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The conversion rate of a photovoltaic inverter refers to the efficiency with which the inverter converts the electricity generated by the solar panel into electricity. In the photovoltaic power generation system, the inverter plays the role of converting the direct current generated by the solar panel into alternating current, and transmits the alternating current to the power company grid. The conversion efficiency of the inverter is high, and the electricity for self-use and sale can Increase.
Grid-connected inverters currently on the market use many different technologies, including the use of newer high-frequency transformers, traditional power-frequency transformers, or transformerless architectures. The high-frequency transformer does not directly provide 120 V or 240 V AC power, but has a multi-step program controlled by a computer to convert the power to high-frequency AC, then to DC, and finally to the voltage and frequency required by the power supply.
In the past, there were some doubts about systems that did not have a transformer and needed to supply power to the grid. The main reason was that there was no galvanic isolation between the DC circuit and the AC circuit. If the DC terminal failed, a large current would flow to the AC terminal. However, since 2005, the National Electrical Code of the National Fire Protection Association (NFPA) allows transformerless inverters. VDE 0126-1-1 and IEC 6210 have also allowed and defined the security mechanisms required by such systems. First, a residual current or ground circuit is required to detect abnormal short-circuit conditions, and an insulation test is also performed to confirm the separation between the DC circuit and the AC circuit.
An inverter converts DC power to AC power for feeding back to the grid. The frequency of the output voltage of the grid-connected inverter needs to be the same as the grid frequency (50 or 60 Hz), which is generally achieved by the oscillator in the machine, and the output voltage is also limited not to exceed the grid voltage. Modern high-quality grid-connected inverters can have an output power factor of 1, which means that the output voltage and current phases are the same, and the phase difference between them and the grid voltage is within 1 degree. There is a microprocessor in the inverter that can sense the AC waveform of the grid, and according to this waveform, generate voltage and send it back to the grid. However, the electricity sent back to the grid needs to have a certain proportion of reactive power, so that the power of the nearby grid is within the allowable limit. noon) its voltage may rise too high.
If the power of the grid is cut off, the grid-connected inverter needs to be disconnected from the grid quickly. This is a regulation of the National Electrical Code (NEC) in the United States to ensure that when the grid is out of power, the grid-connected inverter will not provide power to the grid, and at this time the workers who maintain the grid will not be electrocuted.
Properly configured, grid-tie inverters allow a home to use alternative energy sources that it generates itself (such as solar or wind power) without cumbersome wiring and without the need for batteries. If there is insufficient alternative energy, the insufficient part will still be provided by electricity from the grid.
In general, many solar inverters are designed to be connected to the grid. If the grid is not detected, the inverter will not operate. This type of inverter also has a special circuit to precisely match the magnitude, frequency, and phase of the output voltage with the power supply, so that the best conversion efficiency of the inverter can be exerted and more energy can be saved.
