Search

A generic red, green, and blue (RGB) LED system encompasses complex interactions of power, heat, light, and color, which pose a major challenge for achieving precise control over luminance and color-mixing in high-quality lighting applications. In this article, new nonlinear empirical models of a practical RGB LED system with closed-loop control are formulated. They enable precise prediction of luminous flux and color coordinates by using the three distinct reference voltages as the control variables for independent current regulation across the RGB LED strings. The proposed empirical models are experimentally verified by using a hardware prototype of a dc–dc single-inductor three-output LED driver with proportional–integral compensators and time-interleaving control scheme. The measured values of luminous flux and color coordinates agree closely with the predicted values from the models.

In this article, a single-stage wireless power receiver featuring continuous dc output current, good output regulation, and high conversion efficiency is presented. The topology is achieved via the integration of a diode rectifier circuit into a pair of interleaved buck converters, of which overlapped components are removed. With this, component count (diode's number) reduction is achieved without affecting the combined operation of rectification and voltage regulation. Moreover, its output inductor pair can be conveniently incorporated in integrated-magnetics form to reduce magnetic size. For control, it adopts an ac-input-current-synchronized modulation scheme, which hybridizes phase-shift modulation (PSM) and pulse-width modulation (PWM) control. The PSM enables consistently zero-voltage-switching turn- on of switches and zero-current switching turn- off of diodes for mitigating switching loss, while the PWM modulation performs good regulation of the output voltage of the rectifier. Experimental results of our constructed 100-kHz, 12-V output voltage, 35-W output power prototype show a fairly constant dc output current with 71% current ripple reduction as compared with that of a regular single-phase buck converter, good output regulation with less than 1% regulation error, and efficient ac–dc conversion with a peak efficiency of 96%.

The series-series compensation topology is widely adopted in many wireless power transfer applications. For such systems, their wireless power receiver part typically involves a DC-DC converter with front-stage full-bridge diode rectifier, to process the high-frequency transmitted AC power into a DC output voltage for the load. It is recently reported that the current source nature of the series-series compensation will introduce right-half-plane (RHP) zeros into the small-signal transfer functions of the DC-DC converter of the wireless power receiver, which will severely affect the stability and dynamic response of the system. To resolve this issue, in this paper, it is proposed to adopt a different rectifier configuration for the system such that the input current to the DC-DC converter becomes controllable to eliminate the presence of RHP zeros of the small-signal transfer functions of the system. This rectifier can be applied to different wireless power receivers using the buck, buck-boost, or boost converters. As compared with the original wireless power receivers, the modified ones feature minimum-phase characteristics and hence ease the design of compensator. Theoretical and experimental results are provided. The comparative experimental results verify the elimination of the RHP zero, improved dynamic responses of reference tracking and against load disturbances, and a larger stability margin., Comment: IEEE Transactions on Power Electronics, 2021

Emerging wearable electronics, wireless communication, and tissue engineering require the development of conductive fiber-shaped electrodes and biointerfaces. Ti3C2Tx MXene nanosheets serve as promising building block units for the construction of highly conductive fibers with integrated functionalities, yet a facile and scalable fabrication scheme is highly required. Herein, a cation-induced assembly process is developed for the scalable fabrication of conductive fibers with MXene sheaths and alginate cores (abbreviated as MXene@A). The fabrication scheme of MXene@A fibers includes the fast extrusion of alginate fibers followed by electrostatic assembly of MXene nanosheets, enabling high-speed fiber production. When multiple fabrication parameters are optimized, the MXene@A fibers exhibit a superior electrical conductivity of 1083 S cm-1, which can be integrated as Joule heaters into textiles for wearable thermal management. By triggering reversible de/hydration of alginate cores upon heating, the MXene@A fibers can be repeatedly contracted and generate large contraction stress that is >40 times higher than the ones of mammalian skeletal muscle. Furthermore, the MXene@A springs demonstrate large contraction strains up to 65.5% and are then fabricated into a reconfigurable dipole antenna to wirelessly monitor the surrounding heat sources. In the end, with the biocompatibility of MXene nanosheets, the MXene@A fibers enable the guidance of neural stem/progenitor cells differentiation and the promotion of neurite outgrowth. With a cation-induced assembly process, our multifunctional MXene@A fibers exhibit high scalability for future manufacturing and hold the prospect to inspire other applications.

