Effect Of Load Resistance Research Articles

Prediction of the effect of load resistance and heat input on the performance of thermoelectric generator using numerical and artificial neural network models

The load resistance in the thermoelectric generators (TEGs) is crucial for optimizing power output, and managing load resistances and operating conditions are integral elements of TEG system design. In this context, it is very important to predict the performance of TEGs at variable operating conditions. This research addresses an important problem in TEG by predicting the effects of load resistance and heat input on performance using both numerical and ANN models. The three-dimensional finite volume methods applied by employing ANSYS software, and the results were compared with experimental and ANN results in terms of voltage, current, power output and efficiency. In case of ambient temperature values of 17 °C, the average absolute errors of ANN and numerical model were calculated as 2.09 % and 4.22 % for voltage output, 0.79 % and 7.73 % for current output, 5.35 % and 12.09 % for power output, 4.14 % and 12.09 % for efficiency, respectively. As a result, it was observed that the ANN model gives better results compared to the numerical model. The highest power output was obtained at load resistance of 5.4 Ω and hot surface temperature of 150 °C, with the value of 0.827 W experimentally, 0.905 W numerically, and 0.824 W with ANN models. Besides, to evaluate the effect of ambient temperature, two additional temperatures (10 °C and 25 °C) were tested and it was found that decreasing the ambient temperature increased the TEG performance. The results showed that significant improvements on power and efficiency performance of the TEG can be achieved with optimised operating conditions.

Approximate analytical solutions of the 1:3 internal resonance response of piezoelectric energy harvester considering two types of coupled frequency components

The 1:3 internal resonance effect in the L-shaped piezoelectric vibration energy harvester leads to an expanded frequency band for energy harvesting and better matching of external excitation frequency in the environment. The electromechanical-coupled governing equations for this vibration energy harvester have been validated in our previous work (Nie et al., 2019). The effect of load resistance on the energy harvester’s natural frequency and damping ratio is addressed. The quadratic and cubic nonlinearities in this system leads to two types of coupled frequency components appear, they ultimately affect the approximate solution of the voltage response. The method of multiple scales is used to derive the two types of coupled frequency components of the system along with their contribution to the output responses. The revised approximate analytical solutions of the output responses are then presented. The system’s stability is assessed through the Jacobi matrix of modulation equations. The nonlinear softening phenomenon that favors the broadening of the bandwidth of the energy harvester is analyzed. The vibration patterns in regions with nonlinear softening and non-softening behavior are investigated through frequency spectra, phase trajectories, and Poincaré cross-sections. The findings reveal that the load resistance significantly affects the damping ratio of the harvester. Inclusion of quadratic and cubic nonlinearities results in three frequency components in the output responses spectrum, with an approximate ratio of 1:2:3. Two types of coupled frequency components appeared in the spectrum of the system’s output responses. The contribution of coupled frequency components to the output response proves crucial, and the revised approximate solutions are in good agreement with that of numerical solutions. The output responses are significantly affected by the initial conditions in the nonlinear softening region, the large and small initial conditions yield solutions in the upper and lower branches, respectively.

A new one-dimensional model of free-piston Stirling engine based on quasi-steady flow approximation and simi-implicit numerical method

