In 2017, the results of the national supervision and random inspection of the quality of China's photovoltaic grid-connected inverters were announced. This time, a total of 27 batches of photovoltaic grid-connected inverters produced by 27 companies in 5 provinces and municipalities including Shanghai, Jiangsu, Zhejiang, Anhui, and Guangdong were randomly inspected. Protection connection, touch current, power frequency withstand voltage of solid insulation, rated input and output, conversion efficiency, harmonic and waveform distortion, power factor, DC component, AC output side over/under voltage for photovoltaic grid-connected inverter products Nine items including protection were tested.
In 2017, the unqualified rate of solar inverters reached 22%
The results showed that 6 batches of products did not meet the requirements of the standard, involving rated input and output, conversion efficiency, harmonic and waveform distortion, power factor, DC component, AC output side over/under voltage protection items.
What is worrying is that 6 batches of the 27 batches of photovoltaic grid-connected inverters that were spot-checked were unqualified, and the product failure rate reached 22%, which was 10 percentage points higher than that in 2016. Although there were 6 batches of unqualified solar inverters in 2016, a total of 52 batches of photovoltaic grid-connected inverters were randomly checked, and the unqualified rate of products was 11.5%.
Annoying AC output side over/under voltage protection
According to the two-year spot check results, the solar inverters in 2016 are mainly two items of AC output side over/under voltage protection, harmonics and waveform distortion. In the past two years, the over/under voltage protection on the AC output side has become the most problematic item. So what function does this project refer to the inverter? Why does this project always go wrong?
It is understood that the so-called over-voltage/under-voltage protection on the AC output side means that when the photovoltaic power station supplies power to the grid through the grid-connected inverter, when it is detected that the voltage at the AC output terminal of the inverter exceeds (or falls below) the allowable voltage of the grid When the range is reached, the inverter will automatically disconnect the AC contactor, stop supplying power to the grid, and send out a warning signal at the same time. The role of this function of the inverter is obvious, that is, to ensure the safe power supply of the photovoltaic power station under the premise of ensuring the stability of the grid. For the power grid, the access of a large amount of power exceeding the allowable voltage range is likely to cause damage to the stability of the power grid. Due to the instability of the photovoltaic power station itself, the performance of the overvoltage/undervoltage protection on the AC output side of the inverter determines the grid friendliness of photovoltaic power generation, and its importance is self-evident.
The national standard for the overvoltage and undervoltage protection value of the inverter is 195.5V-253V. Logically speaking, this is not a difficult technical standard to achieve. But why has it become the hardest hit area for unqualified solar inverters for several consecutive years? This may be related to the uneven level of domestic power grid construction. For example, in some areas of China, the distribution transformer capacity is insufficient, and the load is too large or too small, which leads to the high voltage range of the power grid. Due to the complex situation in these areas, some businesses may expand the range of overvoltage and undervoltage protection values of the inverter to enhance the adaptability of the inverter.
In addition, in the era when power generation is king, a wider range of overvoltage and undervoltage protection values allows the power station to integrate more power into the grid, which can increase the power station's revenue. However, if all photovoltaic power plants output electricity beyond the safe range regardless of the stability of the grid, this will inevitably damage the stability of the grid and bring safety hazards. Once the stability of the power grid is affected by the access of photovoltaic power, then power cuts will also be inevitable.
To solve these problems, on the one hand, China's power grid construction must be strengthened, and power grid technology improvements should be made according to the characteristics of new energy power such as photovoltaics and wind power, so as to overcome the difficulty of unstable new energy power and maximize access to new energy power. . On the other hand, it is necessary to improve the stable output of photovoltaic power plants to ensure that the output voltage of photovoltaic power is within a safe range.
Photovoltaic inverter quality is facing challenges
In 2015, the quality inspection results released by the General Administration of Quality Supervision, Inspection and Quarantine showed that the pass rate of China's grid-connected solar inverters was less than 80%. As soon as this data was released, it caused an uproar in the industry. The results of this survey improved in 2016, but in 2017 the pass rate was again less than 80%.
In recent years, the photovoltaic industry has developed rapidly. With the continuous expansion of the scale of power stations, what the industry needs more is to improve the quality of power stations. As a core component of a photovoltaic system, the quality and performance of a photovoltaic grid-connected inverter is particularly important. Especially in the current outbreak of distributed photovoltaics, photovoltaic products have begun to enter thousands of households, and the quality of photovoltaic systems is related to the future development of the industry. Although the photovoltaic industry is developing rapidly, there is a certain degree of disorder and confusion, and the decline in the pass rate of photovoltaic grid-connected inverters seems to confirm this point.
Among all the components of the photovoltaic system, brackets, components, etc. can already achieve a service life of about 20 years, but the service life of photovoltaic inverters still needs to be improved. Today, as household photovoltaics are booming, since modules, inverters and other products are provided by different manufacturers, after-sales service for photovoltaic systems will become a big problem in the future. If the service life of photovoltaic inverters can reach about 20 years, it will bring about changes to the household photovoltaic market. China's photovoltaic inverters have been at the forefront of the world, and their prices have dropped significantly in recent years, down to about 0.2 yuan/W. I believe that with the continuous progress and innovation of various inverter companies, the future photovoltaic inverters will bring us surprises in terms of quality and performance.
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