Takenobu Kajikawa

Comparison of maximum power point control methods for thermoelectric power generator

This paper describes the comparison of operating point control methods such as maximum power point tracking control (MPPT) and a constant voltage control applied to the thermoelectric devices. To experimentally evaluate the power control methods, a one-chip micro controller controlled DC-DC converter was inserted between the thermoelectric module and a load. The derived power from the module by constant voltage control is the same with the MPPT control method if the temperature difference keeps constant value. On the other hand, a mismatch power loss of constant voltage method increases with a fluctuation magnitude from the reference value and the fluctuation frequency. The maximum mismatch power loss of constant voltage method by fluctuation is around 20% regardless of a change of maximum temperature difference when the reference output voltage coincides with the optimized value of the maximum temperature difference.

Mismatch Power Loss Reduction on Thermoelectric Generator Systems Using Maximum Power Point Trackers

A new concept of maximum power point tracking control method for Thermoelectric Power Generator (TEG) systems has been developed. The virtual load conductance of the load is feedback controlled to maintain the same value of the internal conductance of the thermoelectric (TE) array using DC-DC converter. The prototype Maximum Power Point Tracker (MPPT) circuit, which is composed of buck-boost DC-DC converter, has been developed successfully. The circuit showed excellent tracking ability as MPPT against the change of load and heat source temperature as well as having wide matching ability

Thermoelectric power generation systems recovering heat from combustible solid waste in Japan

The status and future prospects on the development of thermoelectric power generation systems utilizing heat from the municipal solid waste in Japan are reviewed in this paper. Two ongoing research and development programs related to this application in Japan are briefly introduced. The characteristics of heat from the solid waste processing system lead to the peculiar concept of thermoelectric power generation system. The theoretical and experimental studies including small scale onsite experiment are shown to discuss several technological problems and the guideline for the development of such systems.

Thermoelectric properties of magnesium silicide processed by powdered elements plasma activated sintering method

Efficient, inexpensive and non-toxic thermoelectric elements such as silicides should be developed for large scale application such as recovering the combustion heat of municipal solid waste, of which the characteristics are greatly fitted to thermoelectric power generation. This paper introduces the characterization and thermoelectric properties of undoped and doped n-type magnesium silicide processed by the powdered elements spark plasma sintering method. The patterns by powder X-ray diffractometry showed that it had typical polycrystalline phase. The temperature dependence of thermoelectric properties such as the Seebeck coefficient and electrical conductivity were measured for the temperature range from 300 K to 773 K. As a result, a power factor value 6.0/spl times/10/sup -4/ (W/mK/sup 2/) was obtained at 773 K for a doped sample.

Status and future prospects on the development of thermoelectric power generation systems utilizing combustion heat from municipal solid waste

The characteristics of combustion heat from the municipal solid waste are fitted for a large-scale application of thermoelectric power generation potentially. The status and future prospects of thermoelectric power generation systems to recover electricity from this heat source in Japan are reviewed and discussed. Experimental results on three different types of small-scale (500 W class) thermoelectric power generation systems installed in the real municipal solid waste processing systems to demonstrate the technological feasibility and to extract the technological problems are briefly introduced. The conceptual designs of a small scale system for the next phase of the R&D program are presented. From the view point of large-scale realization the thermoelectric material and modules configurations required for this application are also discussed. A case study on the marginal cost estimation shows the cost reduction to be less than 0.4-0.5 Million Yen/kW in order to make a profit on this system.

Evaluation of multi MPPT thermoelectric generator system

A large scale Thermoelectric Generator System (TEG) has temperature distribution for both heat source and heat sink, leading mismatch power loss. The insertion of power conditioner witch has impedance matching ability between TEG and a load has a potential to recover the mismatch power loss of the system effectively. The practical maximum power point tracking (MPPT) conditioner for TEG with the size of 30times60 mm2, which can be used up to 30 W has been developed. The power conditioner is composed of Buck-Boost converter, internal power supply, and microcontroller. The microcontroller controls the virtual conductance of the load to match the internal conductance of the connected thermoelectric modules. The effect of MPPT power conditioner insertion is evaluated using the experimental TEG system, which composed of four thermoelectric module (TEM) strings. We confirmed each MPPT power conditioner connected in parallel maintains optimum operating condition. The results suggest that introducing MPPT power conditioner has a potential to reduce mismatch power loss and improve load matching ability of TEG system.

