MPPT for Electromagnetic Energy Harvesters Having Nonnegligible Output Reactance Operating Under Slow-Varying Conditions

Most maximum power point trackers (MPPTs) for electromagnetic energy harvesters (EMEHs) are based on resistive matching technology, where the input resistance of the MPPT is made equal to the magnitude of the output impedance of the harvester. This is valid when the output reactance of the EMEH is much smaller than its output resistance. However, some EMEHs, such as permanent magnet generator, have nonnegligible output reactance. The discrepancy between the power extracted by the resistive matching technology and the maximum extractable power will increase as the output reactance increases. Under high excitation frequency and low operating temperature, the effect of the output reactance will become more dominant. In order to deal with such issue, an MPPT that can counteract the effect of the coil inductance and match with the coil resistance is presented. It does not require knowing coil parameters a priori and the harvester will be operated at its true maximum power point. A 7-W prototype for testing the proposed algorithm has been built and evaluated. Its performance is favorably compared with the amount of power extracted with the resistive matching technology.