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The feedforward schemes of the voltage at point of common coupling (PCC) have been widely used in grid-connected inverters to reject the current harmonics caused by the grid voltage distortion. However, in weak grid, the PCC-voltage feedforward tends to destabilize the grid-connected inverters due to the effect of time delay. In this article, this stability issue is explicitly elaborated by the impedance-based stability criterion and then addressed with an improved feedforward scheme, which uses the grid voltage instead of the PCC voltage as the feedforward variable. Considering that it is hard to sense the real grid voltage directly, a method to extract the grid voltage from the sensed PCC voltage is put forward to implement the proposed feedforward scheme. By carefully arranging the sampling instants according to the duty cycle, a dual sampling mode is adopted to ensure an accurate extraction of the grid voltage. Finally, simulations and experiments are performed on a 6-kW single-phase grid-connected inverter, which confirm that the proposed grid-voltage feedforward achieves superior harmonic rejection ability and strong stability under weak grid condition.

Abnormal expression levels of peroxynitrite anion (ONOO−) in human cells have relation to many diseases, especially cancer. Here, we constructed a novel sensing platform for directly detecting ONOO− using hyper-cross-linked polymeric nanotubes (HNTs)–modified glassy carbon electrode. The HNTs nanohybrids were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), FT-IR spectroscopy, and cyclic voltammetry (CV). The prepared HNTs/GCE sensor exhibited outstanding performance in detecting ONOO−, which provided a wide linear range from 2.34 × 10−8 M to 1.74 × 10−4 M and a low detection limit of 7.43 nM (S/N = 3). Moreover, it was also used to measure the ONOO− released from HeLa cells induced by stimulus. The designed sensor may provide great potential for expand applications in the matter of cancer treatment and biomedicine.

The prosperity of market in multi‐charging devices has made the researches on multi‐load magnetically coupled resonant (MCR) wireless power transfer (WPT) technique be an urgent issue nowadays. For the sake of load recognition and controllable power distribution, the concept of multi‐frequency excitation was introduced into multi‐load MCR WPT systems. However, the transferred power components at different frequencies inevitably suffer the cross interference at receivers, which negatively affects the accuracy of load recognition and power distribution. To suppress the cross interference, a methodology by using the metamaterial composed of a printed circuit board (PCB) spiral inductor and a lumped capacitor was proposed. The concept of equivalent mutual inductance (Meq) was presented to quantitatively describe the influence of metamaterials on the couplings between the transmitting (Tx) and receiving (Rx) coils. By magnetic field simulation, a series of Meq curves versus operating frequency under different metamaterial parameters were plotted and an optimal design was adopted to suppress the power components at non‐targeted frequencies. Moreover, a detailed circuit model was built to characterize the output power of multiple loads after introducing the metamaterial. Finally, the experiments from a prototype was carried out and the experimental results verified the effectiveness of proposed suppression methodology.

With urgent market demand for multiload electronic applications, multiload magnetically coupled resonant (MCR) wireless power transfer (WPT) system has caused widespread concern. In the practical applications, multiload MCR WPT system should have the capability to realize targeted power distribution among loads and stable output power against misalignment of load. To achieve this goal, a multiphase multifrequency system with multiple loads is proposed in this article, where multi-phase structure of transmitting coils can enhance the misalignment tolerance, and multiple operating frequencies are beneficial to achieve multiload identification and targeted power distribution. For simplicity, this article mainly studies a two-phase dual-frequency system with two loads and proposes two phase-shifted control strategies. The equivalent circuit model of the system is established, and the output power in the open-loop system under two phase-shifted control methodologies are analyzed. According to that, the targeted power distribution strategy by adjusting the resonant frequency of the transmitter is implemented. Moreover, the closed-loop control schemes based on phase-shifted control methodologies are adopted to realize stable output power precisely against the misalignment of loads. Finally, a prototype of two-phase dual-frequency MCR WPT system with two loads is built in the laboratory. The experimental results prove the correctness of the theoretical analysis.

