Control design for an automotive turbine Rankine Cycle system based on nonlinear state estimation

This paper investigates the problem of control design for an Organic Rankine Cycle (ORC) for Waste Heat Recovering (WHR). Based on a moving boundary heat exchanger model derived from energy and mass conservation principles, an implicit model, control-oriented and experimentally validated, is presented. Then, a first controller which consists on a gain-scheduled PID combined to a dynamic feedforward is implemented on the pump speed to maintain the superheat close to the set point value. A second controller is a nonlinear feedback law which allows to adjust the evaporating pressure to time-varying demand with a good accuracy. To implement these two controllers, an observer is designed to achieve the state estimation from pressure measurement, typically available in WHR applications. The observer and the control approach are validated on realistic operating conditions.