A Novel Identification Method of Thermal Resistances of Thermoelectric Modules Combining Electrical Characterization Under Constant Temperature and Heat Flow Conditions

The efficiency of a Thermoelectric Module (TEM) is not only influenced by the material properties, but also by the heat losses due to the internal and contact thermal resistances. In the literature, the material properties are mostly discussed, mainly to increase the well-known thermoelectric figure of merit ZT. Nevertheless, when a TEM is considered, the separate characterization of the materials of the p and n elements is not enough to have a suitable TEM electrical model and evaluate more precisely its efficiency. Only a few recent papers deal with thermal resistances and their influence on the TEM efficiency; mostly, the minimization of these resistances is recommended, without giving a way to determine their values. The aim of the present paper is to identify the internal and contact thermal resistances of a TEM by electrical characterization. Depending on the applications, the TEM can be used either under constant temperature gradient or constant heat flow conditions. The proposed identification approach is based on the theoretical electrical modeling of the TEM, in both conditions. It is simple to implement, because it is based only on open circuit test conditions. A single electrical measurement under both conditions (constant-temperature and constant-heat) is needed. Based on the theoretical electrical models, one can identify the internal and thermal resistances

Service Continuity of PV Synchronous Buck/Buck-Boost Converter with Energy Storage†

Numerous advantages offered by Photovoltaic (PV) generation systems coupled with the increasing power demands for clean energy put PV systems in the front of many research works. For stand-alone applications powered with PV systems, the reliability of the power conversion stage is essential to ensure the continuous supply of energy. Therefore, in the case of any failure occurring in the power conversion stage, it is mandatory to provide remedial actions to guarantee the service continuity of the produced electrical power. This paper analyses the service continuity of a two-stage buck/buck-boost converter with energy storage, driven with synchronous control. The initial two-stage converter is made fault-tolerant and robust to failures of its two switches by adding only one additional switch associated with two diodes. In this study, only open-circuit switch faults are considered. The proposed fault-tolerant circuit and the initial one have the same electrical behavior when synchronous control is used. The applied synchronous control in both healthy conditions and post-fault operation ensures the same functionalities without degrading the system’s performances. The proposed two-stage synchronously-controlled circuit is validated through simulation in the cases of open circuit faults on the two switches of the initial converter. The obtained results show the feasibility of the proposed functional redundancy and the continuity of operation at full power after switch fault diagnosis

Influence of contact thermal resistances on the Open Circuit Voltage MPPT method for Thermoelectric Generators

International audienc

Service Continuity of PV Synchronous Buck/Buck-Boost Converter with Energy Storage†

Numerous advantages offered by Photovoltaic (PV) generation systems coupled with the increasing power demands for clean energy put PV systems in the front of many research works. For stand-alone applications powered with PV systems, the reliability of the power conversion stage is essential to ensure the continuous supply of energy. Therefore, in the case of any failure occurring in the power conversion stage, it is mandatory to provide remedial actions to guarantee the service continuity of the produced electrical power. This paper analyses the service continuity of a two-stage buck/buck-boost converter with energy storage, driven with synchronous control. The initial two-stage converter is made fault-tolerant and robust to failures of its two switches by adding only one additional switch associated with two diodes. In this study, only open-circuit switch faults are considered. The proposed fault-tolerant circuit and the initial one have the same electrical behavior when synchronous control is used. The applied synchronous control in both healthy conditions and post-fault operation ensures the same functionalities without degrading the system’s performances. The proposed two-stage synchronously-controlled circuit is validated through simulation in the cases of open circuit faults on the two switches of the initial converter. The obtained results show the feasibility of the proposed functional redundancy and the continuity of operation at full power after switch fault diagnosis

Equivalent electrical circuit of thermoelectric generators under constant heat flow

International audienc

Equivalent Electrical Circuits of Thermoelectric Generators under Different Operating Conditions

Energy harvesting has become a promising and alternative solution to conventional energy generation patterns to overcome the problem of supplying autonomous electrical systems. More particularly, thermal energy harvesting technologies have drawn a major interest in both research and industry. Thermoelectric Generators (TEGs) can be used in two different operating conditions, under constant temperature gradient or constant heat flow. The commonly used TEG electrical model, based on a voltage source in series with an electrical resistance, shows its limitations especially under constant heat flow conditions. Here, the analytical electrical modeling, taking into consideration the internal and contact thermal resistances of a TEG under constant temperature gradient and constant heat flow conditions, is first given. To give further insight into the electrical behavior of a TEG module in different operating conditions, we propose a new and original way of emulating the above analytical expressions with usual electronics components (voltage source, resistors, diode), whose values are determined with the TEG’s parameters. Note that such a TEG emulation is particularly suited when designing the electronic circuitry commonly associated to the TEG, to realize both Maximum Power Point Tracking and output voltage regulation. First, the proposed equivalent electrical circuits are validated through simulation with a SPICE environment in static operating conditions using only one value of either temperature gradient or heat flow. Then, they are also analyzed in dynamic operating conditions where both temperature gradient and heat flow are considered as time-varying functions

Service continuity of PV synchronous Buck/Buck-Boost converter with energy storage

International audienceRenewable Energy sources present an efficient and economically viable energy supply approach for stand-alone applications. Electricity produced with Photovoltaic (PV) panels is among the most important energy contributions in energy harvesting systems. Moreover, the produced electrical power should not be interrupted, especially in critical applications. In this paper, the service continuity of a Buck/Buck-Boost converter, used as an interface between the PV source and the load, is discussed. A new fault tolerant converter topology is proposed, which allows to guarantee service continuity in open circuit switch fault cases, when a synchronous control is applied. A single additional switch, associated with two diodes, allows to keep the same power exchanges capabilities after open switch fault diagnosis, without modifying the synchronous control applied in healthy conditions. The resulting fault tolerant system is validated by simulation and the obtained results confirm the effectiveness of service continuity under open circuit switch fault

Identification of thermal resistances of thermoelectric modules by electrical characterization

International audienc

A thermoelectric energy harvester with a single switch unified control for autonomous applications

International audienceIn the past decades, due to the increasing environmental concerns, many research works have targeted the use of energy harvesting technologies as an alternative to the fossil fuels. Free availability of heat makes harvesting energy from Thermoelectric Generators (TEGs) as one of the most viable sources of electricity. In a thermoelectric energy harvester, it is mandatory to perform Maximum Power Point Tracking (MPPT), aiming at maximizing the extracted energy irrespective of the temperature gradient conditions. The Open Circuit Voltage (OCV) MPPT method appears as the most widely used and suitable for TEGs. Moreover, the output voltage across the load must also be regulated. To perform MPPT and output voltage control simultaneously, conventional two-stage DC-DC converters are usually used. In this paper, we propose an unified control for a Single Switch DC-DC Converter (SSC), performing both, the MPPT and the output voltage control. Moreover, the reduction of the number of switches decreases the cost of the harvester as well as the size and the control complexity. The resulting harvester has been modeled and simulated; the results confirm the effectiveness and the robustness of the simultaneous MPPT and output voltage regulation