Multirate controller design for resource- and schedule-constrained automotive ECUs

Automotive software mostly consists of a set of applications controlling the vehicle dynamics, engine and many other processes or plants. Since automotive systems design is highly cost driven, an important goal is to maximize the number of control applications to be packed onto a single processor or electronic control unit (ECU). Current design methods start with a controller design step, where the sampling period and controller gain values are decided based on given control performance objectives. However, operating systems (OS) on the ECU (e.g., ERCOSek) are usually pre-configured and offer only a limited set of sampling periods. Hence, a controller is implemented using an available sampling period, which is the shorter period closest to the one determined in the controller design step. However, this increases the load on the ECU (i.e., the processor runs the controller more often than what is actually required by design). This reduces the number of applications that can be mapped, and increases costs of the system. To overcome this predicament, we propose a multirate controller, which switches between multiple available sampling periods offered by the OS on the ECU. Apart from meeting all control objectives, this avoids the unnecessary ECU overload resulting from always sampling at a constant, higher rate.