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Classification of photovoltaic inverters

Views: 193     Author: Site Editor     Publish Time: 2022-07-26      Origin: Site

There are many ways to classify inverters. For example, according to the number of phases of the inverter's output AC voltage, it can be divided into single-phase inverters and three-phase inverters. According to the different types of semiconductor devices used in the inverter, it can be divided into transistor inverters, thyristor inverters and turn-off thyristor inverters. According to the principle of the inverter circuit, it can also be divided into self-excited oscillation inverter, stepped wave superposition inverter and pulse width modulation inverter. According to the application in grid-connected system or off-grid system, it can be divided into grid-connected inverter and off-grid inverter. In order to facilitate optoelectronic users to choose inverters, here only the inverters are classified according to the different applicable occasions.

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1. Centralized inverter

The centralized inverter technology is that several parallel photovoltaic strings are connected to the DC input end of the same centralized inverter. Generally, three-phase IGBT power modules are used for high power, field effect transistors are used for low power, and DSP is used at the same time. Converting the controller to improve the quality of the power produced, making it very close to a sine wave current, is typically used in systems for large photovoltaic power plants. The biggest feature is that the power of the system is high and the cost is low, but because the output voltage and current of different PV strings are often not completely matched (especially when the PV strings are partially blocked due to cloudy, shade, stains, etc.), the centralized inverter is adopted. Changing the way will lead to a reduction in the efficiency of the inversion process. At the same time, the power generation reliability of the entire photovoltaic system is affected by the poor working state of a photovoltaic unit group.

2. String inverter

The string inverter is based on the modular concept. Each PV string passes through an inverter, has the maximum power peak tracking at the DC end, and is connected to the grid in parallel at the AC end. It has become the most popular in the international market. inverter.

The advantage of the string inverter is that it is not affected by module differences and shading between strings, and at the same time reduces the mismatch between the optimal operating point of the photovoltaic module and the inverter, thereby increasing the power generation. These technical advantages not only reduce system cost, but also increase system reliability. At the same time, the concept of "master-slave" is introduced between the strings, so that the system can connect several groups of photovoltaic strings together, and make one or several of them work when the power of a single string cannot make a single inverter work. Thereby producing more electricity.

3. Micro inverter

In a traditional photovoltaic system, the DC input end of each string inverter is connected in series by about 10 photovoltaic panels. When one of the 10 series-connected panels does not work well, this string will be affected. If the same MPPT is used for multiple inputs of the inverter, then each input will also be affected, greatly reducing the power generation efficiency. In practical applications, various occlusion factors such as clouds, trees, chimneys, animals, dust, ice and snow will cause the above factors, and the situation is very common. In the photovoltaic system of the micro-inverter, each panel is connected to a micro-inverter. When one of the panels fails to work well, only this one will be affected. All other photovoltaic panels will operate at their best, making the overall system more efficient and generating more power. In practical applications, if the string inverter fails, it will cause the panels of several kilowatts to fail to function, while the impact of the micro-inverter failure is quite small.

4. Power optimizer

The addition of a power optimizer to a solar power generation system can greatly improve the conversion efficiency, and simplify the inverter functions to reduce costs. In order to realize a smart solar power generation system, the device power optimizer can really make each solar cell perform its best performance, and monitor the battery consumption status at any time.

The power optimizer is a device between the power generation system and the inverter, and its main task is to replace the original optimal power point tracking function of the inverter. The power optimizer performs extremely fast optimal power point tracking scanning by analogy by simplifying the circuit and a single solar cell corresponds to a power optimizer, so that each solar cell can truly achieve the optimal power point tracking , In addition, the battery status can be monitored anytime and anywhere by inserting a communication chip, and the problem can be reported immediately so that the relevant personnel can repair it as soon as possible.

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