Fast Engine Torque Variation Compensation for HEVs Using Permanent Magnet Synchronous Motor and Explicit MPC 2021-01-0718

This research proposes to leverage the fast response time of Permanent Magnet Synchronous Motors (PMSMs) to compensate for crank angle resolved engine torque variations caused by cycle-by-cycle combustion variations. This method reduces powertrain vibration and enables engine calibrations with high combustion variation that produces low fuel consumption. This research integrates a Field Oriented Control (FOC) strategy with an Explicit Model Predictive Control (EMPC) to trace previewed current references. The previewed current references are computed from the engine torque difference between predicted nominal operation and the measured torque output. This research reveals that the MPC can track a d-q current reference without overshoot, rendering current magnitude constraints unnecessary in the MPC formulation. A control rate penalty is used to tune the aggressiveness of transient voltage demand and meet with the DC voltage limit. The proposed MPC formulation significantly improves computational efficiency and allows for an increased preview horizon length. Simulation results show that the proposed EMPC based PMSM control reduces electric motor torque response time from 45 ms, for a baseline FOC strategy, to less than 5 ms. A case study is performed, showing the proposed PMSM control strategy can completely compensate 4.8% Coefficients of Variation of IMEP (COV of IMEP) from the engine while the baseline FOC control strategy failed to respond. The investigated engine operating condition also demonstrates a 12.7% fuel economy improvement compared to a baseline that is stoichiometric without Exhaust Gas Recirculation (EGR) dilution. The electrical system energy losses caused by the EMPC strategy resulted in a 2.3% loss of equivalent engine efficiency, but a net fuel economy gain of 10.4% is still achieved from this case study.