One-dimensional modeling of TE devices considering temperature-dependent parameters using SPICE

Based on simplified one-dimensional steady-state analysis of thermoelectric phenomena and on analogies between thermal and electrical domains, we propose both lumped and distributed parameter electrical models for thermoelectric devices. A couple of important advantages of the presented models are that the temperature dependence of material properties is considered and that they can be easily simulated using an electronic simulation tool such as SPICE. For a single free-standing pellet, comparisons are made between SPICE simulations using the proposed models and with numerical simulations carried out with Mathematica software. Results illustrate accuracy of the distributed parameter models and show how inappropriate it is to assume, in some cases, constant material parameters for an entire thermoelectric element.     

New Physical Model for Thermoelectric Generators

In this paper we describe a new analytical physical model for thermoelectric generators (TEGs). The model includes the Thomson effect, the Peltier heat, a parameterization of the Joule heat, as well as all thermal and electrical resistances. Geometry optimization and investigations of the influence of Peltier heat and the heat source, as well as heat sink conditions and the load resistance, which affect the output power, are presented. The results are compared with measurements of commercially available thermoelectric generators and the fundamental thermodynamic limit. A comparison between the generators is performed.     

Thermoelectric Generators for Automotive Waste Heat Recovery Systems Part I: Numerical Modeling and Baseline Model Analysis

A numerical model has been developed to simulate coupled thermal and electrical energy transfer processes in a thermoelectric generator (TEG) designed for automotive waste heat recovery systems. This model is capable of computing the overall heat transferred, the electrical power output, and the associated pressure drop for given inlet conditions of the exhaust gas and the available TEG volume. Multiple-filled skutterudites and conventional bismuth telluride are considered for thermoelectric modules (TEMs) for conversion of waste heat from exhaust into usable electrical power. Heat transfer between the hot exhaust gas and the hot side of the TEMs is enhanced with the use of a plate-fin heat exchanger integrated within the TEG and using liquid coolant on the cold side. The TEG is discretized along the exhaust flow direction using a finite-volume method. Each control volume is modeled as a thermal resistance network which consists of integrated submodels including a heat exchanger and a thermoelectric device. The pressure drop along the TEG is calculated using standard pressure loss correlations and viscous drag models. The model is validated to preserve global energy balances and is applied to analyze a prototype TEG with data provided by General Motors. Detailed results are provided for local and global heat transfer and electric power generation. In the companion paper, the model is then applied to consider various TEG topologies using skutterudite and bismuth telluride TEMs.     

Methods and Equipment for Quality Control of Thermoelectric Materials

Step-by-step control is very important in the manufacturing of thermoelectric generators and cooling modules. Of key importance is quality control of thermoelectric material rods, and discs cut from such rods. This work describes two installations for measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity of rods, as well as for measuring the Seebeck coefficient and electrical conductivity of discs. It is established that using such devices in the practice of manufacture of cooling modules enables enhancement of module quality and reduction of material waste by 7% to 15%.     

Chalcogenide Thermoelectrics Empowered by an Unconventional Bonding Mechanism

Thermoelectric materials have attracted significant research interest in recent decades due to their promising application potential in interconverting heat and electricity. Unfortunately, the strong coupling between the material parameters that determine thermoelectric efficiency, i.e., the Seebeck coefficient, electrical conductivity, and thermal conductivity, complicates the optimization of thermoelectric energy converters. Main‐group chalcogenides provide a rich playground to alleviate the interdependence of these parameters. Interestingly, only a subgroup of octahedrally coordinated chalcogenides possesses good thermoelectric properties. This subgroup is also characterized by other outstanding characteristics suggestive of an exceptional bonding mechanism, which has been coined metavalent bonding. This conclusion is further supported by a map that separates different bonding mechanisms. In this map, all octahedrally coordinated chalcogenides with good performance as thermoelectrics are located in a well‐defined region, implying that the map can be utilized to identify novel thermoelectrics. To unravel the correlation between chemical bonding mechanism and good thermoelectric properties, the consequences of this unusual bonding mechanism on the band structure are analyzed. It is shown that features such as band degeneracy and band anisotropy are typical for this bonding mechanism, as is the low lattice thermal conductivity. This fundamental understanding, in turn, guides the rational materials design for improved thermoelectric performance by tailoring the chemical bonding mechanism.     