Free-piston Stirling engine is a widely used device for thermal-to-electric conversion especially in aerospace applications. A dynamic model for free-piston Stirling engine is established in this paper for the purpose of modeling the free-piston Stirling engine more accurately and understanding its operation characteristics. This paper proposes a new one-dimension numerical model with quasi-steady flow approximation for free-piston Stirling engine with linear alternator, which can be categorized as third-order theoretical model for Stirling engine. The corresponding simi-implicit discretizationmethod is presented. In order to accurately obtain the thermal efficiency of the Stirling machine, various energy loss mechanisms are taken into consideration. A beta type free-piston Stirling engine, Component Test Power Convertor, is studied to demonstrate the correctness and accuracy of the numerical model established in this paper. The dynamic steady-state anticipated operation condition is simulated first. Then, the sensitivity analysis is carried out in which the effect of load resistance, heater temperature and cooler temperature, and charged pressure on the system operation parameter is studied. The predicted system parameters including frequency, displacer and piston amplitude, output power, and alternator output voltage and current agrees well with the designed value. Under the dynamic steady operation condition, the simulated indicated power is 15.51 kW and the electric power is 13.12 kW. The relative deviation between the predicted electric power and the measured output electric power of 12.78 kW is 2.66 %. The corresponding indicated efficiency and thermal-to-electric efficiency is 25.06 % and 21.20 % respectively. The amplitude of displacer and piston is 13.96 mm and 13.69 mm for this condition. Compared with the experimental data at different piston amplitude, the derivation of predicted engine parameters is within 10 %. The comparison with experimental results proves the accuracy of the proposed model in this paper. Compared with the previous model based on the adiabatic thermodynamic model, the third-order model presented in this paper shows higher accuracy on system parameter prediction for free-piston Stirling engine.

A comprehensive comparison of micro heterojunction thermoelectric generators based on a carrier transport model

To be a crucial aspect in the performance of thermoelectric generators, carrier transport in thermoelectric materials cannot be captured by existing multiphysics models. In this work, a carrier transport model for heterojunction thermoelectric generators (TEG) is developed with the drift-diffusion equation comprehensively considering the effect of carrier mobility on the current density. Subsequently, based on the concept of inverse- and homo-heterojunction, three micro TEG are designed considering Si and Si0.7Ge0.3 bases with the doped boron and arsenic and compared with the original design for revealing the effects of load resistance and temperature difference on the thermoelectric performance. It has been demonstrated that for homo-heterojunction, the thermoelectric power and conversion efficiency are significantly improved at hot temperatures from 600 to 1000 K, with a maximum improvement of 18.09% compared to the conventional TEG. For inverse-heterojunction, the optimal temperature of the thermoelectric performance is 1100–1300 K, and its efficiency is 23.50% higher than that of the conventional TEG. Both the doping impurity ionization and intrinsic carrier excitation contribute to a high density of majority carriers and are responsible for the better performance of homo-heterojunction at low working temperatures. For inverse-heterojunction, a high working temperature can significantly promote the excitation of minority carriers because of the built-in electric field and leads to better performance. Finally, we propose a novel heterojunction by combining both homo- and inverse-heterojunction which can improve thermoelectric efficiency by up to 27.72%.

Nonlinear 1:2 internal resonance response of L-shaped piezoelectric energy harvester under the influence of electrical damping

The internal resonance mechanism is widely used to improve the output performance of vibration energy harvester owing to its modal interaction between modes. The electromechanical-coupled theoretical model has been verified by experiments in our previous work (Nie et al., 2019). The approximate analytical solutions of the electromechanical-coupled governing equations of the harvester are derived using the method of multiple scales, and verified by the numerical method. The equilibrium stability of the output responses are determined by the eigenvalues of Jacobian matrix of the modulation equations. The effects of load resistance on electrical damping, natural frequency and primary resonance responses of the harvester are investigated. The results show that the harvested power is associated with the electrical damping caused by the load resistance. The threshold of the excitation amplitude that triggers the internal resonance from the perspective of load resistance are investigated. Under the influence of load resistance and excitation amplitude, the saturation phenomenon, jumping phenomenon, softening phenomenon, Hopf bifurcation and saddle–node bifurcation are explored. The results indicate that the internal resonance responses of the harvester vary with the excitation amplitude and load resistance, and jump between the upper and lower branches depending on initial displacement.

