Yinhong Li

Multiobjective Optimal Reactive Power Flow Using Elitist Nondominated Sorting Genetic Algorithm: Comparison and Improvement

Elitist nondominated sorting genetic algorithm (NSGA-II) is adopted and improved for multiobjective optimal reactive power flow (ORPF) problem. Multiobjective ORPF, formulated as a multiobjective mixed integer nonlinear optimization problem, minimizes real power loss and improves voltage profile of power grid by determining reactive power control variables. NSGA-II-based ORPF is tested on standard IEEE 30-bus test system and compared with four other state-of-the-art multiobjective evolutionary algorithms (MOEAs). Pareto front and outer solutions achieved by the five MOEAs are analyzed and compared. NSGA-II obtains the best control strategy for ORPF, but it suffers from the lower convergence speed at the early stage of the optimization. Several problem-specific local search strategies (LSSs) are incorporated into NSGA-II to promote algorithm’s exploiting capability and then to speed up its convergence. This enhanced version of NSGA-II (ENSGA) is examined on IEEE 30 system. Experimental results show that the use of LSSs clearly improved the performance of NSGA-II. ENSGA shows the best search efficiency and is proved to be one of the efficient potential candidates in solving reactive power optimization in the real-time operation systems.

A method for coherency identification based on singular value decomposition

A novel method to identify coherent generator groups based on singular value decomposition (SVD) in power system is presented in this paper. Via the SVD algorithm, the high-dimensional real-time rotor-angle data of generators is projected into low-dimensional subspace, and the key characteristic coefficients indicating the information of coherency is obtained. Then, the coherency identification is realized by running k-means clustering algorithm on the coefficients. The dimensionality reduction for clustering algorithm by SVD speeds up the coherency identification. Using the real-time rotor-angle data, the proposed method has the potential to be applied to measured data to implement coherency identification. The effectiveness of this method is demonstrated by the simulation results on IEEE 39-bus system.

Provision of Two-area Automatic Generation Control by Demand-side Electric Vehicle Battery Swapping Stations

Application of demand-side resources to automatic generation control (AGC) has a great significance for improving the dynamic control performance of power system frequency regulation. This paper investigates the possibility of providing regulation services by demand-side energy storage in electric vehicle battery swapping stations (BSS). An interaction framework, namely station-to-grid (S2G), is presented to integrate BSS energy storage into power grid for giving benefits to frequency regulation. The BSS can be regarded as a lumped battery energy storage station through S2G framework. A supplementary AGC method using demand-side BSS energy storage is developed considering the vehicle user demand of battery swapping. The effects to the AGC performance are evaluated through simulations by using a two-area interconnected power grid model with step and random load disturbance. The results show that the demand-side BSS can significantly suppress the frequency deviation and tie-line power fluctuations.

Study on power system heterogeneous graphics exchange based on IEC 61968 location package and SVG

The diversity of graphics models and data models in the electric utility software environment leads to much repetitive work and impede information sharing greatly. CIM in IEC 61970 defines most of the main objects in the electric utility enterprise, which can facilitate data exchange among heterogeneous applications. Howerver, with the development of power system, graphics information exchange among heterogeneous applications becomes more and more desirable. By analyzing two graphics exchange approaches proposed by CCAPI, the way to exchange graphics information in a standardized form combining IEC 61968 Location package and SVG is introduced. An asynchronous graphics exchange mechanism based on publish/subscribe architecture is proposed, which can greatly reduce the redundancy information and enhance the exchange efficiency.

Enhancing the Performance of Biogeography-Based Optimization Using Multitopology and Quantitative Orthogonal Learning

Two defects of biogeography-based optimization (BBO) are found out by analyzing the characteristics of its dominant migration operator. One is that, due to global topology and direct-copying migration strategy, information in several good-quality habitats tends to be copied to the whole habitats rapidly, which would lead to premature convergence. The other is that the generated solutions by migration process are distributed only in some specific regions so that many other areas where competitive solutions may exist cannot be investigated. To remedy the former, a new migration operator precisely developed by modifying topology and copy mode is introduced to BBO. Additionally, diversity mechanism is proposed. To remedy the latter defect, quantitative orthogonal learning process accomplished based on space quantizing and orthogonal design is proposed. It aims to investigate the feasible region thoroughly so that more competitive solutions can be obtained. The effectiveness of the proposed approaches is verified on a set of benchmark functions with diverse characteristics. The experimental results reveal that the proposed method has merits regarding solution quality, convergence performance, and so on, compared with basic BBO, five BBO variant algorithms, seven orthogonal learning-based algorithms, and other non-OL-based evolutionary algorithms. The effects of each improved component are also analyzed.

Assessment of transmission reliability margin using stochastic response surface method

Transmission reliability margin (TRM) is the amount of transmission capability ensuring that the transmission network is secure from the uncertainty in system operating condition. The accurate evaluation of TRM is of great importance in the calculation of available transfer capability (ATC). This paper presents a fast assessment method of TRM using stochastic response surface method (SRSM). The statistics and probability distributions of TRM can be accurately estimated with less computational cost. The effectiveness of the proposed method is demonstrated by several case studies of the modified IEEE 30-bus standard test systems with wind farm integration.

Research on branches group based method for adding mutual inductance branches to Y-matrix and Z-matrix

In the process of constructing Y-matrix and Z-matrix by traditional method of adding branches, the additional of mutual inductance line is more complex than non-mutual inductance line. A novel algorithm of constructing Y-matrix and Z-matrix based on branches group is put forward in this paper. The algorithm can unify the calculation method of mutual inductance branches and non-mutual inductance branches efficiently. The calculation amount of adding mutual inductance branches is reduced to as same as that of non-mutual inductance branches. Case studies show that the computing method based on the algorithm provided by this paper is simple and unified, reduces the amount of computation and improves the computational efficiency.

Comparison and classification of objective-converting methods in multi-objective reactive power optimization using contour lines

Objective-converting methods (OCMs) are commonly used to solve multi-objective reactive power optimization (MRPO) problem. In this paper, contour line, a common concept in geography, is introduced to compare and classify OCMs in MRPO. Firstly, OCMs adopted in MRPO problem are summarized. Then, contour lines of different OCMs are drawn in objective function space and search direction of OCMs is analyzed. Based on the shape and characteristics of contour lines, different OCMs are compared and classified. All of studies are a good reference for the further study in MRPO.