In the photovoltaic power generation system, the proportion of photovoltaic inverter is not large, only about 5% to 8%, it is generally believed that the main role of photovoltaic inverter is to convert direct current into alternating current, as everyone knows, solar inverter in the photovoltaic system, not only to change the direction of the power supply, but also to play a number of very important roles, such as diagnosing photovoltaic modules and lines. Disconnect the circuit in time of danger, record the daily operating status, and send and receive information externally.

1. Overview of the inverter

Inverter is a power adjustment device composed of semiconductor devices, mainly used to convert DC power into AC power, generally by the boost circuit and inverter bridge circuit. The boost circuit increases the DC voltage of the solar cell to the DC voltage required for the output control of the inverter; The inverter bridge circuit converts the DC voltage after voltage boost into the AC voltage of common frequency equivalent.

2. Classification of inverters

Inverter classification methods are many, according to the nature of the source can be divided into active inverters and passive inverters, according to the inverter input AC voltage phase number can be divided into single-phase inverters and three-phase inverters, according to different uses, can be divided into off-grid inverters and grid-connected inverters.

3. Working principle of the inverter

The core of the inverter is the inverter switching circuit (referred to as the inverter circuit). This circuit can complete the function of inverter by switching on and off the power electronic switch.

4. Characteristics of the inverter

1. High efficiency is required: Due to the high price of solar cells at present, in order to maximize the use of solar cells and improve system efficiency, we must try to improve the efficiency of the inverter.
2. High reliability is required: At present, the photovoltaic power station system is mainly used in remote areas, and many power stations are unattended and maintained, which requires the inverter to have a reasonable circuit structure, strict component screening, and requires the inverter to prepare a variety of protection functions, such as: input DC polarity reverse protection, AC output short-circuit protection, overheating, overload protection.
3. The input voltage is required to have a wide range of adaptation: Because the terminal voltage of the solar cell changes with the load and sunshine intensity. Especially when the battery aging its terminal voltage change range is large, such as 12V battery, the terminal voltage may change between 10V to 16V, which requires the inverter in a large DC input voltage range to ensure normal operation.

5. Functions of the inverter

The inverter not only has the function of direct AC conversion, but also has the function of maximizing the performance of the solar cell and the function of system fault protection. It has automatic operation and shutdown function, maximum power tracking control function, anti-separate operation function (for grid-connected systems), automatic voltage adjustment function (for grid-connected systems), DC detection function (for grid-connected systems), DC grounding detection function (for grid-connected systems).