Jul 05, 2024
Photovoltaic inverter, also known as power regulator, can convert the variable DC voltage generated by photovoltaic solar panels into AC power of mains frequency, which can be fed back to the commercial power transmission system or used for off-grid power grid.
1. Working principle of photovoltaic inverter
The inverter is mainly composed of switching elements such as transistors. By regularly switching the switching elements repeatedly on and off, the DC input is converted into AC output. Of course, the inverter output waveform generated by the open and close loop is not practical. Generally, high-frequency pulse width modulation is required to narrow the voltage width near the two ends of the sine wave and widen the voltage width in the middle of the sine wave, and always let the switching element move in one direction at a certain frequency within the half cycle, so as to form a pulse wave train. Then let the pulse wave pass through a simple filter to form a sine wave.
2. Function of photovoltaic inverter
Photovoltaic inverter not only has the function of direct-to-alternating conversion, but also has the function of maximizing the function of solar cells and system fault protection. In summary, there are active operation and shutdown functions, maximum power tracking control function, anti-independent operation function, active voltage adjustment function, DC detection function, and DC grounding detection function.
(1) Active operation and shutdown function
After sunrise in the morning, the intensity of solar radiation gradually increases, and the output of solar cells also increases accordingly. When the output power required by the inverter task is reached, the inverter automatically starts to operate. After entering operation, the inverter will monitor the output of the solar cell module at all times. As long as the output power of the solar cell module is greater than the output power required by the inverter task, the inverter will continue to operate; until the sunset, the inverter can operate even on rainy days. When the output of the solar cell module becomes smaller and the inverter output is close to 0, the inverter will form a standby state.
(2)Maximum power tracking MPPT function
(3)Detection and control function of island effect
During normal power generation, the photovoltaic grid-connected power generation system is connected to the power grid and transmits effective power to the power grid. However, when the power grid loses power, the photovoltaic grid-connected power generation system may continue to work and is in an independent operation state with the local load. This phenomenon is called the island effect. When the inverter has an island effect, it will cause great safety hazards to personal safety, power grid operation, and the inverter itself. Therefore, the inverter access standard stipulates that the photovoltaic grid-connected inverter must have the detection and control function of the island effect.
(4)Grid detection and grid connection function
Before the grid-connected power generation, the grid-connected inverter needs to take power from the grid, detect the voltage, frequency, phase sequence and other parameters of the power transmission of the grid, and then adjust its own power generation parameters to synchronize with the grid parameters. Only after completion will it be connected to the grid for power generation.
(5)Low voltage ride-through function
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