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In this section of Resonance, we invite readers to pose questions likely to be raised in a classroom situation. We may suggest strategies for dealing with them, or invite responses, or both. "Classroom" is equally a forum for raising broader issues and sharing personal experiences and viewpoints on matters related to teaching and learning science. Beyond the maximum power transfer theorem, we suggest a class of linear two-terminal circuits where impedance matching is the condition for maximum power transfer to a fixed load resistor. As such a discrete case, for a given total number of identical cells, impedance matching has been used to find the maximum load current (MLC) (hence, maximum load power) when all possible series-parallel combinations (SPCs) of cells are connected to a load resistor. When the impedance matching solution is located between two adjacent SPCs in the ordered list of SPCs, a simple selection rule for determining which of the two combinations gives the MLC without directly calculating and comparing their load currents is presented in this article. As a by-product, the spectrum of SPCs producing the MLC for a given total number of cells can be obtained as a function of the resistance ratio (internal resistance of the cell/load resistance). [ABSTRACT FROM AUTHOR]

Objective: Maximum power extraction from piezoelectric energy harvesters is of key importance in the development ofvarious current technologies. However, direct use of the maximum power transfer theorem on this type of energy harvesterproduces unstable and non-causal load models, which prevent its synthesis through a power electronic circuit and reducethe power available for the application’s specific hardware. This article presents the computation of a causal and stabletransfer function that approximates the maximum power extraction load of a linear piezoelectric harvester. Methodology: Such a model is obtained using the Particle Swarm Optimization (PSO) algorithm, selected due to the sim-plicity of its implementation. In this study, a variation of the original algorithm is used to include the stability constraints. Results: The algorithm was employed to obtain 7th, 8th, 16th, and 20th-degree models to evaluate the impact of modelcomplexity on the obtained objective function values. The minimum cumulative square error resulted in an objective function value of approximately6·10−7Ω−2, attained by the 7th-degree model. Conclusions: A stable and causal system model was obtained through a PSO implementation. Results suggest a low de-pendence of the minimum objective function value on increasing model degrees. Nevertheless, the best model matchedthe degree of the admittance transfer function. Finally, the implementation of the unconstrained PSO algorithm obtained better results, suggesting that a different optimization algorithm can attain better results. Financing: This study was funded by the Corporación Nacional de Educación Superior CUN

In this research, a modified fractional order proportional integral derivate (FOPID) control method is proposed for the photovoltaic (PV) and thermoelectric generator (TEG) combined hybrid renewable energy system. The faster tracking and steady-state output are aimed at the suggested maximum power point tracking (MPPT) control technique. The derivative order number (µ) value in the improved FOPID (also known as PIλDµ) control structure will be dynamically updated utilizing the value of change in PV array voltage output. During the transient, the value of µ is changeable; it's one at the start and after reaching the maximum power point (MPP), allowing for strong tracking characteristics. TEG will use the freely available waste thermal energy created surrounding the PVarray for additional power generation, increasing the system's energy conversion efficiency. A high-gain DC-DC converter circuit is included in the system to maintain a high amplitude DC input voltage to the inverter circuit. The proposed approach's performance was investigated using an extensive MATLAB software simulation and validated by comparing findings with the perturbation and observation (P&O) type MPPT control method. The study results demonstrate that the FOPID controller-based MPPT control outperforms the P&O method in harvesting the maximum power achievable from the PV-TEG hybrid source. There is also a better control action and a faster response. [ABSTRACT FROM AUTHOR]

In this paper, a maximum power control and optimization of a 4-phase 8/6-pole Switched Reluctance Generator (SRG) are realized for a wind energy conversion system by using MATLAB/Simulink. Unlike conventional generators, using of the SRGs has increased in variable speed wind turbines due to important advantages such as lower copper losses, simple structure, flexible control, and a good performance in a wide speed range. However, since SRGs work with switching logic, their torque production is fluctuating and optimum turn-on/turn-off angles of the phases must be determined to work as a generator. Therefore, in this study, these angles are optimized based on the speed of the SRG and Maximum Power Point Tracking (MPPT) is realized. Besides, a voltage control is provided by keeping the DC bus voltage at the output of the system constant at the desired value with the help of a chopper controlled unloader. The results obtained from the optimized model for variable wind speed conditions are compared with that of the unoptimized model. It is observed that the SRGs can work more stable with a proper optimization method and the power obtained from the system follows the maximum output power. [ABSTRACT FROM AUTHOR]

In this paper, a new three-phase unbalanced distribution load flow (DLF) technique is proposed to study the impact of distributed generations (DGs) installed in the distribution networks in mitigating the voltage sag. Distributed generations are modeled as variable reactive power and constant power factor source with both wind- and solar-powered DG in the case study. The proposed DLF technique is based on the application of set theory. Effect of DGs in mitigating voltage sag is mathematically explained with the help of phasor diagram. The proposed technique is tested over standard IEEE 13 and IEEE 123 bus distribution networks with programming in MATLAB platform. To justify the claims, different cases have been studied like load increment and increasing maximum power limit of DGs. Also, a comparison is drawn between proposed DLF technique and traditional backward–forward sweep method where the efficacy of proposed technique is proved over the traditional method. [ABSTRACT FROM AUTHOR]

Predicting the power obtained at the output of the photovoltaic (PV) system is fundamental for the optimum use of the PV system. However, it varies at different times of the day depending on intermittent and nonlinear environmental conditions including solar irradiation, temperature and the wind speed, Shortterm power prediction is vital in PV systems to reconcile generation and demand in terms of the cost and capacity of the reserve. In this study, a Gaussian kernel based Support Vector Regression (SVR) prediction model using multiple input variables is proposed for estimating the maximum power obtained from using perturb observation method in the different irradiation and the different temperatures for a short-term in the DC-DC boost converter at the PV system. The performance of the kernel-based prediction model depends on the availability of a suitable kernel function that matches the learning objective, since an unsuitable kernel function or hyper parameter tuning results in significantly poor performance. In this study for the first time in the literature both maximum power is obtained at maximum power point and short-term maximum power estimation is made. While evaluating the performance of the suggested model, the PV power data simulated at variable irradiations and variable temperatures for one day in the PV system simulated in MATLAB were used. The maximum power obtained from the simulated system at maximum irradiance was 852.6 W. The accuracy and the performance evaluation of suggested forecasting model were identified utilizing the computing error statistics such as root mean square error (RMSE) and mean square error (MSE) values. MSE and RMSE rates which obtained were 4.5566 * 10-04 and 0.0213 using ANN model. MSE and RMSE rates which obtained were 13.0000 * 10-04 and 0.0362 using SWD-FFNN model. Using SVR model, 1.1548 * 10-05 MSE and 0.0034 RMSE rates were obtained. In the short-term maximum power prediction, SVR gave higher prediction performance according to ANN and SWD-FFNN. [ABSTRACT FROM AUTHOR]

