Voltage Limit Violations Research Articles

Energy storage configuration method for distribution networks based on moment difference analysis

The integration of a high proportion of distributed PV into distribution networks can cause power backfeeding and voltage limit violations. This paper introduces moment difference analysis theory for distribution networks, reframing PV consumption as the balancing moment difference equations. When maximum node voltage approaches the upper limit, the moment difference between PV and load stabilizes to an approximately constant, termed the standard moment difference. The standard moment difference represents the limit of the network's capacity to consume distributed PV. Essentially, the PV moment is the target for integration, while the load moment serves as the resource to consume the PV moment. Based on this theory, a method for energy storage configuration is proposed. Simplifying a complex multi-branch distribution network into single-branch lines and solving linear equations determines the optimal storage configuration. This method was tested on the Jibei Power Grid and the IEEE 33 and 69 bus systems, increasing computational efficiency by 1611.47–4973.82 times compared to the PSO algorithm, while maintaining an error margin of less than 2.6 %. Furthermore, the discharging strategy reduces the ESS capacity to between 12.39 % and 31.69 % of the original estimate, thereby enhancing both the economic and practical appeal of the approach.

Distributed battery energy storage systems for deferring distribution network reinforcements under sustained load growth scenarios

Energy storage systems can be leveraged in electricity distribution network planning as mitigation alternatives to traditional grid reinforcements if they are strategically installed and operated to reduce congestion and voltage limit violations. This paper examines the technical and economic viability of distributed battery energy storage systems owned by the system operator as an alternative to distribution network reinforcements. The case study analyzes the installation of battery energy storage systems in a real 500-bus Spanish medium voltage grid under sustained load growth scenarios. The results show that, in general, dedicated battery energy storage systems are only a cost-efficient alternative in distribution system planning under very specific conditions, such as when low load growth rates are expected. Nevertheless, they are only required for peak shaving a few days per year. For the analyzed case study, the recoverable portion of their total cost through deferral of distribution system upgrades is higher than the fraction of cycles required for peak shaving under all sustained load growth scenarios. Therefore, it is also explored if mobile battery energy storage systems, capital grants, and revenue stacking can enable battery energy storage systems to become an efficient distribution system planning alternative.

Distributed control of virtual energy storage systems for voltage regulation in low voltage distribution networks subjects to varying time delays

Distributed communication-based strategies are popular for regulating nodal voltages in distribution networks with high penetration of Photovoltaic (PV) sources. Time delays inevitably pose challenges to efficient voltage regulation and power sharing. In response, this paper presents a distributed, event-triggered voltage regulation approach that enables power sharing across virtual energy storage systems (VESS) with different parameters while accommodating diverse time delays. The process begins by determining the delay margin for the primary Volt/Watt controller in a low-voltage distribution network (LVDN), laying the foundation for stable feedback control gain design. To accommodate any arbitrary large and time-varying delays, a distributed resilient event-triggered secondary controller for VESS is designed to share voltage regulation tasks according to their capacities and state of energy (SoE) values. A mathematical analysis, grounded in the Lyapunov–Krasovskii approach, evaluates the stability and convergence of the proposed controller amidst time delays thoroughly. To validate the proposed method, simulation studies are conducted, which demonstrate the effectiveness in mitigating voltage limit violations, even with variable communication delays, and highlight balanced power sharing and SoE among VESS.

Research on a Distributed Photovoltaic Two-Level Planning Method Based on the SCMPSO Algorithm

In response to challenges such as voltage limit violations, excessive currents, and power imbalances caused by the integration of distributed photovoltaic (distributed PV) systems into the distribution network, this study proposes at two-level optimization configuration method. This method effectively balances the grid capacity and reduces the active power losses, thereby decreasing the operating costs. The upper-level optimization enhances the distribution network’s capacity by determining the siting and sizing of distributed PV devices. The lower-level aims to reduce the active power losses, improve the voltage stability margins, and minimize the voltage deviations. The upper-level planning results, which include the siting and sizing of the distributed PV, are used as initial conditions for the lower level. Subsequently, the lower level feeds back its optimization results to further refine the configuration. The model is solved using an improved second-order oscillating chaotic map particle swarm optimization algorithm (SCMPSO) combined with a second-order relaxation method. The simulation experiments on an improved IEEE 33-bus test system show that the SCMPSO algorithm can effectively reduce the voltage deviations, decrease the voltage fluctuations, lower the active power losses in the distribution network, and significantly enhance the power quality.

