Advancements in Real-Time Simulation of Power and Energy Systems

Modern power and energy systems are characterized by the wide integration of distributed generation, storage and electric vehicles, adoption of ICT solutions, and interconnection of different energy carriers and consumer engagement, posing new challenges and creating new opportunities. Advanced testing and validation methods are needed to efficiently validate power equipment and controls in the contemporary complex environment and support the transition to a cleaner and sustainable energy system. Real-time hardware-in-the-loop (HIL) simulation has proven to be an effective method for validating and de-risking power system equipment in highly realistic, flexible, and repeatable conditions. Controller hardware-in-the-loop (CHIL) and power hardware-in-the-loop (PHIL) are the two main HIL simulation methods used in industry and academia that contribute to system-level testing enhancement by exploiting the flexibility of digital simulations in testing actual controllers and power equipment. This book addresses recent advances in real-time HIL simulation in several domains (also in new and promising areas), including technique improvements to promote its wider use. It is composed of 14 papers dealing with advances in HIL testing of power electronic converters, power system protection, modeling for real-time digital simulation, co-simulation, geographically distributed HIL, and multiphysics HIL, among other topics

Cyber-Security Solutions for Ensuring Smart Grid Distribution Automation Functions

The future generation of the electrical network is known as the smart grid. The distribution domain of the smart grid intelligently supplies electricity to the end-users with the aid of the decentralized Distribution Automation (DA) in which intelligent control functions are distributed and accomplished via real-time communication between the DA components. Internet-based communication via the open protocols is the latest trend for decentralized DA communication. Internet communication has many benefits, but it exposes the critical infrastructure’s data to cyber-security threats. Security attacks may not only make DA services unreachable but may also result in undesirable physical consequences and serious damage to the distribution network environment. Therefore, it is compulsory to protect DA communication against such attacks. There is no single model for securing DA communication. In fact, the security level depends on several factors such as application requirements, communication media, and, of course, the cost.There are several smart grid security frameworks and standards, which are under development by different organizations. However, smart grid cyber-security field has not yet reached full maturity and, it is still in the early phase of its progress. Security protocols in IT and computer networks can be utilized to secure DA communication because industrial ICT standards have been designed in accordance with Open Systems Interconnection model. Furthermore, state-of-the-art DA concepts such as Active distribution network tend to integrate processing data into IT systems.This dissertation addresses cyber-security issues in the following DA functions: substation automation, feeder automation, Logic Selectivity, customer automation and Smart Metering. Real-time simulation of the distribution network along with actual automation and data networking devices are used to create hardware-in-the-loop simulation, and experiment the mentioned DA functions with the Internet communication. This communication is secured by proposing the following cyber-security solutions.This dissertation proposes security solutions for substation automation by developing IEC61850-TLS proxy and adding OPen Connectivity Unified Architecture (OPC UA) Wrapper to Station Gateway. Secured messages by Transport Layer Security (TLS) and OPC UA security are created for protecting substation local and remote communications. Data availability is main concern that is solved by designing redundant networks.The dissertation also proposes cyber-security solutions for feeder automation and Logic Selectivity. In feeder automation, Centralized Protection System (CPS) is proposed as the place for making Decentralized feeder automation decisions. In addition, applying IP security (IPsec) in Tunnel mode is proposed to establish a secure communication path for feeder automation messages. In Logic Selectivity, Generic Object Oriented Substation Events (GOOSE) are exchanged between the substations. First, Logic Selectivity functional characteristics are analyzed. Then, Layer 2 Tunneling over IPsec in Transport mode is proposed to create a secure communication path for exchanging GOOSE over the Internet. Next, communication impact on Logic Selectivity performance is investigated by measuring the jitter and latency in the GOOSE communication. Lastly, reliability improvement by Logic Selectivity is evaluated by calculating reliability indices.Customer automation is the additional extension to the smart grid DA. This dissertation proposes an integration solution for the heterogeneous communication parties (TCP/IP and Controller Area Network) in Home Area Network. The developed solution applies Secure Socket Layer in order to create secured messages.The dissertation also proposes Secondary Substation Automation Unit (SSAU) for realtime communication of low voltage data to metering database. Point-to-Point Tunneling Protocol is proposed to create a secure communication path for Smart Metering data.The security analysis shows that the proposed security solutions provide the security requirements (Confidentiality, Integrity and Availability) for DA communication. Thus, communication is protected against security attacks and DA functions are ensured. In addition, CPS and SSAU are proposed to distribute intelligence over the substations level

