CRS and PS-optimised PID controller for nonlinear, electrohydraulic suspension systems

The compromise between ride comfort, suspension travel, road holding, vehicle handling and power consumption determines the success of an active vehicle suspension system (AVSS). The simplicity of Proportional-Integral-Derivative (PID) controllers has made it the controller of choice for many mechatronic systems including AVSS. This investigation studies the effectiveness of optimal control policies such as Pattern Search (PS), and Controlled Random Search (CRS)-based PID controllers in dealing with the inherent trade-offs of AVSS. A nonlinear servo-hydraulic quarter-car AVSS is considered in this article. The success of these optimal PID controllers may provide a contemporary foundation in selecting optimal gains PID for a control system, which at the moment is a rather rigorous and time consuming process. The objective function is chosen such that each of the AVSS trade-offs are addressed. The PS routine improved significantly from the manually tuned and uncontrolled cases with an overall improvement in ride comfort, suspension travel, settling time and road holding. However, this was attained at the cost of greater power consumption and actuation force. The CRS routine showed a substantial improvement from the manually tuned case in terms of ride comfort and settling time, but exhibited weaker characteristics in terms of road holding and transient behaviour, which implies that its solution may have been caught in a local minimum.