Evaluation of Power Conditioning Architectures for Energy Production Enhancement in Thermoelectric Generator Systems

A large-scale thermoelectric generator (TEG) system has an unbalanced temperature distribution among the TEG modules, which leads to power mismatch among the modules and decreases the power output of the TEG system. To maximize the power output and minimize the power conversion loss, a centralized–distributed hybrid power conditioning architecture is presented, analyzed, and evaluated for a TEG system. The novel architecture is a combination of a conventional centralized architecture and a fully distributed architecture. By using the proposed architecture, most of the harvested power is processed by the centralized stage while only the mismatched power among the TEG modules is processed by the distributed stages. As a result, accurate and distributed maximum-power-point tracking (MPPT) for each TEG module and single-stage power conversion between the modules and load can be achieved. It offers the benefit of implementing high MPPT efficiency and high conversion efficiency simultaneously. A 50-W TEG system composed of two TEG modules is built and tested. Experimental results show that the proposed hybrid power conditioning architecture generates up to 5% more energy for a temperature difference between the two modules of only 10°C.     

Individual Module Maximum Power Point Tracking for Thermoelectric Generator Systems

In a thermoelectric generator (TEG) system the DC/DC converter is under the control of a maximum power point tracker which ensures that the TEG system outputs the maximum possible power to the load. However, if the conditions, e.g., temperature, health, etc., of the TEG modules are different, each TEG module will not produce its maximum power. If each TEG module is controlled individually, each TEG module can be operated at its maximum power point and the TEG system output power will therefore be higher. In this work a power converter based on noninverting buck–boost converters capable of handling four TEG modules is presented. It is shown that, when each module in the TEG system is operated under individual maximum power point tracking, the system output power for this specific application can be increased by up to 8.4% relative to the situation when the modules are connected in series and 16.7% relative to the situation when the modules are connected in parallel.     

Power Conditioner with Variable Switching Control for Thermoelectric Generator Systems

A thermoelectric (TE) power conditioner maintaining high efficiency over a wide input power range has been developed. Variable switching frequency operation is shown to give an improvement in efficient operating range. The input range showing more than 90% conversion efficiency is expanded to more than 25% by introducing a low-power controller circuit and variable switching frequency control. The TE power conditioner showed excellent response against a change in thermoelectric generator (TEG) output and load, making it suitable for automotive applications.     

Achieving Maximum Power in Thermoelectric Generation with Simple Power Electronics

A thermoelectric generator typically delivers a relatively low power output, and hence it is of great practical importance to determine a design and operating condition close to those which can provide the maximum attainable power. To maintain a favorable condition for the maximum power output, power electronics circuits are usually applied. One of the simplest methods is to control the operating voltage at half the open-circuit voltage, assuming that the typical impedance-matching condition, in which the load and internal resistances are matched, yields the maximum power output. However, recent investigations have shown that, when external thermal resistances exist between the thermoelectric modules and thermal reservoirs, the impedance-matching condition is not identical to the condition for the maximum power output. In this article, it is argued that, although the impedance-matching condition is not the condition for maximum power output, the maximum power is still achievable when the operating voltage is kept at half the open-circuit voltage. More precisely, it is shown that the typical V–I curve for thermoelectric generators must show approximately linear behavior, which justifies the use of a simple strategy in thermoelectric power generation applications. The conditions for the validity of the approximation are mathematically discussed, supported by a few examples. Experimental evidence at room temperature is also provided.     

High Step-Up Active-Clamp Converter With Input-Current Doubler and Output-Voltage Doubler for Fuel Cell Power Systems

A high-efficiency high step-up dc–dc converter is proposed for fuel cell power systems. The proposed system consists of an input-current doubler, an output-voltage doubler, and an active-clamp circuit. The input-current doubler and the output-voltage doubler provide a much higher voltage conversion ratio without using a high turns ratio in the transformer and increase the overall efficiency. A series-resonant circuit of the output-voltage doubler removes the reverse-recovery problem of the rectifying diodes. The active-clamp circuit clamps the surge voltage of switches and recycles the energy stored in the leakage inductance of the transformer. The operation principle of the converter is analyzed and verified. A 1 kW prototype is implemented to show the performance of the proposed converter. The prototype achieved a European efficiency of 96% at an input voltage of 30 V.      

