Distribution System Security Region Research Articles

Decoupling and dimension reduction method for distribution system security region

AbstractThe application of the security region methodology in a practical distribution system with large scale normally requires large computer memory and high computation time. To overcome this problem, this article proposes a decoupling and dimension reduction method, which can significantly accelerate the calculation of distribution system security region (DSSR) and is important for the application of the DSSR theory in large‐scale distribution systems. First, the definition of DSSR dimension reflecting the size of solution space and the time complexity is proposed. And the solution algorithm for DSSR dimension is also given. Second, a decoupling and dimension reduction method suitable for the analysis of DSSR is proposed. Following the method, an incidence matrix can be obtained from the DSSR expressions, which can be further divided into multiple block matrices. According to the feeder combinations of the block matrices, the distribution system can be decoupled into multiple sub‐networks for more efficient analysis. Finally, a 10kV distribution network is used in case study to validate the proposed method. The results for a time‐consuming calculation, that is, TSC curve calculation, show that the proposed method can reduce the computation time significantly, making the time‐consuming calculation suitable for the analysis of large‐scale cases.

Concavity-convexity of distribution system security region. Part I: Observation results and mechanism

This paper observes the concavity-convexity of the distribution system security region (DSSR) and explains the observation results. Firstly, DSSR is observed in 2D space, and more complex 2D images are newly discovered. Secondly, to explain how the new images are formed, the concave regions are observed in 3D space, and their inner space and surface characteristics are discovered by convex decomposition. There are two kinds of concave regions, i.e., simple-concave regions and complex-concave regions. The former is only a backup region, while the latter also contains a sectional region covering the surface of the backup region, partially compensating for the dent of the former. Thirdly, based on the load transfer after an N-1 contingency, the mechanisms of the concave regions and new images are revealed. It is found that a concave region is generated by the union of sub-regions formed from multiple load transfer paths. Finally, the observation results and mechanisms are tested on an expanded IEEE RBTS-Bus4 case. This paper is the first in a two-part series on the concavity-convexity of DSSR. It reveals the concave-convex characteristics and mechanisms of DSSR through direct observation, which lays a theoretical foundation for security assessment and optimal control based on DSSR. Part Ⅱ will reveal the concave-convex principle of DSSR through mathematical deduction.

Geometric property of distribution system security region: Size and shape

This paper studies the geometric properties of Distribution System Security Region (DSSR) by defining four indexes, including volume, surface area, volume to surface area ratio, and roundness. First, the volume is defined as the size of DSSR, while the surface area is defined as the size of all the security boundaries of DSSR. Then, two algorithms based on Monte-Carlo sampling are proposed for calculating the volume and surface area of DSSR. To investigate the relationship between volume and surface area, a new index named volume to surface area ratio (VSR) is proposed, which represents the reciprocal of the surface area to form a unit volume. Furthermore, the roundness of DSSR is defined by comparing the DSSR VSR with the geometry VSR, which indicates how close the shape of a DSSR is to a circle. Finally, two distribution network cases are used to verify the proposed concepts and methods. The distribution networks with the same total supply capability may have significantly different DSSR, indicating that the new indexes help distinguish planning schemes more effectively. This paper quantifies the size and shape of DSSR, which improves our observation of distribution networks and opens new possibilities for distribution network plan.

Region based reconfiguration of distribution network: A post-contingency security solution

The N-1 security principle is a key principle for distribution operation. However, it is not taken into account in modern distribution network reconfiguration models, which cannot satisfy security demands. And in order to solve this fundamental problem, this paper proposes a new reconfiguration method for distribution network considering N-1 security constraints. Firstly, distribution system security region are introduced to analyze real-time security as well as sub-concepts of security boundary and security distance are analyzed. Secondly, distribution feeder reconfiguration model is introduced to minimize the net loss considering N-1 security operation constraints. Thirdly, the model is solved by the improved genetic algorithm. Finally, the model of this paper is compared to the existing model and the results show that the reconfiguration strategy can satisfy the N-1 security principle and is better than modern models considering security of power systems, which prove that the proposed model and solving method are correct and effective.

