Implementation of reactive and resistive load matching for optimal energy harvesting from piezoelectric generators

This paper discusses the implementation of an equivalent resistive-reactive load for the optimum energy harvesting from vibration sources. In photovoltaic applications, the converter impedance that ensures the maximum power is real and the Maximum Power Point Tracker (MPPT) uses a single variable optimization algorithm (resistive load matching). The piezoelectric generator, instead, is characterized by a high capacitive impedance. Thus, the optimal power generation is obtained by a resistive and reactive load impedance (resistive and reactive load matching). Taking into account that the load matching inductor should be changed depending on the excitation frequency and it is usually impractically large if implemented by a passive element, the adaptive resistive-inductive (RL) impedance is here implemented using a bidirectional dc-dc converters and their parameters are tuned using a two-dimentional MPPT using the downhill simplex method. Simulation and experimental results obtained on a prototype, where the digital control has been implemented on a microcontroller platform, confirm the proposed analysis and the performance achievable by the proposed method. The resistive and reactive load matching strongly increases the power generation especially for excitation frequencies different from the resonant and antiresonant frequencies of the piezoelectric generator.