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In this paper, an interleaved coupled-inductor (CI) based bidirectional dc-dc converter (BDC) is proposed with a higher voltage conversion ratio (VCR). In proposed interleave CI-based BDC (ICI-BDC), the CIs can operate as both a filter inductor and a transformer simultaneously, so that the power density is improved. As a transformer, the turns ratio of CIs is used to improve the VCR with a voltage stress reduction purpose. Furthermore, the interleaved technique can well achieve the low current ripple and reduced current stress in this topology. To control ICI-BDC, the PWM plus phase-shift (PPS) control is employed, where the duty cycle is used to match the two side voltages, and the phase-shift angle is used to control the amount and direction of power flow. Uniquely, a difference value is set between the two side duty cycles The duty cycle of the high voltage side (HVS) is smaller than that of the low voltage side (LVS) by a fixed value. All the switches can achieve soft-switching even at light load condition, which can improve the transmission efficiency. Experimental results obtained from a 1-kW prototype show a high efficiency under all loading conditions, validating the proposed ICI-BDC topology and control method.

H2SO4-Ti3C2Tx ion-gel micro-supercapacitors self-assembled from Ti3C2Tx slurry in H2SO4 exhibit high rate performance by mitigating restacking for rapid ion transport.

Model predictive power control (MPPC) is considered as a promising algorithm utilised in grid-connected inverter due to its fast dynamic response, simple control structure and multi-objective optimisation. However, under unbalanced network, the grid current with excessive distortion troubles the application of MPPC. Based on the conventional MPPC, this study proposes a model predictive flexible power control (MPFPC) to reduce the current total harmonic distortion and achieve three flexible targets, including the cancellation of the active- and reactive-power oscillation and the negative-sequence grid current. In this algorithm, the power references are divided into two parts, which are used as reference values for the instantaneous active power control (IAPC) and the instantaneous reactive power control (IRPC), respectively. The three flexible targets are achieved by regulating the ratio of the two parts of power reference. Meanwhile, the grid current of MPFPC is the sum of IAPC and IRPC; therefore, the grid current distortion can be suppressed effectively. Simulation and experimental platform constructed by a three-level inverter are established to validate the effectiveness of MPFPC, and the results exhibit that the MPFPC meets the above expectations.

Under an unbalanced network, model predictive control (MPPC) with a new definition of the instantaneous reactive power has attracted a great deal of attention due to its simple control structure and outstanding steady-state performance. However, the reactive power cannot precisely trace the nonzero reference. In this paper, a model predictive DC-component power control (MPDCPC) is proposed to tackle the above-mentioned problem. Additionally, the MPDCPC can eliminate oscillations on the reactive power and the negative-sequence current. Then, the corresponding mathematical formulas are derived to extract the DC-component powers, to calculate the DC-component power derivative and to modify the power reference. By regulating the DC-component power to trace the modified reference, the MPDCPC can reduce the current harmonic and remove the oscillations on the active power, reactive power or negative-sequence current. Simulation and experimental platforms are established to demonstrate the validity of MPDCPC. Results demonstrate that the MPDCPC can effectively suppress current distortion and remove oscillations on active power, reactive power or negative-sequence current. In addition, the MPDCPC can successfully break through the restrictions of the MPPC with a new definition of instantaneous reactive power.

In this study, a simple carrier-based pulse-width modulation (CBPWM) method is proposed for a three-phase three-level neutral-point-clamped converter with neutral-point (NP) balancing, which can be applied to three-phase three-wire (TPTW) and three-phase four-wire (TPFW) converter systems simultaneously. First, the effect of each switching state for the NP potential in TPTW and TPFW systems is analysed in detail, and a newly NP control strategy by reconstructing the switching state and adjusting the corresponding duration time is deduced for all operation conditions, it only needs to add the offset voltage to the modulation reference voltage to guarantee the NP balance and is easy to implement. Then, under all operating conditions, the mathematical model of NP current is derived and analysed to evaluate the low-frequency voltage oscillation in the NP. Finally, the effectiveness and feasibility of the proposed CBPWM strategy are verified by the experimental results based on a 12 kVA laboratory prototype.

