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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.

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.

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.

Multi-module series-parallel (MMSP) power systems have the superiority of easy scalability and high reliability, and is the prospective candidate for high-power conversion. In this paper, the MMSP configuration is implemented in wireless power transfer (WPT) applications. However, the voltage and current sharing issues have not been analyzed precisely in existing researches. To obtain the inherent principle of voltage and current sharing in the MMSP WPT system, the dual-module series-parallel WPT systems with four configurations are studied as examples. By the fundamental harmonic analysis, the characteristics of a WPT module are obtained, and then the imbalance mechanism of voltage and current under four kinds of parameters mismatches are revealed. The results of circuit simulation verify the correctness of the theoretical analysis.

High-power magnetically coupled resonant (MCR) bidirectional wireless power transfer (BWPT) within long distance can be potentially used in various applications. However, the coupling between transmission coils will drastically decrease with the rise of distance to diameter (d-D) ratio, and voltage/current stresses on resonant components tend to increase apparently, which further deteriorate the system efficiency and stability. In this paper, the relationship between the coupling coefficient and the d-D ratio in high-power BWPT systems is analyzed by mathematics methods. The correlations of transferred power and system efficiency with d-D ratio are presented consequently. The scheme of coils magnetic concentration and double-layer coils in parallel is adopted to improve the system performance. The theoretical analysis is demonstrated by the experimental results of a 2kW prototype, and the system efficiency is improved from 70.7% to 77.47% under the d-D ratio of 1 (300mm-300mm).

For multi-source and multi-load wireless power transfer (WPT) applications, a novel architecture of modular stacked multi-port wireless energy interconnection system (WEIS) with virtual AC bus is presented in this paper, which has following advantages: 1) it can serve as the interface among multiple sources and multiple loads; 2) bipolar coils are applied to eliminate the cross-coupling among multiple coils; 3) the relay coils with constant current characteristics are adopted as a virtual AC bus, and the system power distribution is greatly simplified by the proposed phase-shifted control method; 4) the modularization of power converters, coils and compensation networks greatly enhances the system applicability and scalability. A four-port WEIS prototype with the rated power of 2kW was built, and experiments were carried out for typical operation modes including single-source three-load mode and dual-source dual-load mode, which verified the effectiveness of the proposed system architecture.

Hydrogen peroxide (H2O2) is closely related to our daily life and health, so it is urgent to accurately detect and analyze its content. Herein, a non-enzymatic H2O2 electrochemical sensor was successfully constructed based on electrodeposited silver nanoparticles (Ag NPs) on carbon nanospheres (CNs). Electrochemical characterization results showed that Ag NPs/CNs/GCE displayed good electrocatalytic performance for H2O2. The diffusion coefficient (D) and heterogeneous rate constant (k0) of hydrogen peroxide were calculated separately. In addition, the sensor had a wide linear range of 4.98 × 10−9 ∼ 7.29 × 10−3 M and a low detection limit of 1.66 × 10−9 M. It also presented excellent anti-interference properties in the presence of various substances. The content of hydrogen peroxide was further detected in real samples of makeup remover, milk and disinfectant with satisfactory recovery rates, confirming its application potential in routine detection.

In this paper, a novel electrochemical sensor was fabricated based on nitrogen-doped reduced graphene oxide (N-RGO). The morphology, structure and electrochemical properties of N-RGO were investigated by transmission electron microscopy (TEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). AFM indicated the thickness of N-RGO is about 1.0 nm. The electrochemical experiments demonstrated that N-RGO possesses a relatively large surface area, strong adsorptive ability and excellent electrical conductivity. It was believed that N-RGO is a promising candidate for applications in electrochemical sensors and biosensors. Moreover, N-RGO modified glassy carbon electrode (N-RGO/GCE) exhibited good electrochemical response toward the oxidation of guanine with a linear range covering 4.14 × 10−7–3.71 × 10−4 M, and the corresponding detection limit (LOD) of 1.38 × 10−7 M. Eventually, the proposed sensor could be used to monitor cell necrosis by means of detecting the increase of the current response of guanine. Thus, the work is very meaningful in the field of biological cytology and pathology. A sensitive sensor for guanine detection is constructed based on nitrogen-doped reduced graphene oxide (N-RGO), which was synthesized by a facile method. This paper is the first time to monitor cell necrosis by detecting the increase of guanine content.

It is of great significance to realize the detection of trace amounts of superoxide anions (O

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.

In multi-frequency multi-load magnetically coupled resonant wireless power transfer (MCR WPT) system, multiple inverters are usually employed to respectively provide a single frequency excitation voltage, and then a multi-frequency excitation voltage can be obtained through superposition methodology. However, the system still has the limitation due to complicated architecture and bulky volume. In this paper, only one single-phase full-bridge inverter is adopted in multi-load MCR WPT system, and a multi-frequency pulse width modulation (MFPWM) control strategy is proposed to integrate multiple frequency components into the single-phase inverter. In view of different excitation voltage characteristics, the unipolar and bipolar strategies are proposed respectively, along with the corresponding algorithm. The differences between the two control strategies in the modulation ratio range and harmonic content are discussed in detail. Finally, a hardware platform is built for experimental verification.

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is capable of supplying power to multiple loads simultaneously. To realize load identification and efficient power distribution in multi-load MCR WPT system, a multi-frequency driving method was implemented. However, this methodology allows loads to receive power at different frequencies, leading to a cross interference among multiple loads and deteriorating the power distribution accuracy. In this paper, a double-frequency double-load MCR WPT system was investigated as an example. To suppress the cross interference in the system, a printed circuit board (PCB) type metamaterial slab was designed to reduce the equivalent mutual inductance between transmitter (Tx) and receiver (Rx) coils at non-targeted frequencies, blocking the transfer channel of non-targeted power components. The suppression effect to cross interference was confirmed by the experiment results.

