Maxwell 2D - SIMPLORER Co-simulation Getting Started Guide

1. Introduction

Maxwell 2D is an interactive, GUI-driven software package that uses the finite element analysis (FEA) to solve two-dimensional (2D) electromagnetic field applications. To analyze a problem, the user specifies the geometry, material properties, sources of energy and boundary conditions. In this guide Maxwell 2D is used to solve a motor application (2D transient with motion finite element problem) with the driving circuits being supplied by a SIMPLORER model. SIMPLORER is a circuit and system simulator for the virtual prototyping of large-scale mechatronic, power electronic, and electromechanical systems. This co-simulation capability offers the user the combined accuracy of the finite element method solution of complex electromagnetic components such as electric motors, actuators, etc. and the complexity of the attached driving and control circuits.

This getting started guide aims to provide an introduction into the co-simulation type of application. The example presented is relatively simple such that the exercise of setting up the application as described here can be accomplished by a Maxwell 2D/SIMPLORER user in 2 ½ - 3 hours. The proposed application is a single phase induction motor (modeled as a FEM Maxwell 2D model) with the simple driving circuits in SIMPLORER. To avoid the task of creating the geometry of the motor in Maxwell 2D, RMxprt will initially be used here to provide a convenient way of expediting the otherwise work-intensive task of creating from scratch the geometry of the motor. Thus the present getting started guide will be structured in three main parts: a) creating the RMxprt model; b) creating the Maxwell 2D motor (FEM) model; c) Creating the SIMPLORER model and the coupling to Maxwell 2D. For existing Maxwell 2D transient applications it is possible to directly couple the finite element model with SIMPLORER driving circuits as described later in this document.

2. Creating the RMxprt model of the single phase (capacitor run) induction motor

As widely known, RMxprt provides a fast analytical solution to a wide range of electric rotating machines types. The RMxprt interface provides a simple way of creating the model for the single phase induction motor as described below.

2.1 Start RMxprt

Start Maxwell and from the Maxwell Control panel select the PROJECTS button. The panel in Fig. 1 appears. Select (or add) the project directory to contain your RMxprt model and click the New… button.

Fig. 1 Maxwell Projects panel

In the panel shown in Fig. 2 enter the desired project name (1ph_rmxprt, for example) and select the project type (Maxwell RMxprt Version 5, for example).

Fig. 2 Project name and type panel

Select OK to open the project. From the machine type panel that appears next, select the Single-Phase Induction Motors option and click OK.

2.2 Create the RMxprt model of the single – phase induction motor

RMxprt allows you to define the model via a number of pages designed with the specificity of each motor type in mind. For the single phase induction motor you have access to six such pages which can be open by selecting the corresponding tab. The data to be entered in each of the six pages is described next. Select sequentially each of the six tabs and then enter the respective data as presented in Fig. 3 – Fig. 8.

Fig. 3 Data for General1 Page

In the page in Fig. 3 make sure that Constant Power is selected as Load Type.

Fig. 4 Data for General2 Page

In the General2 page presented in Fig. 4 select C-Run as operation mode (leave the Run Capacitance and Resistance fields to their default values of zero, such that RMxprt calculates the respective optimum values in the Design Output File) and set the Speed-Adjust Mode to None.

Fig. 5 Data for Stator1 Page

In the Stator1 page in Fig. 5 set the slot type to 2.

Fig. 6 Data for Stator2 Page

In the Stator2 page shown in Fig. 6 set the winding type to 32 and uncheck the Auto Design Box.

Fig. 7 Data for Rotor1 Page

In the page shown in Fig. 7 select 1 as Slot Type.

Fig. 8 Data for Rotor2 Page

2.3 Run RMxprt and create the Maxwell 2D project

To Run the RMxprt simulation select the Run/Analytical Design command from the RMxprt general interface. The solution time should be a few short seconds. Results can be accessed from the output text file via the command Post Process/Design Output. Some of the information contained in that output file will be useful later, during the setup of the Maxwell 2D FEM analysis. To view the winding layout, select the command Post Process / View Winding Layout. The connection diagram of the winding is presented in a graphical format as shown in Fig. 9. To make the connections visible, right-mouse click on the surface of any of the stator slots and select the command Connect all coils.

