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Comparison of different stator topologies for BLDC drives
Mitja Garmut, 2020, magistrsko delo

Opis: The focus of this Master's thesis was to increase the output-power density of a fractional-horsepower BLDC drive. Different stator segmentation topologies were analyzed and evaluated for this purpose. The presented analysis was performed by using various models with different complexity levels, where a Magnetic Equivalent Circuit (MEC) model and a 2D transient Finite Element Method (FEM) model combined with a power-loss model, were applied systematically. Characteristic behavior of the BLDC drive was obtained in this way. The models were validated with measurement results obtained on an experimental test drive system. The influence of the weakening of the magnetic flux density and flux linkage, due to segmentation were analyzed based on the validated models. Furthermore, the increase of the thermal-stable output power and efficiency was rated, due to the consequently higher slot fill factor. Lastly, a detailed iron-loss analysis was performed for different stator topologies. The performed analysis showed that segmentation of the stator can enable a significant increase of the output power of the discussed BLDC drives, where the positive effects of segmentation outweigh the negative ones from the electromagnetic point of view. Segmentation, however, also impacts other domains, such as Mechanical and Thermal, which was out of the scope of this thesis, and will be performed in the future.
Ključne besede: fractional-horsepower BLDC drive, stator segmentation, fill factor increase, thermal-stable output power, Finite Element Method model
Objavljeno: 17.11.2020; Ogledov: 211; Prenosov: 0
.pdf Celotno besedilo (1,69 MB)

Tine Konjedic, 2015, doktorska disertacija

Opis: This thesis investigates the possibilities for increasing the power conversion efficiency and power density of a single-phase single-stage AC-DC converter with power factor correction capability. Initially, the limitations are investigated for simultaneous increase of power density and efficiency in hard switched bidirectional converters. The switching frequency dependent turn-on losses of the transistors have been identified as the main limiting factor. In order to avoid the increase in total power losses with increasing the switching frequency, a control approach is proposed for achieving zero voltage switching transitions within the entire operating range of a bidirectional converter that utilizes power transistors in a bridge structure. This approach is based on operation in the discontinuous conduction mode with a variable switching frequency. Operation in the discontinuous conduction mode ensures the necessary reversed current that naturally discharges the parasitic output capacitance of the transistor and thus allows this transistor to be turned on at zero voltage. On the other hand, the varying switching frequency ensures that the converter operates close to the zero voltage switching boundary, which is defined as the minimum required current ripple at which zero voltage switching can be maintained. Operation with the minimum required current ripple is desirable as it generates the lowest magnetic core losses and conduction losses within the power circuit. The performance and effectiveness of the investigated approach were initially verified in a bidirectional DC-DC converter. A reliable zero voltage switching was confirmed over the entire operating range of a bidirectional DC-DC converter, as well as the absence of the reverse recovery effect and the unwanted turn-on of the synchronous transistor. In order to justify its usage and demonstrate its superior performance, the proposed zero voltage switching technique was compared with a conventional continuous conduction mode operation which is characterized by hard switching commutations. After successful verification and implementation in a bidirectional DC-DC converter, the investigated zero voltage switching approach was adapted for usage in an interleaved DC-AC converter with power factor correction capability. Comprehensive analysis of the converter's operation in discontinuous conduction mode with a variable switching frequency was performed in order to derive its power loss model. The latter facilitated the design process of the converter's power circuit. A systematic approach for selecting the converter's power components has been used while targeting for an extremely high power conversion efficiency over a wide operating range and a low volume design of the converter. The final result of the investigations performed within the scope of this thesis is the interleaved AC-DC converter with power factor correction capability. Utilization of interleaving allows for increasing the converter's power processing capability, reduces the conducted differential mode noise and shrinks the range within which the switching frequency has to vary. The proposed zero voltage switching control approach was entirely implemented within a digital signal controller and does not require any additional components within the converter's circuit. The experimental results have confirmed highly efficient operation over a wide range of operating powers. A peak efficiency of 98.4 % has been achieved at the output power of 1100 W, while the efficiency is maintained above 97 % over the entire range of output powers between 200 W and 3050 W.
Ključne besede: zero-voltage switching, power factor correction, variable switching frequency, discontinuous conduction mode, reverse recovery, unwanted turn-on, bidirectional DC-DC converter, bidirectional AC-DC converter, control of switching power converters
Objavljeno: 13.10.2015; Ogledov: 1492; Prenosov: 166
.pdf Celotno besedilo (23,37 MB)

Improved frequency characteristics of the randomized PWM boost rectifier
Franc Mihalič, Miro Milanovič, Carlos Cuoto, 2003, izvirni znanstveni članek

Opis: A randomized pulse width modulation (RPWM) algorithm is applied in the control unit of the boost rectifier to achieve improved frequency characteristics in the wide band. First, the introduction of the RPWM switching is reflected in a smaller increase of the total harmonic distortion (THD) factor in the input current. Nevertheless, decrease of the power factor is negligibly small. Second, the power spectrum density (PSD) of the input current is estimated and measured to evaluate the influence of randomization in the high-frequency range. This approach offers an effective and credible prediction method for reduction of conductive electromagnetic interference (EMI) by using the RPWM switching.
Ključne besede: rectifiers, boost rectifiers, randomized pulse width modulation, estimation methods, total harmonic distortion, power factor, conductive electromagnetic interference
Objavljeno: 01.06.2012; Ogledov: 1615; Prenosov: 65
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