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Power electronic transformer (PET) is the key equipment to realize the power conversion and routing of AC/DC hybrid distribution network, which can greatly enhance the flexibility and controllability of power grid. At present, PET with cascaded H-bridge (CHB) and series resonant dual active bridge (SRDAB) is widely used because of its modular structure and high efficiency. In this paper, a 1.5 MW 10 kV AC-750 V DC PET uesd in practical engineering is analyzed. Firstly, the different switching transient characteristics under the forward and reverse power flow direction are described, and the reasons for the difference are analyzed. Secondly, the current on the rectifier side of SRDAB only flows through the diode. Therefore, the switching loss of SRDAB can be reduced by locking the power semiconductor device on the rectifier side, so as to improve the efficiency of PET. Finally, the experimental test on the PET project site proves the correctness of the loss analysis and the effectiveness of the efficiency optimization method. Using the proposed method, the PET operation efficiency can be improved by about 0.2%.

This paper presents a constant-frequency multi-variable coordinated control strategy based on a series-series compensated dual-active-bridge wireless-power-transfer converter to eliminate real-time wireless feedback communication (RTWFC) and optimize efficiency. The use of switch-controlled capacitors as the primary and secondary resonant capacitors allows the continuous change of the compensation capacitance for the inverter soft-switching and reactance matching, respectively. The output voltage is regulated by tuning the phase-shift angle in the active rectifier bridge. The optimal load resistance for efficiency improvement is matched by adjusting the phase difference between the rectifier voltage and current based on the load and mutual inductance estimation. Moreover, the phase shift of the inverter, which is load-independent, and the coupling coefficient between the coils are positively correlated. Nevertheless, the drawbacks of the proposed control strategy are that optimal load matching is only valid for heavy load and constant current cannot be realized while keeping the constraint of the decoupled control. The proposed control strategy is experimentally validated on a prototype. The efficiency improvement is 5% compared to the conventional voltage tuning with a diode rectifier at the rated output power and in the normal position, and the peak efficiency reaches 93.6% at a 24 V output under the coupling coefficient of 0.3. In addition, a faster transient response was demonstrated in the proposed control strategy without RTWFC for output regulation.

The building space cooling is accounting for a significant portion of global energy use, and it is essential to enhance chiller efficiency for energy reduction and climate change mitigation. Chiller systems with multiple compressors provide the flexibility to meet varying cooling demands. The load-sharing strategy controls how the cooling load is distributed among the compressors. The load-sharing strategy optimization can significantly affect the chiller overall power consumption. This paper presents a mathematical analysis of the power consumption of centrifugal compressors under specific ambient temperatures. The influence of the inlet guide vane and the variable frequency drive efficiency on the compressor power consumption are considered and discussed briefly. An optimal load-sharing strategy for commonly used systems with identical compressors is proposed. Additionally, the scenarios involving a mix of different compressors are investigated. To validate the proposed strategies, a case study using the established performance data of a commercial centrifugal compressor is conducted. The case study results align with the mathematical analysis and the proposed strategy. This study provides valuable insights for designing and managing efficient chiller systems. • A mathematical study on the load-sharing strategy for chillers with multiple centrifugal compressors is presented. • Equal load-sharing strategy is found to be the most energy-efficient for chiller with identical compressors. • A simple and practical method, named DTPCOP, is proposed to determine the optimal number of active compressors. [ABSTRACT FROM AUTHOR]

Featured Application: 3-phase industrial PFC converter. In this paper, the main aim of the study was the investigation of the possibilities of power inductor design, reflecting the performance of the component itself, as well as the operational efficiency of the power factor correction (PFC) converter. PFC inductors represent a key component of the converter, while within the design of any magnetic component, several design rules must be considered to provide proper operational performance. Here we discuss skin-effect, while the proximity effect and formation of fringing flux pose a more serious problem in terms of mitigating their negative impact. Therefore, in this study, the space is devoted exclusively to the analysis of the impact of the fringing flux of the PFC inductor and subsequently to the possibilities of its suppression. The resulting optimizations are reflected in the investigation of the operational efficiency of the PFC converter. [ABSTRACT FROM AUTHOR]

The topology and parameter characteristics of the wireless energy transmission system are the main factors affecting the system's performance. A series–parallel–series–parallel (spsp) topology for magnetically coupled wireless energy transmission is proposed to address the problems of low efficiency and low output power when transmitting electrical energy in the conventional magnetically coupled topology. The spsp topology is compared with the conventional topology based on circuit theory, and the two structures are modeled, characterized, and verified in detail. Simulations and tests are performed for the transmission conditions, an improved Gray Wolf optimization algorithm is proposed, and a physical system is built. Experiments show that the spsp structure is superior near the designed circuit parameters when the network works in a resonant state. The improved Gray Wolf optimization algorithm is then used to find the optimal parameters, and the transmission efficiency reaches 90.53%, which effectively improves the transmission performance of the system. The established physical system utilizes the optimized parameters for coil structure and coil offset experiments, and the average transmission efficiency is 83.75%, with an error of 6.78% calculated by data measurement. The rationality of the proposed structure and the correctness of the simulation parameter design method are verified, and it is hoped that the proposed system and circuit structure in this paper will provide a reference for the design of a magnetically coupled wireless energy transmission system. [ABSTRACT FROM AUTHOR]

