INTRODUCTION A hybrid electric vehicle (HEV) uses an internal combustion (IC) engine and one or more electric machines (EM) as power plants. IC engines have a narrow range of efficient operating conditions, typically under full throttle and mid-RPM operation. Inclusion of an EM in the powertrain avoids inefficient low power engine operations. Additionally, an EM supplements the IC engine in terms of its torque characteristics since an EM's full torque is available from near zero speed; this ultimately leads to sizing of smaller and more efficient engines. Lastly, the EM can recapture some of the vehicle's braking energy that would be lost otherwise. Efficient cooperation of the two types of power plants must be ensured to optimize the overall fuel usage of the powertrain. There are three major types of HEV architectures: series, parallel and power-split [ 1,2]. A series HEV employs a full size engine to drive an electric generator which in turnpowers a traction motor. The engine-generator combination on the series architecture can always operate at its maximum efficiency point independent of wheel speed or torque requirement. Since only the traction motor drives the wheels, it must be full-sized. Additionally, the engine and the generator must be full-sized as well, unless the powertrain includes a large battery, to guarantee range and drivability of the series HEV. The aforementioned factors lead to higher cost of the powertrain and lower flexibility in EM sizing. Parallel HEVs use a full-sized or reduced-sized engine, augmented with an electric machine. Fuel economy (FE) improvement is achieved through downsizing of the engine and through regenerative braking. However, the engine is not decoupled from the wheels, therefore inefficient engine operations can still occur. The Power-split HEVs combine the features of the series and parallel architectures by using two EMs with a continuously variable transmission (CVT). Typically, the CVT is based on planetary gear (PG) sets with the gear ratio varied by one EM, while the other EM provides 2013-01-0815 Published 04/08/2013 Copyright © 2013 SAE International doi:10.4271/2013-01-0815 saealtpow.saejournals.org Forward-Looking Simulation of the GM Front-Wheel Drive Two-Mode Power-Split HEV Using a Dynamic Programming- Informed Equivalent Cost Minimization Strategy Dekun Pei Michael Leamy Georgia Institute of Technology ABSTRACT This paper presents a forward-looking simulation (FLS) approach for the front wheel drive (FWD) General Motors Allison Hybrid System II (GM AHS-II). The supervisory control approach is based on a dynamic programming-informed Equivalent Cost Minimization Strategy (ECMS). The controller development uses backward-looking simulations (BLS), which execute quickly by neglecting component transients while assuming exact adherence to a specified drive cycle. Since ECMS sometimes prescribes control strategies with rapid component transients, its efficacy remains unknown until these transients are modeled. This is addressed by porting the ECMS controller to a forward-looking simulation where component transients are modeled in high fidelity. Techniques of implementing the ECMS controller and commanding the various power plants in the GM AHS-II for FLS are discussed. It is shown that FLS-derived component states agree well with states commanded using the BLS-derived robust control strategy, with any difference being accounted for by transient effects. Fuel economy results from FLS decrease, as to be expected, by approximately 3-7% from that of BLS due to the increase in propulsion energy required by component transients. Overall, these two points of good agreement demonstrate the viability of the DP-informed ECMS as an online-implementable supervisory control strategy. CITATION: Pei, D. and Leamy, M., "Forward-Looking Simulation of the GM Front-Wheel Drive Two-Mode Power-Split HEV Using a Dynamic Programming-Informed Equivalent Cost Minimization Strategy," SAE Int. J. Al