Saif Siddique Butt

Robust input-output linearization with input constraints for an engine cooling system

In this paper, a nonlinear control approach of an innovative engine cooling system for vehicles is presented. The electrically driven coolant pump and a servo-controlled bypass valve as control inputs, however, are subject to saturation due to physical limitations of the maximum pump volume flow and the limited opening section of the bypass valve. Based on a control-oriented system representation, a robust decentralized control employing sliding-mode techniques is proposed: an input-output linearizing control is designed for the engine outlet temperature, whereas an exact linearization is performed for the engine inlet temperature. At this control design, the given actuator limitations are explicitly taken into account. The controllers are implemented with small sampling time and combined with a discrete-time Extended Kalman Filter that estimates unknown heat flows within the system. In an experimental investigation, the performance of two alternative stabilizing control laws is compared: a linear stabilizing control law as reference and the robust sliding-mode approach leading to a nonlinear error dynamics. The obtained results highlight the effectiveness and the control performance of the proposed robust control strategy.

Nonlinear state observers and extended Kalman filters for battery systems

Abstract The focus of this paper is to develop reliable observer and filtering techniques for finite-dimensional battery models that adequately describe the charging and discharging behaviors. For this purpose, an experimentally validated battery model taken from the literature is extended by a mathematical description that represents parameter variations caused by aging. The corresponding disturbance models account for the fact that neither the state of charge, nor the above-mentioned parameter variations are directly accessible by measurements. Moreover, this work provides a comparison of the performance of different observer and filtering techniques as well as a development of estimation procedures that guarantee a reliable detection of large parameter variations. For that reason, different charging and discharging current profiles of batteries are investigated by numerical simulations. The estimation procedures considered in this paper are, firstly, a nonlinear Luenberger-type state observer with an offline calculated gain scheduling approach, secondly, a continuous-time extended Kalman filter and, thirdly, a hybrid extended Kalman filter, where the corresponding filter gains are computed online.

Nonlinear model-predictive control for an engine cooling system with smart valve and pump

In this paper, a nonlinear control approach based on a control-oriented model of an engine cooling system for vehicles is presented. An electrically driven coolant pump and a servo-controlled bypass valve act as control inputs. Due to physical limitations regarding the volume flow provided by the coolant pump as well as the opening section of the servo-controlled bypass valve, a constrained control problem arises. Therefore, a nonlinear model-predictive controller is employed, which explicitly takes the actuator limitations into account. A reduced-order disturbance observer is used to estimate unmeasured heat flows within the system in order to obtain a reliable prediction. An experimental analysis highlights the effectiveness of the nonlinear model-predictive control strategy in combination with a reduced-order observer.

Multi-variable flatness-based control of a helicopter with two degrees of freedom

In this paper, a multi-variable nonlinear control of a twin rotor aerodynamical system (TRAS) is presented. A control-oriented state-space model with four states is derived employing Lagranges equations. Using this system representation, a multi-variable flatness-based control is designed for an accurate trajectory tracking concerning both the pitch angle characterising the vertical motion and the azimuth angle related to the horizontal motion. Due to unmeasurable states as well as disturbance torques affecting the pitch axis and the azimuth axis, a discrete-time Extended Kalman Filter (EKF) is employed and combined with a discrete-time implementation of the multi-variable flatness-based control. The effectiveness of the proposed control strategy is highlighted by experimental results from a test rig that show an excellent tracking behaviour.

Model-based control of an electro-pneumatic clutch using a sliding-mode approach

This paper presents a nonlinear model-based control design for an electro-pneumatic clutch for heavy trucks, which is required at start-up or during gear shifts to disconnect the combustion engine from the gear box. This automated actuator disburdens the driver and provides the necessary actuation force according to the large torque transmitted through the powertrain. The proposed cascaded control structure consists of a fast inner control loop for the internal pressure, which is estimated by a nonlinear reduced-order observer, as well as an outer control loop for the clutch position. The design of the feedback part for the clutch position is based on sliding-mode techniques. A Lyapunov-based approach is used for the inner control loop of the internal pressure, which is usually not measured in truck applications. Thereby, high tracking accuracy is achievable for the piston position as controlled variable. The efficiency of the proposed control structure is demonstrated by experimental results from a dedicated test rig.

