Voltage Multistability and Pulse Emergency Control for Distribution System with Power Flow Reversal

High levels of penetration of distributed generation and aggressive reactive power compensation may result in the reversal of power flows in future distribution grids. The voltage stability of these operating conditions may be very different from the more traditional power consumption regime. This paper focused on demonstration of multistability phenomenon in radial distribution systems with reversed power flow, where multiple stable equilibria co-exist at the given set of parameters. The system may experience transitions between different equilibria after being subjected to disturbances such as short-term losses of distributed generation or transient faults. Convergence to an undesirable equilibrium places the system in an emergency or \textit{in extremis} state. Traditional emergency control schemes are not capable of restoring the system if it gets entrapped in one of the low voltage equilibria. Moreover, undervoltage load shedding may have a reverse action on the system and can induce voltage collapse. We propose a novel pulse emergency control strategy that restores the system to the normal state without any interruption of power delivery. The results are validated with dynamic simulations of IEEE $13$-bus feeder performed with SystemModeler software. The dynamic models can be also used for characterization of the solution branches via a novel approach so-called the admittance homotopy power flow method.Comment: 13 pages, 22 figures. IEEE Transactions on Smart Grid 2015, in pres

A Novel Smart Grid State Estimation Method Based on Neural Networks

The rapid development in smart grids needs efficient state estimation methods. This paper presents a novel method for smart grid state estimation (e.g., voltages, active and reactive power loss) using artificial neural networks (ANNs). The proposed method which is called SE-NN (state estimation using neural network) can evaluate the state at any point of smart grid systems considering fluctuated loads. To demonstrate the effectiveness of the proposed method, it has been applied on IEEE 33-bus distribution system with different data resolutions. The accuracy of the proposed method is validated by comparing the results with an exact power flow method. The proposed SE-NN method is a very fast tool to estimate voltages and re/active power loss with a high accuracy compared to the traditional methods

Enhanced Network Voltage Management (NVM) Techniques Under the Proliferation of Rooftop Solar PV Installation in Low Voltage Distribution Network (LVDN)

Proliferation of rooftop solar PV distributed generator (PVDG) installation in low voltage distribution network (LVDN) imposes voltage fluctuation challenges that are a threat to distribution system operators. Reactive power control (RPC) methods are insufficient in isolation to combat the overvoltage fluctuations manifested in LVDN with significant grid-tied PVDG installations. Whereas active power curtailment (APC) control can alleviate the voltage fluctuation in such situations and it is achieved at the cost of reduced active power injection. This paper explores how deficiencies in both RPC and APC as separate approaches can be mitigated by suitably combining RPC and APC algorithms. Strategies combining two RPCs and one RPC in conjunction with APC are proposed as two coordinating algorithms by means of instantaneous measurement of node voltage and active power. These coordinating algorithms are embedded in all the rooftop PVDG grid-tied-inverters (GTI), where the GTI coordinates among them for voltage support without exceeding individual inverter VA rating. The result of the combined approach show significant improvement in managing and stabilising the voltage and allows the penetration of PVDG to be increased from 35.65% to 66.7% of distribution transformer (DT) kVA rating

Distributed Generation: Issues Concerning a Changing Power Grid Paradigm

Distributed generation is becoming increasingly prevalent on power grids around the world. Conventional designs and grid operations are not always sufficient for handling the implementation of distributed generation units; the new generation may result in undesirable operating conditions, or system failure. This paper investigates the primary issues involved with the implementation of distributed generation and maintaining the integrity of the power grid. The issues addressed include power flow, system protections, voltage regulation, intermittency, harmonics, and islanding. A case study is also presented to illustrate how these issues can be addressed when designing distributed generation installation on an existent distribution system. The case study design is performed on the campus distribution system of California Polytechnic State University, San Luis Obispo, with the design goal of implementing renewable energy sources to make the campus a net zero energy consumer

The impact of PV generation and load types on the impedance relays during both balanced and unbalanced faults

