Variable frequency drive (VFD) is a power control device that applies frequency conversion technology and microelectronics technology to control AC motors by changing the frequency of the motor's operating power supply. The frequency conversion process mainly involves the following key steps: 1. Rectification process
Rectification is the first step in frequency conversion of a frequency converter, which aims to convert the input alternating current (AC) into direct current (DC). The rectification part is usually composed of a three-phase bridge uncontrolled rectifier, which uses a diode bridge to limit the movement of the AC sine wave in only one direction, thereby converting the AC waveform into a DC waveform. 2、 Filtering process
In the rectified DC voltage, there is a pulsating voltage with a frequency six times that of the power supply. In order to suppress this voltage fluctuation, the filtering element in the frequency converter will use inductors and capacitors to absorb pulsating voltage (current). The function of the filtering process is to ensure the stability of the DC voltage and provide a smooth DC power supply for the subsequent inverter process. 3、 Inverse process
Inverter is a key step in the frequency conversion of a frequency converter, which aims to convert direct current (DC) back into alternating current (AC), and the frequency and voltage of this AC can be controlled. The inverter section is usually composed of IGBT (Insulated Gate Bipolar Transistor) three-phase bridge inverters, which use high-speed switching transistors to create DC "pulses" that simulate all three phases of AC sine waves. The width and height of these pulses determine the voltage and frequency of the wave. Modern frequency converters typically use pulse width modulation (PWM) technology to regulate voltage and frequency, thereby achieving precise frequency control. 4、 Control process
The control process is the core of variable frequency control implemented by the frequency converter. It usually consists of an arithmetic circuit, a voltage/current detection circuit, a driving circuit, a speed detection circuit, and a protection circuit. The operation circuit is responsible for comparing external speed, torque, and other commands with the current and voltage signals of the detection circuit to determine the output voltage and frequency of the inverter. The voltage/current detection circuit is used to detect the voltage and current of the main circuit, ensuring the safe operation of the frequency converter. The driving circuit is used to drive the conduction and turn off of the main circuit components. The speed detection circuit is used to detect the speed of the motor and adjust the speed of the motor based on instructions and calculation results. The protection circuit is used to detect parameters such as voltage and current of the main circuit, and take timely measures to protect the inverter and motor when abnormal conditions such as overload or overvoltage occur.
The frequency converter achieves precise control of the AC motor power frequency through processes such as rectification, filtering, inversion, and control, thereby achieving the goals of speed regulation and energy conservation.