Dynamic sliding mode control of an innovative engine cooling system

In this paper, a robust nonlinear control approach based on a control-oriented model of an engine cooling system for vehicles is presented. The angular velocity of an electrically driven radiator fan is considered as the control input to adjust the cooling heat flow corresponding to a desired engine cooling performance. For smooth control actions and an avoidance of chattering, a dynamic sliding mode control is presented to track the desired trajectories of the engine outlet temperature. For the estimation of unmeasured heat flows, a gain-scheduled version of a modified Utkin sliding mode observer is employed, which uses both an output error feedback and a switching term for the stabilisation of the observer error. The estimated heat flows are used in the control design to compensate for the disturbances acting on the system. Experiments on a dedicated test rig highlight the effectiveness of the robust observer-based control strategy during the normal vehicle operation as well as a start/stop scenario.

Flatness-based control and observer design scheme for hybrid synchronous machines

In this paper, a nonlinear control-oriented model of the hybrid synchronous machine is developed using the dq-axis transformation. A flatness-based multi-variable controller is proposed to track a predefined reference trajectory for the angular velocity. Furthermore, a comparison is made for two alternative observer designs. In the first case, a combination of a gain-scheduled Luenberger-type state observer and a nonlinear reduced-order observer is used to estimate the angular velocity and the load torque of the mechanical load connected to the hybrid synchronous machine, respectively. In the second case, only a nonlinear reduced-order observer is used to estimate both the angular velocity and the load torque. A simulation analysis highlights the effectiveness of the control strategy with excellent tracking behavior as well as small estimation errors of both angular velocity and load torque.

Passivity-based tracking control for a twin rotor helicopter with an Unscented Kalman Filter

In this paper, a passivity-based tracking control for a twin rotor aerodynamic system (TRAS) with two degrees of freedom is proposed. A control-oriented state-space model is derived using Lagranges method. The resulting nonlinear fourth-order model possesses two control inputs, and is affected by two unknown disturbance torques due to modelling simplifications and unmeasurable torques. Accordingly, an Unscented Kalman Filter (UKF) is employed to estimate these lumped disturbances and unmeasurable states as well. The proposed passivity-based control in combination with UKF is implemented and validated on a laboratory test rig. The effectiveness of the passivity-based control is highlighted by experimental results showing an excellent tracking behaviour.

Cascaded backstepping control of a Duocopter including disturbance compensation by unscented Kalman filtering

A cascaded control strategy for an innovative Duocopter test stand - a helicopter with two rotors combined with a guiding mechanism - is presented in this paper. The guiding mechanism consists of a rocker arm with a sliding carriage that enforces a planar workspace of the Duocopter. The Duocopter is connected to the carriage by a rotary joint and offers 3 degrees of freedom. The derived system model has similarities with a PVTOL and a planar model of a quadrocopter but involves additional terms due to the guiding mechanism. In the paper, a model-based cascaded control strategy is proposed: the outer MIMO control loop is given by the inverted system model to control the horizontal and the vertical Duocopter position with a nonlinear error dynamics derived from backstepping techniques. The rotation angle of the Duocopter is controlled in a linear inner control loop of high bandwidth. Due to uncertain system parameters and reasonable simplifications at the modelling of the test stand, the control structure is extended by an unscented Kalman filter. Thereby, an excellent tracking performance in vertical and horizontal direction can be achieved. The efficiency of the proposed control strategy is demonstrated by both simulations and experiments.

Input-output linearisation with input constraints for an innovative engine cooling system

A nonlinear control approach of an innovative engine cooling system for vehicles is presented in this paper. The electrically driven coolant pump and a servo-controlled bypass valve as control inputs, however, are subject to saturation due to physical limitations of the maximum pump volume flow and the limited opening section of the bypass valve. Based on a control-oriented system representation, a decoupling, input-output-linearising control is designed for the engine outlet temperature and the engine inlet temperature. At this control design, the given actuator limitations are explicitly taken into account. The multi-variable control is implemented with a small sampling time and combined with a discrete-time Extended Kalman Filter that estimates unknown heat flows within the system. Experimental results from a dedicated test rig highlight the effectiveness and the performance of the proposed control approach.