To improve transient torque response of an aggressively downsized turbocharged SI engine a series sequential boosting configuration that utilizes an electrically driven supercharger to assist the main turbocharger compressor is controlled in this paper. A frequency separation controller is designed to decouple the dynamics of the multiple-input-single-output (MISO) system. The controller separates the electric supercharger and turbocharger control actions into different frequency bands that are well suited for the characteristics of each device. The controller can be easily implemented with traditional decentralized single input single output (SISO) control loops.
Significant improvements to the baseline turbocharger only system in transient boost pressure response are observed both in simulation and in vehicle test results. Transitions between the electric supercharger and turbocharger are smooth, without noticeable disturbances, with good coordination between electric supercharger and wastegate control actions.