Research on 3D simulation of loosely coupled transformer based on ANSYS

Introduction

As the core component of the rotary steerable intelligent drilling system, the controllable eccentric uses the motor pump to generate power to push the ribs to extend and retract. When the motor pump is used, the energy of the motor pump comes from the downhole turbine generator. Due to the mechanical structure of the controllable eccentric, the motor pump must be installed on the non-rotating sleeve, and the generator must be installed on the rotating main shaft, which involves the problem of energy transmission between rotation and non-rotation. In the past, the contact slip ring energy transmission method has been used. Due to the defects of the contact slip ring, such as inconvenient installation, easy wear during rotation, and easy corrosion by downhole drilling fluid, water and mud, a new non-contact energy transmission method is urgently needed-loosely coupled power transmission technology. As the core part of the loosely coupled power transmission technology-loosely coupled transformer, its research is particularly important.

Due to the harsh environment and space and other factors in the downhole, it is difficult for us to study the loosely coupled transformer. The solid modeling capability of ANSYS can quickly and accurately simulate the three-dimensional loosely coupled transformer. ANSYS 3D simulation has its own unique advantages in modeling, meshing and post-processing, especially in post-processing, electromagnetic force, magnetic induction intensity, magnetomotive force and so on in all directions can be observed. The following introduces the 3D simulation analysis process of ANSYS10.0 software in loosely coupled transformers.

ANSYS 3D simulation of loosely coupled transformers

For loosely coupled transformers, we use the magnetic vector potential method for simulation. The magnetic vector potential method (MVP) is one of the two node-based analysis methods supported by ANSYS for 3D static, harmonic and transient analysis. The vector potential method has magnetic vector potentials AX, AY, AZ in the X, Y and Z directions respectively. Three more degrees of freedom are introduced in the load-voltage or circuit coupling analysis: current (CURR), voltage drop (EMF) and voltage (VOLT). In the 3-D vector potential equation, the INFIN111 far-field unit (AX, AY, AZ three degrees of freedom) is used to model the infinite boundary.

Unit type selection, real constant and material property setting

Field-circuit coupling can be used for 2D and 3D simulation. To establish the circuit unit, CIRCUI24 unit is needed to model the established circuit model and couple the established circuit model with the finite element solid model. Among them, the solid model can choose PLAN53 (2D), SOLID97 (3D) and SOLIDll7 (3D-20node) units. For the node method 3-D analysis, the optional unit is the 3D vector SOLID97 unit. Different from the 2D unit, the degrees of freedom are: AX, AY, AZ, AX, AY, AZ, CUR, EMF; the coil real constant setting and material property setting are shown in Table 1 and Table 2.

Table 1: Coil real constants



Table 2: Material properties

Solid modeling

The loosely coupled transformer is made of manganese-zinc ferrite and has a structure of upper and lower can-shaped magnetic rings. A three-dimensional model can be established according to the actual size of the magnetic ring. The Emag module of ANSYS10.0 is used to perform a three-dimensional field-circuit coupling simulation analysis on the transformer. The physical model of the transformer is shown in Figure 1. The analysis process is as follows:

Figure 1 Transformer physical picture

According to the transformer physical model shown in FIG1 , entity modeling is performed, and the model is modeled from top to bottom through command flow or GUI method. The three-dimensional model is shown in FIG2 .

Figure 2 ANSYS 3D model

Then meshing is performed. GUI and command flow can also be used. There are many ways to mesh. Here, three-dimensional free meshing is mainly used.

Establish a circuit model

Establish an independent voltage source and set the voltage to a sinusoidal voltage source. And set the amplitude, frequency, phase and other parameters of the voltage source.

Establish a circuit model for the twisted coil and set parameters such as its real constant and unit type.

Set the circuit model for the coil internal resistance, and the resistance is measured by a multimeter.

The secondary coil is loaded with R3. The entire model is established as shown in Figure 3.

Perform transient analysis to solve the CURR degrees of freedom of all nodes of the coupled twisted coil and apply boundary conditions.

If the loaded voltage is 15V, the frequency is 10kHz, the air gap between the magnetic rings is 1mm, and the load is 100Ω, 16 load steps are used in one sinusoidal cycle, and the time interval of each load step is 6.25e-6s. Each load step is divided into 5 sub-steps to achieve. In this article, the solution is applied after 20 load steps.

Background processing, result observation 3-D vector analysis cannot obtain flux lines (magnetic lines of force), but the flux density vector display can be used to observe the flux path. Use the Post1 general background processor to observe the magnetic induction intensity B vector diagram of the last load step result, as shown in Figure 4.

Figure 3 Field-circuit coupling finite element model

Figure 4 Magnetic induction intensity vector diagram

Use the Post26 time history background processor to view the induced electromotive force of the secondary load R3 and output a curve graph, as shown in Figure 5.

Figure 5 Secondary load induced electromotive force curve

Comparison of three-dimensional simulation data and measured data

For the convenience of analysis, the magnetic core is set as a linear magnetic material in the simulation, and the relative magnetic permeability is set to: 2500; eddy current loss is not considered; air gap spacing: 1mm; primary voltage is a sine wave with an amplitude of 15V and a frequency of 10kHz; the load is 100Ω. According to the above analysis, the experimental data and simulation data are shown in Table 3:

Table 3: Comparison of measured and simulated data

From the analysis and comparison of Table 3, it can be seen that the efficiency error between the three-dimensional simulation and the actual measurement is about 5%. The secondary current and voltage values ​​are basically consistent with the actual measured current and voltage values. Due to space limitations, the table only lists the case where the primary voltage is 15V and the frequency is 10kHz. Because in the simulation, the magnetic permeability of the core is assumed to be linear, and the actual ferrite magnetic properties are represented by a nonlinear BH hysteresis loop, so there is a certain error between the simulation and the actual measurement.

Comparison of three-dimensional simulation data with two-dimensional simulation data

In order to verify the accuracy of the three-dimensional simulation, it is compared with the two-dimensional simulation done before. The simulation environment: primary voltage 15V sine wave, load 100Ω, air gap 1mm; by changing the frequency, observe the changes in the secondary induced voltage and transmission efficiency, as shown in Figures 6 and 7.

Figure 6 Efficiency curve comparison

Figure 7 Secondary induced voltage curve comparison

As can be seen from the above figure, the curve trends of the three-dimensional simulation and the two-dimensional simulation are basically the same when the frequency changes, but there are certain errors due to the differences in the selected entity units, the way of setting parameters and the analysis method.

Conclusion

Using ANSYS to model and simulate the loosely coupled transformer, the key parameters of the transformer can be changed. The load and other parameters can be changed by using field-circuit coupling, and the current and voltage of the primary and secondary can be calculated, and then the efficiency of the transformer can be calculated; by changing the main parameters of the loosely coupled transformer, the key parameters affecting the efficiency of the loosely coupled transformer and their influence on the efficiency of the loosely coupled transformer can be obtained; especially the ANSYS three-dimensional simulation is not limited by the shape of the model, and the transformer model can be changed at will, thereby promoting the research on the loosely coupled transformer.