Fig. 9 Connection diagram of the stator coils(main and auxiliary windings)

Select File/Exit to return to the RMxprt main menu window.

To create the Maxwell 2D project, select the Post Process/Create Maxwell 2D Project command to launch a panel as shown in Fig. 10. Enter the name for the FEM project (for example 1ph_fea) and select a project directory path for it.

Fig. 10 Name and directory for the Maxwell 2D Transient project

3. Maxwell 2D Transient Model

The Maxwell 2D transient project has been created –in part- from RMxprt and contains the geometry. Additional work is necessary to finalize the setup.

3.1 Grouping objects

Open the newly created Maxwell 2D transient project by selecting the respective name in the Projects window and click the Open… button.

To assign material properties and excitations efficiently it is useful to group together objects that belong to the same winding. To do that, from the Executive Commands window, select Define Model/Group Objects command. A window containing a list of all objects created by RMxprt appears (Fig. 11). Note that objects belonging to certain categories have similar names. For example all rotor bar are named Bar0, Bar1, etc. These objects are grouped together as indicated below.

Fig. 11 Grouping objects

Select simultaneously objects Bar0 to Bar5 and click on the Group button, when prompted give this group the name Bar and click OK. Select objects PhA0, PhA1, PhA10 and PhA11, click the Group button and give this group the name PhA. Similarly, select objects PhB0, PhB1 and PhB10 and give this group the name PhB, then select objects PhReB0, PhReB1 and PhReB2 and give this group the name PhReB. When the grouping is complete, the grouping window will look as in Fig. 12. Note that for this particular problem, due to the use of symmetry, our model includes the “go” conductors (PhA) but doesn’t include the return conductors of the winding. The finite element solver will appropriately handle this situation. On the other hand the auxiliary “B” winding includes both conductors belonging to the “go” part and to the “return” part of the winding. RMxprt automatically gives those conductors names as appropriate (for example PhBx and PhReBx, respectively with x=0,1,2…).

Fig. 12 List of objects after grouping

Exit and save the changes.

3.2 Applying the material properties

From the Executive Commands window select Setup Materials… and the window similar the one presented in Fig. 13 appears

Fig. 13 Set up material properties

Part of the material properties we want to use for the finite element model are not in the default material library and thus need to be added there for this particular application. These new material will carry a “local” status and can be defined and or modified by the user as desired.

We start with defining the property of the rotor bars to correspond to what has been used in RMxprt. Select the Material/Add command, change the name under Material Properties to Aluminum_bar and enter the corresponding conductivity to be 2.304E7 S/m as shown in Fig. 14. Click the Enter button to finalize the process of defining the new material property, select the object [Bar] in the object list box, select the newly defined material property in the Material Definition list box and click the Assign button.

Fig. 14 Material property (electrical conductivity) definition

Next, define the material properties for the steel in the stator and rotor. Here RMxprt helps again with “equivalent” BH curves that take into account the effect of the stacking factor. Thus, rather then defining the respective curves, we can import them from the corresponding RMxprt project folder.

Select Material/Add command, enter the name “stator_steel” under Material Properties, check the B-H Nonlinear Material box and select the “B H Curve…” button. In the appearing B-H Curve Entry window select the “Import…” command and browse to the respective project folder to select the corresponding file containing the respective material property as shown in Fig. 15. Select OK a number of times to finalize the import process. Exit and do not forget to select “Enter” to have the material property defined locally. Then assign it to the stator object.

Fig. 15 Importing the B-H characteristic for the stator

Repeat the same process for the rotor object.

Assign “vacuum” or “air” material property for AirGap, AirStator, Band and Shaft objects and “copper” material property to [PhA], [PhB], [PhReB] objects to finalize the material property assignment process. Select the “background” object and exclude it from the simulation. Then select Exit and Save the changes before closing.