Effect of resistive load characteristics on the performance of Organic Rankine cycle (ORC)

The effects of various organic Rankine cycle (ORC) components, such as evaporator, expander and condenser on the performance of the system have been extensively studied. However, only a handful of studies have focused on studying the influence of external load characteristics. A small-scale ORC test rig of 3 kWe was constructed to experimentally investigate the effect of resistive load on the performance of the system. In order to achieve this, the study combined the thermodynamic method with electrical analysis. The results showed that the increase in output power caused a simultaneous increase in rotational speed, torque and inlet pressure of the expander under constant load resistance conditions. However, the fluid mass flow rate only affected the expander's inlet pressure. The decrease in load resistance increased the expander's inlet pressure and torque, and reduced the superheating and rotational speed. The influences of load resistance on the isentropic efficiency and net efficiency were mainly thorough the expander's inlet pressure and superheating. The net efficiency also benefited from the ideal cycle efficiency due to that decreasing load resistance enlarged the enthalpy drop of expander. The effects of load resistance on performance parameters were restricted by the mass flow rate of the fluid.

Design and Investigation the Characteristics of the Components of a DC Regulated Power Supply Using Multisim 14.2 Simulator

In an ordinary (unregulated) power supply the voltage regulation is poor (i.e. the DC output voltage also changes due to variations in the input AC voltage). These variations in DC voltage may cause unreliable operation of electronic circuits; Therefore, regulated DC power supply is the only solution in such situations. In this paper, the V-I characteristics of a PN junction diode in both forward and reverse directions was investigated using Multisim 14.2, simulator and graphically discusses, the V-I characteristics of a Zener diode in both forward and reverse bias conditions and used it as voltage regulator was determined and discusses graphically, the effect of load resistance and filter capacitor on ripple factor of half wave was determined and discusses graphically, the effect of load resistance and filter capacitor on ripple factor full wave rectifiers was

The Effect of Load Resistance and Coupling Coefficient on the Operational Stability of a Transcutaneous Inductive Power Transfer System with Capacitive Tuning

The Effect of Load Resistance and Coupling Coefficient on the Operational Stability of a Transcutaneous Inductive Power Transfer System with Capacitive Tuning

Electromechanical Performance Analysis of the Hybrid Piezoelectric-Electromagnetic Energy Harvester under Rotary Magnetic Plucking Excitation

This paper presents an analysis of the hybrid piezoelectric-electromagnetic energy harvester (P-EMEH) driven by contactless rotary magnetic plucking. A lumped-parameter model of the hybrid P-EMEH is developed, and the model parameters are determined from the finite element analysis (FEA) method. A parametric study is conducted to investigate the effects of driving force parameters, load resistance, and electromechanical coupling strengths (EMCSs) on the maximal displacements and velocities, average power inputs and outputs, and energy efficiencies of the system for indicating the performance of the hybrid P-EMEH. The results show that the hybrid P-EMEH can obtain the improved power inputs by reducing the gyration radii of the rotary magnet and shortening the gaps between the two magnets. The structural vibrations can be strongly suppressed owing to the optimal piezoelectric power outputs, which can lead to the occurrence of valleys’ power of the electromagnetic element. At weak coupling, the hybrid P-EMEH can achieve higher power outputs than the single piezoelectric energy harvester (PEH) and the single electromagnetic energy harvester (EMEH). At strong coupling, the use of the PEH is more advantageous for energy harvesting due to wider power bandwidths at high dimensionless frequencies when compared with the hybrid P-EMEH. This work provides a fundamental understanding on the effect of load resistance and EMCSs on the dynamic and electrical characteristics of the magnetically plucked hybrid P-EMEH.