A new comprehensive framework for cascading outage simulation in power systems

Simulating accurately and fast cascading outages play a critical role in power system security and resilience assessment. This paper proposes a new comprehensive framework for cascading outage simulation, articulated around an extended AC power flow. To address the key modelling features of cascading outage simulation, the proposed framework develops new algorithms for: a) detecting possible islanding, b) frequency control in each island: primary frequency control (PFC), under-frequency load shedding (UFLS) and over-frequency generator tripping (OFGT) and c) improved under-voltage load shedding (UVLS) and load models to avoid the divergence of AC power flow and allow handling voltage instability during the cascade. Tests on a realistic 60-bus system show that the proposed cascading outage simulator can successfully handle islanding, PFC, UFLS, OFGT, and UVLS; it simulates the cascade until there is no violation of system frequency, voltage, and power flow limits in islands that do not experience blackout.

Analysis of voltage limit‐induced barrier for connecting inverter‐based distributed generators to medium voltage networks: Australian case studies

AbstractInverter‐based distributed generators (IBDGs), mainly solar photovoltaic, connected in medium‐voltage (MV) networks cause challenges, such as voltage limit violations, for distribution network service providers (DNSPs), and require advanced network management strategies to mitigate these challenges. A theoretical analysis of the voltage limit‐induced barrier to IBDG connection and their export limits due to the change in network characteristics is imperative for developing new strategies. The authors formulated a relationship between the network equivalent impedance and the IBDG's connection point in the network and further explored the link between the network equivalent impedance and voltage magnitude due to the IBDG connection point. The authors also assessed the voltage limit‐induced barrier to IBDG connections in MV networks and proposed solutions to overcome issues with the dynamic export limit of IBDGs. Four representative Australian MV networks are analysed in DIgSILENT PowerFactory under different scenarios, such as variation in IBDG location and static and dynamic export limits. The authors found that an IBDG connected at the end of the network can achieve better performance in supporting the network voltage. An IBDG with a dynamic export limit can export three times more energy than the static export limit, which benefits both the DNSPs and IBDG owners.

Cyberattack on Phase-Locked Loops in Inverter-Based Energy Resources

This article reveals power grid vulnerabilities by manipulating the phase-locked loop (PLL) in an inverter-based energy resource (IBER). An attacker can exploit the off-nominal frequency operation of a power grid coupled with stability and tracking properties of an IBER PLL to manipulate the inverter and grid operations during strong and weak grid conditions. Employing a modified IEEE-14 bus system, simulation studies show that PLL-based attacks can cause: (i) revenue losses to IBER operators in weak and strong grid conditions, (ii) voltage limit violations and voltage profile deterioration at IBER bus under weak grid condition, and (iii) system-wide power-angle instability under weak and strong grid conditions. To detect the PLL-based attack, we propose attack severity index (ASI) by generating a detection error signal from local grid voltage measurements and PLL estimation. The attack is mitigated by incorporating security as an integral part of the PLL design, yielding a security-aware PLL.

Investigation on Using Low Voltage Automatic Regulation to Minimize the Impacts of Charging Plug-in Electric Vehicles in Distribution Systems

The growth of micro and mini distributed generation and, more recently, the use of electric energy storage systems and the incentives for electric mobility are important examples of the transformations that distribution networks have been going through. In this context, this paper firstly presents the impacts of uncoordinated plug-in electric vehicles (PEVs) charging in a real Brazilian distribution system. Four scenarios were elaborated with different PEVs penetration levels and the results show increased voltage unbalance, system losses, and violations of the steady-state voltage limits, even in the presence of an automatic voltage regulator installed in the medium voltage network. Then, as the main contribution, the potential usage of automatic voltage regulation at the low voltage network was investigated to minimize the negative impacts of uncontrolled PEV charging on distribution system steady-state operation. It is important to highlight that this is not a common practice of utilities in Brazil. The obtained results showed that regulating the voltage at the low voltage side could be an effective solution to keep the voltages within statutory limits.