Novel Methods for Loss of Mains Protection

Small-scale generation connected to distribution networks has increased significantly in recent years. This trend is driven by developments in distributed generation (DG) technologies, environmental concerns and economic reasons. The diffusion of generation into the distribution network level has many potential benefits, but it also raises challenges, such as unintentional islanding, which is hazardous to the safety of both personnel and equipment. Due to the safety risks, all DG units need to be equipped with a loss of mains (LOM) protection scheme capable of rapidly detecting and stopping islanding. LOM protection methods can be divided into passive, active and communication-based methods. Passive methods rely on detecting islanding by monitoring chosen system quantities. These methods are affordable and applicable to all types of DG units, but their performance is highly dependent on the local power imbalances between the production and consumption in the islanded zone. Most, if not all, passive methods, fail to detect islanding if the local production closely matches the local consumption. The set of power imbalance combinations that lead to non-detected islanding is referred to as the non-detection zone (NDZ). Active methods are based on deliberately injecting small perturbations to the grid and monitoring the response of the system. These methods generally have smaller NDZ than passive methods. However, this comes at the cost of degraded power quality. Communication-based methods rely on other means than the local monitoring of system quantities, which makes them immune to the NDZ problem. However, these methods tend to be costly.The performance of passive and active methods can be improved by applying more sensitive LOM protection settings. However, if the LOM protection settings are too sensitive, voltage dips caused by faults in the transmission grid may result in a cascading disconnection of DG. In order to avoid such risks, which threaten the system’s stability, many grid codes include fault-ridethrough (FRT) requirements, which specify the depth and duration of voltage dips which DG units need to be able to withstand. FRT requirements often also require the DG units to feed reactive current to the grid during the voltage dip in order to support the system voltages. The work conducted for this thesis indicates that FRT requirements significantly degrade the performance of LOM protection. This thesis also studies how the type of the protected DG unit affects LOM protection. The frequency of an islanded circuit sustained by a directly-coupled synchronous generator is determined by the local active power imbalance, whereas the frequency of an islanded circuit sustained by a converter-coupled DG unit is determined by the local reactive power imbalance. However, when there are both directly-coupled synchronous generators and convertercoupled DG units in an islanded circuit, the synchronous generator seems to dominate these relationships. This has significant implications on the performance of active LOM protection schemes.One of the main issues distribution system operators face when they are evaluating the adequacy of LOM protection for DG installations is the lack of suitable analysis tools. This thesis proposes a novel LOM risk management procedure which utilizes the existing analysis tools embedded in a modern network information system (NIS). This NIS-based procedure analyzes what kind of power imbalance combinations are possible in the studied network sections. Based on the possible combinations of power imbalances and predefined NDZ mappings of optional LOM protection schemes, the procedure tells protection engineers if there are any risks of non-detected islanding in the analyzed network sections and proposes which LOM protection schemes would be most suitable for each DG installation. Although the proposed LOM risk management tool is presented at the concept level only here, it is clearly a promising area for future research.Two active LOM protection methods and one communication-based protection automation concept were also developed during this thesis work. The first of the active LOM protection methods is based on forcing the frequency of an islanded circuit out of the utilized frequency thresholds by constant injection of reactive power pulses and a dedicated reactive power versus frequency droop. The knowledge gained during the development of this method resulted in a second, significantly more advanced, active LOM protection scheme. This is based on forcing the rate-ofchange-of-frequency of an islanded circuit to a desired value by applying a dedicated reactive power versus frequency droop. This method is able to detect islanding rapidly and reliably even if the local power imbalances are negligible. Moreover, this can be achieved with a very modest injection of reactive power. The communication-based protection automation concept is designed to solve typical DG related protection challenges and to automatically change the feeding path of the protected DG unit in case if the original feeding route becomes faulted. However, the successfulness of the automatic feeding path changing depends on many factors such as DG unit type, network parameters and the momentary input power provided by the primary energy source.The methods developed in this thesis have slightly different purposes. The proposed NIS-based LOM risk assessment procedure is useful for evaluating the adequacy of existing LOM protection as well as for choosing optimal LOM protection schemes for new DG installations. If the LOM risk assessment procedure indicates that the local power imbalances will always be very large, then passive LOM protection schemes are a sensible choice. However, should the LOM risk assessment procedure reveal that the local power imbalances could be so small that reliable LOM protection cannot be ensured with passive LOM protection schemes, then active or communication-based LOM protection schemes are preferable. Active LOM protection schemes are suitable if the ratio of converter-coupled to directly-coupled generator capacity in the analyzed zone is large. This is because certain active LOM schemes, such as the one proposed in this thesis, are able to detect islanding reliably and rapidly even if the local active- and reactive power imbalances would be negligible, provided that the ratio between converter coupled to directly coupled synchronous generator capacity is large. However, if a significant proportion of the generation capacity in the analyzed network section is synchronous generator based, then sensitive and rapid LOM protection cannot always be guaranteed. In such cases, it is advisable to utilize advanced communication-based LOM protection schemes which are immune to the NDZ problem

