Voltage stability of power systems with renewable-energy inverter-based generators: A review

© 2021 by the authors. The main purpose of developing microgrids (MGs) is to facilitate the integration of renewable energy sources (RESs) into the power grid. RESs are normally connected to the grid via power electronic inverters. As various types of RESs are increasingly being connected to the electrical power grid, power systems of the near future will have more inverter-based generators (IBGs) instead of synchronous machines. Since IBGs have significant differences in their characteristics compared to synchronous generators (SGs), particularly concerning their inertia and capability to provide reactive power, their impacts on the system dynamics are different compared to SGs. In particular, system stability analysis will require new approaches. As such, research is currently being conducted on the stability of power systems with the inclusion of IBGs. This review article is intended to be a preface to the Special Issue on Voltage Stability of Microgrids in Power Systems. It presents a comprehensive review of the literature on voltage stability of power systems with a relatively high percentage of IBGs in the generation mix of the system. As the research is developing rapidly in this field, it is understood that by the time that this article is published, and further in the future, there will be many more new developments in this area. Certainly, other articles in this special issue will highlight some other important aspects of the voltage stability of microgrids

Towards Better Understanding of Failure Modes in Lithium-Ion Batteries: Design for Safety

In this digital age, energy storage technologies become more sophisticated and more widely used as we shift from traditional fossil fuel energy sources to renewable solutions. Specifically, consumer electronics devices and hybrid/electric vehicles demand better energy storage. Lithium-ion batteries have become a popular choice for meeting increased energy storage and power density needs. Like any energy solution, take for example the flammability of gasoline for automobiles, there are safety concerns surrounding the implications of failure. Although lithium-ion battery technology has existed for some time, the public interest in safety has become of higher concern with media stories reporting catastrophic cellular phone- and electric vehicle failures. Lithium-ion battery failure can be dangerously volatile. Because of this, battery electrochemical and thermal response is important to understand in order to improve safety when designing products that use lithium-ion chemistry. The implications of past and present understanding of multi-physics relationships inside a lithium-ion cell allow for the study of variables impacting cell response when designing new battery packs. Specifically, state-of-the-art design tools and models incorporate battery condition monitoring, charge balancing, safety checks, and thermal management by estimation of the state of charge, state of health, and internal electrochemical parameters. The parameters are well understood for healthy batteries and more recently for aging batteries, but not for physically damaged cells. Combining multi-physics and multi-scale modeling, a framework for isolating individual parameters to understand the impact of physical damage is developed in this work. The individual parameter isolated is the porosity of the separator, a critical component of the cell. This provides a powerful design tool for researchers and OEM engineers alike. This work is a partnership between a battery OEM (Johnson Controls, Inc.), a Computer Aided Engineering tool maker (ANSYS, Inc.), and a university laboratory (Advanced Manufacturing and Design Lab, University of Wisconsin-Milwaukee). This work aims at bridging the gap between industry and academia by using a computer aided engineering (CAE) platform to focus battery design for safety

The Effects of Interface Protection Requirements on the Stability of Embedded Generation Connected to the Irish Distribution System

The electricity sector in Ireland has undergone a number of changes in the last 20 years. In the early 90’s the fuel mix was predominantly fossil fuel based with a very small percentage of renewables on the system. The electricity generation portfolio was dominated by coal/gas/peat fired power stations which used large synchronous machines to generate electricity. These synchronous machines provided the necessary system inertia and kept the system frequency stable. However, rising fuel costs, dwindling fossil fuel supplies, climate change etc. has driven the growth of renewable energy especially in the electricity sector. Current targets for renewable energy in the electricity sector are set at 40% by 2020. This is outlined in detail in the RES-E targets. As of July 2011, approximately 1700MW of renewable generation capacity was connected to the Irish power system with wind been the largest contributor. Furthermore, in April 2011 wind generation output reached 1323MW. With current projections indicating somewhere between 3000-5000MW of wind energy on the system by 2020, serious concerns are beginning to be raised especially in the area of system stability. With the percentage of electricity generated from wind turbines increasing, it is vital to ensure that this wind generation is not needlessly disconnected from the system. This project focuses on the interface protection requirements to determine if a loosing of the protection requirements could aid system stability. The project will also look at international practice in regards to interface protection requirements with a view to determining if certain international practices could be adopted on the Irish power system. This project will focus mainly on the Doubly Fed Induction Generator wind turbine as this is the predominant turbine on the system. This project will be carried out in PSS/E simulation software

