A Natural-Gas-Fired Thermoelectric Power Generation System

This paper presents a combustion-driven thermoelectric power generation system that uses PbSnTe-based thermoelectric modules. The modules were integrated into a gas-fired furnace with a special burner design. The thermoelectric integrated system could be applied for self-powered appliances or micro-cogeneration. A mathematical model for the integrated energy system was established that considered irreversibilities in the thermal-to-electric energy conversion process. The electric power output and electrical efficiency of the system were simulated using the established model. A prototype system was developed and its performance was investigated at various operating conditions. Applicability of thermoelectric devices to self-powered heating systems was demonstrated. The thermoelectric integrated combustion system could provide the consumer with heating system reliability and a reduction in electric power consumption. The integrated system could also offer other advantages including simplicity, low noise, clean operation, and low maintenance.     

Heat-Pipe-Associated Localized Thermoelectric Power Generation System

The present study focused on how to improve the maximum power output of a thermoelectric generator (TEG) system and move heat to any suitable space using a TEG associated with a loop thermosyphon (loop-type heat pipe). An experimental study was carried out to investigate the power output, the temperature difference of the thermoelectric module (TEM), and the heat transfer performance associated with the characteristic of the researched heat pipe. Currently, internal combustion engines lose more than 35% of their fuel energy as recyclable heat in the exhaust gas, but it is not easy to recycle waste heat using TEGs because of the limited space in vehicles. There are various advantages to use of TEGs over other power sources, such as the absence of moving parts, a long lifetime, and a compact system configuration. The present study presents a novel TEG concept to transfer heat from the heat source to the sink. This technology can transfer waste heat to any location. This simple and novel design for a TEG can be applied to future hybrid cars. The present TEG system with a heat pipe can transfer heat and generate power of around 1.8 V with T _TEM = 58°C. The heat transfer performance of a loop-type heat pipe with various working fluids was investigated, with water at high heat flux (90 W) and 0.05% TiO₂ nanofluid at low heat flux (30 W to 70 W) showing the best performance in terms of power generation. The heat pipe can transfer the heat to any location where the TEM is installed.     

Autonomous Underwater Vehicle Thermoelectric Power Generation

Autonomous underwater vehicles (AUVs) are a vital part of the oceanographer’s toolbox, allowing long-term measurements across a range of ocean depths of a number of ocean properties such as salinity, fluorescence, and temperature profile. Buoyancy-based gliding, rather than direct propulsion, dramatically reduces AUV power consumption and allows long-duration missions on the order of months rather than hours or days, allowing large distances to be analyzed or many successive analyses of a certain area without the need for retrieval. Recent versions of these gliders have seen the buoyancy variation system change from electrically powered to thermally powered using phase-change materials, however a significant battery pack is still required to power communications and sensors, with power consumption in the region of 250 mW. The authors propose a novel application of a thermoelectric generation system, utilizing the depth-related variation in oceanic temperature. A thermal energy store provides a temperature differential across which a thermoelectric device can generate from repeated dives, with the primary purpose of extending mission range. The system is modeled in Simulink to analyze the effect of variation in design parameters. The system proves capable of generating all required power for a modern AUV.     

新能源发电中的若干电力电子问题综述

本文从电力电子技术的立场,探讨风力发电、光伏发电、燃料电池发电对电力电子技术提出的要求,分析并指出了需要关注的技术难点和尚未解决的问题。     

Evaluation of High Step-Up Power Electronics Stages in Thermoelectric Generator Systems

To develop practical thermoelectric generator (TEG) systems, especially radioisotope thermoelectric power supplies for deep-space exploration, a power conditioning stage with high step-up gain is indispensable. This stage is used to step up the low output voltage of thermoelectric generators to the required high level. Furthermore, maximum power point tracking control for TEG modules needs to be implemented into the power electronics stages. In this paper, the temperature-dependent electrical characteristics of a thermoelectric generator are analyzed in depth. Three typical high step-up power converters suitable for TEG applications are discussed: an interleaved boost converter, a boost converter with a coupled inductor, and an interleaved boost converter with an auxiliary transformer. A general comparison of the three high step-up converters is conducted to study the step-up gain, conversion efficiency, and input current ripples. The interleaved boost converter with an auxiliary transformer is found to be the most suitable topology for TEG applications, which is verified by experiments.     

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.     