The traditional method of operating photovoltaic (PV) systems on the right side of the maximum power point (MPP) may cause the voltage to be close to the open‐circuit voltage of the PV panel, resulting in a large oscillation of the PV power. In contrast, the change in dP/dU value of the curve on the left of the MPP is small, which is more conducive to adjusting the output power of the PV. A frequency regulation control strategy is proposed for a single‐stage PV power plant (PVPP), maintaining the PV string operating on the left side of the MPP. This paper proposes an optimal step‐size calculation method based on the flexible power tracking evaluation function. This calculation method is suitable for PV operating on the left side of the MPP and can improve the dynamic and steady‐state performance of the PV power tracking process. In addition, the system response is analyzed by establishing a small‐signal model with PV operating on the left side of the MPP. Finally, simulations and experiments verify the correctness and accuracy of the proposed primary frequency regulation strategy and step‐size calculation method. [ABSTRACT FROM AUTHOR]

The effectiveness of inductive power transfer (IPT) presents a serious challenge for improving the global recharge system performance. An electric vehicle (EVs) needs to be charged rapidly and have maximum power when it is charged with wireless technology. Based on various research, the performance of this recharge system is attached to several points and the frequency resonance is one of those parameters that can influence. In this paper, we try to explore the relationship between the obtained power and the signal input frequency for charging a lithium battery, solve the class imbalance problem and understand the maximum allowed frequency. To obtain the results, a mathematical model was first created to demonstrate the relationship, then the dynamic model was validated and tested using the Matlab Simulink platform. The performance of the worldwide wireless recharging system in terms of frequency variation is depicted in a summary graph. [ABSTRACT FROM AUTHOR]

The comparison between I-V (current-voltage) curves measured on site and I-V curves declared by the manufacturer allows to detect decrease of performance and control the degradation of photovoltaic modules and strings. On site, I-V curves are usually obtained under operating conditions (OPCs), i.e. at variable solar radiation and module temperature. OPC curves must be translated into standard test conditions (STCs), at a global irradiance of 1000 W/m2 and a module temperature of 25 °C. The correction at STC conditions allows to estimate the deviation between the power of the examined module and the maximum power declared by the manufacturer. A possible translation procedure requires two correction parameters: Rs', the internal series resistance, and k', the corresponding temperature coefficient. The aim of this work is to determine the correction parameters carrying out specific experimental tests as indicated by IEC 60891. A set of brand-new photovoltaic modules was experimentally characterized determining their I-V curves by means of an indoor solar flash test device based on a class A+ AM 1.5 solar simulator. Using the OPC I-V curves, obtained at several conditions of irradiance and temperature, it was possible to determine the correction parameters of the photovoltaic modules being considered. [ABSTRACT FROM AUTHOR]

We develop a framework to understand the performance of tandem organic photovoltaic (OPV) cells consisting of a series-connected stack of an arbitrary number of sub-cells. The power conversion efficiency penalty, Δη, is defined as the loss incurred when the tandem cell is at its maximum power point (MPP) but one or more sub-cells are not operating at their individual MPPs. To minimize Δη, the current at the MPP for each sub-cell must be equal. We also develop a method to calculate the tandem cell spectral mismatch factor and fill factor, showing that they are related to both the fill factors and short circuit currents of all the constituent sub-cells. By including the current generated in the dark, exciton dissociation at the donor-acceptor heterojunction, and photoconductivity, along with current losses due to polaron-pair and bimolecular recombination, we simulate the operation of small molecule bilayer and mixed-layer sub-cells used in the tandem, and from these results derive the behavior of the integrated device. This analysis is used to understand and optimize tandem OPV cell performance. [ABSTRACT FROM AUTHOR]

This study promotes a critical discussion about the phasor measurement unit (PMU)-based equivalent methods in order to investigate the impact of the Thévenin equivalent (TE) parameters on real-time power system voltage stability assessment. Although several articles indicate good performance at impedance magnitude matching theory, they neglect the influence of TE impedance angle and voltage source magnitude, introducing inaccuracies or mathematical inconsistencies in stability evaluation. The former three parameters are highlighted in this study due to being directly used to compute active power margins and indexes, according to the maximum power transfer theorem. The approach identifies the methods' robustness and weaknesses by the use of generic expressions. The main contribution of this study is presenting equations for directly calculating the parameters that may lead to inconsistent interpretations, particularly when measurement noise is considered. Disregarding these inconsistencies may result in an incorrect determination of the system's critical limit, increasing the risk of voltage instability. The conception of the new formulation relies on network equivalents based on the least-squares method, Tellegen's theorem and adaptive method. Following the simulations carried out in Nordic Test System, and 9, 14 and 39 Bus Test Cases available in MATPOWER, analyses substantiated in the derived expressions are given. [ABSTRACT FROM AUTHOR]

Under partial shading conditions, photovoltaic (PV) arrays exhibit multiple local maximum power points and a single global maximum power point in the P-V characteristics curves. Therefore, efficient global maximum power point tracking (GMPPT) control techniques are the prerequisite for improving the performance of the PV array under such situations. In the literature, various GMPPT techniques have been developed to track accurately the global maximum power point among different local maxima. The objective of this study is to provide a review on recent GMPPT techniques for users to select the most appropriate method based on application requirements and system specifications. The proposed work classifies and analyzes these new strategies that are used to maximize the output power of the photovoltaic system and presents the advantages and disadvantages of each method. In addition, it gives views on the use of each method, which helps to choose the most appropriate method according to the PV application. This work will serve as a useful reference for researchers working in the field. [ABSTRACT FROM AUTHOR]

