Control of a Base Load and Load-Following Regulating Organic Rankine Cycle for Waste Heat Recovery in Heavy-Duty Diesel Powertrain

Abstract

This paper builds upon previous work on modeling and controlling an organic Rankine Cycles (ORC) used for heavy-duty diesel powertrain. The novel contribution of this paper is operating the ORC as a base load regulating waste heat recovery (WHR) system in addition to the pressure regulation examined in previous work. Specifically, the expander power is expected to follow a power demand while maintaining pressure regulation. The ORC’s heat exchangers are modeled as control-oriented, nonlinear Moving Boundary models. The pump and expander, which are coupled to the engine crankshaft, have relatively faster dynamics than the heat exchangers and are modeled as static components. The driving cycle produces transient heat source and engine conditions for the ORC to recover waste heat energy. The ORC operating point is chosen at a steady-state that meets operating constraints, which may be violated from the heat source transients. During operation, low and high constant demand loads are given to the ORC’s expander to follow while regulating to pressure setpoints. A varying square-wave demand is also examined for partload operation. The ORC is to maintain pressure and power setpoints through independent proportional-integrator controllers (PI). A pair of PI controllers are designed for regulating the evaporating and condensing pressures and a third PI controller to follow the power demand. The results demonstrate pressure and base load power regulation to setpoints when the base load is feasible for constant and varying loads. When the base load power demand is infeasibly too high, both pressure and power regulations exhibit steady-state error. In the considered scenarios, initial pressure transients violate constraints and show the need for advanced controllers. The ORC improves the engine power efficiency by 0.5–2.5%.