A multi-modular second life hybrid battery energy storage system for utility grid applications

The modern grid system or the smart grid is likely to be populated with multiple distributed energy sources, e.g. wind power, PV power, Plug-in Electric Vehicle (PEV). It will also include a variety of linear and nonlinear loads. The intermittent nature of renewable energies like PV, wind turbine and increased penetration of Electric Vehicle (EV) makes the stable operation of utility grid system challenging. In order to ensure a stable operation of the utility grid system and to support smart grid functionalities such as, fault ride-through, frequency response, reactive power support, and mitigation of power quality issues, an energy storage system (ESS) could play an important role. A fast acting bidirectional energy storage system which can rapidly provide and absorb power and/or VARs for a sufficient time is a potentially valuable tool to support this functionality. Battery energy storage systems (BESS) are one of a range suitable energy storage system because it can provide and absorb power for sufficient time as well as able to respond reasonably fast. Conventional BESS already exist on the grid system are made up primarily of new batteries. The cost of these batteries can be high which makes most BESS an expensive solution. In order to assist moving towards a low carbon economy and to reduce battery cost this work aims to research the opportunities for the re-use of batteries after their primary use in low and ultra-low carbon vehicles (EV/HEV) on the electricity grid system. This research aims to develop a new generation of second life battery energy storage systems (SLBESS) which could interface to the low/medium voltage network to provide necessary grid support in a reliable and in cost-effective manner. The reliability/performance of these batteries is not clear, but is almost certainly worse than a new battery. Manufacturers indicate that a mixture of gradual degradation and sudden failure are both possible and failure mechanisms are likely to be related to how hard the batteries were driven inside the vehicle. There are several figures from a number of sources including the DECC (Department of Energy and Climate Control) and Arup and Cenex reports indicate anything from 70,000 to 2.6 million electric and hybrid vehicles on the road by 2020. Once the vehicle battery has degraded to around 70-80% of its capacity it is considered to be at the end of its first life application. This leaves capacity available for a second life at a much cheaper cost than a new BESS Assuming a battery capability of around 5-18kWhr (MHEV 5kWh - BEV 18kWh battery) and approximate 10 year life span, this equates to a projection of battery storage capability available for second life of >1GWhrs by 2025. Moreover, each vehicle manufacturer has different specifications for battery chemistry, number and arrangement of battery cells, capacity, voltage, size etc. To enable research and investment in this area and to maximize the remaining life of these batteries, one of the design challenges is to combine these hybrid batteries into a grid-tie converter where their different performance characteristics, and parameter variation can be catered for and a hot swapping mechanism is available so that as a battery ends it second life, it can be replaced without affecting the overall system operation. This integration of either single types of batteries with vastly different performance capability or a hybrid battery system to a grid-tie 3 energy storage system is different to currently existing work on battery energy storage systems (BESS) which deals with a single type of battery with common characteristics. This thesis addresses and solves the power electronic design challenges in integrating second life hybrid batteries into a grid-tie energy storage unit for the first time. This study details a suitable multi-modular power electronic converter and its various switching strategies which can integrate widely different batteries to a grid-tie inverter irrespective of their characteristics, voltage levels and reliability. The proposed converter provides a high efficiency, enhanced control flexibility and has the capability to operate in different operational modes from the input to output. Designing an appropriate control system for this kind of hybrid battery storage system is also important because of the variation of battery types, differences in characteristics and different levels of degradations. This thesis proposes a generalised distributed power sharing strategy based on weighting function aims to optimally use a set of hybrid batteries according to their relative characteristics while providing the necessary grid support by distributing the power between the batteries. The strategy is adaptive in nature and varies as the individual battery characteristics change in real time as a result of degradation for example. A suitable bidirectional distributed control strategy or a module independent control technique has been developed corresponding to each mode of operation of the proposed modular converter. Stability is an important consideration in control of all power converters and as such this thesis investigates the control stability of the multi-modular converter in detailed. Many controllers use PI/PID based techniques with fixed control parameters. However, this is not found to be suitable from a stability point-of-view. Issues of control stability using this controller type under one of the operating modes has led to the development of an alternative adaptive and nonlinear Lyapunov based control for the modular power converter. Finally, a detailed simulation and experimental validation of the proposed power converter operation, power sharing strategy, proposed control structures and control stability issue have been undertaken using a grid connected laboratory based multi-modular hybrid battery energy storage system prototype. The experimental validation has demonstrated the feasibility of this new energy storage system operation for use in future grid applications.

