Readers are familiar with grid-connected inverters. Off-grid inverters and grid-connected inverters are exactly the same in the main circuit, with the same capacitors, the same key components such as IGBTs. The 500KW and above grid-connected inverters used in the early large-scale ground power stations were all produced by Siemens, Emerson, Toshiba, Mitsubishi and other companies. These companies have ready-made UPS power supply production lines. UPS is an inverter, which is an off-grid inverter. The only difference is the control method. In layman’s terms, the driver programs that control the “how to turn on” and “how much to turn on” of the IGBT are different.
Use the three-phase inverter bridge module in the MATLAB module library to represent the main circuit of the inverter, the input port G of the main circuit represents the driver program writing port of the inverter IGBT module (A, B, C represent the three-phase output port, the left The positive and negative poles on the side represent DC input, and N represents DC 0 potential). The label Off represents the driver program written to the off-grid inverter, and the label grid represents the driver program written to the grid-connected inverter.
The output of the off-grid inverter is 220/380V voltage and 50Hz frequency within the precision range of this type of equipment. No matter how the power at the load terminal changes, the voltage frequency will not change. Table 1 shows the inverter parameters dedicated to Xiamen Kehua’s communication industry.
The output of grid-connected inverter is “slightly changed” 220/380V voltage and 50Hz frequency. Since the grid-connected inverter is connected to the grid, it needs to be consistent with the grid voltage and frequency within the “standard”. For example, the frequency can be adjusted within the range of 49.5-50.2Hz. When the voltage drops, there will be a short-term “low-voltage ride-through” requirement, and when the voltage rises, there will be a short-term “high-voltage ride-through” requirement.
Generally, tens of watts to less than 2KW are called small off-grid power generation systems, which are characterized by providing 12V or 24V DC power for users to use. 2KW-50KW is called a medium-sized off-grid system, which is characterized by providing single-phase 220V AC power for users. More than 50KW is generally called a large off-grid system, which is characterized by providing three-phase 380V AC power for users.