributions. To address this issue, NATAF transformation was adopted to transform the correlated wind speeds and loads following arbitrary distributions into the variables that are subject to standard normal distributions. The collection points could be selected to establish the polynomial relationship among the independent standard normal variables and the output responses. Then, the probability distributions and statistics of the responses could be accurately and efficiently estimated. The modified IEEE 14-bus system, involving an additional VSC-MTDC system, wind speeds following various distributions, and diverse consumer behaviors, was used to demonstrate the validity and capability of the proposed method.
Highlights
In modern power systems, the use of wind power is drawing great attention
Hybrid grids can be properly and efficiently considered; The proposed method could keep a good balance between computational accuracy and speed in the probabilistic load flow (PLF) analysis of AC/VSC-MTDC grids; The means, standard deviations (STDs), probability distribution functions (PDFs), and cumulative distribution functions (CDFs) of the PLF responses can be accurately obtained using the proposed method, without using any SEMs
The key idea of the stochastic response surface method (SRSM) lies in the application of polynomial chaos expansion with input variables following standard Gaussian distributions to simulate the response of a system like the PLF calculation of hybrid AC/VSC-MTDC
Summary
The use of wind power is drawing great attention. By the end of 2020, wind power is predicted to provide 12% of the world’s electricity [1]. The SRSM has high accuracy and computational efficiency, but it could accurately estimate the PDFs and CDFs of the PLF responses without using SEMs. The key idea of the SRSM is to approximate the inputs and outputs of hybrid AC/DC grid power flow models considering stochastic variables, such as wind speeds and loads, by way of polynomial chaos expansion. Random variables following diverse distributions even with correlations in the AC/VSC-MTDC hybrid grids can be properly and efficiently considered; The proposed method could keep a good balance between computational accuracy and speed in the PLF analysis of AC/VSC-MTDC grids; The means, standard deviations (STDs), PDFs, and CDFs of the PLF responses can be accurately obtained using the proposed method, without using any SEMs
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