Photovoltaic inverter (PV inverter or solar inverter) is an inverter that converts the variable DC voltage generated by photovoltaic (PV) solar panels into mains frequency alternating current (AC), which can be fed back to the commercial power transmission system or supply and disconnect Grid use of the net. Photovoltaic inverter is one of the important system balance (BOS) in photovoltaic array system, and it can be used with general AC power supply equipment. Solar inverters have special functions that cooperate with photovoltaic arrays, such as maximum power point tracking and islanding protection.

The core of the inverter device is the inverter switch circuit, referred to as the inverter circuit for short. This circuit completes the function of inverter by turning on and off the power electronic switch.

What are the protection functions of photovoltaic inverters

There are many ways to classify inverters. For example, according to the number of phases of the 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, Divided into transistor inverter, thyristor inverter and turn-off thyristor inverter, etc. According to the principle of the inverter circuit, it can 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 are only classified according to the application occasions of inverters.

What are the protection functions of photovoltaic inverters?

Centralized inverter technology is that a number of parallel photovoltaic strings are connected to the DC input 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. The conversion controller is used to improve the quality of the generated electric energy, making it very close to the sine wave current, which is generally used in the system of large photovoltaic power stations (>10kW). The biggest feature is the high power and low cost of the system. However, because the output voltage and current of different photovoltaic strings are often not completely matched (especially when the photovoltaic strings are partially shaded due to cloudy, shade, stains, etc.), a centralized The method of change will lead to a decrease in the efficiency of the inverter process and a decrease in 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 status of a photovoltaic unit group. The latest research direction is the use of space vector modulation control and the development of new inverter topology connections to obtain high efficiency under partial load conditions.

The string inverter is based on the modular concept. Each photovoltaic string (1-5kw) passes through an inverter, has maximum power peak tracking at the DC end, and is connected in parallel at the AC end. It has become an international 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 shadows between strings, and at the same time reduces the mismatch between the optimal working point of the photovoltaic module and the inverter, thereby increasing the power generation. These technical advantages not only reduce system costs, but also increase system reliability. At the same time, the concept of "master-slave" is introduced between the strings, which makes the system connect several PV strings together and let one or several of them work when a single string of electric energy cannot make a single inverter work. , Thereby producing more electricity.

The latest concept is that several inverters form a "team" to replace the "master-slave" concept, which makes the reliability of the system a step further. Currently, transformerless string inverters have taken the lead.

In the traditional PV system, the DC input end of each string inverter will be connected in series by about 10 photovoltaic panels. If one of the 10 panels connected in series does not work well, this string will be affected. If the inverter uses the same MPPT for multiple inputs, each input will also be affected, greatly reducing the power generation efficiency. In practical applications, various sheltering 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 does not work well, only this one will be affected. All other photovoltaic panels will run in the best working condition, 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, and the impact of the micro-inverter failure is quite small.

The installation of a power optimizer (OptimizEr) in the solar power generation system can greatly increase the conversion efficiency and simplify the inverter (Inverter) function to reduce costs. In order to realize a smart solar power generation system, the device power optimizer can ensure the best performance of each solar cell and monitor the battery consumption status at any time. The power optimizer is a device between the power generation system and the inverter. Its main task is to replace the original best power point tracking function of the inverter. The power optimizer uses analogy to perform extremely fast best power point tracking scans by simplifying the circuit and a single solar cell corresponds to a power optimizer, so that each solar cell can indeed achieve the best power point tracking In addition, you can also monitor the battery status anytime and anywhere by inserting a communication chip, report problems in real time, and allow relevant personnel to repair them as soon as possible.

What are the protection functions of photovoltaic inverters

The grid-connected photovoltaic power generation system consists of solar cell components, grid-connected inverters, metering devices and power distribution systems (as shown in the figure below. Solar energy is converted into DC power through solar cell components, and then the DC power is converted into grid-connected photovoltaic inverters. The sine wave current synchronized with the grid frequency and phase and feeds this power into the grid. The photovoltaic grid-connected inverter is the key equipment in the solar power generation system.