JMAG for Power Converter and Transformer

Introduction

JMAG was developed over more than 30 years to solve the complex magnetic, thermal and structural analysis problems in different technology areas. It is an efficient tool for designing the power transformer, converters and wireless power transfers. Whereas the determination of transformer parameters, impedance, winding hot spots temperature, insulation effects, defaults, etc. are the major challenges while designing these kings of electric machines. It also enables the visualization of the phenomena and ease in moving forward with analyzing causes. It also makes possible quantitative evaluations of temperature rising inside objects or noise where measurement is difficult.

From geometry modelling of power transformer components, model setup, and material modelling to high mesh quality generation, insulation, transformer cooling, design integration, vibration and acoustic noise, this comprehensive software give more accurate solutions on variety of investigations that are possible in the power converter design. JMAG can simulate both winding and iron losses including the harmonic effects of the drive circuit. Generally, it can be used for example, to design and optimize:

• Designed Power transformers and converters which have an essential impact of power network because they are the cores of energy conversion and transmission in power network which is also the most important and expensive equipment. With the increase of capacity of the power transformer, JMAG can deeply and accurately simulate the increasing magnetic leakage field which may enlarge the stray loss in the structure parts of power transformer. It is especially important to estimate the effects on peripheral equipment from coil disconnection caused by a lightning strike or aging deterioration. We can use our JMAG product to perform a surge voltage evaluation when a coil has disconnected in a three-phase power transformer. After that, we will confirm whether the insulation between the coils in a lightning resistant transformer has been maintained during a lightning strike.
• Wireless power transfer. This can be done quickly using the parametric analysis tool. This tool will not only predict optimal positioning and efficiency, but it will also help develop a robust and reliable design.

Specific Analysis

The studies for Linear/Rotative motors that can be solved by JMAG are:

• 2D/3D Magnetic Field Analysis (Static, Transient, Frequency)

• 2D/3D Iron Loss Analysis (Transient, Frequency)

• 2D/3D Thermal Analysis (Static, Transient)

• 2D/3D Structural Analysis (Static, Eigenmode, Transient, Frequency)

• 3D Electric Field Analysis (Static, Frequency, Current distribution)

• 2D/3D Thermal Stress Analysis (Static, Transient)

• 2D/3D Transformer Analysis (Static, Transient, Frequency)

Some examples of the results obtained after performing these analyses are listed below:
Magnetic flux, Magnetic field, Magnetization, Flux linkage, Voltage, Current, Electromagnetic force, Lorentz force, Magnetostriction force, Inductances, Resistances, Permeability, Stored energy, Joule losses, Hysteresis losses, Iron losses, Dielectric losses, Electric field, Electric potential, Electric Charge, Electric power, Vector potential, Temperature, Heat flux, Heat flow, Heat source, Thermal resistance, Electric potential, Displacement, Deformation, Velocity, Acceleration, Stress, Strain, Sound pressure and Sound Pressure level.

Specific features

CAD modelling

JMAG-Designer has many tools with different methods to create and import CAD geometry of the Power Converters and Transfers.

• Different available CAD formats can be imported (SolidWorks, CATIA, Pro/ENGINEER, NX, SolidEdge, STEP, Universal, ACIS, etc.). The CAD can also be linked to a CAD model created with another CAD system.
• Geometry Editor: Create a CAD models directly from JMAG CAD modeler interface.
• Transformer Template: Use the predefined transformer models from the Transformer Modeling tool containing into the JMAG Database to create a 3D transformer model

JMAG's transformer template tool has geometry templates of transformers and inductors that are often used. The model geometry can be created by simply specifying the dimensions. Geometry from the TDK core catalog is built into the database so that our users can model core geometry simply by selecting what they need. The bobbin geometry and the coil arrangement are also specified easily using templates. Users that want to investigate core geometries with characteristics that cannot be expressed by the existing templates can use features for importing CAD models.

Mesh modelling

Highly customizable mesh can be generated with higher quality. the Automatic Mesh feature recognizes any model geometry and automatically generates a high-quality mesh over the entire model including the surrounding air region and air gaps. The adaptive mesh feature uses simulation results to control the mesh size to provide a more optimal mesh.