Development for Advanced Thermoelectric Conversion Systems

ldquoDevelopment for advanced thermoelectric conversion systemsrdquo supported by the new energy and industrial technology development organization (NEDO) has been successfully completed as one of the Japanese national energy conservation projects. Three types of the cascaded thermoelectric modules operating up to 850 K in high electrode temperature and two types of Bi-Te thermoelectric modules operating at 523 K in maximum electrode temperature in consideration with the durability have been developed. In order to proceed to the practical phase four types of advanced thermoelectric power generation systems have been experimentally demonstrated for the waste heat recovery from the industrial electric heating furnace, the waste heat recovery using two types heat exchanger systems from the diesel engine co-generation system, the waste heat recovery from a large scale electric transformer, and the waste heat recovery from a projector lamp. Results of the experiments on the performance and durability for the advanced modules and for the demonstration systems are summarized.

Thermoelectric figure of merit of impurity doped and hot-pressed magnesium silicide elements

Intermetallic magnesium compounds and their solid solutions have been known as potentially promising thermoelectric materials for the middle temperature power generation application. Spark plasma sintering and subsequent hot-pressing were used to make the impurity doped Mg/sub 2/Si thermoelectric elements. The temperature dependence of thermoelectric properties such as the Seebeck coefficient, electrical conductivity and thermal conductivity was measured to clarify the optimum performance of sintered Mg/sub 2/Si elements. Moreover, the semiconducting properties such as Hall mobility and carrier concentration were measured by the van der Pauw method. In the case of 0.6 at%Sb doped n-type sintered elements the maximum power factor was obtained 3.0/spl times/10/sup -3/ W/mK/sup 2/ at 773 K and the figure of merit was 0.87/spl times/10/sup -3/ K/sup -1/ and dimensionless figure of merit ZT was 0.67. Concerning p-type Mg/sub 2/Si elements, silver doped, sintered Mg/sub 2/Si was made by the same procedure as n-type antimony doped sintered elements. The junction of a Mg/sub 2/Si element with the electrode was also studied to check the junction resistance between the thermoelectric element and the electrode. It was found that Fe was suitable as an electrode.

Development of thermoelectric power generation system utilizing heat of combustible solid waste

The paper presents the development of thermoelectric power generation system utilizing heat of municipal solid waste. The systematic classification and design guideline are proposed in consideration of the characteristics of solid waste processing system. The conceptual design of thermoelectric power generation system is carried out for a typical middle scale incinerator system (200 ton/day) by the local model. Totally the recovered electricity is 926.5 kWe by 445 units (569,600 couples). In order to achieve detailed design, one dimensional steady state model taking account of temperature dependency of the heat transfer performance and thermoelectric properties is developed. Moreover, small scale on‐site experiment on 60 W class module installed in the real incinerator is carried out to extract various levels of technological problems. In parallel with the system development, high temperature thermoelectric elements such as Mn‐Si and so on are developed aiming the optimization of ternary compound and high...

Thermoelectric properties of high temperature transition metal silicides prepared by spark plasma sintering method

From the viewpoint of the most efficient utilization of fossil fuel resources as heat, the combustion temperature should be as high as possible to apply to the energy cascading system. Therefore, thermoelectric energy conversion as a topping system is recognized to be very important. High temperature metal silicides such as chromium silicide (M.P. 1763 K) and tungsten silicide (M.P. 2433 K) and so on have been known as a group of metal silicides. The spark plasma sintering method was selected to prepare thermoelectric elements of chromium silicide and tungsten silicide as examples of the high temperature, transition metal silicides. It is clarified that the spark plasma sintering method is very useful to make such a high temperature alloy. The temperature dependence of thermoelectric properties such as the Seebeck coefficient, electrical resistivity, power factor, thermal conductivity, carrier concentration and Hall mobility was measured to find out the preferable preparation conditions such as doping level and solid solution for these materials systems. The maximum power factor was 0.7/spl times/10/sup -02/ W/mK/sup 2/ at 900 K for chromium silicide, and 3.0/spl times/10/sup -02/ W/mK/sup 2/ at 1000 K for tungsten silicide as the p-type thermoelectric element respectively in the experiment.