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Posted on 17 July 2019

IPOSIM Web-based Design Support Tool for IGBT Applications

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Simulation based Loss and Thermal Evaluation for Applications Using Infineon Power Modules and Disk Devices

There is no simple criterion or rule of thumb to properly select suitable semiconductor devices for the wide variety of traction and industrial applications. Wide ranges of input and output voltages, line, switching and output frequency, inverter power rating, overcurrent and over-load capability and last but not least the impact of different cooling conditions make it challenging to find the right module for the application requirements.

By Thomas Schütze, Infineon Technologies Thomas Barucki, Adapted Solutions Uwe Knorr, Transim Technology

 

A detailed analysis for each specific case, accounting for the semiconductor device characteristics and the application’s operating conditions is compellingly necessary for a proper dimensioning. By use of the newly launched web-based Infineon power simulation program IPOSIM, the device selection can conveniently be accomplished by loss and thermal calculations for most of the popular power electronics circuits.

While more and more simulation tools are used for such detailed analyses it is often quite involved to setup an application for a first selection trade-off analysis. Therefore Infineon already provided an Excel based design spreadsheet, which helped engineers to select products quickly under a variety of operating conditions. However the analytical calculations available in Excel are limited to the selection of a typical sine-triangle control, which in many cases does not reflect the actual stress a part can see under varying controller and load conditions.

Building on the positive feedback for Infineon’s SimPort design support portal the company recently completed an effort to develop a simulation based online version of IPOSIM. Please visit: http://infineon.transim.com/iposim/

This new online tool makes it very easy for users to logon and perform an entire design from product and topology selection to thermal and electrical analysis in a short 10 – 20 minutes online session – no need for downloads and installations. IPOSIM covers a wide variety of power electronic applications and controls.

Topology and Device Selection

At present Infineon’s high power product spectrum covers appr. 800 power devices in various voltage and current ratings as well as package designs. While the AC/AC and AC/DC applications build on a database with more than 350 diode or thyristor disks and modules, the DC/DC and DC/AC topologies can choose from more than 440 IGBT modules in numerous configurations.

After selecting a topology from the list shown in Figure 1, the users can define their design requirements in an easy to use online design interview.

Available circuit topologies and components in IPOSIM

For DC/AC inverters, where the control of the application has significant impact on the losses, a wide variety of algorithms is available. This allows a far more accurate prediction of losses and to better pinpoint a suitable IGBT module.

The design requirement input values are used to perform a pre-selection of devices from the product database. The algorithms consider a suited device voltage class as per given link voltage and the adherence of the device’s peak current capability. A restriction to a specific package type is possible.

Topology dependent input menu (example 3 level inverter)

The user may request a recommendation of parts which adheres the devices thermal limits by defining cooling methods and cooling conditions.

The benchmark functionality of IPOSIM allows selecting up to 5 devices and performs a comparative simulation. For this, further application relevant data like gate resistors and either user or pre-defined heat sink characteristics can be modified.

Up until here IPOSIM assumed steady state operation. Once users have made a preselection they now can dive into a more detailed analysis applying complete load cycles. The user interface allows an easy entry of load cycles in form of x-y data pairs in tabular form. Figure 3 shows a typical example for a traction cycle comprising an acceleration phase, coasting and braking.

Load cycle input

This load cycle analysis is made possible by deploying a sophisticated simulation engine with the web based design environment using WebSIM® (for more information please visit www.transim.com). WebSIM® allows the remote simulation of electrical engineering problems. For IPOSIM the Portunus simulation engine is deployed (for more information please visit http://www.adapted-solutions.com), which combines a number of simulation languages, such as block diagrams, state machines and electrical and electro-mechanical systems.

Once the benchmarking simulations have finished, the results are displayed in a design summary report. The report contains a summary of all design requirements entered by the user, a comparison table with product information and calculated losses and temperature prediction graphs, making it easy to compare the chosen devices.

For documentation purposes the design summary can easily be printed or saved as a PDF document. Additionally users can save designs for later re-use.

Losses and Thermal Behaviour Prediction using Simulation

The availability of a wide range of modelling capabilities, its easy to use and windows compliant automation interface and a unique feature allowing a combined steady-state (DC) and transient analysis made Portunus the ideal candidate to run as simulation engine behind the scenes.

In order to keep simulation times low it was necessary to represent rectifier diodes and thyristors (AC/DC and AC/AC) as a behavioural model representing an equivalent line approximation without consideration of temperature dependencies. Since typical frequencies of 50 or 60 Hz are assumed, there is not even a need for the calculation of the ripple of the junction temperature.

The simulation of the impact of a load cycle is done in two steps. First the power dissipations for all operating points are determined. In a second step these values are fed into a thermal network in order to get the resulting temperatures.

Load cycle simulations distinguish between two modes: The user may enter a certain number of cycles for which the simulation shall be performed. In this case all temperatures start at ambient temperature and the temperature rise at junction and case can be observed. The second mode assumes a virtually infinite load cycle with all temperatures rising and falling around their steady-state average values. In this case Portunus performs a DC calculation first, which produces the initial values for the following transient simulation. During this transient simulation a state machine integrated in each simulation model detects steady state operation and automatically stops the simulation run, thereby saving valuable simulation time.

Simulations for DC/AC topologies require far more complex models and specific algorithms. Unlike for AC/DC and AC/AC topologies, the junction temperature may be subject to bigger changes if the output frequency is getting very low and therefore the on and off times of the IGBTs and diodes are getting longer. In addition, the switching losses of the devices have to be determined depending on the operation point (voltage, current, junction temperature) and gate resistances.

Results page

Again using highly complex semiconductor physics based models for a proper calculation of the switching transients would be much too time-consuming. Instead averaged models have been implemented in Portunus. The basic idea is to describe the static characteristics as well as the switching losses by means of analytical functions and reduce the computational effort for each switching instants to a single simulation step. This allows for a significant acceleration by increased step sizes which are mainly determined by the PWM pattern.

The next challenge solved in IPOSIM is the extremely long simulation to reach thermal steady state for an application due to the long thermal time constants. Instead of running very long simulations scriptcontrolled, iterative calculation of the steady-state average temperatures are performed. These scripts iteratively run a simulation for one period of the output frequency in order to determine the average losses at a given junction temperatures. Then the script calculates the average junction temperatures that follow from these losses. After each iteration the junction temperature is updated until the change between from the previous iteration falls below an error limit. Once this error limit has been reached, a final transient simulation is performed in order to determine the temperature ripple.

Hiding al that complexity behind an easy to use and easily accessible graphical user interface was one of the major reasons to go online. IPOSIM eliminates the need for setting up all tests and automatically performs the analyses that a user would have to perform in many steps manually. However for experienced users all application schematics are available in form of a library that comes with the stand-alone version of Portunus. The Power Electronics Library contains a variety of models and building blocks, such as for the generation of the PWM switching commands for several algorithms. It also contains a number of pre-defined control algorithms as for example natural sampling and space vector modulations. The average models of IGBTs and free-wheeling diodes are available as well. Based on these models a comprehensive library for Infineon power modules and thyristors has been included as well.

Accelerating Custom Designs

The now available IPOSIM online tool provides a quick and easy way for Infineon customers to select and analyze IGBTs and rectifiers for a wider range of power electronics applications. IPOSIM uses sophisticated WebSIM ® remote simulation capabilities powered by the unique simulation of Portunus. Utilizing simulation technologies the tool allows an accurate prediction of losses in a variety of applications, which can help making design tradeoffs, that often happen much later in the design process.

 

 

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