Hybrid Solid Oxide Fuel Cell and Thermoelectric Generator for Maximum Power Output in Micro-CHP Systems

One of the most obvious early market applications for thermoelectric generators (TEG) is decentralized micro combined heat and power (CHP) installations of 0.5 kWe to 5 kWe based on fuel cell technology. Through the use of TEG technology for waste heat recovery it is possible to increase the electricity production in micro-CHP systems by more than 15%, corresponding to system electrical efficiency increases of some 4 to 5 percentage points. This will make fuel cell-based micro-CHP systems very competitive and profitable and will also open opportunities in a number of other potential business and market segments which are not yet quantified. This paper quantifies a micro-CHP system based on a solid oxide fuel cell (SOFC) and a high-performance TE generator. Based on a 3 kW fuel input, the hybrid SOFC implementation boosts electrical output from 945 W to 1085 W, with 1794 W available for heating purposes.     

Impact of Thermal Interface Materials for Thermoelectric Generator Systems

A primary challenge still exists in the field of thermoelectric generators (TEG) for practical applications in which a thermal system of the TEG is a crucial factor in TEG power generation. The material development for TEG has contributed significantly towards advancement in TEG applications over a decade, the need for a thermal system configuration is inevitable considering the applications. The thermal efficiency of TEG depends upon the temperature difference across its modules (between the hot and cold surfaces). Thermal design of the thermoelectric system is important to ensure that there exists a maximum temperature difference across the hot and cold surfaces of the TEG. Thermal Interface Material (TIM) in thermoelectric systems plays a main role in improving the efficiency of thermoelectric systems by reducing the temperature difference between the heat source and the hot surface of the TEG and similarly, the temperature difference between the cold surface of TEG and the heat sink. This review paper predominantly focuses on the thermal interfaces between the TEG modules which reduces the performance of a thermoelectric system. The characteristics of TIM in a TEG system (contact pressure, surface roughness and thermal conductivity) were analyzed with a mathematical model to emphasize the importance of TIM in a TEG system. This paper also highlights the existing challenges for Thermal Interface Materials in TEG applications and concludes with a brief discussion on future directions of TIM in TEG thermal systems.     

Thermoelectric Analysis for Helical Power Generation Systems

The performance of a three-dimensional helical thermoelectric generation (TEG) system is examined by exposing it to a temperature difference with hot and cold sources. The helical paths for the two thermal fluids give the TEG device the potential to efficiently convert thermal energy. The characteristic performance of the helical system is numerically analyzed by using the finite-volume method in a compact system. The helical system is compared with a straight system in which all the thermoelectric (TE) elements present equivalent geometry. The difference in the TE performance between the two systems is not significant when the TE surfaces are maintained at constant temperatures. Both the electromotive force and the current in the TEG system increase linearly with the temperature difference ΔT applied at the two module surfaces. The current preferentially flows through a main path determined by the geometry of the TE element. The merits of the helical design are its compactness, space saving, and smooth fluid flow due to gravity, compared with the straight system.     

Power Generation Characteristics of Mg2Si Uni-Leg Thermoelectric Generator

Mg₂Si thermoelectric (TE) elements were fabricated by a plasma-activated sintering method using a commercial polycrystalline n-type Mg₂Si source produced by the Union Material Co., Ltd. This material typically has a ZT value of ??0.6. A monobloc plasma-activated sintering technique was used to form Ni electrodes on the TE elements. The dimensions of a single element were 4.0?mm?×?4.0?mm?×?10?mm, and these were used to construct a TE module comprising nine elements connected in series. To reduce the electrical and thermal contact resistance of the module, each part of the module, i.e., the elements, terminals, and insulating plates, was joined using a Ag-based brazing alloy. In addition, to maintain the temperature difference between the top and bottom of the module, a thermal insulation board was installed in it. The observed values of open-circuit voltage (V _OC) and output power (P) of a uni-leg structure module were 594?mV and 543?mW, respectively, at a maximum ??T?=?500?K.     