Total supply and accommodation capability curves for active distribution networks: Concept and model

This paper proposes the concept and model of total supply capability (TSC) curve and total accommodation capability (TAC) curve, which is a novel approach to assess the overall capability of an active distribution network (ADN) based on distribution system security region (DSSR). The TSC curve describes the full load supply capability while the TAC curve depicts the full distributed generation (DG) accommodation capability. For the TSC curve and the TAC curve, an ADN has both the upper curves and the lower curves, because both growth and reduction of either load or DG may result in security criticality, and form the upper and lower security boundaries, respectively. A simple test system and IEEE 33-node test system are used to demonstrate the proposed concepts and models. The TAC curve is compared with existing methods to show its advantages and applications. Additionally, it is found that supply capability and accommodation capability are dual; and the operational conditions of the ADN are divided by the four TSC/TAC curves.

Dimension of distribution system security region: concept, calculation and application

This study proposes the concept, calculation and application of dimension of distribution system security region (DSSR). Two forms of DSSR dimension are presented: one is named binary dimension; the other is called unary dimension. First, the binary dimension is defined as the number of security boundaries and the number of variables in them. A method based on main transformers connection vector can obtain binary dimension without listing model expressions of DSSR. Second, the unary dimension is proposed, which uses a single value in the form of Ne × Ne to describe the scale. This form is convenient to compare the scale of different DSSRs. Moreover, a method based on association matrix is also presented. Third, a case is used to illustrate proposed definitions and methods. The relationship between distribution network and its DSSR dimension is analysed separately. Finally, the application of DSSR dimension is discussed. The unary dimension is applied to solve the problem of large-scale combinations for two-dimensional observation on DSSR. Any two feeders are possible to be combined, but many combinations are unnecessary. By the proposed method, the combinations that are really needed can be accurately obtained, and the use of DSSR is simplified.

Mathematical Base and Deduction of Security Region for Distribution Systems With DER

This paper presents the mathematical definition and deduction for distribution system security region (DSSR), which lays a foundation for the DSSR theory. The DSSR is the set of all the N-1 secure operating points in the state space of a distribution system. First, this paper proposes the strict mathematical definition of DSSR, which defines that a set can be called a “region” only if three mathematical conditions are satisfied. Then, the N-1 security is deducted, based on which DSSR is proved existing and is mathematically deducted. As a basic feature of the future smart distribution system with distributed energy resources, the bidirectional power flow is fully considered in the deduction. In the conclusion, the observation and mathematical deduction both show the existence of security region for any distribution system.

Distribution Network Security Situation Awareness Method Based on Security Distance

Situation awareness (SA) refers to the process of perception, comprehension, and state projection of the system, elements, and environmental factors within a volume of time and space. The security assessment is an important part of SA for distribution networks. In this paper, the distribution system security region (DSSR) is used for SA for the first time, and a security SA method based on security distance (SD) is proposed. First, based on the existing DSSR, which is defined as the set of all operating points (OPs) satisfying N - 1 security criterion, this paper supplements the N - 0 DSSR satisfying normal operating constraints. Second, calculate SDs between the OP and security boundaries to determine whether an OP is secure. If one is secure, its SDs can give the security margin; while if one is insecure, its SDs can give the degree of insecurity and the fault, or the overload components can be recognized via the cross security boundary analysis. The situation comprehension for the distribution network security is realized through the above-mentioned information. Third, the security level of distribution networks in the future can be predicted by the trends of SDs. Finally, the feasibility and effectiveness of the proposed method are verified by an actual distribution network case.

Distribution network reconfiguration comprehensively considering N −1 security and network loss

Efficiency pursuit of the distribution system operation should be on the premise of security. This study proposes the network reconfiguration (NR) approach comprehensively considering N -1 security and network loss. A new approach called distribution system security region (DSSR) is first applied in NR problem. The DSSR is the feasible operation space of a system within N -1 security criterion and can quantify the N -1 security margin. Then, the NR is formulated by using the minimum network loss as objective function and the N -1 security margin, which is provided by the DSSR, as constraints. Moreover, the security margin constraints can be customised for each feeder individually, yielding proper compromises between security-related and efficient concerns. Different NR results for multiple security and efficiency requirements are presented on an extended IEEE-RBTS test system. Compared with the traditional minimum-loss NR, the proposed approach reduces the network loss as much as possible with desired security margin, well balancing the security and efficiency of NR.