This paper presents a novel maximum power point tracking (MPPT) method based on the grey wolf optimisation (GWO) technique for photovoltaic (PV) power generation systems. The proposed method utilises previous working duty cycles and their corresponding voltage and current data to compute the instantaneous DC impedance of a PV string. To determine the peak power characteristics of any PV string, the impedance variation of that PV string is used as an efficient shading factor. This shading factor simplifies the calculation of the GWO-MPPT algorithm to obtain multiple peak targets under partial shading conditions. Thus, the efficiency of the proposed power tracking technique can be improved considerably. The effectiveness of this method was validated through both simulation and hardware implementations. Results revealed that the search performance of five iterations of the proposed method was similar to that of ten iterations of a traditional GWO-MPPT method under normal conditions without shading. These results confirm the practicability of the proposed method in various applications. [ABSTRACT FROM AUTHOR]

Abstract Power delivered by a Photovoltaic (PV) cell reduces significantly due to non-uniform irradiance. Consequently, in the case of PV module or array, the generated output power get reduces and further deteriorates the overall system performance. The reduction of output power is not directly proportional to the shading area but depends on the shading pattern and type of array configuration chosen. Many solutions have been reported in the literature to reduce partial shadings. However, the reported solutions may fail to enhance maximum power to the possible extent. Therefore, to compensate these power losses a promising technique is required which relies on reconfiguration strategies, namely reconfigure the PV modules within the PV array in order to increase maximum power at a higher level. These strategies are classified into dynamic and static reconfiguration techniques. This paper presents the state of the art of reconfiguration strategies for PV array's to increase maximum power under partial shading and mismatch conditions. In addition to this, the challenging issues for hardware implementation of both dynamic and static reconfiguration techniques are discussed in this paper. Based on the review study, it can be concluded that the dynamic reconfiguration techniques are relatively expensive, but this can effectively compensate the partial shading and mismatch effects in PV array as compared to static technique. [ABSTRACT FROM AUTHOR]

Highlights • Considering renewable energy resources. • Proposing fuzzy logic controllers (FLC) to improve the MPPT in PV system. • Implementing fuzzy logic controller to improve the dynamic performance. • Reporting optimized using Firefly Algorithm (FA) to generate the proper duty cycle. Abstract P-V characteristic of the solar cells are nonlinear and depends on the environmental conditions such as irradiations, sunlight incident angle, cell temperature, and load conditions. Therefore it is crucial to operate the photovoltaic module at its maximum power point (MPP) all the time. Hence, a Maximum power point tracking (MPPT) methods are used to maximize the PV module output power by tracking continuously the MPP. In this paper, fuzzy logic controllers (FLC) are designed for maximum power point tracking (MPPT) in a photovoltaic system and then fuzzy membership functions of the fuzzy controller are optimized using Firefly Algorithm (FA) to generate the proper duty cycle. FA which is inspired by natural species to optimize nonlinear functions is one of the most successful and low-cost algorithms in this field. Finally, PV system with FLC-FA is compared with other methods like perturbation and observation (P&O) and fuzzy controller- Particle swarm optimization (PSO). According to the simulation results, asymmetric fuzzy membership functions based on FA increase tracking speed of MPPT and improve tracking accuracy compared to P&O, symmetric fuzzy membership functions and asymmetric fuzzy membership functions based on PSO. [ABSTRACT FROM AUTHOR]

This paper proposes a maximum power point tracking (MPPT) method with partial shading (PS) detection based on modified PI incremental conductance (IC) for photovoltaic inverters. To accurately trigger the algorithm, a PS detecting approach based on voltage deviation is derived through the comparison of voltage and current characteristics under uniform and non-uniform insolation. To track the global maximum power point (GMPP) precisely and fast, a global search scheme considering appropriate voltage reference, search direction and termination criteria is presented. The modified PI-based IC method is implemented in the local search process. In order to verify the effectiveness of the algorithm, the proposed method is utilised in the two-stage grid-connected photovoltaic inverters built in MATLAB/Simulink. The performance of the scheme is compared with the traditional IC method under step-changing and gradual-changing insolation and various temperature. In all simulation cases, the proposed approach can identify the PS with multiple local maxima, accurately trigger the global search process and track the GMPP. The search periods are around 0.1–0.2 s, and the efficiencies of PV generation under steady state are normally above 99.5%. The presented method can improve the efficiency of distributed and centralised PV system. [ABSTRACT FROM AUTHOR]

Existence PV generation mostly operates under the Maximum Power Point Tracking (MPPT) mode and has no ability to increase or decrease active power, accordingly, PV generation does not participate in grid frequency regulation. Due to an increasing penetration of grid-connected PV generation, when a frequency contingency event occurs, grid may have neither enough inertia response nor governor support and frequency deviation may have a risk of exceeding the limit. Therefore, a novel adapted de-loading control strategy without MPPT for grid-connected inverters is proposed here. This control strategy provides a reserve power in PV system to meet the frequency control demand and an online output Active Power-Voltage Matching (APVM) technique, which is generated as a control flowchart, is implemented in this control strategy to make it possible to adjust PV output voltage performance matching different active power demand with different operation modes. The proposed control strategy of PVs is simulated using PSCAD/EMTDC Software. Results verify the correctness and effectiveness of the proposed adapted de-loading control strategy under several operating conditions. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes a maximum power point tracking (MPPT) algorithm for the development of a three-phase induction motor angular speed drive. A Dc-to-Dc boost power converter, powered by photovoltaic (PV) panels, feeds the three-phase power inverter. The MPPT algorithm is based on the Exact Static Error Dynamics Passive Output Feedback Controller (ESEDPOF) technique together with an Algebraic Estimator of the impedance. The estimated value is the equivalent impedance that exists between the boost converter and the three-phase inverter, and then this value is used in real-time to generate the desired reference variables of the MPPT algorithm. The angular speed-tracking controller for the induction motor is based on the well-known Field-Oriented Control (FOC) technique. An Experimental set-up was developed using an array of two PV panels. Then, a realistic scenario is carried out, and real-time results at low-speed, with and without load, are presented in order to show the effectiveness and robustness of the proposed MPPT scheme. Under this scenario, the boost converter achieves an electric power efficiency of 80%, when a nominal load torque is applied to the induction motor shaft. Highlights • A MPPT for an induction motor speed-drive powered by PV-system is proposed. • The MPPT is based on the passivity based control and an algebraic estimator. • Experimental results show the effectiveness of the speed drive powered by PV array. [ABSTRACT FROM AUTHOR]

