• 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)
      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.
    • Impedance interaction modeling and analysis for bidirectional cascaded converters

      Tian, Yanjun; Deng, Fujin; Chen, Zhe; Sun, Xiaofeng; Hu, Yanting (2015-06)
      For the cascaded converter system, the output impedance of source converter interacts with the input impedance of load converter, and the interaction may cause the system instability. In bidirectional applications, when the power flow is reversed, the impedance interaction also varies, which brings more uncertainty to the system stability. An investigation is performed here for showing that the forward and reverse interactions are prominently different in terms of dynamics and stability even though the cascaded converter control remains unchanged. An important guideline has been drawn for the control of the cascaded converter. That is when voltage mode converter working as the load converter; the constant power mode converter as the source converter, the system is more stable. The concluded findings have been verified by simulation and experimental results.
    • Isolation of a Ferroelectric Intermediate Phase in Antiferroelectric Dense Sodium Niobate Ceramics

      Yang, Bin; Zhang, Hangfeng; Yan, Haixue; Abrahams, Isaac (Elsevier, 2019-08-22)
      Switchable ferroelectric/antiferroelectric ceramics are of significant interest for high power energy storage applications. Grain size control of this switching is an interesting approach to controlling polarization and hence dielectric properties. However, the use of this approach in technologically relevant ceramics is hindered by difficulty in fabricating dense ceramics with small grain sizes. Here an intermediate polar ferroelectric phase (P21ma) has been isolated in dense bulk sodium niobate ceramics by grain size control through spark plasma sintering methods. Our findings, supported by XRD, DSC, P-E (I-E) loops and dielectric characterization, provide evidence that the phase transition from the antiferroelectric (AFE) R-phase, in space group Pnmm, above 300 C, to the AFE P-phase, in space group Pbma, at room temperature, always involves the polar intermediate P21ma phase and that the P21ma to Pbma transition can be suppressed by reducing grain size.
    • 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.
    • Microstructure and broadband dielectric properties of Zn2SiO4 ceramics with nano-sized TiO2 addition

      Weng, Zhangzhao; Song, Chunxiao; Xiong, Zhaoxian; Xue, Hao; Sun, Wenfeng; Zhang, Yan; Yang, Bin; Reece, Michael J.; Yan, Haixue; Xiamen University; Capital Normal University; University of Chester; Queen Mary, University of London; China Electronic Product Reliability and Environmental Testing Research Institute (Elsevier, 2019-04-06)
      Zn2SiO4 ceramics with nano-sized TiO2 addition (ZST) were synthesized by conventional solid state method. The association between the new composite’s microstructures and dielectric properties reveals that reduced pores, increased density and average grain sizes with increasing sintering temperatures, have contributed to the increased permittivities at kHz and microwave bands; the decrease of the permittivities at 1275 0C is due to the form of twin planes. At the terahertz band, the competition of generating oxygen vacancies and forming them into twin crystallographic shear planes dominates the change of permittivities: the crystallographic shear planes decrease the permittivity at the sintering temperature 12250C and 12500C, and the high-rate generation of oxygen vacancies at 1275 0C increases the permittivities. The ZST ceramics demonstrate stable permittivity and low dielectric losses (<10-3 from 10 kHz to microwave band; and < 10-2 at THz range); and the temperature coefficient of resonant frequency is optimized to close zero. These advanced dielectric properties and low sintering temperature (<13000C) provide the ZST ceramics great potential in designing microwave and THz devices.
    • Microwave and terahertz dielectric properties of MgTiO3–CaTiO3 ceramics

      Huang, Jinbao; Yang, Bin; Yu, Chuying; Zhang, Guang; Xue, Hao; Xiong, Zhaoxian; Viola, Giuseppe; Donnan, Robert S.; Yan, Haixue; Reece, Michael J.; et al. (Elsevier, 2015-10-05)
      The THz dielectric properties of MgTiO3–CaTiO3 ceramics are reported. The ceramics were prepared via a solid-state reaction route and the sintering conditions were optimized to obtain ceramics with high permittivity and low loss in the terahertz frequency domain. The amount of impurities (MgTi2O5) and grain size increased with increasing sintering temperature. The dielectric properties improved with increasing density, and the best terahertz dielectric performance was obtained at 1260 °C, with a permittivity of 17.73 and loss of 3.07×10−3. Ceramics sintered above 1260 °C showed a sharp increase in loss, which is ascribed to an increase in the impurity content.
    • Perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 ceramics with polar nano regions for high power energy storage

