Vcesat, Eon, Eoff, Vf, and Erec reflect the technical characteristics of IGBT/FWD chips. Therefore, different IGBT/FWD chip technologies result in different Vcesat, Eon, Eoff, Vf, and Erec.

The relationship between Vcesat and Ic can be represented by the approximate linear method in the left figure:  

Vcesat = Vt0 + Rce x Ic 

Conduction loss of IGBT:  

Pcond = d * Vcesat x Ic, where d is the conduction duty cycle of the IGBT 

The magnitude of the IGBT saturation voltage is related to the current (Ic), the junction temperature of the chip (Tj), and the gate voltage (Vge).

The reason for the switching energy loss in IGBT is that there is an overlap period of current and voltage at the moment of turning on and off.

When Vce is close to the test conditions, Eon and Eoff can be approximately considered proportional to Ic and Vce:

Eon = EON x Ic/IC,NOM x Vce/test conditions

Eoff = EOFF x Ic/IC,NOM x Vce/test conditions

Switching loss of IGBT:

Psw = fsw × (Eon + Eoff), where fsw is the switching frequency.

The magnitude of the IGBT switching energy loss is related to the current (Ic), voltage (Vce), and the junction temperature of the chip (Tj).

The relationship between Vf and If can be represented by the approximate linear method in the left figure:

Vf = U0 + Rd x If 

Conduction loss of FWD: Pf = d * Vf x If, where d is the conduction duty cycle of FWD.

The magnitude of the forward conduction voltage of FWD is related to the current (If) and the junction temperature of the chip (Tj).

Reverse recovery is an inherent characteristic of FWD, occurring at the moment of transition from forward conduction to reverse blocking, manifested as returning to the reverse blocking state after passing through reverse current.

When Vr is close to the test conditions, Erec can be approximately considered proportional to If and Vr:

Erec = EREC x If/IF,NOM x Vr/test conditions

Switching loss of FWD:

Prec = fsw x Erec, fsw is the switching frequency.

The magnitude of the FWD reverse recovery energy loss is related to the current (If) during forward conduction, the rate of change of current dif/dt, the reverse voltage (Vr), and the junction temperature of the chip (Tj).

IGBT

Conduction loss:

1) Related to IGBT chip technology 

2) Related to operating conditions: proportional to current, proportional to IGBT duty cycle, increases with Tj.

3) Related to driving conditions: decreases with the increase of Vge 

Switching loss:

2) Related to working conditions: proportional to switching frequency, current, and voltage, increases with Tj.

2) Related to operating conditions: proportional to current, proportional to IGBT duty cycle, increases with Tj.

3) Related to driving conditions: increases with the increase of Rg, decreases with the increase of gate turn-off voltage.

FWD

1) Related to IGBT chip technology

1) Related to FWD chip technology

2) Related to working conditions: proportional to current, proportional to FWD duty cycle. 

Switching loss:

1) Related to FWD chip technology

2) Related to working conditions: proportional to switching frequency, current, and voltage, increases with Tj.

The temperature difference △T of each part of the IGBT module depends on

1) Loss (chip technology, operating conditions, driving conditions); 

2) Thermal resistance (module Specification, Size) 

The junction temperature of the module chip is the sum of the temperature differences of each part and the ambient temperature:

Tj = △Tjc + △Tch + △Tha + Ta

If we assume that the case temperature Tc is constant, then Tj = △Tjc + Tc;

If we assume that the heat sink temperature Th is constant, then Tj = △Tjh + Th.

The average junction temperature of the IGBT depends on the average loss, Rthjc, and case temperature Tc.

During actual operation, the junction temperature of the IGBT fluctuates, and the amplitude of the fluctuation depends on the transient loss and Zthjc, which is related to the operating conditions (such as the output frequency of the inverter).

The peak junction temperature of the IGBT is the average junction temperature plus the fluctuation amplitude. 

Conclusion: 

The junction temperature (average/peak) of the IGBT is related to chip technology, operating conditions, driving conditions, IGBT Specification.

Module size, heat sink size, and ambient temperature.

Safe operation of the IGBT module.

Basic conditions for safe operation:

Temperature: IGBT junction temperature peak 

Tj_peak ≤  125°C (150°C*) 

Tjmax = 150°C (175°C*) - refers to the steady-state condition without switching operation;.

Tvj(max) = 125°C (150°C*) - refers to the normal switching operation state.

Tvj(max) specifies the maximum junction temperature allowed for IGBT turn-off current, short circuit, and power cycling (PC).

* 600V IGBT3; 1200V and 1700V IGBT4; 3300V IGBT3

Short circuit time:Vcc=2500V, Vge ≤ 15V, Tvj=150°, Tp ≤ 10us

Others:

Vce ≤ VCES (i.e., the voltage specification of the IGBT)

Vge ≤ VGES (±20V)

Ic is specified by RBSOA under continuous switching conditions, not exceeding 2xIC,NOM. Minimum turn-on time, etc.