Requirements to Testing of Power System Services Provided by DER Units

The present report forms the Project Deliverable ‘D 2.2’ of the DERlab NoE project, supported by the EC under Contract No. SES6-CT-518299 NoE DERlab. The present document discuss the power system services that may be provided from DER units and the related methods to test the services actually provided, both at component level and at system level

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

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 entire system [1], 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 real-time 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[3]) to a real-time simulator (an RTDS – Real Time Digital Simulator[2]) 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 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 proposed in [4]. 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

Optimizing the roles of unit and non-unit protection methods within DC microgrids

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

International White Book on DER Protection : Review and Testing Procedures

This white book provides an insight into the issues surrounding the impact of increasing levels of DER on the generator and network protection and the resulting necessary improvements in protection testing practices. Particular focus is placed on ever increasing inverter-interfaced DER installations and the challenges of utility network integration. This white book should also serve as a starting point for specifying DER protection testing requirements and procedures. A comprehensive review of international DER protection practices, standards and recommendations is presented. This is accompanied by the identifi cation of the main performance challenges related to these protection schemes under varied network operational conditions and the nature of DER generator and interface technologies. Emphasis is placed on the importance of dynamic testing that can only be delivered through laboratory-based platforms such as real-time simulators, integrated substation automation infrastructure and fl exible, inverter-equipped testing microgrids. To this end, the combination of fl exible network operation and new DER technologies underlines the importance of utilising the laboratory testing facilities available within the DERlab Network of Excellence. This not only informs the shaping of new protection testing and network integration practices by end users but also enables the process of de-risking new DER protection technologies. In order to support the issues discussed in the white paper, a comparative case study between UK and German DER protection and scheme testing practices is presented. This also highlights the level of complexity associated with standardisation and approval mechanisms adopted by different countries

European White Book on Real-Time Power Hardware in the Loop Testing : DERlab Report No. R- 005.0

The European White Book on Real-Time-Powerhardware-in-the-Loop testing is intended to serve as a reference document on the future of testing of electrical power equipment, with specifi c focus on the emerging hardware-in-the-loop activities and application thereof within testing facilities and procedures. It will provide an outlook of how this powerful tool can be utilised to support the development, testing and validation of specifi cally DER equipment. It aims to report on international experience gained thus far and provides case studies on developments and specifi c technical issues, such as the hardware/software interface. This white book compliments the already existing series of DERlab European white books, covering topics such as grid-inverters and grid-connected storag

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

Measurement-based analysis of the dynamic performance of microgrids using system identification techniques

The dynamic performance of microgrids is of crucial importance, due to the increased complexity introduced by the combined effect of inverter interfaced and rotating distributed generation. This paper presents a methodology for the investigation of the dynamic behavior of microgrids based on measurements using Prony analysis and state-space black-box modeling techniques. Both methods are compared and evaluated using real operating conditions data obtained by a laboratory microgrid system. The recorded responses and the calculated system eigenvalues are used to analyze the system dynamics and interactions among the distributed generation units. The proposed methodology can be applied to any real-world microgrid configuration, taking advantage of the future smart grid technologies and features

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

Postponing surgery to optimise patients with acute right-sided obstructing colon cancer - A pilot study

Background: Right-sided obstructing colon cancer is most often treated with acute resection. Recent studies on right-sided obstructing colon cancer report higher mortality and morbidity rates than those in patients without obstruction. The aim of this study is to retrospectively analyse whether it is possible to optimise the health condition of patients with acute right-sided obstructing colon cancer, prior to surgery, and whether this improves postoperative outcomes. Method: All consecutive patients with high suspicion of, or histologically proven, right-sided obstructing colon cancer, treated with curative intent between March 2013 and December 2019, were analysed retrospectively. Patients were divided into two groups: optimised group and non-optimised group. Pre-operative optimisation included additional nutrition, physiotherapy, and, if needed, bowel decompression. Results: In total, 54 patients were analysed in this study. Twenty-four patients received optimisation before elective surgery, and thirty patients received emergency surgery, without optimisation. Scheduled surgery was performed after a median of eight days (IQR 7–12). Postoperative complications were found in twelve (50%) patients in the optimised group, compared to twenty-three (77%) patients in the non-optimised group (p = 0.051). Major complications were diagnosed in three (13%) patients with optimisation, compared to ten (33%) patients without optimisation (p = 0.111). Postoperative in-hospital stay, 30-day mortality, as well as primary anastomosis were comparable in both groups. Conclusion: This pilot study suggests that pre-operative optimisation of patients with obstructing right sided colonic cancer may be feasible and safe but is associated with longer in-patient stay.</p