      Wu, Jiyue; Mahajan, Amit; Riekehr, Lars; Zhang, Hangfeng; Yang, Bin; Meng, Nan; Zhang, Zhen; Yan, Haixue; Queen Mary University of London; Uppsala University; University of Chester (Elsevier, 2018-06-06)
      Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 (x=0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behaviour with low remnant polarization (Pr) and high maximum polarization (Pmax). Moreover, Pmax was further increased due to reversible electric field induced phase transitions. Comprehensive structural and electrical studies were performed to confirm the PNRs and the reversible phase transitions. And finally a high energy density (1.70 J/cm3) with an excellent efficiency (87.2%) was achieved using the contribution of PNRs and field-induced transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage.
    • The power of VNA-driven quasi-optics to sense group molecular action in condensed phase systems

      Donnan, Robert S.; Tian, Kun V.; Yang, Bin; Chass, Gregory A.; University of Chester (2014-12-08)
      The versatility for quasi-optical circuits, driven by modern vector network analysers, is demonstrated for the purpose of low energy (meV) coherent spectroscopy. One such example is shown applied to the curing dynamics of a non-mercury-based dental cement. This highlights the special place the methodology holds as a `soft-probe' to reveal the time-resolved energetics of condensed phased systems as they self-organise to adopt their low energy state.
    • Power System with Variable Speed Wind Turbine and Diesel Generation Units

      Hu, Yanting; Chen, Zhe; Glyndwr; Aalborg University (EER, 2014-01-20)
      Thispaper presents a power system consisting of wind turbines, diesel generation units, and energy storage system. Both wind turbines and diesel engine adopt variable speed operation mode;and power electronic interface are used for the generation units which provide flexible and wide range of control on the power. The system configuration, characteristics, operation principles are presented. The controller and control strategies are discussed. The simulation studies have been performed and the results are presented.
    • Programmable logic controllers and Direct digital controls in Buildings

      Khalid, Yousaf; University of Chester (2018-09)
      The concept of programmable logic controller (PLC) originated over the last century that has revolutionised the industrial sector. In the last few decades PLC in the form of DDC has been commonly used in Building Energy Management Systems (BEMS). The contribution of this work is to analyse PLC/DDC role in the ongoing BEMS advancements in the building sector. Currently DDC are not understood by building design and simulation engineers who assess the controllability of the building in practice. This paper would enhance the understanding of integrating DDC in buildings and influence creation of better modelling and simulation tools for assessing their impact on energy performance in practice.
    • Q-V droop control using fuzzy logic and reciprocal characteristic

      Wang, Lu; Hu, Yanting; Chen, Zhe; Glyndwr University; Aalborg University (Engineering and Technology Publishing, 2014-01-01)
      Today, the conventional power system is facing some global environmental problems, which is leading to a new trend of power grid by using “green and clear” energy sources. As the platform of smart grid technology, the microgrid associated with distributed energy resources (DERs) may provide electric power at distributed voltage level, which not only is an autonomous system, but also can be connected to the main grid. To improve the stability and controllability of the power grid, this paper presents an improved Q-V droop control strategy using fuzzy logic controller and reciprocal characteristic. Matlab/Simulink is used for analysing the performance of system. The feasibility of the improved droop control strategy has been verified and discussed. The results demonstrate the improved Q-V droop control strategy could have good effects in grid-connected and islanded mode, and during operation mode transitions.
    • Quality Mapping of Offset Lithographic Printed Antenna Substrates and Electrodes by Millimeter-Wave Imaging

      Zhang, Jiao; Tang, Jianhua; Sun, Wenfeng; Zhang, Yan; Yang, Bin; Wang, Xinke; University of Chester (MDPI, 2019-06-14)
      Offset lithographic printed flexible antenna substrate boards and electrodes have attracted much attention recently due to the boost of flexible electronics. Unmanned quality inspection of these printed substrate boards and electrodes demands high-speed, large-scale and nondestructive methods, which is highly desired for manufacturing industries. The work here demonstrates two kinds of millimeter (mm)-wave imaging technologies for the quality (surface uniformity and functionality parameters) inspection of printed silver substrates and electrodes on paper and thin polyethylene film, respectively. One technology is a mm-wave line scanner system and the other is a terahertz-time domain spectroscopy-based charge-coupled device (CCD) imaging system. The former shows the ability of detecting transmitted mm-wave amplitude signals only; its detection is fast in a second time scale and the system shows great potential for the inspection of large-area printed surface uniformity. The latter technology achieves high spatial resolution images of up to hundreds of micrometers at the cost of increased inspection time, in a time scale of tens of seconds. With the exception of absorption rate information, the latter technology offers additional phase information, which can be used to work out 2D permittivity distribution. Moreover, its uniformity is vital for the antenna performance. Additionally, the results demonstrate that compression rolling treatment significantly improves the uniformity of printed silver surfaces and enhances the substrate’s permittivity values.
    • Quality-Control of UV offset Lithographicaly Printed Electronic-Ink by THz Technology

