Inverter is generally divided into photovoltaic (pv) grid inverter, home inverter, pure sine wave inverter,inverter the for caravan and other power equipment inverter . Off grid inverter the biggest characteristic is the high power, low cost system.
Off grid inverter generally used in large photovoltaic power station system, connecting multiple parallel pv group received the same concentration of inverter dc input, generally adopts three-phase IGBT power modules, the use of small power field effect transistor, and USES the DSP conversion controller to improve the quality of power, so that it is very close to the sine wave current.
Pure going wave makes each pv module connected to an inverter, each module has a single peak maximum power tracking, so that the module and inverter work better. It is usually used in photovoltaic power stations of 50W to 400w, and its total efficiency is lower than that of series inverters.
This increases the complexity of ac side connections and makes them difficult to maintain due to the parallel connection of ac. Another problem need to be solved is how to more effectively link power grid, a simple method is to communicate directly by ordinary socket connection, this can reduce the cost and equipment installation, but usually the grid safety standards may not be allowed to do so, power companies may object to connect directly to power generation equipment and the ordinary families user normal socket. Another safety-related factor requires the use of isolating transformers (high or low frequencies) or allows the use of transformerless inverters. Off the grid makes in photovoltaic (pv) grid inverter, glass curtain wall, solar grid inverter is the most widely used.
The core of the inverter device is the inverter switch circuit, referred to as the inverter circuit. The circuit completes the function of the inverter through the switch of the power electronic switch.
Features:
(1) efficiency needs to be improved.
Due to the high price of solar cells, in order to maximize the use of solar cells and improve the efficiency of the system, we must strive to improve the efficiency of the inverter.
(2) higher reliability is required.
At present, the photovoltaic power station system is mainly used in remote areas, many power plants unattended and maintain, inverter apparatus has reasonable circuit structure, strict element block, and demanded that the inverter has a variety of protection function, such as the input dc reverse polarity protection, ac output short circuit protection, overheating protection, overload protection, etc.
(3) the input voltage must have a wide range of adaptability.
The terminal voltage of the solar cell changes with the load and sunshine intensity, especially when the battery ages, the terminal voltage changes greatly, such as the 12V battery, the terminal voltage may vary between 10V and 16V, which requires the inverter to work normally within a large dc input voltage range.