Ants Kallaste

• Doctor of Philosophy
• Professor at Tallinn University of Technology

The paper is about the design and prototyping of directly driven outer rotor permanent magnet generator for small scale wind turbine. In the paper, the initial design of the generator is given. Main issues and phenomena affecting the generator design, such as cogging torque and its reduction possibilities, selection and demagnetization risk assessm...

The paper discusses the current developments in the recycling of electrical machines. The main attention is devoted to three types of motors: synchronous reluctance motor, permanent magnet assisted synchronous reluctance motor, and induction motor. Base materials of such electrical machines are also described in the paper. Rare-earth permanent magn...

A Simulink/DriveSize based model for the mutual pressure and flow control of a centrifugal pumping plant with a variable speed drive is proposed. The model provides the possibility of power calculation during both throttling and speed control and to estimate the optimal working point according to these calculations. The model is developed to provid...

This paper presents a thermal study to define the appropriate correlations allowing the determination of the convective heat transfer coefficient over large parallel rectangular fins for a permanent magnet synchronous generator coil. For this purpose, an experimental setup is developed for both horizontal and vertical orientations and different inp...

This paper presents a hybrid thermal modeling methodology to analyze the temperature performance of radial flux electrical machines. For this purpose, the 2D finite element model of the active part of the machine is coupled with a lumped parameters thermal circuit of the end-winding region. A synchronous reluctance machine is used to validate the p...

This paper presents a thermal study to determine the convective heat transfer coefficient over the flat side of a permanent magnet synchronous generator coil in horizontal and vertical directions by using the empirical correlation. To validate the results, an experimental setup is developed for both horizontal and vertical orientations and differen...

A model for the sliding electrical contact units is proposed. The proposed model employs the change of the parameters of the transition capacitance and resistance by means of a relay, operating in a pulsed mode. The designed model enables to estimate electromagnetic processes, taking place in the transitional layer of the sliding contacts. A series...

Centrifugal pump systems are one of the dominant parts in water distribution systems, irrigation networks, oil and chemical industries. Simulation of an electric drive system for throttling purposes in centrifugal pumps is proposed. Specific electric drive model is developed to provide all necessary possibilities for simulation. The model consists...

This study presents induction machine fault detection possibilities using smartphone recorded audible noise. Acoustic and audible noise analysis for fault detection is a well-established technique; however, specialised equipment for diagnostic purposes is often very expensive and difficult to operate. To overcome this obstacle, a simple pre-diagnos...

This paper presents a novel approach to traction effort calculation for a self-driving car. Self-driving cars usually require reliable and accurate path planning algorithms to operate in dynamically changing environment. The first self-driving car project in Estonia started with the cooperation of Tallinn University of Technology and Estonian compa...

Abstract — Centrifugal pump systems are integral parts of water distribution systems, sewerage networks, oil and other industries. Simulation of flow control system for centrifugal pumps is proposed. Specific centrifugal pump model is developed to provide all necessary possibilities for simulation. The model consists of several main components: cen...

This paper investigates the difference between Field-Oriented Control (FOC) strategies for induction and synchronous reluctance motors. It illustrates the concept of model-based control scheme for both types of motors. The simulation models developed for both types of motors take into consideration the differences between these motors and allow not...

The paper presents an analytical thermal calculation of a synchronous reluctance motor (SynRMs) to predict the temperature of different part of the motor. For the analytical calculation, a lumped parameter thermal network (LPTN) is developed and analyzed. To validate the developed model, measurements are carried out on an experimental setup includi...

The paper presents analytical and experimental determination of the forced convection heat transfer coefficients over the flat side of a permanent magnet synchronous generator coil. In the analytical part, the forced convection coefficients at different wind speeds are calculated based on various known equations of the forced convection heat transf...

The fault detection of squirrel cage induction motors due to its importance in the industry has become a highly developed area of interest for researchers. Typically, the electrical machine is designed for stable operation with minimum noise and vibrations under normal conditions. When the fault emerges, some additional distortions appear. The nece...

