What heat dissipation issues should be considered when using diodes in inverters?

一, Optimization design of heat dissipation path

1. PCB thermal design optimization
Copper foil expansion: Increasing the anode/cathode copper foil area (such as upgrading from 1oz to 2oz) can reduce thermal resistance by 30%. For example, by arranging heat dissipation vias (diameter 0.5mm, spacing 1mm) around the diode pads, heat can be conducted to the bottom layer of the PCB, improving heat dissipation efficiency by 25%.
Layout isolation: To avoid thermal coupling between power diodes and control circuits, it is recommended to have a spacing of ≥ 5mm. Due to insufficient spacing between MOSFETs and diodes in a certain car inverter, the temperature of the control chip exceeded the standard, causing false protection actions.
2. Selection of heat dissipation method
Air cooling heat dissipation: suitable for scenarios with power density<5W/cm ³, requiring control of airflow velocity ≥ 2m/s. For example, a 10kW household energy storage inverter uses an axial fan to control the diode junction temperature within 110 ℃.
Liquid cooling heat dissipation: When the power density is greater than 10W/cm ³, the liquid cooling system can reduce the junction temperature by 40 ℃. After adopting liquid cooled modules, the lifespan of diodes in a data center UPS has been extended from 8 years to 15 years.
Phase change material (PCM): In a confined space, PCM can absorb instantaneous thermal shock. Experiments have shown that embedding PCM in a 5kW inverter reduces the amplitude of diode temperature fluctuations by 60%.
二, Key measures in engineering practice
1. Device selection criteria
Voltage and current margin: The rated voltage of the diode should be ≥ 1.5 times the maximum system voltage, and the rated current should be ≥ 2 times the average current. For example, in a 1000V photovoltaic system, a 1200V voltage resistant diode needs to be selected.
Low VF and low IR characteristics: Devices with VF<0.5V (Schottky diodes) or VF<1.5V (SiC diodes) are preferred. After using STPS30H100 Schottky diode (VF=0.4V) in a certain micro inverter, the efficiency was improved by 1.2%.
2. Real time temperature monitoring
NTC thermistor: Embedded with NTC inside the diode package, it can monitor junction temperature in real time. A certain photovoltaic inverter dynamically adjusts the switching frequency through NTC feedback, reducing the fluctuation range of diode junction temperature from ± 15 ℃ to ± 5 ℃.
Infrared thermal imaging: Regular infrared detection is used to identify local hotspots. During the maintenance of a wind power converter, it was found that the diode solder pads were virtual, causing a local temperature rise of up to 80 ℃. After repair, the system efficiency was restored to 98.5%.
3. Reduced usage strategy
Adjust output power according to ambient temperature:

40 ℃ environment: use with a 5% reduction in rating;
60 ℃ environment: use with a 20% reduction in rating.
A desert photovoltaic power station implemented a derating strategy, reducing the diode failure rate from 0.8%/year to 0.2%/year.