A single-switch bidirectional wireless power transceiver aiming at cost-effective and reliable peer-to-peer charging applications is proposed. The transceiver comprises a single-switch resonant power circuit, a frequency synchronization circuit, and a microcontroller. It can operate in either transmitter mode or receiver mode. As a transceiver, the required number of semiconductor devices is minimized, i.e., only single active switch is used. This makes it easy to implement and is relatively reliable and cost-effective. The bidirectional power flow and dc output regulation are achieved solely by adjusting the phase shift ratio of the control signal. To make the phase shift power control feasible and to secure wide operating range ZVS operation, a holistic design method is provided such that the ac voltage waveforms remain relatively constant and independent of the coupling and the phase shift ratio changes. The operating principles, steady-state and dynamic models, and design considerations are discussed. Simulation and experiments are performed on a prototype based on the design. The results validate the features of relatively constant ac voltage waveforms of the transceiver, the effectiveness of the time-domain model, the ZVS turn on and turn off operations over wide operating power range, phase shift regulated transmission power control, bidirectional power flow, and accurate output regulation.

Summary Physical unclonable function (PUF) is a cornerstone of anticounterfeiting. However, conventional PUF key-based secure tags encounter several bottlenecks, such as complicated manufacturing, specialized and tedious readout, long authentication time, and insufficient stability. Here, we utilize various two-dimensional materials (2DMs), including Ti3C2Tx MXene and graphene oxide, to construct multigenerational microstructures as PUF patterns. Two intermediate treatments, cation intercalation and moisture-induced lubrication, are introduced in between sequential contractions to engineer the multiscale patterns in a transfer-free and scalable fashion. A deep learning (DL)-facilitated software is developed to pre-categorize the hierarchical topographies with classifiable features. Thereafter, the search-and-compare is conducted within a smaller database to shorten the overall authentication time. The synergy between 2DM tags and DL-facilitated software enables a reliable and environmentally stable anticounterfeiting technology, DeepKey, showing superior encoding capacity (>10144,494) and short authentication time (∼3.5 min). Our 2DM anticounterfeiting tag is finally integrated with QR codes to provide two-layer information security.

Emerging soft exoskeletons pose urgent needs for high-performance strain sensors with tunable linear working windows to achieve a high-precision control loop. Still, the state-of-the-art strain sensors require further advances to simultaneously satisfy multiple sensing parameters, including high sensitivity, reliable linearity, and tunable strain ranges. Besides, a wireless sensing system is highly desired to enable facile monitoring of soft exoskeleton in real time, but is rarely investigated. Herein, wireless Ti3C2Tx MXene strain sensing systems were fabricated by developing hierarchical morphologies on piezoresistive layers and incorporating regulatory resistors into circuit designs as well as integrating the sensing circuit with near-field communication (NFC) technology. The wireless MXene sensor system can simultaneously achieve an ultrahigh sensitivity (gauge factor ≥ 14,000) and reliable linearity (R2 ≈ 0.99) within multiple user-designated high-strain working windows (130% to ≥900%). Additionally, the wireless sensing system can collectively monitor the multisegment exoskeleton actuations through a single database channel, largely reducing the data processing loading. We finally integrate the wireless, battery-free MXene e-skin with various soft exoskeletons to monitor the complex actuations that assist hand/leg rehabilitation.

Stretchable color-changing fibers are urgently demanded for smart textiles/clothing due to their perfect implantability, permeability of vapor and heat, and flexibility/ stretchability. Herein, stretchable electrothermochromic fibers were fabricated with unconventional stretchable conductive fibers as core layers and thermochromic coatings as shell layers. In the stretchable conductive fibers, hierarchical porous structures with percolative one-dimensional (1D) conductive networks were constructed through phase inversion of carbon nanotube/polyurethane (CNT/PU) solutions. With the deposition of silver nanoparticles (AgNPs) on the surface of micro-pores, electrically conductive dual-pathways consisting of 0D AgNPs and 1D CNTs were formed to significantly enhance the electric conductivity and thus improve the electrothermal performance of the fibers. More importantly, because of the connective CNTs and AgNPs, such dual-pathways ensured the electron transport under the stretching state, preventing the sharp decay of conductivity and electrothermal performance. Through the continuous wet-spinning method, the stretchable conductive fibers can be easily obtained with the length up to several meters. At last, stretchable electrothermochromic fibers were prepared with two color-changing modes and implanted into textile perfectly, advancing their applications in wearable display and military adaptive camouflage of smart clothing.

