Oscar Flärdh

A New Feedback Control Mechanism for Error Correction in Packet-Switched Networks

Error correction mechanisms enable control and other real-time applications to be executed over unreliable packet-switched networks. By adding carefully adjusted redundancy to transmitted data at the sender, it is possible to recover lost data at the receiver and thereby improve effective throughput. We describe simple models for packet loss, which allow us to find the optimal redundancy as a function of packet loss probability. Two feedforward control mechanisms based on the packet loss probability are presented: one that is computed off-line and another one using an on-line algorithm. A drawback with these approaches is their dependency on accurate network state information and precise loss models. To cope with these issues, we propose a new feedback solution that tracks the optimum using gradient estimation. Simulations in ns-2 illustrate the behavior of the error correction schemes, demonstrating that the feedback solution outperforms the feedforward solution in presence of model erros.

Optimal Air Path Control During Load Transients on a Spark Ignited Engine With Variable Geometry Turbine and Variable Valve Timing

In recent years, the main goal of the automative industry has been to reduce fuel consumption. Downsizing is a promising way to achieve this, which has shown success. Downsized, turbocharged engines suffer from slow transient torque response. This slow response is due to the slow dynamics of the turbocharger. This paper investigates the torque response of a spark ignited engine with variable geometry turbine (VGT) and variable valve timing. Optimal open-loop trajectories for the overlap and the VGT position for a fast transient response are found. This optimization is based on a 1-D simulation model. Based on this optimization, a generic feedback strategy for controlling the VGT is found. This strategy is implemented and evaluated on an engine and shows good performance.

Nonlinear exhaust pressure control of an SI engine with VGT using partial model inversion

An important target for car manufacturers when developing new cars is to reduce fuel consumption. One approach to this problem is to use a downsized turbocharged engine. To fully utilize the benefits of the new hardware introduced, good control systems are needed. This paper presents a nonlinear controller for controlling the exhaust pressure in a SI engine equipped with VGT. A mapping from the states, inputs and disturbances to future outputs is formed, and inverting the input-output relation in this mapping gives a control law. An analysis shows that the controller adapts its gain to the input-output sensitivity. The controller is evaluated using both simulations and measurements on a real engine, showing the benefit of using the nonlinear controller over a corresponding linear controller.

Modeling the Effect of Variable Cam Phasing on Volumetric Efficiency, Scavenging and Torque Generation

In a mean value engine model, the mass flow of air through thecylinders is determined by the air density, the engine speed, and thevolumetric efficiency. For modern engines the volumetric efficienc ...

Analysis of a Quasi-Steady Extension to the Turbine Model in Mean Value Engine Models

The aim to reduce fuel consumption and emissions has been targeted by several approaches. One of them is downsizing, where a small engine is equipped with a turbocharger in order to give the same power as a larger engine, but with less fuel consumption. This in turn requires advanced control systems to take full benefit from the downsizing. Recent hardware advancements have enabled the use of variable geometry turbochargers also on SI engines, pushing the control demands further. This paper investigates possible extensions to control oriented mean value engine models for turbocharged SI-engines, focusing on the turbine. Mean value models do not take the pulsating phenomena in the exhaust manifold into account. This is assumed to cause large model errors, especially for the turbine efficiency and turbine power. The main contribution of this paper is to present an investigation of the effects of incorporating pressure pulses in the mean value model, together with an analysis of the effects of the pulsation on the turbine performance maps. An evaluation of the extended mean value model using measurements on a four cylinder SI engine with a variable geometry turbocharger is also presented. The evaluation show little difference between using pressure pulses and mean values. An analysis of the expression for turbine power shows that, when treating the maps quasi-steady, the calculated turbine power is almost the same when using pressure pulsations as when using just the mean pressure ratio. The analysis also indicates that this is due to the fact that the turbine power is an approximately linear function of the turbine pressure ratio.

Analysis of a Simple Feedback Scheme for Error Correction over a Lossy Network

A control theoretic analysis of a simple error correction scheme for lossy packet-switched networks is presented. Based on feedback information from the error correction process in the receiver, the sender adjusts the amount of redundancy using a so called extremum-seeking controller, which do not rely on any accurate model of the network loss process. The closed-loop system is shown to converge to a limit cycle in a neighborhood of the optimal redundancy. The result are validated using packet-based simulations with data from wireless sensor network experiments.

Optimal speed trajectory for a heavy duty truck under varying requirements

The optimal speed trajectory for a heavy duty truck is calculated by using the Pontryagins maximum principle. The truck motion depends on controllable tractive and braking forces and external forces such as air and rolling resistance and road slope. The solution is subject to restrictions such as maximum power and position dependent speed restrictions. The intended application is driving in environments with varying requirements on the velocity due to e.g. legal limits and traffic. In order to limit the vehicle to a speed trajectory that follows the normal traffic flow, data from real truck operation have been analysed and used for setting upper and lower boundaries for the decelerations. To evaluate the solution, simulations have been performed on a segment of a road normally used as a distribution test cycle. Three different policies were compared where the solution adopts to free optimization, optimization following traffic flow and finally cruise control using look-ahead control. Results from the simulations show that fuel consumption and trip time can be reduced simultaneously while following the traffic flow.