Due to importance of squirrel cage induction motor in today’s industry, the fault detection on that type of motors has become a highly developed area of interest for researchers. The electrical machine is designed for stable operations with minimum noise and vibrations under the normal conditions. When the fault emerges, some additional distortions...

this paper presents the analytical thermal analysis of a permanent magnet generator stator coil. The analytical analysis consists of a lump parameter thermal network (LPTN) to predict the steady state and transient temperature of the coil module. In the steady state part the average temperature of different parts of the network are estimated by usi...

This paper analyses the influence of selected magnet materials on the design of slow-speed permanent magnet synchronous generators for use in wind applications. The design procedure, including setting of the initial design parameters of the machine, calculations of machine dimensions, magnetic flux in the air-gap, and electrical parameters as well...

The paper discusses problems concerning the influence of permanent magnet material characteristics on the low-speed permanent magnet generator losses and output characteristics. The variability of the magnet material and its effect on the output parameters of the machine has been quantified. The characteristics of six different grades of neodymium...

The paper presents an investigation for determination of the natural heat extraction, consist of radiation and natural convection from the flat surface of one permanent magnet synchronous generator’s coil in horizontal and vertical directions by using the analytical and experimental methods. For the experimental purpose, the coil is put inside the...

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 stranded Litz wire....

Comparative analysis is performed for different motors from the standpoint of damage inflicted by them during their lifecycle. Three types of motor have been considered: the synchronous reluctance motor, the permanent magnet assisted synchronous reluctance motor and the induction motor. The assessment of lifecycle has been made in terms of its four...

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...

This paper presents an analysis of the environmental and life cycle costs of a synchronous reluctance machine (SynRM). Focusing exceptionally on consumption is no longer sufficient, energy savings initiatives must now account for all life cycle assessment (LCA), including construction, use and end-of-life. The analysis was carried out according to...

Detection of broken bar faults of the induction motor is important in electrical machine fault prediction. The proper model of the motor with a broken bar can be a useful tool for fault determination studies as well as a basic material for the development of inverse theory implementation possibilities in electrical machine diagnostics. In this pape...

The paper gives an insight to the importance of choosing one certain value in a range for the permanent magnets parameters given by manufacturers. The purpose of the research is to test the influence of chosen parameters values, which are given in a range and are used in computational modeling, on the devices main characteristics, as nowadays scien...

This paper presents a review of losses calculation and also loss reduction control methods of permanent magnet assisted synchronous reluctance drives. Reluctance machines as well as drive systems containing such machines are gaining popularity and hence need closer investigation and optimization. The paper introduces the topic, describes the possib...

This paper presents analytical and numerical thermal analysis of three different toroidal coils levitated on an aluminum plate. The analytical method consists of a network of thermal resistances that make it possible to estimate the average temperature of the coils. In the numerical method, by using the FEM thermal and magnetic analysis, the averag...

The paper analyzes the reasonability of using an off-grid hybrid power supply system or in other words a local grid for sparsely populated areas as well as the necessary components selection and price development of such system. Typical consumers are selected and all estimations and calculations are based on them. Consumer profiles are set and anal...

In this paper, the effect of wind parks on the efficiency of thermal power plants (TPPs) is studied. Main attention is put towards the change in fuel consumption of TPPs and polluting emissions in case of cooperation with alternative energy sources. As known, the efficiency of TPP reduces with the decreased loads. On the contrary, green energy has...

This paper presents the necessity of posing and solving inverse problems in the diagnostic procedures of electric machines. This is essential in order to achieve better and more precise results in the condition monitoring of the machines due to the growing complexity of the machine setups, which challenges the traditional electric machine diagnosis...

This paper describes the environmental considerations that have to be taken into account in lifecycle based design and optimization of electrical machines. As the electrical machines and electric motor-drives are the most electrical energy consuming apparatuses, in depth optimization of them during the design process is essential to support energy...

