1、 Basic principles for selecting radiators
1. The basic basis for selecting radiators
The selection of IGBT heat sink should be comprehensively considered based on the device's dissipated power, device shell thermal resistance, contact thermal resistance, and cooling medium temperature.
2. Requirements for tightening force between devices and heat sinks
To ensure good thermal contact between the device and the heat sink after assembly, it is necessary to have appropriate installation force or torque, which is given by the device manufacturer or device standards. During assembly, it should be strictly followed and not exceed the specified range.
3. Rated cooling conditions of the radiator
Self cooling radiator: The ambient temperature should not exceed 40 ℃. When installing, the radiator fins should be arranged vertically, and there should be no obstruction on the upper and lower end faces, so that there is a good environment and channel for natural air convection around the radiator.
Air cooled radiator: The inlet air temperature should be controlled below 40 ℃, and the inlet wind speed should ideally reach 6 meters per second.
Water cooled radiator: The inlet water temperature shall not exceed 35 ℃. The water flow rate should be determined based on the total heat dissipation required and the design temperature difference between the inlet and outlet water.
4. Comprehensive considerations for selecting heat sinks
The selection of heat sinks should comprehensively consider the range of heat dissipation capacity, cooling method, technical parameters, and structural characteristics of the heat sink. For a device, only from the perspective of technical parameters, there may be two or three types of heat sinks that can meet the requirements, but the selection should be combined with cooling, installation, universal interchangeability, and economic considerations.

2、 General methods for selecting heat sinks
The selection of heat sinks by users should be based on the actual cooling conditions during device operation, stable and transient load conditions, and appropriate consideration of safety factors. The consideration should be based on the maximum operating junction temperature of the device under steady-state conditions.
1. Based on the current waveform and conduction angle of the device operating in the circuit, the average current IAV during device operation is determined, and the effective value of this current (IRMS) is calculated using IAV
IRMS=F · IAV F is the waveform coefficient.
2. Determine the device model based on IRMS or IAV at a 180 ° conduction angle, combined with device surge current. IAV=IRMS/1.57.
3. Based on the relationship curve between the maximum allowable shell temperature Tc of the selected device and the main current IAV, find the Tc value corresponding to the operating point IAV of the device. Or calculate the Tc value according to the relevant parameters of the selected device using the following method.
Tc=Tjm - Rjc · PAV
Tjm is the maximum allowable maximum junction temperature of the device, which is 150 ℃ for ordinary rectifiers, 125 ℃ for ordinary thyristors, and 115 ℃ for fast thyristors
Rjc is the shell thermal resistance of the device.
PAV is the dissipated power of the device. The calculation formula is:
PAV=0.785 VTM · IAV+0.215 VTO · IAV or
PAV=VTO · IAV+2.47rT0 · IAV
VTM is the on state peak voltage drop of the device.
VTO is the threshold voltage of the device. When the device parameter table is not marked, it can be taken as follows: rectifier tube 0.8V, ordinary thyristor 1.0V, fast thyristor 1.2V.
RT0 is the on state slope resistance of the device.
4. Calculate the maximum allowable heat sink surface temperature TS from the following equation
TS=Tc - RCS · PAV
RCS represents contact thermal resistance, with spiral devices taking 1/3 Rjc and flat devices taking 1/5 Rjc
5. Calculate the thermal resistance value of the radiator using the following equation
Rsa=(Ts Ta)/PAV
Ts is the ambient temperature, measured during the experiment.
6. When the working conditions of the radiator are consistent with the rated cooling conditions, select the radiator with the same or less thermal resistance value but closest to the calculated value from the radiator data manual based on the calculated value Rsa. When there is inconsistency, check the relationship curve between the heat resistance of the radiator and the flow rate of the cooling medium to determine.