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Wireless power transfer (WPT) for portable electronic applications has been gaining a lot of interest over the past few decades. This study provides a comprehensive review of the recent advancements in WPT technology, along with the challenges faced in its practical implementation. The modeling and design of WPT systems, including the effect of cross-coupling in multiple receivers, have been discussed and the techniques for efficiency improvement have been highlighted. The challenges of coil design, EMI shielding, and foreign object detection have been pointed out and various cutting-edge solutions have been presented. With improvements in wide bandgap technology, there is a push to operate WPT systems at mega-hertz frequencies. The reason for this is twofold: the miniaturization of the system and the ability to achieve a better magnetic link efficiency. However, with higher frequency comes the challenge of operating the power electronic components efficiently by using soft-switching techniques. Hence, an in-depth discussion on soft-switched topologies such as the Class D and Class E converters and their variations has been provided. Finally, the effects of magnetic field exposure on humans along with safety standards have been discussed.

Microscopic imaging in three dimensions enables numerous biological and clinical applications. However, high-resolution optical imaging preserved in a relatively large depth range is hampered by the rapid spread of tightly confined light due to diffraction. Here, we show that a particular disposition of light illumination and collection paths liberates optical imaging from the restrictions imposed by diffraction. This arrangement, realized by metasurfaces, decouples lateral resolution from depth-of-focus by establishing a one-to-one correspondence (bijection) along a focal line between the incident and collected light. Implementing this approach in optical coherence tomography, we demonstrate tissue imaging at 1.3 μm wavelength with ~ 3.2 μm lateral resolution, maintained nearly intact over 1.25 mm depth-of-focus, with no additional acquisition or computation burden. This method, termed bijective illumination collection imaging, is general and might be adapted across various existing imaging modalities.

Commercialization of organic solar cells (OSC) is imminent. Interlayers between the photoactive film and the electrodes are critical for high device efficiency and stability. Here, the applicability of SnO

This article presents a new nonisolated dc–dc converter with bidirectional power flow capability. The proposed converter operates in triangular conduction mode (TCM). Consequently, reverse-recovery losses are completely eliminated, zero voltage switching characteristics are obtained, and the inductor size can be reduced. However, in comparison with other converters in TCM that suffer from a large input-current-ripple, the proposed converter benefits from very low input-current-ripple. Furthermore, in the proposed converter, the voltage stress of the main switches is reduced, the converter voltage-gain is increased, the output current is nonpulsating, the input and output sources share a common ground, and only a single magnetic core is required. The proposed power circuit topology is theoretically analyzed and experimental results are provided to verify its feasibility and demonstrate its superior performance.

This article presents a three-port dc/dc converter along with a new control system to integrate solar panels and energy storage in a dc nanogrid. The proposed control system utilizes the duty cycle as well as the switching frequency to control the power flow between the three ports. The proposed converter offers a low number of components, low cost, and high reliability. Moreover, it is capable of providing bidirectional power flow for the energy storage system and the dc grid while having soft-switching for power semiconductors. The converter demonstrates high design flexibility in accommodating different applications. Theoretical analysis and experimental results verify the feasibility and demonstrate the superior performance of the proposed converter.

This article presents a novel isolated dc–dc converter circuit topology, which is able to offer high performance for a wide range of operating conditions. The prominent features of the proposed circuit topology include its direct power transfer (DPT) capability, quasi-rectangular waveform for the input current, and soft-switching performance for a wide range of operating conditions. The amount of power processed by the power switches and transformer is reduced through DPT. In addition, the quasi-rectangular waveform of the input current decreases its peak and root-mean-square values, leading to reduced conduction losses associated with the magnetics and power semiconductors. In the proposed structure, the power switches benefit from zero-voltage-switching characteristics, while the output diodes operate under zero-current-switching conditions. Thus, the proposed topology minimizes both the conduction and switching losses, thereby improving the overall efficiency. Extensive simulation and experimental results are provided to verify the feasibility of the proposed circuitry and demonstrate its superior performance.

