Ants Kallaste

Magnetic properties of reduced Dy NdFeB permanent magnets and their usage in electrical machines

This paper describes the magnetic properties of different permanent magnet materials and their industrial usage as crucial components of permanent magnet electric machines. As the prices of rare earth materials, especially neodymium-iron-boron (NdFeB), has been rising rapidly during the last few years and has been quite unstable during the past decade, the search of new cheaper and yet durable alloys has started. One of the possibilities of cutting the price of NdFeB alloys is the decreasing of the dysprosium (Dy) content of such material. Possibilities of using these new materials in electrical machines as well as potential risks are analyzed in the paper. An overview of the development of low Dy magnets is presented. Necessity of further investigations is pointed out.

Analysis of the eccentricity in a low-speed slotless permanent-magnet wind generator

This paper presents the analytical analysis of different eccentricities in the rotor of a novel slotless wind power generator. The analytical expressions for the air gap eccentricity have been derived and the effects of these eccentricities on the air gap flux density, the resultant unbalanced magnetic pull and the induced emf are investigated. The analysis shows a strong pull in the case of static eccentricity, which is not seen when the case of elliptic eccentricity for example. The analysis shows also that the induced emf per coil can vary very much but due to the series connection of the coil per phase emf is uniform but has higher rms value than in the case of healthy machine. The analytical equations are verified for the case of healthy machine on a constructed laboratory prototype.

Direct Liquid Cooling in Low-Power Electrical Machines: Proof-of-Concept

This paper evaluates the feasibility of a direct liquid cooling approach in the thermal management of an axial flux permanent-magnet machine. To demonstrate the cooling method, a test motor was fitted with helical tooth coil windings formed from a hybrid conductor comprising a stainless steel coolant conduit tightly wrapped with a stranded Litz wire. The motor is a 100-kW permanent-magnet, axial-flux, double-stator, single-rotor machine. The proof of concept integrated the motor with a closed liquid coolant loop, appropriate instrumentation, and a data acquisition system. The general performance of the motor was examined at various power levels using polyalphaolefin oil as the cooling fluid. The results show the proposed cooling method to be feasible, and furthermore, to provide significant improvements to the machine thermal management.

Exterior-rotor permanent magnet synchronous machine with toroidal windings for unmanned aerial vehicles

This paper represents the study of the multimode permanent magnet synchronous machine constructed for a small-sized unmanned aircraft. An overview of commonly used electrical machine types for unmanned aircrafts is also given within this paper. The main objective of the research was to create an electrical machine that could be used in addition to the combustion engine as a motor-generator. Based on the specifics of the area and the goal of the research the most suitable and optimal solution of the machine topology is considered. The paper gives an overview of the design of the permanent magnet electrical machine and its mechanical and electrical parameters. The test bench for experimental study of the prototype permanent magnet machine was also designed and built. Using the test bench the no-load test was carried out and corresponding characteristics were charted in a generator mode of the machine.

Analysis of a slow-speed slotless permanent magnet synchronous generator

Department of Electrical Engineering at Tallinn University of Technology has been involved in the development of novel electrical machines for wind applications. This paper presents the analysis of the electrical parameters of a novel slow-speed slotless permanent magnet synchronous generator. Firstly, some of the design parameters are calculated and a simplified analytical mathematical model of the generator is constructed to calculate the output variables under different operational conditions. Secondly, some FEM calculations are carried out to check the validity of the analytical model. Thirdly, test results are analyzed and compared to the calculated values. Finally, the analytical model is evaluated and final output parameters of the generator are determined.

Lifecycle-based design and optimization of electrical motor-drives - Challenges and possibilities

This paper describes the procedure of lifecycle-based design and optimization of electrical motor-drives as well as related methodologies to be developed. As the electric motor-drives are the most electrical energy consuming apparatuses, thorough and in depth optimization of the drives during their design process is essential to support energy efficient and environmental friendly development in electrical engineering and industry processes. Lifecycle-based optimization would grant a possibility to evaluate a wider range of variables that affect the environment and energy consummation of the drives. An overview of existing optimization techniques and related literature is presented. Necessity of new methodologies is pointed out.

Load-resonant converter with changing resonant tank topology for welding applications

In this paper a new approach and corresponding converter based on varying resonant tank topology for supplying DC loads like welding arc is presented. In order to describe suggested topology the circuitry of proposed converter and some design aspects are discussed in relation to typical load conditions during welding process. Simulation and first experimental data are also provided and analyzed. The obtained natural characteristic of this converter has a constant power mode in the range of welding currents and inherent parametrical short-circuit limitation. Also, its fast “natural” response to change of load conditions could probably yield in better arc stability and more even weld bead quality.

Sensorless Detection of Induction Motor Rotor Faults Using the Clarke Vector Approach

Sensorless Detection of Induction Motor Rotor Faults Using the Clarke Vector Approach Due to their rugged build, simplicity and cost effective performance, induction motors are used in a vast number of industries, where they play a significant role in responsible operations, where faults and downtimes are either not desirable or even unthinkable. As different faults can affect the performance of the induction motors, among them broken rotor bars, it is important to have a certain condition monitoring or diagnostic system that is guarding the state of the motor. This paper deals with induction motor broken rotor bars detection, using Clarke vector approach.

Reactive power compensation for spot welding machine using thyristor switched capacitor

High-power industrial spot-welding machines make use of transformers that have very high reactive power consumption. Simple reactive power compensation schemes cannot be used however, because of the cyclic nature of the spot welding transformer operating. This paper describes the development of a simple reactive power compensator solution for the spot-welding machines. Focus is also put on the transformer saturation and current transients that can emerge from deployment of such reactive power compensation methods.

Review of thermal analysis of permanent magnet assisted synchronous reluctance machines

This paper presents a review of the losses and thermal analysis of permanent magnet assisted synchronous reluctance motors. Various types of solutions for critical parts of heat extractions and different empirical correlation for determination of each part are presented in details. Finally the experimental methods for determination of the critical parameters are presented. In this paper has tried to give advices how to calculate the critical parameter for constructing more accurate lumped parameter thermal network.