Excessive uptake of nitrite will damage the human health. Hence, there is a rising requirement to construction a highly sensitive electrochemical sensor for detecting the level of nitrite in food precisely. In this work, an electrochemical nitrite sensor was successfully constructed with the porous hollow carbon nanoparticles as the electrode material. The morphology and structure of the synthesized material were characterized by scanning electron microscopy, transmission electron microscope, Brunauer–Emmett–Teller, and Fourier transform infrared spectroscopy. Meanwhile, the electrochemical behavior of nitrite was studied by cyclic voltammetry and amperometry (i − t). As a result, the as-constructed sensor exhibited high electrocatalytic activity, high sensitivity (275.7 µA mM−1 cm−2), wider linear range (0.037–6950 μM), and lower limit of detection (10.41 nM) toward nitrite oxidation. Finally, the sensor was successfully applied to the detection of nitrite in pickle directly, indicating its feasibility for practical applications. The results showed that the porous hollow carbon nanospheres hold great prospect in sensitive detection of nitrite.

Multi-phase magnetically coupled resonant (MCR) wireless power transfer (WPT) technology can fulfill the requirements of time-varying spatial positions of loads in mid-range applications, as it can generate a rotating magnetic field around sending coils, and effectively reduce the limits of spatial positions on transfer characteristics including output power and transfer efficiency. Nevertheless, the design of coils parameters and control strategies put a great influence on the realistic transfer characteristics, which should be considered elaborately in practice. In this paper, a three-phase MCR WPT system with cylinder-shaped coils is investigated, the equivalent circuit model is built to carry out the theoretical analysis. Based on that, the influence on zero-voltage-switching (ZVS) conditions of power switches and the output power of the system, resulting from different phase-shifted angles between each phase, coil turns and angular misalignments of the receiving coil, is analyzed comprehensively. Detailed discussions on relationships among coil turns, the angular misalignment, ZVS conditions, and the output power are completed under different phase-shifted angles. Furthermore, the parametric optimization of coil turns, as well as phase-shifted angles, are proposed to ensure the power switches realize ZVS and ensure the system realize stable output power within the full range of angular misalignment. Finally, experiments are carried out to evaluate the accuracy of theoretical analysis and confirm the validity of the proposed optimal design.

Capacitor-current-feedback active damping has been widely used in LCL -type grid-connected inverters. However, the damping performance is deteriorated due to the negative equivalent resistance resulted by the digital control delays, and thus the grid-connected inverter is apt to be unstable under the grid impedance variation. To address this issue, this paper proposes the capacitor-current proportional-integral (PI) positive feedback active damping method that can ensure a positive equivalent resistance almost within the Nyquist frequency, i.e., the full controllable frequency range. In theory, the proposed damping method can be implemented by feeding back the capacitor current through a PI function. However, the integral term will continuously accumulate the noise and dc bias arising from the feedback signal. To overcome this drawback, a more practical implementation solution is drawn in this paper. Furthermore, a straightforward design procedure is presented for the convenience of selecting the proper controller parameters. With the proposed damping method and its practical implementation, high inverter robustness against the grid impedance variation can be achieved. Experiments are performed on a 6-kW prototype and the experimental results are in well agreement with the theoretical expectations.

Ti-Zr-Hf-Nb-Ta system refractory high-entropy alloys (RHEAs) exhibits outstanding tensile ductility in room temperature. However, the moderate yield strength of them is insufficient. In this work, the Fe element with small atomic radius was added into a non-equiatomic Ti-Zr-Hf-Nb-Ta RHEA for furtherly improving the yield strength. As a result, the yield strength of modified RHEA is as high as ~970 MPa, while retains a considerable fracture train of ~17.5%. However, the Hf2Fe brittle precipitates were formed at grain boundary after aging treatment, leading to a further increment of yield strength but severe deterioration of ductility.