This article presents a new droop-based supervisory-level controller for nanogrids (NGs) in the islanded mode of operation. The proposed control system is able to significantly improve the dynamics of power electronic interfaces in NGs. Unlike the existing techniques, the proposed controller takes into account the input-side (i.e., source-side) and the output-side (i.e., load-side) parameters as well as the dc-bus voltage dynamics. Theoretical analysis, simulation results, and experimental results confirm the feasibility of the proposed control system and demonstrate its superior performance.

OLEDs have become prominent in commercial display and lighting applications, mainly for television and smartphone screens, and in many electronic gadgets due to superior features over other display technologies such as Liquid Crystal Displays (LCDs). In the evolution of OLED fabrication, roll-to-roll (R2R) solution-based techniques, which are low-cost and high throughput, have emerged as next-generation manufacturing methods for OLED production. Researchers and scientists all over the world are investigating R2R upscaling methods. Thus far, the existing R2R fabrication methods for manufacturing high performance OLEDs have had limited success due to film thickness variations, aggregation in films, challenges in forming the multi-layer structure, and scarcity of efficient interlayers. Slot-die coating is a very promising fabrication technique that can facilitate R2R manufacturing of OLEDs and address some of the aforementioned challenges. In this review, a summary of the developments in OLED fabrication using slot-die coating methods is presented. First, we highlight the research work on the slot-die coating of single and multi-layer OLEDs, and then we present various modifications of slot-die heads to fabricate micro-sized OLEDs for high-resolution display applications. Lastly, we present a qualitative comparison between the performance of OLEDs fabricated by slot-die coating and the ones fabricated by other R2R techniques. While many review articles have been published on OLED materials and devices, there is not one collection of reports detailing the slot-die coating, an additive manufacturing method, of OLEDs.

We have designed and synthesized three N-annulated perylene diimide (PDI) compounds containing sterically bulky alkyl-substituted benzyl moieties (PDI-X, where X = 1, 2, 3) with photoluminescence quantum yield (PLQY) in the solid-state >20%. The PDI molecules show PLQY of ∼0.8 in solution and ∼0.2 as neat films. Organic light-emitting diodes (OLEDs) have been fabricated using these new PDI molecules as light emitters with the active layer being solution processed from non-halogenated solvents. The OLED devices had brightness of ∼2000 cd m−2 and low turn-on voltage of ∼3 V, among the best for PDI based red colored OLEDs.

This article presents a novel sensorless control system for a solar tile microinverter employing the flyback topology. The elimination of current sensors from the circuit lowers the overall cost and reduces measurement noise introduced into the control system. The proposed control system eliminates both the high frequency inductor current measurement as well as the photovoltaic (PV) module current measurement. Additionally, an inductance observer is combined with the proposed technique to increase the accuracy of the high frequency inductor current estimation. A stability analysis proves the system to be stable. The proposed control system is experimentally validated on a microinverter prototype. Simulation and experimental results affirm the feasibility and performance of the control system. The experimental setup includes a grid simulator and a PV module simulator to test the system at varying irradiance levels. The proposed control system is also compared to methods presented in previous literature to demonstrate its superior characteristics.

In this article, a new control system is introduced for use in uninterruptible power supply (UPS) systems. The proposed control system is able to improve the dynamic performance of UPS systems, facilitating their integration into smart grids. The proposed control system isolates the battery from the double-frequency ripple both in the normal mode (charging) and in the backup mode (discharging). The new UPS control system is tailored for single-phase systems utilizing lithium-ion battery storage systems, where current ripple must be limited. Simulation and experimental results verify the feasibility of the proposed control system and demonstrate its superior performance.

This article presents a new digital control system for dual active bridge dc/dc converters. The proposed control system includes a novel compensator with asymmetric half-cycle modulation. The proposed compensator is based on a novel geometric-sequence-control algorithm, which is a model-based predictive current control. The proposed control system provides fast and seamless tracking of the reference current and ensures zero dc current in the transformer windings (prevents transformer saturation). Moreover, it offers high robustness against perturbations and uncertainties in the converter. It also allows symmetric growth of transformer current during transients, thereby eliminating potential temporary saturation issues. Analysis, simulation, and experimental results are provided to demonstrate the superior performance of the proposed control in achieving high precision output regulation, fast and seamless transient response, and high robustness.

