Paul Crolla

Optimizing the Roles of Unit and Non-unit Protection Methods Within DC Microgrids

Summary form only given. The characteristic behavior of physically compact, multiterminal dc networks under electrical fault conditions can produce demanding protection requirements. This represents a significant barrier to more widespread adoption of dc power distribution for microgrid applications. Protection schemes have been proposed within literature for such networks based around the use of non-unit protection methods. This paper shows however that there are severe limitations to the effectiveness of such schemes when employed for more complex microgrid network architectures. Even current differential schemes, which offer a more effective, though costly, protection solution, must be carefully designed to meet the design requirements resulting from the unique fault characteristics of dc microgrids. This paper presents a detailed analysis of dc microgrid behavior under fault conditions, illustrating the challenging protection requirements and demonstrating the shortcomings of non-unit approaches for these applications. Whilst the performance requirements for the effective operation of differential schemes in dc microgrids are shown to be stringent, the authors show how these may be met using COTS technologies. The culmination of this work is the proposal of a flexible protection scheme design framework for dc microgrid applications which enables the required levels of fault discrimination to be achieved whilst minimizing the associated installation costs.

Comparison of multiple power amplification types for power Hardware-in-the-Loop applications

This Paper discusses Power Hardware-in-the-Loop simulations from an important point of view: an intrinsic and integral part of PHIL simulation - the power amplification. In various publications PHIL is discussed either in a very theoretical approach or it is briefly featured as the used method. In neither of these publication types the impact of the power amplification to the total PHIL simulation is discussed deeply. This paper extends this discussion into the comparison of three different power amplification units and their usability for PHIL simulations. Finally in the conclusion it is discussed which type of power amplification is best for which type of PHIL experiment.

Methodology for testing loss of mains detection algorithms for microgrids and distributed generation using real-time power hardware-in-the-loop based technique

The effective integration of distributed energy resources in distribution networks demands powerful simulation and test methods in order to determine both system and component behaviour, and understand their interaction. Unexpected disconnection of a significant volume of distributed generation (DG) could have potentially serious consequences for the wider power system, and this means DG sources can no longer be treated as purely negative load. This paper proposes a method of testing loss-of-mains (LOM) detection and protection schemes for distributed energy resources (DER) using realtime power hardware-in-the-loop (RT PHIL). The approach involves connecting the generator and interface under test (e.g. motor-generator set or inverter, controlled by an RTS — Real Time Station) to a real-time simulator (in this case an RTDS — Real Time Digital Simulator) which simulates the local loads and upstream power system. This arrangement allows observation of the interaction with other controls in the network beyond the local microgrid area. These LOM detection schemes are of increasing importance because with growing penetration levels of distributed generation the network operator has less visibility and control of the connected generation. Furthermore when the generation and load in a particular network area are closely matched (e.g. a grid-connected microgrid), it becomes increasingly difficult to detect a loss of grid supply at the generator. This work builds upon the existing LOM testing methodology developed previously for the Energy Networks Association in the United Kingdom. By utilising RT PHIL and a laboratory microgrid, the testing environment has been brought to a new level of functionality where system integrity can be more rigorously and realistically evaluated.

Distributed Energy Resources Management in a Low-Voltage Test Facility

The electric energy demand will increase in the future, and the will to exploit larger amounts of generation from renewable resources requires the development of new strategies to manage a more complex electrical system. Different techniques allow the smart management of distribution networks such as load shifting, peak shaving, and short-term optimization. This work aims to test, in a real low-voltage (LV) active network (LV test facility of Strathclyde University of Glasgow), a Microgrid Smart Energy Management System, which adopts a two-stage strategy. The two levels of the proposed energy control system are composed of: 1) midterm controller that, according to weather, load, and generation forecasts, computes the profile of the controllable resources (generation, load, and storage), the dispatch problem is then solved through an optimization process; and through 2) short-term controller, which controls the power absorption of the active network. This procedure is hierarchically designed to dispatch the resources/loads, according to priority signals with the objective to contain the energy consumption below predetermined thresholds. The scalability and effectiveness of the architecture, which is validated in a real test bed, demonstrates the feasibility of implementing such a type of controller directly connected to the LV breakers, delivering a part of a real smart grid.

Ancillary service provision by demand side management: A real-time power hardware-in-the-loop co-simulation demonstration

The role of demand side management in providing ancillary services to the network is an active topic of research. However, their implementation is limited due to lack of practical demonstrations and tests that can rigorously quantify their ability to support the grids integrity. In this paper, provision of time critical frequency control ancillary service is demonstrated by means of integrating PowerMatcher, a well discussed demand side management mechanism in literature, with real-time power hardware. The co-simulation platform enables testing of demand side management techniques to provide ancillary services.

Evaluation of narrowband power line communications on a smart grid testbed

Power line communications (PLC) has been popularly used for in-home networking in the broadband case, where a number of useful channel models exist. For narrowband PLC applicable to longer distances and smart grid communications, few measurement campaigns and channel models exist. In this paper, we aim to report on an anticipated measurement campaign, and its impact both on the construction of a suitable channel model as well as its application to a filter-bank based transmultiplexer, which can be optimally adjusted based on parameters informed by such channel measurements.

Dynamic performance of a low voltage microgrid with droop controlled distributed generation

Microgrids are small-scale highly controlled networks designed to supply electrical energy. From the operational point of view, microgrids are active distribution networks, facilitating the integration of distributed generation units. Major technical issues in this concept include system stability and protection coordination which are significantly influenced by the high penetration of inverter-interfaced distributed energy sources. These units often adopt the frequency-active power and voltage-reactive power droop control strategy to participate in the load sharing of an islanded microgrid. The scope of the paper is to investigate the dynamic performance of a low voltage laboratory-scale microgrid system, using experimental results and introduce the concept of Prony analysis for understanding the connected components. Several small disturbance test cases are conducted and the investigations focus on the influence of the droop controlled distributed generation sources.

Using real-time simulation to assess the impact of a high penetration of LV connected microgeneration on the wider system performance during severe low frequency

In addition to other measures such as energy saving, the adoption of a large amount of microgeneration driven by renewable and low carbon energy resources is expected to have the potential to reduce losses associated with producing and delivering electricity, combat climate change and fuel poverty, and improve the overall system performance. However, incorporating a substantial volume of microgeneration within a system that is not designed for such a paradigm could lead to conflicts in the operating strategies of the new and existing centralized generation technologies. This paper investigates the impact of tripping substantial volumes of LV connected microgeneration on the dynamic performance of a large system during significant low frequency events. An initial dynamic model of the UK system based on a number of coherent areas as identified in the UK Transmission Seven Year Statement (SYS) has been developed within a real time digital simulator (RTDS) and this paper presents the early study results.

Modeling of distributed energy resources using laboratory-experimental results

In this paper measurement results from a low voltage microgrid test facility are presented and analyzed using a black box modeling methodology based on Prony analysis. Several test cases are investigated with the microgrid operating in grid-connected and islanded mode, including step changes in loads and distributed generation units. The black-box modeling methodology is applied to the measurement results and can provide information considering the amplitude, the frequency and the damping of the oscillations appearing in the microgrid responses. Results show that the black-box model can represent with good accuracy the dynamic behavior of the microgrid.