Stochastic resonance in a piecewise bistable energy harvesting model driven by harmonic excitation and additive Gaussian white noise

Strategies for the energy harvesting of low-frequency vibration modes such as sphygmus and human body motions are immature due to the rigorous resonance issue. Stochastic resonance seems to be an appropriate solution to the energy harvesting of low-frequency vibrations. This paper presented the mathematical model of piecewise bistable energy harvesters and solved numerically. Taking the piecewise slope into consideration, the Kramers rate and signal to noise ratio (SNR) of piecewise bistable systems were studied, and the effects of piecewise slope on dynamic output characteristics of piecewise bistable energy harvesters were analyzed. The effect of load resistance on the efficiency of energy harvesting of piecewise bistable energy harvesters compared with their counterparts is evaluated. Furthermore, the influences of ambient periodic excitation and additive noise on the energy harvesting performance of piecewise bistable energy harvesters were investigated. Additionally, the evaluation of piecewise bistable energy harvesters using the measured input signal was completed. The numerical simulations indicate that piecewise bistable energy harvesters with small piecewise slope make great contributions to the enhancement of SNR and energy harvesting; the increases in resonant amplitude of ambient periodic excitation or additive noise intensity cause the transition from monostable to bistable, and piecewise bistable systems with smaller piecewise slope have larger unsaturation for ambient energy harvesting. The maximum electric power can be achieved by using optimal load resistance which can be identified numerically. The evaluation of piecewise bistable energy harvesters by employing the measured input signal shows that piecewise bistable energy harvesters with small piecewise slope perform satisfactory under ultra-low frequency excitation.

Effects of Flexoelectricity and Surface Elasticity on the Nonlinear Magnetoelectric Coupling in Unsymmetric Composites

Flexoelectricity is the development of an electric field under an applied strain gradient. This effect is highly size-dependent and is significant at nanoscales. Unsymmetric magnetoelectric (ME) composites undergo bending deformations under a magnetic field that results in non-zero strain gradients. Hence, it is important to give due consideration to flexoelectricity, along with direct piezoelectricity in these composites. This article presents a finite-element model that predicts the static and dynamic behavior of ME nanobeams subjected to magnetic fields. The effect of material nonlinearity of the ferromagnetic phase and flexoelectricity in the ferroelectric phase on the ME coupling are determined, and the obtained results show agreement with the literature. It is found that flexoelectricity results in substantially higher static ME coefficients. However, the resonant ME response is weakened by flexoelectricity. The effect of surface elasticity on the ME coupling coefficient is also investigated by making use of the Gurtin–Murdoch theory. The surface effects are found to improve the ME coefficient at bending resonance, while its effect is trivial at static and axial resonant conditions. Furthermore, the effect of load resistance on the ME voltage and charge coefficients is determined. The results indicate clear changes in the trend between short-circuit and open-circuit conditions.

Electrical and mechanical analysis of a segmented solar thermoelectric generator under non-uniform heat flux

Optimization of segmented solar thermoelectric generator for power output enhancement has been well researched however, the mechanical reliability study of such devices is usually neglected. In addition, assumed heat flux distribution or uniform flux distribution from solar concentrators is usually used for solar thermoelectric generator however, this is not accurate. Therefore, this study presents a detailed three-dimensional numerical investigation on the effect of non-uniform and uniform heat flux on the electrical and mechanical performance of segmented and non-segmented solar thermoelectric generator. Flux distribution from a compound parabolic concentrator is obtained by ray tracing using Lighttools software and COMSOL 5.4 Multiphysics software is used to perform the numerical study based on finite element method. Thermal stress analysis in a full-scale solar thermoelectric generator is presented and the effects of load resistance, solar radiation and cold side temperature on performance of solar thermoelectric generator is analysed. Results show that the power output of the segmented solar thermoelectric generators in Case 3, Case 4 and Case 5 increased by 44.07%, 59.12% and 37.9% respectively compared to that of Case 1 (bismuth telluride non-segmented solar TEG) at 13000W/m2. Results from this study will provide valuable guidance for segmented and non-segmented solar thermoelectric generator design.