Thermoelectric Materials with Potential High Power Factors for Electricity Generation

The thermoelectric figure of merit ZT of materials limits the performance of a thermoelectric power generator. To date, the main gains from the worldwide effort in either engineered bulk materials or low-dimensional systems have been mostly based on the strategies of reducing the thermal conductivity. We explore several bulk thermoelectric materials that have respectable mecha- nical strength and chemical stability at elevated temperatures for potential power generation. Our strategy is to first explore the avenue of significantly increasing the power factor (PF), then the avenue of lowering thermal conductivity, perhaps by nanocompositing. We examine the layered cobaltates with sharp resonant peaks in the electronic density of states near the Fermi energy level due to strong electron correlation. We suggest that electron correlation may be used as a new tuning parameter to significantly increase the PF. We also report that a substantial increase (over 30%) in PF can be achieved in filled skutterudites (such as p-type CeFe₄Sb₁₂) through nonequilibrium synthesis by rapid conversion of the amorphous materials made by the melt spinning to single-phase crystalline materials under pressure. This process, in conjunction with the rattling to lower the lattice thermal conductivity, could further enhance the ZT values of the filled skutterudites.     

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.     

Power Delivery from an Actual Thermoelectric Generation System

Similar to photovoltaic (PV) and fuel cells, thermoelectric generators (TEGs) supply direct-current (DC) power, essentially requiring DC/alternating current (AC) conversion for delivery as electricity into the grid network. Use of PVs is already well established through power conditioning systems (PCSs) that enable DC/AC conversion with maximum-power-point tracking, which enables commercial use by customers. From the economic, legal, and regulatory perspectives, a commercial PCS for PVs should also be available for TEGs, preferably as is or with just simple adjustment. Herein, we report use of a PV PCS with an actual TEG. The results are analyzed, and proper application for TEGs is proposed.     

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.     

Hardware Implementation of Maximum Power Point Tracking for Thermoelectric Generators

This work describes the practical implementation of two maximum power point tracking (MPPT) algorithms, namely those of perturb and observe, and extremum seeking control. The proprietary dSPACE system is used to perform hardware in the loop (HIL) simulation whereby the two control algorithms are implemented using the MATLAB/Simulink (Mathworks, Natick, MA) software environment in order to control a synchronous buck–boost converter connected to two commercial thermoelectric modules. The process of performing HIL simulation using dSPACE is discussed, and a comparison between experimental and simulated results is highlighted. The experimental results demonstrate the validity of the two MPPT algorithms, and in conclusion the benefits and limitations of real-time implementation of MPPT controllers using dSPACE are discussed.     

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...     

Approach to the Practical Use of Thermoelectric Power Generation

The results of research and development in the Japanese national project “Development for Advanced Thermoelectric Conversion Systems” are summarized, and the approaches to practical use of advanced thermoelectric modules and power generation systems are presented. The 5-year national project was successfully completed in March 2007. Three kinds of high- efficiency cascaded thermoelectric modules and two kinds of innovative Bi-Te thermoelectric modules were successfully developed. Heat cycle tests for three types of modules were also completed. Moreover, four types of advanced thermoelectric power generation systems were experimentally demonstrated for recovery of waste heat from the industrial and private sectors. In order to proceed further, thermoelectric power generation systems using practical heat sources were followed after installation of the developed modules. In parallel, various approaches for practical use by private companies, as well as plans for the next-phase project by the National Institute of Advanced Industrial Science and Technology (AIST) and the Engineering Advancement Association (ENAA), were also followed. The scenarios to proceed to the commercial phase of thermoelectric power generation are discussed on the basis of the results of the national project.     

A Digital Coreless Maximum Power Point Tracking Circuit for Thermoelectric Generators

This paper describes a maximum power point tracking (MPPT) circuit for thermoelectric generators (TEG) without a digital controller unit. The proposed method uses an analog tracking circuit that samples the half point of the open-circuit voltage without a digital signal processor (DSP) or microcontroller unit for calculating the peak power point using iterative methods. The simulation results revealed that the MPPT circuit, which employs a boost-cascaded-with-buck converter, handled rapid variation of temperature and abrupt changes of load current; this method enables stable operation with high power transfer efficiency. The proposed MPPT technique is a useful analog MPPT solution for thermoelectric generators.     

Experimental Characterization of Thermoelectric Modules and Comparison with Theoretical Models for Power Generation

The interest in thermoelectrics for power generation applications has dramatically increased over the past decade as a result of recent advancements in thermoelectric materials. Although measuring thermoelectric properties of materials has received significant attention, measuring thermoelectric module (TEM) power generation performance has received less attention. Characterizing TEMs is vital for validating module-level models used in optimizing TEM designs. Measurements of module performance can also be used for the optimal incorporation of TEMs into power generation systems. A TEM test apparatus has been developed and characterized to test current and future modules under a wide range of temperature and loading conditions. In addition to temperatures and electrical performance metrics, heat rates, and mechanical loading conditions are monitored. The developed technique extracts module parameters, which can be used for system-level design, to measure performance of advanced TEMs, and to validate theoretical models for module design optimization. Experimental results are compared with standard analytical TEM models and a newly developed model.     