Voltage Stability of Power Systems with Renewable-Energy Inverter-Based Generators: A Review

The main purpose of developing microgrids (MGs) is to facilitate the integration of renewable energy sources (RESs) into the power grid. RESs are normally connected to the grid via power electronic inverters. As various types of RESs are increasingly being connected to the electrical power grid, power systems of the near future will have more inverter-based generators (IBGs) instead of synchronous machines. Since IBGs have significant differences in their characteristics compared to synchronous generators (SGs), particularly concerning their inertia and capability to provide reactive power, their impacts on the system dynamics are different compared to SGs. In particular, system stability analysis will require new approaches. As such, research is currently being conducted on the stability of power systems with the inclusion of IBGs. This review article is intended to be a preface to the Special Issue on Voltage Stability of Microgrids in Power Systems. It presents a comprehensive review of the literature on voltage stability of power systems with a relatively high percentage of IBGs in the generation mix of the system. As the research is developing rapidly in this field, it is understood that by the time that this article is published, and further in the future, there will be many more new developments in this area. Certainly, other articles in this special issue will highlight some other important aspects of the voltage stability of microgrids

A Study of Computationally Efficient Advanced Battery Management: Modeling, Identification, Estimation and Control

Lithium-ion batteries (LiBs) are a revolutionary technology for energy storage. They have become a dominant power source for consumer electronics and are rapidly penetrating into the sectors of electrified transportation and renewable energies, due to the high energy/power density, long cycle life and low memory effect. With continuously falling prices, they will become more popular in foreseeable future. LiBs demonstrate complex dynamic behaviors and are vulnerable to a number of operating problems including overcharging, overdischarging and thermal runaway. Hence, battery management systems (BMSs) are needed in practice to extract full potential from them and ensure their operational safety. Recent years have witnessed a growing amount of research on BMSs, which usually involves topics such as dynamic modeling, parameter identification, state estimation, cell balancing, optimal charging, thermal management, and fault detection. A common challenge for them is computational efficiency since BMSs typically run on embedded systems with limited computing and memory capabilities. Inspired by the challenge, this dissertation aims to address a series of problems towards advancing BMSs with low computational complexity but still high performance. Specifically, the efforts will focus on novel battery modeling and parameter identification (Chapters 2 and 3), highly efficient optimal charging control (Chapter 4) and spatio-temporal temperature estimation of LiB packs (Chapter 5). The developed new LiB models and algorithms can hopefully find use in future LiB systems to improve their performance, while offering insights into some key challenges in the field of BMSs. The research will also entail the development of some fundamental technical approaches concerning parameter identification, model predictive control and state estimation, which have a prospect of being applied to dynamic systems in various other problem domains

Virtual Synchronous Generator Operation of Full Converter Wind Turbine ‒ Control and Testing in a Hardware Based Emulation Platform