This paper uses the three-stage DEA method to measure the input–output efficiency of China's 23 listed power generation companies (mainly thermal power generation) in 2019, and uses the SFA regression model to eliminate environmental elements and random disturbances. The results show that in a non-homogeneous environment, the scale efficiencies of most power generation companies are greater than or equal to their pure technical efficiencies. These companies should first improve management and technical levels, and then optimize the scale of investment. Furthermore, after removing environmental variables, half of the companies should turn to increasing economies of scale instead of diminishing economies of scale. It can be seen that environmental factors, such as the degree of regional development and IPO time, have reduced the economies of scale of enterprises, so they should strengthen the communication between different regions, and the government should provide assistance to companies that are listed late. [ABSTRACT FROM AUTHOR]

This paper aims to study, develop and implement a system that uses scalar control with energy efficiency optimization for driving three-phase induction motors. The proposal consists of changing the relationship between voltage and frequency of the drive, which is traditionally kept constant under scalar control, to optimize the air gap flux according to the mechanical load coupled to the shaft. Three different operation modes have been proposed: two in open-loop (super-economical and economical modes) and a closed-loop one. Both open- and closed-loop control strategies are tested to validate the proposal, obtaining a consumption reduction of up to 48.06% in open loop and 35.9% in closed loop. [ABSTRACT FROM AUTHOR]

During permanent magnet synchronous generator (PMSG) operation, aside from improving the rapid response of torque and reducing the rippling of torque and flux to guarantee the operational reliability, the loss of the PMSG itself cannot be ignored either. Aiming at this problem, an improved model predictive direct torque control (MPDTC) method is proposed, which suppresses the torque ripple and achieves PMSG efficiency optimization. Firstly, based on the conventional MPDTC and the loss model of PMSG, the predicted stator active current is determined, which is utilized for obtaining the predicted torque. Secondly, combined with the generator loss model, the set value of the stator energetic current is obtained; combined with the wind power system maximum power point tracking method, the set value of generator torque is obtained. Thirdly, by converting the torque control error and current control error into a per unit value, the influence of the weight coefficient in the cost function on the control effect is reduced. Finally, the key results verified the effectiveness and superiority of the proposed control scheme by simulation and experiment. [ABSTRACT FROM AUTHOR]

In this paper, an improved online particle swarm optimization (PSO) is proposed to optimize the traditional search controller for improving the operating efficiency of the permanent magnet synchronous motor (PMSM). This algorithm combines the advantages of the attraction and repulsion PSO and the distributed PSO that can help the search controller to find the optimal d - axis air gap current quickly and accurately under non-stationary operating conditions, thereby minimizing the air gap flux and then improving the motor efficiency. To verify the effectiveness and stability of this proposed algorithm, the operating efficiency of PMSM as using this proposed algorithm is compared with that of traditional search controller under non-stationary operating conditions. The results show that the proposed algorithm can improve the operating efficiency of PMSM by 6.03% on average under non-stationary operation conditions. This indicates that the search controller based on the improved PSO has a better adaptation to the variation of external operating conditions, and can improve the operation efficiency of PMSM under non-stationary condition.

Global maximum power point tracking (GMPPT) refers to the extraction of the maximum power from photovoltaic (PV) modules in real time under changing ambient conditions. Due to the installation of PV systems in densely built-up areas, partial shading scenarios are commonplace. Commercially established GMPPTs suffer from low tracking speeds and inefficiency. A novel GMPPT algorithm is proposed here based on the rectangular power comparison (RPC), which exploits the fundamental relationship between the shading factor, the bypass diode voltage and the global maximum power point. The entire theoretical formulation of RPC is presented systematically for the first time. This method boasts of increased conversion speeds owing to the precomputation of the module voltage versus the shading factor correlations using the regression of diode model from the experimentally obtained bypass diode characteristics. The proposed method is simple to implement with the computational complexity of order $n$ , which represents the number of uniquely shaded PV modules in a series string. The proposed approach addresses the much-needed intersection problem between the distributed and centralized PV systems and therefore targets PV strings which are most common in residential and small to medium scale commercial PV installations world over. The proposed approach is validated with the in-house developed prototype hardware set-up and software control implementation giving a 99% tracking efficiency with a recorded tracking time of 10 ms. The experimental results show 50 times improvement in speed and 95% increase in power gain as compared to the other popular existing methods namely scanning based GMPPT and local MPPT methods respectively, with negligible computational burden and less than 0.5% added cost to the conventional PV energy conversion system.