This study presents a single current sensor based hybrid maximum power point tracking method to track the global maximum power point (GMPP) of the photovoltaic (PV) array during the mismatch insolation conditions. This method combines the artificial bee colony (ABC) and hill climbing (HC) algorithms to track the GMPP of a PV array. The proposed method uses the HC algorithm to identify the occurrence of mismatch insolation conditions on PV array. During the mismatch insolation conditions, the proposed method scans the battery charging current (Icharge) versus duty cycle (D) characteristics of the power electronic interface circuit to classify the type of shading pattern of P-V curve and also to identify the vicinity of the GMPP. Based on the kind of shading pattern of a P-V curve, the proposed method operates either ABC or HC algorithm to track the GMPP. To improve the convergence speed of the proposed method, the search space of the ABC algorithm is reduced. The proposed method is modelled and simulated in MATLAB software and its performance is validated experimentally for various mismatch insolation conditions. [ABSTRACT FROM AUTHOR]

Highlights • Absorption layer plays a very important role in the performance of perovskite solar cells. • We calculated the defect state density and carrier mobility of the device under dark current. • The FAPbI 3 solar cells show superior performance compared to the MAPbI 3 -based devices. Abstract Absorption layer plays a very important role in the high efficiency and stability perovskite solar cells, there have been many reports that based on CH 3 NH 3 PbI 3 (MAPbI 3) and NH 2 CH NH 2 PbI 3 (FAPbI 3) perovskite solar cells, but the system compares the performance differences between MAPbI 3 -based and FAPbI 3 -based perovskite solar cells. The MAPbI 3 and FAPbI 3 perovskite solar cells are differences in topography, optical performance, the performance of solar cells, and device stability. It is particularly noteworthy that we calculated the defect state density and carrier mobility of the device under dark current. Through the construction of the solar cells, it has been found that the planar FAPbI 3 perovskite solar cells have better photoelectric conversion efficiency. The FAPbI 3 solar cells show superior performance compared to the MAPbI 3 -based devices, the power conversion efficiency of 16.38% and 18.61% was obtained with high short circuit current density of 21.11 and 23.18 mA/cm2. [ABSTRACT FROM AUTHOR]

Highlights • A comparative and comprehensive review of the PV MPPT techniques is provided. • MPPT techniques are divided into conventional, soft computing (AI and BI), and hybrid. • A novel evaluation index is introduced to rank the MPPT techniques. • Total evaluation from 40 points for the most famous 17 MPPT techniques is introduced. • Technical and economical comparisons of all MPPT techniques based on 17 key issues are provided. Abstract The partially shaded photovoltaic (PSPV) condition reduces the generated power and contributes in hot spot problem. PSPV generates one global peak (GP) and many local peaks (LP) in power versus voltage curve. In recent years, numerous research papers have been focused on highly efficient maximum power point tracking (MPPT) techniques to track the GP and alleviate the partial shading effects. This paper provides a comparative and comprehensive review of the 17 most famous and efficient MPPT techniques. These famous and efficient MPPT techniques are divided into three groups; conventional, soft computing (Artificial Intelligence and Bio-Inspired) and hybrid MPPT techniques. Technical and economical comparisons of these 17 MPPT techniques based on 17 evaluation parameters are then achieved. The findings obtained have not yet been discovered yet before where this is the first time the 17 most famous and efficient MPPT techniques are ranked using a novel evaluation index with a total evaluation from 40 points based on the 8 most important key issues. These issues are tracking speed, convergence speed, complexity, hardware implementation, initial parameters required, performance without PS, performance with PS, and efficiency. Finally, merits, demerits, technical and economical comparisons of all MPPT techniques are also introduced, discussed, and assessed. [ABSTRACT FROM AUTHOR]

Highlights • A new dual-mode maximum power point tracking algorithm is proposed. • It prevents the operating point from diverging during fast solar irradiation change. • Its implementation is simple and low cost. • It has been tested by simulations and experimentally. • The extracted energy and the efficiency of the system are increased. Abstract In this paper we present a new maximum power point tracking algorithm based on a modified Perturb and Observe (P&O) algorithm. The proposed algorithm is a dual mode one, the switching between the two modes is based on the value of the derivative of the power with respect to the voltage at the output of the solar panel, which must be null at the maximum power point. The first mode, a conventional P&O is active when the value of the derivative is smaller than a threshold, when its value surpasses the threshold, the second mode is activated, which prevents the voltage at the output of the solar panel to get far away from the maximum power point voltage ( V mpp ). The implementation of the proposed algorithm is very simple, similarly to the P&O, it needs just two sensors, one dedicated for the current and the second for the voltage. In comparison with the P&O, this algorithm has better performance without increasing the implementation cost. The proposed algorithm is tested by simulations using Simulink/Matlab™ to control a boost converter supplying a resistive load R. In order to further test the proposed algorithm, experimental results are presented to prove its effectiveness. The results are compared to those given by the P&O algorithm. Simulation and experimental results show that the proposed algorithm prevents the divergence of the operating point, and has a smaller response time which allows to extract more power and to decrease the losses on the adaptation stage of the solar energy system. [ABSTRACT FROM AUTHOR]

To reveal the general characteristic of the maximum power transfer points of magnetic coupling wireless power transfer (MC-WPT) systems, and to quickly and accurately determine all possible maximum power transfer points for arbitrary coil MC-WPT systems, a novel theoretical analysis method is proposed in this paper. Based on the modal theory, an accurate time-domain model of an n-coil MC-WPT system is established and the analytical current response on each coil is derived. According to the current response of the load, a detailed power spectrum distribution is presented, based on which the mathematic expressions of all possible maximum power transfer points, including the maximum output powers and corresponding operating frequencies, are deduced. The theoretical results are verified in experiment prototypes practically. The experimental results show that: 1) the output power reaches its maximum value at the modal frequencies rather than the designed natural frequency of the resonators in MC-WPT systems; 2) there are n modal frequencies of an n-coil MC-WPT system. The analysis results provide useful information to choose the operating frequency for practical MC-WPT systems with arbitrary number of coils. [ABSTRACT FROM AUTHOR]

