The paper describes a mathematical model to be used in calculating the current distribution among the coils in the low-voltage winding of the furnace transformer. The method is derived from the leakage magnetic-field distribution in the transformer based on the minimum magnetic-field energy. The energy is calculated by using the principle of the minimum reactive power in the transformer window. The results are validated by using the finite-element model. The knowledge of the proper current distribution is very useful in designing the furnace-transformer cooling system to avoid local overheating.
COBISS.SI-ID: 9305684
In this paper, a simple method for additional on-line detection of broken rotor bars in a squirrel cage induction motor controlled in rotor field co-ordinates using existing hardware is presented. Based on a previously presented approach, an algorithm for on-line calculation of the variance of stator voltage reference, which depends on the number of broken bars, has been developed. Due to its simplicity, it could run in parallel with a standard control algorithm in field reference frame using contemporary fixed- and floating-point processors, thus requiring minimum processing time. The algorithm uses internal reference values of the stator voltage; therefore no additional dedicated measurements are needed. Results were obtained at different operating points on an induction motor with gradually damaged rotor. Comparison with commonly used diagnostic method confirms the validity of the approach.
COBISS.SI-ID: 9208660
Transverse flux motors (TFMs) are playing an increasingly important role in various drive systems owing to their high power densities, high efficiency, high torque at low speeds and reduced weight. The TFM is suitable for a variety of direct-drive applications where high efficiency and low maintenance are required. However, one of the main drawbacks of the TFM is its high parasitic torque pulsations, which severely limit its use in high-end applications where torque smoothness is very important. To overcome this limitation, an iterative learning control scheme that eliminates periodic torque-ripple effects has been studied and implemented. In detail, an indirect, D-type, frequency-domain approach in a stand-alone configuration was proposed. Simulations and an experimental verification of the proposed approach demonstrate the reduction of parasitic torque pulsations.
COBISS.SI-ID: 9331540
This paper describes an adjustable speed drive system for driving an induction motor beyond its nominal speed, even in the presence of input voltage sags. The system is based on the Z-source inverter, which offers several advantages over traditional current or voltage source inverters as it can operate in both buck or boost mode. The boost operation is achieved with controlled short-circuiting of the inverter phase legs that is otherwise forbidden in traditional inverters. These shoot through states are accomplished with the modification of the space vector modulation which is thoroughly explained. In order to assure the required output voltage and ride-through ability during voltage sags, the method for selecting the proper inverter voltage is introduced. The control of the induction motor is carried out with the field oriented control coupled with the field weakening regime of the induction motor. The experimental setup is based on a prototype with a DSP control system to verify the operation of the proposed system.
COBISS.SI-ID: 9515348
Evaluation of parameters of a three-phase induction motor with broken rotor bars is described. Using standard d-q model of induction motor the electric and magnetic asymmetry can be expressed through differently modified rotor parameters in both axes. A non-standard, one-phase measuring method was employed. To assess the measurement results of the method and to predict various situations which can not be achieved by measurements an extensive finite element analysis has been performed.
COBISS.SI-ID: 8870228