Power electronic converters for electric vehicles (EVs) have been the subject of great interest over the last several decades. This article presents a thorough review of different EV power electronic converters on which the authors have worked for more than one decade. The readers will find this review interesting to design current products and to devise/invent new converters for emerging applications in EV.

In this article, a novel dual-switch discontinuous current-source gate driver (CSD) suitable for driving the high-side mosfet (HS mosfet ) of buck voltage regulator module (VRM) is presented. The proposed gate driver completely solves the gate current diversion problem, which most of the previous CSDs suffer from, during turn- off transition. Thus, in comparison to most of the previous CSDs, the proposed gate driver achieves to turn- off the power mosfet considerably faster and with much higher effective gate current, which leads to significant reduction of turn- off losses. Whereas, turn- on losses of buck VRM HS mosfet driven by the proposed CSD and the previous CSDs are equal. Furthermore, the introduced gate driver consists of the minimum number of control switches and circuit elements, compared to previous CSDs. The proposed gate driver is analyzed and a prototype of the driver operating at 1 MHz is implemented in order to validate the theoretical analysis.

This paper presents a new harmonic compensation system along with a hybrid load observer used for micro-grids in the islanded mode. The proposed control system includes an online hybrid load observer, which is able to precisely estimate the harmonic contents of the load as well as the equivalent load impedance in the islanded mode. One of the main features of the proposed control system is its capability to deal with unknown load harmonics, which is a big challenge in micro-grids. Basically, the proposed control system is able to detect, estimate, and compensate various load disturbances and harmonics (e.g., synchronous and asynchronous harmonics, and dc components). Theoretical analysis, simulation results, and experimental results verify the feasibility and performance of the proposed control system.

In this paper, a soft-switched three-phase resonant converter with a low quality factor (Q) design is proposed for Photovoltaic (PV) energy harvesting systems with a very wide range of operating conditions. Due to the low quality factor (Q ≤ 1), the voltage stress across the capacitors is drastically reduced. However, a major challenge of using a low Q design is the wide switching frequency range required for operation over a wide range of load and input conditions. In order to reduce the switching frequency range, this paper introduces a hybrid modulation technique employing asymmetric pulse width modulation (APWM) along with variable frequency modulation. The proposed modulation scheme also substantially extends the soft-switching range of the converter from full-load upto 10–35% load condition over a wide range of line voltages. To sustain soft-switching in the entire operating region of the converter, the converter is operated in a hybrid structure with single-phase and burst modes at light load conditions. A comprehensive time-domain analysis of the proposed converter is presented, which greatly improves accuracy over conventional frequency-domain modeling. Experimental results from a 1 kW prototype are presented to verify the performance of the converter and validate the theoretical analysis.

This article proposes a real-time dynamic maximum efficiency tracking algorithm for wireless power transfer (WPT) systems with multiple receivers. The algorithm sequentially varies the net reactance of each of the receivers using switched capacitor circuits (SCCs) to reach the maximum efficiency point (MEP). The MEP in multiple-receiver systems varies in the presence of cross-coupling. This article provides an in-depth analysis of the effects of cross-coupling and proves that cross-coupling could be beneficial or detrimental to efficiency, depending on circuit conditions such as the load resistances and coupling factors among the coils. Hence, unlike previous research, this article emphasizes the improvement of the link efficiency in the presence of cross-coupling rather than the complete elimination of its effects. Experimental results have been included for a single-transmitter and two-receiver system to validate the feasibility of the proposed algorithm.

Recent advancements in high power light-emitting diode (LED) technology have presented greenhouse industry with a more efficient and flexible alternative light source for horticulture. However, the light distribution on the plant remains a challenge that has notable implications on the plant growth. A non-uniform light distribution on the canopy with hot spots is well-known to adversely affect the yield. Here, we present a technique to engineer the light wavefront of a solid-state source using a single-surface optics, which yields a highly uniform light distribution across the plant. This technique achieves over 90% illuminance uniformity, preserved at various distances from the source, for a cone of light with an up to 120° angular range. This work aids the paradigm shift towards LEDs as a competitive light source in horticulture.

