pone.0358867.t003 - <p> </p>

Nevertheless, vibration suppression and energy harvesting often compete with each other due to using single-objective control methods and the tradeoff has limited the effectiveness of current systems. To reduce the tradeoff, the innovation of this paper is to propose a bi-objective control strategy in which vibration suppression and energy harvesting are optimized by two independent objective functions.

Firstly, the state equation of the quarter-suspension SVSEH system is derived and nonlinear restoring force is linearized. Then the reduced-tradeoff control of the quarter-suspension SVSEH system is first equivalent to a bi-objective H2−norm optimization subject to an H∞−norm constraint. Next, the mixed H2/H∞ state feedback-based control method is presented in detail and a low-pass filter is adopted to ensure the “strictly proper” condition of H2 control.