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Design and implementation of a highly efficient piezoelectric power harvesting and vibration damping system

Over the last few years, piezoelectric elements have gained popularity as a convenient and relatively inexpensive interface between the electrical and mechanical domains of power harvesting and vibration damping systems. Power harvesting is commonly performed by placing a bridge rectifier across the piezoelectric element and feeding the output into a capacitor and matched load, in much the same manner as used in a standard power supply circuit. However, the overall efficiency of the electrical power harvesting system using this approach can be quite low. Therefore, there is a continued search for circuit architectures and techniques to enhance the efficiency and performance of such systems. It is shown that using piezoelectric devices for electrical power harvesting is closely related to vibration damping using the same devices. This paper proposes that focusing on the reflected mechanical power could produce more efficient systems than focusing on electrical power transfer alone. In exploring this proposition an attempt was made to identify important parameters in the design of such systems. This exploration has demonstrated the importance of maximizing the voltage across the piezoelectric element as the primary means of maximizing the reflected mechanical power. Complexity and cost are often issues when operating piezoelectric devices at high voltages, which led to the development of a relatively simple charge polarity reversal mechanism. Such a mechanism has been demonstrated to improve the efficiency of energy harvesting and/or vibration damping. Simulation of this concept shows a substantial improvement over the bridge rectifier concept. Whilst the magnitude of improvement is dependent on how high the voltage across the piezoelectric element can be raised, the scenario shown in detail gives an improvement of approximately two orders of magnitude.