Engelbert Gruenbacher

Robust inverse control for combustion engine test benches

In this paper the application of a robust inverse tracking method to the test bench control in order to achieve a high tracking performance is presented. This controller consists of a feedforward part which is the inverse realization of the approximate model of the combustion engine test bench and a robustifying feedback controller, which is for compensating the approximation error or unknown input disturbances. The robustifying controller is simply an extension of a central robust stabilizing controller which usually is the solution of a Hamilton Jacobi inequality. To this end, an iterative way to find a solution of this partial differential equation is applied here. Finally, the presented tracking controller for the combustion engine test bench is compared to a standard decoupled control strategy in a simulation environment.

Suppression of Frequency Varying Periodic Disturbances in Continuous Casting using an Internal Model Predictor

At continuous casting plants the liquid steel level in the mold has to be stabilized by the mold level controller. Many plants are however perturbed by an effect called dynamic bulging, which is an almost periodic disturbance consisting of the fundamental and harmonics up to the 6th order. Its frequency can be assumed to be approximately known, but can change with a known parameter, given by the casting speed. A measurement, which can be used to estimate the periodic disturbance is available, hence the periodic components of this signal can be observed and predicted with an internal model observer and be applied as disturbance feedforward to the control input. The prediction of the signal is necessary because the plant has a substantial input delay. Since the internal model depends on the frequency, which is available as parameter, LPV techniques are used to show convergence of the observer.

Bandwidth extension of dynamical test benches by modified mechanical design under adaptive feedforward disturbance rejection

In this paper we present a mechatronical approach for bandwidth extension of a combustion engine test bench consisting of the reconfiguration of the mechanical design and the introduction of an adaptive feedforward like disturbance rejection scheme. The mechanical design of the test bench is improved by the use of a stiff shaft engine to dynamometer connection. This yields a shift of the resonance frequency of the test bench into the frequency range excited by the combustion oscillations and hence results in the need of a disturbance suppression algorithm. Therefore the repeatability of the almost periodic disturbance is exploited to predict an estimate of future values using an extended FIFO memory to compensate input delays. The algorithm is tested in simulation and furthermore applied to a real test bench. The experimental results will verify the effectiveness of the proposed method.

Model based nonlinear observers for torque estimation on a combustion engine test bench

Torque is an important quantity in combustion engine test bench control but unfortunately very difficult to measure. Observers can be used as an alternative to sensors to estimate the torque based on a nonlinear model and the available measured output signals, engine speed and dynamometer speed. In this paper three nonlinear observers are designed for a combustion engine test bench simulator including combustion oscillations as well as noisy measurements and disturbed inputs. The well known extended Kalman filter (EKF), a high gain observer (HGO) and a sliding mode observer (SMO) are compared in terms of the quadratic estimation error, computing time and convergence rate.

Discrete-time nonlinear observer and output feedback design for a combustion engine test bench

Combustion engine control design depends strongly on the availability and the quality of the measurement of quantities involving in the controller construction. In general, not all quantities are available through direct measurement, and therefore an observer is often necessary to realize the controller. In this paper, a discrete-time partial state observer design for a combustion engine test bench is proposed. The observer is used to estimate the torque and the torsion angle of the engine, based on the measurement of the engine and the dynamometer speeds. The convergence of the observer is shown, and separation principle is also proved. The observer is used for constructing an output feedback controller for set point tracking of the test bench. Some numerical simulations are performed, showing the performance of the observer and also comparing the performance of the output feedback controller with the state feedback controller. A discussion, comparing a so called ¿static observer¿ and a ¿dynamic observer¿ which are possible to construct using the same approach, is also presented.

Output tracking of non input affine systems using extended Hammerstein models

Tracking is a very important issue for control and has received considerable treatment in the input affine framework. Unfortunately, many real systems exhibit a behavior which is clearly non input affine. To cope with this, an integral extension of the model can be used to produce an extended input affine system, hiding the input nonlinearity in the drift term of the new model. This approach, however, has several disadvantages. In this paper, we consider a different approach, motivated by physical considerations and practical experiences, which is based on the transformation or approximation of the original system by a cascade of a nonlinear non input affine map and a following input affine nonlinear system. As the paper shows, well known results of tracking control can be easily extended to this class yielding the solution of the original problem. Simulation results are presented to confirm the validity of the proposed techniques.

Online trajectory shaping strategy for dynamical engine test benches

Virtual vehicle testing on combustion engine test benches is becoming increasingly important to enhance testing speed in the automobile industry. To be able to achieve this target, dynamical test benches must be used which allow reproducing the load conditions on the engine crankshaft as occurring in the real vehicle. Dynamical testing usually consists in tracking speed versus torque profiles, which represent the expected vehicle operation. This also allows testing conditions which can not be measured in a real vehicle, and can lead to the situation in which the dynamics limit of the test bench and of the combustion engines are trespassed. This often leads to a chaotic performance of the test bench and to unreliable results. To cope with this problem we present an online capable algorithm which ensures that the test cycle is inside the performance limits. The algorithms are based on prefiltered design, the computation of feasible sets and of the use of augmented Kalman Filters to enforce feasibility. To prove the efficiency of the approach the algorithms are presented and simulation results are shown

Guaranteed robustness bounds for actuator disturbance nonlinear control

Abstract The paper deals with a class of non linear systems consisting of the cascade of a static nonlinear map depending on the state and the input and a dynamic input affine system. The static nonlinearity is approximatively inverted and the approximation error is treated as an input disturbance acting in the same direction as the control input. For this class of systems it is possible to compute a priori an upper bound for the H*infin; attenuation level achieved by the optimal L 2 controller and the suboptimal H ∞ central controller. Notably, these bounds depend only on the function mapping the control input to the performance variable.

Idle mode control on a combustion engine test bench via internal model control

In this paper we present an adaptive output regulation approach for idle mode simulation on combustion engine test benches. The combustion oscillations are modeled applying a parameter dependent exosystem whose parameter is related to the mean value engine speed which is a partly unknown quantity. Due to this reason we adapt existing literature on redundant adaptive internal model design and reduced order internal model design in order to achieve a fast converging output regulator. Furthermore we present the idea of an non-adaptive internal model based regulator in the case when the combustion oscillations are modeled by a reduced order nonlinear exosystem. At the end the methods are compared to a standard H∞ feedback controller and the advantages of the presented approaches are discussed.

ROBUST TRAJECTORY TRACKING FOR A CLASS OF UNCERTAIN NONLINEAR SYSTEMS

Abstract In this paper we consider the output tracking problem of an uncertain nonlinear system under the action of an inverse control thus making a robustifying feedback component necessary. Conventionally, the robustifying control is designed taking into account an operating point. We present a nonlinear robustifying controller for tracking any trajectories inside its stability range. The design procedure of this nonlinear controller is based on a simple extension of a stabilizing H2 or H∞ controller. If sufficient conditions are satisfied, robustness in terms of the L2 gain from the disturbance input to the tracking error performance variable can be guaranteed and calculated a priori. Finally simulation results verify the proposed method.