The Role of Photovoltaic Inverters in Solar Photovoltaic Power Generation Systems
An inverter is a device that converts direct current (DC) into alternating current (AC). Solar cells generate DC electricity under sunlight, and the electricity stored in batteries is also DC. However, DC power systems have significant limitations, as common household appliances such as fluorescent lamps, televisions, refrigerators, and fans operate on AC power and cannot be powered by DC sources. Therefore, to make photovoltaic power generation widely applicable in our daily lives, inverters that can convert DC into AC are indispensable.
As an essential component of photovoltaic power generation, the primary function of a photovoltaic inverter is to convert the DC electricity generated by photovoltaic modules into AC electricity. In addition to its DC-to-AC conversion function, an inverter also maximizes the performance of solar cells and provides system fault protection. The following sections briefly introduce the automatic operation and shutdown functions and the maximum power point tracking (MPPT) control function of photovoltaic inverters.
1. Maximum Power Point Tracking (MPPT) Control Function
The output of solar cell modules varies with the intensity of solar radiation and the temperature of the solar cells (chip temperature). Additionally, due to the characteristic that the voltage of solar cell modules decreases as the current increases, there exists an optimal operating point where maximum power can be obtained. Since the intensity of solar radiation is constantly changing, the optimal operating point is also changing. MPPT control continuously adjusts the operating point of the solar cell modules to ensure they always operate at the maximum power point, thereby maximizing the power output from the solar modules. The most significant feature of inverters used in solar power generation systems is the inclusion of the MPPT function.
2. Automatic Operation and Shutdown Function
In the morning, as the sun rises and the intensity of solar radiation gradually increases, the output of the solar cells also increases. Once the output power reaches the level required for the inverter to operate, the inverter automatically starts running. Once operational, the inverter continuously monitors the output of the solar cell modules. As long as the output power of the solar cell modules exceeds the required operating power of the inverter, the inverter continues to run; it remains operational until sunset or even during cloudy or rainy days. When the output of the solar cell modules decreases to near zero, the inverter switches to standby mode.
Besides the two functions described above, photovoltaic inverters also include other features such as anti-islanding protection (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). In a solar power generation system, the efficiency of the inverter is a crucial factor in determining the capacity of the solar cells and the battery.
