Showing papers by "Jeroen Ploeg published in 2013"

Graceful degradation of CACC performance subject to unreliable wireless communication

Abstract: Cooperative Adaptive Cruise Control (CACC) employs wireless intervehicle communication, in addition to onboard sensors, to obtain string-stable vehicle-following behavior at small intervehicle distances. As a consequence, however, CACC is vulnerable to communication impairments such as packet loss, in which case it would effectively degrade to conventional Adaptive Cruise Control (ACC), thereby increasing the minimal intervehicle distance needed for string-stable behavior. Therefore, a control strategy for graceful degradation of one-vehicle look-ahead CACC is proposed to partially maintain the string stability properties of CACC. This strategy is based on estimating the preceding vehicle's information, here acceleration, using the onboard sensors. Whenever needed, this estimated acceleration can be used as an alternative to the desired acceleration transmitted through wireless communication for this type of CACC. It is shown through simulations and experiments that the proposed strategy results in a noticeable improvement of string stability characteristics, when compared to the situation in which ACC is used as a fallback scenario.

Fault tolerancy in Cooperative Adaptive Cruise Control

Abstract: Future mobility requires sound solutions in the field of fault tolerance in real-time applications amongst which Cooperative Adaptive Cruise Control (CACC) This control system cannot rely on the driver as a backup and is constantly active and therefore more prominent to the occurrences of faults (such as packet loss in the wireless communication) This paper presents an algorithm which uses the availability of sensor-data in each moment in time to calculate in real-time a safe distance for the CACC system This safe distance consists of a velocity dependent part and a constant part, both important settings in the spacing policy for the CACC A critical scenario for which CACC should still be functional is chosen, mathematical models of the system response are derived and errors are modeled The model enables the calculation of differences in braking distances, which leads to a required safe distance This approach makes the dynamic algorithm useful for sensor faults The algorithm is implemented in a test vehicle and test results are presented

Vehicle spacing control

Abstract: A method of determining a safe distance (d safe ) between a first vehicle (1) and a second vehicle (2) moving ahead of the first vehicle, each vehicle having a state which comprises at least one of a position (s 1 , s 2 ), a speed and an acceleration of the respective vehicle, the method comprising the steps of: - collecting sensor data relating to the state of the vehicles (1, 2), - determining, using the sensor data and a time-dependent description of the state of the second vehicle (2), a state of the second vehicle (2) as a result of a maximum deceleration of said second vehicle, - determining, using a time-dependent model of the behaviour of the first vehicle (1) and said state of the second vehicle (2), a state of the first vehicle (1) as a result of said maximum deceleration of said second vehicle (2), and - determining, using said state of the second vehicle (2) and said state of the first vehicle (1), the safe distance (d safe ). Said state of the second vehicle (2) and said state of the first vehicle (1) involve uncertainties introduced by the sensor data, thus increasing the safety margin of the method.

Optimal control for non-exponentially stabilizable spatially invariant systems with an application to vehicular platooning

Abstract: This paper considers the optimal control problem for a class of infinite-dimensional systems, namely spatially invariant systems. A common assumption in the scope of such optimal control problem is the exponential stabilizability of the infinite-dimensional plant. We propose sufficient conditions for the optimizability of spatially invariant systems that are not exponentially stabilizable. The practical significance of this problem setting is motivated by vehicular platooning, for which it is desired to design controllers that attenuate the effect of disturbances, both in time and space, i.e., over the vehicle index.

Performance analysis of a cooperative adaptive cruise controller subject to dynamic time headway

Abstract: The current paper shows string stability of a platoon of vehicles when the spacing policy within the platoon is dynamic, i.e., it has time-varying parameters. This problem setup is to address the safety issues that arise due to malfunction of some redundant sensing/communicating devices installed on the vehicles. In such a faulty situation, the controller is still functional due to the redundancy of the sensing/communicating devices as well as estimating resources which provide the controller with the required information. However, the accuracy of the controller will be reduced. This loss of accuracy should be compensated by doing a more conservative design of safety important parameters such as the safe inter-vehicle distance, which is selected based on the string stability requirement. The decision of a change in the inter-vehicle distance, or equivalently the spacing policy, is made by a so called “safety checker” function which can be introduced into the loop of vehicle and controller. Here, it is shown that an adopted cooperative adaptive cruise controller renders the string of vehicles stable even if the spacing policy is time variant. The stability requirement of the closed-loop system is that the switching signal suggested by the safety checker unit being piecewise constant, i.e., the safe inter-vehicle distance policy does not change continuously.