• Active Power and DC Voltage Coordinative Control for Cascaded DC–AC Converter With Bidirectional Power Application

      Tian, Yanjun; Chen, Zhe; Deng, Fujin; Sun, Xiaofeng; Hu, Yanting; University of Chester (IEEE, 2015-10-31)
      Two stage-cascaded converters are widely used in dc–ac hybrid systems to achieve the bidirectional power transmission. The topology of dual active bridge cascaded with inverter DABCI) is commonly used in this application. This paper proposes a coordinative control method for DABCI and it is able to reduce the dc-link voltage fluctuation between the DAB and inverter, then reduce the stress on the switching devices, as well as improve the system dynamic performance. In the proposed control method, the DAB and inverter are coordinated to control the dc-link voltage and the power, and this responsibility sharing control can effectively suppress the impact of the power variation on the dc-link voltage, without sacrificing stability. The proposed control method is also effective for DABCI in unidirectional power transmission. The effectiveness of the propose control has been validated by both simulations and experiments.
    • Comparing Terahertz transmission response on pH-dependent apomyoglobin proteins dynamics with circular dichroism

      Qiu, Junyi; Yang, Bin; Sushko, Oleksandr; Pikersgill, Richard W.; Donnan, Robert S.; University of Chester (IEEE, 2014-12-08)
      Terahertz time domain spectroscopy (THz-TDS) was used to study the transmission responses of pH-dependent apomyoglobin (ApoMb) dissolved solutions in 0.2-2.2 THz frequency domain, the THz-TDS technique was also benchmarked against circular dichroism (CD) by studying pH-related folding states changes of ApoMb protein. Results revealed that differences of pH-dependent ApoMb/water dynamics can be detected directly by the THz refractive index spectrum, and these differences are further proved to be caused mainly the effect of protonation of water and possibly water response leaded by protein conformation change.
    • A Compensation Method for Active Phased Array Antennas : Using a Strain-Electromagnetic Coupling Model

      Shi, Yu; Wang, Congsi; Wang, Yan; Yuan, Shuai; Duan, Baoyan; Lian, Peiyuan; Xue, Song; Du, Biao; Gao, Wei; Wang, Zhihai; et al.
      Physical deformation due to service loads seriously degrades the electromagnetic performance of active phased array antennas. However, traditional displacement-based compensation methods are moderately difficult to use because displacement measurements generally require stable references, which are hard to realize for antennas in service. For deformed antennas, strain information is directly related to their displacement, and strain sensors can overcome carrier platform constraints to measure real-time strain without affecting the antenna radiation-field distribution. We thus present a compensation method based on strain information for in-service antennas. First, the minimum number of strain sensors is determined as the main modal-order-based modal effective mass fraction. According to the modal method and analysis of spatial phase-distribution errors related to strain, a coupled strain-electromagnetic model is established to evaluate antenna performance from the measured strain. The corresponding excitation phase from the measured strain is adjusted to compensate antenna performance. Finally, the method is experimentally validated using an X-band active phased array antenna under the influence of typical deformation conditions for both boresightand scanned beams. The results demonstrate that the presented method can effectively compensate for the performance of service antennas directly from the measured strain information.
    • Contextual Network Navigation to provide Situational Awareness for Network Administrators

      Gray, Cameron C.; Ritsos, Panagiotis D.; Roberts, Jonathan C.; Bangor University; University of Chester (IEEE, 2015-10-26)
      One of the goals of network administrators is to identify and block sources of attacks from a network steam. Various tools have been developed to help the administrator identify the IP or subnet to be blocked, however these tend to be non-visual. Having a good perception of the wider network can aid the administrator identify their origin, but while network maps of the Internet can be useful for such endeavors, they are difficult to construct, comprehend and even utilize in an attack, and are often referred to as being “hairballs”. We present a visualization technique that displays pathways back to the attacker; we include all potential routing paths with a best-efforts identification of the commercial relationships involved. These two techniques can potentially highlight common pathways and/or networks to allow faster, more complete resolution to the incident, as well as fragile or incomplete routing pathways to/from a network. They can help administrators re-profile their choice of IP transit suppliers to better serve a target audience.
    • DC-Link Voltage Coordinated-Proportional Control for Cascaded Converter with Zero Steady-State Error and Reduced System Type