The series LC-parallel LC (LCLC) resonant converter with capacitive output filter is an emerging favorite for high frequency, high output voltage applications. Existing literature utilizes conventional fundamental harmonic approximation (FHA) based techniques for steady-state analysis due to its simplicity. However, FHA results in limited accuracy when applied on low-quality factor (Q

Three-phase resonant converters are preferred for high power applications as they provide several advantages such as reduced component stress, small filter size requirement, and high power density. The analysis of these converters is generally performed in frequency-domain using a single-phase equivalent circuit which provides approximate results and may lead to the erroneous design of the converter. This paper presents a time-domain modeling technique for the analysis of a low Q three-phase series resonant converter operating under asymmetric pulse width and variable frequency modulation. This method can also be applied to analyze converters with different resonant tank and transformer configurations without compromising accuracy.

In this contribution we report on solution processed red OLEDs based upon an N-annulated perylene diimide dimer, namely tPDI2N-EH, a red-light emitting molecule. OLED devices with the architecture of glass/ITO/PEDOT:PSS/EML/LiF/Ag (EML = emitting layer) were fabricated with EMLs comprised of tPDI2N-EH neat and blended with poly(9,9-dioctylfluorene, PFO), all solution processed from non-halogenated solvents. The photophysical and electrophysical performance of PFO:tPDI2N-EH-blend films with different composition ratios were investigated. The PFO : tPDI2N-EH-based OLEDs with a 2 : 18 ratio exhibited the best performance. The PFO:tPDI2N-EH-based OLEDs gave red electroluminescence with the emission wavelength of 635 nm and the CIE (international commission on illumination) coordinates of (x = 0.672, y = 0.321). OLEDs with EMLs fabricated using roll-to-roll compatible methods are also demonstrated.

Flexible red OLEDs based on a quadruple-layer stack, in between electrodes, with 160 mm2 active area were fabricated in ambient air on PET via slot-die-coating. For the OLED structure PET/ITO/PEDOT...

This paper presents a novel resonant power converter for transcutaneous power transmission in retinal prosthesis applications. In retinal prosthetic applications, the frequency and power of the transmitted signal must be limited to a specific range such that the living tissue is not harmed. The design goal is to transmit power with maximum efficiency, and minimum sensitivity to the nonideal power transfer link. The proposed wireless power-transfer circuit offers significant advantages over conventional ones, which usually use Class E converters. The proposed approach has very low sensitivity to coupling factor/load variations in the inductive link and demonstrates very fast dynamic response. In addition, the proposed approach does not require a dc–dc converter to control the output power. Soft switching is achieved for the proposed circuitry despite the variations in the coupling coefficient. Thus, superior efficiency can be obtained using the proposed approach. Theoretical analysis and various simulations validate the superior performance of the proposed approach. In addition, a 1-MHz experimental prototype has been prepared to verify the feasibility of the proposed wireless power-transfer circuit.

This paper presents a new dc/ac inverter for low-power applications (i.e., high-voltage, low-current applications), which offers soft switching of the power semiconductors and low output current ripple. In the proposed power circuitry, a novel ripple steering approach is used that can provide soft switching for the power semiconductors and significantly attenuate the high-frequency current ripple of the inverter. The proposed ripple steering technique utilizes the switching frequency and the duty cycle in order to perform the aforementioned tasks. Basically, the ripple steering technique steers the energy of the ripple to the output capacitances of the power semiconductors in order to provide the soft-switching condition. Theoretical analysis, simulation results, and experimental results verify the feasibility of the proposed technique and demonstrate the superior performance of the proposed inverter.

This letter presents an active dc-eliminating method for dc/dc converters in order to prevent the transformer saturation. The proposed method is based on the asymmetry in the voltage ripple waveform caused by the dc component of the transformer current. The proposed dc-eliminating technique is able to quickly eliminate the dc component of the transformer current during transients as well as steady-state operation. The main advantage of the proposed method is that it avoids transformer saturation without the need for dc blocking capacitor or any use of current sensors and their additional circuitry. Also, since the proposed method is implemented in the control system, it does not create any power losses or distortions in the waveforms. The simulation and experimental results show the feasibility of the proposed technique.