      Zeng, Yang; Donnan, Robert S.; Edwards, Marc; Yang, Bin; University of Chester (IEEE Conference Publications, 2017-10-16)
      In this paper, a novel quality-monitor method of inkjet-printed electronics based on terahertz (THz) sensing is presented. Specifically, two different approaches, namely THz reflection spectroscopy and THz near-field scanning, are proposed.
    • Research on the synchronization control strategy for microgrid-connected voltage source inverter

      Cao, Yuanzhi; Hu, Yanting; Hu, Rui; Chen, Jianfei (IEEE, 2015-06)
      Microgrid is intended and featured to be able to operate in both grid-connected and islanded mode to ensure high quality and reliable power supply. In order to achieve stable operation of the microgrid-connected voltage source inverter (MVSI) units under paralleled or grid-connected mode, a novel synchronization method based on droop control is proposed in this paper. The difference of phase and amplitude between different MVSI units is detected and is used to calculate the output frequency and amplitude of the MVSI. This method can smooth transfer the MVSI units from standalone mode to paralleled mode. The simulation and experimental results show that the proposed method is effective in achieving paralleled operation of the MVSI units.
    • Smart guaranteed time-slot allocation algorithm for industrial wireless sensor networks emergency message transmission

      Chen, Qinyin; Hu, Yanting; Chen, Zhe; Davies, John N.; Excell, Peter (IET, 2015-04)
      This paper presents investigation on application of wireless sensor networks (WSNs) in wind power generation systems and highlights an important issue associated with the deadline for the delivery of messages among nodes based on the IEEE 802.15.4E standard. Owing to the limits of standard and the power system application requirements, this research proposes a smart guaranteed time slot (S-GTS) allocation algorithm which is based on the urgent/important matrix. This proposed algorithm promotes the utilisation of contention free period in a superframe. Besides, over seven GTSs can be allocated in a superframe, there are only seven GTSs that can be used in the standard. In addition, this study proves the value of BO and SO upper bound is 6 for the WSN application in power systems. Moreover, the network delay of S-GTS performs better than the 16-time-slot mechanism and i-GAME mechanism.
    • Spreadsheet tools to estimate the thermal transmittance and thermal conductivities of gas spaces of an Insulated Glazing Unit

      Nammi, Sathish K.; Shirvani, Hassan; Shirvani, Ayoub; Edwards, Gerard; Dunn, Jeremy; Anglia Ruskin University, Anglia Ruskin University, Anglia Ruskin University, University of Chester, Glazing Vision (Anglia Ruskin Research Online, 2014-03)
      An Insulated Glazing unit (IGU) is constructed with two or more layers of glass panes sealed together by gas spaces in-between. IGUs are prevalent in windows, doors and rooflights, primarily due to their improved thermal resistance. Today, most IGUs are either two or three layered. Adding further layers of glass improves thermal insulation but with the penalty of increased cost and weight. Low emissivity (Low-e) film coatings, when deposited on the glass panes, reduce long-wavelength radiative heat losses. Furthermore, filling the gas spaces with the inert gases (e.g. Argon, Krypton, Xenon and SF6), further reduce conduction and natural convection across the gap. In summary, higher thermal insulation performance of an IGU can be achieved with gas fillings and Low-e coatings on glass. This report discusses spreadsheets that have been developed, capable of estimating the thermal transmittance values of IGU, as per BS EN 673. The spreadsheet tools also have the ability to estimate the thermal conductivity of the gas spaces between the panes of IGU.
    • SrFe12O19 based ceramics with ultra-low dielectric loss in the millimetre-wave band

