Low Voltage Active Distribution Networks Research Articles

A Benchmarking Testbed for Low-Voltage Active Distribution Network Studies

The evolution of distribution networks to active systems as a consequence of the increased penetration of distributed energy resources and the electrification of traditionally fuel-based activities have changed drastically the landscape of power systems operation promoting the necessity of benchmarking tools for planning studies. Nevertheless, there is a scarcity of such tools that enable the holistic analysis of modern power systems according to the new grid standards. In this paper, a multi-purpose benchmarking testbed for low-voltage active distribution networks is introduced. The testbed comprises a granular residential appliance-level dataset, a benchmarking framework based on quasi-static simulations, a set of technical indices and a non-intrusive load monitoring tool. A suite of benchmark case studies including overvoltage, undervoltage and line congestion is presented, supported by ancillary trouble-shooting services, such as voltage control and demand response. The proposed testbed can be a useful tool for distribution system operators to evaluate the operating conditions of the grid without violating technical limitations, test new technologies, identify operational challenges, and foresee grid investments.

Research on Fault Location Method for Low-Voltage Active Distribution Network Based On Correlation Of Main Frequency Components

In order to solve the problems of poor fault tolerance and low fault identification rate, a fault location method based on the correlation of main frequency components is proposed. Based on the distribution network of main frequency components extracted by Prony algorithm, this paper introduces the fault location model of low-voltage active distribution network built by hierarchical algorithm, and realises the correlation of main frequency components based on the research of fault location method of low-voltage active distribution network based on intelligent algorithm. The experimental results show that the fault tolerance rate of the proposed method based on the correlation of main frequency components is over 76% and the fault recognition rate is over 60%, which appears to be higher than several other methods. It is consequently believed that the proposed method may stand a good chance to offer better fault location performance.

Research on fault location method for low-voltage active distribution network based on correlation of main frequency components

Research on fault location method for low-voltage active distribution network based on correlation of main frequency components

A composite power quality index for low-voltage active distribution networks

Abstract In active distribution networks, it is a challenging task for the utility and system operators to identify and analyze the power quality (PQ) disturbance and its cause. Likewise, the consumers are curious about the quality of power supply being provided and the economic impacts of low PQ. Thus, continuous monitoring of the overall quality of the power at the consumer end has become a significant concern in distribution networks. This paper presents a new composite power quality index (CPQI) for low-voltage distribution networks. The CPQI is formulated as a weighted average of five basic parameters, namely voltage level, current harmonic quality, voltage harmonic quality, power factor, and system frequency. The main emphasis is on quantifying the overall quality of the power supply under different PQ disturbance conditions. The CPQI estimate helps in a preliminary investigation of tracking the low PQ location and its source. The proposed CPQI is evaluated on a variety of simulated signals obtained from a CIGRE low-voltage microgrid network. Furthermore, the formulated CPQI is investigated on a LabVIEW-based virtual instrumentation platform with LED loads. It is interpreted from the results that the proposed CPQI is able to evaluate the overall PQ at a load terminal with diverse load conditions subjected to different power quality disturbances.

Hierarchical faulted line section location method for low‐voltage active distribution network considering information distortion

Distortion of fault monitoring information is an important factor that affects the accuracy of faulted line section location in low-voltage active distribution networks (ADNs). This paper proposes a faulted line section location method that considers the layered solution for monitoring information distortion, to improve the accuracy and efficiency of fault location in low-voltage ADNs. A multi-target fault section location optimization model that considers information distortion, multipoint faults, and multiple information distortion types is formulated. A combination of information distortion factors is introduced to represent various types of information distortion and to transform the original optimization model into an unconstrained 0-1 programming problem. A hierarchical fault location algorithm for segmenting the distribution network is designed to solve the low accuracy and efficiency of direct solutions for fault location models resulting from a large number of active distribution line sections. Simulation results show that the fault location method considering information distortion effectively guarantees the accuracy and solution efficiency of faulted line section location of low-voltage ADN.

Robust Fault Protection Technique for Low-Voltage Active Distribution Networks Containing High Penetration of Converter-Interfaced Renewable Energy Resources

With the decentralization of the electricity market and the plea for a carbon-neutral ecosystem, more and more distributed generation (DG) has been incorporated in the power distribution grid, which is then known as active distribution network (ADN). The addition of DGs causes numerous control and protection confronts to the traditional distribution network. For instance, two-way power flow, small fault current, persistent fluctuation of generation and demand, and uncertainty of renewable energy sources (RESs). These problems are more challenging when the distribution network hosts many converter-coupled DGs. Hence, the traditional protection schemes and relaying methods are inadequate to protect ADNs against short-circuit faults and disturbances. We propose a robust communication-assisted fault protection technique for safely operating ADNs with high penetration of converter-coupled DGs. The proposed technique is realizable by employing digital relays available in the recent market and it aims to protect low-voltage (LV) ADNs. It also includes secondary protection that can be enabled when the communication facility or protection equipment fails to operate. In addition, this study provides the detail configuration of the digital relay that enables the devised protection technique. Several enhancements are derived, as alternative technique for the traditional overcurrent protection approach, to detect small fault current and high-impedance fault (HIF). A number of simulations are performed with the complete model of a real ADN, in Shenyang, China, employing the PSCAD software platform. Various cases, fault types and locations are considered for verifying the efficacy of the devised technique and the enabling digital relay. The obtained simulation findings verify the proposed protection technique is effective and reliable in protecting ADNs against various fault types that can occur at different locations.

