MIMO Control of a Turbogenerator for Energy Recovery

Abstract

Market trends for increased engine power and more electrical energy on the powergrid (3kW+), along with customer demands for fuel consumption improvements and emissions reduction, are driving requirements for component electrification, including turbochargers. GTDI engines waste significant exhaust enthalpy; even at moderate loads the WG (Wastegate) starts to open to regulate the turbine power. This action is required to reduce EBP (Exhaust Back Pressure). Another factor is catalyst protection, where the emissions device is placed downstream turbine. Lambda enrichment or overfueling is used to perform this. However, the turbine has a temperature drop across it when used for energy recovery. Since catalyst performance is critical for emissions, the only reasonable location for an additional device is downstream of it. This is a challenge for any additional energy recovery, but a smaller turbine is a design requirement, optimized to operate at lower pressure ratios. A WAVE model of the 2.0L GTDI engine was adapted to include a TG (Turbogenerator) and TBV (Turbine Bypass Valve) with the TG in a mechanical turbocompounding configuration, calibrated with steady state dynamometer data. This includes power and fuel consumption, and additionally a sensitivity analysis and knock impact assessment. Further work includes transient verification with WAVE-RT on WLTP and RDE drive cycles, estimating dynamic energy recovery, assessing electrical turbocompounding, interfacing to the powergrid, and calibration optimisation, using combined WG and TBV settings. Development of more advanced MIMO (Multiple-Input, Multiple-Output) control system algorithms and prototype testing on dynamometer or vehicle could be performed to verify design assumptions and simulation results.

Modeling Transient Control of a Turbogenerator on a Drive Cycle

“…Turbocompounding solutions presented in [4]; however, there are few details in the literature about controller design or full simulation.…”

“…This paper presents full transient control of TG device (as previously defined in [4]). The TG system is built up in a 1D modeling environment, then a real-time controller built around it in Ricardo WAVE in a co-simulation environment, after extensive model calibration is performed.…”

“…The 1-D simulation environment was set up in Ricardo WAVE and included the LPT downstream the catalyst with a continuously variable bypass. A summary of keypoint analysis is included in [4]. There were 2 controls loops: throttle controlling the BMEP and the WG controlling the intake manifold pressure.…”

“…In the case of ICE-powered vehicle (PHEV, HEV or with minimal electrification, energy recovery can aid efficiency which can equate to more driven emissions-free kilometers. However, although ICE-equipped vehicles have more and more efficient combustion engines ( [3] Nissan claim 50% BTE with ePOWER series), there is still a considerable amount of heat wasted through the exhaust which could be put to better use [4]. Indeed, several turbocharging companies still foresee a need for electrified turbos in HEV powertrains [5].…”