      Tian, Yanjun; Loh, Poh C.; Deng, Fujin; Chen, Zhe; Hu, Yanting; 1. Department of Energy Technology, Aalborg University, Denmark; 2. Faculty of Science and Engineering, University of Chester, UK (IEEE, 2015-06-11)
      Cascaded converter is formed by connecting two sub-converters together, sharing a common intermediate DC-link voltage. Regulation of this DC-link voltage is frequently realized with a Proportional-Integral (PI) controller, whose high gain at DC helps to force a zero steady-state tracking error. Such precise tracking is however at the expense of increasing the system type, caused by the extra pole at the origin introduced by the PI controller. The overall system may hence be tougher to control. To reduce the system type while preserving precise DC-link voltage tracking, this paper proposes a coordinated control scheme for the cascaded converter, which uses only a proportional DC-link voltage regulator. The resulting converter is thus dynamically faster, and when compared with the conventional PI-controlled converter, it is less affected by impedance interaction between its two sub-converters. The proposed scheme can be used with either unidirectional or bidirectional power flow, and has been verified by simulation and experimental results presented in the paper.
    • Dead-zone logic in autonomic systems

      Eze, Thaddeus; Anthony, Richard; University of Chester and University of Greenwich (IEEE, 2014-07-31)
      Dead-Zone logic is a mechanism to prevent autonomic managers from unnecessary, inefficient and ineffective control brevity when the system is sufficiently close to its target state. It provides a natural and powerful framework for achieving dependable self-management in autonomic systems by enabling autonomic managers to smartly carry out a change (or adapt) only when it is safe and efficient to do so-within a particular (defined) safety margin. This paper explores and evaluates the performance impact of dead-zone logic in trustworthy autonomic computing. Using two case example scenarios, we present empirical analyses that demonstrate the effectiveness of dead-zone logic in achieving stability, dependability and trustworthiness in adaptive systems. Dynamic temperature target tracking and autonomic datacentre resource request and allocation management scenarios are used. Results show that dead-zone logic can significantly enhance the trustability of autonomic systems.
    • Design and specification of building integrated DC electricity networks

      Stewart, M.; Counsell, John M.; Al-Khaykan, A.; University of Chester (IEEE, 2017-01-19)
      Adoption of millions of small energy efficient, low power digital and DC appliances at home and at work is resulting in a significant and fast growing fraction of a building's electricity actually consumed in low voltage DC form. Building integrated energy systems featuring renewable photovoltaics are also increasingly attractive as part of an overall electricity and emissions reduction strategy. This paper details design and specification of a novel system level method of matching building integrated photovoltaic electricity generation with local low voltage DC appliances in office and other ICT intensive environments such as schools. The chosen scenario considers load components consisting of a diverse range of modern low power ICT and DC appliances, networked and powered by industry certified smart DC distribution technologies. Energy supply to the converged DC, IT and ICT network is described as featuring a roof-mounted or other on-site photovoltaic array in combination with conventional supply from the local grid infrastructure. The direct and strategic benefits of smart DC infrastructures are highlighted as the enabling technology for optimal demand reduction through fully integrated energy management of DC systems in buildings.
    • An Efficient SSHI Interface With Increased Input Range for Piezoelectric Energy Harvesting Under Variable Conditions

      Du, Sijun; Jia, Yu; Do, Cuong D.; Seshia, Ashwin A.; University of Cambridge; University of Chester (IEEE, 2016-08-10)
      Piezoelectric vibration energy harvesters have been widely researched and are increasingly employed for powering wireless sensor nodes. The synchronized switch harvesting on inductor (SSHI) circuit is one of the most efficient interfaces for piezoelectric vibration energy harvesters. However, the traditional incarnation of this circuit suffers from a significant start-up issue that limits operation in low and variable amplitude vibration environments. This paper addresses this start-up issue for the SSHI rectifier by proposing a new architecture with SSHI startup circuitry. The startup circuitry monitors if the SSHI circuit is operating correctly and re-starts the SSHI interface if required. The proposed circuit is comprehensively analyzed and experimentally validated through tests conducted by integrating a commercial piezoelectric vibration energy harvester with the new interface circuit designed in a 0.35-μm HV CMOS process. Compared to conventional SSHI rectifiers, the proposed circuit significantly decreases the required minimum input excitation amplitude before energy can be harvested, making it possible to extract energy over an increased excitation range.
    • Eight parametric resonances in a multi-frequency wideband MEMS piezoelectric vibration energy harvester