This paper presents a multi-variable hybrid control strategy that can simultaneously adjust both operating switching frequency, f s , and duty cycle of a dc-dc resonant converter in response to variation of either input voltage or load conditions. Conventional resonant converter control strategies are mono--variable i.e., either f s or duty cycle is changed at a time in response to varying operating conditions. This strategy might eliminate MOSFET turn-ON losses due to zero voltage switching (ZVS). However, such control strategy may inadvertently cause large circulating reactive current flow which can nullify ZVS power savings. Hence, it is necessary to operate the converter such that ZVS operation with minimum primary circulating current is guaranteed while ensuring output power regulation for a wide range of operating conditions. A multi-variable ZVS control strategy that achieves simultaneous variation of f s and duty cycle to changing operating conditions is implemented using a F-D control law relationship. This control law has been developed for a hybrid Frequency modulated (FM)-Phase-shift modulated (PSM) LLC resonant converter based on ZVS boundary conditions established using FHA. Efficiency improvements of at most 1.5% are observed when compared with mono-variable FM-PSM control.

This paper presents a new design architecture for mechanically flexible light-emitting diode (LED) signage modules for applications in digital advertising on curved surfaces. The new design comprises an array of commonly used rigid printed circuit boards (PCBs) but of smaller size with some spacing between them, which is encapsulated by a flexible substrate or potting material, instead of a large single rigid PCB in the entire LED module as in the case of conventional LED signage modules. Commonly used through-hole type red-green-blue (RGB) LEDs are considered. To demonstrate the design, manufacturing, and mechanical flexibility of the design, a prototype LED signage module with a typical industry standard size of 304 mm × 304 mm × 10 mm was designed and fabricated. Experimental testing and finite element simulations were conducted to analyze mechanical flexibility and internal stresses in the module. The results demonstrate that the new design provides flexible LED modules, without altering the conventional LED control system. It is shown that maximum stress occurs in the spacing between the PCBs and is small even for large module deflection. As the curvature of module deflection was decreased, the maximum stress increased, indicating an important design parameter for the module deflection. The proposed design architecture will enable both indoor and outdoor digital advertising using billboards on a wide range of curved surfaces.

