Maximum Power Point Tracking for Subway Rail Potential-Based Energy Harvester Using the Open Circuit Voltage Method

Sensors are used in the DC metro system for monitoring. Still, there is a problem of high costs using cable and battery power supply, while achieving self-powered technology through ambient energy harvesting is difficult on underground tracks. To address this issue, considering that the rail in the subway dc power supply system has a certain potential relative to the ground, this work proposes a subway rail potential-based energy harvester (RPEH). An energy-harvesting equivalent circuit is constructed to analyze the output characteristic of the rail potential. To achieve maximum energy harvesting, the open-circuit voltage method is applied. However, the open-circuit voltage method requires disconnecting the energy harvesting device to obtain the open-circuit voltage. To significantly shorten the open-circuit monitoring time, this work designs an energy harvesting device based on a two-stage MOSFET structure. Additionally, the energy harvesting circuit fully utilizes low-power analog discrete components without relying on programmable controllers, thereby reducing system complexity and power consumption. The experimental results show that the RPEH can quickly track the optimal energy point under varying voltage levels and reduce the open-circuit detection time to less than 2ms. It demonstrates that the proposed method can achieve maximum power point tracking, rapid response, and low power consumption, meeting the power supply needs of underground track sensors.