Predictive torque control and Immediate flux control are original methods whose aim is to obtain excellent dynamics of AC machines with relatively low switching frequency. Both approaches rely on a predictive computation of control variables throughout a very short sampling time interval. Due to its simplicity, the entire control requires minimal processing time. The method is characterized by a transient without overshoot.
COBISS.SI-ID: 6000724
Modern microprocessors used for process control enable fast real-time computation. Therefore, an application of predictive methods in modulation and control in power electronics (active power filters, electrical drives), is possible. The predictivity shows itself in anticipation of output variables (currents or voltages) at the end of sampling interval, the latter being in order of some tens of microseconds. The submitter of the project proposal and his team have developed an original method for predictive control that enables complete monitoring over inverters' variables. Depending on the specific application, the methods have been named direct current control (DCC), immediate flux control (IFC) and predictive torque control (PTC). The main advantage of these approaches is in complete control over variables at considerably reduced switching losses and exceptional dynamics compared to the traditional approaches. The algorithms have been tested on very heterogeneous final applications (active power filters, synchronous and induction motor drives), which indicates the versatility of the method while conserving the above mentioned advantages.
COBISS.SI-ID: 7112020
Several measures for reducing cogging torque of permanent-magnet motors are presented. When proper methods are employed, it is theoretically possible to minimize its level or even to eliminate it. FFT analyses of cogging torque in mass-produced motors have shown additional harmonic components, which are in tight correlation with assembly tolerances and/or permanent-magnet imperfections. Finite element method has been used to study the sensitivity of different motor models relative to manufacturing tolerances and to determine rules for detecting imperfections in mass-production.
COBISS.SI-ID: 6958164
In recent years, fault diagnosis of electrical machines during their operation in a plant has gained a noticeable momentum. Its goal is to detect various types of faults at an early stage, thus preventing radical breakdown and enabling planning of a repair. In most cases, contemporary methods require expensive equipment and complicated procedures for detecting the faults. The method, presented in this paper, is intended for an early detection of broken rotor bars in induction motors. With this procedure, no additional hardware is necessary, except for a simple and fast algorithm that can run in parallel with an existing control program and can be implemented in an already present microprocessor circuitry. From voltage measurement through existing voltage probes, an average deviation from normal values, can be determined. This data serves as a diagnostic index that depends on the number of broken bars, i.e. the degree of the fault.
COBISS.SI-ID: 7819604
This paper presents results of a comparative study of two possible hybrid filter topologies, comprised of a passive and active stage, which can be implemented in any general dc supply distribution system. The active stage is incorporated into the passive part in order to: 1) improve its insufficient attenuation in the low-frequency range and 2) source or sink any surplus energy flow between the dc source and load in case of low frequency current dynamics. In the low-frequency range nearly for 15 dB higher attenuation compared to the passive filter is achieved.
COBISS.SI-ID: 7554388
Electroporation based therapies and treatments (e.g. electrochemotherapy, gene electrotransfer for gene therapy and DNA vaccination, tissue ablation with irreversible electroporation and transdermal drug delivery) require a precise prediction of the therapy or treatment outcome by a personalized treatment planning procedure. Recent studies have reported that the uncertainties in electrical properties predefined in linear numerical models (i.e. tissue conductivity is constant) have large effect on electroporation based therapy and treatment effectiveness. In our study we showed that the changes in electrical conductivity due to electroporation need to be taken into account when an electroporation based treatment is planned or investigated. We concluded that the model of electric field distribution that takes into account the increase in electric conductivity due to electroporation (i.e. nonlinear electroporation model) yields more precise prediction of successfully electroporated target tissue volume. The findings of our study can significantly contribute to the current development of individualized patient¬specific electroporation based treatment planning.
COBISS.SI-ID: 9707348
Synchronous motors are gradually replacing induction and DC motors in demanding applications with servo drives. In the area of control of AC machines, two methods have established themselves: field orientation control (FOC) and direct torque control (DTC). The first one enables reliable control, whilst the second offers better dynamics. At the same time, both methods exhibit some drawbacks: FOC is relatively complicated and contain inherent delays, while DTC is characterized by high torque ripple. The proposed method uses advantages of FOC, since the variables are transformed into field coordinates. On the other side instead of using space vector modulation (SVM) it implements original method, named direct current control (DCC). The presented results obtained on a laboratory model of a synchronous motor show very good dynamic performance while reducing the switching losses.
COBISS.SI-ID: 7253844
This paper presents a low-cost fault-tolerant system for open-phase fault (OPF) in a converter-fed permanent-magnet synchronous machine. The proposed fault-tolerant system is based on field orientation control with additional fault tolerance functionality. A current predictive method for OPF detection is presented, together with an estimation of the threshold level for detection. The proposed method is based on the prediction of stator current for the next sampling interval. Furthermore, a new method for postfault operation of the machine is proposed. For optimal performance of the complete drive, a prefiring angle is introduced in order to avoid the temporary generation of negative torque. This improvement increases the average generated postfault electromagnetic torque, and consequently, it reduces the mechanical stress on various machine parts. The proposed fault detection and postfault operation solutions were simulated in MATLAB, and they were also tested on an experimental setup. The results show several advantages of the proposed fault-tolerant solution, like its short fault-detection time, substantial robustness against variation of machine parameters or load fluctuations, and negligible implementation costs, since no hardware modifications are needed. The fault detection algorithm does not require high computing power, and it operates well even during transients.
COBISS.SI-ID: 11176276
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 differentialmode 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 6.5 kW 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
Permeance variation in the air gap of the permanent-magnet synchronous machine induces eddy-current losses in its permanent magnets even in the absence of stator currents. This paper proposes a new analytical approach to analyze these losses using the permeance-variation vector function introduced for the air-gap magnetic-flux density distribution to take into account the stator teeth. The Laplace equation is employed to derive the radial dependency of the stator slotting effect on the magnetic-flux density distribution. The induced eddy currents are further calculated by using Faraday’s law. The analytical results are compared with the numerical ones based on the finite-element analysis. The paper offers a faster alternative to the numerically intensive calculations of eddy-current losses, and the method is especially useful in initial design optimization of the electric machine.
COBISS.SI-ID: 9334612