Photovoltaic (PV) power generation and the types of connected loads both have an effect on protective impedance relays' readings. This paper investigates this effect in a real distribution system installed in the State of Kuwait. It is found that both the dynamic loads and the PV plants have considerable effects in the relay impedance value, which vary according to the load type, PV connection, and fault location. Both single phases to ground fault (unsymmetrical fault) and three-phase fault (symmetrical fault) are investigated. When single line to ground fault occurs at the PV bus (far from relay location), the dynamic loads increase the relay impedance, while the PV plant decreases the relay impedance. When a single phase to ground fault occurs at the relay bus (load bus), the dynamic load decreases the relay impedance, and the PV plant increases it. For a three-phase to ground fault at the relay bus, both dynamic load percentages and PV plant power generation have no effect on the protective relay impedance readings. At this condition, the relay impedance totally depends on the fault resistance. The main finding of this paper is that both the load type (especially dynamic load) and the PV plant have dominant effects on the protective impedance relay reading and setting. The distribution system planners and operators must consider the PV plant and types of load during designing, setting, and adjusting the protective impedance relays. The most important point in this paper is considering real case study. This means that the obtained results are more realistic than the assumed system in the other research

Evolution of microgrids with converter-interfaced generations: Challenges and opportunities

© 2019 Elsevier Ltd Although microgrids facilitate the increased penetration of distributed generations (DGs) and improve the security of power supplies, they have some issues that need to be better understood and addressed before realising the full potential of microgrids. This paper presents a comprehensive list of challenges and opportunities supported by a literature review on the evolution of converter-based microgrids. The discussion in this paper presented with a view to establishing microgrids as distinct from the existing distribution systems. This is accomplished by, firstly, describing the challenges and benefits of using DG units in a distribution network and then those of microgrid ones. Also, the definitions, classifications and characteristics of microgrids are summarised to provide a sound basis for novice researchers to undertake ongoing research on microgrids

Förderung des Aufbaus von Smart Grids in Thailand als Zusammenspiel von intelligenten Gebäuden, intelligenten Verbrauchern und einer intelligenten Energiepolitik