Input parallel output parallel (IPOP) DC/DC system is widely utilized in many occasions like data center and hybrid electric vehicle (HEV). However, the efficiency characteristics of different converters usually differs from each other, and the conventional control strategy has difficult to realize efficient conversion of overall power of the system. To address this issue, Buck converter is taken as the module and whose efficiency model under current continuous conduction mode (CCM) is presented. Meantime, parameter identification method based on least square (LS) algorithm is proposed as well. In order to realize the efficiency optimization of the whole parallel system, the constraint conditions of each module are analyzed, and the current distribution calculation method based on sequential quadratic programming (SQP) algorithm for the parallel system is introduced. On this basis, a control strategy of proportional current distribution (PCD) is proposed, which not only ensures that the parallel system can always run as efficiently as possible under different loads, but also realizes the flexible switching between the current-sharing mode and current distribution mode. Finally, the simulation and experimental results prove that the proposed method can achieve 4.46% higher efficiency than conventional method within the given power range of each converter, and realize the efficiency optimization of the IPOP DC/DC system to the greatest extent.

To solve motor heating and life shortening of parallel switched reluctance generator (SRG) induced by uneven output currents due to different external characteristics, we generally adopt current sharing control (CSC) to make each parallel generator undertake large load currents on average to improve the reliability of parallel power generation system. However, the method usually causes additional loss of power because it does not consider the efficiency characteristics of each parallel generator. Therefore, with the efficiency expression for the parallel system of SRG established and analysed, the control strategy based on differential evolution (DE) algorithm is proposed as a mechanism by which to enhance generating capacity and reliability of multi-machine power generation from the perspective of efficiency optimisation. We re-adjust the reference current of each parallel generator to transform the working point of each generator and implement the efficiency optimisation of parallel system. The performance of the proposed control method is evaluated in detail by the simulation and experiment, and comparison with traditional CSC is carried out as well.

Moving image recognition has become a well-explored problem in computer vision. However, it is difficult for the traditional convolutional neural network (CNN) model to effectively capture timing information in motion. For better use of video sequence features and to improve the accuracy of action recognition, Therefore, this paper proposes a Three-dimensional CNN (3DCNN) model based on Gated Recurrent Unit (GRU) with an attention mechanism. The model leverages 3DCNN for deep feature extraction from video frames, employs GRU to capture the temporal dynamics of feature sequences and incorporates an attention mechanism to emphasize key frames, which improves moving image recognition. Demonstrating superior accuracy in'Cross-Subject' and'Cross-View' evaluations, our model surpasses standard benchmarks with accuracies of 83.2% and 87.3% respectively. • We combined 3 DCNN and GRU to classify the sequences of the motion images. • The framework adds attention mechanisms to improve recognition capabilities. • Experimental results show that the action recognition accuracy is increased by 6%. [ABSTRACT FROM AUTHOR]

This paper addresses the critical task of hacker identification within the cyber traceability system. While the latest hacker group identification method based on the heterogeneous graph attention network (HGHAN) holds promise in discovering hacker groups, its potential is hindered by the underutilization of node information and poor training efficiency. Particularly, attribute information dilution during node feature extraction and lengthy training for node embedding vector reassignment when new nodes are added have been observed. To rectify these shortcomings, the paper presents an improved model for hacker group identification. This novel approach leverages dynamic heterogeneous graph node updating to significantly boost efficiency without compromising the original model's classification accuracy. The key aspects of the method involve pre-learning for node attribute training vectors, LSTM (Long Short-Term Memory) and attention mechanisms for node feature vector refinement, and introducing a sparse matrix and dynamic node update scheme. The experimental results demonstrate marked improvements in training efficiency and graph update processes while maintaining classification accuracy. This advancement signifies the improved HGHAN model's capacity to adeptly navigate real-world network dynamics, assisting researchers in pinpointing malicious attackers amid cyber incidents. [Display omitted] • Implement heterogeneous graph node embedding vector updates in dynamic scenarios to replace retraining. • Adopt pre-training in the node feature extraction process to enhance feature utilization. • Introduce a triplet sparse matrix in the node embedding process to save space and improve efficiency. • The experiments show that the proposed model can greatly reduce the time consumption without affecting the identification effect of the basic model. [ABSTRACT FROM AUTHOR]