In this paper, a high power, air suspended stripline (SSL) T junction power divider at L band microwave frequencies is introduced. The power divider operating frequency is centered at 1.3 GHz. In this new configuration, the only dielectric used is air to have maximum power handling capability. An excitation transition from coaxial cable to the SSL transmission line is explained. The SSL was fabricated using aluminum sheets to gain the advantage of low cost. The power divider design was validated using circuit and 3D full wave simulations and confirmed using experimental measurements with all agreements. It has been proved that the power divider attenuation has sharp rejection characteristic at the designed frequency (-20 dB at 1.3 GHz). The power divider can be used as a feeder for devices used in high power applications. [ABSTRACT FROM AUTHOR]

Wind energy has emerged as a dominant alternative power generation source. Conventional energy resources are depleting and their increasing cost cannot be ignored. Wind energy has taken an important role in replacing fossil fuels and nuclear energy. However, optimal exploitation of wind energy systems has remained a thought-provoking problem due to the nonlinear behavior of the wind speed. Distribution generation system and isolated micro-grid (MG) are mainly used in a wind energy system in order to utilize maximum potential of wind through the maximum power tracking algorithm based on DCDC boost power electronic converter. In this paper, authors propose a technique which is effectively workable, highly reliable, of low cost and induces less mechanical stress on the wind generator system (WGS). Experimental results of the proposed system verify that the effectiveness near optimal WGS output power increased approximately up to 50%. Thus, better exploitation of the available wind power is obtained under low wind speeds. [ABSTRACT FROM AUTHOR]

Maximum power point tracking (MPPT) control techniques play a vital role in efficiency improvement of photovoltaic (PV) systems. It is mainly used to extract maximum possible power of the PV modules under both variable climatic and partial shaded condition (PSC). From literature, various types of MPPT techniques have been developed to track the maximum power point efficiently, ranging from conventional methods to artificial intelligence and bio-inspired methods. Each technique has its own advantage and drawbacks. This paper focuses mainly on a review on advancements of global maximum power point tracking (GMPPT) techniques of photovoltaic (PV) system subjected to partial shading conditions (PSC) to help the users to make the right choice when designing their system. The most recent and selected MPPT methods are discussed and classified as optimization, hybrid, mathematical model based methods and other GMPPT methods. This study will serve as interesting guide for researchers working on PV system field. [ABSTRACT FROM AUTHOR]

A new feature for the core calculation of prismatic-block type of Very High Temperature Reactor (VHTR) was added to our in-house code NuCoT. The nodal method used was Hybrid Nodal Green’s Function Method (HNGFM). The conformal mapping method was adopted for handling the hexagonal geometry. The accuracy of the new capability was verified through several benchmark problems. Results of comparable accuracy with other developments were obtained. The method was further verified by performing a 2D simplified HTTR problem and compared with MCNP result. The statistical errors of k eff was <10 pcm and of fission power was <0.1%. The results of Hex-capability of NuCoT showed that using supercell method for cross section generation for homogenization of fuel block gave more accurate results than using single fuel block with periodic boundary condition. For the control rod block that contains three large void channels, using anisotropic diffusion coefficient resulted in more accurate k eff . In the all-rods-out condition and the partially-controlled condition, the difference in k eff was <140 pcm and in maximum power was <0.8%. In the all-rods-in condition, the error in k eff and maximum power error were 413 pcm and 1.1%, respectively. [ABSTRACT FROM AUTHOR]

Maximum power transfer occurs in many energy harvesters at their half open-circuit voltage ( $V_{{\rm{OC}}}/ 2$ ). A novel implementation method of maximum power point finding based on the $V_{{\rm{OC}}}/ 2$ method is presented by exploiting the capacitor charging voltage across a smoothing capacitor connected in parallel with the energy harvester. The presented technique has a specifically designed high-pass filter, which has a peak output voltage that corresponds to the $V_{{\rm{OC}}}/ 2$ of the energy harvester. The control circuit filters and differentiates the voltage across the smoothing capacitor to directly determine the timing of reaching the $V_{{\rm{OC}}}/ 2$ of the energy harvester without having to find the $V_{{\rm{OC}}}$ first and is fully implemented using discrete analog components without the need of a programmable controller, leading to low power consumption of the method. In this paper, the control circuit is used in conjunction with a full-wave diode bridge rectifier and a dc–dc converter to harvest energy from a piezoelectric energy harvester (PEH) as the studied case. The PEH was subjected to various strain levels at low frequencies from 2 to 10 Hz. Experimental results show that the implemented circuit is adaptive to various vibration amplitudes and frequencies and has a maximum power point finding efficiency of up to 98.28% with power consumption as low as 5.16 μW. [ABSTRACT FROM AUTHOR]

This paper presents a model-based method to diagnose single- and multiple-transistor open-circuit (OC) faults in grid-tied three-phase voltage-source inverters (VSIs). The method is based on calculated average bridge arm pole-to-pole (PTP) voltages and error-adaptive thresholds. Only existing signals for closed-loop control are needed; thus, this method can be easily embedded in the system without extra sampling and circuits. Average PTP voltage deviations are chosen as diagnosis variables, which show considerable distinction quickly after fault. Consequently, fast fault diagnosis speed can be achieved. The fault diagnosis time for single fault can be as short as two switching periods. Besides, diagnosis variables show the same faulty characteristics in inverter mode and rectifier mode; thus, this method is effective in both modes. Moreover, for the first time, the variation of inductance caused by conducted current is considered to obtain a more accurate variable-inductance model, and the thresholds are updated according to mathematically estimated diagnosis variable calculation errors from sampling error, inductance error, dead time, and delay time, which maintains high robustness as well as fast speed. Finally, the effectiveness of the proposed method is validated with experiments. [ABSTRACT FROM AUTHOR]

