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Posted on 01 November 2019

Selection, Power Loss Calculation, and Temperature Rise Analysis

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All-in-one efficient online tool for the power modules

MELCOSIM offers a variety of possibilities to calculate the power loss and temperature rise for several different circuits and load conditions in order to give application support for the available Mitsubishi power modules.

By Prasad Bhalerao and Eugen Stumpf, Mitsubishi Electric Europe, Germany

 

In 2004, first time Mitsubishi customers benefited from a direct link to its new calculation tool. With the constant improvement, in 2006, that program has been enhanced and expanded to include even more operating modes and more detailed output data. A power designer can analyse the performance of Mitsubishi’s power devices with this software efficiently, optimizing the productivity by reducing the development time. This article deals with each feature of MELCOSIM and its function in detailed. It describes also the guidelines for the effective use to customers with sample output results of 100A/1200V dual IGBT module (CM100DY-24A).

As a power designer, it is necessary to calculate and analyze the power module performance on the basis of its losses (switching, and conduction losses) and junction temperature rise for the design of the system under given application conditions. In addition to the delivery of high performance and reliable power modules to customers, in order to increase the efficiency of the design and the development Mitsubishi offers an enhanced, compatible online tool for the appropriate module selection and power loss analysis. The power loss analysis can be done in DC-AC inverter and DCDC chopper configuration under the assumption of sinusoidal and constant output currents at inductive loads. Compared to the similar available tools MELCOSIM offers a several advantages such as fully compatible to Windows operating systems, independent on other software platform, dedicated design to implement it for the Mitsubishi modules and easy to use features. MELCOSIM provides calculation results as graphical and text output data at fast speed.

Operational features of MELCOSIM

Customers can access MELCOSIM through the Mitsubishi web site at www.mitsubishichips.com. This software is compatible with Windows98/NT/2000/XP. To provide an updated info time to time for the Mitsubishis customers, a quick registration process is required to access this software. After registration, download of MELCOSIM on own hard disc is possible. Once the zipped file is downloaded, only a quick installation process is needed. For the detailed instruction please open the “Read Me” file first. After the successful installation user will be ready to use this software immediately.

Selection of modules and input of application conditions

The first step in the use of MELCOMSIM is to consider worst-case application operating conditions. User can select the operating conditions parameters like DC-link voltage (VCC), output current (IO), switching frequency (fSW), power factor (PF) and also modulation parameters like modulation ratio (D) or duty cycle (for chopper mode) to realize the calculation conditions comparable to real application conditions.

Figure 1 depicts the main window. The left part of this window is reserved for application conditions input: DC link voltage (VCC) and switching frequency (fSW) are important for switching loss calculations, while modulation ratio (D) and power factor (PF) influences the distribution of conduction losses between the IGBT and FwDi. The output current IO is necessary for both conduction and switching losses. Additionally module type (CM100DY-24A) and its thermal resistances are shown in the above part of main window.

Main window of MELCOSIM

Based on the worst case application conditions module pre-selection must be done. The main criteria for the module type preselection are:

  • The rated current (IC) of the module should be more than the half of the peak output current (ICP)
  • The blocking voltage VCES of the device should be more than 1.5 times the applied DC link voltage (VCC)

Once the appropriate VCES and IC for the device is chosen, the module can be selected from the available in-built product line-up via a module section button from tool menu bar. The present version includes an updated device data file with 45 new devices including HVIGBT IGBTs up to 2400A/1700V and 600A/6500V and the new 600V DIP-IPM Version 4 (Super Mini-DIP-IPMs). Now MELCOSIM can be used for the checking whether pre-selected device is suitable from thermal point of view.

The selected device is marked as a target device in the input and output window. Figure 1 shows an example of loss calculation input and output parameters for better understanding of the each features. The modulation strategy such as 3-arm modulation (continues) 2-Arm modulation (discontinuous space-vector, in which PWM pattern is varied such that each device is subject to switching for two-thirds of a cycle) and DC chopper modes (typically used in DC to DC converter circuits) can be selected depending on the customer’s requirements. Figure 2 shows the typical circuit configuration for 3 arm PWM modulation scheme with the relevant input parameters for loss calculations. The current version of MELCOSIM (version 3.0) is able to calculate the average junction temperature Tjav in transistor (IGBT) and free wheel diode (FWDi). The difference between maximum junction temperature Tjmax and Tjav can be neglected in case of output frequency fout is above 30 Hz. For the junction temperature calculation in case of output frequency is below fout=30 Hz, Tjmax must be considered.

Basic 3 arm PWM modulation and definitions

The next MELCOSIM version 4 will content the possibility of fout input and Tjmax calculation. MITSUBISHI plan to introduce version 4 by end of year 2006.

MELCOSIM is checking all input parameter (application conditions) for the selected module for limits provided in specification. In case an input parameter is not in a specification range, the warning window will be appeared.

