A frequency transformer (VFD) is a motor control device that drives a motor by adjusting the frequency and voltage of the power supply. The VFD can also control acceleration during motor startup or deceleration during stop. Frequency transformer are also known as adjustable speed drivers, adjustable frequency drivers, variable frequency drivers, variable speed drivers, frequency transformer, inverters and power converters.

Because transformer are widely used in industry, there are many different types of transformer. Many single-phase and three-phase transformer have been developed for a wide range of applications. The differences of various types of inverter include: frequency and voltage control mode is different; The difference of harmonic suppression technology. The three major frequency conversion designs used in the inverter include: pulse width modulation (PWM), current source inverter and voltage source inverter. The most common is PWM technology. PWM technology requires that the inverter's power inverter device - the transistor or insulated-gate bipolar transistor (IGBT) - be turned on and off several times to achieve the right level of the voltage's mean square value (RMS). PWM technology is to change the output frequency and output voltage by modulating the pulse width.

The frequency transformer changes the output voltage frequency and amplitude to change the speed, power and torque of the connected induction motor to meet the load conditions. Although the specific configuration of the various parts of the inverter may vary from manufacturer to manufacturer, the basic structure is the same. The rectifier section consists of a set of fast switches that convert the input AC voltage source into a pulsating DC voltage. The intermediate circuit consists of a DC bus and associated circuits to stabilize and smooth the pulsating rectifier output. The DC bus voltage is approximately 1.414 times that of the input AC supply voltage, depending on the design type. The DC bus voltage can be used by the inverter part, and the inverter part synthesizes the AC sine wave voltage output from the DC bus voltage.

The key reason for improving the speed control equipment is to save energy and protect the environment, and the transformer can provide an optimal solution to control the motor speed to adapt to the load requirements. Fine-tuning the motor speed can significantly change energy consumption.