Conventional shredder drives are operated in fixed- speed mode as the drive motor is directly coupled to the supplying power grid. Due to the discontinuous characteristic of the process, this leads to a severe load fuctuations in the drive train as well as at the grid interface. Investigations show, that the shredding process does not necessarily need a constant speed of the process machine, but allows speed variations in a quite wide range around the nominal operating point. In this paper the performance of the traditional fixed-speed drive configuration is evaluated and compared to an innovative concept, that allows a speed-flexible operation by using a Doubly Fed Induction Machine (DFIM) and, thereby, significantly reduces the strain of the drive train components as well as fluctuations in the drawn electrical power. In contrast to the grid-coupled Motor, the proposed speed-elastic proportional control is not able to adequately dampen torsionally oscillations in the drive train alone, so an additional damping controller is proposed. The performance of the drive concepts is compared based on a operational strength analysis using relevant process data.

Shredding processes are traditionally operated with fixed-speed drives, that are directly coupled with the supplying power grid. However, this solution has far-reaching disadvantages in terms of grid interaction and the mechanical stress in the drive train. The implementation of a variable-frequency drive with speed-elastic behavior that uses the kinetic energy of the drive train profitably may drastically improve both of these aspects. A dynamically controlled actuator also enables the mitigation of torsional vibrations and thus further reduces the mechanical loads in the drive train to a minimum. In this paper, an advanced controller design procedure using a cost function to solve the resulting multi-objective optimization problem is presented. The effectiveness of the controller is proven by means of simulation using relevant process data.

Model Predictive Control enables the multi-objective optimization of mechatronic drive systems including the introduction of shaft torque constraints. In this paper, its practical application to a high power drive is discussed. This includes the controller design procedure, that particularly considers the limited torque dynamics of the controlled drive motor and state-estimation errors, that are counteracted by the implementation of soft constraints. As compromise between modelling errors and computational effort, the drive train is approximated as a three-mass model for state estimation and prediction. Simulative investigations indicate, that additional measures must be taken to achieve optimal results as the system performance is severely impacted by the observer’s dynamic reaction on plant perturbations and disturbances. Compared to a PI controller, the Model Predictive Control leads to reduced mechanical stress by decreasing the maximum shaft torques and suppressing the oscillations.

Adjustable speed drives are used in a wide variety of applications which in many cases include loads with relevant mechanical flexibility. Unwanted mechanical oscillations deteriorate the process quality and threaten to damage the drive train. Due to limited overload capabilities of mechanical components in high power drive systems, the reduction of mechanical strain is considered a crucial control objective. Therefore, acurate models reproducing all important system dynamics of the drive train are required, which, at the same time, have the lowest possible dynamic order to be suitable for online as well as offline optimization and model-based control. Within the scope of this paper, the influence of higher eigenmodes and the shortcomings of two- mass drive train models for controller design and performance evaluation is discussed based on simulative investigations on multi-megawatt rolling mill drives. A strategy for determining all performance-relevant eigenmodes of a drive train is presented.

Variable frequency drives in industrial speed-controlled applications with high reduction gear ratios - which are often used in case the driven process demands for high torques - are prone to extensive and lightly damped mechanical oscillations. This is due to the low process-side inertia and notable gear play, which both encourage excitation of the lowest mechanical resonance frequency. Moreover, it is well known, that a significant active damping contribution is hardly realizable through tuning of a classical PI speed controller. Due to multifaceted requirements with respect to control objectives and mandatory robustness properties, ℋ∞theory appears to be a promising instrument for the design of an advanced speed controller for such systems. Therefore, this paper presents a ℋ∞theory-based speed control design methodology. A drive system example with very low load-side inertia is chosen in order to demonstrate the effectiveness of the presented control approach.

H∞ theory can be regarded as a promising approach for the performance optimization in mechatronic drive systems with flexible loads with respect to multiple objectives such as robust stability, precise reference tracking and minimization of mechanical strain due to oscillation damping. Modal decomposition is a fundamental instrument in the analysis and control of mechanical structures. In this paper, model transformation using modal decomposition of the mechanical drive train's torsional dynamics is considered as a concept providing enhanced capabilities in the formulation of the cost-function for a speed-controlled drive application. Promising results are achieved especially for drive trains featuring a second control-relevant mechanical natural mode.

Low power quality and supply reliability within industrial grids cause severe economic damage to Europe's key industry sectors. A modular shunt connected power conditioning systems with the objective of locally improving quality of supply within industrial grids has been proposed. One of its voltage-fed power converter based modules implements functionalities which are comparable to those of well known line interactive uninterruptible power supply systems. This paper discusses the input filter topology choice, its application specific design and points out contrasts to optimization criteria derived for the LCL filter design of converters for permanent grid-connected operation.

The detection of the fundamental frequency and phase angle of the positive sequence grid voltages are utmost necessary for the proper operation of controlled active power converters, which require to operate stable and robust even during the presence of diverse power quality issues. There exist various utility grid synchronization and detection methods based on Phased-Locked Loop (PLL) techniques. In this paper, a grid synchronization technique based on the enhanced PLL implemented in the stationary reference frame is presented. The algorithm has been implemented and validated on an FPGA control board. Simulation studies and experimental investigations have been conducted to evaluate its performance under diverse power quality disturbances.