It has been a hindering issue in perovskite solar cells that the interfaces between the perovskite and charge transport layers show significantly high concentrations of defects with an amount about 100 times more than inside the bulk perovskite layer. The issue causes substantial reduction in both the efficiency and stability of the devices. Herein, a solid-solid contact approach is demonstrated to realize a multifunctional ion-lock layer with strong chemical interaction to the perovskite layer. The multifunctional ion-lock layer remarkably suppresses the interface defects and tunes the work function, contributing to promoting the carrier extraction, increasing the open-circuit voltage, and enlarging the photocurrent. In addition, the multifunctional ion-lock layer successfully locks ions from movement and thus improves the stability of the devices. Finally, with a multifunctional ion-lock layer, the perovskite solar cells deliver an efficiency of up to 23.13% along with desirable long-term operational, storage, and humidity stability. Consequently, the work offers guidelines for establishing defect-suppressed interfaces between perovskites and hole transport layers. Funding Agencies|University Grant Council of the University of Hong Kong [202011159254]; General Research Fund [17200518, 17201819, 17211220, 17200021]; Research Grants Council (RGC) of Hong Kong Special Administrative Region, China [C7035-20G, C5037-18G]; Peacock Team Project from Shenzhen Science and Technology Innovation Committee [KQTD2015033110182370]; Shenzhen Engineering R&D Center for Flexible Solar Cells project from Shenzhen Development and Reform Committee [2019-126]; Guangdong Basic and Applied Basic Research Foundation [2019B1515120083]

Tin-lead (Sn-Pb) perovskites have shown great potential in applications of single-junction perovskite solar cells (PSCs) and tandem devices due to outstanding photoelectrical properties and low band gaps. Currently, Sn-Pb PSCs typically have a p-i-n structure, but choices of hole transport layer (HTL) materials are very limited and there are different concerns in each of them. Eliminating the HTL is a direct and promising strategy to address the concerns, but is rarely studied. In this work, we demonstrate HTL-free and MA-free based Sn-Pb PSCs and a synergistic integration strategy of simultaneously introducing a reducing agent and in situ surface passivation. With the integration strategy, Sn-Pb perovskite films with enhanced antioxidation, reduced trap density, prolonged carrier lifetime, and improved energy-level alignment are achieved. Consequently, final HTL-free PSCs exhibit a champion power conversion efficiency (PCE) of 17.4%, which is a new record for HTL-free and MA-free Sn-Pb PSCs. Meanwhile, the integration strategy-based HTL-free device maintains excellent stability with efficiency unchanged for the first 200 h, and finally retaining 81% of the efficiency after 480 h aging in the air. This study shows the potential of achieving desirable HTL-free and MA-free Sn-Pb PSCs and offers more opportunities for tandem solar cells and other photovoltaic devices.

Electrochemical CO2 reduction (CO2R) powered by renewable energy to convert CO2 molecules into formate is of great interest. It is still challenging to develop an efficient CO2R catalyst with high ...

This paper proposes a single-stage bridgeless isolated AC-DC power factor correction (PFC) topology, and this topology can realize the function of step-up and the galvanic isolation for the AC input and DC output voltages through single-stage power conversion process. Firstly, the operation principle of the topology is analyzed in details. Then, by reasonably designing the series resonant parameters, the zero-voltage-switching (ZVS) turn-on for the power switches in the primary-side and zero-current-switching (ZCS) turn-off for the output rectifier diodes in the secondary-side of the transformer can also be achieved under wide load range, and the voltage stress of the power switches are also reduced based on the active clamping technology. The design procedure for the key components of the proposed converter is also derived. Finally, a 3 kW experimental prototype based on SiC power devices with 85 kHz switching frequency is built to verify the correctness and feasibility of the proposed topology, and the experimental results show a good performance. It can operates in a wide input grid voltage range, 95.7% of peak conversion efficiency and 3.9% of total harmonic distortion(THD) value for grid current could be obtained.

Model predictive power control (MPPC) has been receiving plenty of concern due to its fast dynamic response. However, the varying switching frequency makes the harmonics of output voltage vary over a wide scope, which adds difficulty in designing alternating current (ac) filter. Here, on the basis of the active and reactive power derivatives of each vector and the effect of switching states on neutral point (NP) voltage, we present an MPPC with dual vectors (MPPCDV) to control the three-level (3L) inverter. In this algorithm, a new switching sequence is provided to balance the NP voltage of 3L inverter, and two cost functions are derived to reduce the number of cycle computation. According to the first cost functions, the sector containing optimal switching sequence (OSS) is obtained. The second cost function is assigned to achieve the multiobjective optimization. Simulations and experiments are built to test the effectiveness of MPPCDV. When the 3L inverter adopts the MPPCDV, the majority of the harmonic frequencies in the output voltage is concentrated near the sample frequency, the steady-state performances are improved remarkably, and the dynamic performance is as fast as the conventional MPPC.