Redox flow batteries (RFBs) are a promising technology for grid scale stationary energy storage to complement renewable energy systems. These batteries have a relatively low energy density; however, they offer important advantages, including: long life-time; decoupled energy (arbitrarily large electrolyte volume) and power (electrode area); high round-trip efficiency; scalability and design flexibility; fast response; and low environmental impacts. These advantages make them superior to many energy storage technologies for stationary applications [1-4]. Among the various types of RFBs, vanadium RFBs (VRFBs) are an emerging technology for grid scale energy storage and the integration of renewable energy generation [5]. The membrane is a key component of a VRFB that separates the two half-cell electrolytes and prevents cross-mixing, while allowing the transport of ions during charge-discharge cycles [6]. The VRFB membrane should exhibit low vanadium ion permeability to minimize self-discharge, low cost, and long‐term chemical stability under normal operating conditions. A high proton conductivity and low vanadium ion crossover are known to improve the efficiency of VRFBs [6-7]. In this study, we present a novel composite Nafion based membrane that results in a significant increase in the VRFB performance. The composite membrane has been characterized for its chemical, structural, and thermal properties using appropriate analytical techniques. The battery performance was evaluated in a flow cell using a ‘zero-gap’ design with an electrode area of 5 cm2. The electrolytic solution, 1.6 M VOSO4 in 3 M H2SO4, was circulated through the cell. Thermally treated carbon papers were used as the cathode and anode electrodes. For charge-discharge experiments, a constant current density (10 to 80 mA cm−2) was applied with upper and lower voltage cut-offs of 1.65 and 0.8 V, respectively. The stability of the battery using the composite membrane was evaluated over 100 cycles. Figures 1 and 2 show the energy efficiency and capacity retention during 100 charge-discharge cycles. The results reveal that the energy efficiency was improved from 51% to 63% by using the composite membrane. In addition, the charge-discharge capacity and capacity retention improved by around 200% and 25%, respectively. This improvement can be attributed to a higher proton conductivity and lower vanadium permeability of the composite membrane. References: [1] M. Skyllas-Kazacos, L. Cao, M. Kazacos, N. Kausar, A. Mousa, Vanadium Electrolyte Studies for the Vanadium Redox Battery-A Review, ChemSusChem. 9 (2016) 1521–1543. [2] A.K. Singh, M. Pahlevaninezhad, N. Yasri, E. Roberts, Degradation of Carbon Electrodes in the All-Vanadium Redox Flow Battery, ChemSusChem. (2021). [3] K.E. Rodby, T.J. Carney, Y. Ashraf Gandomi, J.L. Barton, R.M. Darling, F.R. Brushett, Assessing the levelized cost of vanadium redox flow batteries with capacity fade and rebalancing, J. Power Sources. 460 (2020) 227958. [4] M. Pahlevaninezhad, P. Leung, M. Pahlevani, F. C. Walsh, C. Ponce de Leon, and E. P. L. Roberts, Experimental and Computational Studies of Disperse Blue-1 in Organic Non-Aqueous Redox Flow Batteries, J. Power Sources, Volume 500, 15 July 2021, 229942. [5] X.Z. Yuan, C. Song, A. Platt, N. Zhao, H. Wang, H. Li, K. Fatih, D. Jang, A review of all-vanadium redox flow battery durability: Degradation mechanisms and mitigation strategies, Int. J. Energy Res. (2019). https://doi.org/10.1002/er.4607. [6] X. Li, H. Zhang, Zh. Mai, H. Zhang, I. Vankelecom, Ion exchange membranes for vanadium redox flow battery (VRB) applications, Energy Environ. Sci., 2011, 4, 1147. [7] L. Yu, F. Lin, L. Xua, J. Xi, A recast Nafion/graphene oxide composite membrane for advanced vanadium redox flow batteries, RSC Adv., 2016, 6, 3756. Figure 1

Redox flow batteries (RFBs) are a promising technology for grid scale stationary energy storage to complement renewable energy systems. Although RFBs have a relatively low energy density, they offer important benefits such as long lifetime, decoupled energy and power, high round-trip efficiency, scalability and design flexibility, fast response and low environmental impacts. These benefits make them superior to many other stationary energy storage technologies [1-3]. The vanadium RFB (VRFB) is the most widely used RFB in industry for grid scale energy storage and for integration of renewable energy generation systems [4]. However, due to their slow redox reaction rates, their performance and stability are limited and VRFBs would thus benefit from enhancement of the electrode kinetics [5]. Various catalysts have been employed to improve the redox reaction rates [5-6]. Bismuth is considered a suitable candidate due to its good reactivity with oxygen, low toxicity, relatively low cost and comparable catalytic properties to other metal competitors [5, 7-8]. In this study, we present a novel modified VRFB electrode composed of carbonized bismuth-polyaniline (Bi-PANI) on a thermally-treated carbon paper substrate. The battery performance was evaluated in a 5 cm2 flow cell using a ‘zero-gap’ design with a 1.6 M VOSO4 in 3 M H2SO4 electrolyte. Charge-discharge of the VRFB was performed at a constant current density (ranging from 10 to 80 mA cm−2) with upper and lower voltage cut-offs of 1.65 and 0.8 V, respectively. Thermally treated carbon paper electrodes were tested as a comparison, and it was found that the VRFB efficiency was significantly enhanced, from 51% to 68% at a current density of 80 mA cm− 2, due to the modification of the electrodes with Bi-PANI. The charge-discharge capacity was also improved by around 17.2%. In addition, the stability of the battery using the modified electrodes was evaluated for over 200 cycles. The improved battery performance was attributed to the catalytic effect of the Bi particles on the VO2+/VO2 + and V2+/V3+ redox reactions leading to a significant increase in capacity, voltage, and energy efficiency. References: [1] M. Skyllas-Kazacos, L. Cao, M. Kazacos, N. Kausar, A. Mousa, ChemSusChem. 9 (2016) 1521–1543. [2] A.K. Singh, M. Pahlevaninezhad, N. Yasri, E. Roberts, ChemSusChem. (2021). [3] M. Pahlevaninezhad, P. Leung, M. Pahlevani, F. C. Walsh, C. Ponce de Leon, and E. P. L. Roberts, Experimental and Computational Studies of Disperse Blue-1 in Organic Non-Aqueous Redox Flow Batteries, J. Power Sources, Volume 500, 15 July 2021, 229942. [4] X.Z. Yuan, C. Song, A. Platt, N. Zhao, H. Wang, H. Li, K. Fatih, D. Jang, Int. J. Energy Res. (2019). [5] S. Moon, B.W. Kwon, Y. Chung, Y. Kwon, Journal of The Electrochemical Society, 166 (12) A2602-A2609 (2019) [6] W. Lee, C. Jo, S. Youk, H. Y. Shin, J. Lee, Y. Chung, and Y. Kwon, Appl. Surf. Sci., 429, 187 (2018) [7] Z González, A. Sánchez, C. Blanco, M. Granda, R. Menéndez, and R. Santamaria, Electrochem. Commun., 13, 1379 (2011). [8] B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, and W. Wang, Nano Lett., 13, 1330 (2013).