This paper presents a study in the field of electric motor drive testing. One example of propulsion drive load dynamic control system is presented. Mathematical model of the propulsion motor drive of Tesla Roadster is presented. Suggested dynamic load control system is verified using a MATLAB/Simulink computer model and a test bench. The developed...

This paper presents a novel design optimization procedure for an ultra large diameter permanent magnet generator. As the machine features unorthodox electromagnetic and mechanical layouts, basic principles for determining structural loads together with material quantities for cost estimation are described. Finite element modelling with beam element...

The paper represents the study of electric output parameters of a multi-pole exterior-rotor permanent magnet (PM) synchronous machine, which is a part of a hybrid drive for a small unmanned aircraft. The PM synchronous machine's constructional feature is a toroidal or Gramme's type of stator winding. The studied machine is designed to operate as a...

Permanent magnet machines magnetic losses and output characteristics are directly related to the permanent magnet material characteristics. In this paper we study the effect of variability in these characteristics on the operation quantities of a low speed permanent magnet wind generator. The variability itself can emerge as the result of misuse of...

This paper presents a comparative analysis between the energy efficiency of two wind generator designs. A hypothesis is presented that generators for wind applications should be designed based on their energy efficiency instead of rated efficiency. As wind generators are working with variable rotational speeds and power levels, resulting in changes...

This paper describes manufacturing tolerance faults that may occur during the design of electrical machines. Examples of the manufacturing tolerances are based on the design and construction process of a slotless permanent magnet wind generator. Experiments are carried out on the reference machine.

This paper presents the finite element modelling of three-phase squirrel-cage induction motor with broken rotor bar faults. Finite element model based on a real machine is constructed, propagation of broken rotor bar fault and its influence on the magnetic flux density distribution of the machine cage is observed. As the propagation of the fault wi...

Residential generation of electricity from renewable sources has grown substantially owing to active governmental stimulation programs in many countries. Permanent magnet synchronous generators (PMSG) are a preferable solution for residential wind turbines (WTs) due to their high efficiency and reliability. In the design of grid integration equipme...

The paper describes the connection of an electric vehicle to the utility grid and using the vehicle as a part of it. A new topology is presented and verified with experimental and simulation results. The experimental schematic allows to correct power factor of the grid, by using the part of the vehicle traction system. Basically it presents a porta...

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...

This paper analyses the possibilities and cost-efficiency of using different magnetic materials on the rotor of a slow-speed slotless permanent magnet synchronous generator. The experimental tests were carried out using three different magnetic materials - SmCo, NdFeB and ferrite. Cost efficiency analysis of the tested generator concepts is based o...

This paper presents the analysis of electrical parameters in case of air-gap eccentricity in a novel slow-speed slotless permanent magnet synchronous generator. Construction of the novel generator has been explained. Laboratory tests with healthy machine and the machine with an eccentric rotor have been presented. Discussion on how the air-gap ecce...

This paper focuses on the analysis of mechanical vibrations caused by different eccentricities in the rotor of a slow-speed slotless permanent magnet generator. The analysis of different eccentricities and their influences was carried out on a full scale laboratory test machine. Three most common mass center dislocation faults of a generator rotor...

This paper presents the analysis of electrical parameters of a novel slow-speed slotless permanent magnet synchronous generator. Calculations and analyses are based on generator construction using SmCo permanent magnets in one and NdFeB permanent magnets in other case. Some of the design parameters are calculated and a simplified analytical mathema...

This paper describes the design process of a permanent magnet assisted synchronous reluctance machine. The designed machine is meant to be optimized and designed in the viewpoint of lifecycle based optimization methodology proposed by the authors. Suitability of permanent magnet assisted synchronous machines for the use in various applications is e...

This paper presents the analysis of electrical parameters and design process of a novel slow-speed slotless permanent magnet synchronous generator. Main design criteria and the design process itself are explained. FEM calculations are carried out to check the validity of the analytical model and suitability of the chosen magnets to the generator. T...

