Polaris solar PV net news: with the PV inverter dimensions shrink and stand-alone power, increasing demand for the thermal design. Designers must take into account inverter cooling system cooling effect, protection, installation, serviceability, as well as the economic price to pay. Among them, the single power, is an important basis for designing cooling solutions.
Inverter cooling technologies including natural cooling, forced air cooling, liquid cooling and phase change cooling and other forms. Working principle and features in all its forms, as shown in table 1.
Studies have shown that efficiency forced air cooling heat sink is cooled for 10~20 times, more efficient cooling there is liquid-cooled. From the structural complexity and the ease of implementation, forced-air cooling system liquid cooling system is simple, easy to implement, and high reliability. Thus, preferred method of forced air cooling in the power industry, followed by natural cooling, cooling such as liquid cooling.
Figure 1 heat dissipation and heat flux density in (Note: pictures from United States University of Nevada Professor YunusA.Cengel of the Heat and Mass Transfer:Fundamentals and Applications, a book)
Heat flux density is the unit of time, through the heat per unit cross-sectional area of the object. As shown in Figure 1, in the same within the allowed temperature rise, larger heat flux density of the system, the heat dissipation is required harsh.
In General, electronic components within the permissible operating temperature as high as mesophile temperature range. At temperature of 60 ° c upper limit allowed under the conditions, be able to absorb the maximum heat flow density is cooled by natural 0.05W/cm2. When the heat flux is greater than 0.05W/cm2, and by some special means, but managed to increase the cooling effect of natural cooling, but need to sacrifice performance, or economic life of devices such as price. When the heat flux density is greater than 0.05W/cm2, forced air cooling, satisfactory performance and economy. When the heat flux density is increased, you will need to select other cooling such as liquid cooling. For power are in several MW of large wind converter, thermal way are is selection liquid cold; power in 100KW to 1MW Zhijian of concentrated type PV inverse variable device, thermal way for forced wind cold; and power from thousands of w to tens of w of group series type PV inverse variable device, is according to single power of grew up to big, thermal design also from natural thermal upgrade to forced wind cold thermal.
Figure 2 string type PV inverter cooling options
Theoretical analysis into an actual product in the cooling solution on the choice, science Steering Group series PV inverter cooling solutions in product design. As shown in Figure 2, when power is less than 20kW, can be realized by natural cooling products match the optimal size, weight and overall performance when power is greater than 25kW, large heat flux, forced air cooling which is more economical, efficient and practical means of as power 20kW to 25kW, natural cooling and forced air-cooling integrated cost-effective. Different power inverter on the market used in heat dissipation as shown in table 2.
Table 2 different power inverter used in cooling system
Summary: thermal technologies including natural cooling, forced air cooling, liquid cooling and phase change cooling and other forms, based primarily on the selection of inverter power.
Series PV inverters in series work in more than 70 ℃ roofing outdoor environment, System cooling under high temperature environment impact on product performance and service life is particularly important. Below 20kW of power inverters, can use natural cooling method and above 25kW power inverters, using forced-air cooling is more appropriate.