Model Predictive Feedforward Control for High-Dynamic Speed Control of Combustion Engine Test Beds

Hardware-in-the-Loop tests have become a key factor in decreasing development time of various drive systems. In this context, high performance test beds, where feedback control plays a major role, are necessary to meet the demanding requirements such as real driving emissions in the automotive industry. Particularly for combustion engine test beds, periodic combustion strokes cause large oscillations in different measurement signals on engine test beds, which causes severe problems since conventional controllers try to compensate for these periodic disturbances. The control settings are a trade-off between fast reference tracking and undesirably strong disturbance rejection, which may compromise test results. An ordinary two-degree-of-freedom (2-DOF) control with flatness-based feedforward control produces relief in separating reference and disturbance behavior but cannot handle input constraints. Thus, a model predictive feedforward controller (MPFFC) in combination with the 2-DOF strategy is introduced for high-dynamic speed control in this contribution. The MPFFC generates optimal input and output trajectories, which respect constraints of the system. Fast reference tracking is achieved without the risk of falsification by high feedback. Comparisons between the proposed method, a simple feedback and a standard 2-DOF controller with a conventional flatness-based feedforward control are performed on a state-of-the-art 4-cylinder engine test bed. The experiments constitute a rare implementation of a MPFFC on a real system and demonstrate its capabilities of separating reference and disturbance response as well as taking advantage of certain situations to even further improve reference tracking speed.