      Yu, Chuying; Zeng, Yang; Yang, Bin; Wylde, Richard; Donnan, Robert S.; Wu, Jiyue; Xu, Jie; Gao, Feng; Abrahams, Isaac; Reece, Michael J.; et al. (AIP Publishing, 2018-04-02)
      Non-reciprocal devices such as isolators and circulators, based mainly on ferromagnetic materials, require extremely low dielectric loss in order for strict power-link budgets to be met for millimetre (mm)-wave and terahertz (THz) systems. The dielectric loss of commercial SrFe12O19 hexaferrite was significantly reduced to below 0.002 in the 75 - 170 GHz band by thermal annealing. While the overall concentration of Fe2+ and oxygen vacancy defects is relatively low in the solid, their concentration at the surface is significantly higher, allowing for a surface sensitive technique such as XPS to monitor the Fe3+/Fe2+ redox reaction. Oxidation of Fe2+ and a decrease in oxygen vacancies is found at the surface on annealing, which is reflected in the bulk sample by a small change in unit cell volume. The significant decrease in dielectric loss property can be attributed to the decreased concentration of charged defects such as Fe2+ and oxygen vacancies through annealing process, which demonstrated that thermal annealing could be effective in improving the dielectric performance of ferromagnetic materials for various applications.
    • Terahertz Characterisation of UV Offset Lithographically Printed Electronic-Ink

      Zeng, Yang; Edwards, Marc; Stevens, Robert; Bowen, John; Donnan, Robert S.; Yang, Bin; University of London; National University of Defense Technology; University of Chester; Nottingham Trent University; University of Reading (Elsevier, 2017-06-10)
      Inkjet-printed electronics are showing promising potential in practical applications, but methods for real-time, non-contact monitoring of printing quality are lacking. This work explores Terahertz (THz) sensing as an approach for such monitoring. It is demonstrated that alterations in the localised dielectric characteristics of inkjet-printed electronics can be qualitatively distinguished using quasi-optically-based, sub-THz reflection spectroscopy. Decreased reflection coefficients caused by the sintering process are observed and quantified. Using THz near-field scanning imaging, it is shown that sintering produces a more uniform spatial distribution of permittivity in the printed carbon patterns. Images generated using THz-TDS based imaging are presented, demonstrating the combination of high resolution imaging with quantification of complex permittivities. This work, for the first time, demonstrates the feasibility of quality control in printed electronic-ink with THz sensing, and is of practical significance to the development of in-situ and non-contact commercial-quality characterisation methods for inkjet-printed electronics.
    • Titanium Dioxide Engineered for Near-dispersionless High Terahertz Permittivity and Ultra-low-loss

      Chuying, Yu; Zeng, Yang; Yang, Bin; Donnan, Robert S.; Huang, Jinbao; Xiong, Zhaoxian; Mahajan, Amit; Shi, Baogui; Ye, Haitao; Binions, Russell; et al. (Nature Publishing Group, 2017-07-26)
      Realising engineering ceramics to serve as substrate materials in high-performance terahertz(THz) that are low-cost, have low dielectric loss and near-dispersionless broadband, high permittivity, is exceedingly demanding. Such substrates are deployed in, for example, integrated circuits for synthesizing and converting nonplanar and 3D structures into planar forms. The Rutile form of titanium dioxide (TiO2) has been widely accepted as commercially economical candidate substrate that meets demands for both low-loss and high permittivities at sub-THz bands. However, the relationship between its mechanisms of dielectric response to the microstructure have never been systematically investigated in order to engineer ultra-low dielectric-loss and high value, dispersionless permittivities. Here we show TiO2 THz dielectrics with high permittivity (ca. 102.30) and ultra-low loss (ca. 0.0042). These were prepared by insight gleaned from a broad use of materials characterisation methods to successfully engineer porosities, second phase, crystallography shear-planes and oxygen vacancies during sintering. The dielectric loss achieved here is not only with negligible dispersion over 0.2 - 0.8 THz, but also has the lowest value measured for known high-permittivity dielectrics. We expect the insight afforded by this study will underpin the development of subwavelength-scale, planar integrated circuits, compact high Q-resonators and broadband, slow-light devices in the THz band.
    • Verification of calculation code THERM in accordance with BS EN ISO 10077-2

      Nammi, Sathish K.; Shirvani, Hassan; Shirvani, Ayoub; Edwards, Gerard; Whitty, Justin P. M.; Anglia Ruskin University, Anglia Ruskin University, Anglia Ruskin University, University of Chester, University of Central Lancashire (Anglia Ruskin Research Online, 2014)
      Calculation codes are useful in predicting the heat transfer features in the fenestration industry. THERM is a finite element analysis based code, which can be used to compute thermal transmittance of windows, doors and shutters. It is important to verify results of THERM as per BS EN ISO 10077-2 to meet the compliance requirements. In this report, two-dimensional thermal conductance parameters were computed. Three versions of THERM, 5.2, 6.3 and 7.1, were used at two successive finite element mesh densities to assess their comparability. The results were all compliant with the aforementioned British Standard.