What are the classifications of solar photovoltaic inverters? Introduction of suitable inverters for different occasions

There are many ways to classify solar 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; 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 on grid system or off grid system, it can be divided into on grid inverter and off grid inverter. In order to facilitate optoelectronic users to choose inverters, only the inverters are classified here.

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, and field effect transistors are used for low power. At the same time, DSP is used. Converting the controller to improve the quality of the generated power, making it very close to the sine wave current, is generally used in the system of large photovoltaic power plants (>10kW). 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. The change of the way will lead to the reduction of the efficiency of the inverter process and the decrease of the energy of the electricity users. 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. The latest research direction is the use of space vector modulation control and the development of new topological connection of inverters to obtain high efficiency under partial load conditions.

2. String inverter

The string inverter is based on the modular concept. Each PV string (1-5kw) has the maximum power peak tracking at the DC side through an inverter, and is connected in parallel at the AC side. The most popular inverter on the market.
Many large photovoltaic power plants use string inverters. The advantage 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 photovoltaic modules 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 let one or several of them work under the condition that a single string of energy cannot make a single inverter work. , thereby producing more electricity.

3. Micro inverter

In a traditional PV system, about 10 photovoltaic panels are connected in series to the DC input end of each string inverter. When 10 panels are connected in series, if one does not work well, all the panels 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 PV 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.