In summary, the functions include automatic operation and shutdown, maximum power point tracking (MPPT) control, protection against isolated operation (for grid-connected systems), automatic voltage regulation (for grid-connected systems), DC detection (for grid-connected systems), and DC grounding detection (for grid-connected systems). The automatic operation and shutdown function and the MPPT control function are briefly introduced below.
(1) Automatic operation and shutdown function
After sunrise, as solar radiation intensifies, the output of the solar cells increases accordingly. Once the output power required for the inverter to operate is reached, the inverter automatically starts running. Once operational, the inverter constantly monitors the output of the solar panels. As long as the output power of the solar panels exceeds the inverter's required output power, the inverter continues to operate until sunset, even on cloudy or rainy days. When the output of the solar panels decreases and the inverter output approaches zero, the inverter enters standby mode.
(2) Maximum power point tracking control function
The output of a solar cell module varies with the intensity of solar radiation and the module's own temperature (chip temperature). Furthermore, because solar cells exhibit a voltage decrease as current increases, there exists an optimal operating point where maximum power is obtained. Since solar radiation intensity is variable, this optimal operating point also changes. To ensure the system consistently draws maximum power from the solar cells while maintaining their operating point at the maximum power point, in relation to these variations, is called maximum power point tracking (MPPT) control. A key feature of inverters used in solar power systems is the inclusion of MPPT functionality.
Features of photovoltaic inverters:
(1) High efficiency is required. Due to the current high price of solar cells, in order to maximize the use of solar cells and improve system efficiency, it is necessary to find ways to improve the efficiency of the inverter.
(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 the inverter 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, overload protection, etc.
(3) A wide range of input voltage is required. The terminal voltage of solar cells varies with the load and solar radiation intensity. In particular, when the battery ages, its terminal voltage varies greatly. For example, the terminal voltage of a 12V battery may vary between 10V and 16V. This requires the inverter to operate normally within a wide range of DC input voltage.