Modeling of a Thermoelectric Generator for Thermal Energy Regeneration in Automobiles

In the field of passenger transportation a reduction of the consumption of fossil fuels has to be achieved by any measures. Advanced designs of internal combustion engine have the potential to reduce CO₂ emissions, but still suffer from low efficiencies in the range from 33% to 44%. Recuperation of waste heat can be achieved with thermoelectric generators (TEGs) that convert heat directly into electric energy, thus offering a less complicated setup as compared with thermodynamic cycle processes. During a specific driving cycle of a car, the heat currents and temperature levels of the exhaust gas are dynamic quantities. To optimize a thermoelectric recuperation system fully, various parameters have to be tested, for example, the electric and thermal conductivities of the TEG and consequently the heat absorbed and rejected from the system, the generated electrical power, and the system efficiency. A Simulink model consisting of a package for dynamic calculation of energy management in a vehicle, coupled with a model of the thermoelectric generator system placed on the exhaust system, determines the drive-cycle-dependent efficiency of the heat recovery system, thus calculating the efficiency gain of the vehicle. The simulation also shows the temperature drop at the heat exchanger along the direction of the exhaust flow and hence the variation of the voltage drop of consecutively arranged TEG modules. The connection between the temperature distribution and the optimal electrical circuitry of the TEG modules constituting the entire thermoelectric recuperation system can then be examined. The simulation results are compared with data obtained from laboratory experiments. We discuss error bars and the accuracy of the simulation results for practical thermoelectric systems embedded in cars.     

System Modeling and Validation of a Thermoelectric Fluidic Power Source: Proton Exchange Membrane Fuel Cell and Thermoelectric Generator (PEMFC-TEG)

To facilitate the co-design and co-optimization of fluid or combustion systems and thermoelectric devices, a three-dimensional (3D) thermoelectric generator (TEG) model has been proposed and implemented in a computational fluid dynamics (CFD) simulation environment. The model includes all temperature-dependent characteristics of the materials and nonlinear fluid–thermal– electric multiphysics coupled effects. In this paper, the device-level model is first extended to the module level by taking a general geometry, identifying regions such as positive and negative thermoelements, and assigning properties to them. The system-level model is then demonstrated by coupling the module-level model with a fluidic–thermal system model in a single CFD simulator to predict the generation performance based on the thermal equilibrium that is achieved. The linked models are validated experimentally at the system level using data from three real thermoelectric modules installed on the surface of an exhaust pipe-like rig, where the temperature profile as well as the electricity generated can be measured and compared with the simulation results. The rig is intended not only to verify the proposed system model but also to mimic a practical exhaust recovery apparatus for a proton exchange membrane fuel cell (PEMFC). Based on the data obtained from the system-level test rig, a novel low-temperature low-cost application for auxiliary electric power appliances based on the waste heat of the PEMFC can be envisaged. Within the common simulator, it is shown that the thermoelectric model can be connected to various continuum-domain CFD models of the fuel cell itself, thus enabling further possibilities to optimize system efficiency and performance.     

Thermoelectric Properties of High-Doped Silicon from Room Temperature to 900 K

Silicon is investigated as a low-cost, Earth-abundant thermoelectric material for high-temperature applications up to 900 K. For the calculation of module design the Seebeck coefficient and the electrical as well as thermal properties of silicon in the high-temperature range are of great importance. In this study, we evaluate the thermoelectric properties of low-, medium-, and high-doped silicon from room temperature to 900 K. In so doing, the Seebeck coefficient, the electrical and thermal conductivities, as well as the resulting figure of merit ZT of silicon are determined.     

Electrostatic Control of the Thermoelectric Figure of Merit in Ion-Gated Nanotransistors

Semiconductor nanostructures have raised much hope for the implementation of high-performance thermoelectric generators. Indeed, they are expected to make available reduced thermal conductivity without a heavy trade-off on electrical conductivity, a key requirement to optimize the thermoelectric figure of merit. Here, a novel nanodevice architecture is presented in which ionic liquids are employed as thermally-insulating gate dielectrics. These devices allow the field-effect control of electrical transport in suspended semiconducting nanowires in which thermal conductivity can be simultaneously measured using an all-electrical setup. The resulting experimental data on electrical and thermal transport properties taken on individual nanodevices can be combined to extract ZT, guide device optimization and dynamical tuning of the thermoelectric properties.     

Applying Quantitative Microstructure Control in Advanced Functional Composites

Microstructure control in functional materials draws from a historical reserve rich in established theory and experimental observation of metallurgy. Methods such as rapid solidification, eutectoid reaction, and nucleation and growth precipitation have all proven to be effective means to produce microstructure relevant for a wide array of applications. Here, the available parameters to control structure morphology, size, and spacing are discussed using thermoelectric composites as an example. Moreover, exploiting different aspects of a material system's phase diagram enables a controlled introduction of nanostructures. While much of this discussion is pertinent to the rapidly developing field of thermal conductivity control in thermoelectric composites, these techniques can be applied to a variety of other material systems where their use may lead to novel electrical, optical, as well as thermal properties of semiconductors and insulators as it has in the past for the mechanical properties of metals.     