3.3 Set up of Boundary Conditions and Sources

This section of the Maxwell 2D - SIMPLORER Co-simulation Getting Started Guidepresents the general process of setting the boundary conditions but skipping the details of the process. (Such details can be found in documentation about the respective set up process, such as application notes for different motor simulation problems). Detailed explanation will be given to the part dealing with the coupling with SIMPLORER.Select the outer stator edge and apply a zero magnetic vector potential boundary condition (zero magnetic flux). Next apply the Master-Slave boundary condition as shown in Fig. 16.

Master Slave

Fig. 16 Boundary conditions

For the rotor bar connection, select all six rotor bar conductors then choose the Assign/End Connection… command and enter the name for the boundary condition and the end resistance and end inductance values as shown in Fig. 17.

Fig. 17 Set up of the rotor bar end connection

The values to be used for the end connection setup are supplied by RMxprt in the Design Output file in the Transient FEA Input Data section of the text file. For the value to enter in the End inductance field just add together the respective values of End Ring Leakage Inductance and Skew Leakage Inductance.

The set up of the winding is very similar to the usual one for the motor applications where conductors are grouped in windings and the type of source is “External Connection” with the “Strand” option selected.

To set up the main winding, select the PhA group of conductors, give it a name (Aphase for example) and select the “External Connection” and “Strand” radio buttons, then click on the Winding… command. Set the winding as shown in Fig. 18, with positive polarity and 510 turns as supplied by RMxprt in the Design Output file in the Transient FEA Input Data section.

Fig. 18 Set up of main motor winding

Then select both [PhB] and [PhReB] groups and assign them to a stranded external connection and set up the winding with the values in Fig. 19.

Fig. 19 Set up of the auxiliary winding

Now with the windings set up, select the Edit/External Circuit… command and check the Use SIMPLORER Circuit check box and click OK. This way the project will be “marked” as being eligible for coupling with SIMPLORER. This is a convenient way of “marking” new projects for coupling with SIMPLORER without having to define the structure of the respective driving circuit within the Maxwell set up. The circuit connections to the finite element model are to be defined in SIMPLORER. Note that it is also possible to use an existing project with external circuits defined in Maxwell 2D for coupling with SIMPLORER (such projects are also eligible for coupling).

3.4 Solution set up

To finalize the Maxwell project set up, select Setup Solution command from the executive commands window, set the desired time stepping information, model symmetry data and create the mesh suitable for the model. The panel in Fig.20 shows the specific setting for the application presented in this guide.

Fig. 20 Solution set up

3.5 Maxwell to SIMPLORER Link

The link algorithm is similar to the Maxwell internal one used when external connections are defined as sources for the windings. Thus at each time step Maxwell generates a Thevenin equivalent circuit (voltage source with internal impedance) for SIMPLORER and SIMPLORER generates a Norton equivalent source (current generator in parallel with internal admittance). This parameter based coupling enhances solution accuracy and stability. The general communication process occurs over TCP/IP sockets and is presented in Fig. 21

Fig. 21 General scheme of Maxwell 2D – SIMPLORER Transient link

4. SIMPLORER model and set up

In general existing SIMPLORER models can be linked with Maxwell 2D transient finite element models or a new model can be created from scratch. In this getting started guide the second approach will be taken.

4.1 Creating the link between SIMPLORER and Maxwell 2D Transient

The coupling between Maxwell and SIMPLORER is effectively created in the SIMPLORER project. For the purpose of the link, an FEA Link component has been created and can be found on the Model Agent page under ADD Ons/Interfaces. To initiate the link process, place this component (drag and drop) on the SIMPLORER sheet in a position which is appropriate for the electrical and mechanical connections as shown in Fig. 22.

Note that in the case of coupling between Maxwell 2D Transient and SIMPLORER all circuit elements, both electrical, mechanical (possibly others too) must be part of the SIMPLORER model.

Fig. 22 FEA Link Component

Double click the FEA Link component to start the connection process and make sure that the Setup tab is selected. In the properties windows select the Query command to produce a list of Maxwell 2D transient projects eligible for coupling (with blue fonts), as shown in Fig. 23. If the Maxwell software is installed on the same computer with SIMPLORER, the Local Host radio button should be selected. Otherwise use the Remote Host radio button.