This paper proposes a novel Redundant Cooperative Control (RCC) strategy to address the pollination sequence planning problem for a mobile pollination robot in the greenhouse. Firstly, the RCC strategy divides the robot's workspace into subspaces based on the distribution of flowers through clustering. Subsequently, the RCC strategy plans the traveling salesman problem within the visual field of these subspaces, seeking a compromise solution for an optimal path. Finally, the RCC strategy utilizes the redundant motion capabilities of the mobile chassis and robotic arm to accomplish the pollination task during the movement. The RCC strategy exploits the available redundancy in both the agricultural robot's mobile platform and end-effector, carefully balancing computational complexity and path quality. To validate the effectiveness of the RCC strategy, we designed a series of experiments conducted on our pollination robot platform, measuring different strategies. The results demonstrate that the RCC strategy achieves an average pollination rate of 7.5 s per flower, representing a 36.4% improvement compared to the most common intermittence strategy. Furthermore, the RCC strategy can be extended to tasks such as harvesting and pruning, significantly enhancing the efficiency of robot task execution even in industrial and service sectors. • Proposed a redundant cooperative control strategy (RCC). • Designed a tomato pollination robot with redundant motion capability. • The RCC strategy can be applied to pollination in motion. • The pollination robot can achieve a pollination rate of 7.5 s per flower. [ABSTRACT FROM AUTHOR]

In this work, we present the analytical model of buck converter with 3-D in-package air-core inductor ($150~\mu \text{m}$ thick). To optimize the power efficiency at a targeted power density, models including 3-D inductor and power switches are developed. Compared to 3-D electromagnetic (EM) simulation, the proposed inductor model has a modeling error within 12% for the inductance calculation. With the proposed design methodology, an inductor with $Q$ -factor up to 35 at 300 MHz is achieved. From the system aspect, the loss breakdown in the integrated power converter is investigated. A 0.5 ratio buck converter can reach 88.5% efficiency at 1–5 W/mm2 based on the optimized inductor designs, with output voltage ranging from 0.7 to 0.9 V and based on 28 nm CMOS. [ABSTRACT FROM AUTHOR]

The radioisotope batteries have drawn extensive attention due to the high energy density. Nowadays, the radioisotope thermophotovoltaic systems are one of the most promising radioisotope batteries. In this work, the crystal emitter design and the associated performance of the radioisotope thermophotovoltaic generators are investigated. First, the design of photonic crystal emitter together with the adoptions of both the multi-layer insulation and supporting materials are discussed. In order to optimize the system efficiency, the effects of the area of emitters are mainly investigated. We have analyzed the efficiency of system using GaSb cells and Si cells, respectively. With Si cells, the system efficiency can computationally reach about 1. 4 % with an output power of 7 W. When GaSb cells are employed, the system performance is estimated to an efficiency of 1 2. 3 % with 61.6 W output. [ABSTRACT FROM AUTHOR]

In this article, an efficiency-oriented control strategy is proposed for LCC–LCC-compensated wireless power transfer (WPT) system to achieve zero-voltage-switching (ZVS) operation over a wide current regulation range, in which full-bridge (FB) and half-bridge (HB) modes are combined and switchable based on requirements from load. The harmonic-considered time-domain models for FB and HB modes are first built to calculate current through the switches at the turn-off moment accurately. Then, focused on the constant voltage charge stage with variable output current, the ZVS boundaries are identified in HB and FB modes as the preferable control trajectories, which determines the desired current output with joint considerations of frequency, phase-shift angle, and duty ratio. Next, a least squares optimization method is introduced to fit the theoretical control trajectories into a smooth curve that is practical for implementation on microcontrollers. Finally, a 4.4-kW WPT prototype is built to verify the feasibility and validity of the proposed control strategy. Results show that a high system efficiency can be achieved over a wide output current range, with an efficiency of 94.68% even at 20% rated power. [ABSTRACT FROM AUTHOR]

Adaptive synchronous rectification (SR) is a good solution to solve duty cycle loss for LLC resonant converter. Usually, whether the synchronous rectifier is turned off prematurely or late can be detected by whether the body diode is conducted on or not. However, when the switching frequency is below the resonant frequency, both SR turning-off prematurely and late may generate body diode conduction (BDC), which will cause logic errors in the conventional adaptive SR strategy. Then, a large reverse current from load to source will occur, which damages the efficiency. To solve the problem, the time-domain modeling of the SR drain-to-source voltage is established to analyze the mechanism of BDC caused by SR turning-off late. Moreover, an improved adaptive SR driving scheme is proposed, which can identify the two different types of BDC and tune SR to be turned off exactly. Finally, a 280 W LLC prototype is built to verify the established model and the proposed SR method. The prototype proves that both the duty cycle loss and the reverse current are eliminated and efficiency improvement of 0.54% is achieved. [ABSTRACT FROM AUTHOR]

