Fault detection and location in DC systems from initial di/dt measurement

The use of DC for primary power distribution has the potential to bring significant design, cost and efficiency benefits to a range of power transmission and distribution applications. The use of active converter technologies within these networks is a key enabler for these benefits to be realised, however their integration can lead to exceptionally demanding electrical fault protection requirements, both in terms of speed and fault discrimination. This paper describes a novel fault detection method which exceeds the capability of many current protection methods in order to meet these requirements. The method utilises fundamental characteristics of the converter filter capacitance’s response to electrical system faults to estimate fault location through a measurement of fault path inductance. Crucially, the method has the capability to detect and discriminate fault location within microseconds of the fault occurring, facilitating its rapid removal from the network

Impact of converter interface type on the protection requirements for DC aircraft power systems

The utilization of converter interfaces has the potential to significantly alter the protection system design requirements in future aircraft platforms. However, the impact these converters will have can vary widely, depending on the topology of converter, its filter requirements and its control strategy. This means that the precise impact on the network fault response is often difficult to quantify. Through the analysis of example converter topologies and literature on the protection of DC networks, this paper tackles this problem by identifying key design characteristics of converters which influence their fault response. Using this information, the converters are classified based on their general fault characteristics, enabling potential protection issues and solutions to be readily identified. Finally, the paper discusses the potential for system level design benefits through the optimisation of converter topology and protection system design

Comparing policy gradient and value function based reinforcement learning methods in simulated electrical power trade

In electrical power engineering, reinforcement learning algorithms can be used to model the strategies of electricity market participants. However, traditional value function based reinforcement learning algorithms suffer from convergence issues when used with value function approximators. Function approximation is required in this domain to capture the characteristics of the complex and continuous multivariate problem space. The contribution of this paper is the comparison of policy gradient reinforcement learning methods, using artificial neural networks for policy function approximation, with traditional value function based methods in simulations of electricity trade. The methods are compared using an AC optimal power flow based power exchange auction market model and a reference electric power system model

Determination of protection system requirements for DC UAV electrical power networks for enhanced capability and survivability

A growing number of designs of future Unmanned Aerial Vehicle (UAV) applications utilise dc for the primary power distribution method. Such systems typically employ large numbers of power electronic converters as interfaces for novel loads and generators. The characteristic behaviour of these systems under electrical fault conditions, and in particular their natural response, can produce particularly demanding protection requirements. Whilst a number of protection methods for multi-terminal dc networks have been proposed in literature, these are not universally applicable and will not meet the specific protection challenges associated with the aerospace domain. Through extensive analysis, this paper seeks to determine the operating requirements of protection systems for compact dc networks proposed for future UAV applications, with particular emphasis on dealing with the issues of capacitive discharge in these compact networks. The capability of existing multi-terminal dc network protection methods and technologies are then assessed against these criteria in order to determine their suitability for UAV applications. Recommendations for best protection practice are then proposed and key inhibiting research challenges are discussed

Environmental Desirability Responding: One Possibility in Addressing the Attitude-Behavior Gap

One of the underlying assumptions made by many outdoor education programs is that a student\u27s attitude toward the natural environment can be modified toward more pro-environmental beliefs through the acquisition of new knowledge and direct experiences with or in those environments. In tum, these attitudes can lead to behavior changes that possibly lead to more pro-environment actions, such as recycling, reduced consumption patterns, or even advocacy. Thus, using a properly sequenced set of knowledge and experiences in order to develop informed and pro­-environment attitudes and behaviors has become one\u27 standard way to design both outdoor education activities and curricula. One of the more vexing problems associated with this assumption, however, has been the consistent lack of congruency between expressed attitudes regarding the environment and subsequent behaviors. Numerous authors have linked this incongruity to a variety of causes including lack of personal involvement in the natural environments, differing early life experiences, normative values and beliefs, social determinants, and various demographic variables such as gender or age (Corral-Verdugo & Frias-Armenta, 2006; Karp, 1996; Nordlund & Garvill, 2002; Poortinga, Steg, & Vlek, 2004; Sarndahl & Robertson, 1989; Stem, 2000).In this study, we posit another possible explanation of the environmental attitude-behavior gap, namely, environmental desirability responding (EDR). In addition to discussing the concept of EDR, this study also presents an instrument that was developed for measuring the presence of EDR

