Bernd Orlik

Robust output-feedback H/sub /spl infin// control with a nonlinear observer for a two-mass system

In this paper, a positioning control of a nonlinear elastically coupled two-mass system is presented. Structures of two-mass systems can often be found, e.g., in robotics or machine tools. The contained mechanical parts, like gears and shafts, can lead to limit cycles and stick-slip effects. In order to avoid the unwanted effects an H/sub /spl infin// control design is used for the system. Parameter uncertainties and elastic torsion are also taken into account in the control synthesis. If the measurability is limited, so that only the system output can be measured, a nonlinear observer is used. The standard output-feedback H/sub /spl infin// control structure needs some basic changes for this nonlinear observer. The result is an H/sub /spl infin// control, which can handle the nonlinear system, even if only the system output can be measured. The control shows good dynamics, robustness, and can handle disturbances. Measured results are shown in this paper.

Transverse flux machines with distributed windings for in-wheel applications

Transverse flux machine (TFM) useful for in-wheel motor applications is presented. This transverse flux permanent magnet motor is designed to achieve high torque-to-weight ratio and is suitable for direct-drive wheel applications. As in conventional TFM, the phases are located under each other, which will increase the axial length of the machine. The idea of this design is to reduce the axial length of TFM, by placing the windings around the stator and by shifting those from each other by electrically 120° or 90°, for three- or two-phase machine, respectively. Therefore, a remarkable reduction on the total axial length of the machine will be achieved while keeping the torque density high. This TFM is compared to another similar TFM, in which the three phases have been divided into two halves and placed opposite each other to ensure the mechanical balance and stability of the stator. The corresponding mechanical phase shifts between the phases have accordingly been taken into account. The motors are modelled in finite-element method (FEM) program, Flux3D, and designed to meet the specifications of an optimisation scheme, subject to certain constraints, such as construction dimensions, electric and magnetic loading. Based on this comparison study, many recommendations have been suggested to achieve optimum results.

Comparison study of permanent magnet transverse flux motors (PMTFMs) for in-wheel applications

This paper investigates the existing structures of transverse flux machines (TFMs) that can be constructed as an outer rotor in-wheel motor which is suitable for low speed applications. As the main characteristic of TFM is providing the best torque density at low speeds, it would be a suitable choice and having a great future for low speed mobile platforms. Different structures of TFM are re-designed as outer rotor motors with the same diameter, axial length and pole number and they undergo a comparison study through the use of three dimensional (3D) finite element method (FEM). The simulations have been done via Flux3D software from Cedrat. An analytical study of the TFMs is done in terms of highest torque production capability and design optimisation.

Robust state-feedback H/sub /spl infin// control of a nonlinear two-mass system

In this paper, a positioning control of a nonlinear elastically coupled two-mass system is presented. Structures of two-mass systems can often be found, e.g. in robotics or machine tools. The contained mechanical parts, like gears and shafts, can lead to limited cycles and stick-slip effects. In order to avoid these unwanted effects, an H/sub /spl infin// control design is used for the system. In the control, parameter uncertainties and elastic torsion are also taken into account. In the standard H/sub /spl infin// control structure, a basic change is needed. This leads to a state-feedback H/sub /spl infin// control. The result is a linear H/sub /spl infin// control, that can handle the nonlinear system. The control shows good dynamics, robustness and can handle disturbances. Measured results are shown in this paper.

Position control of a transverse flux motor with reduced torque ripples for direct servo-drive applications using shaped currents with harmonics control

This paper presents a control based upon optimised current waveforms with switching on current harmonics to achieve an accurate position and speed control with reduced ripples in torque shape for a transverse flux motor. The approaches are verified by measured results at a two phase prototype of a magnet exicited transverse flux motor.

Flux linkage in Transverse Flux machines with flux concentration

In this paper the flux linkage between the permanent magnets in the rotor and the stator core of a Transverse Flux machine is investigated, with a special focus on the flux concentrating setup, which allows to utilize the core materials up to their saturation limits. FEM simulations are carried out to find the relation between the flux linkage and the size of the permanent magnets. Finally new design guidelines are developed for the construction of TFMs with regard to the magnetic circuit in a flux concentrating setup.

Robust output-feedback H/sub /spl infin//-control with a nonlinear observer for a two-mass system

In this paper a positioning control of a nonlinear elastically coupled two-mass system is presented. Structures of two-mass systems can often be found e.g. in robotics or machine tools. The contained mechanical parts, like gears and shafts, can lead to limited cycles and stick-slip effects. In order to avoid the unwanted effects an H/sub /spl infin// control design is used for the system. Parameter uncertainties and elastic torsion are also taken into account in the control synthesis. If the measurability is limited, so that only the system output can be measured, a nonlinear observer is used. The standard output-feedback H/sub /spl infin// control structure needs some basic changes for this nonlinear observer. The result is a H/sub /spl infin// control, that can handle the nonlinear system, even if only the system output can be measured. The control shows good dynamics, robustness and can handle disturbances. Measured results are shown in this paper.

Analytical model describing the operation behaviour of transverse flux machines in flat magnet configuration

This paper presents an analytical model of the electromechanical behaviour of transverse flux machines in flat magnet configuration. The model is based on the distribution of the magnetic field inside the machine, which will be given special focus, due to its significance in calculating the electric torque by means of the magnetic coenergy.

A paradigm change in wind power station control through emulation of conventional power plant behaviour

With a new control concept presented in this paper, wind power stations with inverter-coupled synchronous generators (SG-WPS) behave to a great extent like the turbine-generator sets of conventional thermal power plants including the ability of the release of active- and reactive reserve power. This allows every single SG-WPS to improve its contribution to power grid stability. The new control concept consists of three main subsystems: The control of the grid-side inverter, the control of the generator-side inverter and the control of the rotor speed with the pitch angle. This paper points to all named subsystems, but the main focus is on the control of the dc-link voltage of the frequency inverter. In contrast to conventional control concepts of SG-WPS, where the dc-link voltage is regulated with the grid-side inverter, here it is controlled with the generator-side inverter. This is a paradigm change in wind power station control. Without the task of dc-link voltage control, the grid-side inverter of the SG-WPS is operated with droop based virtual synchronous machine emulation. It allows the SG-WPS to immediately react to grid disturbances by the release of active- and reactive reserve power. This is an important step in the conversion of a WPS from a “negative consumer” to a voltage source. Simulation results show the dynamic behaviour of the SG-WPS with the new control concept as a whole. A test bench and experimental results for the dc-link voltage control with the generator-side inverter will be presented.

New HVDC-Concept for power transmission from offshore wind farms

The future for wind power generation in Germany is offshore wind energy. The preferred concept for power transmission over long distances from the offshore wind farm to the mainland is the high voltage direct current (HVDC) power transmission. In this paper a new transmission concept based on HVDC is presented.