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 effi...

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 dec...

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 a...

Permanent magnet (PM) machines with tooth coil windings are designed and analyzed. We study how the slot wedge material affects the behavior of PM losses when using tooth coil windings, which generate a significant air gap flux density harmonic content. The losses and cogging torques of a surface permanent magnet rotor and an interior permanent mag...

This paper analyses the reasonability of using an offgrid hybrid power supply system or a local grid for sparsely populated areas. Two typical consumers are selected and all estimations and calculations are based on the two. Consumer profiles are set and analyzed as well as different elements of the local power supply grid and the possibility of co...

This paper analyses the necessary components selection and price development of local power supply systems for sparsely populated areas. Two typical consumers in potential need for local power supply system are found and calculations are made based on the need of the chosen consumer profiles. Estonian example is used in this paper as the country li...

This paper presents the modeling of the construction procedure of a halbach array electrical machine and the corresponding partial demagnetization. Comparison between a static simulation with all magnets at their final positions and dynamic one where one of the magnets is brought to its final position from an initial one shows that the static solut...

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 e...

This paper presents the possibilities of using Clarke vector approach for stator current and voltage analysis for induction motors with broken rotor bars. The equations for performing Clarke transformation on three-phase stator current and voltage are presented. Since this method is generally used for transforming current signals, benefits for usin...

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...

The paper presents investigations carried out on the construction of slow-speed slotless permanent magnet wind generator. As rare earth magnet prices have been rising significantly during the last years, the possibilities of using other magnet materials in this generator have been investigated. In this paper we describe one possible solution using...

All machines, no matter how well they are designed, calculated or produced have the tendency to fail at some point of their existence. If the condition of the machines in use is not monitored in any way and the maintenance is forgotten, the resulting failures may pose a large economic and safety risk. Even the small and at first not important fault...

Department of Fundamentals of Electrical Engineering and Electrical Machines in Tallinn University of Technology has been researching the possibilities for using slow-speed ringshaped permanent magnet generators in wind energy applications. Goliath Wind Ltd and my!Wind Ltd are the industrial partners for this project. There are different benefits a...

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 brok...

During the past few decades there has been a continually increasing interest and investigation into fault detection and diagnostics of induction motors. There are various different diagnostic approaches and methods to detect faults in induction motors. Attention should be paid to the fact that as induction motors are often used in critical duty dri...

A multitude of flexible low-cost communication hardware with sufficient performance is available for control of microgeneration and loads in households, but proprietary software is often limited. Robust and simply maintainable solutions are often required in practical applications besides highly-multifunctional programmable logic controllers develo...

This paper presents an analysis of tendencies in development and design of small-scale wind power applications on the basis of directly driven low-speed multipole permanent magnet synchronous generators. Analysis of primary magnetic field distribution and armature reaction in the conditions of surface-mounted radial magnetic flux permanent magnet s...

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 s...

In principle, a distortion of a waveform shape of AC/DC converter current could be corrected by use of a fast-controlled impedance-matching transformer. Changes in the converter input impedance can be eliminated by means of the varying transformation ratio of this transformer. The paper considers a practical performance of the fast-controlled imped...

The distortion of an AC-DC converter current could be corrected by use of a fast-controlled impedance-matching transformer on a basis of a non-conducting converter with alternating of parallel and series resonance. The basics of the converter performance and operation are described. Changes in the converter input impedance can be eliminated by mean...

This paper analyzes of toroidal winding permanent magnet axial-flux wind generator. Special attention is paid on peculiarities and output characteristics. The experimental generator has been designed and constructed on the base of this construction approach. Testing experimental generator allows to compare test result with simplified calculation me...

Induction motors have become the most used electrical motors in the world. They are rugged, easy to maintain, low in cost and good in perform-ance. Those benefits have made induction motors very popular among users. During their exploita-tion period induction motors are exposed to various stresses that can become fatal to their performance and brin...