Mechanical Power Supply

A principle uses piezoelectric materials that react with charge separation when deformed by motion or periodic vibration. Piezoelectric generators typically generate large voltages in the range of ten to one hundred volts, but only very small currents. They can be built as a resonant cantilever structure or applied directly to surfaces that exhibit mechanical deformation.

Another method of converting mechanical energy into electrical energy are electrodynamic or inductive generators, where a combination of a magnet and a coil are the key elements for power generation. When a combination of these components is subjected to vibration and the magnet moves relative to the coil, an electric current is induced in the coil. After rectification, this current can be used to charge a battery or capacitor. The voltages of an electrodynamic generator are typically lower than those of piezoelectric transducers. The current can be influenced by the characteristics of the coil and magnet.

Electrostatic generators can also be used to generate electrical energy from vibrations. They are comparable to an electrical capacitor in which one capacitor plate is suspended so that it can move relative to the other. By charging the capacitor when the plates are far apart and discharging the capacitor when the plates are nearby, electrical energy can be generated. With this generator principle, the output power depends on the capacitance value of the capacitor and its charging voltage.

The realization of an efficient mechanical power generation system involves various challenges. First of all, a good mechanical coupling from the vibration source to the harvester must be ensured. Mechanical simulations take into account the properties and dimensions of the components and calculate the optimal configuration for the correct coupling.

In addition, a good electrical matching between the mechanical harvester and the electronic power management must be ensured. For this purpose, optimized voltage regulators are used, which can also use techniques to track the maximum power point. Furthermore, a highly efficient charge regulator must be designed to store the energy.

Given the above challenges, a multidisciplinary approach involving materials science, physics and electrical engineering is essential to achieve an energy-efficient and cost-effective power supply.

A critical component alongside the generator itself is power management, which has the task of adjusting the voltage or current profile of the harvester to charge a capacitor or battery. Rectifiers and DC/DC converters are typically used. Challenges here are the high voltages and low currents of piezoelectric generators. An active rectifier can be used when very low voltages are provided by the generators. In certain cases, point followers with maximum power are also used to automatically adapt the power management to the harvester.

We have concentrated on the development of highly efficient power management systems and power supplies as well as complete microsystems.

The special thing about our research results are:

• Processing of smallest currents (less than 3µA) and voltages (less than 20 mV)
• Use of smallest vibrations (less than 100 mg)
• Use of high pulses at low frequencies (below 10 Hz)

• Highly efficient voltage transformers: Maximum voltage range up to 80 volts and high efficiency up to 90%.
• Charge regulator and battery management circuits: Efficient charging of various types of energy storage devices with optional state-of-the-art charge estimation.
• Maximum Power Point Tracker control loops for voltage converters to perform automatic impedance matching
• Characterization of mechanical harvesters: Laboratory equipment for generating defined oscillations and measuring the output power as a function of various parameters
• Mechanical Modeling and Simulation: Software tools for modeling mechanical generators