Aiming to improve the efficiency of the water-filled submersible motor, the method of optimizing the ratio of diameter to shaft length and air-gap length of the motor is proposed to reduce the water friction loss of the water-filled submersible motor. By analyzing the composition of the mechanical loss and the research status of the water friction loss of the water-filled submersible motor, the optimization methods of the water-filled submersible motor efficiency are determined. For the accurate estimation of electromagnetic performance of the submersible motor, 2-D time-harmonic field solutions are employed, which cost less time and computational resources compared to the transient solution. By fitting the curves of water friction loss and electromagnetic losses with the optimized parameters, the influence of the ratio of diameter to shaft length and the length of the air-gap on the efficiency of the motor is analyzed. Finally, the parameters of the motor are determined, with the consideration of the influence of the radial to axial ratio and the air-gap length on the performance parameters of the motor and the requirements of actual working conditions. The results show that the two methods can effectively reduce the water friction loss of the water-filled submersible motor and improve the efficiency of the water-filled submersible motor in the motor design stage. [ABSTRACT FROM AUTHOR]

This paper proposes a new flux control strategy for consequent-pole brushless hybrid excitation (CPBHE) machines to achieve a high efficiency and a fast convergence. Based on an analysis of the mathematical model of a CPBHE machine, a loss model of the CPBHE machine is derived, which demonstrates the feasibility of adopting d-axis flux to search for the optimal efficiency point. Furthermore, to improve the convergence speed of the online search algorithm and to make it suitable for the frequently varying operating conditions of electric vehicles (EVs), an adaptive step search algorithm based on the margin of the voltage limit combined with the offline table lookup method is proposed. Experimental results show that the proposed algorithm can optimize the efficiency of a motor system in the flux-weakening region and that it features a fast optimization process that makes it suitable for EV drives. [ABSTRACT FROM AUTHOR]

CubeSats are miniature satellites used to carry experimental payloads into orbit, where it is often critical to precisely control their attitude. One way to do this is through the use of magnetorquers, which can be integrated into PCBs. This technique saves considerable space and capital when compared with more common torquerod magnetorquer systems. Here we derive a method of analyzing different PCB-integrated magnetorquer geometries, parametrizing them such that the magnetic moment and efficiency are optimized. Furthermore, by modulating the trace width, the trace number, and other electrical characteristics of the magnetorquer coil, this article optimizes the generated magnetic moment. Both constant voltage and constant current sources are analyzed as inputs. These optimizations are then simulated in COMSOL for multiple geometries, and it is found that there exists an optimal geometry, given a specified power dissipation. Simulations verify the general trend and maxima of these derivations, barring small, consistent rescaling in the magnitude of the coil resistance. It is also found that these PCB-integrated magnetorquers provide a sufficient alternative to commercial coil magnetorquers, particularly in volume-restricted configurations. This article extends such analysis to larger CubeSat configurations, and finds that these larger implementations increase magnetorquer efficiency. Optimizations for common PCB-implementable geometries on small satellites are tabulated in the Appendix. [ABSTRACT FROM AUTHOR]

This article presents a two-stage automotive LED driver architecture delivering independently regulated output currents to multiple LED strings. The system consists of a multiphase noninverting buck–boost front-end stage, which allows for a wide battery voltage range, followed by high-frequency immittance-network-based LCL-T resonant converters, which operate as current sources over wide output voltage ranges. The two-stage buck–boost + resonant (BB+resonant) architecture takes advantage of the buck and boost capability of both stages, and the flexibility in setting the intermediate bus voltage to minimize losses. Advantages of the BB+resonant architecture include the use of lower voltage rated devices and soft switching in the resonant stage, leading to reduced losses and size. Experimental results are provided for a prototype consisting of a 250-kHz two-phase front-end stage and 2-MHz LCL-T resonant stages delivering independently regulated 1 A currents to four LED strings with $N = 1$ $-$ 18 LEDs. The measured system efficiency is greater than 88% over wide input (8 $-$ 18 V) and output (3–50 V) voltage ranges, with a peak efficiency of 93%. [ABSTRACT FROM AUTHOR]

In this paper, an improved discharging circuit was proposed to quicken the decay of the current in the drive coil in a reluctance accelerator when the armature reaches the center of the coil. The aim of this is to prevent the suck-back effect caused by the residual current in drive coil. The method is adding a reverse charging branch with a small capacitor in the traditional pulsed discharging circuit. The results under the traditional circuit and the improved circuit were compared in a simulation. The experiment then verified the simulations and they had good agreement. Simulation and experiment both demonstrated the improved circuit can effectively prevent the suck-back effect and increase the efficiency. At the voltage of 800 V, an efficiency increase of 36.34% was obtained.

