Energy considerations in active vibratory systems

Abstract

Active vibration isolation systems can generally offer substantial improvements in dynamic performance. However, their use has been limited due to the burden of cost of their implementation and operation. The cost of operation is mainly because of the external supply of energy required by these systems. In this dissertation, the energy requirements of a class of active systems are considered. A new approach that extends the understanding and analysis of active vibratory systems is developed. The approach constitutes the study of power/energy requirements that in the end will yield designs that achieve high performance but at a lower cost of energy consumption. This is achieved by developing a formulation for the average power/energy of the system components for given disturbances, referred to as the power distribution. Particularly, the power/energy expressions of the control actuator are of interest. By examining the sensitivity of power distribution to design changes, it is shown that energy-efficient designs are possible. Any change in the power distribution corresponds to a certain change in the dynamic performance of the system. The consideration of energy requirements in the face of desired dynamic performance is referred to in this work as the energy trade-offs. Trends in the energy trade-offs emerging from consideration of optimal single DOF systems are studied, and are shown to extend to a higher DOF model that uses the same performance criterion. This approach allows analysis based on more realistic costs and extends the understanding of active systems. It is recognized that the distribution of actuator energy components into power absorption and power delivery is decided by the actuator phase, which is the phase difference between the actuator power variables. It is shown that the feasibility of an energy-efficient system such as a regenerative system depends upon this actuator phase. By providing a way to shape the actuator phase, the power distribution formulation facilitates design of regenerative systems. It is shown how this allows estimation of any loss of dynamic performance in a system designed for a given regeneration potential. Thus the utility of power distribution study in developing energy-efficient systems is demonstrated. Finally, a power distribution formulation for a random disturbance is developed and it is shown that the general trends agree with those obtained from the harmonic case. In random case, the role of the correlation coefficient between the actuator power variables is observed to be similar to that of the actuator phase of the harmonic case.