Mismatched deformation in a bilayer composite with rigid coating on a soft substrate results in complex and uniform topographic patterns, yet it remains challenging to heterogeneously pattern the upper coatings with various localized structures. Herein, a heterogeneous, 3D microstructure composed of Ti3C2Tx titanium carbide (MXene) and single-walled carbon nanotubes (SWNTs) was fabricated using a one-step deformation of a thermally responsive substrate with designed open holes. The mechanically deformed SWNT-MXene (s-MXene) structure was next transferred onto an elastomeric substrate, and the resulting s-MXene/elastomer bilayer device exhibited three localized surface patterns, including isotropic crumples, periodic wrinkles, and large papillae-like microstructures. By adjusting the number and pattern, the s-MXene papillae arrays exhibited superhydrophobicity (>170°), strong and tunable adhesive force (52.3-110.6 μN), and ultra-large liquid capacity (up to 35 μL) for programmable microdroplet manipulation. The electrically conductive nature of s-MXene further enabled proper thermal management on microdroplets via Joule heating for miniaturized antibacterial tests. The s-MXene papillae were further fabricated in a piezoresistive pressure sensor with high sensitivity (11.47 kPa-1). The output current changes of s-MXene sensors were highly sensitive to voice vibrations and responded identically with prerecorded profiles, promising their application in accurate voice acquisition and recognition.

Stretchable skin-like pressure sensing with minimized and distinguishable strain-induced interference is essential for the development of collision-aware surgical robotics to improve the safety and efficiency of minimally invasive surgery in a confined space. Inspired by the multidimensional wrinkles of Shar-Pei dog's skin for tactile sensing, we developed a stretchable pressure sensor consisting of reduced graphene oxide (rGO) electrodes with biomimetic topographies to improve the robot-tissue collision detections. A facile fabrication route for stretchable rGO electrodes was first demonstrated by harnessing the surface instability during the sequential deformation processes. The wrinkle-crumple rGO electrodes exhibited high stretchability (∼100%) and strain-insensitive resistance profiles [a gauge factor (GF) < 0.05], which were next utilized to fabricate piezoresistive pressure sensors. The rGO pressure sensors were highly stretchable and exhibited high sensitivity under uniaxial strains (1.37, 1.30, and 0.98 kPa-1 at 0, 30, and 50% stretching states, respectively) along with distinguishable and reduced stretching responsiveness (a small GF ∼0.2 under 40% strains). The stretchable pressure sensors were next integrated with two surgical robots for the transoral robotic surgery procedure. During the cadaveric testing, the rGO sensors can detect the robot-tissue contacts under joint stretches in real time to enhance the surgeon's awareness for collision avoidance. The stretchable rGO pressure sensor that is highly sensitive under large strains provides great potential in the fields of wearable sensing and collision-aware humanoid robots to improve the human-machine interactions.

In this paper, a highly-efficient single-switch-regulated resonant wireless power receiver with hybrid modulation is proposed. To achieve both high efficiency and good output voltage regulation, phase shift and pulse width hybrid modulation are simultaneously applied. The soft switching operation in this topology is achieved by the cycle-by-cycle phase shift adjustment between the input current and the gate drive signal and also attributed to the reactive components such as the series-compensated secondary coil and the parasitic capacitor of the active switch . The soft switching operation also leads to high efficiency and low EMI. By adjusting the duty ratio of the switch, tight regulation of the output voltage can be attained. The steady-state and dynamic models of the resonant receiver with hybrid modulation are analytically derived in order to properly design the feedback controller. An experimental setup of a two-coil wireless power transfer system, including the hardware prototype of the proposed receiver, is constructed for experimental verification. The experimental results show the effectiveness of the soft-switching operation in the receiver with high efficiency while maintaining good regulation of the output voltage, regardless of line and load variations., in IEEE Journal of Emerging and Selected Topics in Power Electronics. 2020

This paper presents a very-high-voltage-gain DC-DC converter based on a so-called resonant inductive boost technique. In addition to the turn’s ratio n of the transformer, the adopted resonant inductive-boosting technique leverages on the resonance of the inductance (leakage and mutual inductances) of the air core (loosely coupled) transformer used in the converter to achieve a very high voltage gain (>n times). Moreover, the inductive nature of the transformer’s current allows the natural occurrence of ZVS operation of this single-switch converter. The operating principles and design considerations are discussed. A prototype based on this design is built for verification. Experimental results validated the key features of the converter in concurrently achieving a very high voltage gain (87.9 times the input voltage), ZVS operation, low voltage stress, and continuous input current.

Two-stage wireless power receivers, which typically include an ac–dc diode rectifier and a dc–dc regulator, are popular solutions in low-power wireless power transfer applications. However, the interaction between the rectifier and the regulator may introduce beat frequency oscillation on both the dc-link and output capacitors. In this article, the cause of the beat frequency oscillation and its related issues are investigated with the corresponding design solution on alleviating the oscillation discussed. Theoretical and experimental results verifying the presence of beat frequency oscillation in the two-stage wireless receiver system are provided. Our study shows that the beat frequency oscillation can be significantly alleviated if appropriate design solutions are applied.