Traditional three-level (TL) DC−DC converters are suitable for the power conversion with high-input voltage, but the performance of the converter is difficult to be optimized within a wide-input-voltage range. A combined three-phase TL (C-TPTL) DC−DC converter suitable for high and wide input-voltage applications was investigated, and the topology consists of a TL clamping cell and a three-phase full-bridge (TPFB) sub-converter cell. The TL clamping cell ensures that the voltage stress on switches is half of the input voltage, and the TPFB cell reduces the current rating of switches and the output filter requirement. Meanwhile, the C-TPTL converter can operate in the half-input-voltage mode and full-input-voltage mode by controlling the switching sequence of the TL clamping cell. The relationship between the input and output voltages, and the choice of the boundary between different operation modes were discussed. Also, the loss analysis to achieve the optimal efficiency was included. A 200–600 V input and 48 V–20 A output prototype was fabricated and tested in the lab, and the experimental results can effectively verify the theoretical analysis and the performance of the C-TPTL converter.

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is one of the most promising WPT technologies for its remarkable capability of simultaneous noncontact power transfer for multiple independent loads. Nevertheless, diverse energy requirements of different loads and efficiency quota make it difficult to design and optimize the multiload system. In this paper, a novel driver configuration for the MCR WPT system with multiple loads is proposed, in which the transmitting resonant tank is driven synchronously by multiple inverters operating at multiple switching frequency and sharing a common dc voltage source, then a multifrequency superposition methodology is presented to achieve high efficiency and targeted power distribution. The dominant features of the methodology are listed as follows: 1) the multifrequency power components from multiple inverters can be simultaneously delivered to multiple loads through a single transmitter; 2) the receiving coils are elaborately designed at different resonant frequencies that correspond to the operating frequencies of multiple inverters to achieve targeted power transfer and high efficiency; 3) the resonant frequency of the transmitter can be modulated within the adjacent area of multiple operating frequencies, and the power distribution to meet the requirements of selective loads will be realized; and 4) the resonant frequencies of receivers can also be adjusted to effectively realize the power distribution. In this paper, a double-frequency MCR WPT system with two loads is comprehensively investigated as a representative example, and the studied methodology has been experimentally verified by two prototypes of the proposed circuit configurations.

Correction for ‘A novel electrochemical sensor based on microporous polymeric nanospheres for measuring peroxynitrite anion released by living cells and studying the synergistic effect of antioxidants’ by Fuxin Liu et al., Analyst, 2019, 144, 6905–6913, https://doi.org/10.1039/C9AN01693G

Simultaneous non-contact energy transmission for multiple loads with separate receiving coils is a remarkable advantage of magnetically coupled resonant (MCR) wireless power transfer (WPT). A novel multi-frequency driver configuration for MCR WPT system with multiple loads is proposed, where the receiving resonant tanks are severally tuned at different resonant frequencies to make the loads selective. A methodology of adjusting the resonant frequency of the transmitter is presented to satisfy diverse energy requirements of specific loads. However, the cross interference from non-targeted frequencies inherently exerts an influence between multiple receivers, and thus makes power allocation non-constrained through multi-coupling channels, which increase the difficulty of power control and parameters design. In order to reduce and further eliminate the influences of the cross interference and realise targeted power distribution for selective loads, three types of parallel and series resonant compensation circuits are introduced into receivers. By flexibly utilising the impedance characteristics of parallel and series resonant networks, the proposed compensation circuits are proved to be effective, significantly reducing the cross interference and exclusively delivering power to the selective loads corresponding to pre-tuned resonant frequencies. Finally, the experimental results from a prototype have confirmed the effectiveness of the proposed methods.