Thermoelectric Cooling of Heat-Loaded Electronics

Russian Microelectronics - The characteristics of cooling and thermal control systems are calculated depending on the parameters of the thermoelectric module and the heat-loaded element. The values...     

Prototype Combined Heater/Thermoelectric Power Generator for Remote Applications

This study presents a prototype thermoelectric generator (TEG) developed for remote applications in villages that are not connected to the electrical power grid. For ecological and economic reasons, there is growing interest in harvesting waste heat from biomass stoves to produce some electricity. Because regular maintenance is not required, TEGs are an attractive choice for small-scale power generation in inaccessible areas. The prototype developed in our laboratory is especially designed to be implemented in stoves that are also used for domestic hot water heating. The aim of this system is to provide a few watts to householders, so they have the ability to charge cellular phones and radios, and to get some light at night. A complete prototype TEG using commercial (bismuth telluride) thermoelectric modules has been built, including system integration with an electric DC/DC converter. The DC/DC converter has a maximum power point tracker (MPPT) driven by an MC9SO8 microcontroller, which optimizes the electrical energy stored in a valve-regulated lead–acid battery. Physical models were used to study the behavior of the thermoelectric system and to optimize the performance of the MPPT. Experiments using a hot gas generator to simulate the exhaust of the combustion chamber of a stove are used to evaluate the system. Additionally, potential uses of such generators are presented.     

温差发电器的设计

温差发电器是一种利用大自然中广泛存在的温差进行发电的装置。温差发电器主要由半导体温差发电模块和控制器两部分组成,半导体温差发电模块将热能转化为电能,并通过充电电路将电能储存在蓄电池中;控制器主要完成限流、欠压保护功能。同时,还设计了升压电路,从而使温差发电器输出较高的电压。     

Multi-parameter Optimization of a Thermoelectric Power Generator and Its Working Conditions

The global optimal working conditions and optimal couple design for thermoelectric (TE) generators with realistic thermal coupling between the heat reservoirs and the TE couple were studied in the current work. The heat fluxes enforced by the heat reservoirs at the hot and the cold junctions of the TE couple were used in combination with parameter normalization to obtain a single cubic algebraic equation relating the temperature differences between the TE couple junctions and between the heat reservoirs, through the electric load resistance ratio, the reservoir thermal conductance ratio, the reservoir thermal conductance to the TE couple thermal conductance ratio, the Thomson to Seebeck coefficient ratio, and the figure of merit (Z) of the material based on the linear TE transport equations and their solutions. A broad reservoir thermal conductance ranging between 0.01  W/K and 100 W/K and TE element length ranging from 10^-7 m to 10^-3 m were explored to find the global optimal systems. The global optimal parameters related to the working conditions, i.e., reservoir thermal conductance ratio and electric load resistance ratio, and the optimal design parameter related to the TE couple were determined for a given TE material. These results demonstrated that the internal and external electric resistance, the thermal resistance between the reservoirs, the thermal resistance between the reservoir and the TE couple, and the optimal thermoelement length have to be well coordinated to obtain optimal power production.     