A new digital control strategy is presented for a bridgeless single-stage multi-output AC/DC converter previously proposed as an LED grow light. The proposed control system can regulate the output current flowing through each individual LED string, perform power factor correction at the AC side, and provide zero-voltage-switching characteristics for all power semiconductors. Un-like the previous control strategy, the new method reduces conduction losses associated with transformer windings and power semiconductors by adaptively varying the DC bus voltage. Furthermore, the new control system can result in superior transient response. Experimental results of a 600 W prototype for supplying five LED strings are presented to verify the feasibility and performance of the proposed control system.

This paper presents a new bridgeless AC/DC converter for electric vehicle (EV) applications. This converter acts as the power factor correction (PFC) stage with boost capability for EV charging systems. The proposed circuitry offers soft-switching of the power switches for a wide range of operating conditions as well as the ripple attenuation of the input current. The attenuated input ripple allows significantly reduced sizes for the differential mode EMI filter. The soft-switching and the ripple attenuation are performed through a ripple steering technique that is implemented by modifying the input filter of the AC/DC converter. Simulation and experimental results verify the feasibility of the proposed converter and demonstrate its superior performance.

One of the main challenges in future micro-grids is the presence of transients and fluctuations inevitably imposed by nonlinear loads. Therefore, real time identification of transients and fluctuations of the grid is essential for the future micro-grids. This identification can be used in different applications of “grid-connected” and “island” micro-grid such as grid synchronization, harmonic current injection for islanded mode micro-grids, etc. This paper focuses on developing a method to detect and monitor the disturbances and fluctuations in the utility grid. A novel real-time harmonic estimation technique is presented, which is able to quickly and precisely estimate dc component, and synchronous and asynchronous harmonic contents of the grid voltage despite of their unknown nature. The proposed technique can be used in the control system of power converters to potentially enhance the reliability and resiliency of future micro-grids. As a case study, the performance of the proposed harmonic estimator is evaluated in grid synchronization of the power converters. Simulation and experimental results from the case study show the ability of the converter to inject a smooth sinusoidal current in presence of disturbance and fluctuations in the grid voltage. These results verify the fast dynamic and accuracy of the proposed harmonic estimation technique.

This paper presents a current sensorless technique for current-driven full-bridge dc/dc converters. The proposed technique is able to precisely estimate the transformer current and in turn input/output current of the converter. Since the high-frequency current is estimated, different current-based modulations schemes (e.g., self-sustained oscillating control (SSOC), modulators for synchronous rectifications, etc.) can be implemented using the proposed current sensorless technique. In the proposed technique, the current is estimated using the precise model of dc/dc converters instead of the averaged model. Thus, the accurate current waveform is derived within a switching cycle. The mathematical analysis of the system observability and the practical concerns related to the implementation of the proposed technique are also described in detail. Experimental results on a current-driven dc/dc converter are presented to show the feasibility of the proposed technique and verify its performance.

