Photovoltaic inverters are one of the important balance of system (BOS) components in photovoltaic array systems and can be used in conjunction with equipment supplied by general AC power. As the conversion equipment in a photovoltaic power plant, the photovoltaic inverter plays a vital role in the entire power plant.
The role of photovoltaic inverters
A photovoltaic inverter converts the direct current generated by photovoltaic modules into a sinusoidal current, which can be connected to a load or fed into the power grid. It is a core component of a photovoltaic power station system. An inverter can convert the variable DC voltage generated by photovoltaic (PV) solar panels into AC power at the mains frequency, which can be fed back to the commercial power transmission system or used by off-grid power grids.
Functions of photovoltaic inverters
Photovoltaic inverters not only have DC-AC conversion functions, but also active operation and shutdown functions, maximum power point tracking (MPPT) functions, islanding effect detection and control functions, grid detection and grid connection functions, and zero (low) voltage ride-through functions.
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's operation is reached, the inverter automatically starts operating. Once operational, the inverter continuously 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 (MPPT) function
When solar irradiance and ambient temperature change, the input power of photovoltaic (PV) modules exhibits a non-linear change. PV modules are neither constant voltage sources nor constant current sources; their power changes with the output voltage and is independent of the load. Their output current initially remains horizontal as the voltage increases, then decreases as the voltage rises to a certain level, and finally drops to zero when the module's open-circuit voltage is reached.
3. Detection and control functions for the island effect
During normal power generation, a grid-connected photovoltaic (PV) system is connected to the power grid, supplying effective power to it. However, when the grid loses power, the PV system may continue to operate independently of the local load; this phenomenon is known as islanding. Islanding in inverters poses significant safety hazards to personnel, grid operation, and the inverter itself. Therefore, grid connection standards stipulate that PV grid-connected inverters must have islanding detection and control functions.
4. Power grid detection and grid connection function
Before a grid-connected inverter can generate electricity, it needs to draw power from the grid, detect parameters such as voltage, frequency, and phase sequence of the grid power supply, and then adjust its own power generation parameters to be synchronized with the grid parameters before it can generate electricity.