Leveraging Behavioral Correlation in Distribution System State Estimation for the Recognition of Critical System States

State estimation for distribution systems faces the challenge of dealing with limited real-time measurements and historical data. This work describes a Bayesian state estimation approach tailored for practical implementation in different data availability scenarios, especially when both real-time and historical data are scarce. The approach leverages statistical correlations of the state variables from a twofold origin: (1) from the physical coupling through the grid and (2) from similar behavioral patterns of customers. We show how these correlations can be parameterized, especially when no historical time series data are available, and that accounting for these correlations yields substantial accuracy gains for state estimation and for the recognition of critical system states, i.e., states with voltage or current limit violations. In a case study, the approach is tested in a realistic European-type, medium-voltage grid. The method accurately recognizes critical system states with an aggregated true positive rate of 98%. Compared to widely used approaches that do not consider these correlations, the number of undetected true critical cases can be reduced by a factor of up to 9. Particularly in the case where no historical smart meter time series data is available, the recognition accuracy of critical system states is nearly as high as with full smart meter coverage.

Efficient voltage control of low voltage distribution networks using integrated optimized energy management of networked residential multi-energy microgrids

The optimal energy management system (EMS) of individual and networked residential microgrids and multi-energy microgrids (MEMGs) has received a great deal of attention. Several solutions have been studied to mitigate voltage limit violations due to the increasing penetration level of distributed generation resources (DGRs) and other issues. However, a research gap exists in developing a voltage control-oriented EMS for networked MEMGs (NMEMGs) to overcome the under/over voltage concerns. This paper aims to respond to this research gap by proposing a new voltage control-oriented EMS instead of conventional solutions, e.g., on-load tap changers (OLTCs) and limiting/curtailing output power of DGRs. The simultaneous management of the electrical and thermal supply/demand sides empowers the proposed method from the viewpoint of cost reduction and satisfaction of voltage constraints. Another contribution of this research is using the concept of sensitivity matrix information to calculate/control the voltage of NMEMGs, which is adequately fast and accurate. The voltage control of NMEMGs based on the flexibility of controllable residential thermal/electrical loads and appliances is one of the major advantages of this study. Moreover, the emission costs are considered in the proposed framework. The comparative test results illustrate that significant voltage constraint violations appear if the voltage limits are not considered. On the other hand, obtained results show that less than a 12% increase in the operation cost of some MGs/MEMGs has appeared due to additional constraints of the introduced voltage control-oriented EMS, while all voltage constraints are satisfied.

A streamlined and enhanced iterative method for analysing power system available transfer capability and security

Available Transfer Capability (ATC) is a crucial indicator for ensuring the reliable and efficient electric grid as it helps to manage congestion and ensure that the power flows are kept within safe operating limits. This article presents a novel approach named as modified repeated alternating current power flow (MRACPF) with step-size control mechanism and compares it with the existing techniques like direct current power transfer distribution factors (DCPTDF) and repeated alternating current power flow (RACPF) for analyzing the ATC of the power system during bilateral wheeling transactions in MATLAB environment. The study further assesses the ATC in different multilateral wheeling transactions of two standard test systems (IEEE 30-bus and IEEE 118-bus) and evaluates inter-area ATCs for the IEEE 118-bus system under various operational scenarios. The Composite Security Index (CSI) which is based on both line flow limit and bus voltage limit violations is used to identify and rank the most severe (k-1) line contingencies, and is able to differentiate between secure and insecure state of the power system and furthermore, MRACPF with step-size control mechanism is used to assess ATC during the severe (k-1) line outage and generator outage scenarios for various power transactions. The MRACPF method produces comparable results to the RACPF method for obtaining the Available Transfer Capability (ATC), but it takes less time. This time savings can be significant, especially for larger power systems, where the execution time can be reduced by more than 50%.

