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A frequency converter (Frequency Inverter) is a device that controls the speed of a motor by adjusting the frequency of the motor power supply. The frequency conversion principle can be divided into the following steps:

Rectification stage: The input end of the frequency converter receives alternating current (AC), and first converts the AC into direct current (DC) through a rectifier circuit. Rectification circuits usually use components such as diodes or thyristors.

Filtering stage: The rectified DC is usually not stable enough, so the frequency converter will smooth the DC through a filtering circuit (usually a capacitor) to make it more stable.

Inversion stage: The smoothed DC is converted back to AC through an inverter circuit. The function of the inverter circuit is to quickly switch at high frequencies through switching elements (such as IGBT, MOSFET, etc.) to adjust the frequency and amplitude of the output AC. The control of this process is the key to the frequency converter, which can accurately adjust the output frequency.

Control stage: The control system of the frequency converter (usually a microprocessor or digital signal processor) controls the switching elements of the inverter circuit according to the frequency value set as required. By controlling the switching frequency, duty cycle, and phase of these switching elements, the frequency and amplitude of the output current can be changed, thereby adjusting the speed of the motor.

By changing the frequency of the AC power, the inverter can accurately control the speed of the motor, because the speed of the motor is proportional to the input power frequency. For example, at a frequency of 50Hz, the speed of the motor may be 1500 rpm, while at 60Hz it may reach 1800 rpm.

In general, the inverter controls the running speed of the motor by changing the power supply frequency and voltage, achieving energy saving, speed regulation and other functions.