Grid-connected inverters are generally classified into photovoltaic grid-connected inverters, wind power grid-connected inverters, power equipment grid-connected inverters, and other power generation equipment grid-connected inverters. The biggest advantages of grid-connected inverters are high system power and low cost.
Grid-connected inverters are generally used in large photovoltaic power plant systems. Many parallel photovoltaic strings are connected to the DC input terminal of the same centralized inverter. Generally, high-power inverters use three-phase IGBT power modules, while low-power inverters use field-effect transistors. At the same time, DSP conversion controllers are used to improve the quality of the generated power, making it very close to the sinusoidal current.
Module inverters connect each photovoltaic module to an inverter, with each module having its own maximum power point tracking (MPPT), resulting in better module-inverter coordination. They are typically used in 50W to 400W photovoltaic power plants, and their overall efficiency is lower than that of string inverters.
Working principle and characteristics of grid-connected inverters
I. Working principle of grid-connected inverters:
The core of an inverter device is the inverter switching circuit, or simply the inverter circuit. This circuit performs the inversion function by turning on and off power electronic switches.
II. Characteristics of grid-connected inverters:
1. High efficiency is required.
Because solar cells are currently expensive, in order to maximize their utilization and improve system efficiency, it is necessary to find ways to improve the efficiency of inverters.
2. High reliability is required.
Currently, photovoltaic power station systems are mainly used in remote areas, and many power stations are unattended and unmaintained. This requires inverters to have a reasonable circuit structure, strict component selection, and various protection functions, such as input DC polarity reverse protection, AC output short circuit protection, overheat protection, and overload protection.
3. The input voltage should have a wide range of adaptability.
The terminal voltage of solar cells varies with load and solar radiation intensity. In particular, the terminal voltage of batteries can vary greatly as they age; for example, a 12V battery may have a terminal voltage that varies between 10V and 16V. This requires inverters to operate normally over a wide range of DC input voltages.
