Silaghiu, Sorin Mihail (2012)
Design and test of a highly scalable servo drive system based on PM linear synchronous motors.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

In many industrial plants materials have to be transported between several processing stations, where they have to be processed with a high level of accuracy and precision. In the last years, linear electrical drives, especially the long-stator linear motors are used for these types of applications for both processing and transportation tasks. They have higher dynamics and processing precision and lower maintenance costs compared to conventional systems, which require additional mechanical gears. The linear drive system must be modular and highly scalable in order to cover a wide range of applications. For this reason, the track of the plant is made of several stator segments. The excitation part of the motor is represented by permanent magnets (passive vehicles). Each stator segment has a dedicated inverter (Power Processing Unit) and processor (Information Processing Unit). Cheap IPMs (Intelligent Power Modules) are nowadays a good solution for implementing the inverter. A DSP was used as processor. The DSP and the IPM are the main components of the designed servo-controller, which together with a stator segment represents a module of the system. The DSP controls the inverter and is also used for the communication with the DSPs of the adjacent modules. By connecting the ground potential of all servo-controllers to the negative DC-link rail (ca. -280V), a significant reduction in the implementation costs of the servo-controller was achieved. When a vehicle crosses from one stator segment to the adjacent one, the control tasks migrate physically in that respective adjacent DSP. Data exchange is therefore required within each cycle of the current control loop (100 µs) between the adjacent modules. For an arbitrary scalable modular system, there will be also an arbitrary high communication demand. This demand can only be solved by a direct (Point-to-Point) connection between the adjacent DSPs. This connection was realised by means of the cost-effective RS485 data transmission protocol. A central control unit is responsible then for the cyclical (1-10 ms) generation of new position reference values for the vehicles, according to a predefined schedule. The monitoring (assessment of internal variables of the distributed servo-controllers) of the entire system is realised also in real-time. Off-line download and upload actions of firmware or general data is also possible. For these tasks, the communication between the central unit (PC) and the distributed servocontrollers was realised by means of the Ethernet-based fieldbus EtherCAT. Inside the processing stations of the system, the positioning accuracy and precision as well as the dynamic have to be very good. For this reason, inside those stations, position sensors must be used. Outside those stations, for material transportation only, an EMF-based sensorless control was implemented. This will further reduce the overall system costs. A small section of such modular and highly scalable system was realised as an experimental set-up in the context of this work, in order to test the functionality and the reliability of the proposed system.

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