The model predictive direct power control (MPDPC) has attracted significant attention due to its outstanding dynamic response and high power factor. However, the variable switching frequency makes the design of alternating current (ac) filter more challenging, and the heavy computational burden limits the application of MPDPC. This paper proposed a new cost function and four steps’ MPDPC (FSMPDPC) scheme for T-type inverters. The proposed cost function can reduce the number of division operations and does not require calculating the duty cycles of all vectors. Meanwhile, the four steps’ calculation process is divided into four steps to reduce the number of cycle calculations. The first three steps are assigned to adjust the active and reactive powers, and the neutral-point (NP) voltage is balanced in the fourth step. An experimental platform of a T-type inverter is established to demonstrate the superiorities of the proposed FSMPDPC. The results show that FSMPDPC improves the steady-state performance of the T-type inverter with lower current total harmonic distortion (THD) and lower ripples in the active and reactive powers. In addition, the proposed algorithm eases the computational burden of the digital signal processor (DSP).

To solve the problem of variable switching frequency in conventional model predictive power control (MPPC), many modified MPPCs with fixed switching frequency have been proposed. However, as the switching frequency increases, additional current harmonics caused by the dead-time are added into the grid current. In this study, an integrated approach with compensation process and elimination process is proposed to eliminate the adverse effect of dead-time. The elimination process with improving gate signals is applied when the phase current is large enough. In contrast, the compensation process is utilised when the phase current is relatively small and the elimination process is troubled by the misjudgement of the current polarity. The experimental results with different dead-time and active power reference are provided to demonstrate the validity of the integrated approach. The integrated approach can further reduces the total harmonic distortion compared to the pure dead-time compensation approach and almost removes the current harmonics caused by the dead-time. Besides, the static error of the power caused by dead-time is dramatically reduced by utilising the integrated approach.

The development of cost-effective electrocatalysts with high activity and sufficient stability for hydrogen evolution reaction (HER) is crucial for the widespread application of water electrolysis for sustainable H

grid-tied converters transport energy from the wind turbine or solar cell to grid, playing a significant role in distributed power generation systems. However, the overcurrent problem limits the application of the conventional algorithm in the converter under grid voltage dip. Here, an integrated active/reactive power oscillation cancellation (IARPOC) is proposed to obtain the power reference of MPPC. Then, the power reference regulates the oscillation in active/reactive power of model predictive power control (MPPC) to increase the output power capacity and provide overcurrent protection. The active and reactive power references are divided into two parts, which are controlled to achieve the active power oscillation cancellation (APOC) and the reactive power oscillation cancellation (RPOC) respectively. Meanwhile, the relationship between the grid current peak value and the power ratio is derived, and the power ratio is regulated to prevent overcurrent from damaging the power switches. At last, an experimental platform constructed by a three-level (3L) converter is established to demonstrate the effectiveness of the proposed approach. The experimental results show that it avoids the overcurrent with less power capacity reduction, and minimizes the oscillation on active or reactive powers.

Model-predictive direct-power control (MPDPC) has attracted increasing attention from scholars because of its outstanding dynamic response and high-power factor. However, its major shortcoming is the high-computational cost, which limits its application in three-level (3L) converters. By dividing the conventional MPDPC into two steps, a double-step MPDPC (DMPDPC) algorithm is presented to address this problem. The first step of this algorithm is dedicated to searching a sector including an optimal switching state (OSS). In the second step, the OSS in a chosen sector is gained. Furthermore, its driver signals are changed as soon as the OSS is gained and their delay time is detected. Then, the corresponding delay compensation is also proposed to improve the steady-state performance of the 3L-converter. The validity of the proposed approach is demonstrated by the experimental platform with 4 kVA rated power. The experimental results show that the computing time in DMPDPC is 50.82% of that in conventional MPDPC. In addition, the proposed DMPDPC decreases the 3L converter's active and reactive powers ripples, reduces its current harmonic and strengthens its robustness against parameter variation.

A facile method has been suggested for the preparation of poly [2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) membrane that comprises of dense and porous layers for high temperature proton exchange membrane fuel cells (HT-PEMFCs). The porosity as well as the asymmetry of the membrane is formed by the use of component solvent at steadily increasing temperatures. This approach needs not to use any porogen, whereas the resultant asymmetric OPBI membrane indicates an improved phosphoric acid (PA) doping level together with mechanical strength. For instance, the PA doping level of the asymmetric OPBI membrane is almost twice as much as that of the homogenous dense OPBI membrane. The conductivity of asymmetric OPBI arrived at 0.072 S cm−1 at 180 °C. The membrane electrode assembly (MEA) based on the asymmetric OPBI demonstrated an exceptional fuel cell functionality with a peak power density of 393 mW cm−2 at 160 °C under anhydrous conditions.