Recently, pressure/strain sensor based on triboelectric nanogenerator (TENG) has gained great attentions for monitoring daily health status and robotic research fields, because of their simple device structures and self-powered feature. However, higher sensitivity and stretchability are still demanded for satisfying the practical applications. In this work, a self-powered pressure and strain sensor was achieved by utilizing crumpled MXene film as the single-electrode mode TENG. Benefiting from the reconfigurable behavior of the crumpled structure, the MXene TENG showed a maximum areal strain and linear tensile ratio of 2150% and 400%, respectively. Meanwhile, because of the enlarged contact area between triboelectric layers, the output power density of the MXene TENG with micro-crumples was highly improved by 36 times. Therefore, the as prepared sensor exhibited excellent sensitivity of 2.35 V kPa−1 under pressures from 0.3 to 1.0 kPa, which is superior to majority of the reported sensors based on tribo-/piezo- electricity. In addition, the sensor can be easily attached to human joints to capture and collect the complicated movement signals. By combining with Bluetooth transmission technology, wireless real-time monitoring was realized through transmitting human movement signals to a mobile phone App.

A single-switch-regulated wireless power transfer receiver is presented in this letter. Aiming at low-cost applications, the system involves only a single-switch class-E resonant rectifier, a frequency synchronization circuit, and a microcontroller. The number of power semiconductor devices required in this circuit is minimal. Only one active switch is used and no diode is required. As a single-switch solution, this simplifies circuit implementation, improves reliability, and lowers the hardware cost. The single-switch resonant rectifier provides a relatively constant quasi-sinusoidal voltage waveform to pick up the wireless power from the receiver coil. Due to the resonant nature of the rectifier, zero-voltage-switching (ZVS) turn on and turn off are achieved. The steady-state analysis and discussions on the component sizing and the control design are provided. A prototype is built and experimental works are performed to verify the features: achieving 93% efficiency single-switch ac–dc rectification (85% including the auxiliary circuit), −7.17-dB total-harmonic-distortion ac voltage waveform, ZVS turn on and turn off over wide load range, 0.4% output voltage regulation error, 79% cost reduction as compared with the Qi- compliant receivers, 2.5% overshoot/undershoot after load disturbances, and 1% overshoot after line disturbance.

The device assembly plays an important role in affecting the electrochromic (EC) performance of an electrochromic device (ECD). Here, WO 3 ·0.33H 2 O films are fabricated by a hydrothermal method and then PEDOT:PSS are spin-coated on the surface of WO 3 ·0.33H 2 O films. Finally, the WO 3 ·0.33H 2 O/PEDOT films are assembled with electrodeposited prussian blue (PB) to fabricate the WO 3 ·0.33H 2 O/PEDOT-PB complementary electrochromic devices (ECDs). Compared with pure WO 3 ·0.33H 2 O and WO 3 ·0.33H 2 O/PEDOT single-active-layer structure ECDs, the complementary ECD exhibits higher optical modulation, higher coloration efficiency and faster response time, which would provide a promising platform for energy-saving smart (ESS) window.

A very simple geometric structure whose branches can be filled by inductors, capacitors, diodes, short-circuits, or open-circuits is proposed. It serves for generating large dc gain-purposed switching cells by making different choices of the type of component on each branch. The switching cells are integrated in basic converters. It is shown that almost all the high dc gain nonisolated converters based on switched-capacitor-inductor cells proposed in the last years, regardless of their complexity, can be derived through this method. From the same geometric structure, new high dc gain boosting converters can be derived in a systematic manner. The available and the new converters in each class as defined by the number of reactive components are compared in terms of their performance: dc gain, semiconductor elements count, voltage and current stress on transistors and diodes, character of the input current, easiness of the transistor driving, and easiness of the control as determined by common/uncommon line-load ground, power stage efficiency. This comparison allows us to choose the optimal solution for each specific application in conjunction with the green sources of energy, multisource microgrids, electric vehicles, data and communications systems, and so on. The geometric structure is generalized in different ways, allowing for the development of ultrahigh dc gain converters. One of the proposed generalized ultrahigh dc gain converters is fully analyzed and built in the laboratory, with the experimental results verifying the theoretical analysis.

