An energy-efficient CMOS interface circuit with maximum power point tracking and power management capabilities for self-powered sensor node applications using 50/60 Hz transmission line magnetic field harvesters

In this paper, an interface circuit for far-distance energy harvesting from magnetic field of overhead lines is presented. Due to the specific conditions of this type of energy harvesting, such as low available power, low induced voltage in the energy harvester coil, and change of energy harvester impedance, a direct AC/DC switching converter should be used. A maximum power point tracking solution is also necessary to guarantee impedance matching at different operation points. Since the harvested power is in the range of a hundred micro-watts, the power usage of the control circuitry is of significant importance and conventional design approaches based on microcontrollers and FPGAs which require ADCs, DACs and digital signal processing cannot be applied here. The proposed processing circuitry presented in this paper uses three feedback loops to perform the harvesting and energy transfer control. Only low-power comparators and basic digital gates are used as signal-processing elements to limit the power dissipation of the designed control blocks. The impedance matching inner loop samples the H-bridge voltage drop to extract the output load current and perform PWM impedance matching while transferring a rectified current to the output capacitor. Another inner feedback loop is used at the output capacitor using two-level comparison to regulate the output voltage. For maximum power point tracking an outer feedback loop samples the output voltage transfer rate and using a 50 Hz reference generator, adjusts the parameters of the impedance matching circuit of the first inner loop. With the proposed approach, in addition to converting the AC input power to a DC voltage, the output load is regulated at a fixed potential and using the MPPT control loop, the maximum power available from the coil is delivered to the output with relatively low dissipation. The proposed circuit is evaluated using a 0.18 μm standard CMOS technology and operates as a self-powered circuit without an external power source. Based on the obtained results, the efficiency of the proposed circuit at 119 µW input power is about 92.4%, and the MPPT efficiency is about 95%, which is suitable for low-power applications.