Classification of photovoltaic inverters
There are many ways to classify inverters. For example, according to the number of phases of inverter 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 different principle of the inverter circuit, it can also be divided into self-excited oscillation inverter, ladder wave superposition inverter and pulse width modulation inverter. According to the application in the grid-connected system or the off-grid system, it can be divided into grid-connected inverters and off-grid inverters. In order to make it easier for photovoltaic users to choose inverters, here we only classify them according to the different applicable occasions of inverters.
1. Centralized inverter
Centralized inverter technology is that several parallel photovoltaic strings are connected to the DC input terminal of the same centralized inverter. Generally, three-phase IGBT power modules are used for high-power ones, field-effect transistors are used for low-power ones, and DSP is used at the same time. Inversion controllers improve the quality of the generated electrical energy so that it is very close to a sinusoidal current, typically used in systems for large photovoltaic power plants. The biggest feature is the high power and low cost of the system, but because the output voltage and current of different photovoltaic strings are often not completely matched (especially when the photovoltaic strings are partially blocked due to cloudy, tree shade, stains, etc.), centralized inverter The way of inversion will lead to a decrease 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 status of a certain photovoltaic unit group.
2. String inverter
The string inverter is based on the concept of modularization. Each photovoltaic string passes through an inverter, which has the maximum power peak tracking at the DC end, and is parallel-connected to the grid 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 the system cost, but also increase the reliability of the system. 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 let one or several of them work when the power of a single string cannot make a single inverter work. Thus producing more electricity.
3. Micro inverter
In a traditional photovoltaic system, about 10 photovoltaic panels are connected in series to the DC input end of each string inverter. When one of the 10 battery panels connected in series fails to work well, the string will be affected. If the same MPPT is used for multiple inputs of the inverter, each input will also be affected, greatly reducing power generation efficiency. In practical applications, various blocking factors such as clouds, trees, chimneys, animals, dust, ice and snow will cause the above factors, and the situation is very common. In the micro-inverter photovoltaic system, each panel is connected to a micro-inverter, and when one of the panels fails to work well, only this one will be affected. The other photovoltaic panels will all be running at their best, making the overall system more efficient and producing more electricity. In practical applications, if the string inverter fails, it will cause several kilowatts of battery panels to fail to function, while the impact caused by the failure of the micro-inverter is quite small.
4. Power optimizer
The installation of a power optimizer in a solar power generation system can greatly improve conversion efficiency, simplify inverter functions and reduce costs. In order to realize a smart solar power generation system, the device power optimizer can indeed make each solar cell play the 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. By simplifying the circuit and a single solar cell corresponds to a power optimizer, the power optimizer performs an extremely fast best power point tracking scan in an analog way, so that each solar cell can indeed achieve the best power point tracking , In addition, the battery status can be monitored anytime and anywhere by using a communication chip, and the problem can be reported immediately so that relevant personnel can repair it as soon as possible.
