Kari Tammi

Attenuation of Harmonic Rotor Vibration in a Cage Rotor Induction Machine by a Self-Bearing Force Actuator

In this paper, attenuation of flexural rotor vibration in electrical machines is considered. In order to generate force on the machine rotor, an electromagnetic actuator based on self-bearing machine working principle is examined. A control method for attenuating harmonic rotor vibration components is applied in a 30 kW two-pole cage induction machine. The machine is equipped with a four-pole supplementary winding for generation of lateral force on the rotor. Experimental results for the two-pole induction motor are presented. The main contribution of this paper is to apply a control method, specially designed for compensating harmonic excitations, by using a built-in electromagnetic actuator in an induction machine.

Torque Density of Radial, Axial and Transverse Flux Permanent Magnet Machine Topologies

Torque density of radial, axial and transverse flux machine topologies is investigated. A 10-kW, 200-rpm motor is chosen as a test case. Radial and axial flux motors that fulfill the key specifications of the selected test case are designed employing in-house analytical dimensioning tools and MATLAB genetic multi-objective optimization. Rather simple numerical approach is taken to study the transverse flux motor. A 20-pole-pair radial flux motor is found to outperform its axial and transverse flux counterparts in terms of torque density.

Efficient Parallel 3-D Computation of Electrical Machines With Elmer

After its recent improvements described here, open source finite element software Elmer is shown to be a highly efficient option for electrical machine modeling. The parallelization of computational burden is shown to be a necessity. The methods implemented enable applying fully parallel computation to electrical machine models, including rotation and electrical circuits. Computational experiments performed demonstrate that Elmer can effectively utilize several hundreds of computational cores in parallel, making it an attractive alternative when computational speed is of high importance.

Modelling of flexural rotor vibration and time-periodic system dynamics in a two-pole cage induction machine equipped with a self-bearing force actuator

Abstract In this paper, linear time–periodic system dynamics in rotor vibration of electrical machines is examined. We consider a two-pole cage induction machine equipped with a built–in force actuator for active generation of lateral force on the rotor. The main contribution of the work is to identify and model the sources of time-periodic system dynamics in the coupled electromechanical actuator-rotor system. Especially, the effect of higher spatial harmonics of the magnetic field on the generated force is considered. In this work, a linear time–periodic model for the actuator-rotor system is derived. The parameters of the analytical model are estimated by using time-stepping finite-element analysis of the machine.

High-resolution hybrid pixel sensors for the e+e− TESLA linear collider vertex tracker

Abstract In order to fully exploit the physics potential of a future high-energy e+e− linear collider, a Vertex Tracker, providing high-resolution track reconstruction, is required. Hybrid silicon pixel sensors are an attractive option, for the sensor technology, due to their read-out speed and radiation hardness, favoured in the high-rate environment of the TESLA e+e− linear collider design, but have been so far limited by the achievable single point space resolution. In this paper, a conceptual design of the TESLA Vertex Tracker, based on a novel layout of hybrid pixel sensors with interleaved cells to improve their spatial resolution, is presented.

Electric City Bus Energy Flow Model and Its Validation by Dynamometer Test

Battery electric city bus model has been created and the simulation results compared against the measured results from the full scale city bus developed for heavy vehicle research. The model utilizes multi- physics modelling approach with multiple-domains from friction-tyre and transmission model to electrical drive and a simplified battery model. The modelled and measured motor torque, current and voltages in the battery and inverter and the bus speed were compared under a driving cycle based on a local bus line. The simulated results were in good agreement with the experimental measured results; the error between the simulated and measured energy consumption was 1.4 %. The measured average energy consumption was 0.581 kWh/km while the simulation estimated 0.589 kWh/km.

Hybrid city bus design evaluation using system level simulations

Effects of different design parameters on the performance of a hybrid city bus were studied. A system simulation model of the hybrid city bus was developed and used for studying the effects of drive motor torque and vehicle mass on vehicle performance, fuel consumption and stability during regenerative braking. Increasing the maximum torque by 60 % from the nominal value was found to improve the fuel efficiency by 8.3 % when the vehicle was driven on Braunschweig cycle. On the other hand, vehicle stability during regenerative braking was analysed to understand the influence of the braking torque on vehicle stability. This is particularly important when operating at limited traction conditions. In situations where only regenerative braking was applied, the stability was found insufficient.

Scalable open- and balance-type calorimeter for measuring power electronics and motors

Accurate measurement of losses of high-efficiency power electronics devices and electrical motors is difficult by using input and output powers. In the calorimetric method, these losses are measured directly. However, the calorimeters have to be designed for a certain power loss range, and therefore, the same system cannot be applied to different power devices. In this paper, a functional and scalable power loss measurement concept is suggested for the measurement of losses between 10 W and 30 kW with a reasonable measurement accuracy. Such a power loss range can be applied, for example, to devices with 97% efficiencies with input powers between 333 W and 1 MW. The concept is introduced, verified, and demonstrated by laboratory measurements.

Finite element analysis for bearingless operation of a multi flux barrier synchronous reluctance motor

Self levitation principle for electrical machines has been a promising research area in the last two decades. Bearingless operation of a motor with two different windings (torque and levitation force windings) requires certain design parameters such as winding space and conductors per slot to be chosen correctly. This paper discusses the design aspects of a bearingless synchronous reluctance motor (SynRM) with multiple flux barriers. This type of machine can be very effective in the smooth torque and levitation force production. A finite element analysis is presented to identify the feasibility and practical challenges for the bearingless operation of a SynRM.

Magnetic bearing as Switched Reluctance Motor - feasibility study for bearingless Switched Reluctance Motor

This paper shows a general review of Switched Reluctance Motors (SRM), reports the conversion of Active Magnetic Bearing (AMB) to SRM and discusses methods to estimate the torque produced in SRM. AMB converted to SRM has been tested on a laboratory scale test rig and its torque production measured. The novelty of this paper is the modified analytical method to estimate fringing flux paths enabling more accurate mathematical model to estimate torque. The reason for careful analysis of the air gap forces is the demand for electromagnetic models of the motor to be used in the motor controller. The ultimate goal of our work is to develop self-bearing (self-levitating bearingless) SRM.