Probabilistic approach to investigate the impact of distributed generation on voltage deviation in distribution system

The increasing penetration of renewable-based generation in the distribution network adds randomness to the bus voltage due to its stochastic characteristics. Consequently, the distribution network faces voltage limit violations at multiple buses. In this scenario, the traditional voltage control method fails to maintain the voltage profile of the network due to its slow response time. A fast and dynamic voltage control technique can be achieved by utilizing the voltage-controlling capability of available DGs in the network with the information about the impact of DG-integrated bus on change in voltage at any bus in the network. Evaluating this information using the traditional probabilistic load flow method is computationally inefficient for real-time applications. Therefore, in this paper, a principal component analysis (PCA)-based novel probabilistic voltage sensitivity index (PVSI) is proposed. It ranks the DG-integrated buses by evaluating the impact of power perturbation at DG-integrated buses on changes in voltage at any bus in the network. The PVSI is analytically derived to reduce the computation time for ranking. Further, the proposed PVSI is validated on the 69-bus and the 141-bus distribution systems by comparing it with the traditional Monte Carlo simulation (MCS) and joint differential entropy (JDE) in terms of accuracy and computation time. From the simulation, it is observed that PVSI gives a similar ranking as both methods in less computation time. Due to the advantage in computation time, the proposed method enables the distribution system operator (DSO) to use this information for fast and dynamic voltage control in a real-time scenario.

False Data Injection Impact on High RES Power Systems with Centralized Voltage Regulation Architecture

The increasing penetration of distributed generation (DG) across power distribution networks (DNs) is forcing distribution system operators (DSOs) to improve the voltage regulation capabilities of the system. The increase in power flows due to the installation of renewable plants in unexpected zones of the distribution grid can affect the voltage profile, even causing interruptions at the secondary substations (SSs) with the voltage limit violation. At the same time, widespread cyberattacks across critical infrastructure raise new challenges in security and reliability for DSOs. This paper analyzes the impact of false data injection related to residential and non-residential customers on a centralized voltage regulation system, in which the DG is required to adapt the reactive power exchange with the grid according to the voltage profile. The centralized system estimates the distribution grid state according to the field data and provides the DG plants with a reactive power request to avoid voltage violations. A preliminary false data analysis in the context of the energy sector is carried out to build up a false data generator algorithm. Afterward, a configurable false data generator is developed and exploited. The false data injection is tested in the IEEE 118-bus system with an increasing DG penetration. The false data injection impact analysis highlights the need to increase the security framework of DSOs to avoid facing a relevant number of electricity interruptions.

A successive linearization based optimal power-gas flow method

Optimal power-gas flow (OPGF) problem is a fundamental coordinated operation problem. However, the nonlinear AC power flow model and nonconvex gas flow model pose a huge challenge to OPGF calculation. The common treatments in the existing literature adopt simplified modeling of power and gas systems to obtain a relatively tractable model, which may produce an inaccurate and insecure solution (e.g., violation of voltage limits). Therefore, this paper considers the nonlinear AC power flow modeling and nonconvex gas flow modeling in the OPGF problem. To address the nonconvexities arising from the nonlinear AC power flow model, nonconvex Weymouth equations, and compressors’ gas consumption equations, the concept of successive linearization is introduced and then a successive mixed-integer quadratic programming (SMIQP) method is developed to solve the nonconvex OPGF problem. Numerical results demonstrate the effectiveness of the proposed SMIQP-based OPGF method in terms of high accuracy and high computational efficiency.

Distributed Nodal Voltage Regulation Method for Low-Voltage Distribution Networks by Sharing PV System Reactive Power

With the intensive integration of photovoltaic (PV) sources into the low-voltage distribution networks (LVDN), the nodal voltage limit violations and fluctuation problem cause concerns on the safety operation of a power system. The intermittent, stochastic, and fluctuating characteristics of PV output power leads to the frequent and fast fluctuation of nodal voltages. To address the voltage limit violation and fluctuation problem, this paper proposes a distributed nodal voltage regulation method based on photovoltaic reactive power and on-load tap changer transformers (OLTC). Using the local Q/V (Volt/Var) feedback controller derived from the grid sensitivity matrix, the voltage magnitude information is adopted to adjust the output of PV systems. Moreover, in order to share the burden of voltage regulation among distributed PV systems, a weighted distributed reactive power sharing algorithm is designed to achieve the voltage regulation according to the rated reactive power. Theoretical analysis is provided to show the convergence of the proposed algorithm. Additionally, the coordination strategy for distributed PV systems and OLTC is provided to reduce the reactive power outputs of PV systems. Five simulation case studies are designed to show the effectiveness of the proposed voltage regulation strategy, where the voltage regulation and proportional reactive power sharing can be achieved simultaneously.