Model for Increasing the Power Obtained from a Thermoelectric Generator Module

We have developed a model for finding the most efficient way of increasing the power obtained from a thermoelectric generator (TEG) module with a variety of operating conditions and limitations. The model is based on both thermoelectric principles and thermal resistance circuits, because a TEG converts heat into electricity consistent with these two theories. It is essential to take into account thermal contact resistance when estimating power generation. Thermal contact resistance causes overestimation of the measured temperature difference between the hot and cold sides of a TEG in calculation of the theoretical power generated, i.e. the theoretical power is larger than the experimental power. The ratio of the experimental open-loop voltage to the measured temperature difference, the effective Seebeck coefficient, can be used to estimate the thermal contact resistance in the model. The ratio of the effective Seebeck coefficient to the theoretical Seebeck coefficient, the Seebeck coefficient ratio, represents the contact conditions. From this ratio, a relationship between performance and different variables can be developed. The measured power generated by a TEG module (TMH400302055; Wise Life Technology, Taiwan) is consistent with the result obtained by use of the model; the relative deviation is 10%. Use of this model to evaluate the most efficient means of increasing the generated power reveals that the TEG module generates 0.14 W when the temperature difference is 25°C and the Seebeck coefficient ratio is 0.4. Several methods can be used triple the amount of power generated. For example, increasing the temperature difference to 43°C generates 0.41 W power; improving the Seebeck coefficient ratio to 0.65 increases the power to 0.39 W; simultaneously increasing the temperature difference to 34°C and improving the Seebeck coefficient ratio to 0.5 increases the power to 0.41 W. Choice of the appropriate method depends on the limitations of system, the cost, and the environment.     

Thin-Film Thermoelectric Module for Power Generator Applications Using a Screen-Printing Method

A new process for fabricating a low-cost thermoelectric module using a screen-printing method has been developed. Thermoelectric properties of screen-printed ZnSb films were investigated in an effort to develop a thermoelectric module with low cost per watt. The screen-printed Zn _x Sb_1−x films showed a low carrier concentration and high Seebeck coefficient when x was in the range of 0.5 to 0.57 and the annealing temperature was kept below 550°C. When the annealing temperature was higher than 550°C, the carrier concentration of the Zn _x Sb_1−x films reached that of a metal, leading to a decrease of the Seebeck coefficient. In the present experiment, the optimized carrier concentration of screen-printed ZnSb was 7 × 10¹⁸/cm³. The output voltage and power density of the ZnSb film were 10 mV and 0.17 mW/cm², respectively, at ΔT = 50 K. A thermoelectric module was produced using the proposed screen-printing approach with ZnSb and CoSb₃ as p-type and n-type thermoelectric materials, respectively, and copper as the pad metal.     

接触效应对小型半导体温差发电器性能的影响

针对小型半导体温差(TEG)发电器中接触热阻和接触电阻的影响进行了分析研究.结果表明,接触热阻和接触电阻只在2mm以内的电偶臂长度内有明显影响;在电偶臂长度小于1mm时,输出功率和热电效率均有一个急剧上升的变化阶段;当长度超过5mm后,输出功率和热电效率均趋于定值;在冷热端温度分别为283和383K,Z=0.0024K-1、电偶臂长为2mm、接触热阻比0.2和接触电阻比0.1条件下,热电功率约为4mW/mm2,热电效率约为3.5%,而理想无接触热阻和电阻的热电效率约为4.2%.由此可知,半导体温差发电器中接触热阻和接触电阻的影响不可忽视.     

接触效应对小型半导体温差发电器性能的影响

针对小型半导体温差(TEG)发电器中接触热阻和接触电阻的影响进行了分析研究.结果表明,接触热阻和接触电阻只在2mm以内的电偶臂长度内有明显影响;在电偶臂长度小于1mm时,输出功率和热电效率均有一个急剧上升的变化阶段;当长度超过5mm后,输出功率和热电效率均趋于定值;在冷热端温度分别为283和383K,Z=0.0024K-1、电偶臂长为2mm、接触热阻比0.2和接触电阻比0.1条件下,热电功率约为4mW/mm2,热电效率约为3.5%,而理想无接触热阻和电阻的热电效率约为4.2%.由此可知,半导体温差发电器中接触热阻和接触电阻的影响不可忽视.     

电力电子系统集成化的前景概述

本文阐述通过先进的集成化改进功率处理技术的可能方向。其中心焦点是除了电力半导体开关组件的集成化外还应推动电磁功率无源元件、电磁干扰滤波器、和电力变换器中的控制、传感、互联结构等的集成化。文中将讨论电子功率处理的基本功能、材料、流程、划分与集成的途径以及将来的概念。