Direct current (dc) microgrids are highly compatible with photovoltaic (PV) sources due to their dc nature. However, as PV penetration increases, conventional current-source control configurations tracking the maximum power point may encounter the overvoltage problem, among others. This paper presents a $V$ – ${d}p/{d}v$ droop control strategy, which enables the PV sources to work in the maximum power point tracking (MPPT) mode, as well as behave as voltage sources to participate in dc-bus voltage regulating. The $V$ – ${d}p/{d}v$ droop method unifies MPPT and dc-bus voltage regulating in the sense of using the same control configuration, which avoids the controller reconfiguration during the PV mode switching. Further, the coordinated operation of multiple PV sources in the dc microgrid, including autonomous mode switching and primarily power sharing, is achieved by the proposed control strategy without any communication. Hardware-in-loop tests are presented to demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of adaptive power control based on outage probability minimization in Vehicular Ad Hoc Networks (VANETs), called a Power Control Algorithm Based on Outage Probability Awareness (PC-OPA). Unlike most of the existing works, our power control method aims at minimizing the outage probability and then is subject to the density of nodes in certain area. To fulfill power control, cumulative interference is assumed to be available at the transmitter of each terminal. The transmitters sent data by maximum power and then get the cumulative interference-aware outage probability. Furthermore, we build the interference model by stochastic geometric theory and then derive the expression between outage probability and cumulative interference. According to the expression, we adjust the transmitter power and optimize the outage probability. Simulation results are provided to demonstrate the effectiveness of the proposed power control strategies. It is shown that the PC-OPA can achieve a significant performance gain in terms of the outage probability and throughputs. Comparing MPC (Maximum Power Control algorithm) and WFPC (Water-Filled Power Control algorithm), the proposed PC-OPA decreased by 23% in terms of the outage probability and increased by 25% in terms of throughputs. [ABSTRACT FROM AUTHOR]

An overall synthesis of biology and non-equilibrium thermodynamics remains a challenge at the interface between the physical and life sciences. Herein, theorems from finite-time and control thermodynamics are applied to biological processes to indicate which biological strategies will succeed over different time scales. In general, living systems maximize power at the expense of efficiency during the early stages of their development while proceeding at slower rates to maximize efficiency over longer time scales. The exact combination of yield and power depends upon the constraints on the system, the degrees of freedom in question, and the time scales of the processes. It is emphasized that biological processes are not driven by entropy production but, rather, by informed exergy flow. The entropy production is the generalized friction that is minimized insofar as the constraints allow. Theorems concerning thermodynamic path length and entropy production show that there is a direct tradeoff between the efficiency of a process and the process rate. To quantify this tradeoff, the concepts of compensated heat and waste heat are introduced. Compensated heat is the exergy dissipated, which is necessary for a process to satisfy constraints. Conversely, waste heat is exergy that is dissipated as heat, but does not provide a compensatory increase in rate or other improvement. We hypothesize that it is waste heat that is minimized through natural selection. This can be seen in the strategies employed at several temporal and spatial scales, including organismal development, ecological succession, and long-term evolution. Better understanding the roles of compensated heat and waste heat in biological processes will provide novel insight into the underlying thermodynamic mechanisms involved in metabolism, ecology, and evolution. [ABSTRACT FROM AUTHOR]

This paper proposes a novel maximum power point tracking scheme for efficient and speedy extraction of maximum power from a pressure retarded osmosis process subject to rapid salinity variation. The scheme is designed using the Whale Optimization with Differential Evolution algorithm, a nature-inspired metaheuristic technique. The algorithm has facilitated the developed maximum power point tracking controller with features that have helped overcome limitations such as lower tracking efficiency and steady state oscillations as encountered in the conventional methods. Previously, a number of widely used algorithms including perturb & observe, incremental mass resistance and mass feedback controller were used to design maximum power point control schemes for a PRO process to reduce power loss due to rapid salinity variation. However, in using these techniques, a trade-off between the oscillations and the respond time was required to adjust the operation. The proposed scheme is used to solve this problem and is implemented in simulation on a scaled-up PRO system. The performance of the scheme is compared with some popularly used maximum power point tracking controllers. It is observed from results that the proposed method not only outperforms other widely used methods but is also more robust. [ABSTRACT FROM AUTHOR]

This paper presents a new output power smoothing control strategy for a wind farm based on the allocation of wind turbines. The wind turbines in the wind farm are divided into control wind turbines (CWT) and power wind turbines (PWT), separately. The PWTs are expected to output as much power as possible and a maximum power point tracking (MPPT) control strategy combining the rotor inertia based power smoothing method is adopted. The CWTs are in charge of the output power smoothing for the whole wind farm by giving the calculated appropriate power. The battery energy storage system (BESS) with small capacity is installed to be the support and its charge and discharge times are greatly reduced comparing with the traditional ESSs based power smoothing strategies. The simulation model of the permanent magnet synchronous generators (PMSG) based wind farm by considering the wake effect is built in Matlab/Simulink to test the proposed power smoothing method. Three different working modes of the wind farm are given in the simulation and the simulation results verify the effectiveness of the proposed power smoothing control strategy. [ABSTRACT FROM AUTHOR]

This brief presents an interface design for electromagnetic energy harvesting for wearable applications. A transducer design is proposed. Multiple segments of coils with alternating winding directions improve the induced voltage and power. Due to the source’s wideband nature in target applications, we avoid the use of springs common in conventional designs. The corresponding equivalent circuit model is presented. A system-level analysis is then performed that leads to the following power interface circuit design. It includes a differential rectifier and a switched-inductor boost converter. The harvested power is maximized with a constant-resistance load that can be adjusted through a variable-gain amplifier’s gain. Implemented in a 0.18-\mu \textm CMOS process and tested at 20 Hz, measurement results show >80% impedance matching efficiency with >0.7-V input voltages. The system is able to harvest \sim 320~\mu \textW when shaken by hand at 2.5~3 Hz. [ABSTRACT FROM PUBLISHER]

