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High-power high-voltage inverters often require extremely high reliability. The main form that affects power equipment failure is thermal failure. According to statistics, more than 50% of electronic thermal failures are mainly caused by temperatures exceeding the rated value. From the structural design point of view, the heat dissipation technology is the key link to ensure the normal operation of the equipment. Due to the high power of the three-ring high-voltage inverter equipment, it is generally MW-class, which will generate a lot of heat during normal operation. In order to ensure the normal operation of the equipment, a large amount of heat is dissipated, the heat dissipation and ventilation scheme is optimized, reasonable design and calculation are carried out, and efficient heat dissipation of the equipment is realized, which is necessary for improving the reliability of the equipment.
When the high-voltage inverter is in normal operation, the heat source is mainly the isolation transformer, reactor, power unit, control system, etc., which is the heat dissipation of the power device of the main circuit electronic switch, the heat dissipation design of the power unit and the heat dissipation of the power cabinet. Ventilation design is the most important. For igbt or igct power devices, the pn junction must not exceed 125 ° C and the package housing is 85 ° C. Studies have shown that component temperature fluctuations exceed ± 20 ° C, and its failure rate will increase by 8 times.
Precautions for heat dissipation design (1) Use components and materials with good heat resistance and thermal stability to increase the allowable operating temperature;
(2) Reduce the amount of heat generated inside the device (device). To this end, more micro-power devices should be selected, such as low-loss igbt, and the number of heat-generating components should be minimized in the circuit design, and the switching frequency of the device should be optimized to reduce the heat generation;
(3) Use proper heat dissipation method and appropriate cooling method to reduce the ambient temperature and speed up the heat dissipation.
Exhaust air calculation Calculate the minimum wind speed when the maximum temperature of the radiator reaches the demand in the worst case temperature. The amount of exhaust air is determined according to the redundancy rate according to the wind speed. The formula for calculating the exhaust air volume is: Qf=Q/(Cp?ρ?△T)
In the formula:
Qf: The amount of air required to force the air cooling system.
Q: Total thermal power consumption of the device being cooled, W.
Cp=1005J/(kg?°C): air specific heat, J/(kg?°C).
ρ = 1.11 (m3/kg): air density, m2/kg.
△T=10°C: temperature difference of air at the inlet and outlet, °C.
According to the air volume and wind pressure, the fan model is determined, so that the fan works at the highest efficiency point, which increases the fan life and improves the ventilation efficiency of the device.
The air duct design series air duct is formed by the radiators of each power module up and down, forming upper and lower corresponding air ducts. The characteristics are formed by connecting the upper and lower power units in series, the structure is simple, the air duct vertical makes the wind resistance small; There is a problem that the air is heated in order from bottom to top, resulting in a small temperature difference between the above power unit and a poor heat dissipation effect.
In the parallel air duct, the air is introduced from the front of each power unit, and the corresponding air inlets are arranged in parallel, and are summed up by the wind turbine in the rear wind chamber, and the whole power cabinet is generally redundant, and multiple fans are operated in parallel. The overall heat dissipation effect is good and the reliability of the device is improved. However, the wind chamber is formed behind the cabinet, which increases the volume of the equipment. At the same time, due to the different distances from the back end of each power unit to the fan, the wind flow of each power unit is inconsistent, which is a difficult design.
According to the characteristics of the series air duct and the parallel air duct, the high-voltage frequency converter of Sanhuan Co., Ltd. selects the parallel air duct design and forms a unique patented structure technology.
Simulation analysis The simulation software can be used to perform efficient, accurate and simple quantitative analysis of system heat dissipation, temperature field and internal fluid motion state in various structures and levels. According to the simulation results, the heat dissipation structure is evaluated, modified, and then simulated again until the desired result is obtained. In this way, we have a good control of thermal failure, which greatly improves the reliability and stability of the equipment.