Short Primary Linear Drive Designed for Synchronous and Induction Operation Mode with On-Board Energy Storage

• Main Author: Fernandes Neto, Tobias Rafael
• Format: Others
• Language: English; en
• Published: 2012
• Online Access: http://tuprints.ulb.tu-darmstadt.de/3026/1/Diss_Final_Tobias.pdf; Fernandes Neto, Tobias Rafael <http://tuprints.ulb.tu-darmstadt.de/view/person/Fernandes_Neto=3ATobias_Rafael=3A=3A.html> : Short Primary Linear Drive Designed for Synchronous and Induction Operation Mode with On-Board Energy Storage. Technische Universität, Darmstadt [Ph.D. Thesis], (2012)

The idea of a flexible industrial manufacturing system for the transfer of material, tooling, processing/filling, etc., in which several vehicles can travel with high speed, high degree of independency and high precision is proposed in this thesis. Such flexible systems show a meaningful economic potential for modern manufacturing systems. The basic concept is that a linear motor has the secondary part fixed to the track while the primary (moving winding) travels along the track (short primary topology). The same principle can work in the other way around, arranging the primary in segments and letting the secondary (carrier) to move from segment to segment (long primary topology). The concept's implementation involves technical issues, such as: the position measurement, the energy and information transfer, the individual position and speed control of the vehicle in which varying speeds increase the possibility of collision, and the smooth transition between segments or different types of the secondary. Finally, multiple vehicles traveling at high speed, high positioning repeatability and rapid acceleration rates increase the production throughout and the reliability compared to conventional manufacturing conveyor systems. As an example, a transporting and processing system based on linear drives is a continuous and closed structure with multiple loops, which permits the safe transport of fragile loads. Although such solutions often need higher investment costs, the lack of mechanical coupling parts and wearing elements in these motors greatly increases their reliability. The long primary topology allows a passive and lightweight vehicle (secondary), avoiding brushes and cables to transfer energy and information. For long distances, the primary is arranged in several electrical independent segments. On the other hand, the short primary configuration uses the winding mounted on the moving part (active vehicle) to produce the traveling wave, the secondary as guide way (induction rail or stationary magnets), and the energy and information should be transmitted contactless to the active vehicle. Regarding the features of the material handling application, the short or long primary topology can be used. Short primary linear drives on passive track are advantageous in material handling applications, where high precision, moderate dynamic, very long track and closed paths are required. Nevertheless, depending on the requirements of the section, the costs can be reduced considerably by using a simple induction rail at the long transporting sections, instead of permanent magnets on the track. Therefore, in this thesis a combined operation of permanent magnet linear synchronous motor (PMLSM) and linear induction motor (LIM) is applied to operate the short primary as vehicle, avoiding adjustment or releasing of the material during the drive cycle. In summary, the passive track will consist of two section types: a high thrust force section (processing station) with PMLSM and a low thrust force section with LIM (transporting section). To the author's knowledge, using two operation modes (PMLSM / LIM) in the same drive is a new approach. A theoretical and experimental study was conducted to assess the feasibility of employing the short primary linear motor for a flexible manufacturing system, in which a contactless energy transmission provides the basic power and an ultracapacitor (UC) storage system provides the peak power. The system uses a bidirectional DC-DC converter between the ultracapacitor bank and the DC-link, to make sure that the ultracapacitor can store the braking energy and supply the peak power demanded by the active vehicle. A control strategy has been developed for controlling the ultracapacitor to deliver the peak of power, to charge, to protect against overvoltage and to recover the energy generated when the vehicle is braking. A control strategy for the transition between the two operation modes (PMLSM / LIM) has been developed to provide a low speed drop, a sufficient thrust force, an optimal dynamic performance and a low power consumption, when it moves between the permanent magnets and the induction rail sections and considering that the linear scale is installed along the whole track. Moreover, a sensorless transition control strategy was implemented in sections where no fast speed changes are necessary (transporting section). Then, a suitable motion strategy is necessary, especially during the transition between synchronous to induction motor operation (or vice versa) and between sensor based and sensorless sections of the track. The classic MRAS (Model Reference Adaptive System) speed and flux estimators are only activated in the sensorless induction motor operation mode. Surely, the costs can be reduced installing the position sensing system only within the processing station and its surrounding. An experimental setup composed by software and hardware, was developed and implemented for the proposed system to perform a smooth transition between the different secondaries, and between sensor based and sensorless sections of the track. Finally, the obtained experimental data confirm the feasibility of the presented approach.