      Jia, Yu; Du, Sijun; Seshia, Ashwin A.; University of Cambridge; University of Chester (IEEE, 2016-01-24)
      This paper presents a multi-order parametric resonant MEMS piezoelectric disk membrane, for the purpose of broadening the operational frequency bandwidth of a vibration energy harvester by employing the nonlinearity-induced bandwidth broadening associated with this phenomenon as well as the multi-frequency response associated with the higher orders. The fundamental mode -3dB bandwidth at 2.0 g recorded 55 Hz, while the first parametric resonant peak exhibited 365 Hz and the -3dB of the first 8 orders accumulated to 604 Hz. The membrane parametric resonator also experimentally demonstrated over 3-folds improvement in power density compared to a conventional direct resonator (cantilever), when subjected to band-limited white noise.
    • Evaluating current practice and proposing a system to enhance knowledge assets within a small software development unit

      Fannoun, Sufian; Kerins, John; The University of Chester (IEEE, 2018-06-25)
      Knowledge management and knowledge transfer within organisations challenge continuity and resilience in the face of changing environments. While issues are principally addressed within large organisations, there is scope to evaluate how knowledge assets are managed within small and medium enterprises and to consider how the process might be enhanced. The research reported here aimed to evaluate practice within an evolving software development unit to understand how knowledge has been acquired and utilised to further organisational development. In-depth interviews were carried out with members of the unit to elicit an understanding of individual and collective learning. Qualitative analysis of the data revealed key changes in thinking and practice as well as insight into the development of individuals' contextual knowledge and tacit understanding. This analysis led to the proposal of a bespoke, lightweight web-based system to support knowledge capture and organisational learning. This work is still in progress but it is anticipated that the results will provide a potentially novel and beneficial method for enhancing knowledge assets in small enterprises and consolidating valuable, and potentially scarce, expertise.
    • Experimental and theoretical study of a piezoelectric vibration energy harvester under high temperature

      Arroyo, Emmanuelle; Jia, Yu; Du, Sijun; Chen, Shao-Tuan; Seshia, Ashwin A.; University of Cambridge; University of Chester (IEEE, 2017-08-01)
      This paper focuses on studying the effect of increasing the ambient temperature up to 160 °C on the power harvested by an MEMS piezoelectric micro-cantilever manufactured using an aluminum nitride-on-silicon fabrication process. An experimental study shows that the peak output power decreases by 60% to 70% depending on the input acceleration. A theoretical study establishes the relationship of all important parameters with temperature and includes them into a temperature-dependent model. This model shows that around 50% of the power drop can be explained by a decreasing quality factor, and that thermal stresses account for around 30% of this decrease.
    • Formal Verification of Astronaut-Rover Teams for Planetary Surface Operations

      Webster, Matt; Dennis, Louise A; Dixon, Clare; Fisher, Michael; Stocker, Richard; Sierhuis, Maarten; University of Liverpool; University of Chester; Ejenta, inc.
      This paper describes an approach to assuring the reliability of autonomous systems for Astronaut-Rover (ASRO) teams using the formal verification of models in the Brahms multi-agent modelling language. Planetary surface rovers have proven essential to several manned and unmanned missions to the moon and Mars. The first rovers were tele- or manuallyoperated, but autonomous systems are increasingly being used to increase the effectiveness and range of rover operations on missions such as the NASA Mars Science Laboratory. It is anticipated that future manned missions to the moon and Mars will use autonomous rovers to assist astronauts during extravehicular activity (EVA), including science, technical and construction operations. These ASRO teams have the potential to significantly increase the safety and efficiency of surface operations. We describe a new Brahms model in which an autonomous rover may perform several different activities including assisting an astronaut during EVA. These activities compete for the autonomous rovers “attention’ and therefore the rover must decide which activity is currently the most important and engage in that activity. The Brahms model also includes an astronaut agent, which models an astronauts predicted behaviour during an EVA. The rover must also respond to the astronauts activities. We show how this Brahms model can be simulated using the Brahms integrated development environment. The model can then also be formally verified with respect to system requirements using the SPIN model checker, through automatic translation from Brahms to PROMELA (the input language for SPIN). We show that such formal verification can be used to determine that mission- and safety critical operations are conducted correctly, and therefore increase the reliability of autonomous systems for planetary rovers in ASRO teams.
    • Gradient-based optimization method for producing a contoured beam with single-fed reflector antenna