Loss calculation

The total average power loss of an IGBT with sinusoidal output current is the sum of IGBT static loss and IGBT switching losses. Similarly, the total loss of free-wheeling diode is a sum of switching loss and static loss. The static loss of IGBT is given in equation (1) and equation (2) calculates the switching loss of IGBT. The equation (3) and equation (4) gives the steady state loss and recovery loss of the free-wheeling diode respectively.

Equations 1-4

Where ICP: Peak value of sinusoidal output current, PF: power factor, VCE(sat): IGBT saturation voltage drop at ICP and Tj =125°C, D: modulation index, ESW(on) and ESW(off): IGBT’s turn-on and turn-off switching energy per pulse at peak collector current ICp and Tj= 125°C, Irr: Diode peak reverse recovery current, trr: Diode reverse recovery time, VCE(peak): Peak voltage across the diode at recovery, VEC: Diode forward voltage drop.

Calculation results display the total loss in one module, total loss in an IGBT/Diode and the separate IGBT/Diode loss, switching and conduction loss components. The results of the power loss can be plotted graphically such as:

Av. Power loss (P) vs. peak output current (ICP) as shown in Figure 3.
Av. Power loss (P) vs. switching frequency (fsw)

On the right part of graphical output the fixed application conditions are given. The red line provides IGBTs result and the blue line FWDi results. The variable application condition Icp (Figure 3) is limited by two times of module rated current: Icp(max)=200A for CM100DY-24A. This limit is corresponded to the RBSOA specification.

MELCOSIM Graphical output p vs. ICP

Figure 4 shows the part of the main window, where the power loss and junction temperature of IGBT and diode in the module CM100DY-24A are summarized.

The window where the power loss of IGBT and diode is summarized.

Temperature rise calculation

The calculation of the temperature rise is necessary for checking whether pre-selected module is suitable for the given application, for the heat sink design and also for the consideration of over temperature protection.

Figure 5 shows the equivalent thermal model of IGBT and Free-Wheeling Diode (FWDi) for the calculation of the temperature rise. The crosstalk between transistor and diode loss are occurred already in the module baseplate. For the calculation in MELCOSIM, thermal resistance values of the IGBT and FWDi are measured just under the chip. MELCOSIMs interface to user is heatsink temperature Tf must be measured direct under the IGBT/Diode chip. In addition to the magnitude junction temperature MELCOSIM provides the average temperature rise between junction (j) and module baseplate (c) as well as module baseplate (c) and heatsink (f) of IGBT and Diodes All temperature calculation results are summarized in the output part of main window shown in Figure 4.

Thermal Model of IGBT and Free-wheel Diode

In addition to above mentioned results calculated for one operation condition, MELCOSIM is able to provide graphical output with changeable parameters Icp and fsw: Junction temperature (Tj) vs. peak output current (ICP).

Junction temperature (Tj) vs. switching frequency (fsw) as shown in Figure 6.

The line with red colours shows IGBT temperature and line with blue colours shows FWDi temperature. The striped rectangular on Figure 6 shows not recommended area above Tj=125 degrees. The max specified junction temperature is Tj=150 degrees.

Temperature rise graphical analysis by MELCOSIM

The graph of peak output current (ICP) vs. switching frequency (fsw) at fixed junction temperature is interesting for selection of the proper power module. This graph is shown in Figure 7. The target junction temperature can be adjusted in a separate window for Tj input. The target junction temperature in Figure 7 is Tj=125 degrees. For a particular switching frequency, the graphical analysis shows directly the peak value of the output current at selected junction temperature. Figure 7 shows that for module CM100DY-24A by using of switching frequency fsw=5kHz the maximal collector current Icp=150A can be reached provided that junction temperature will not exceed Tj=125 degrees.

MELCOSIM Graphical output ICP vs. fsw at target juntion temperature Tj

The end result data can be stored or transmitted graphically and in text format. Multiple calculations with varying conditions can be compared by saving one calculation window and creating a new window by clicking on the “new window” button on your toolbar.

Summary

In short, MELCOSIM helps to select the suitable Mitsubishi power module for specific design considered the customers worst-case application conditions. Additionally MELCOSIM provides a quick and easy way for junction temperatures and power loss calculation by simply entering module types of interest and then adjusting the defaulted specifications to match customers application conditions. The program will instantaneously calculate junction temperatures and power loss of IGBT and FWD under the given application conditions in a short time.

Points to be aware of while using the MELCOSIM:

The module data based on the respective IGBT module data sheet. The data used in MELCOSIM may subject to changes, improvements or correction without prior notice to user. Calculations are based on the linear approximations. Due to slight deviation in the operating condition parameters, the program may not replace a detailed reflection of the customer application with all its operating conditions.

 

 

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