How much do you know about string inverter high protection outdoor fans

1. Introduction

With the vigorous development of distributed photovoltaics, string inverters with power levels of 25~60kW are widely used on industrial and commercial roofs and small hill power stations. In order to improve the heat dissipation performance of the inverter and extend the actual service life of the inverter, most mainstream string inverters with power levels above 25kW use outdoor fans with high protection capabilities of IP65 for heat dissipation. Since string inverters are generally installed under or next to the components, they face the challenges of harsh operating environments such as wind, sun, and even dust. Can the external fans configured for string inverters meet the waterproof, dustproof and salt spray requirements required for outdoor use? The author will now lead everyone to conduct an in-depth analysis of the high-protection outdoor fans selected by a well-known domestic string inverter manufacturer.

2. Necessity of fan cooling for string inverters

The article "The choice of heat dissipation scheme mainly depends on the inverter power" theoretically analyzes that when the power of a string inverter is greater than 25kW, the heat flux density is large, and forced air cooling is more suitable from the perspective of heat dissipation effect. The article "Investigation on the heat dissipation capacity of string inverters with different heat dissipation methods" compares the heat dissipation capacity of string inverters of two manufacturers with different heat dissipation methods through experiments and finds that under the same ambient temperature, the internal ambient temperature and core device temperature of the forced air cooling inverter are about 20℃ lower than those of the naturally cooled inverter. The forced air cooling inverter has better heat dissipation performance and more guaranteed actual service life. The inverter can output at full power at a higher ambient temperature to ensure power generation. A survey on the operation status of a domestic photovoltaic power station found that due to poor heat dissipation performance, the string inverter using natural cooling will experience derating operation in a high temperature environment, resulting in a loss of inverter power generation. This once again verifies the correctness of the design view that "when the power of a string inverter is greater than 25kW, it is more appropriate to use forced air cooling". Through research, the author found that most mainstream inverter manufacturers' products with a power level of more than 25kW adopt forced air cooling, such as SMA, Sungrow, Delta, etc., and use outdoor fans with a high protection level of IP65 to improve the heat dissipation performance of the inverter while meeting the IP65 protection level of the inverter.

3. This fan is not the same as that fan: protection

The world's first fan originated in 1880. American Schuler first installed blades on an electric motor and connected the power supply. The blades rotated rapidly, and gusts of cool breeze blew on the face. Some people may still have the impression that fans are noisy, have poor waterproof and dustproof capabilities, and the coils are prone to rust, have a short service life, and are easy to break. However, with the diversification of fan usage occasions, the use environment continues to challenge the fan protection design and life. After continuous design innovation by fan manufacturers, the fan protection ability and life have been greatly improved. At present, high-protection, long-life outdoor fans have been used in communication, telecommunications, power electronics and other fields. This fan refers to the high-protection outdoor fan used in string inverters, while the other fan refers to the traditional ordinary unprotected fan or low-protection fan. There are certain differences in the performance of the two fans. It is necessary to conduct an in-depth analysis of the two fans to change people's inherent impression of fans.

3.1 Introduction to fan high protection technology

High-protection outdoor fans are mainly composed of six parts: frame, fan blades, PCB board, stator, rotor, and bearing. The fan protection process is mainly aimed at protecting the internal coils and electronic components on the PCB board. For ordinary unprotected fans or low-protection fans, the fan coil windings and some electronic components are directly exposed to the air, as shown in Figure 1(a). Due to the low protection level, if the electronic components on the PCB board are exposed to moisture or dust accumulation, it is very easy to cause the fan to fail. At the same time, the fan coil will also rust if it is exposed to the air for a long time. Compared with the protection process of low-protection fans, high-protection outdoor fans use epoxy resin or silicone to completely seal the entire fan coil and PCB board to prevent the influence of moisture, dust, salt spray, etc. on the windings and electronic components. It can achieve the IP65 protection level or above specified by the IEC60529 standard and can be placed outdoors for use, as shown in Figure 1(b).

Figure 1 Fan protection process (click to see larger image)

In order to verify the protective performance of high-protection outdoor fans again from an experimental perspective, the author selected a brand-new mainstream high-protection outdoor fan and a high-protection outdoor fan that had been used in a photovoltaic power station for 3 years as test samples, and conducted waterproof, dust-proof, and salt spray-proof performance tests. By testing the core electrical indicators of the high-protection outdoor fan before and after the test, such as speed, current, and insulation resistance, it was found that the core electrical indicators before and after the test were within the error range, which fully met the design requirements of the IP65 protection level specified in the IEC60529 standard.