The equivalent resistance of the battery will change during charging in practical applications, so it is difficult to design a wireless power transfer (WPT) system with accurate constant current (CC) and constant voltage (CV) output characteristics. In addition, the WPT system efficiency is also affected by the change of equivalent resistance. Therefore, this paper studies the charging control and efficiency optimization strategy for the WPT system with dynamic loads. The WPT system with a structure of double-sided LCC compensation topology and containing controllable rectifier circuit at the secondary side is established, and the working process of full-bridge controllable rectifier circuit is analyzed. Then the output characteristics of the WPT system are analyzed. The expressions of the optimal transmission efficiency and the optimal equivalent impedance of the full-bridge rectifier are derived. The relationships between the equivalent impedance of the capacitor-filtered full-bridge controllable rectifier circuit and the phase shift angle, the charging current and the phase shift angle are also obtained. In this paper, the CC and CV charging strategies based on phase shift control of controllable rectifier circuit and efficiency optimization strategy based on dynamic equivalent impedance matching are proposed, which can improve the WPT system transmission efficiency while realizing CC and CV charging. Finally, the effectiveness of the proposed control strategy is verified by simulation and experiment. The WPT system realizes CC charging mode and CV charging mode in turn when the load resistance changes from $5~\Omega $ to $30~\Omega $ , and the overall efficiency is up to 90.71% at the transmission distance of 15cm.

In this paper, an optimal design of a high-efficiency DC-DC boost converter is proposed for RF energy harvesting Internet of Things (IoT) sensors. Since the output DC voltage of the RF-DC rectifier for RF energy harvesting varies considerably depending on the RF input power, the DC-DC boost converter following the RF-DC rectifier is required to achieve high power conversion efficiency (PCE) in a wide input voltage range. Therefore, based on the loss analysis and modeling of an inductor-based DC-DC boost converter, an optimal design method of design parameters, including inductance and peak inductor current, is proposed to obtain the maximum PCE by minimizing the total loss according to different input voltages in a wide input voltage range. A high-efficiency DC-DC boost converter for RF energy harvesting applications is designed using a 65 nm CMOS process. The modeled total losses agree well with the circuit simulation results and the proposed loss modeling results accurately predict the optimal design parameters to obtain the maximum PCE. Based on the proposed loss modeling, the optimally designed DC-DC boost converter achieves a power conversion efficiency of 96.5% at a low input voltage of 0.1 V and a peak efficiency of 98.4% at an input voltage of 0.4 V.

In this article, a parameter design method is proposed to improve the dc–dc efficiency of the capacitive power transfer (CPT) system. Similar to the inductive power transfer (IPT) system, the capacitive coupler is analyzed by using a T-type model, giving direct insight into the impedance refracted from the secondary side. Compared to the IPT system, the external capacitor of the capacitive coupler introduces extra design freedom, making it easy to realize the optimal load condition by adjusting the external capacitance. To quantify the relationship between the optimal load and the external capacitance, the impedance characteristic of the rectifier is discussed. Then, the efficiency analysis is conducted in detail. Considering the impact of the resonant frequency, and the external capacitance that determines the coupling coefficient, a parameter design method is proposed to improve the dc–dc efficiency. Although the design example is conducted with the double-sided LC compensated CPT system, the analysis and design process can be extended to other compensation networks easily. The effectiveness of the proposed design method is verified with a 100-W output CPT system. The experimental results show that the dc–dc efficiency can reach 89.39% with 10-W output, and reach 93.02% with 100-W output. [ABSTRACT FROM AUTHOR]

The efficiency analysis and optimization methods for achieving optimal efficiency in two-coil wireless power transfer (WPT) systems have been considerably discussed. Recently, that the efficiency of three-coil WPT can be higher than its two-coil WPT counterpart with an extended transmission distance has been verified. Nevertheless, the research on the efficiency analysis and optimization of the three-coil WPT system still needs to be examined. Therefore, this paper systematically investigates the efficiency characteristics of the three-coil WPT system. Especially, an optimal current ratio control strategy is developed with an active rectifier to achieve efficiency optimization and keep the output voltage constant. Consequently, overall efficiency can be improved using the optimal current ratio compared with traditional three-coil WPT systems. A scaled-down experimental prototype is established to validate the effectiveness of the proposed coupling structure and the feasibility of the proposed control approach. Overall, a three-coil WPT system with an active rectifier is proposed, which utilizes the optimal current ratio control strategy. Experimental results successfully validate that the proposed methods can substantially improve the efficiency of three-coil WPT. [ABSTRACT FROM AUTHOR]