Smart grid technology can enhance renewable energy in the electricity system by integrating information communication technology (ICT) into the existing electricity network. Residential and commercial buildings can perform as a power plant with an energy design concept by integrating renewable energy and energy storage system. However, there has been relatively little focus on how to enhance the residential sector in smart grid development in the context of Thailand. This research focuses on residential buildings only. The technology assessment shows that energy efficiency measures (EEM) must be implemented to reduce the energy demand of the building. The Ice thermal energy storage system (ITES) is an appropriate energy storage system application that can provide cooling energy, which is the major energy consumer in residential building. The integration of EEM, the PV system, and the ITES system can reduce the primary energy demand by 87%, compared to the reference building without comprehensive energy concept design. The power quality assessment shows that the PV hosting capacity is limited up to 75%, which keeps the voltage level in the permissible range. The distributed energy storage system allows the PV prosumer to perform an active role by providing reactive power service to the system at the critical electricity feeder. The economic assessment reveals that the ITES is the most cost-effective investment option, where the battery energy storage (BES) system can become more attractive with incentive support and future cost reduction. The results from the consumer survey reveal that the willingness to pay (WTP) of the EEM and PV system in the detached single-family house is higher than the investment cost, which benefits both consumer and house developer. Technology is a key driver for providing the energy service to the energy system, while consumer behavior and acceptance can increase technology adoption. The Thai government should encourage the residential sector to become a smart user by taking technology, consumer behavior background, and essential energy policy into account.Intelligente Netztechnik, sogenannte Smart Grid-Technologie, kann durch die Einbindung von Informations- und Kommunikationstechnologie die Integration von erneuerbaren Energien in das bestehende Stromnetz verbessern. Wohn- und Gewerbegebäude können mit Hilfe eines Energiekonzepts durch die Integration von erneuerbaren Energien und Energiespeichern als Kleinkraftwerk fungieren. Allerdings gibt es in Thailand bisher wenig Analysen, wie man den Wohnungssektor für die Entwicklung intelligenter Netze nutzbar machen kann. Diese Forschungsarbeit konzentriert sich daher ausschließlich auf Wohngebäude. Die Technologiebewertung zeigt, dass Energieeffizienzmaßnahmen (EEM) umgesetzt werden müssen, um den Energiebedarf der Gebäude zu reduzieren. Ein thermischer Energiespeicher basierend auf Eis (ITES) ist eine geeignete Speicheranwendung, um Kühlenergie bereitzustellen, die der Hauptenergieverbraucher in Wohngebäuden ist. Durch die Integration von EEM, dem PV-System und dem ITES-System kann der Primärenergiebedarf um 87% reduziert werden, verglichen mit einem Referenzgebäude ohne umfassendes Energiekonzept. Die vorliegende Forschungsarbeit zeigt, dass die PV-Aufnahmekapazität auf bis zu 75% ausgeweitet werden kann, ohne dass Spannungsgrenzen verletzt werden. Der dezentrale Energiespeicher ermöglichst es zudem dem PV-Prosumer, durch Blindleistungseinsatz eine aktive Rolle im Stromsystem einzunehmen und Spannungsprobleme in kritischen Leitungssträngen zu reduzieren. Die wirtschaftliche Bewertung zeigt, dass das ITES die kostengünstigste Investitionsoption ist und das Batteriespeichersystem (BES) durch Anreize und künftige Kostensenkungen an Attraktivität gewinnen kann. Die Ergebnisse der durchgeführten Verbraucherbefragung zeigen, dass die Zahlungsbereitschaft für die EEM und das PV-System in Einfamilienhäusern höher ist als die Investitionskosten, was sowohl dem Verbraucher als auch dem Bauherrn des Hauses zugutekommt. Neue Technologien sind zentrale Elemente, um die Bereitstellung von Energiedienstleistungen im Energiesystem zu ermöglichen. Jedoch sind auch Nutzerverhalten und -akzeptanz wichtig, um die Verbreitung der Technologie zu erhöhen. Die thailändische Regierung sollte den Einsatz von Intelligenz im Wohnungssektor fördern und dabei Technologien, Verbraucherverhalten und wesentliche energiepolitische Aspekte berücksichtigen

Analysis of Local Anti-Islanding Detection Methods for Photovoltaic Generators in Distribution Systems

In the current decade, technology innovations and cost reduction of inverter-based Distributed Energy Resources (DERs) have led to higher integration of distributed energy storage and photovoltaic (PV) solar power systems. Increasing growth in PV penetration to the distribution system can raise operational and safety concerns especially in case of an unintended islanding. In general, standards require distributed generators (DGs) to detect islanding from the main grid and cease to energize the local system. Multiple methods have been introduced in the literature to detect these islands reliably and quickly. In order to connect an inverter to distribution system, inverter should pass certain certification tests such as UL 1741 certification test. The anti-islanding test in UL 1741 standard tests only one type of load over a limited range of loading conditions with a single inverter and lumped load and no impedances in between them. The overall goal of this thesis is to determine those parameters to which run-on times (ROTs) are relatively insensitive and thus do not need to be emphasized in certification testing or risk of islanding studies. This thesis presents a generic MATLAB Simulink inverter model and studies sensitivity of anti-islanding tests to parameters such as inverter location, inverter operating point, load location, load type and circuit impedance. Inverters in these studies are equipped with Group 2A and Group 2B anti-islanding methods. The key contributions in this thesis can be summarized as follows: A comprehensive review of anti-islanding techniques in the literature. An anti-islanding detection model was developed in MATLAB software with at least one method from different groups of anti-islanding methods; the model can be used further for industrial applications and research purposes. The result of analyses indicated that the level of phase-phase imbalance, constant-power load, harmonic-current load and irradiance level have a low or negligible impact on anti-islanding and can be omitted from these studies. These findings are expected to lower the cost and improve the speed of these studies, in large distribution systems. Adviser: Sohrab Asgarpoo