Owing to its high wettability and the resulting compatibility with the future industrial device fabrication process, the conjugated polyelectrolyte (CPE) has becoming a promising hole-transporting material (HTM) in the inverted perovskite solar cell (iPSC); however, only a few highly efficient CPEs have been reported probably due to the limited pool of molecular designing strategies. Here we construct a CPE named DTB(Na) with the same main-chain of a polymer DTB(EH) that was previously employed as a dopant-free HTM in a highly efficient regular type PSC (rPSC) and with simple water/alcohol soluble side-chains. Compared with its analog bearing the only variation of less thiophene units in the main-chain, DTB(Na) shows stronger capacities of hole-extraction and defect-passivation, which should be ascribed to the more intensive exposure of thiophene functional unit to the perovskite layer. As a result, the DTB(Na) iPSC device presents enhanced values on all the photovoltaic parameters and long-term stability, and a power conversion efficiency of 19.92% is realized. Our results demonstrate the feasibility for efficient polymeric HTMs in rPSCs and iPSCs to share the same main-chains, thus enriching the molecular designing strategies and probably expanding the library of efficient HTMs for iPSCs.

Rational design of unique pre‐catalysts for highly active catalysts toward catalyzing the oxygen evolution reaction (OER) is a great challenge. Herein, a Co‐derived pre‐catalyst that allows gradual exposure of CoOOH that acts as the active center for OER catalysis is obtained by both phosphate ion surface functionalization and Mo inner doping. The obtained catalyst reveals an excellent OER activity with a low overpotential of 265 mV at a current density of 10 mA cm−2 and good durability in alkaline electrolyte, which is comparable to the majority of Co‐based OER catalysts. Specifically, the surface functionalization produces lots of Co‐PO4 species with oxygen vacancies which can trigger the surface self‐reconstruction of pre‐catalyst for a favorable OER reaction. Density functional theory calculations reveal that the Mo doping optimizes adsorption‐free energy of *OOH formation and thus accelerates intrinsic electrocatalytic activity. Expanding on these explorations, a series of transition metal oxide pre‐catalysts are obtained using this general design strategy. The work offers a fundamental understanding toward the correlation among surface‐structure‐activity for the pre‐catalyst design., Unravelling the intrinsic mechanism, especially what the “true” catalyst for the oxygen evolution reaction (OER) is, is still highly challenging. Herein, a Co‐based pre‐catalyst is designed that enables rational control over exposure of true active CoOOH centers by in situ self‐reconstruction to deliver excellent electrocatalytic performance, representing one of the state‐of‐the‐art OER catalysts.

Optimal-switching-sequence model-predictive-control (OSS-MPC) strategy, a popular kind of continuous-control-set MPC (CCS-MPC), has been used to address the variable frequency of finite-control-set MPC (FCS-MPC). Since the digital signal processor (DSP) does not have a dedicated divider, it requires a large amount of computation for the division operations in OSS searching. Here, a simplified OSS-MPC absorbing the merits of FCS-MPC is proposed to reduce the computational burden of conventional OSS-MPC. The proposed method uses a novel cost function whose candidates are the finite center vectors instead of switching sequences, which can avoid duty cycle computation and convert the moving horizon optimization of CCS-MPC into that of FCS-MPC. Besides, the derivatives of the active and reactive powers are divided into the constant terms and variable terms. The constant terms are extracted from the cost function. Experimental and simulation results show that the computational amount of the proposed algorithm is only 36.34% of that of the conventional OSS-MPC. Meanwhile, the simplified OSS-MPC still maintains the excellent dynamic and steady state performance of conventional OSS-MPC.

In a battery management system (BMS), battery equalizer is used to achieve voltage consistency between series connected battery cells. Recently, serious inconsistency has been founded to exist in retired batteries, and traditional equalizers are slow or inefficient to handle the situation. The multicell-to-multicell (MC2MC) topology, which can directly transfer energy from consecutive strong cells to consecutive weak cells, is promising to solve the problem, but its performance is limited by the existing converter. Therefore, this paper proposes an enhanced MC2MC equalizer based on a novel bipolar-resonant LC converter (BRLCC), which supports flexible and efficient operation modes with stable balancing power, can greatly improve the balancing speed without much sacrificing the efficiency. Mathematical analysis and comparison with typical equalizers are provided to illustrate its high balancing speed and good efficiency. An experimental prototype for 8 cells is built, and the balancing powers under different operation modes are from 1.426 W to 12.559 W with balancing efficiencies from 84.84% to 91.68%.