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

Modelling the impact of micro generation on the electrical distribution system

In the UK and elsewhere there is considerable debate as to the future form of the electricity distribution system. The coming years will see a rise in the amount of micro-generation connected to the network at low voltages and the emergence of highly-distributed power systems (HDPS). However, there is considerable uncertainty as to the impact that this micro-generation will have on the quality of power supplied to our homes or to the stability of the electricity system as a whole. To address these engineering challenges the UK Engineering and Physical Sciences Research Council (EPSRC) is funding a three year research programme featuring a multi-disciplinary team from a variety of UK Universities: Supergen HDPS. This paper documents one piece of work emerging from the consortium, where a multi-tool approach is used to analyse the impact of micro-generation on the electricity system. This used a building simulation tool to produce electrical generation profiles for domestic cogeneration device models. These, along with profiles produced for other micro-generation technology models and electrical load profiles are then replicated and aggregated using a customised statistical approach. The profiles were then used as boundary conditions for a set of electrical load flow simulations on a model of a section of real network, where the number of microgenerators was varied according to different scenarios for the future of the UK electricity grid. The results indicate that a significant number of micro-generation devices can be accommodated before any power quality problems arise, however this is dependent upon maintaining a robust central grid

Increasing security of supply by the use of a local power controller during large system disturbances

This paper describes intelligent ways in which distributed generation and local loads can be controlled during large system disturbances, using Local Power Controllers. When distributed generation is available, and a system disturbance is detected early enough, the generation can be dispatched, and its output power can be matched as closely as possible to local microgrid demand levels. Priority-based load shedding can be implemented to aid this process. In this state, the local microgrid supports the wider network by relieving the wider network of the micro-grid load. Should grid performance degrade further, the local microgrid can separate itself from the network and maintain power to the most important local loads, re-synchronising to the grid only after more normal performance is regained. Such an intelligent system would be a suitable for hospitals, data centres, or any other industrial facility where there are critical loads. The paper demonstrates the actions of such Local Power Controllers using laboratory experiments at the 10kVA scale

Co-location of CHP units for high power charging of battery electric vehicles : a comparison of the fuel efficiency for AC and DC coupled systems

This paper proposes the co-location of gas reciprocating generator sets with High Power Charging (HPC) stations for Battery Electric Vehicles (BEVs), to offer a low carbon source of heat and power which could help to meet national government transportation and heating strategies while minimizing the impact that HPC systems will have on the power network. Three different Combined Heat and Power (CHP) connection configurations are considered to determine the most fuel-efficient per forecasted utilization rates of the HPC station. The use of variable speed generators connected directly to the dc bus of the HPC station can offer improved fuel-efficiency performance compared to fixed speed, especially under part-loading conditions, however, the sizing of engine-generator sets based on expected utilization rates of the HPC station has the most influence on fuel efficiency

Modeling and simulation enabled UAV electrical power system design

With the diversity of mission capability and the associated requirement for more advanced technologies, designing modern unmanned aerial vehicle (UAV) systems is an especially challenging task. In particular, the increasing reliance on the electrical power system for delivering key aircraft functions, both electrical and mechanical, requires that a systems-approach be employed in their development. A key factor in this process is the use of modeling and simulation to inform upon critical design choices made. However, effective systems-level simulation of complex UAV power systems presents many challenges, which must be addressed to maximize the value of such methods. This paper presents the initial stages of a power system design process for a medium altitude long endurance (MALE) UAV focusing particularly on the development of three full candidate architecture models and associated technologies. The unique challenges faced in developing such a suite of models and their ultimate role in the design process is explored, with case studies presented to reinforce key points. The role of the developed models in supporting the design process is then discussed