An energy-independent wearable electronic system is being researched, where the energy required for its operation is obtained from human body movements and heat flow. The system power source consists of an electromagnetic motion energy harvester (mass up to 70 g, peak power reaching 38 mW depending on the intensity of movement), a thermoelectric harvester (mass 112 g, peak power up to 3 mW), power converters and a storage capacitor. The functional part of the system consists of a temperature and humidity sensors and a wireless data transmission module, while the energy-aware power management and the main function control is accomplished by a microcontroller, maintaining a safe input voltage range by adjusting the average consumption of the device. Only off-the-shelf components that provide greater configurability and could utilize a broader harvested voltage range were used. This study demonstrates that using a common energy storage element provides an energy flow stabilization effect that reduces the overall power instability, which can be a limiting factor for a single energy harvester system. The prototype was tested in controlled environment by walking on a treadmill and provided the necessary amount of energy for a sustained system operation even during motion pauses. Electrical energy storage efficiency of the system averaged at 17 %, with a peak efficiency reaching 21 %.

A combined human motion and heat energy harvesting system are under investigation. Main parts of the developed human motion energy harvester are flat, spiral-shaped inductors. Voltage pulses in such flat inductors can be induced during the motion of a permanent magnet along its surface. Due to the flat structure, inductors can be completely integrated into the parts of the clothes, and it is not necessary to allocate extra place for movement of the magnet as in usual electromagnetic harvesters. Prototypes of the clothing with integrated proposed electromagnetic human motion energy harvester are created and tested. Voltage of generated impulses is shown to be high enough to be effectively rectified with commercially available diodes and ready to be stored; however, efficiency depends on properties of controlling circuit. In order to increase the sustainability of the energy source and its stability, an option for combining a motion energy harvester with a human body heat energy harvester is also considered. Thermoelectric generator that harvests electricity from waste heat of human body is presented, and generated voltage and power are compared at different activity levels and ambient temperatures. Power generated with thermoelectric generator located on lower leg reached up to 35 mW with peak voltages reaching 2 V at certain conditions. A possible power management set-up and its efficiency are discussed.

Energy harvesting offers a promising solution for powering a growing variety of low-power electronics; however, harnessing energy from human motion, with its irregular and low-frequency bursts of power, presents conversion challenges. As rectification is a common part of it, this study investigates the influence of smoothing capacitor values on rectifier output for short, intermittent signals. We propose an analytical model that identifies an optimal smoothing capacity for the full-bridge rectifier, considering harvester internal resistance, frequency, and load resistance and leading to the highest average output voltage after rectification. The model was validated with detailed computer simulations; furthermore, a similar effect was revealed on a voltage multiplier circuit as well. Experimental measurements demonstrate that deviating from the optimal smoothing capacity results in up to 10% decrease in rectified RMS voltage, leading to significant drops in output power in specific energy harvesting systems. A real-world experiment with a human motion energy harvester further confirmed the findings in a naturally varying generation environment.

The paper presents results of Latvian distribution system operator Sadales tikls AS (ST) and Riga Technical University (RTU) joint research on possibilities to increase the permissible loading level of the operating MV cables in order to improve the efficiency of the existing network assets usage and increase the supply reliability. Permissible loading level determination of the operating MV cables from the heating point of view is affected by many variable factors such as ambient environment, temperature, number and configuration of the cables etc. To estimate the temperature characteristics in dependence of load current of the operating MV cables in the real environment at different climatic and ambient environments (cable channels, ladders, soil and pipes) in the cities of Latvia a special MV cable sheath and ambient environment temperature monitoring device is designed. Sheath and ambient environment temperature monitoring of nine 10 kV and 20 kV cables at four ST 110/10-20 kV substations is carried out for a period of one year. By analyzing the acquired temperature monitoring data, dynamics of the cable sheath temperature in dependence of load current, ambient environment and temperature is determined. A mathematical model for maximum achievable MV cable sheath temperature prediction is developed.

Electromagnetic human motion energy harvesters have shown good results previously. As the direct output of a harvester cannot be used for powering electronic devices, the paper focuses on a complete setup of rectifier, ultra-low voltage converter and a capacitor charger. The aim is to evaluate performance of off-the-shelf elements and modules for electromagnetic human motion harvester. Three commercially available converters were tested in a controlled environment and on a human separately. The best configuration obtained 4.9V on a capacitor in less than 5 minutes with peak efficiency of 22.7%, presenting a fully autonomous wearable human motion harvester as a usable voltage source.

The Thesis studies human energy harvesting in individual development stages, which are confirmed experimentally.