This paper presents a novel fuzzy control design method for maximum power-point tracking (MPPT) via a Takagi and Sugeno (TS) fuzzy model-based approach. A knowledge-dynamic model of the PV system is first developed leading to a TS representation by a simple convex polytopic transformation. Then, based on this exact fuzzy representation, a H∞ observer-based fuzzy controller is proposed to achieve MPPT even when we consider varying climatic conditions. A specified TS reference model is designed to generate the optimum trajectory which must be tracked to ensure maximum power operation. The controller and observer gains are obtained in a one-step procedure by solving a set of linear matrix inequalities (LMIs). The proposed method has been compared with some classical MPPT techniques taking into account convergence speed and tracking accuracy. Finally, various simulation and experimental tests have been carried out to illustrate the effectiveness of the proposed TS fuzzy MPPT strategy. [ABSTRACT FROM AUTHOR]

With the arrival of global industrialization, the energy shortage becomes increasingly probable and severe. Solar energy as a renewable resource begins to catch the attention of human. As a result, the photovoltaic power generation becomes to be more and more important. The proposed in this paper Maximum Power Point Tracking (MPPT) algorithm can effectively improve the utilization rate of solar energy in the process of photovoltaic power generation. This study describes an improved MPPT algorithm. It presents a predictive control made on the original basis and establishes a stimulation model using the Matlab/Simulink model for experiment. The performed experiment suggests that the improved algorithm can enhance the tracking efficiency of MPPT control and the utilization rate of solar energy, which is of a great significance for the promotion of photovoltaic systems. [ABSTRACT FROM AUTHOR]

This paper deals with the study on 233 Wp HIT PV module characteristics that defines its performance and operation. The chosen HIT PV module is exposed to outdoor conditions at Saida City of Algeria. The module is tested in high irradiance and low irradiance situations that were recorded over a specific year. Based on the monitored data in these two situations, its performance characteristics were evaluated and compared with standard test condition parameters. From the results it is observed that, irradiance variation effects the HIT PV module characteristics. The variation in maximum power extracted, efficiency, and fill factor were observed. Apart from this weather parameters like ambient temperature, module temperature, wind speed, and relative humidity had also influenced the performance characteristics of HIT PV module. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the energy efficiency (EE) for K -user multiple-input multiple-output (MIMO) interference channels with simultaneous wireless information and power transfer (SWIPT) and interference alignment (IA). Specifically, power splitting architecture is leveraged at each receiver for information decoding (ID) and energy harvesting simultaneously. Taking the quality of service (Qos) requirement and harvested power constraints into consideration, we maximize the system EE by jointly designing transmit beamformers, transmit power, power splitters and receive filters. To solve the nonconvex EE optimization problem, we first eliminate the interference among users for ID via the maximal signal to interference plus noise ratio (Max-SINR) IA method, which yields a two-dimensional EE optimization problem. And then, we propose an EE-Max algorithm coupled with the Max-SINR, nonlinear fraction programming and one dimension searching to solve the reformulated problem. Simulation results show the effectiveness of the proposed EE optimization algorithm and reveal the influence of the maximum transmit power constraint and the QoS requirement on the system EE. [ABSTRACT FROM AUTHOR]

The Power-Voltage characteristic of a photovoltaic (PV) array exhibits non-linear behaviour when exposed to uniform solar irradiance. Maximum Power Point (MPP) tracking is challenging due to the varying climatic conditions in a solar PV system. Moreover, the tracking algorithm becomes more complicated due to the presence of multiple peaks in the power voltage characteristics under the condition of partial shading. This research is devoted to the Stochastic Beam Search (SBS) based algorithm and Stochastic Hill Climbing (SHC) for a maximum power point tracking (MPPT) at a partial shading condition in the PV system. To give a partial shading effect over the entire array of a PV system, a mast is placed in front of the modules. The modules in the array are connected in such a way that one does not need to rewire the electrical connection during the rearrangement of modules. It is validated that the power generation performance of an array under a moving shading condition is increased. Furthermore, it is observed that the SHC method outperforms the SBS method in the MMP tracking. [ABSTRACT FROM AUTHOR]

For modern horizontal axis wind turbines (WTs), a yaw drive mechanism is utilized to adjust the nacelle position to face the wind direction. Depending on historical signals from wind direction sensors, conventional yaw control methods could not provide sufficient performance in tracking winds, and thus result in a reduction of wind power extraction. This issue needs to be tackled using advanced control solutions. Taking advantage of predicted wind directions, a novel control solution is proposed in this study. Specifically, the proposed solution refers to a novel control structure that consists of a wind direction predictive model and a novel yaw control method. Under the proposed control structure, a hybrid autoregressive integrated moving average method-based Kalman filter (ARIMA-KF) model is used to predict the wind direction, and two novel yaw control methods are proposed: one created by using the predicted wind direction as the tracking reference, and the other based on a model predictive control (MPC) using a finite control set. To demonstrate the feasibility and the superiority of the proposed solution, two novel yaw controllers are developed and tested through some simulation tests using industrial data. Their performance is compared to the one of two industrial yaw controllers. Comparison results show that the two novel yaw controllers are capable of reducing yaw error, and thus increase wind power extraction for the WTs. Meanwhile, it is noticeable that the MPC-based controller has an advantage in the aspect of reducing yaw actuator usage. [ABSTRACT FROM AUTHOR]

Maximum power extraction for PV systems with multiple panels under partial shading conditions (PSCs) relies on the configuration of the system and the optimal searching algorithms used. This paper described a PV system with multiple PV panels in series. Each panel has a dc-dc step-down converter, hence allowing independent control of load and source power ratio corresponding to the irradiation levels. An H-bridge terminal inverter is also used for grid connection. An advanced searching algorithm (TSPSOEM) is proposed in the paper for the distributed maximum power point tracking (DMPPT). This applies the basic particle swarm optimization (PSO) procedure but with an extended memory and incorporating the grouping concept from shuffled frog leaping algorithm (SFLA). The new algorithm is applied simultaneously to all PV-converter modules in the chain. The system can exploit the variable converter ratios and reduces the effect of differential shading, both between panels and across panels. The paper presents the system and the proposed new algorithm and demonstrating superior results obtained when compared with other conventional methods. [ABSTRACT FROM AUTHOR]

