Fast and Robust Hybrid Starter and Generator Speed Control for Improving Drivability of Parallel Hybrid Electric Vehicles

Speed control algorithms were studied to improve vehicle fuel economy and driving performance by rapidly combining two power sources—the engine and the driving motor. A hybrid starter and generator (HSG) was used in parallel hybrid vehicles, improving vehicle drive system efficiency by eliminating torque converters. The proposed zero-overshoot and zero-phase-error speed controller with active damping has the following three characteristics. First, it has an active damping structure resistant to load fluctuations (e.g., cranking torque fluctuation during engine starting). Second, there is no speed overshoot for the step command corresponding to the minimum engine running speed. Finally, it has no steady-state error for the ramp command generated by the moving vehicle. These control features reduce the time required to match the speeds of the two power sources, reducing delay when the vehicle starts and reducing energy consumption by minimizing unnecessary engine rotation. Simulation and vehicle test results proved that the proposed algorithm produced faster response characteristics and smaller steady-state errors than conventional control algorithms such as proportional-integral, integral-proportional, and two-degree-of-freedom algorithms. In this study, the fuel efficiency and driving performance of the hybrid vehicle could be improved by improving the performance of the speed control alone without any additional hardware changes.