Robust Finite Element Model for the Design of Thermoelectric Modules

Thermoelectric devices for power generation have been receiving increased attention as an emerging sustainable energy technology because of recent advances in thermoelectric materials and the tremendous thermal resources available. Little focus has been given to the effective implementation of thermoelectric materials in power generation modules and efficient module design. With recent exploration into new module configurations, it is imperative that a comprehensive model be developed as a design tool. A new three-dimensional, device-level, multiphysics modeling technique is developed for the purposes of designing and evaluating thermoelectric module configurations. Using the new model, we identify and explore several geometric parameters which are critical to module performance. The impact on device performance of solder, ceramic interface, and electrical contact thickness, as well as the leg spacing, is evaluated for a standard unicouple configuration. Results are compared to the standard one-dimensional constant property models commonly used in thermoelectric module design.     

Investigation of Maximum Power Point Tracking for Thermoelectric Generators

In this paper, a thermoelectric generator (TEG) model is developed as a tool for investigating optimized maximum power point tracking (MPPT) algorithms for TEG systems within automotive exhaust heat energy recovery applications. The model comprises three main subsystems that make up the TEG system: the heat exchanger, thermoelectric material, and power conditioning unit (PCU). In this study, two MPPT algorithms known as the perturb and observe (P&O) algorithm and extremum seeking control (ESC) are investigated. A synchronous buck–boost converter is implemented as the preferred DC–DC converter topology, and together with the MPPT algorithm completes the PCU architecture. The process of developing the subsystems is discussed, and the advantage of using the MPPT controller is demonstrated. The simulation results demonstrate that the ESC algorithm implemented in combination with a synchronous buck–boost converter achieves favorable power outputs for TEG systems. The appropriateness is by virtue of greater responsiveness to changes in the system’s thermal conditions and hence the electrical potential difference generated in comparison with the P&O algorithm. The MATLAB/Simulink environment is used for simulation of the TEG system and comparison of the investigated control strategies.     

Thermal Cycling, Mechanical Degradation, and the Effective Figure of Merit of a Thermoelectric Module

Thermoelectric modules experience performance reduction and mechanical failure due to thermomechanical stresses induced by thermal cycling. The present study subjects a thermoelectric module to thermal cycling and evaluates the evolution of its thermoelectric performance through measurements of the thermoelectric figure of merit, ZT, and its individual components. The Seebeck coefficient and thermal conductivity are measured using steady-state infrared microscopy, and the electrical conductivity and ZT are evaluated using the Harman technique. These properties are tracked over many cycles until device failure after 45,000 thermal cycles. The mechanical failure of the TE module is analyzed using high-resolution infrared microscopy and scanning electron microscopy. A reduction in electrical conductivity is the primary mechanism of performance reduction and is likely associated with defects observed during cycling. The effective figure of merit is reduced by 20% through 40,000 cycles and drops by 97% at 45,000 cycles. These results quantify the effect of thermal cycling on a commercial TE module and provide insight into the packaging of a complete TE module for reliable operation.     

Optimal Electrical Conductivity for Maximum Thermoelectric Figure of Merit

A frequently employed approach for determination of the maximum thermoelectric figure of merit of a material involves a calculation of its maximum electrical power factor and the corresponding thermal conductivity. In this study, we show that the thermoelectric figure of merit determined using this approach is likely to be limited by the Lorenz factor. The maximum thermoelectric figure of merit is achieved at a different electrical conductivity. A simple way of estimating the optimal electrical conductivity for obtaining the maximum thermoelectric figure of merit is presented.     

Optimized Characterization of Thermoelectric Generators for Automotive Application

New developments in the field of thermoelectric materials bring the prospect of consumer devices for recovery of some of the waste heat from internal combustion engines closer to reality. Efficiency improvements are expected due to the development of high-temperature thermoelectric generators (TEG). In contrast to already established radioisotope thermoelectric generators, the temperature difference in automotive systems is not constant, and this imposes a set of specific requirements on the TEG system components. In particular, the behavior of the TEGs and interface materials used to link the heat flow from the heat source through the TEG to the heat sink must be examined. Due to the usage patterns of automobiles, the TEG will be subject to cyclic thermal loads, which leads to module degradation. Additionally, the automotive TEG will be exposed to an inhomogeneous temperature distribution, leading to inhomogeneous mechanical loads and reduced system efficiency. Therefore, a characterization rig is required to allow determination of the electrical, thermal, and mechanical properties of such high-temperature TEG systems. This paper describes a measurement setup using controlled adjustment of cold-side and warm-side temperatures as well as controlled feed-in of electrical power for evaluation of TEGs for application in vehicles with combustion engines. The temperature profile in the setup can be varied to simulate any vehicle usage pattern, such as the European standard driving cycle, allowing the power yield of the TEGs to be evaluated for the chosen cycle. The spatially resolved temperature distribution of a TEG system can be examined by thermal imaging. Hotspots or cracks on thermocouples of the TEGs and the thermal resistance of thermal interface materials can also be examined using this technology. The construction of the setup is briefly explained, followed by detailed discussion of the experimental results.     

