Adopting frequency conversion technology and microelectronics technology, Variable-frequency Drive, a kind of power control, changes its working power frequency in order to control AC motor.

The VFD is mainly composed of rectification (AC to DC), filter, inverter (DC to AC), braking unit, drive unit, detection unit, micro-processing unit, etc.

Dependent on switching on or off internal IGBT, the VFD can adjust the voltage and frequency of output power supply. For the purpose of energy saving and speed adjustment, it can provide the power and voltage needed in accordance with practical demand of motors. Besides, it also supports many protection functions to avoid terrible consequences caused by overcurrent, overvoltage, overload and so on.

The working principle of VFD is to adopt circuit control to control main circuit, whose rectifier converts AC power into DC power that will be filtered and smoothed in DC intermediate circuit. Then the inverter finally converts the DC power into AC power of the required frequency and voltage. Some VFD will also add CPU and other components to perform necessary torque calculations.

The VFD is an electrical device that can convert power frequency into any frequency and any voltage, which is used to adjust the power and speed of motors. It can be divided into 2 parts: the control circuit and main circuit, and the latter is composed of rectifiers and inverters.

The power frequency of VFD is generally 50Hz or 60Hz, and its frequency and voltage remains the same regardless of being applied in domestic use or production use. Those motors which work at power frequency will cause power loss when adjusting speed. While after the adjustment of VFD, the motor can reduce loss.

As the requirement of industrial automation becomes enhanced and advocacy of energy conservation is prevailing , the VFD get an increasing application, such as in frequency conversion energy saving, automation system, improvement of crafting products qualities and motor soft starting.