Dynamic stability and performance analysis of a galloping-based piezoelectric energy harvester for different order representations of the aerodynamic force

In the present work, a non-linear electromechanical distributed parameter model is proposed for galloping based piezoelectric energy harvester (GPEH) and the impact of different order polynomial representation of aerodynamic force coefficient on the dynamic behavior of the system is investigated. Both geometric and aerodynamic nonlinearity (till9thorder polynomial) is introduced in the proposed model. The derived model is universally valid for both series and parallel connection of piezoelectric bimorph patches. The dynamic responses of the system, for different order representations of aerodynamic force, are extensively studied and then compared with experimental results from the literature. It is shown that a minimum till 7th order polynomial should be chosen for representing the galloping force coefficient in order to get a good agreement with experimental results. It is also shown from the model that the overall efficiency of the system is highest near the onset of galloping speed and decreases with an increase in wind speed. Further, a parametric study is done to find the effect of load resistance on the dynamic behavior of the system. It is seen that the error between experimental and predicted power decreases with an increase in the order of polynomial at a particular value of load resistance. The present analysis based on the proposed model emphasizes the importance of representation of aerodynamic force coefficients and geometric nonlinearity in predicting the accurate response for GPEH.

Fabrication of silver-doped zinc oxide nanorods piezoelectric nanogenerator on cotton fabric to utilize and optimize the charging system

Textile-based piezoelectric nanogenerator generates electrical energy from human motion. Here a novel type of textile-based piezoelectric nanogenerator is reported which is fabricated using the growth of silver-doped zinc oxide on carton fabric. Along with the optical and structural characterization of silver-doped zinc oxide nanorods, the electrical characterization was also performed for silver-doped zinc oxide piezoelectric nanogenerator. The silver-doped zinc oxide piezoelectric nanogenerator was found to generate three times greater power compared to undoped zinc oxide piezoelectric nanogenerator. By applying external mechanical force of 3 kgf and 31 MΩ of load resistance, the silver-doped zinc oxide piezoelectric nanogenerator generated an output power density of 1.45 mW cm−2. The effect of load resistance and load capacitor was determined and optimum values were calculated. The maximum output power was observed at a load resistance of 31 MΩ. The silver-doped zinc oxide piezoelectric nanogenerator was utilized to charge load capacitors and found that maximum energy could be stored at optimum load capacitance of 22 nF in 600 s (1800 cycles). This research may provide the opportunity to design high-output textile-based nanogenerators for practical applications like powering portable devices and sensors.

The Effect of Load Resistance on uncontrolled Rectifier Performance

This paper presents the usefulness of the circuit simulator Multisim software moreover, the understanding the operation of full-wave single phase rectifier circuit with RC load and study the effect of the load resistance on the voltage, output current were discussed , the output power, the ripple factor and the total harmonic distortion ( THD). Simulation results are existing along with the theoretical analysis. It can obtain a power factor by simulated is unity, to be excellent results

Parametric Analysis and Experimental Verification of a Hybrid Vibration Energy Harvester Combining Piezoelectric and Electromagnetic Mechanisms

Considering coil inductance and the spatial distribution of the magnetic field, this paper developed an approximate distributed-parameter model of a hybrid energy harvester (HEH). The analytical solutions were compared with numerical solutions. The effects of load resistances, electromechanical coupling factors, mechanical damping ratio, coil parameters and size scale on performance were investigated. A meso-scale HEH prototype was fabricated, tested and compared with a stand-alone piezoelectric energy harvester (PEH) and a stand-alone electromagnetic energy harvester (EMEH). The peak output power is 2.93% and 142.18% higher than that of the stand-alone PEH and EMEH, respectively. Moreover, its bandwidth is 108%- and 122.7%-times that of the stand-alone PEH and EMEH, respectively. The experimental results agreed well with the theoretical values. It is indicated that the linearized electromagnetic coupling coefficient is more suitable for low-level excitation acceleration. Hybrid energy harvesting contributes to widening the frequency bandwidth and improving energy conversion efficiency. However, only when the piezoelectric coupling effect is weak or medium can the HEH generate more power than the single-mechanism energy harvester. Hybrid energy harvesting can improve output power even at the microelectromechanical systems (MEMS) scale. This study presents a more effective model for the performance evaluation and structure optimization of the HEH.