      Lian, Peiyuan; Wang, Congsi; Xiang, Binbin; Shi, Yu; Xue, Song; Xidian University; University of Chester; Chinese Academy of Sciences (IEEE, 2019-03-07)
      A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics (PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States (CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.
    • Impedance coordinative control for cascaded converter in bidirectional application

      Tian, Yanjun; Deng, Fujin; Chen, Zhe; Sun, Xiaofeng; Hu, Yanting; University of Chester (IEEE, 2015-06-30)
      Two stage cascaded converters are widely used in bidirectional applications, but the negative impedance may cause system instability. Actually the impedance interaction is much different between forward power flow and reversed power flow, which will introduce more uncertainty to the system stability. This paper proposes a control method for the constant power controlled converter in cascaded system, and consequently it can change the negative impedance of constant power converter into resistive impedance, which will improve the cascaded system stability, as well as merge the impedance difference between forward and reversed power flow. This paper addresses the analysis with the topology of cascaded dual-active-bridge converter (DAB) with inverter, and the proposed control method can also be implemented in unidirectional applications and other general cascaded converter system. The effectiveness has been validated by both simulation and experimental results.
    • The Implementation and Validation of a Virtual Environment for Training Powered Wheelchair Manoeuvres

      John, Nigel W.; Pop, Serban R.; Day, Thomas W.; Ritsos, Panagiotis D.; Headleand, Christopher J.; University of Chester; Bangor University; University of Lincoln (IEEE, 2017-05-02)
      Navigating a powered wheelchair and avoiding collisions is often a daunting task for new wheelchair users. It takes time and practice to gain the coordination needed to become a competent driver and this can be even more of a challenge for someone with a disability. We present a cost-effective virtual reality (VR) application that takes advantage of consumer level VR hardware. The system can be easily deployed in an assessment centre or for home use, and does not depend on a specialized high-end virtual environment such as a Powerwall or CAVE. This paper reviews previous work that has used virtual environments technology for training tasks, particularly wheelchair simulation. We then describe the implementation of our own system and the first validation study carried out using thirty three able bodied volunteers. The study results indicate that at a significance level of 5% then there is an improvement in driving skills from the use of our VR system. We thus have the potential to develop the competency of a wheelchair user whilst avoiding the risks inherent to training in the real world. However, the occurrence of cybersickness is a particular problem in this application that will need to be addressed.
    • An Information-Theoretic Approach to the Cost-benefit Analysis of Visualization in Virtual Environments

      Chen, Min; Gaither, Kelly; John, Nigel W.; McCann, Brian; University of Oxford; University of Texas at Austin; University of Chester (IEEE, 2018-08-20)
      Visualization and virtual environments (VEs) have been two interconnected parallel strands in visual computing for decades. Some VEs have been purposely developed for visualization applications, while many visualization applications are exemplary showcases in general-purpose VEs. Because of the development and operation costs of VEs, the majority of visualization applications in practice have yet to benefit from the capacity of VEs. In this paper, we examine this status quo from an information-theoretic perspective. Our objectives are to conduct cost-benefit analysis on typical VE systems (including augmented and mixed reality, theatre-based systems, and large powerwalls), to explain why some visualization applications benefit more from VEs than others, and to sketch out pathways for the future development of visualization applications in VEs. We support our theoretical propositions and analysis using theories and discoveries in the literature of cognitive sciences and the practical evidence reported in the literatures of visualization and VEs.
    • Mechanism between Material Microstructures and Terahertz Dielectric Properties