As a prevailing solar energy utilization equipment, the three-phase grid-connected photovoltaic (PV) inverter is widely operated in partially shaded conditions and thus tends to generate multiple local maximum power points on its power-to-voltage and current-to-voltage characteristic curves. In order to identify the global maximum power point (GMPP) quickly and precisely, this paper proposes a ripple-based maximum power point tracking method. It aims to perform the optimization of tracking using the segmented scanning of DC-side voltage. An improved adaptive perturb and observe (AP&O) method is introduced to maximize the solar conversion and to increase working stability. This method applies a hybrid model of fixed and variable step-size perturbation to restrain the fluctuation of PV-side voltage. It belongs to a two-stage GMPP tracking method. That is, when environmental factors such as irradiance and temperature change quickly PV power fluctuates sharply. Correspondingly, the AP&O method tracks the latest maximum power point (MPP) with a large fixed-step voltage reference command. When the PV power fluctuates smoothly under a slow environmental change rate, the algorithm applies multiple small and variable step-size voltage perturbations to vibrate round the location of GMPP. Simulation and experimental results show that this method improves the efficiency of the PV inverter tracking performance. In addition, the stability of DC bus voltage is guaranteed, and the operational stability of the photovoltaic power generation system is improved. [ABSTRACT FROM AUTHOR]

In this paper, a new approach for photovoltaic (PV) arrays modeling and maximum power point estimation (MPPE) in real operating conditions is presented. The PV array polynomial model is developed from its single-diode equivalent circuit, and the parameters of the proposed model are estimated by measuring the voltage and current of three points around the maximum power point (MPP). The maximum power point voltage (MPPV) is then calculated from the proposed model, and the PV array voltage is fixed at MPPV. Therefore, unlike the maximum power point tracking (MPPT) algorithms, there is no oscillation around the MPP. Using the PV array polynomial model with only three measurements around the operating point, results in less calculation burden, increases the estimation speed and decreases the I–V curve estimation process loss. In order to validate the proposed MPPE algorithm, we have compared it with the most commonly used perturb and observe (P&O) MPPT algorithm, a zero oscillation adaptive P&O technique, and a fast MPPT method by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Maximum power transfer tracking (MPTT) is meant to track the maximum power point during the system operation of wireless power transfer (WPT) systems. Traditionally, MPTT is achieved by impedance matching at the secondary side when the load resistance is varied. However, due to a loosely coupling characteristic, the variation of coupling coefficient will certainly affect the performance of impedance matching, therefore MPTT will fail accordingly. This paper presents an identification method of coupling coefficient for MPTT in WPT systems. Especially, the two-value issue during the identification is considered. The identification approach is easy to implement because it does not require additional circuit. Furthermore, MPTT is easy to realize because only two easily measured DC parameters are needed. The detailed identification procedure corresponding to the two-value issue and the maximum power transfer tracking process are presented, and both the simulation analysis and experimental results verified the identification method and MPTT. [ABSTRACT FROM AUTHOR]

Grid connected PV systems are becoming increasingly popular due to an exponential energy demand and also due to depletion of fossil fuels and environmental concerns. However, extraction of peak power for such system which reduce cost has always been an area of concern. Many Maximum power point tracking (MPPT) algorithms were proposed for a two stage and single stage grid connected system with some limitations in system performance. A simple strategy to extract peak power from the grid connected PV with nonlinear load at Point of common coupling (PCC) is attempted. To achieve the same task in a single stage Photovoltaic (PV) grid system, two PV emulated virtual DC voltage sources are connected in series with the PV array. The operation of this strategy is tested under low irradiation and Voltage swell at the PCC connected to the grid. A control strategy to achieve dual mode control for MPPT and to regulate DC link voltage is achieved simultaneously by the proposed control. Analysis of the control strategy is carried out using MATLAB and experimentally validated with a TMS320F28335 controller. [ABSTRACT FROM AUTHOR]

An axisymmetric Reynolds averaged Navier-Stokes solver is used along with an actuator disk model for the analysis of shrouded wind turbine flowfields. Following this, an efficient blade design technique that maximizes sectional power production is developed. These two techniques are incorporated into an optimization framework that seeks to design the geometry of the shroud and rotor to extract maximum power under thrust constraints. The optimal solution is also evaluated using a full three-dimensional Reynolds averaged Navier-Stokes solver, suggesting the viability of the design. The predicted optimal designs yield power augmentations well in excess of the Betz limit, even if the normalization of the power coefficient is performed with respect to the maximum shroud area. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of reactive support by Wind Farms (WF) on the maximum power transfer, and thus the voltage stability limit of a transmission system. An insecure snapshot in a weak area of the Hellenic Interconnected System is examined, as well as a simpler test system. MV feeder characteristics and substation controls (feeder resistance and reactance, switched capacitors, LTC controls) are modelled in detail. Most importantly, the converter current limits, as well as the overvoltage limitations on the MV feeder, are taken into consideration in assessing the effect of the WF support. [ABSTRACT FROM AUTHOR]

The problem of determining the optimal loads for realizing maximum power transfer in a wireless energy link between one transmitter and multiple receivers has been considered and solved by applying the maximum power transfer theorem for an $N$ -port. Simple analytical expressions for the load impedances have been derived and validated through experiments and circuital simulations. These expressions are also valid in the case of mutual coupling between receivers. [ABSTRACT FROM PUBLISHER]

Wireless power transfer using a magnetic field through inductive coupling is steadily entering the market in a broad range of applications. However, for certain applications, capacitive wireless power transfer using electric coupling might be preferable. In order to obtain a maximum power transfer efficiency, an optimal compensation network must be designed at the input and output ports of the capacitive wireless link. In this work, the conjugate image theory is applied to determine this optimal network as a function of the characteristics of the capacitive wireless link, as well for the series as for the parallel topology. The results are compared with the inductive power transfer system. Introduction of a new concept, the coupling function, enables the description of the compensation network of both an inductive and a capacitive system in two elegant equations, valid for the series and the parallel topology. This approach allows better understanding of the fundamentals of the wireless power transfer link, necessary for the design of an efficient system. [ABSTRACT FROM AUTHOR]