A 42-V Electrical and Hybrid Driving System Based on a Vehicular Waste-Heat Thermoelectric Generator

A 42-V powernet has been recognized as the next generation of vehicle electrical systems, and the waste-heat thermoelectric generator is becoming the future of vehicular energy conservation and emission reduction technologies. In this paper, effective utilization of vehicular waste-heat energy is proposed by introducing an electrical and hybrid driving system, which is an assemblage of a waste-heat thermoelectric generator, a 42-V powernet, and an integrated starter and generator (ISG). A vehicle model and the submodels for the new system have been built on the ADVISOR platform based on MATLAB/Simulink, and the dynamic performance of the vehicle model tested using the Economic Commission for Europe?CEurope Urban Dynamometer Cycle driving cycle. The simulation results indicate that application of a 42-V waste-heat thermoelectric vehicle could be an integrated approach for fuel economy improvement and emission reduction, compared with a conventional internal combustion engine vehicle and an ISG-type 42-V vehicle.     

温差电器件接触电阻和接触热阻的测试及分析

接触电阻和接触热阻是影响温差电器件性能的两个重要的工艺参数，直接反映器件制造的工艺水平。因此，对器件的接触电阻和接触热阻进行测试分析，将能够定量地了解现行工艺对器件温差电性能的影响程度。本文首先介绍接触电阻的测试方法和实验结果，然后利用所测的数据，再通过对器件输出功率特性的测试，间接地导出器件的接触热阻。据笔者所知，这是温差电器件接触热阻实测数值的首次报道。     

Re-Doped p-Type Thermoelectric SnSe Polycrystals with Enhanced Power Factor and High ZT > 2

Thermoelectric technology enables the direct interconversion between heat and electricity. SnSe has received increasing interest as a new promising thermoelectric compound due to its exceptionally high performance reported in crystals. SnSe possesses intrinsic low thermal conductivity as a congenital advantage for thermoelectric, but high thermoelectric performance can be hardly achieved due to the difficulty to realize efficient doping to raise its low carrier concentration to an optimal level. In this work, it is found that a series of rare earth elements are effective dopants for SnSe, which can greatly improve the electrical transport properties of p-type polycrystalline SnSe. In particular, the remarkable enhancement in electrical conductivity and power factor is achieved by Na/Er co-doping at 873 K. The lattice thermal conductivity is reduced due to the presence of abundant defects (dislocations, stacking faults, and twin boundaries). Consequently, a peak thermoelectric figure of merit ZT (2.1) as well as a high average ZT (0.77) are achieved in polycrystalline SnSe.     

Thermoelectric figure of merit for bulk nanostructured composites with distributed parameters

The effective properties of composites whose structure includes nanocontacts between bulk-phase macrocrystallites are considered. A model for such a nanostructured composite is constructed. Effective values of the thermoelectric power, thermal and electrical conductivities, and thermoelectric figure of merit are calculated in the mean-field approximation.     

High Temperature Thermoelectric Device Concept Using Large Area PN Junctions

A new high temperature thermoelectric device concept using large area nanostructured silicon p-type and n-type (PN) junctions is presented. In contrast to conventional thermoelectric generators, where the n-type and p-type semiconductors are connected electrically in series and thermally in parallel, we experimentally demonstrate a device concept in which a large area PN junction made from highly doped densified silicon nanoparticles is subject to a temperature gradient parallel to the PN interface. In the proposed device concept, the electrical contacts are made at the cold side eliminating the hot side substrate and difficulties that go along with high temperature electrical contacts. This concept allows temperature gradients greater than 300 K to be experimentally applied with hot side temperatures larger than 800 K. Electronic properties of the PN junctions and power output characterizations are presented. A fundamental working principle is discussed using a particle network model with temperature and electric fields as variables, and which considers electrical conductivity and thermal conductivity according to Fourier’s law, as well as Peltier and Seebeck effects.