      Yang, Bin; University of Chester (IEEE, 2019-10-21)
      Significant progress has been made in developing reliable Terahertz (THz) measurement spectroscopy to extract materials’ dielectric properties, however, systematic research on exploring intrinsic mechanism between microstructure of ceramics and THz dielectric properties such as loss, permittivity and dispersive characters has barely started. The paper focuses on one dielectric ceramic system (TiO2), its addition with Zn2SiO4 dielectrics and one hexa-ferromagnetic system to expatiate the association.
    • Micromachined Thick Mesh Filters for Millimeter-Wave and Terahertz Applications

      Wang, Yi; Yang, Bin; Tian, Yingtao; Donnan, Robert S.; Lancaster, Michael J.; University of Bolton (IEEE, 2014-03-01)
      This paper presents several freestanding bandpass mesh filters fabricated using an SU-8 based micromachining technique. The important geometric feature of the filters, which SU8 is able to increase, is the thickness of the cross-shaped micromachined slots. This is 5 times its width. This thickness offers an extra degree of control over the resonance characteristics. The large thickness not only strengthens the structures, but also enhances the resonance quality factor (Q-factor). A 0.3 mm thick, single layer, mesh filter resonant at 300 GHz has been designed, fabricated and its performance verified. The measured Q-factor is 16.3 and the insertion loss is 0.98 dB. Two multi-layer filter structures have also been demonstrated. The first one is a stacked structure of two single mesh filters producing a double thickness, which achieved a further increased Q-factor of 27. This is over six times higher than a thin mesh filter. The second multi-layer filter is an electromagnetically coupled structure forming a two-pole filter. The coupling characteristics are discussed based on experimental and simulation results. These thick mesh filters can potentially be used for sensing and material characterization at millimeter-wave and terahertz frequencies.
    • Multimodal Shear Wave Deicing Using Fibre Piezoelectric Actuator on Composite for Aircraft Wings

      Shi, Yu; Jia, Yu; University of Chester
      The formation and accretion of ice on aircraft wings during flight can be potentially disastrous and existing in-flight deicing methods are either bulky or power consuming. This paper investigates the use of shear wave deicing driven by a macro fibre piezoelectric composite actuator on a composite plate typically used for aircraft wings. While the few existing research on this novel deicing approach focused on either theoretical studies or single frequency mode optimization that required high-excitation amplitudes, this study revealed that the use of multimodal excitation through broadband frequency sweeps has the potential to promote the chance of shear stress induced deicing at a relatively small excitation amplitude. The results reported here form the foundation for a pathway towards low power and lightweight deicing mechanism for in-flight aircraft wings.
    • Panel adjustment and error analysis for a large active main reflector antenna by using the panel adjustment matrix

      Lian, Peiyuan; Wang, Congsi; Xue, Song; Xu, Qian; Wang, Na; xiang, Binbin; Shi, Yu; Jia, Yu; Xidian University; University of Chester; Aston University; Chinese Academy of Sciences
      Active panels are generally applied in large aperture and high frequency reflector antennas, and the precise calculation of the actuator adjustment value is of great importance. First, the approximation relationship between the adjustment value and panel elastic deformation is established. Subsequently, a panel adjustment matrix for the whole reflector is derived to calculate the reflector deformation caused by the actuator adjustment. Next, the root mean square (rms) error of the deformed reflector is expressed as a quadratic form in the matrix form, and the adjustment value can be derived easily and promptly from the corresponding extreme value. The solution is expected to be unique and optimal since the aforementioned quadratic form is a convex function. Finally, a 35 m reflector antenna is adopted to perform the panel adjustments, and the effect of the adjustment errors is discussed. The results show that compared to the traditional model, where the panel elastic deformation is not considered, the proposed method exhibits a higher accuracy and is more suitable for use in large reflectors with a high operation frequency. The adjustment errors in different rings exert different influences on the gain and sidelobe level, which can help determine the actuator distribution with different precisions.