A stretchable and multicolor electrothermal chromatic fiber is prepared based on reduced graphene oxide (RGO) functionalized elastic conductive fibers and various thermochromic materials. The colors of the fibers can be switched within 15s due to the good resistive-heating performance of the conductive fibers. Through a combination of different thermochromic materials, abundant and reversible color changes are clearly observed by the naked eye (e.g., from orange, red, green to yellow, purple, blue and white, respectively). Moreover, the fibers exhibit excellent color changing stability even after 1000 resistive-heating or stretching/releasing cycles owing to the structural stability of the multilayered fibers and the excellent electrothermal stability of RGO. Finally, they are easily woven into textiles and plaited into colorful hand chains, which showed huge application value especially for stretchable visual sensors and clothing integrated wearable displays.

A simple graph with four nodes and eleven branches is defined. Its branches are filled in different ways with passive elements (capacitors, inductors, diodes) or replaced by shortcircuits in order to get potential voltage step-up switching cells. These cells are inserted in boost converter, obtaining thus non-isolated power electronics circuits with a very high dc gain. Such circuits are necessary today in the green energy systems. The proposed circuits feature a lower voltage stress on its semiconductors (both switch and diodes) than that on the equivalent devices of a boost stage. A state-space-based dc and ac analysis allows for deriving the dc gain, the switches voltage and current stresses, and the frequency characteristics of the obtained converters. The steady-state analysis is performed for both the continuous and discontinuous conduction mode operations. The converters belonging to the new family are compared between them and then compared with available solutions of similar complexity as defined by the component count. Simulation and experimental results confirm the theoretical equations.

In this paper, the analysis and design of an active class-E resonant regulated wireless power transfer (WPT) receiver with phase-shift controlled output regulation is presented. This WPT receiver uses only one power semiconductor device. The output regulation is achieved via the control of the phase difference between the rectifier's input current and input voltage. To facilitate the phase-shift control, the rectifier is designed to have a relatively constant AC input voltage waveform, which is independent of changes of phase difference and operating load. This design also enables a wide- load-range soft-switching operation. A prototype of the WPT system, including a full-bridge transmitter, WPT coils with series-to-series compensation, and the active class-E resonant regulated receiver, is constructed for verification. Experimental results validated the effectiveness of the class-E resonant regulated receiver in achieving AC-DC rectification and good output regulation against the line and load variations.

Conventional resonant DC−DC converters are typically limited to a narrow range of operating input voltage. In this paper, a multimode high-frequency LLC resonant DC−DC converter designed to operate with a wide range of input voltage, is proposed. The converter has three operating modes. It can provide a variable and wide voltage gain conversion via mode switching. Besides, this converter can attain a constant switching frequency operation, as well as ZVS operation for its switches and ZCS operation for its rectifier diodes. A 200 W prototype is constructed. Experiments are conducted to verify its features. Results show that the converter is functional over a wide range of input voltage (25 V-200 V) to provide a fixed output voltage of 200 V, while maintaining the ZVS and ZCS operations and high-efficiency power conversion.

The tight integration of actuation, sensing, and communication capabilities into origami robots enables the development of new-generation functional robots. However, this task is challenging because the conventional materials (e.g., papers and plastics) for building origami robots lack design opportunities for incorporating add-on functionalities. Installing external electronics requires high system integration and inevitably increases the robotic weight. Here, a graphene oxide (GO)-enabled templating synthesis was developed to produce reconfigurable, compliant, multifunctional metallic backbones for the fabrication of origami robots with built-in strain sensing and wireless communication capabilities. The GO-enabled templating synthesis realized the production of complex noble metal origamis (such as Pt) with high structural replication of their paper templates. The reproduced Pt origami structures were further stabilized with thin elastomer, and the Pt-elastomer origamis were reconfigurable and served as the multifunctional backbones for building origami robots. Compared with traditional paper and plastic materials, the reconfigurable Pt backbones were more deformable, fire retardant, and power efficient. In addition, the robots with conductive Pt-elastomer backbones (Pt robots) demonstrated distinct capabilities-such as on-demand resistive heating, strain sensing, and built-in antennas-without the need for external electronics. The multifunctionality of Pt robots was further demonstrated to extend beyond the capabilities of traditional paper-based robots, such as melting an ice cube to escape, monitoring/recording robotic motions in real time, and wireless communications between robots. The development of multifunctional metallic backbones that couple actuation, sensing, and communication enriches the material library for the fabrication of soft robotics toward high functional integration.

