Virtual prototyping of vehicular electric steering assistance system using co-simulations

Sammanfattning: Virtual prototyping is a practical necessity in the vehicle system development. From the desktop simulation towards the test track, several simulation approaches, e.g., co-simulation and hardware-in-loop (HIL) simulation, are used. However, the testing results consistency might not be guaranteed due to interfacing issues. Correspondingly, the inherent shortcomings come from the numerical coupling error and the non-transparent HIL interface, which involves the control tracking error, delay error, attached hardware and noise effects. Hence, this work aims to address these problems and to provide seamless virtual prototypes for the vehicle and electric power assisted steering (EPAS) system development. On a basic level, accuracy and stability properties of the explicit parallel cosimulation and the HIL simulation are investigated. The imperfect factors propagate in the simulation tools like perturbations, and yield inaccuracy and even instability according to the system dynamics. Based on this, the problems are considered as how to reduce the perturbations (coupling problem) and how to robustify the system (architecture problem). In the coupling problem, a delay compensation method relying on adaptive filters is developed for the real-time simulation. A novel co-simulation coupling method on H-infinity synthesis is developed, showing accuracy improvement for a wide frequency range and a small computational cost. In the architecture problem, a force(torque)-velocity coupling approach is taken. With the force(torque) variable applied to the larger impedance, e.g., the steering rack (EPAS motor), it yields a smaller loop gain and more robust co-simulation and HIL simulation. On a given EPAS HIL system, an interface algorithm is developed to virtually shift the impedance and thus enhances system robustness. The theoretical findings and developed methods are tested on generic benchmarks, and implemented on the vehicle-EPAS engineering case. Besides increased simulation speed, accuracy and robustness are improved at the same time. Consequently, consistent testing results and extended validated ranges of the virtual prototypes are obtained.