The flux lines for losses caused by the proximity and skin effects are a vital aspect of the power converters and transfer analysis. Therefore, a specialized mesh and analysis functions has been developed. This innovation allows an analysis for example, to account for effects of litz wire swiftly, which was very difficult to include up until now. Some example of mesh functions are described below:

• Skin Depth Mesh: Mesh divisions that can accurately express offsets in magnetic flux distribution from the skin effect are necessary to evaluate the effects from eddy currents that flow through a conductor. The Skin Depth function can be used to generate a layered mesh of a specified thickness on the surface of a part. Firstly, this makes it possible to accurately express offsets in magnetic flux distribution caused by the skin effect, and secondly, to generate a mesh capable of evaluating the effects of eddy currents.
• Thin sheet mesh and Layered Mesh: Automatically generates a layer mesh for thin plate models like the tank or shield plate. The layered mesh function is necessary for the detailed modeling of the lamination steel sheets. the thin plate mesh feature can generate a sufficiently large mesh in the plane direction based on the layer of mesh that is generated in the thickness direction. The analysis time is reduced and the accuracy improved for problems related to the scale of a model, such as analyzing shield rooms and the eddy currents that are produced in thin plates.

Material modeling

The key to analysis accuracy depends on whether an analysis is run using the right material properties. An analysis performed with the most detailed model will not obtain accurate results if the wrong material properties are used. Catalog data from TDK, JFE, and Hitachi Metals are included in the JMAG material database offering ferrite that is often used for high frequency transformers.

Catalog data from Sumitomo Metals, Nippon Steel, JFE, and China Steel are also included for the material properties of magnetic steel so that analysis accounting for nonlinear characteristics of the material properties can be performed. In addition, material properties for iron loss characteristics and stress dependency for each manufacturer are included in addition to the BH curves to increase the analysis accuracy. The material properties can be set just like conditions by simply selecting a material from the material database and dragging and dropping the material on the model in the graphics window.

We can run the FEA simulation by using any electromagnetic steel sheet materials taking to account their Anisotropic or Isotropic behaviors with the following properties:

• Magnetic properties: BH curve, hysteresis loop
• Electrical properties: Electrical conductivity, band structure and dielectric constants
• Mechanical or Structural properties: Density, Young/Shear modulus, Poisson ratio, elastic constants, mechanical tensions and magnetostriction type, residual strain
• Thermal properties: Specific heat, thermal conductivity, and coefficient of thermal expansion
• Loss properties: Iron loss density table, Hysteresis loss density and joule loss density tables

The lamination steel sheet properties such as lamination direction, lamination factor, lamination thickness and saturation factor can be also accounted into the simulation.

Some Present requirements

JMAG's transformer analysis is a specialized magnetic field analysis for evaluating transformers and inductors. The procedures necessary to perform an analysis from creating the model to evaluating the analysis results have been dramatically simplified by limiting the analysis target to transformers based on the reputable features of JMAG's magnetic field analysis. The geometry and conditions that can quickly become complicated can now be created and specified easily. Transformer designers who are unfamiliar with CAE simulations can perform highly accurate analysis right after JMAG is implemented by using JMAG's transformer analysis.

Advanced features

Litz wire modeling

Higher and higher frequencies are being used for the drive frequency in small-scale power transformers in order to reduce their size even more. These higher frequencies lead to problems such as increased loss and localized heat generation because of skin effects and proximity effects in the windings. In order to reduce loss and localized heat generation, the use of litz wire has increased, and therefore so has the need for analysis that accounts for litz wire.
The number of litz wires per bundle that can be used and the solving speed in analysis within transformer studies have been greatly increased. It is not unusual for the number of strands in a litz wire bundle to be more than 100, but investigation using transformer studies is made possible by the great increase in calculating ability.

Stray Losses

Localized heating due to stray losses affect the transformer’s insulation and insulation oil. This causes dielectric strength to deteriorate
Predicting stray loss distribution requires a magnetic field analysis. Magnetic field analysis allows designers to model the transformer and its surrounding components to better determine how stray losses are affecting the design.

Iron Losses

Iron loss is determined by the time variation of magnetic flux density. Anisotropic laminated steel is used as the iron core of transformer.
Thus, in a transformer analysis, the magnetic material properties for the easy axis and hard axis of a core are independently defined. Due to anisotropic effects occurring nearby the joint where leg and yoke parts connect in a V-shape, concentrated iron loss occurs in frame-shaped lamination cores.

Thermal Cooling

Coil vibration and Excitation noise due to magnetostriction

Dielectric Strength

In addition to normal power conversion, a transformer’s insulation structure has to be designed to be able to withstand lightning strikes and excess voltage during short circuits.
The dielectric strength of a transformer is mainly determined by the insulation oil.
The vicinity of the press board of the high-voltage side winding is an area where localized high electric field tends to occur. The electric field analysis forecasts whether the localized electric field does not exceed the insulation limit.

Inrush Current and Lorentz Force

Inrush currents are caused when power is turned on and results in excessive compressive forces on the winding due to the Lorentz force which arises in a coil is so large that it is possible to observe coil deformation. This compressive force is.