The appearance of frequency converter simplifies the complex speed control. The combination of frequency converter and AC squirrel-cage induction motor replaces most of the work that can only be done by DC motor, which reduces the volume and maintenance rate and makes the transmission technology develop to a new stage.
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Classification of frequency converters:
1.Classification by input voltage level
Inverter can be divided into low-voltage inverter and high-voltage inverter according to the input voltage level. The common low-voltage inverters in China are single-phase 220V inverter, three-phase 220V inverter and I-phase 380V inverter. There are 6kV and 10kV transformers commonly used in high-voltage converters, and the control mode is generally changed by high-low high-frequency converter or high-high high-frequency converter.
2. According to the method of frequency conversion classification.
Frequency converters are divided into AC-AC frequency converters and AC-DC frequency converters according to frequency conversion methods.
AC-AC inverter can directly convert power frequency AC into AC with controllable frequency and voltage, so it is called direct inverter.
The AC-DC-AC frequency converter is also called indirect frequency converter, which first converts power frequency alternating current into direct current through rectifier device, and then converts direct current into alternating current with adjustable frequency and voltage.
3. According to the nature of DC power supply.
In AC-DC-AC inverter, DC power supply can be divided into voltage inverter and current inverter according to the process of converting main circuit power supply into DC power supply.
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