Closed-form solutions for forced vibrations of piezoelectric energy harvesters by means of Green’s functions

In this article, the closed-form solutions are obtained for the forced vibrations of cantilevered unimorph piezoelectric energy harvesters. A tip mass is attached at the free end, and the moment of its inertia to the fixed end is considered. Timoshenko beam assumptions are used to establish a coupled electromechanical model for the harvester. Two damping effects, transverse and rotational damping effects, are taken into account. Green’s function method and Laplace transform technique are used to solve the coupled electromechanical vibration system. The conventional case of a harmonic base excitation is considered, and numerical calculations are performed. The present model is validated by comparing its predictions with the existing data, the experimental results, and the finite element method solutions. The influences of shear deformation and rotational inertia on the predictions are discussed. The effect of load resistance on the electrical power is studied, and the optimal load resistances are obtained. Ultimately, the optimal schemes are proposed to improve electricity generation performance for the soft piezoelectric materials: PZT-5A/5H.

Asynchronous-Switching Map-Based Stability Effects of Circuit Parameters in Fixed Off-Time Controlled Buck Converter

Both constant on-time (COT) and fixed off-time (FOT) control techniques are suitable for various applications requiring fast transient response. However, the discrete-time model of COT controlled buck converter only has two switched borderlines, whereas that of FOT controlled buck converter has four switched borderlines. Based on the derivations of these borderlines, an asynchronous-switching map of FOT controlled buck converter is established. With the decrease of equivalent series resistance (ESR) of output capacitor, instability and mode shifting from continuous conduction mode (CCM) to discontinuous conduction mode (DCM) are discussed. Furthermore, with small ESR of output capacitor, stability effects of load resistance and inductance on dynamical behaviors are investigated, and the approximate stability criteria and the corresponding normalized critical conditions are obtained. The theoretical analyses and experimental results show that the converter operates in DCM chaos via period-doubling and border-collision bifurcation routes, and its instability caused by small ESR can be removed by choosing appropriate load resistance, inductance, and voltage transfer ratio, which are very suitable for the circuit design of FOT controlled buck converter.

A conceptual study on the dynamics of a piezoelectric MEMS (Micro Electro Mechanical System) energy harvester

The mechanical behavior of a bimorph piezoelectric micro cantilever exposed to harmonic base excitation is investigated. The governing motion equation coupled with the equation of the output electrical circuit is discretized using Galerkin method and numerically integrated over the time. Two different types of output circuits including parallel and series connections are examined and the most effective output circuit from the power delivery point of view on the domain of the governing parameters is introduced. The energy conservation is examined by comparing the input and harvested energies. It is concluded that the energy harvesting in the absence of mechanical damping resembles the behavior of a damped mechanical oscillator due to the exponential attenuation of the motion amplitude. It is shown that the output power in terms of the load resistance of the output circuit, exhibits Lorenzian behavior revealing the multi factorial dependency of the power on the governing parameters. The effect of load resistance and the effective piezoelectric stress constant on the equivalent damping ratio is investigated. Subjected to harmonic base excitation, the steady state voltage, current and power responses are presented. The results are presented for various piezoelectric materials and on the plane of load resistance and effective piezoelectric stress constant, the output power delivery as well as the equivalent non-dimensional damping coefficient is determined.

Modeling and Simulation of a Piezoelectric Vibration Energy Harvester

The paper presents a lumped parameter model of a vibration energy harvester consisting of a bimorph piezoelectric cantilever with end mass. Stress on the piezoelectric material which is primarily accountable for the generation of electrical energy in the harvester is obtained along the beam length in terms of the end mass displacement. The model is applicable for parallel as well as series connection of the piezoelectric layers, and used to obtain resonant frequency, displacement of end mass and generated voltage across resistive load. Effect of load resistance on the resonant frequency and generated power is studied, and the results are verified with the finite element analysis in COMSOL Multiphysics.