Continuous developments in Proton Exchange Membrane Fuel Cells (PEMFC) make them a promising technology to achieve zero emissions in multiple applications including mobility. Incremental advancements in fuel cells materials and manufacture processes make them now suitable for commercialization. However, the complex operation of fuel cell systems in automotive applications has some open issues yet. This work develops and compares three different controllers for PEMFC systems in automotive applications. All the controllers have a cascade control structure, where a generator of setpoints sends references to the subsystems controllers with the objective to maximize operational efficiency. To develop the setpoints generators, two techniques are evaluated: off-line optimization and Model Predictive Control (MPC). With the first technique, the optimal setpoints are given by a map, obtained off-line, of the optimal steady state conditions and corresponding setpoints. With the second technique, the setpoints time profiles that maximize the efficiency in an incoming time horizon are continuously computed. The proposed MPC architecture divides the fast and slow dynamics in order to reduce the computational cost. Two different MPC solutions have been implemented to deal with this fast/slow dynamics separation. After the integration of the setpoints generators with the subsystems controllers, the different control systems are tested and compared using a dynamic detailed model of the automotive system in the INN-BALANCE project running under the New European Driving Cycle. • The control structure of a PEM fuel cell system in an automotive application is described. • An off-line optimal setpoint generator is compared to MPC techniques. • Slow and fast dynamics are split in the MPC design for computational burden reduction. • Simulations are based on a model tuned using experimental data from a real automotive fuel cell system. [ABSTRACT FROM AUTHOR]

In this paper, the main aim of the study was the investigation of the possibilities of power inductor design, reflecting the performance of the component itself, as well as the operational efficiency of the power factor correction (PFC) converter. PFC inductors represent a key component of the converter, while within the design of any magnetic component, several design rules must be considered to provide proper operational performance. Here we discuss skin-effect, while the proximity effect and formation of fringing flux pose a more serious problem in terms of mitigating their negative impact. Therefore, in this study, the space is devoted exclusively to the analysis of the impact of the fringing flux of the PFC inductor and subsequently to the possibilities of its suppression. The resulting optimizations are reflected in the investigation of the operational efficiency of the PFC converter.

Aiming at the direct methanol fuel cell system is too complicated, difficult to model, and the thermal management system needs to be optimized. The article attempts to bypass the internal complexity of direct methanol fuel cell, based on experimental data, use neural networks to approximate arbitrarily complex non-linear functions ability to apply neural network identification methods to direct methanol fuel cell, a highly non-linear thermal management system optimization modelling. The paper uses 1000 sets of battery voltage and current density experimental data as training samples and uses an improved back propagation neural network to establish a battery voltage-current density dynamic response model at different temperatures. The simulation results show that this method is feasible, and the established model has high accuracy. It makes it possible to design the real-time controller of the direct methanol fuel cell and optimize the thermal energy management system’s efficiency. [ABSTRACT FROM AUTHOR]

The use of wireless power transfer technology in unmanned aerial vehicle (UAV) systems is rapidly improving in different application areas. The main limitations of electric-powered UAVs are their charging range and stability in dynamic conditions. To solve these, this article proposes a hybrid control method based on dc-link and switched capacitor control with a fixed operating frequency. The dc-link voltage is regulated by the boost power factor correction converter to smoothen the output voltage, and the switched capacitor is used to dynamically compensate for self-inductance variations under dynamic coupling conditions. The output voltage stabilization and near-unity power factor of the input impedance can be achieved by applying the hybrid control method. Therefore, efficiency improvement can be achieved. Furthermore, the proposed control method can also be applied to systems with large coupling variations. To verify the proposed control method, a 500-W prototype was set up in the laboratory, and the experimental results proved that the control method could ensure a stable output voltage with horizontal and vertical offsets of 200 and 62 mm. respectively. Additionally, the results show that the maximum efficiency of the proposed control method is 91.9%, demonstrating that the proposed method effectively improves the efficiency. [ABSTRACT FROM AUTHOR]

In order to get rid of plug-in/out actions for container terminals and to save space, a power-relay inductive power transfer system is employed for reefer container wireless charging. Besides, a load-power-based efficiency model is proposed to analyze system efficiency. The function of efficiency against the input voltage and the load power distributions of the system is analyzed in detail. Then, system efficiency can be improved by regulating the input voltage according to the input-voltage-lookup table, which is generated as per various power distributions of loads. Finally, a prototype with three loads is built to validate the performance of the proposed approach. The experimental results show that the efficiency is greater than 94.29% with an improvement by 7.6%, 7.2%, and 6.0%, compared with those without optimization (fixed input voltage 213 V) at one load (@80 W), two loads (@80 and 80 W), and three loads (@80, 80, and 80 W), respectively. [ABSTRACT FROM AUTHOR]

