Mechatronics & Automotive
Mechatronic systems, which comprise both mechanical and electrical parts, represent an important application field of control engineering. Due to the limited computing power of the used ECUs, the application of modern control methods in these systems is associated with particular challenges. The Chair of Automatic Control researches control methods for, for example, electric drives, automatic transmissions and vehicles.
Mechatronics is a combination of the classical engineering disciplines of mechanical and electrical engineering. Accordingly a mechatronic system is the conjunction of a mechanical and electrical subsystem. To further increase the performance of the whole system it is of utmost importance to consider and model the separate subsystems as one system. Synchronous machines and power shift transmissions are examples for systems that are studied at our institute.
Permanent magnet synchronous machines (PMSM) play an increasingly important part in modern drive technology. They are used in industrial as well as automotive applications by virtue of their high efficiency and torque density. Besides an energy optimal operation the high performance control of those machines requires the adherence of a variety of nonlinear input and state constraints.
Heavy duty/Off-road applications
The development of combustion engines has been focused on the improvement of fuel efficiency in the past. Nowadays the compliance with increasingly restrictive exhaust emission regulations affects engine development. As a result, combustion engines have become very complex systems with many degrees of freedom. As the combustion is highly nonlinear, the use of classical control algorithms is evermore sophisticated.
Model predictive control (MPC) is also a suitable approach for this application as the control problem can be easily formulated as constrained optimal control problem. Nevertheless, its solution using accurate models typically leads to a high numerical load. Thus, the real-time feasible applicability on a standard electronic control unit is a challenging. This computational burden can be drastically reduced using suboptimal MPC approaches.
As the name indicates, MPC is based on reliable models. Thus, precise models are needed despite unavoidable model deviations for instance due to engine wear. Computational intelligence techniques that are applied in a wide range of applications can be used to cope with this challenge. This way, suitable engine models can be tracked online.
Because of their higher efficiency and shifting comfort dual clutch transmissions are increasingly used over conventional transmissions. Those advantages are paid for with a significantly more complex shifting process which can hardly be handled without methods of modern control theory. Input constraints in the form of torques and state constraints in the form of shaft revolutions can be taken into account by those methods, thereby decreasing the application costs considerably.
To fulfil those requirements model predictive control strategies for the aforementioned systems are developed at our institute. The real time capability of the control strategies is of key importance with sampling rates typically in the (sub-)millisecond range and available computing capacity severely limited, especially on electric control units. Besides the nonlinearities of the models different control concepts are considered.
Besides the automotive industry, automation of industrial or agricultural vehicles is of increasing importance. By introducing automated driving functions, the driver should be relieved or completely replaced for everyday tasks. Both optimization-based methods of path planning and vehicle control are being researched at the Chair of Automatic Control and developed for real-time use in vehicles.
The challenges in off-road vehicle control are quite different compared to on-road. On the one hand, it is important to consider limitations and actuator dynamics. In addition, there are usually combinations of vehicle and trailer or vehicle and work equipment. Aside from that, the vehicle parameters are permanently varying due to changing loads and environments. In contrast to on-road, the speeds are lower, but the grounds are often unpaved and slippery. This must also be considered by the vehicle controller.
The challenges of global path planning includes manoeuvring in narrow space, such as reverse parking of a trailer truck. In order to be able to react to dynamic obstacles, the local path planning ensures that collision-free and drivable trajectories are generated. In addition, the trajectories have to consider the entire vehicle combination and comply with certain comfort requirements.
An important field of application for control systems is the automotive sector. Today’s high demands on ride comfort, vehicle dynamics and compliance with emission and efficiency targets have made electronic control systems an integral part. Both in vehicle suspension systems and the hybrid powertrains as well as in concepts of e-mobility the increasing complexity of the systems requires the use of appropriate control methods.
In order to meet the high demands, the institute develops model-based control strategies for horizontal dynamics of over-actuated vehicles, vehicle vertical dynamics as well as longitudinal dynamics and drives.
Horizontal dynamics of overactuated vehicles
The increasing electrification of motor vehicles opens the possibility to switch to decentralized actuator configurations. In these, each wheel can be individually driven, braked and steered and a more flexible interior design is made possible. This leads to a system that has more actuators than are required for the specification of even vehicle motion. The control of such overactuated vehicles is the subject of the considerations. By using this overactuation, an increase in driving safety or fault tolerance can be achieved.
Vehicle vertical dynamics
With active suspension systems, the existing conflict between driving comfort and driving safety can be mitigated compared to a passive suspension system design. The control of such systems under changing roadway characteristics and the estimation of these characteristics from the movement of wheels and vehicle body are examined. The improvement of the vehicle response to driver steering and braking interventions with simultaneously reduced vehicle reaction to uneven roads is the goal.
Longitudinal dynamics and drives
Today, the longitudinal dynamic behavior of a vehicle no longer results from the mechanical actuation of the engine and transmission by the driver, but rather from an interaction of complex, highly-automated powertrain structures. On the one hand, control strategies for components (e.g. friction clutches) are developed whose behavior significantly influences this interaction. On the other hand, concepts for automating this interaction are considered, which also include the driver-vehicle interface and, for example, the operating strategy of hybrid drives.