Hybrid tilted fiber grating based refractive index and liquid level sensing system

We report a refractive index (RI) and liquid level sensing system based on a hybrid grating structure comprising of a 45° and an 81° tilted fiber gratings (TFGs) that have been inscribed into a single mode fiber in series. In this structure, the 45°-TFG is used as a polarizer to filter out the transverse electric (TE) component and enable the 81°-TFG operating at single polarization for RI and level sensing. The experiment results show a lower temperature cross-sensitivity, only about 7.33 pm/°C, and a higher RI sensitivity, being around 180 nm/RIU at RI=1.345 and 926 nm/RIU at RI=1.412 region, which are significantly improved in comparison with long period fiber gratings. The hybrid grating structure has also been applied as a liquid level sensor, showing 3.06 dB/mm linear peak ratio sensitivity.

High speed and high resolution demodulation system for hybrid WDM/FDM based fiber microstructure sensor network by using Fabry-Perot filter

Hybrid WDM/TDM enabled microstructure based optical fiber sensor network with large capacity is proposed. Assisted by Fabry-Perot filter, the demodulation system with high speed of 500Hz and high wavelength resolution less than 4.91pm is realized. © OSA 2015.

Adaptive control of hybrid battery energy storage systems under capacity fade

There is an increasing call for applications which use a mixture of batteries. These hybrid battery solutions may contain different battery types for example; using second life ex-transportation batteries in grid support applications or a combination of high power, low energy and low power, high energy batteries to meet multiple energy requirements or even the same battery types but under different states of health for example, being able to hot swap out a battery when it has failed in an application without changing all the batteries and ending up with batteries with different performances, capacities and impedances. These types of applications typically use multi-modular converters to allow hot swapping to take place without affecting the overall performance of the system. A key element of the control is how the different battery performance characteristics may be taken into account and the how the power is then shared among the different batteries in line with their performance. This paper proposes a control strategy which allows the power in the batteries to be effectively distributed even under capacity fade conditions using adaptive power sharing strategy. This strategy is then validated against a system of three different battery types connected to a multi-modular converter both with and without capacity fade mechanisms in place.

High resolution demodulation platform for large capacity hybrid WDM/FDM microstructures sensing system assisted by tunable FP filter

In this paper we proposed a demodulation scheme based on tunable FP filter for the WDM/FDM sensing system of the microstructure mentioned in the previous work. Simulation is done to prove the feasibility of demodulating the microstructure with the tunable FP filter. The experiments result showed high consistence with the simulation. And with the help of the high speed FPGA module and a high resolution AD/DA card, the system has achieved a very high resolution, up to 2.5 pm, and wavelength ranges 1520nm to 1590 nm.

Book review: Laurel Kamada, Hybrid Identities and Adolescent Girls: Being Half in Japan. Bristol: Multilingual Matters, 2010

