Assignment:

Introduction:

The chosen switch to be used in an inverter is an IGBT (Insulated Gate Bipolar junction Transistor), the voltage-controlled drive side of a MOSFET with the power side of a power transistor. One design issue for these devices is to ensure that they do not overheat and therefore fail. Your task is to check whether the SEMIKRON SKM75GB12T4 is an appropriate choice for the application. The specifications for this unit are available from the StudyDesk.

This question relies heavily on Figs. 1 and 3 from those specifications. The gate drive voltage (VGE) is the input voltage to the switch and for a particular rated current (IC) and temperature (Ti) there is a specific voltage drop across the switch (VCE) which occurs. The greater the value of VCE, the greater the energy losses (Eon + Eoff) and thereforethe more likely it is that the switch will overheat. Your task is to determine whether the energy losses are below the critical value Ecrit for your particular application. The switch will overheat if the energy losses reach the critical value. For your assignment, the following values are to be used:

I_C = 1.8126 × 5 + 25 A

V_GE = 0.77473 ÷ 3 + 11 V

T_i = 150^oC

E_crit = 4.2762 × 2 mJ

V_CC = 600 V , 

where V_CC is the bus voltage.

Requirements:

For this assessment item, you must perform hand calculations based on Figs. 1 and 3 from the SEMIKRON spec. sheet:

1. For the value of T_i and V_GE = 15 V, determine the values of V_CE for I_C = 25 A, 50 A and 75 A.

2. Using the values from Requirement 1, use linear interpolation to determine the value of V_CE for your value of I_C.

3. Repeat Requirement 1 for V_GE = 11 V.

4. Repeat Requirement 2 for V_GE = 11 V.

5. Using your results from Requirements 2 and 4, estimate the value of V_CE for your value of V_GE.

6. For your value of I_C, determine the values of Eon and Eoff for V_GE = 15 V.

You must also produce MATLAB code which uses the data from Figs. 1 and 3 in the SEMIKRON spec. sheet:

7. Using the values from Requirement 1, use linear interpolation to determine the value of V_CE for your value of I_C (obtain the same answer as Requirement 2).

8. Repeat Requirements 4 and 5. Verify your result against that from Requirement 5.

9. Calculate the result from Requirement 8 directly from the data in Requirements 1 and 3 (i.e. perform one linear interpolation operation to determine the answer). Compare your result with that from Requirement 8 and discuss why they are similar or different.

10. Estimate the error in your calculation of Requirement 7. As part of this error estimation, use the formula:

Discuss the size of the error and how accurate you consider the answer from Requirement 8 to be.

11. The values from Requirement 6 are proportional to V_CE. Determine the values of E_on and E_off for your value of V_CE from Requirement 8. Thereby test whether this switch will overheat for the given operating conditions.

12. Has appropriate comments throughout.