Wind is one of the most promising renewable energy forms that can be harvested to into the electrical power system. The installation has been rising worldwide in the past and will continue to steadily increase. The high penetration of wind energy has bought about a number of difficulties to the power system operation due to its stochastic nature, lack of exhibited inertia, and differing responses to the traditional energy sources in grid disturbances. Various grid support functions are then proposed to resolve the issues. One solution is to allow the renewable energy sources to behave like a traditional synchronous generator in the system, as a virtual synchronous generator (VSG). On the other hand, testing the control of the future power grid with high penetration renewable often relies on digital simulation or hardware-based experiments. But they either suffer from fidelity and numerical stability issues, or are bulky and inflexible. A power electronics based power system emulation platform is built in the University of Tennessee. This Hardware Testbed (HTB) allows testing of both system level and component level controls, with a good balance between the fidelity of the hardware-based testing platform, and the coverage of the digital simulation.This dissertation proposal investigates the VSG operation of the full converter wind turbine (FCWT), focusing on its control and testing in the HTB. Specifically, a FCWT emulator was developed using a single converter to include its physical model and control strategies. The existing grid support functions are also included to demonstrate their feasibility.The comprehensive VSG controls are then proposed for a FCWT with short term energy storage. The dynamic response of the FCWT can be comparable to the traditional generation during grid disturbance. The control can also allow the FCWT to be dispatched by the system operator, and even operate stand-alone without other grid sources.To study the system response under faults, a short circuit fault emulator was developed in the HTB platform. Four basic types of the short circuit faults with various fault impedance can be emulated using the emulator. The power system transient stability in terms of critical clearing time can be measured using the developed fault emulator

Wind turbine type IV simulation with grid-following and grid-forming control

The demand for renewable energy is rapidly increasing for several reasons, including global warming, environmental effects, and energy independence for nations that now import the ma- jority of their energy needs. Europe, as a whole, imports more fossil fuels than any other region in the globe, but the continent made the bold choice to become carbon neutral by 2050. Utilizing as much renewable energy as possible, including wind and solar, will be crucial to meet that goal. In many European nations, wind energy is one of the major sources of electricity, and its proportion will rise. Since wind power over the oceans and seas is more plentiful and powerful than wind power on land, off-shore wind farms are one of the keys to advancing the higher penetration of renewables. Repairs and maintenance in offshore wind farms can be complex, in addition to the difficulties brought on by activities on the sea and the problems caused by humidity. The wind turbine Type IV is typically utilized in off-shore applications to reduce maintenance concerns since it may be gearless and may use a permanent magnet generator and full-scale converter. As the penetration of renewables with power converters grows, new control approaches must be considered, and the benefits and drawbacks of each control structure must be weighed. A wind turbine Type IV model with grid-following and grid-forming control was built in Simulink and PSCAD during this project, and their behavior in an IEEE 9-bus system was evaluated at the completio

Electronic identification systems for asset management

Electronic identification is an increasingly pervasive technology that permits rapid data recovery from low-power transponders whenever they are placed within the vicinity of an interrogator device. Fundamental benefits include proximity detection not requiring line-of-sight, multiple transponder access and data security. In this document, electronic identification methods for asset management are devised for the new target application of electrical appliance testing. In this application mains-powered apparatus are periodically subjected a prescribed series of electrical tests performed by a Portable Appliance Tester (PAT). The intention is to enhance the process of appliance identification and management, and to automate the test process as far as possible. Three principal methods of electronic identification were designed and analysed for this application: proximity Radio Frequency Identification (RFID), cable RFID and power- line signalling. Each method relies on an inductively coupled mechanism that utilities a signalling technique called direct-load modulation. This is particularly suited to low- cost passive transponder designs. Physical limitations to proximity RFID are identified including coil size, orientation and susceptibility to nearby conducting surfaces. A novel inductive signalling method called cable RFID is then described that permits automatic appliance identification. This method uses the appliance power cable and inlet filter to establish a communication channel between interrogator and transponder. Prior to commencing the test phase, an appliance is plugged into the PAT and identified automatically via cable RFID. An attempt is made to extend the scope of cable RFID by developing a novel mains power-line signalling method that uses direct-load modulation and passive transponders. Finally, two different implementations of RFID interrogator are described. The first takes the form of an embeddable module intended for incorporation into electronic identification products such as RFID enabled PAT units. Software Defined Radio (SDR) principles are applied to the second interrogator design in an effort to render the device reconfigurable