Thermoelectric Power Supply

The so-called Seebeck effect is used to generate energy from temperature differences. In this case, an electric current flows between two contact points of two electrical conductors, which have a different temperature. Since the voltages generated by the Seebeck effect are extremely small (a few microvolts per degree of temperature difference), Fraunhofer IIS has been researching for several years to use very small voltages and energy quantities through electrical circuitry and to reduce the energy requirements of electrical systems. Our current developments can already be operated permanently with 2 degrees Kelvin.

The realization of an efficient thermal harvesting system faces different challenges. First, a good thermal conductivity from the heat source to the thermoelectric generator (TEG) and from the TEG to the heat sink and the environment must be realized. Thermal simulations take into account the properties and dimensions of the materials and components involved and calculate the optimal configuration for the best heat flow. In addition, a good electrical matching between the TEG and the electronic power management must be ensured. Optimized voltage regulators are used for this purpose which, if necessary, also use maximum power point adjustment (MPPT) techniques when the temperature gradient has some variability. To use even the smallest amounts of energy from the environment, such as on the human body or on buildings, ultra-low voltage start-up voltage boosters can be used to operate with the lowest voltage levels of TEGs. Finally, a highly efficient charge controller must be developed to store the energy in an application-specific energy store.

Taking into account the challenges outlined above, a multidisciplinary approach, including materials science, physics and electrical engineering, is required to arrive at an energy and cost-efficient energy supply.

• Highly integrated voltage transformers: starting voltages below 20 mV and high efficiency up to 90%
• Charge Controllers and Battery Management Circuits: Efficient charging of various types of energy storage with optional charge state estimation
• Maximum power point tracker for voltage transformers for automatic impedance matching
• Characterization of thermoelectric harvesters: Laboratory equipment for the generation of defined thermal differences and for the measurement of the output power depending on various parameters
• Thermal Modeling and Simulation: Software tools for modeling thermoelectric generators, heat sinks and interface structures to optimize heat flow and power output