The principle of an inverter power supply: The circuit that converts direct current into alternating current is called an inverter circuit. In specific situations, the same thyristor converter circuit can be used for both rectification and inversion. When the inverter is working in the inverter state, if the AC side of the inverter is connected to the AC power source, and the DC power is inverted into AC power of the same frequency and sent back to the grid, it is called active inverter. If the AC side of the inverter is not connected to the power grid, but directly connected to the load, that is, the DC power is inverted into AC power of a certain frequency or adjustable frequency and supplied to the load, it is called passive inverter. Communication frequency conversion speed regulation works based on this principle. Active inverters are not only used in DC reversible speed control systems, but also in cascade speed control of AC wound rotor asynchronous motors and high-voltage DC transmission.