Thin-Film Thermoelectric Modules for Power Generation Using Focused Solar Light

We demonstrated the fabrication of thin-film thermoelectric generators and evaluated their generation properties using solar light as a thermal source. Thin-film elements of Bi_0.5Sb_1.5Te₃ (p-type) and Bi₂Te_2.7Se_0.3 (n-type), which were patterned using the lift-off technique, were deposited on glass substrates using radiofrequency magnetron sputtering. After annealing at 300°C, the average Seebeck coefficients of p- and n-type films were 150???V/K and ?104???V/K, respectively, at 50°C to 75°C. A cylindrical lens was used to focus solar light to a line shape onto the hot side of the thin-film thermoelectric module with 15 p?Cn junctions. The minimum width of line-shaped solar light was 0.8?mm with solar concentration of 12.5 suns. We studied the properties of thermoelectric modules with different-sized p?Cn junctions on the hot side, and obtained maximum open voltage and power values of 140?mV and 0.7???W, respectively, for a module with 0.5-mm p?Cn junctions. The conversion efficiency was 8.75?×?10^?4%, which was approximately equal to the value estimated by the finite-element method.     

Thermoelectric Power Generation System Using Waste Heat from Biomass Drying

This paper looks at thermoelectric power generation from waste heat from a biomass drier. In this study, the researchers selected four thermoelectric modules: two thermoelectric cooling modules (Model A: MT2-1,6-127 and Model B: TEC1-12708) and two thermoelectric power generation modules (Model C: TEP1-1264-3.4 and Model D: TEG1-1260-5.1) for testing at temperatures between 25°C and 230°C. Test results indicated that the thermoelectric TEC1-12708 could generate a maximum power output of 1 W/module and TEP1-1264-3.4, TEG1-1260-5.1, and MT2-1,6-127 could generate 1.07 W/module, 0.88 W/module, and 0.76 W/module, respectively. Therefore, the thermoelectric cooling of TEC1-12708 was appropriate to use for thermoelectric power generation from waste heat. The experiments used four ventilation fans (6 W, 2.50 m³/s) and 12 thermoelectric modules which were installed in the back of a charcoal brazier. The experiments were conducted and tested in conditions of recycling 100%, 75%, 50%, and 25% of outlet air. Testing results identified that the temperatures of the drying room were 81°C, 76°C, 70°C, and 64°C, respectively. The power generation system could generate about 22.4 W (14 V, 1.6 A) with an air flow of 9.62 m³/s. The thermoelectric module can convert 4.08% of the heat energy to electrical energy.     

太阳能发电技术与应用 第三讲:最大功率点跟踪技术

3.1硅太阳电池的等效电路太阳电池一般由半导体材料制成,图1是常见的硅太阳电池在日照情况下的等效电路。图中Isc称之为光生电流,或短路电流,其值正比于太阳电池的面积和入射光的辐照度,而且它是在负载RL短路时,太阳电池可能输出的最大电流;ID为暗电流,是太阳电池在无光照情况下外加电压时,流过内部p-n结的单向电流。     

High-Temperature Performance of Stacked Silicon Nanowires for Thermoelectric Power Generation

Deep reactive-ion etching at cryogenic temperatures (cryo-DRIE) has been used to produce arrays of silicon nanowires (NWs) for thermoelectric (TE) power generation devices. Using cryo-DRIE, we were able to fabricate NWs of large aspect ratios (up to 32) using a photoresist mask. Roughening of the NW sidewalls occurred, which has been recognized as beneficial for low thermal conductivity. Generated NWs, which were 7 μm in length and 220 nm to 270 nm in diameter, were robust enough to be stacked with a bulk silicon chip as a common top contact to the NWs. Mechanical support of the NW array, which can be created by filling the free space between the NWs using silicon oxide or polyimide, was not required. The Seebeck voltage, measured across multiple stacks of up to 16 bulk silicon dies, revealed negligible thermal interface resistance. With stacked silicon NWs, we observed Seebeck voltages that were an order of magnitude higher than those observed for bulk silicon. Degradation of the TE performance of silicon NWs was not observed for temperatures up to 470°C and temperature gradients up to 170 K.