Selami Balci

Core material investigation of medium-frequency power transformers

Medium-frequency power transformers are used in DC-DC converters topologies such as photovoltaic, wind turbines, fuel cells, electric vehicles and uninterruptible power supply systems. In the design of magnetic circuit components such as transformer and inductor, the choice of the core material is of great importance in terms of losses and magnetic induction. For determining the size of the medium-frequency transformer, frequency and magnetic flux density are also two key parameters. In this study, the core volume change with the frequency is mathematically analyzed and modeled by using finite element analysis method. Parametric analysis provides very useful information in order to determine the excitation voltage level, which does not cause the saturation in the core, for the switching frequency. Thus, parameters of the designed transformer equivalent circuit can be optimized. Then, medium-frequency transformer is operated in power electronic circuits and saturation effect and core losses according to the preferred magnetic materials are investigated by performing co-simulation.

Comprehensive analysis of inductors for an interleaved buck converter

Interleaved DC-DC buck converters are used in medium to high power applications with their advantages such as low electromagnetic interference and output voltage ripples. Although, discrete core inductors can be used, coupled inductors which use the same magnetic core can be used to obtain optimum design such as volume, cost and efficiency in interleaved converters. Also, in coupled inductor applications, duty ratio, saturation effect and interactions of the windings should be analyzed carefully. In this study, selection of core structure with different types of coupled inductors is investigated for whole operation range. Simulations are performed with co-simulations of Ansoft-Maxwel 3D and Simplorer software. Inductors that are designed in Maxwell by using Kool Mu E cores are used with buck converter, which was modeled in Simplorer. Results obtained from simulation studies are reported and compared with each other.

A comparison of single and three phase DC/DC converter structures for battery charging

In order to obtain uninterrupted power in many critical applications such as control, protection, and communication; high current capacity battery groups are used as a replacement energy source. Charging the battery groups is made by DC/DC converters which are fed over power factor corrected rectifiers in a single or three-phase network according to their charging power level. Because of their high voltage conversion ratio, a single or three-phase inverter is used in conjunction with high-frequency transformers in the structure. Thus, the combination of electromagnetic knowledge and experiences with power electronics is concerned. It is known that FEM software brings the simulation opportunity of the power electronic circuits together with the magnetic circuit elements. This software is used in the fields of high-frequency application and provides more contribution to the design process. Also it makes the simulation more similar to the real environment. In this study, the performances of single-phase and three-phase DC/DC converters tested depending on their design values. In addition, the effects of three-phase three-limb core and five-limb core structures on the transformer losses and ripple have been analyzed. The saturation effects and the core losses were investigated by visualizing the AC and DC choke within the converter structure and flux distributions over transformers cores. The most suitable design and flux distribution has been investigated for the single and three phases, three and five limb transformer structures.

Design and loss analysis of LCL filter inductors for two-level and three-level inverters

Grid connected inverters with LCL output filters are widely used in exporting energy generated from renewable energy sources. The LCL filter and inductors used in this filter has important effect on inverter performance. Although it is different in high power levels nowadays, powder cores are commonly used in inductor design in low and medium power levels. In this study, inductors for LCL filter of the grid-connected inverter are designed. The co-simulation studies are performed and performance and losses of the designed filter is analyzed for two-level and three-level inverter topologies. It is seen that, total losses of the LCL filter of three-phase three-level inverter is 35.9% lower than two-level inverter.

Performance analysis of interleaved quadratic boost converter with coupled inductor for fuel cell applications

DC-DC converters are commonly used in many fields such as renewable energy sources, electrical vehicles, power supplies, battery chargers and fuel cell applications. These converters are used for purposes such as voltage conditioning, regulation of their outputs, obtaining maximum power and providing isolation. In practice, various criteria such as cost, performance, efficiency and size are considered while converter topology is determined. Filter components (L-C) which are used in DC-DC converter determine the converter size. In this study, an interleaved quadratic boost converter is designed for fuel cell applications and different inductor designs are investigated for the proposed quadratic boost converter. Four different inductor models are designed and simulation studies of the interleaved quadratic boost converter with these inductor models are carried out. Effects of the designed inductors on converter output waveform quality, total weight and volume, and converter efficiency are investigated and obtained results are compared. It is seen from obtained results that, the coupled inductor improves performance and efficiency of the interleaved quadratic boost converter.

A comparative study of nanocrystalline and SiFe core materials for medium-frequency transformers

As a result of advances in power electronics, in medium to high frequency high power conversion has become widespread. The performance and the sizing of the medium-frequency power transformer vary depending on material properties and operating frequency. While the core size determined by the power requirements, the specific core loss which varies depending on the frequency and the flux values becomes important. On the other hand, power handling capability of transformer varies according to the core material type and operation frequency. In this study, %3 SiFe 0.1mm material was compared with the nanocrystalline material for the medium-frequency transformer cores. SiFe and nanocrystalline core materials are modeled, tested and analyzed for the different frequency values. Thus, the relationship between the frequency increase with the power handling capability and core losses were uncovered.