Power System Digital Twins and Real-Time Simulations in Modern Grids

Power systems are in a state of constant change with new hardware, software and applications affecting their planning, operation, and maintenance. Power system control centers are also evolving through new technologies and functionalities to adapt to current needs. System control rooms have moved from fully manual to automated operations, from analog to digital, and have become an embedded and complex information, communication, computation and control system. Digital twins are virtual representations of physical systems, assets and/or processes. They are enabled through software, hardware and data integration, and allow real-time monitoring, controlling, prediction, optimization, and improved decision-making. Consequently, digital twins arise as a technology capable of incorporating existing control systems along with new ones to collect, classify, store, retrieve and disseminate data for the future generation of control centers. Power system digital twins (PSDTs) can uplift how data from power grids and their equipment is processed, providing operators new ways to visualize and understand the information. Nevertheless, complexity and size of modern power systems narrow the scope a current digital twin can have. Furthermore, the services provided are limited to only certain phenomena and/or applications. This thesis addresses the need for a flexible and versatile solution that is also robust and adaptable for monitoring, operating and planning future power systems. The modular design for implementation of the next generation of PSDTs is proposed based on grid applications and/or services they can provide. From a modeling perspective, this thesis also distinguishes how real-time simulations enable the design, development, and operation of a PSDT. First, the need for enhanced power system modeling and simulation techniques is established. Moreover, the necessity of expanding to a more complete and varied open-source library of power system models is identified. The thesis continues by designing, developing, and testing models of inverter-based resources that can be used by the industry and researchers when developing PSDTs. Furthermore, the first-of-its-kind synthetic grid with a longitudinal structure, the S-NEM2300-bus benchmark model, based on the Australian National Electricity Market is created. The synthetic grid is, finally, used to illustrate the first steps towards implementing a practical PSDT

Relay in the loop test procedures for adaptive overcurrent protection

Doctor of PhilosophyElectrical and Computer EngineeringAnil PahwaNoel N. SchulzMicrogrids with distributed generators have changed how protection and control systems are designed. Protection systems in conventional U.S. distribution systems are radial with the assumption that current flows always from the utility source to the end user. However, in a microgrid with distributed generators, currents along power lines do not always flow in one direction. Therefore, protection systems must be adapted to different circuit paths depending on distributed generator sites in the microgrid and maximum fuse ampere ratings on busses. Adaptive overcurrent protection focuses on objectives and constraints based on operation, maximum load demand, equipment, and utility service limitations. Adaptive overcurrent protection was designed to protect the power lines and bus feeders of the microgrid with distributed generators by coordinating fuses and relays in the microgrid. Adaptive overcurrent protection was based on the relay setting group and protection logic methods. Non-real-time simulator (NRTS) and real-time simulator (RTS) experiments were performed with computer-based simulators. Tests with two relays in the loop proved that primary relays tripped faster than backup relays for selectivity coordination in the adaptive overcurrent protection system. Relay test results from tripping and non-tripping tests showed that adaptive inverse time overcurrent protection achieved selectivity, speed, and reliability. The RTS and NRTS with two relays in the loop techniques were described and compared in this work. The author was the first graduate student to implement real-time simulation with two relays in the loop at the Burns & McDonnell - K-State Smart Grid Laboratory. The RTS experimental circuit and project are detailed in this work so other graduate students can apply this technique with relays in the loop in smart grid research areas such as phasor measurement units, adaptive protection, communication, and cyber security applications