A photoelectrochemical cell can be used as a self-powered photodetector based on the photovoltaic effect. Here, we report an effective way to enhance the self-powered photoresponse performance of the ZnO nanowire arrays (NAs)/Cu2O photoanodes by introducing graphene interlayers. The self-powered photodetectors based on ZnO NAs/graphene (G)/Cu2O have large responsivities of 21.2 mA/W and 17.1 mA/W for ultraviolet (UV) and visible light, respectively, and fast rise and decay times (0.6 ms). Introduction of the Cu2O film improves the visible light-harvesting ability, and the step-like band alignment between ZnO and Cu2O benefits the separation of photoexcited carriers. Furthermore, the graphene interlayers also contribute to the carrier separation and transfer process because of their excellent charge collection capacity. The results demonstrate the ZnO/G/Cu2O heterojunction can be a promising configuration for self-powered UV–visible photodetecting.

A three-phase three-level (TPTL) converter is an optimal alternative for high-input and high-power dc/dc conversion system. The voltage stress on the primary switch is only half of the input voltage due to its three-level (TL) structure, and the current rating of power devices can be reduced by the three-phase configuration. To achieve soft switching and improve efficiency, the resonant tank can be introduced to optimize the performance of the converter. In this paper, a novel TPTL LC -type series resonant converter with few switches and simple configuration is proposed. The voltage stress on all switches can be reduced to the half of the input voltage, and the voltage across output rectifiers is clamped to the output voltage; as a result, the proposed converter is suitable for high-input/output applications. Meanwhile, the ripple frequency of the output current can be increased significantly, resulting in a reduced filter requirement. Variable frequency control strategy is adopted in order to obtain zero-voltage switching for all switches and zero-current switching for all rectifier diodes in wide input voltage and load range. In this paper, the comprehensive analysis on the proposed converter is carried out, including the operation mode classification, the operating mechanism under different operation mode, along with the circuit model, and gain characteristics of the converter by the fundamental harmonic analysis. Experimental results from a 440–590 V input and 400 V/5 A output are presented to verify the theoretical analysis and the performance of the converter.

We report a powerful approach to improve the photoelectrochemical (PEC) performance of the Si/ZnO nanowire array (NWA) photoanodes via incorporating a graphene layer. The Si/Graphene/ZnO NWAs shows the highest photocurrent, which is, respectively, 1.6 times of that for the Si/ZnO NWAs, and 6.2 times of that for the Si wafers. The introducing of ZnO NWAs and graphene greatly reduces the light reflectance, especially in the UV light region. Carrier recombination at the effective n-Si/n-ZnO junction can compensate the high valence band level of Si and thus enhances the contribution of Si to the photocurrent. The graphene interlayers offer a fast passway for the photogenerated electrons in ZnO to recombine with the photogenerated holes in Si, resulting in enhanced PEC performance of the Si/graphene/ZnO NWAs. This study demonstrates the n/graphene/n heterojunction is a promising configuration for efficient solar water splitting.

Previous work reveals that the magnetically coupled resonant (MCR) wireless power transfer (WPT) technology is efficient and practical for mid-range wireless energy transmission, able to handle nontrivial amount of power. This paper presented an equivalent analytical model for MCR WPT system to incorporate spatial misalignments between the transmitting coils and receiving coils. The mutual inductance formulas were derived when receiving coils are laterally, angularly or generally misaligned from transmitting coils. The relationship among the output power, transmission efficiency and the mutual inductance, load resistance were analyzed in detail. Experiments had also been carried out to facilitate quantitative comparison and validate the theoretical analysis.

In the renewable hybrid power system, multiple-input converters (MICs) serve as the interface of several sources with a load, and provide the energy to the load simultaneously or individually, which can optimize the utilization of sources, simplify the system configuration, and reduce the overall cost. In the applications with isolated requirement, available MICs usually have complex configuration and numerous transformer windings. In this paper, a family of asymmetrical half-bridge double-input converters (DICs) adopting pulsating voltage source cells (PVSCs) for low power applications is proposed. Compared with available isolated DICs, the proposed converters have advantages of simple architecture, soft-switching realization, and high conversion efficiency. In this paper, the derivation and feasible control strategy for the proposed converters are illustrated. Specifically, the operation principle of DIC composed of two buck PVSCs is analyzed. Finally, theoretical analysis is validated by the experimental results from a 240 W prototype.