In this paper, a single-switch DC-shifted harmonics-boosted resonant DC-DC converter topology that can achieve a high-step-up conversion ratio is proposed. In addition to the fundamental resonant component, this converter utilizes the high-order harmonic components and DC component to further increase the actual achievable voltage gain of the resonant converter. The operating principle and design of the proposed converter are presented. It is illustrated that with proper design, the proposed converter can attain a fairly constant conversion ratio (around 12.8% variance) and can maintain zero voltage switching (ZVS) operation for load ranging from no load to full load. A 500 kHz, 35 V input, 380 V output at 280 W prototype is constructed and tested. Experimental results are provided to illustrate the various properties of the proposed converter: low voltage stress, high dc voltage gain, soft switching operation, continuous input current, and line-load common ground.

Hydrogels possess exceptional physical and chemical properties that render them appealing components for soft actuators, wearable technologies, healthcare devices, and human interactive robots. Especially, the stimuli-responsive hydrogels can sense and perform smart functions in the presence of various stimuli that collectively contribute to the intelligence of the soft machine systems. Furthermore, facile modification of hydrogels with other functional groups/additives/nanofillers substantially expands their functionalities and further broadens the scope of their application. Designing suitable hydrogels with adequate capabilities and engineering effective configurations are of supreme importance for the development of advanced hydrogel-based soft machines. Herein, this review summarizes recent advances of stimuli-responsive hydrogels in multifunctional soft machines, such as robotics, actuators, and sensors. Functions including multistimuli responsiveness, self-healing, and high biocompatibility can be endowed to the soft machines through designing advanced hydrogel materials, which would not be possible with an approach based on conventional elastic materials (e.g. rubbers, elastomers). To close, future opportunities and challenges this field faces are emphasized and discussed for the development of exciting new hydrogel-based devices in real-world conditions.

Materials with synchronous capabilities of color change and actuation have prospects for application in biomimetic dual-stealth camouflage and artificial intelligence. However, color/shape dual-responsive devices involve stimuli that are difficult to control such as gas, light or magnetism, and the devices show poor coordination. Here, a flexible composite film with electrochromic/actuating (238° bending angle) dual-responsive phenomena, excellent reversibility, high synchronization, and fast response speed (< 5 s) utilizes a single active component, W18O49 nanowires. From in situ synchrotron X-ray diffraction, first principles calculations/numerical simulations, and a series of control experiments, the actuating mechanism for macroscopic deformation is elucidated as pseudocapacitance-based reversible lattice contraction/recovery of W18O49 nanowires (i.e. nanostructure change at the atomic level) during lithium ion intercalation/de-intercalation. In addition, we demonstrate the W18O49 nanowires in a solid-state ionic polymer-metal composite actuator that operates stably in air with a significant pseudocapacitive actuation., Materials that exhibit synchronous color change and actuation may benefit biomimetic camouflage, but stimuli can be difficult to control. Here the authors report a composite with electricity-driven electrochromic and actuating capabilities for use in a solid-state ionic polymer-metal composite actuator.

By applying two diode-capacitor voltage multipliers (VMs) to the conventional coupled-inductor boost converter, a novel non-isolated DC-DC converter is obtained, which is suitable for renewable generation systems. The proposed converter has the following features: a large DC conversion ratio with moderate duty cycle, recycling leakage inductance energy by a VM and clamping low voltage on the switch, and thus using low voltage rating switch with low on-resistance to minimize conduction losses. The derivation of the proposed converter as well as the DC steady-state analysis including calculations of the DC gain, voltages stress and conduction losses are presented in detail. A comparison with available converters of similar structures demonstrates the superiorities of the proposed converter. A converter prototype with a 25 V input, 400 V output, 16 times of the voltage step-up gain at the nominal duty cycle 0.5 is designed and built up. Experimental results are in accordance with simulations. The converter achieves 94.1% power conversion efficiency at the nominal output of 200W.

A transformerless single-phase symmetric Z-source HERIC inverter featuring low leakage currents is presented in this paper. It is an attempt to utilize the Highly Efficient and Reliable Inverter Concept (HERIC) and an impedance source (Z-source) network to maintain a constant common mode voltage and thus low leakage currents in PV applications. The symmetric Z-source HERIC inverter requires two extra active switches. Nevertheless, the operation frequency of the two switches is the line frequency, leading to negligible losses. More importantly, the performance in terms of low leakage currents and harmonics is improved. Experimental tests are performed to validate the analysis and performance of the proposed system.

This paper presents a family of cost-effective magnetically-coupled impedance source inverters for renewable energy systems. The inverters are derived from magnetically-coupled impedance source networks, featuring low cost and no ground leakage current when used in PV system. The numbers of required semi-conductor switches is reduced. More important, the elimination of leakage currents makes it particularly suitable for high-efficiency photovoltaic (PV) applications. A comparison among prior-art PV inverters is then performed. The Performances of the inverters are evaluated analytically as well as by simulations. The analysis and simulation show the superiority of the proposed inverter in terms of leakage current suppression and low cost.