Fig. 23 FEA Link properties window

The projects appearing in red fonts cannot be used for coupling even though they are Maxwell 2D transient projects. Possible reasons for those projects not being selectable are: missing mesh, incomplete setup, inexistence of external connection for the windings, etc.

Select the desired Maxwell project from the list (make sure that you choose one which it is eligible for co-simulation) and click the Setup button (note that the available pins for connection and their nature (ELECTRICAL, ROTATIONAL, etc) are listed on the right side of the properties window) and then select OK. Now the selected component, updated, looks as in Fig. 24 with the electrical pins on the left and the mechanical ones on the right.

Fig. 24 Updated component on the simulation sheet

4.2 Finalize the SIMPLORER model

Add the elements desired to be connected with the finite element model. An example of a simple driving circuit is presented in Fig. 25.

Fig. 25 Complete electric driving circuit & mechanical connections

Both the main winding and auxiliary winding have series end leakage inductance calculated by RMxprt (these are 3D effects calculated analytically by RMxprt) for added accuracy of the simulation. The user can get these end leakage inductance values via the RMxprt Design Output command, in the Transient FEA Input Data section of the file. On the mechanical side a constant velocity source has been applied such that other mechanical elements (such as inertia and or damping) are not necessary here.

For each of Maxwell’s model external windings two electrical pins are provided to be connected in the SIMPLORER model. If a rotating or moving object exists in the Maxwell project, two corresponding mechanical pins will be available for connection in the SIMPLORER model, either torque-angle or force-displacement as appropriate.

4.3 SIMPLORER solution setup

The solution time and time step for both SIMPLORER and Maxwell solvers are controlled from the SIMPLORER side. To access the respective setting values select Simulation/Parameters… command. Refer to Fig. 26 for information on the data to enter in order to control the time stepping in both simulators.

Fig. 26 Co-simulation solution set up

Note that settings on the Maxwell side that depend parametrically on time, speed or position will be updated accordingly.

4.4 Preparing post processing in SIMPLORER

Results of interest can be output in a number of 2D View post processing elements that the user should drag and drop on the simulation sheet. In each of these 2D View windows right-mouse click to access the properties window (see Fig. 27) and there select the first button (“Outputs”) under the Y-Axis set up menu. In the Outputs window select the quantity to plot by selecting the respective element and the quantity of interest.

Fig. 27 Set up of 2D View post processing windows

Note that the FEA Link component can also be selected and available electro-mechanical quantities from Maxwell (such as torque for example) can be chosen for post processing.

4.5 Start the co-simulation

To start the co-simulation select the Simulation/Start command or simply select the “Start” icon from the main SIMPLORER tool bar. For a successful start it is not absolutely necessary that the Maxwell software is started but it is necessary that the project selected for the co-simulation is not open at the time of the desired beginning of the co-simulation (“open” Maxwell projects are automatically “locked” and cannot be used). Progress of the solution can be monitored by the evolution of the results in the selected SIMPLORER post processing windows where the monitored signals are updated at each time step.

5. Results

5.1 Results in SIMPLORER

Example of results are shown in Fig. 28 where the current in the auxiliary winding and the electromagnetic torque on the motor rotor are plotted.

Fig. 28 Current and torque sample plots

In general in SIMPLORER environment it is possible to visualize all electrical signals that relate to the driving circuit used and to other adjacent control elements if the simulation sheet contains any. It is also possible to post process all electro-mechanical quantities available from Maxwell and exchanged between the two software packages during co-simulation. Additional post processing is available in Maxwell.

5.2 Results in Maxwell

Results available in Maxwell for post-processing are the usual ones: global quantities that relate to the defined windings and field quantities. As examples, below are presented samples of quantities such as currents, voltages and flux lines (Fig. 29 – Fig. 32).

Fig. 29 Current in the auxiliary winding

Fig. 30 Electromagnetic torque

Fig. 31 Back EMF in the two coils

Fig. 32 Field lines distribution at the end of the analysis