37.

T. Rösmann and S. Soter, "Analysis of instability of direct powered DC-compound machines in pitch systems of large wind turbines" in 2010 IEEE International Conference on Industrial Technology, 2010, pp. 323--329.

Abstract:
DC machines are commonly used as pitch drives enabling the possibility to drive into the feathering position also if power electronics fails. The pitch system of a wind turbine has to fulfill two functions: Limiting the turbine power during strong wind conditions but also braking the turbine via pitching into the feathering position. The second task is safety critical and therefore the pitch system must be equipped with a backup storage in order to react autonomously under grid failure conditions. State of art for electrical pitch systems are lead fleece accumulators due to big experience and cost attractiveness of this technology. Compared with standard DC machines, compound types combine the advantages of a shunt and series machines for direct battery connection: They are naturally able to resist low and regenerative torque conditions like shunt machines by also able to provide a torque even if the battery voltage is low e.g. in case of defect battery cells. But compound machines can show an unstable behavior if the machines changes from motor to regenerative operation during direct powered emergency drive. If this effect appears, the machine generates a dynamic regenerative current peak that causes electromechanical transients stressing the whole pitch drive train. In order to analyze and understand this phenomena a detailed dynamical model of the DC compound machine was developed.

36.

R. Wegener, S. Gruber and S. Soter, "Development of a low cost embedded diagnosis system for servo controlled drives including data mining technologies" in 2009 IEEE 18th International Symposium on Industrial Electronics (ISIE), 2009, pp. 373--377.

Abstract:
This paper deals with an embedded diagnosis device which improves the reliability of a machine including servo controlled drives by monitoring the system parameters and detecting abnormalities and creeping changes. The detection algorithm is based on data mining technologies, well known in business administration. The presented system consists of a low cost processor board with an SD-card slot for data storage and a field bus connection and is completely independent of the main machine control. The additional benefits are online monitoring possibilities and the storage of the process variables in a high efficient way during the complete lifetime of the machine.

35.

S. Gruber, C. Junge, F. Senicar and S. Soter, "Optimization of a high force tubular linear drive concept with discrete wound coils to fulfill safety standards in industrial applications" in 2009 IEEE Energy Conversion Congress and Exposition, 2009, pp. 2431--2435.

Abstract:
This paper deals with the next step of development of a tubular permanent magnet linear drive concept for industrial applications up to 3000 N thrust force where low cogging forces are required to fulfill safety standards. The presented linear drive concept is designed for easy production and assembly of a few hundred units per year. It can be manufactured on standard production machines because all ferromagnetic parts are made of standard not-laminated steel. This results in a very economic product. Further more the drive concept includes an internal low cost position sensor based on the hall-effect. The different steps of development are proven by measurements of thrust and cogging forces of different prototypes.

34.

C. Junge, F. Senicar, R. Wegener and S. Soter, "Pressure control of a nonlinear system with a linear-PMSM and a standard inverter" in 2009 IEEE International Electric Machines and Drives Conference, 2009, pp. 83--88.

Abstract:
This paper deals with a high dynamic hydraulic pressure control. The pressure is generated by an inverter driven linear drive which applies a force on a hydraulic cylinder. The linear drive has to generate a pressure profile into the hydraulic system and has to keep it at a constant value after reaching the demanded pressure. The controlled system, containing hydraulic oil, dissolved air and overall three spring packs, is showing a highly non-linear characteristic. The control cascade of the inverter is based on a standard position control loop, which is enhanced by a PI based pressure controller, a dynamically adapted position feed-forward and an active anti-windup of the controller in order to provide optimal control behavior of the nonlinear system.

33.

T. Rösmann and S. Soter, "Regenerative Operation of DC-Series Machines in Pitchsystems for Multimegawatt Windturbines" in 2008 IEEE Industry Applications Society Annual Meeting, 2008, pp. 1--7.