Observation of Security Region Boundary for Smart Distribution Grid

This paper observes the boundary of distribution system security region (DSSR). DSSR is defined as a set of all the operating points satisfying N-1 security constraints. First, the basic concepts of N-1 security are introduced for distribution system under smart grid background. Then, the dividing phenomenon of operating points security is reported, which indicates that DSSR boundary of a given distribution network exists. Moreover, an approximation method based on N-1 simulation is proposed in order to find DSSR boundary. Then, the observation results of the DSSR boundary are presented for the expanded reliability Busbar test system BUS4 case. The topological characteristics of DSSR boundary are further summarized, which show that the DSSR is a dense set and its boundary is approximately linear. This paper indicates the existence of DSSR and gives a method to observe it. Finally, the benefit of DSSR is illustrated by its typical applications.

Distribution management system framework based on security region for future low carbon distribution systems

In this paper, a new Distribution Management System (DMS) framework based on security region is proposed. First, the concept of Distribution System Security Region (DSSR) is introduced. DSSR is capable to describe the N − 1 security boundary of the whole distribution network, including the secure output range of DGs. This new theoretic tool provides a chance for the implementation of real-time security analysis and active controls in DMS. Second, this paper proposes and describes five security states for distribution system. Third, an upgraded DMS enhanced with DSSR is proposed, which consists of advanced security functions such as preventive and predictive control of the trajectory of operating points. Finally, a practical case is presented to simulate the proposed DSSR-enhanced DMS, in which both the security region of network and the output range of DGs are calculated. Typical security functions are also demonstrated. In conclusion, the new DMS framework aims to help operate the system closed to its security boundary in order to improve the efficiency significantly within same security standard. This work is beneficial for future low carbon distribution systems with high penetration rate of DGs.

Model and Topological Characteristics of Power Distribution System Security Region

As an important tool of transmission system dispatching, the region-based method has just been introduced into distribution area with the ongoing smart distribution grid initiatives. First, a more accurate distribution system security region (DSSR) model is proposed. The proposed model is based on detailed feeder-interconnected topology, and both substation transformer and feeder N-1 contingencies are considered. Second, generic characteristics of DSSR are discussed and mathematically proved. That is, DSSR is a dense set of which boundary has no suspension and can be expressed by several union subsurfaces. Finally, the results from both a test case and a practical case demonstrate the effectiveness of the proposed modeling approach; the shape of DSSR is also illustrated by means of 2- and 3-dimensional visualization. Moreover, the DSSR-based assessment and control are preliminary illustrated to show the application of DSSR. The researches in this paper are fundamental work to develop new security region theory for future distribution systems.

Distribution system security region: definition, model and security assessment

The region-based method has been successfully applied in transmission systems. This study proposes the definition, model and applications of security region for distribution systems. With the ongoing smart grid initiatives, a large amount of real-time network information will be available. This is the motivation of an accurate calculation of the security boundary. First, this study presents the concepts of distribution system security region (DSSR); and discusses N -1 contingency scenarios for both substation transformers and feeders. Second, distribution system security boundary is modelled in the Euclidean space as several intersected hyperplanes. Furthermore, DSSR for substation transformer contingency is modelled as the space surrounded by the security boundaries and the set of all operating points that ensure the distribution system N -1 security. Third, distance from an operating point to a security boundary is formulated and a new index is also presented for security evaluation. The proposed DSSR-based security assessment method provides a new approach for future smart distribution system operation. Finally, the results from a real distribution system have demonstrated the effectiveness of the proposed concepts and methods; and the geometric characteristics of DSSR are also illustrated by means of two-dimensional visualisation of the test system.