Medium-frequency Power Transformer Research Articles

A medium frequency transformer design for spot welding machine using sizing equation and finite element analysis

In this study, a medium frequency power transformer has been designed analytically and its sizes have been obtained. The transformer’s analyses were made numerically by 2D AnsysMaxwell Solver software package. The Solver has also helped to study suitable transformer core and winding samples. Unlike medium frequency transformer, which is generally driven by unipolar PWM method, the designed transformer is driven by bipolar PWM method in the study. The core losses were obtained for different core materials (Trafoperm N3 and Amorfous 2605SA1) by AnsysMaxwell numerical and analytical calculations. The calculated losses for no-load working conditions were compared with each other. The designed transformer has been analyzed for its noload and loaded working conditions magnetically. Finally, the radial and axial forces created in the windings have also been examined for loaded working condition.

Medium-frequency power transformer using GOES for a three-phase dual active bridge

Medium-frequency transformers are used in high power electronic dc/dc converters. In case of the three-phase dual active bridge topology (DAB3), a six-step voltage is applied to the transformer. In this study, a 200 kVA three phase power transformer prototype is using 0.18 mm thick high permeability Grain Oriented Electrical Steel (GOES) at B = 1.5 T and f = 1000 Hz. The prototype has been designed and built in link with a transformer manufacturer. In this paper, a complete test bench is set up to validate GOES as a suitable material for medium-frequency transformers. The efficiency of the components is evaluated at different operating points.

Design and analysis of a 35 kVA medium frequency power transformer with the nanocrystalline core material

Medium frequency power transformers embedded into power electronics converters are frequently encountered in many applications such as electrical transportation and renewable energy systems and power supplies. Thus, researchers have been focused on soft magnetic materials such as amorphous and nanocrystalline materials to obtain smaller and more efficient transformer designs with the improvements on manufacturing technologies of the high frequency core materials. In this study, the transformer design methodology is proposed with the finite element analysis method, and a 35 kVA medium frequency transformer with nanocrystalline core material is designed. After the sizing stage, three-dimensional model of the transformer is created with finite element analysis software, and then co-simulations of this electromagnetic transformer model with a power electronics converter circuit are performed for practical operation conditions. Furthermore, thermal behavior of the prototype transformer is determined with the thermal coupling analysis, and temperature distribution of the prototype transformer is visualized with a thermal imaging camera. The transformer efficiency, exact equivalent circuit of the transformer and flux distributions in the transformer core are obtained from these simulation studies. In addition, the prototype of the designed transformer is produced and tested. The design conditions and simulation results are validated with experimental studies.

Design Methodology and Optimization of a Medium-Frequency Transformer for High-Power DC–DC Applications

The medium-frequency power transformer (MFPT) is one of the key elements of an isolated bi-directional dc–dc converters in applications such as future all-dc offshore wind farms, traction, and solid state transformers. This paper describes a design methodology taking into account loss calculation, isolation requirements, and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a design example to find the highest power density while the efficiency, isolation, thermal, and leakage inductance requirements are all met.

An Investigation of Ferrite and Nanocrystalline Core Materials for Medium-Frequency Power Transformers

In this study, two transformers are designed using the ferrite N87 and the nanocrystalline core materials for the same power level and operating frequency. The operating frequency is defined as 10 kHz, which is suitable␣for both materials. Modeling and simulation studies have been performed with the same finite element analysis software and the obtained results have been reported. The nanocrystalline and the ferrite N87 core materials have been compared according to both electrical and mechanical parameters. In these comparisons, many features such as core and winding losses, flux distributions, leakage flux, efficiency, and both electrical and mechanical performance have been reported comparatively in the case of rectangular waveform excitation of the transformer. Obtained results show that the weight and the volume of the transformer are reduced and more compact transformer is designed by using the nanocrystalline core material. In addition, besides the core loss, winding losses are also reduced in this design.

Description and Efficiency Comparison of Two 25 kVA DC/AC Isolation Modules

In the frame of the European project UNIFLEX-PM, two AC/AC converter topologies have been studied and implemented. Both converters, rated for 25 kVA, are isolated by a medium frequency power transformer. The first topology is based on a dual active bridge containing two additional voltage source inverters for the connection of both DC links to the interfaced grids. The second topology is based on a cycloconverter for the connection of the secondary side of the transformer to the grid without a DC link capacitor. Both topologies have an identical primary side so the efficiency study is focussed on the chain link from one DC link to a 25 kW output load. Experimental efficiencies are compared to theoretical expectations. Due to soft-switching operation in the dual active-bridge, the cycloconverter based solution shows a lower efficiency than in the symmetrical topology.

Global Loss Evaluation Methods for Nonsinusoidally Fed Medium-Frequency Power Transformers

Medium-voltage conversion systems, such as traction and grid-connected converters, are continuously evolving toward higher power densities. Consequently, volume, weight, and material reductions are becoming major design issues, which lead the research focus toward high-/medium-frequency isolated power conversion systems. An optimized design of these conversion systems requires a detailed transformer-loss evaluation considering both copper and core losses. This paper presents a simple and flexible methodology to analyze global medium-frequency transformer losses in an isolated DC-DC converter fed by general nonsinusoidal waveforms. Various loss evaluation approaches are considered, pointing out their validity and limitations by means of finite-element simulations and experimental tests.

The feasibility to model a 3-leg core type medium frequency power transformer by use of a dual Cauer circuit

A model for medium frequency power transformers is suggested. The model is able to treat arbitrary topologies by use of Cauer circuits for core and windings. An implementation example is given for a 1-phase transformer with turn ratio 1:1. The model can be extended to include winding insulation materials by use of lumped capacitive and resistive circuit elements.

The application of amorphous magnetic alloys in induction heating medium-frequency transformers

The economics of the use of amorphous magnetic alloys in the design of medium-frequency power transformers for induction heating applications is considered in the paper. The comparison between conventional and amorphous core materials, developed on the basis of the total owning cost, shows that amorphous alloys can represent to-day a cost effective alternative to the conventional thin-lamination Grain Oriented Silicon Steel (G.O.S.S.).

Ferritkern-leistungsübertrager für schaltnetzteile

Switched-power packs have become fairly well-established as the power supply of electronic instruments. They feature a medium-frequency power transformer which is one order of magnitude smaller than the corresponding system transformer of a conventional power pack. These transformers are succesfully equipped with ferrite cores. The interdependences of ferrite properties, construction, size, and transferable power of the transformer are discussed. The induction of the ferrite is limited by either saturation or losses of the core material to an admissible or optimal value. In the process, the core and copper losses become dependent on thermal resistance and permissible temperature rise. Optimal inductions, thermal resistances, and at different operation modes, transferable powers are given for power transducers equipped with special core types. Interfering leakage inductances can be kept to a minimum by interspersing tightly coupled wiring. The wires can be interspersed economically within one layer by using pre-manufactured flat cables.