Voltage limit violation risk evaluation method considering communication failures in distributed voltage regulation system

With the complexity and scale expansion of distribution network, the active operational management based on cyber physical system has been widely used in distribution network. Distributed voltage regulation is an advanced operational management approach, which requires reliable communication system. In order to evaluate the influence of communication failures on distributed voltage regulation, this paper proposes a voltage limit violation risk evaluation method considering communication failures. First, the model of distributed voltage regulation system is established and the consensus algorithm in distributed voltage regulation is detailed. On this basis, an improved consensus algorithm concerning the impact of communication failures is proposed. Second, a curve clustering algorithm is proposed to cope with the uncertainties of distributed generations. Then, a voltage limit violation risk evaluation method considering the uncertainties of communication failures and distributed generations is proposed. Finally, the proposed method is proved to simulate the distributed voltage regulation procedure considering communication failures. This study could provide a technical foundation for the planning and operation of active distribution network.© 2017 Elsevier Inc. All rights reserved.

Appraisal of Available Transfer Capability Determination Methods in Competitive Electricity Market

The existing power market is contentiously promoting sustainability and competitiveness in the electricity industry. It has raised the transmission networks' transfer capacity as an emerging area for researchers. The electricity production units and consumers share the same transmission network. All stakeholders try to generate power from cheaper sources to make more significant profit margins. This situation creates transmission congestion, violation of voltage and thermal limits, and system security threats. The accurate measurement and optimal use of the available transfer capability (ATC) shall resolve this issue up to some extent. Thus, efficient evaluation of ATC is needed to ensure system security, and it provides an open and trending research topic. This article presents a review of the various techniques for ATC determination and provides the characteristics, practices, and features of the methods. This analysis demonstrates the issues of ATC evaluation techniques and provides the research areas to the researchers.

Research and application of voltage coordinated control method for distributed photovoltaic connected to low voltage distribution network

Distributed photovoltaic access is likely to cause the problem of voltage limit violations, which greatly affects the consumption of distributed photovoltaics. At present, the existing methods do not consider the coordinated control of multiple voltage levels. In response to this problem, this article firstly analyzes the multi-voltage coordinated control method of distribution network. On the basis of data analysis, this paper formulates a control method for regulating the low-voltage distribution network by using the medium-voltage network.. In addition, optimized calculations were carried out on the voltage condition range of distributed photovoltaic access to the low-voltage distribution network. Finally, this paper analyzes the impact of distributed photovoltaic access on the voltage level of the distribution network, and provides a technical reference for the economic operation of the distribution network.

Effective Volt/var Control for Low Voltage Grids with Bulk Loads

This paper investigates the voltage and reactive power control problem in low voltage grids with connected prosumers and bulk loads. The X(U) local control, which maintains the voltage at the feeders’ ends within a predefined band, and its combination with Q-Autarkic customer plants are the most effective and reliable strategies in grids with high prosumer share. However, these strategies may need adaptations to guarantee voltage limit compliance when bulk loads, such as electric vehicle parking garages and community-owned photovoltaic systems, are connected to the low voltage feeders. This paper extends the X(U) local control concept to involve bulk loads in Volt/var control and investigates the resulting load flows in different real low voltage grids. The results show that the extended control arrangement reliably removes all voltage limit violations by deteriorating the effectiveness of the original X(U) local control arrangement: reactive power flows and equipment loading within the low voltage grids are increased.

A Framework for Analytical Power Flow Solution Using Gaussian Process Learning

This paper proposes a novel analytical solution framework for power flow (PF) solutions in active distribution networks under uncertainty. We use the Gaussian process (GP) regression to learn node voltage as a function of effective bus load or negative net-injection vector. The proposed approximation is valid over a subspace of load and provides an understanding of system behavior under uncertainty via GP interpretability. We interpret the relative variation extent of different node voltages using the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">quality ratio</i> (QR) defined based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hyper-parameters</i> of GP. Further, the application of the proposed framework in calculation of voltage limit violation probability and dominant voltage influencer ranking has also been presented. Through test simulations for 33-bus and 56-bus systems, the proposed method achieves low mean absolute error (MAE) of order E-05 (pu) in voltage magnitude and E-04 (rad) in angle. The discussions on salient features of the proposed method and comparative analysis with large-scale Monte-Carlo simulations, and state-of-art methods is also presented for the proposed applications.