Arguably, the catalyst for the best research studies using social analysis of discourse is personal ‘lived’ experience. This is certainly the case for Kamada, who, as a white American woman with a Japanese spouse, had to deal first hand with the racialization of her son. Like many other mixed-ethnic parents, she experienced the shock and disap-pointment of finding her child being racialized as ‘Chinese’ in America through peer group taunts, and constituted as gaijin (a foreigner) in his own homeland of Japan. As a member of an e-list of the (Japan) Bilingualism Special Interest Group (BSIG), Kamada learnt that other parents from the English-speaking foreign community in Japan had similar disturbing stories to tell of their mixed-ethnic children who, upon entering the Japanese school system, were mocked, bullied and marginalized by their peers. She men-tions a pervasive Japanese proverb which warns of diversity or difference getting squashed: ‘The nail that sticks up gets hammered down’. This imperative to conform to Japanese behavioural and discursive norms prompted Kamada’s quest to investigate the impact of ‘otherization’ on the identities of children of mixed parentage. In this fascinat-ing book, she shows that this pressure to conform is balanced by a corresponding cele-bration of ‘hybrid’ or mixed identities. The children in her study are also able to negotiate their identities positively as they come to terms with contradictory discursive notions of ‘Japaneseness’, ‘whiteness’ and ‘halfness/doubleness’.The discursive construction of identity has become a central concern amongst researchers across a wide range of academic disciplines within the humanities and the social sciences, and most existing work either concentrates on a specific identity cate-gory, such as gender, sexuality or national identity, or else offers a broader discussion of how identity is theorized. Kamada’s book is refreshing because it crosses the usual boundaries and offers divergent insights on identity in a number of ways. First, using the term ‘ethno-gendering’, she examines the ways in which six mixed-ethnic girls living in Japan accomplish and manage the relationship between their gender and ethnic ‘differ-ences’ from age 12 to 15. She analyses in close detail how their actions or displays within certain situated interactions might come into conflict with how they are seen or constituted by others. Second, Kamada’s study builds on contemporary writing on the benefits of hybridity where identities are fluid, flexible and indeterminate, and which contest the usual monolithic distinctions of gender, ethnicity, class, etc. Here, Kamada carves out an original space for her findings. While scholars have often investigated changing identities and language practices of young people who have been geographi-cally displaced and are newcomers to the local language, Kamada’s participants were all born and brought up in Japan, were fluent in Japanese and were relatively proficient in English. Third, the author refuses to conceptualize or theorize identity from a single given viewpoint in preference to others, but in postmodernist spirit draws upon multiple perspectives and frameworks of discourse analysis in order to create different forms of knowledge and understandings of her subject. Drawing on this ‘multi-perspectival’ approach, Kamada examines grammatical, lexical, rhetorical and interactional features from six extensive conversations, to show how her participants position their diverse identities in relation to their friends, to the researcher and to the outside world. Kamada’s study is driven by three clear aims. The first is to find out ‘whether there are any tensions and dilemmas in the ways adolescent girls of Japanese and “white” mixed parentage in Japan identify themselves in terms of ethnicity’. In Chapter 4, she shows how the girls indeed felt that they stood out as different and consequently experienced isolation, marginalization and bullying at school – although they were able to make better sense of this as they grew older, repositioning the bullies as pitiable. The second aim is to ask how, if at all, her participants celebrate their ethnicity, and furthermore, what kind of symbolic, linguistic and social capital they were able to claim for themselves on the basis of their hybrid identities. In Chapter 5, Kamada shows how the girls over time were able to constitute themselves as insiders while constituting ‘the Japanese’ as outsiders, and their network of mixed-ethnic friends was a key means to achieve this. In Chapter 6, the author develops this potential celebration of the girls’ mixed ethnicity by investigating the privileges they perceived it afforded them – for example, having the advantage of pos-sessing English proficiency and intercultural ‘savvy’ in a globalized world. Kamada’s third aim is to ask how her participants positioned themselves and performed their hybrid identities on the basis of their constituted appearance: that is, how the girls saw them-selves based on how they looked to others. In Chapter 7, the author shows that, while there are competing discourses at work, the girls are able to take up empowering positions within a discourse of ‘foreigner attractiveness’ or ‘a white-Western female beauty’ discourse, which provides them with a certain cachet among their Japanese peers. Throughout the book, Kamada adopts a highly self-reflexive perspective of her own position as author. For example, she interrogates the fact that she may have changed the lived reality of her six participants during the course of her research study. As the six girls, who were ‘best friends’, lived in different parts of the Morita region of Japan, she had to be proactive in organizing six separate ‘get-togethers’ through the course of her three-year study. She acknowledges that she did not collect ‘naturally occurring data’ but rather co-constructed opportunities for the girls to meet and talk on a regular basis. At these meetings, she encouraged the girls to discuss matters of identity, prompted by open-ended interview questions, by stimulus materials such as photos, articles and pic-tures, and by individual tasks such as drawing self-portraits. By giving her participants a platform in this way, Kamada not only elicited some very rich spoken data but also ‘helped in some way to shape the attitudes and self-images of the girls positively, in ways that might not have developed had these get-togethers not occurred’ (p. 221). While the data she gathers are indeed rich, it may well be asked whether there is a mismatch between the girls’ frank and engaging accounts of personal experience, and the social constructionist academic register in which these are later re-articulated. When Kamada writes, ‘Rina related how within the more narrow range of discourses that she had to draw on in her past, she was disempowered and marginalized’ (p. 118), we know that Rina’s actual words were very different. Would she really recognize, understand and agree with the reported speech of the researcher? This small omission of self-reflexivity apart – an omission which is true of most lin-guistic ethnography conducted today – Kamada has written a unique, engaging and thought-provoking book which offers a model to future discourse analysts investigating hybrid identities. The idea that speakers can draw upon competing discourses or reper-toires to constitute their identities in contrasting, creative and positive ways provides linguistic researchers with a clear orientation by which to analyse the contradictions of identity construction as they occur across time in different discursive contexts