As an important part of photovoltaic power generation, the main function of the inverter is to convert the direct current generated by the photovoltaic module into alternating current. At present, the common inverters on the market are mainly divided into centralized inverters, string inverters and distributed inverters. So what are the characteristics of these three inverters?
1. The centralized inverter
The centralized inverter converts the DC power generated by the PV modules into AC power, and then boosts and connects to the grid. Therefore, the power of the inverter is relatively large. A centralized inverter of more than 500 kW is generally used in photovoltaic power plants.
1) The advantages of a centralized inverter are as follows:
a. High power, small quantity, easy to manage; few components, good stability, easy to maintain;
b. Low harmonic content, high power quality; complete protection function and high safety;
c. There are power factor adjustment function and low voltage ride-through function, and the power grid is well regulated.
2) The disadvantages of a centralized inverter are as follows:
a. The centralized inverter MPPT voltage range is narrow, and it is impossible to monitor the operation of each component. Therefore, it is impossible to make each component at the optimal working point, and the component configuration is not flexible;
b. The centralized inverter has a large area and requires a dedicated machine room, and the installation is not flexible;
c. The power consumption of the self and the ventilation and heat dissipation of the equipment room consume a large amount of electricity.
2. String inverter
The string inverter is a direct conversion of the direct current generated by the photovoltaic module into an alternating current, followed by boosting and grid connection. Therefore, the power of the inverter is relatively small. In the photovoltaic power station, a string inverter of 50 kW or less is generally used.
1) The advantages of the string inverter are as follows:
a. It is not affected by the difference between the modules of the string and the shadow occlusion, and at the same time, the optimal working point of the photovoltaic cell module is not matched with the inverter, and the power generation is maximized;
b. The MPPT voltage range is wide, and the component configuration is more flexible; in the rainy days, the foggy area is more, and the power generation time is longer;
c. Small size, small footprint, no need for a dedicated machine room, flexible installation;
d. Low self-consumption and low impact.
2) The disadvantages of the string inverter are as follows:
a. The power device has small electrical clearance and is not suitable for high altitude areas; there are many components, integrated, and the stability is slightly poor;
b. Outdoor installation, wind and sun exposure can easily lead to aging of the outer casing and heat sink;
c. The number of inverters is large, the total failure rate will increase, and the system monitoring is difficult;
d. Without isolation transformer design, electrical safety is slightly poor, and it is not suitable for negative electrode grounding system of thin film components.
3. The distributed inverter
The distributed inverter is a new inverter form proposed in the past two years. Its main features are “centralized inverter” and “distributed MPPT tracking”. The distributed inverter is a product that combines the advantages of both the centralized inverter and the string inverter. It achieves the low cost of the centralized inverter and the high power generation of the string inverter. ".
1）The advantages of a distributed inverter are as follows:
a. Compared with centralized, “distributed MPPT tracking” reduces the probability of mismatch and increases the amount of power generation;
b. Compared with the centralized and string type, the distributed inverter has a boost function, which reduces the line loss;
c. Compared with the string type, “centralized inverter” has more advantages in terms of construction cost.
2）The disadvantages of the distributed inverter are as follows:
a. Less engineering experience. Because it is a new form in the past two years. After all, the application of engineering projects is still a minority;
b. The characteristics of safety, stability and high power generation also need to go through the inspection of engineering projects;
c. Because of the “centralized inverter”, the large area and the disadvantages of the dedicated equipment room also exist in the distributed inverter.
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