Three-phase dc/dc converters have the superior characteristics including lower current rating of switches, the reduced output filter requirement, and effective utilization of transformers. To further reduce the voltage stress on switches, three-phase three-level (TPTL) dc/dc converters have been investigated recently; however, numerous active power switches result in a complicated configuration in the available topologies. Therefore, a novel TPTL dc/dc converter adopting a symmetrical duty cycle control is proposed in this paper. Compared with the available TPTL converters, the proposed converter has fewer switches and simpler configuration. The voltage stress on all switches can be reduced to the half of the input voltage. Meanwhile, the ripple frequency of output current can be increased significantly, resulting in a reduced filter requirement. Experimental results from a 540-660-V input and 48-V/20-A output are presented to verify the theoretical analysis and the performance of the proposed converter.

Hybrid power systems continuously deliver power to the load from several renewable energy sources. For such systems, the use of a multiple-input converter (MIC) has the advantage of simpler circuit structure and lower cost, compared to the use of several single-input converters. By decomposing converters into basic cells, namely, pulsating source cells and output filters, a set of basic rules for generating multiple-input converter topologies is proposed. Specifically, two families of multiple-input converters are systematically generated. In the first family of MICs, all the input sources can power the load simultaneously or individually. In the second family, only one power source is allowed to transfer energy to the load at a time. Furthermore, some isolated MICs are simplified for reducing the complexity of the circuit configuration.

This paper proposes a zero-voltage and zero-current-switching (ZVZCS) PWM combined three-level (TL) dc/dc converter, which is a combination of a ZVZCS PWM TL converter with a ZVZCS PWM full-bridge converter. The proposed converter has the following advantages: all power switches suffer only half of the input voltage; the voltage across the output filter is very close to the output voltage, which can reduce the output filter inductance significantly; and the voltage stress of the rectifier diodes is reduced too, so that the converter is very suitable for high input voltage and wide input voltage range applications. The converter also can achieve zero-voltage-switching for the leading switches and ZCS for the lagging switches in a wide load range to achieve higher efficiency. The design considerations and procedures are presented in this paper. The operation principle and characteristics of the proposed converter are analyzed and verified on a 400-800-V input and 54-V/20-A output prototype.

A novel zero-voltage-switching (ZVS) combined three-level (TL) converter is proposed in this paper. It is essentially a hybrid combination of a half-bridge TL section and a full-bridge section. The main advantages of the proposed converter are given as follows: the voltage stress of all the switches is ensured to be only half of the input voltage; the secondary rectified voltage is very close to the output voltage, so the high-frequency content is very low, leading to a reduced output filter requirement; the voltage stress of the rectifier diodes is also reduced; and the switches can achieve ZVS with the use of the leakage inductances of the transformers and the intrinsic capacitors of the switches. This paper describes the operating principles and design procedures for the proposed converter. Experimental results from a 1080 W prototype converter operating at 100 kHz are presented to validate the theoretical analysis and demonstrate the performance of the proposed converter

This paper proposes an improved zero-voltage-switching pulse-width-modulation three-level converter (ZVS PWM TL converter), which is improved from the original ZVS PWM TL converter just by exchanging the position of the resonant inductor and the transformer, such that the transformer is connected with the lagging switches. The improved converter has several advantages over the original one, e.g., the clamping diodes conduct only once in a switching period, and the resonant inductor current is smaller in zero state, leading to a higher efficiency and reduced duty cycle loss. A blocking capacitor is usually introduced to the primary side to prevent the transformer from saturating, this paper analyzes the effects of the blocking capacitor in different positions, and a best scheme is determined. A 2.5-kW prototype converter verifies the effectiveness of the improved converter and the best scheme for the blocking capacitor