Recently, LCCL-LC compensated magnetically coupling resonant wireless power transfer (MCR WPT) systems are widely used to achieve the constant and load independent output voltage performance compared with other counterparts. To analyze the zero-voltage-switching (ZVS) conditions of the system, the fundamental harmonic approximation (FHA) model is usually utilized, but the analytical results are not accurate due to the neglect of high order harmonics. In this paper, a time domain model considering high order harmonics was proposed to solve this issue. Based on that, a method of modulating the compensated capacitor was put forward to realize ZVS within the full range of loads. However, this method will cause the system to deviate from its full resonance state and further deteriorate the system efficiency. To enable the system to realize ZVS in the full resonance state, the improved optimization method to modulate the compensated inductor was proposed. Finally, a 1kW prototype was built and a series of experiments were carried out, the experimental results demonstrate the effectiveness of the parameters optimization for ZVS realization. The overall efficiency enhancements by the two proposed methods are 0.47% and 1.31% respectively.

In medium-to-high power magnetically coupling resonant wireless power transfer (MCR WPT) systems, either voltage stress or current stress on resonant components tends to be an important issue, depending on the input and output specifications. High current stress will increase the conduction loss on coils and reduce the efficiency, while high voltage stress will bring the difficulty to the design of resonant components and also will deteriorate the system reliability. In this paper, a parameter design methodology based on voltage/current stress optimization is proposed for LCCL-LC compensated MCR WPT systems. By designing the resonant frequency and the self-inductance of two coils properly, the voltage/current stress of the components are effectively controlled. A 1kW LCCL-LC compensated MCR WPT system is built, the trade-off of voltage/current stress among all the resonant components was obtained, and the high efficiency up to 92.2% is also achieved.

Nowadays, bidirectional wireless power transfer (BWPT) technology has caused increasingly concern, but its application is greatly limited when the number of sources and loads increases. In this paper, the concept of multi-port wireless energy router (Wi E-Router) is proposed to realize energy transfer wirelessly among multiple sources and loads for the multi-source and multi-load wireless power transfer (WPT) applications. Specifically, a three-port magnetically coupling resonant (MCR) Wi E-Router with LCC hybrid compensation network is investigated in detail. The equivalent circuit model of the three-port Wi E-Router is built and the power transfer characteristics are analyzed. Based on the circuit model, the relationships between the power magnitude as well as flowing direction and the shifted phase among or inside multiple ports are revealed. Moreover, a zero-power-flow control scheme is put forward for the case when one port quits from the system. By regulating the outer shifted phase, the power transfer among other ports can still be realized when the idling port achieves zero power flow. Finally, the validity of the above theoretical analysis is verified by experiments.

To suppress the background harmonics in the point of common coupling (PCC) voltage on the injected current, feedforward schemes of PCC voltage have been widely used for LCL-type grid-connected inverters. Especially, the unit feedforward scheme is attractive due to its simplicity and utility. However, when the unit feedforward scheme is applied to single-loop current control, unstable open-loop poles may appear due to the variation of grid impedance, which will degrade the robustness of the system or even lead to system instability. Therefore, the robust region of LCL resonance frequency against grid impedance variation is limited to be lower than $f_{s}/3 (f_{s}$ is the sampling frequency). Nevertheless, in terms of the cost and volume of the filter, it is preferable to design the LCL resonance frequency higher. Aim at the trouble in the application of the unit feedforward scheme under LCL resonance frequency beyond $f_{s}/3$ , a weighted average feedforward scheme is proposed in this paper, in which PCC voltage and the filter capacitor voltage are fed forward complementarily. The proposed method can guarantee the robustness of the inverter without the constraint of the LCL resonance frequency. Simulations and experimental results validate the effectiveness of the proposed feedforward scheme.

Capacitor-current-feedback active damping (CCF AD) is widely applied to damp the LCL resonance peak. However, it suffers from the wide-range variation of grid impedance. To address this issue, a passivity-based CCF AD scheme is proposed in this paper, where the optimal CCF coefficient is analytically derived, avoiding the time-consuming interactions, and the computation delay elimination helps the inverter immune to filter parameters fluctuation. The superiority of the proposed design is confirmed by the experimental results.

Thanks to sensor-less and simplicity benefits, the filter-based active damping, being directly plugged into the current regulator, is attractive for the $LCL$ -filtered grid-connected inverter. Typically, the notch filter (NF) is employed and yields a good damping effect when the notch frequency $f_{n}$ is placed higher than the $LCL$ resonance frequency $f_{r}$ . However, for the frequencies above $f_{n}$ , excessive phase lead is provided, worsening the damping effect and giving rise to limited robustness. To address this issue, a quasi-notch filter (QNF) is proposed in this paper, which provides suitable phase compensation to cover a wide range of $f_{r}$ up to the Nyquist frequency $(f_{s/2)}$ . As a result, the high robustness against the variations of $LCL$ parameters and grid impedance can be achieved. The effectiveness of the proposed method is validated by experimental results.

The single-loop weighted average current (WAC) control is attractive for the LCL-type grid-connected inverter owing to its inherent active damping. High robustness can be naturally harvested without any additional damping methods, but it requires two current sensors. Depending on the different weight values, a family of the splitting current single-loop control schemes with the associated filter configurations is developed in this paper, where only one current sensor is needed. As a result, high robustness, high-quality grid current and cost-efficiency can be concurrently achieved. Finally, experimental results from a 6-kW setup confirm the effectiveness and practicality of the splitting current single-loop control.