A high step-up switched-capacitor based converter is proposed in this paper. The proposed converter features high conversion ratio, low voltage stress and continuous input current, which makes it very suitable for renewable energy applications like photovoltaic systems. More importantly, the proposed switched-capacitor cells in series with converter can be generalized in two ways, resulting in dc-dc converters of ultra-high dc conversion ratios. Theoretical analysis, simulation and experimental tests have demonstrated the superior performance of the proposed converter in terms of high dc voltage gain, low voltage stress on the switches, continuous input current, and relatively high efficiency.

These fibers are prepared using stainless steel wires (SSWs) as a substrate. Three kinds of electrochromic materials (poly(3,4-ethylenedioxythiophene), poly(3-methylthiophene), and poly(2,5-dimethoxyaniline)) are quickly deposited on the surface of the SSWs by electrochemical polymerization. A polymer gel electrolyte is then coated onto the electrochromic layer, and another finer stainless steel wire is twisted on, in succession. The obvious RGB colors and gradient color phenomenon from gray to dark blue are observed by the naked eye besides color changes from oxidized to reduced states. Moreover, these electrochromic fibers have very short response times (millisecond scale), excellent flexibility, and good structural stability even though the bending and folding occurred. They also can be implanted into fabrics to achieve more color combinations through regulating the voltages and parallel connection of different circuits.

This paper presents a new soft-switched, current-driven full-bridge converter. A simple snubber is used in order to get ZVS for all the main switches. The soft-switching realization is independent of the load. The snubber is placed in parallel with the bridge. All the resonant circuit energy is recycled by the load in each half cycle. No additional current stresses appear on the main switches. A design-oriented steady-state analysis leads to the expressions of the dc voltage conversion ratio and ZVS analytical conditions, allowing for a trade-off design of the resonant inductor. A prototype has been built with a high energy transfer efficiency. The simulation and experiment results confirm the detailed theoretical analysis.

By inserting a simple cell formed by a capacitor and diode into quadratic boost structures, new converters are obtained. They feature: a larger dc gain compared with that of quadratic boost converters and a smaller voltage stress on the switch and output diode, non-pulsating input current, as required for the use in conjunction with the environmental-friendly energy cells, easiness of the transistor driving, line-to-load common ground. The proposed cell can be easily generalized for enhancing the dc gain. The new converters compare favorably with available ones with the same reactive elements count. Simulations and experimental results confirm the theoretical analysis of the proposed converter.

A mixed switched-capacitor cell is proposed by integrating a voltage divider with a voltage multiplier. It is inserted in a boost stage for achieving a converter with high conversion ratio, low voltage stress on switches, non-pulsating input current as required as front-end to electrical grids supplied by renewable energy sources. The generalization of the proposed cell allows to achieve an ultra-high dc conversion ratio. Analysis and experimental data show the superiority of the proposed converter over other hybrid converters with similar complexity: higher dc voltage gain and less voltage stress on the switches.

In this paper, the parallel-connected three-phase voltage source inverter system is modeled and a state space model is obtained. A control algorithm based on finite control set model predictive control (FS-MPC) is proposed. It is applied to the distributed generation (DG) inverters that are able to provide high power quality, load current sharing and plug-n-play operation in microgrids. In this algorithm, the control objectives (voltage tracking and current sharing) are integrated into a weighted cost function. To reduce the computational burden, an alternate calculation scheme is adopted. Analysis and testing results verify the effectiveness and show the advantages of the proposed algorithm.

A step-up DC-DC converter is proposed by inserting a new switched-capacitor cell in a modified PWM boost circuit. The obtained hybrid PWM non-isolated converter is able to provide a large DC gain, as necessary for serving as front-end to electrical grids supplied by solar or fuel cells. It features low voltage stress on the switches compared with traditional boost converter, allowing for the use of low-voltage rated components, with smaller nominal parasitic on-resistances. Analysis, simulation and experimental data show the superiority of the proposed converter over other hybrid converters in a trade-off of complexity, components count, voltage ratio and voltage stress on the switches.