• An improved cascade method for compression-absorption heat pump is proposed. • The improved cascade heat pump can output temperature 110 °C at inlet source 10 °C. • The energy performance of improved cascade method is 16.2% higher than existing mode. • The exergy performance of novel cascade method is raised by 19.2% than existing mode. • The novel cascade method can increase the available heat capacity by 238.4%. Air is a readily available and renewable source, but its efficient utilization for industrial heating is hindered by the significant temperature mismatch between the low-grade air source and the high-temperature industrial demand. Heat pumps can elevate the source temperature from low to high levels. However, there is still a significant knowledge gap in achieving output temperature exceeding 90 °C when the input source is below 30 °C. While there are some preliminary studies on air-source heat pumps operating in the mentioned temperature range, they have yet to distinguish the respective coupling temperatures required for different cascaded components. Therefore, the optimal cascade configuration between various sub-cycles has not been established, and the full efficiency potential remains untapped. To address the identified limitations, in this work, an advanced cascade method is proposed and applied to the compression-absorption heat pump (CAHP). The novel cascade method allows independent control of the coupling temperature in different branches as needed, facilitating an optimal cascade configuration between various subloops. Consequently, the operating efficiency of CAHP is optimized. Simulation results show that the proposed cascade method reduces the exergy destruction of CAHP by 6.3% compared to the existing mode. Moreover, it always achieves higher efficiencies in the studied conditions, with a maximum increase in the coefficient of performance and exergy coefficient of performance by 16.2% and 19.2%, respectively. Under ambient temperature of 10 °C to –30 °C and an output temperature of 100 °C, the improved cascade CAHP exhibits an increase in heating capacity, ranging from 57.2% to 238.4% higher than the existing mode. These advantageous features contribute to achieving cleaner industrial heating with air source heat pumps. [ABSTRACT FROM AUTHOR]

In wireless sensor networks (WSNs), spectrum efficiency and energy efficiency are two challenging issues to be addressed due to the scarcity of spectrum and its limited energy. In this paper, we study efficient parallel scheduling with power control and successive interference cancellation (SIC) aimed at maximizing spectrum and energy efficiency, and formulate the efficiency maximization scheduling (EMS) problem as a mixed integer nonlinear programming (MINIP) problem. Given the high complexity caused by mixed variables, we first analyze the critical variables affecting efficiency to transform the MINIP problem into a combinatorial linear programming (LP) problem, which is further decomposed into two linear minimization problems. Then, a recursive relationship between the optimization variables is explored, through which we propose a two-stage scheme that solves the minimization problems with lower complexity. Finally, distributed implementation of the scheduling scheme is provided to iteratively explore the maximum feasible concurrent links in the networks. Extensive results demonstrate the superior performance of our proposed scheme in improving spectrum and energy efficiency. Specifically, our scheme achieves 12.16% to 66.15% higher spectrum efficiency and 18.84% to 88.20% higher energy efficiency than the existing schemes. [ABSTRACT FROM AUTHOR]

Liquid air energy storage (LAES) technology is a promising large-scale energy storage solution due to its high capacity, scalability, and lack of geographical constraints, making it effective for integrating renewable energy sources. The core unit of the LAES system is the cold energy storage (CES) unit, which significantly influences its overall efficiency. However, the current mainstream liquid-phase and solid-phase CES methods have inherent drawbacks, including safety, environmental issues, and the dynamic effect of the thermocline. Moreover, previous research has often over-idealized the CES unit and neglected the actual heat transfer processes during the CES and cold energy release (CER) processes. In the innovative study, a gravity-driven moving packed bed (MPB) based LAES system (MPB-LAES) adopting quartz sand as the CES medium is proposed. A thermodynamic model for the LAES system is constructed, and the gas-solid counterflow coupling heat transfer model for the MPB is developed based on the continuous solid-phase model and finite difference method. The accuracy of the model is validated through experimentation using the constructed test apparatus. The research findings reveal the gas-solid coupling heat transfer characteristics in the low-temperature region of −180 ° C to 30 ° C , particularly the asymmetry during the CES and CER processes. The cold energy transfer mechanism within the CES unit is also uncovered, and the analysis of exergy destruction within various components is carried on. Through design parameter analysis and optimization of the MPB-LAES system, an impressive round-trip efficiency of 57.0% is achieved. This marks a significant breakthrough as it is the first report that a LAES system based on solid-phase CES has attained a round-trip efficiency (RTE) of over 55.0% while considering the actual heat transfer processes. • The LAES system utilizing moving packed beds is proposed. • The gas-solid coupling heat transfer model is established and verified. • The cold energy transfer mechanism in the CES is uncovered. • Irreversible analyses are performed in the CES and CER processes. • An RTE of 57.0% is achieved considering actual heat transfer for the first time. [ABSTRACT FROM AUTHOR]

The efficiency of asynchronous motor is higher near the rated working point, but it will decrease significantly under light load. A hybrid search method is proposed to optimize the efficiency of asynchronous motor drive by current source at the light load operating condition. The approximate optimal flux is obtained according to the loss model method and the convergence speed is determined by the golden section method. Hybrid optimization control method has the advantages of fast response and global optimization of efficiency without relying on motor parameters. It not only shortens the search time but also effectively reduces the system loss. The control system stability is higher and the optimization performance has been significantly improved. The simulation results show that the hybrid search method has the advantages of fast optimization speed and good robustness. Especially under the condition of light load, the motor efficiency can be obviously improved.