A universal high frequency three phase electric motor model to be used in the design process of the electric motor drive systems is proposed. The model can be combined with the models of the filter, cable and inverter to form a complete drive system. It allows for a common and differential mode high frequency analysis in studying the bearing currents, electromagnetic interference and overvoltages in the motor windings caused by the high frequency reflections. The model phase is symmetrical meaning that the beginning and end of each phase are equal and the central part is inserted between them. This enables modelling of both the delta and star winding connections of the three phases. The equations used to calculate the model parameters are presented. They are based on the common and differential mode impedance measurements. The model can be simplified when considering only electric discharge machining bearing currents, as they are affected only by the common mode states. A simplified model to be used in the delta winding connection is also presented. The model calculated common and differential mode impedances are compared with the impedances measured on a 6.5kW outer rotor brushless direct current motor. The paper ends by providing the obtained simulation and measurement results for the common and differential mode.
COBISS.SI-ID: 10861908
In this paper first a current predictive method for single open-phase fault detection in a three phase drive with a permanent magnet synchronous machine is presented. The proposed method is based on a predictive stator current calculation. For each sampling interval the difference between the actual stator current and its predicted value in a previous sampling interval is calculated. To identify the location of a single open-phase fault, an identification method is presented which is based on the analysis of the stator current vector angle. After the single open-phase fault is detected and identified it is desirable for the electrical machine to continue operating with a reduced number of phases. For this purpose, a modified direct torque control algorithm for the fault-tolerant control is implemented. In order to improve the performance of the drive, a prefiring angle is additionally introduced. All proposed methods have been simulated in Matlab/Simulink and verified on an experimental model.
COBISS.SI-ID: 10892372
Apparent current density is the most common criterion used in literature to estimate bearing endangerment due to bearing currents. In the paper, a new criterion called the normalized Joule integral is proposed as a more reliable and accurate one. This approach is more general and gives good correlation between current in the bypass bridge and bearing current. Furthermore, it considers the whole current that causes bearing damage, not just its peak value. The choice of the normalized Joule integral is theoretically explained and supported by measurements and simulations. The levels of bearing endangerment related to the normalized Joule integral of bearing currents are estimated.
COBISS.SI-ID: 10627924
Many equipments connected to the power distribution network employ rectification to produce a non-sinusoidal line current. Since the number of such equipment has been gradually increasing, the power transmission losses and decreased quality of the electric energy have become a serious problem. For this reason, a standardization activity was carried out to limit the line current harmonics for various groups of the equipment connected to the power distribution network. In the paper, the presented converter – a low-voltage galvanic isolated power supply with a PFC input stage – meets the requirements of the modern power supplies like the compact structure, modularity, galvanic isolation, high power factor, fast dynamic response, legislation, etc. As the rectifier consists of two stages, the energy conversion takes place in two distinctive steps. The input stage employs a PFC boost converter to provide rectification of the line voltage and to control the DC voltage and, in order to gain the desired power factor, it shapes the sine line current. In the second step, the DC/DC conversion is carried out to adjust the voltage levels and ensure galvanic isolation. This stage consists of a bridge converter with a high-frequency transformer. Its construction was simplified by applying the current doubler topology in the secondary circuit. At the end of the paper, the properties and the operation of the proposed power supply was confirmed with the measurements on an experimental model.
COBISS.SI-ID: 10804308
A 3D numerical simulations model for analysis of electro-thermal properties of a 250 kVA three-phase transformer is presented. The focus is on thermal analysis and evaluation of temperature distribution in the transformer. Different temperature distributions are shown for the cases using air or insulation oil as a cooling medium in forced cooled transformer.