Bus injection relaxation based OPF in multi-phase neutral equipped distribution networks embedding wye- and delta-connected loads and generators

A novel Optimal Power Flow (OPF) model, based on Semi-Definite Programming approach, for multi-phase active Distribution Networks (DNs) equipped with neutral conductor(s) and both wye- and delta-connected loads/Distributed Generators (DGs) is proposed in this paper. The coupled power injection across phase-neutral and phase-phase conductors is decoupled by modelling of a shunt load/DG through a correction current injection approach and, consequently, explicit power injections are obtained for each conductor of a node. Furthermore, the complete ZIP load representation is considered in the OPF model and two approximations, based on the first-order Taylor series and approximation of the first-order Taylor series, are introduced for the modelling of constant current component of a ZIP load in terms of an optimization variable. Simulations are carried out on several medium and low voltage active DNs under various parameters of the ZIP models for the minimization of either slack-bus power or network losses objective functions. It is successfully demonstrated that the proposed relaxation recovers the global optimal solution of the original OPF problem for both load types (wye and delta) under various combinations of ZIP parameters in the case of lightly or moderately unbalanced DNs, whereas in the case of highly unbalanced DNs, a rank-2 solution is obtained when constant current component dominates the other load components. Furthermore, the impact of unrealistic assumption of Kron reduction approach on the quality of the proposed relaxation for a single or multiple point grounded DNs is also discussed. From a computational point of view, the proposed methodology can be realized on a real-time basis for small DNs. However, for medium and large DNs, the incorporation of additional sparsity exploitation or distributed algorithm techniques are required for its real-time implementation.

Centralized OPF in Unbalanced Multi-Phase Neutral Equipped Distribution Networks Hosting ZIP Loads

The Optimal Power Flow (OPF) model for low voltage active Distribution Networks (DNs), which are equipped with neutral conductors, requires an explicit representation of both phases and neutral conductors in its formulation to obtain complete information about the state variables related to these conductors. In this regard, a centralized OPF relaxation based on semi-definite programming is presented in this paper for neutral-equipped DNs hosting ZIP loads and neutral-ground impedance, and contain a significant level of unbalance. The major restriction in the development of an OPF model for these networks is the coupled power injection across the conductors which is successfully handled by deriving the explicit active and reactive power injections for each conductor through a network admittance matrix-based approach. The shortcomings of existing voltage magnitude-based technique for the modelling of ZIP loads are comprehensively reported and a novel complex voltage variable-based approach is proposed which successfully incorporates ZIP loads in the developed multi-phase OPF relaxation. For the handling of constant current load, a modelling approach based on the first-order-Taylor series is introduced as well. Furthermore, the impact of the application of Kron reduction approach on the global optimal solution of single- and multiple-point grounded DNs is discussed in detail. Three metrics, eigenvalue ratio, power mismatch and cumulative normalized constraint violation, are utilized to evaluate the exactness of proposed relaxation. Simulations, carried out on several medium and low voltage DNs, show that the proposed relaxation is numerically exact under several combinations of ZIP load parameters and a reasonable range of grounding impedance value for both time-varying and extreme system loading scenarios irrespective of the degree of unbalance in a network.

Congestion Management Method of Low-Voltage Active Distribution Networks Based on Distribution Locational Marginal Price

Large-scale distributed energy resources, such as electric vehicles (EVs) asymmetric access to low-voltage distribution systems, may cause security problems, including line congestion, voltage violation, and three-phase unbalance. In this paper, a congestion management method of low-voltage active distribution networks is proposed. The soft open point, a flexible power electronic device, is considered as a direct control means to solve the congestion problem first. A semidefinite programming model based on a symmetrical component method is constructed to optimize the operation strategy that can be efficiently solved to meet the demands of rapid centralized control. To guide the charging behaviors of flexible load represented by EVs, a market mechanism suitable for the low-voltage unbalanced network is further considered. Though linear approximation and sensitivity analysis, a pricing model of flexible load is established accounting for the effect of network loss, voltage variation, voltage three-phase unbalance, and line overload to distribution locational marginal price. Case studies are carried out on the modified IEEE 33-node and IEEE 123-node system to verify the effectiveness and efficiency of the proposed method.

Modeling and Synchronization Stability of Low-Voltage Active Distribution Networks With Large-Scale Distributed Generations

With the large-scale penetration of demand-side distributed generations (DG), the conventional low-voltage distribution network is becoming increasingly complex in the terms of synchronization stability and control. This paper presents the evolution process of energy transfer topology in the mathematical model, analyzes the network model and the synchronization stability of large-scale DGs in a low-voltage active distribution network. Topological mathematical models are established as the object to research incorporate DGs into three networks (i.e., star-shaped, circle-shaped, and tree-shaped networks) without changing the network architecture. Based on the Kuramoto oscillator form from a complex network theory perspective, the large-scale DGs with the frequency-droop controllers in the network can be transformed into a generalized Kuramoto model. Accordingly, by comparing the above proposed models with the standard networks (i.e., fully coupled network, NW small world network, and BA scale-free network), we discuss the synchronization stability for different topology structures of an active distributed network. The effectiveness and the superiority of the proposed topology structure are further demonstrated through numerical simulation methods, including frequency stability, phase stability, order parameters, and spectrum analysis. Furthermore, the improvement of Iceland 189-node grid is employed to prove the better stability with the star-shaped connection.