Linear Quadratic Integral control of an Organic Rankine Cycle for waste heat recovery in heavy-duty diesel powertrain

This paper presents controller designs for a nonlinear Organic Rankine Cycle (ORC) model used for transient waste heat recovery (WHR) in heavy-duty diesel powertrain. The ORC´s heat exchangers are described by Moving Boundary models based on energy and mass conservation principles. The control-oriented, dynamic heat exchanger models are connected to static expander and pump models that are coupled to the engine crankshaft. The controllers in this paper are designed to regulate evaporating and condensing pressures in the presence of engine transient disturbances (heat sources and crankshaft speed) generated from a driving cycle. The Proportional Integral (PI) and Linear Quadratic Integral (LQI) controllers are designed and compared for different actuator configurations. The controllers are designed on a linearized ORC model, but are applied on the nonlinear model. Simulations show that both the PI and LQI controllers cannot meet pressure setpoints under the 2-actuator configuration. The 3-actuator configuration improved ORC controllability and allowed the LQI controller to regulate to the pressure setpoints. The results show benefits of multi-input multi-output (MIMO) LQI control over single-input single-output (SISO) PI control for the nonlinear ORC in the presence of automotive transient disturbances.