# Analysis of the heat sink thermal resistance Rthha of IPOSIM

How to evaluate the loss and junction temperature of an IGBT module? Infineon’s official website online simulation tool IPOSIM is an important reference for IGBT modules in the selection stage. This article will give you some clear and in-depth analysis of the heat sink thermal resistance parameter Rthha in the IPOSIM simulation.

Author: ​Zhang Hao: Infineon Technologies Greater China Application Engineer

How to evaluate the loss and junction temperature of an IGBT module? Infineon’s official website online simulation tool IPOSIM is an important reference for IGBT modules in the selection stage. This article will give you some clear and in-depth analysis of the heat sink thermal resistance parameter Rthha in the IPOSIM simulation.

• Definition of Rthha in IPOSIM: converted to the heat sink thermal resistance of each Switch (switch)

• Conversion idea: For conventional modules, first determine the total thermal resistance of the heat sink, and then convert the thermal resistance Rthha according to the number of Switches included in the heat sink. For PIM modules, the heat sink thermal resistance requires additional calculations.

1. Definition and setting of Rthha in two-level simulation

In the two-level inverter topology, the basic unit of each Switch is: T1+D1 Two-level example: 3XFF600R12KE4 per Inverter (FF600R12KE4)

The half-bridge module packaged in 62mm is as above, and the three half-bridge modules are placed on the radiator to form a complete three-phase inverter topology.Assuming that each module loses 200W and the temperature rise of the radiator is 30°C, the total thermal resistance of the radiator is

30℃/(200W*3)=0.05K/W.

The heat sink contains a total of 6 Switch basic units, so the Rthha in IPOSIM is: 0.05*6=0.30K/W.

2. Definition and setting of Rthha in three-level simulation

The three-level topology is relatively complex. Take the three common topologies NPC1, NPC2 and ANPC as examples to illustrate: In the NPC1 topology, the basic unit of each Switch is: T1+D1+T2+D2+D5 In the NPC2 topology, the basic unit of each Switch is: T1+D1+T2+D2 In the ANPC topology, the basic unit of each Switch is: T1+D1+T2+D2+T5+D5

Three-level NPC1 example:

3XF3L150R07W2E3_B11 per Inverter (F3L150R07W2E3_B11)

In small and medium power three-level applications, one module can hold one or even three three-level bridge arms. For example, the three-level module F3L150R07W2E3_B11 packaged by Easy2B has one NPC1 bridge arm in the module, and three modules are placed on the radiator to form a complete three-level three-phase inverter topology. Assuming that each Easy2B module loses 200W and the temperature rise of the radiator is 30℃, the total thermal resistance of the radiator is: 30℃/(200W*3)=0.05K/W.

The heat sink contains a total of 6 Switch basic units, so the Rthha in IPOSIM is: 0.05*6=0.30K/W.

Three-level ANPC example:

3XFF600R12ME4_B72 per phase (FF600R12ME4_B72)

In high-power three-level applications, multiple modules are often required to form a three-level bridge arm, such as the half-bridge module FF600R12ME4_B72 in EconoDual3™ package, three modules form one bridge arm of ANPC or NPC1, the same 3 One module is placed on the heat sink, just one phase of the three-level topology. Assuming that the total loss of 3 modules is 1200W and the temperature rise of the radiator is 50℃, the total thermal resistance of the radiator is 50℃/1200W=0.042K/W.

The heat sink only contains 2 Switch basic units, so the Rthha in IPOSIM is: 0.042*2=0.084K/W.

3. Definition and setting of Rthha in the simulation of inverter PIM module

In the application of small and medium power inverters, PIM modules (including rectification, braking and inverter) are often used, such as Infineon’s latest IGBT7 series EasyPIM module FP25R12W2T7_B11. As shown in the figure below, it is the surface temperature distribution of the heat sink based on the finite element thermal simulation: the ambient temperature is 50 °C, the maximum temperature of the heat sink surface is 82.3 °C, the loss of each rectifier diode RD is 3W, and the loss of each IGBT is 10W, The loss per FWD is 4W. Considering the mutual influence of the rectifier part and the inverter part in the module, we can calculate the heat sink thermal resistance Rthha corresponding to the Switch of the inverter (Inv) and rectifier (Rec) parts respectively, where:

Heat sink thermal resistance Rthha(Inv)=(82.3℃-50℃)/(10W+4W)=2.30K/W of inverter part of PIM module
PS: If the thermal resistance of the inverter part is converted according to the total thermal resistance of the radiator X6, there will be an underestimation:
The total thermal resistance of the heat sink=(82.3℃-50℃)/(6*10W+6*4W+6*3W)=0.317K/W,
That is, 0.317*6=1.90K/W,
It is about 18% lower than the above thermal resistance value of 2.30K/W.
Variation of radiator (total) thermal resistance under different working conditions
The thermal resistance of the heat sink is not a fixed value, but varies with the distribution of the heat source.

In some high-power three-level applications, on the one hand, the loss between modules is different; at the same time, the loss difference between modules will also change with different working conditions. Therefore, it is necessary to pay special attention to the total thermal resistance of the heat sink at this time. changes. As follows, take the common white module and black module three-level NPC1 topology as an example to conduct a simple analysis.

Case number one

Based on EconoDual™ 3 white module NPC1 three-level, under certain water cooling conditions, the total thermal resistance of the radiator under different working conditions:   Case 2   Based on PrimePACK™3 black module NPC1 three-level, under certain water cooling conditions, the total thermal resistance of the radiator under different working conditions:

Therefore, it is necessary to consider the thermal resistance under the worst working conditions, or adopt different thermal resistance responses of the radiator when simulating under different working conditions, so as to obtain more accurate simulation results.

In summary, the article summarizes the Rthha parameters in IPOSIM, the definitions and settings in two-level and three-level applications, and some common problems, hoping to help you how to correctly select Rthha for accurate IPOSIM simulation.

On paper, I feel shallow at the end, and I absolutely know that this matter has to be done.

Quickly open IPOSIM and try it.