Existing control techniques of parallel-connected inverters are often complicated with multiple voltage and current loops. A large amount of tuning effort is required to ensure system stability, and the power quality is usually deteriorated due to voltage deviations. This paper proposes a new control method for parallel-connected three-phase voltage source inverters using model predictive control (MPC). High-quality voltages for local loads can be obtained. In addition, each inverter can adjust the output current to achieve proper load sharing according to the power ratings of distributed generation (DG) sources. Hot-swap capability is also achieved to facilitate the connection or disconnection operations to the common AC bus. Started with State-Space function which includes time-consuming matrix calculation can be done in PC. Thus, control gains are found and MPC can be achieved based on a digital signal processor (DSP). The proposed method is simple without complex coordinate transformation or proportional-integral (PI) regulators. The effectiveness of the proposed control strategy are verified by the test results under various scenarios, presenting promising applications in microgrids.

The rapid development of wearable electronics in recent years has brought increasing energy consumption, making it an urgent need to focus on personal energy harvesting, storage and management. Herein, a textile-based personal energy management device with multilayer-coating structure was fabricated by encapsulating commercial nylon cloth coated with silver nanowires into polydimethylsiloxane using continuous and facile dip-coating method. This multilayer-coating structure can not only harvest mechanical energy from human body motion to power wearable electronics but also save energy by keeping people warm without losing heat to surroundings and wasting energy to heat empty space and inanimate objects. Fluoroalkylsilanes (FAS) were grafted onto the surface of the film through one single dip-coating process to improve its energy harvesting performance, which has hardly adverse effect to heat insulation and Joule heating property. In the presence of FAS modification, the prepared film harvested mechanical energy to reach a maximum output power density of 2.8 W/m(2), charged commercial capacitors and lighted LEDs, showing its potential in powering wearable electronics. Furthermore, the film provided 8% more thermal insulation than normal cloth at 37 °C and efficiently heated to 40 °C within 4 min when applied the voltage of only 1.5 V due to Joule heating effect. The high flexibility and stability of the film ensures its wide and promising application in the wearable field.

Three diode-capacitor-inductor networks which can be operated for stepping-up the input voltage are proposed. These networks differ one from the other by the number and position of their components. By inserting these networks into a general converter structure, three novel large DC gain non-isolated converters are generated. The single MOSFET switch in each of these converters is referenced to the ground, rendering the drive circuit relatively simple. The smaller size of capacitors in these converters can decrease the size of the overall converter, resulting in a higher power density. These converters can achieve considerably large DC voltage conversion ratios, what is necessary in many high step-up applications like those in conjunction with the environmental friendly sources of energy.

A new step-up basic switching cell formed by four passive elements and two diodes is proposed. It is inserted in a boost converter in order to obtain a new hybrid PWM non-isolated converter able to provide a large DC gain, as required as front-end to electrical grids supplied by solar or fuel cells. A family of converters can be created by inserting the defined switching structure in any step-up converter. Analysis, simulation and experimental data show the superiority of the proposed converter over other hybrid converters with similar complexity and the same voltage ratio: less voltage stresses on the switches.

A classical step-down switched-capacitor cell is transformed into a step-up cell. By inserting it in a boost converter, a single-switch, low voltage stress, non-pulsating input current, large dc gain hybrid converter is proposed. The theoretical, simulation and experimental results prove the merits of the simple new solution in comparison with the available ones.

Electrochemical capacitor systems based on Al ions can offer the possibilities of low cost and high safety, together with a three-electron redox-mechanism-based high capacity, and thus are expected to provide a feasible solution to meet ever-increasing energy demands. Here, highly efficient Al-ion intercalation into W18O49 nanowires (W18O49NWs) with wide lattice spacing and layered single-crystal structure for electrochemical storage is demonstrated. Moreover, a freestanding composite film with a hierarchical porous structure is prepared through vacuum-assisted filtration of a mixed dispersion containing W18O49NWs and single-walled carbon nanotubes. The as-prepared composite electrode exhibits extremely high areal capacitances of 1.11–2.92 F cm−2 and 459 F cm−3 at 2 mA cm−2, enhanced electrochemical stability in the Al3+ electrolyte, as well as excellent mechanical properties. An Al-ion-based, flexible, asymmetric electrochemical capacitor is assembled that displays a high volumetric energy density of 19.0 mWh cm−3 at a high power density of 295 mW cm−3. Finally, the Al-ion-based asymmetric supercapacitor is used as the power source for poly(3-hexylthiophene)-based electrochromic devices, demonstrating their promising capability in flexible electronic devices.

In this paper, we propose a coarse-to-fine approach to discovery motion patterns. There are two phases in the proposed approach. In the first phase, the proposed median-based GMM achieves coarse clustering. Moreover, the number of clusters can be heuristically found by the proposed algorithm. In the second phase, to refine coarse clustering in the first phase, a Fisher optimal division method is proposed to examine the boundary data points and to detect the change point between motion patterns. The experimental results show that the proposed approach outperforms the existing algorithms.