Comparison of Control Strategies and Electromechanical Devices for the Backpack Energy Harvesting System

This article provides a general overview on the control strategies and their implications for the backpack energy harvesting system. The control strategies include reactive control and resistive damping. The study is performed for three cases of electric generator: the direct drive linear generator, the rotary machine integrated with the trans-rotary magnetic gear (MITROMAG), and the rotary machine coupled with a mechanical rack and pinion (MRP). Equivalent circuits based upon electrical-mechanical analogies are employed to help understand the system dynamics under the two control strategies. It is shown that in all cases, upon reactive control, more power can be harvested; however, it comes at the cost of a higher velocity, peak power, and force requirement. Moreover, it is shown that for most of the operating points considered, the direct drive linear generator outperforms the geared electromechanical devices in terms of the harvested power. Furthermore, it is revealed that the low stiffness of the MITROMAG slightly increases its harvested power compared to the MRP under the resistive damping strategy.