Operating temperature has a great impact on the life of the inverter!

It is widely known that temperature has a significant impact on photovoltaic modules.

Photovoltaic modules generally have three temperature coefficients: open circuit voltage, peak power, and short circuit current. When the temperature rises, the output power of the photovoltaic module will inevitably decrease! Therefore, temperature reduction is a factor that has a great impact on system efficiency. If the local temperature is too high, hot spots will occur, which will affect the life of the photovoltaic module.

However, how much influence does temperature have on the life of the inverter? Not many people understand this.

In order to verify the effect of temperature on the life of the inverter, the following experiment was designed.

1. Experimental methods and conditions

Experimental conditions: 480V DC voltage, 400V AC voltage, 50℃ ambient temperature;

Experimental samples: 30kW air-cooled inverter (sample 1) and 20kW natural cooling inverter (sample 2).

Experimental purpose: To illustrate the impact of temperature on the overall life of the inverter by testing the impact of temperature on the life of key components of the inverter.

2. Experimental methods and conditions

The two samples ran stably at full load under experimental conditions, and the temperature values ​​of key components inside the test collection equipment are shown in the following table.

Table 1: Temperature of key components under experimental conditions

1 Effect of temperature on the life of membrane capacitors Based on the measured data of the internal temperature of the sample products, assuming that the ripple current is the same, the relationship between the ratio of the working voltage (Vw) to the rated voltage (Vn) (Vw/Vn) and the membrane life is shown in Figure 1.

Figure 1: Relationship between membrane capacitor life and temperature

From the above figure we can see the life of the membrane capacitor at different temperatures and different Vw/Vn values.

Table 2: Temperature of key components under experimental conditions

Note: Since the membrane capacitor cannot reach the above temperature when operating at less than full load, according to my country's resource conditions and based on the conservative value of 2200h per year at full load, the actual life should be greater than the value in the above table.

It can be seen that if the working temperature of the membrane capacitor rises from 70℃ to 85℃, the lifespan will drop to about 1/3~1/5 of the original lifespan, and the lifespan decreases as the Vw/Vn value increases. When Vw/Vn<1.1, the lifespan of sample 1 can basically reach 25 years, and overload will reduce its lifespan; while the lifespan of sample 2 does not reach 25 years due to the high temperature.

2 Impact of temperature on module life As the core component of the inverter, the module's internal junction temperature directly affects its service life during operation. Figure 2 is a curve showing the relationship between wafer junction temperature and life provided by Infineon.

Figure 2: Correlation curve between module life and junction temperature

According to the internal temperature of the modules of sample 1 and sample 2 in Table 1, the module junction temperature and the comparison of the module life of the two are calculated as shown in Table 3 (the calculation process is highly professional and will not be repeated here).

Table 3: Effect of module temperature and lifespan

It can be seen from the above table that under the experimental conditions, for the key device module, the life of sample 1 with a lower temperature is 1.7 times that of sample 2 with a higher temperature, but both have not reached the expected life of 25 years.

3 Effect of temperature on fan life Fans are mature industrial devices. The NMB fan used in the air-cooled inverter of sample 1 has a protection level of IP65 and can work normally in any dusty environment, even when completely immersed in water. Figure 3 shows the life curve of the NMB fan.

According to Figure 3, the normal operating time is 60319 hours, calculated based on the maximum ambient temperature of 50℃ for the inverter. Through intelligent forced air cooling control, the fan will only rotate fully when the module temperature of the inverter reaches above 70℃. In a normal day, the time to meet the full rotation condition is about 6 hours, which is equivalent to 27.5 years. In addition, considering factors such as rainy days and ambient temperature below 50℃, the operating life of the fan will be longer.

3. Summary

Under the experimental conditions (480V DC voltage, 400V AC voltage, 50℃ ambient temperature), the different cooling methods of sample 1 and sample 2 resulted in significant differences in the lifespan of key components.

For film capacitors, when Vw/Vn<1.1, the life of sample 1 can basically reach 25 years, and overload will reduce its life; while the life of sample 2 did not reach 25 years due to the high temperature.

For the modules, the life of sample 1 is 1.7 times that of sample 2, but both modules have not reached the expected life of 25 years.

Fans are mature industrial components with a service life of more than 25 years.

In summary, when new technologies such as containerized inverters and natural cooling inverters are widely used, the impact of these new technologies on heat dissipation and the life of the inverter should be fully considered.