Wide Range Energy Harvesting Technique for Current Transformer Based on Coil Adaptive Switching

Current transformer (CT) power harvesting systems are the main power supply for sensors on ac transmission lines. However, CT power harvesting systems have difficulty adapting to the wide range of currents on ac transmission lines, failing to activate or obtain sufficient power at very low currents and having difficulty suppressing excessive voltage spikes due to deep saturation of the core at very high currents or reducing excessive temperature rise due to high induced currents. This article proposes a coil adaptive switching technology of the secondary side of the CT, using the thyristor and three-phase diode rectifier bridge to form a switching circuit, generating the trigger current of the thyristor by the secondary-side voltage of the transformer, and making the trigger current to follow the changes in the secondary-side voltage, so that the thyristor automatically triggered to conduction, so as to change the turns of the coil of the secondary side of the transformer, that is, when the current of the ac transmission line is weak, it is switched to the coil group with fewer turns, and when the current is high, it is switched to the coil group with more turns, which broadens the scope of CT energy harvesting system adapting to the change of the current of the ac transmission line. Through prototype experiments, it is verified that the proposed technology can enable the CT energy harvesting system to start-up with outputing the power of 100 mW at ac transmission line current as low as 2 A and withstand high current over 1250 A, and work stably at 1.25 kA.