Abstract:
Modern windmills and multimegawatt turbines are nearly exclusively equipped with electrical pitchsystems.The pitchsystem itself has to fulfill the following functions: In the case of strong wind conditions during normal operation, the system is responsible to limit the generator torque. On the other hand, the feathering position of the blades is needed to brake down the turbine in stop or emergency situations. In modern windturbines this aerodynamical brake is necessary, because the mechanical brake is designed as a holding brake and is not able to prevent overspeed conditions. The last function described is safety relevant. Because of this, pitch systems are equipped with an backup energy storage. So the blade can be put into feathering position in any case. DC-machines are preferred in pitch systems because of their capability to be supplied directly by the DC-storage unit without any control or powerelectronics. The motor must be designed especially for this battery driven operation because current and speed during emergency battery drive are depending on the mechatronical behaviour of the machine. Actually two different DC machine types are used in pitch systems: DC-series and DC-compound machines. DC- compound machines were introduced because of their natural 4Q operation area. But an actual development allows the regenerative operation also for DC-series machines and makes them very cost attractive for multimegawatt pitchsystems.

32.

R. Wegener, S. Gruber, K. Nötzold and S. Soter, "Optimization of a Low-Cost Position Sensor for a Permanent Magnet Linear Drive" in PCIM Asia 2008, 2008.

31.

R. Wegener, S. Gruber, K. Nötzold, F. Senicar, C. Junge and S. Soter, "Development and Test of a High Force Tubular Linear Drive Concept with Discrete Wound Coils for Industrial Applications" in 2008 IEEE Industry Applications Society Annual Meeting, 2008, pp. 1--5.

Abstract:
This paper deals with the development of a tubular permanent magnet linear drive with radial magnetized armature and discrete wound coils mounted on a star-shaped stator part. The rated force of the developed machine is 500 N per segment. This presented particular design results in a very economic product because all primary parts, except of the permanent magnets and coils, are made of standard non-laminated steel and are optimized for easy production and assembly. The control of this machine with a specially built low cost linear sensor based on the Hall-effect is also presented. The suitability of the design is proven by the demonstration of a prototype with measurements of thrust and cogging force.

30.

S. Soter, "Wind Converters and Farms -- Technologies and Control", Electrical Energy Systems -- University Enterprise Training Partnership, vol. 2008, no. 4, 2008.

29.

S. Soter and R. Wegener, "Development of Induction Machines in Wind Power Technology" in 2007 IEEE International Electric Machines & Drives Conference, 2007, pp. 1490--1495.

Abstract:
This paper gives an overview of the development of the induction machine as a generator for wind turbines from the middle of the 20th century up to now. After a short history chapter the different energy conversion concepts are presented. At first a squirrel cage machine is direct coupled to the grid (Danish concept). To adjust the machine speed the second step is a wound rotor machine with collector rings to change rotor resistance. This concept allows the first adaption of the operating point of the wind turbine and the induction machine. Another concept is to connect the stator of a squirrel cage machine with a full inline voltage source converter to the grid to get the flexibility in rotational speed and to control the reactive power. The doubly fed induction machine is the latest development. This concept uses a bidirectional voltage source converter in the rotor circuit with a rated power of only 30{%} of the rated generator power. Now it is possible to change the rotational speed and the reactive power independently and in a wide range. A generalized control scheme of a modern doubly fed induction machine (DFIG) is shown in the last part to explain the variability and the range of application. Today over 70{%} of the wind turbines are build up with DFIG.

28.

R. Wegener, F. Senicar, C. Junge and S. Soter, "Low Cost Position Sensor for Permanent Magnet Linear Drive" in 2007 IEEE 2nd International Conference on Power Electronics and Drive Systems (PEDS), 2007, pp. 1367--1371.

Abstract:
This paper deals with a custom made low cost sensor for measuring the position of a permanent magnet linear motor. The principle how to measure position and movement direction with two analog hall sensor elements is described. The following simulated and detailed error and failure treatment is very important to know exactly the performance and the possibilities of this low cost sensor element. Afterwards this position sensor is build and some measurements with a linear machine is done. After filtering, the accuracy of the two signals is high enough to be an input of a converter control to determine the correct current which has to be injected. If there is another higher ranking closed-loop control, e.g. pressure, flow or force, in the control system this low cost sensor is sufficient and works very well. It is possible to implement the very small sensor in the housing of the linear drive. This sensor costs less than 15 dollar and can not be compared to a very precise working linear senor for some hundred dollar in order to position the linear drive very exact but the accuracy is high enough to build a lower ranking closed-loop control and to stabilize a complex control system of converter, linear drive and load.