This paper presents an advanced current controller for grid-connected bidirectional ac/dc converters used for energy storage systems (ESSs). The proposed control scheme is designed to incorporate both the time-domain and frequency-domain dynamics to achieve superior transient and steady-state performance. The advanced current controller can overcome the various challenges faced by the conventional current controllers used in this application, which lead to sluggish transients and steady-state errors when tracking the sinusoidal reference for the grid current. Combining the time-domain dynamics with the frequency-domain dynamics creates a more intelligent controller compared to existing methods, which only consider the dynamics of one domain. The proposed controller is able to eliminate steady-state error by adaptively changing the controller coefficients in the frequency domain according to the current error. In the time domain, the control scheme minimizes the derivative of a defined energy function in order to optimize the transient performance. Simulation and experimental results obtained from a 3.3-kW grid-connected ac/dc converter demonstrate its superior performance.

Strong visible light absorption is essential to achieve high power conversion efficiency in indoor organic photovoltaics (iOPVs). Here, we report iOPVs that exhibit high efficiency with high voltage under excitation by low power indoor lighting. Inverted type organic photovoltaic devices with active layer blends utilizing the polymer donor PPDT2FBT paired with fullerene, perylene diimide, or ring-fused acceptors that are 6.5-9.1% efficient under 1 sun are demonstrated to reach efficiencies from 10 to 17% under an indoor light source. This performance transcends that of a standard silicon photovoltaic device. Moreover, we compared iOPVs with active layers both spin-cast and slot-die cast from nonhalogenated solvents and demonstrate comparable performance. This work opens a path towards high-efficiency iOPVs for low power electronics.

In this contribution we report on solution processed red OLEDs based upon a N-annulated perylene diimide dimer, namely tPDI2N-EH, a red-light emitting molecule. OLED devices with the architecture of glass/ITO/PEDOT:PSS/EML/LiF/Ag (EML = emitting layer) were fabricated with EMLs comprised of tPDI2N-EH neat and blended with poly (9,9-dicotylfluorene, PFO), all solution processed from non-halogenated solvents. The photophysical and electrophysical performance of PFO:tPDI2N-EH-blend films with different composition ratios were investigated. The PFO:tPDI2N-EH-based OLEDs with a 2:18 ratio exhibited best performance. The PFO:tPDI2N-EH-based OLEDs gave red electroluminescence with the emission wavelength of 635 nm and the CIE (international commission on illumination) coordinates of (x = 0.672, y = 0.321). OLEDs with EMLs fabricated using roll-to-roll compatible methods are also demonstrated.

Flexible red OLEDs based on a quadruple layer stack in-between electrodes with 160 mm2 active area were fabricated in ambient air on PET via slot-die coating. For the OLED structure PET/ITO/PEDOT:PSS/PVK/PFO:tPDI2N-EH/ZnO/Ag the ink formulations and coating parameters for each layer were systematically evaluated and optimized. The air-stable red-light emitting material tPDI2N-EH was successfully utilized as blended homogeneous film with PFO for the emitting layer. The use of an organic hole-transport layer (PVK) and inorganic electron injection layer (ZnO) significantly improved the brightness of the reference device from 4 cd/m2 to 303 cd/m2. Surface analysis using AFM measurements showed that PVK interlayer reduced the surface roughness of the hole injection layer (PEDT:PSS) from 0.45 nm to 0.17 nm, which improved the ability to form uniform emitting layers on top. In addition, the ZnO interlayer improved the average roughness of the device from 1.26 nm to 0.85 nm and reduced the turn-on voltage of the device from 5.0 V to 2.8 V.

This paper studies the performance of a wireless power and data transfer (WPDT) circuit for cochlear implants. Main features of the studied circuit include: 1) power transfer with high efficiency and low sensitivity to misalignment between coils, 2) simultaneous data transfer with high bandwidth, and 3) without the requirement of an extra DC-DC converter to control the output power. Having a controllable quality factor, this converter represents superior performance compared to conventional WPDT circuits. Unlike class E converters, this circuit employs a small input inductance, which results in better data transmission performance. Experimental results of a 1 MHz prototype are presented to verify its functionality.