Three phase pulse width modulation (PWM) rectifiers has the problems of input current distortion and output voltage ripple under unbalanced grid voltage. In order to reduce the input current harmonics and the output voltage ripple of three phase PWM rectifiers under unbalanced voltage dips conditions, the stationary frame control strategy is adopted. However, its current loop error will cause higher harmonics of the input currents. To further reduce the input current harmonic, an improved control strategy of the current loop is proposed in this paper. In this control strategy, the current loop adopt an improved dual vector based model predictive current control with time delay compensation, which can effectively reduce the input current harmonics. The effectiveness of the proposed method is confirmed by simulation results.

When the unbalanced voltage occurs in grid, the current harmonic of converter with conventional model power predictive control (MPPC) will increase rapidly. In order to address this problem, the active and reactive powers DC components is deduced and expressed by the grid current, the grid voltage and the grid voltage quadrature signal with 90 electrical degrees delay. Meanwhile, the cost function of MPPC only includes the predictive value of the active and reactive power DC components. Thus, the improved MPPC regulate the active and reactive powers DC components directly to trace the reference active and reactive powers by selecting the optimal switching state (OSS). An experimental platform is established to validate the proposed approach. The experimental results show that the current harmonic is decreased remarkably and the waveforms of three grid current are close to purify sinusoidal wave.

Metal-Nx-C based materials have emerged as one of the most promising electrocatalysts for electrochemical reduction of carbon dioxide (ERCD). Co-based macrocyclic compounds have shown unique performance, however, of which the relationship between the ligands structure surrounding Co–N4 centers and reaction mechanism remains vague. To explore this issue, here, a series of Co-based macrocyclic compounds are elaborately chosen as model catalysts, including phthalocyanine cobalt (CoPc), cobalt (II) meso-Tetraphenylporphine (CoTp) and cobalt tetramethoxyphenylporphyrin (CoTop), which possess well-defined Co-N4 coordinated centers but different ligands structure surrounding Co-N4. Electrochemical measurements show that CoPc possesses higher activity and selectivity for CO with Faradaic efficiency (FE) above 62% at −0.7 V (vs. RHE) relative to those of CoTp and CoTop. Combining density functional theory (DFT) calculations, it can be further confirmed that CoPc is more favorable for ERCD to CO due to the rapid formation of key intermediate COOH* and the desorption of CO, demonstrating that the structure of ligands (phthalocyanine) surrounding Co-N4 plays a crucial role in the high CO selectivity. It can be anticipated that an exclusive strategy will pave a new avenue for further understanding the ERCD mechanism of Co-Nx-C catalysts.

Due to their unique activity towards formation of alcohols and hydrocarbons, copper (Cu) based catalysts have been widely used in the electrochemical reduction of carbon dioxide (ERCD). Cu foam naturally possesses three-dimensional (3D) porous structure and catalytically active Cu elements, exhibiting very good catalytic ability for ERCD. Herein, nanostructured self-supporting Cu electrodes with Cu foam as the substrate, with progressive morphologies of nanowires (CuNW), nanosheets (CuNS) and nanoflowers (CuNF), are in-situ prepared by simply adjusting the reaction time in a strongly alkaline oxidizing solution. It is found that the performance and products distribution of ERCD are affected by both the morphology of the as prepared nanostructured self-supporting Cu electrodes and the electrolyte species. As electrode micromorphology evolves from nanowire to nanoflower, the initial electrode potential required for C2 products generation shifts to more positive values. The CuNS electrode shows the highest Faradaic efficiency (FE) of 86.9% at −0.4 V (vs. RHE) and superior performance, owing to its nanosheet morphology that can better stabilize the intermediate state products. Moreover, both total FE and products distribution are affected by the electrolyte anion species. The highest total FE in the investigated electrolyte on CuNS electrode obeys the following order: KHCO3 (86.9%, −0.4 V (vs. RHE)) > KCl (54.7%, −0.5 V (vs. RHE)) > KH2PO4 (1.0%, −0.9 V (vs. RHE)). In 1.0 mol L−1 KHCO3, the CuNS electrode shows a very complex products distribution; in 1.0 mol L−1 KCl, the products distribution can be feasibly controlled by the applied potential; while in 1.0 mol−1 L KH2PO4, ERCD is almost totally suppressed by hydrogen evolution reaction (HER). It is the first time that the CuNS electrodes are applied for ERCD with low cost, simple synthesis, easy scale-up and high activity. Combined with the flexible control ability in FE and products distribution, CuNS electrode possesses great potential for the industrial application of ERCD.