Observer for a vehicle longitudinal controller
Independent thesis Basic level (professional degree), 20 points / 30 hpStudent thesisAlternative title
Observatör för en längsregulator i fordon (Swedish)
The longitudinal controller at DaimlerChrysler AG consists of two cascade controllers. The outer control loop contains the driver assistance functions such as speed limiter, cruise control, etc. The inner control loop consists of a PID-controller and an observer. The task of the observer is to estimate the part of the vehicle's acceleration caused by large disturbances, for example by a changed vehicle mass or the slope of the road.
As observer the Kalman filter is selected. It is the optimal filter when the process model is linear and the process noise and measurement noise can be modeled as Gaussian noise. In this Master's thesis the theory for the Kalman filter is presented and it is shown how to choose the filter parameters. Simulated annealing is a global optimization technique which can be used when autotuning, i.e., automatically find the optimal parameter settings. To be able to perform autotuning for the longitudinal controller one has to model the environment and driving situations.
In this Master's thesis it is verified that the parameter choice is a compromise between a fast but jerky, or a slow but smooth estimate. As the output from the Kalman filter is directly added to the control value for the engine and brakes, it is important that the output is smooth. It is shown that the Kalman filter implemented in the test vehicles today can be exchanged with a first-order lag function, without loss in performance. This makes the filter tuning easier, as there is only one parameter to choose.
Change detection is a method that can be used to detect large changes in the signal, and react accordingly - for example by making the filter faster. A filter using change detection is implemented and simulations show that it is possible to improve the estimate using this method. It is suggested to implement the change detection algorithm in a test vehicle and evaluate it further.
Place, publisher, year, edition, pages
Institutionen för systemteknik , 2007. , 105 p.
Kalman filter, longitudinal controller, filter tuning, simulated annealing, change detection
IdentifiersURN: urn:nbn:se:liu:diva-8820ISRN: LiTH-ISY-EX--2007/3950--SEOAI: oai:DiVA.org:liu-8820DiVA: diva2:23522
2007-04-11, Systemet, Hus B, Linköpings Universitet, Linköping, 10:00