Working Principle Of Frequency Converter

A frequency converter is a power control device whose core principle is based on the proportional relationship between motor speed and power supply frequency (for AC asynchronous motors: n = 60f/p, where n is the speed, f is the frequency, and p is the number of pole pairs).

Core Task

Converting the constant AC power supplied by the power grid into AC power with adjustable frequency and voltage required by the motor, thereby precisely controlling the motor's speed and torque.

Basic Working Principle of a Frequency Inverter: Core Process: AC-DC-AC Conversion
1. Rectification (AC to DC)
Input: The frequency inverter receives AC power at a fixed voltage and frequency (50Hz or 60Hz) from the power grid.
Process: The internal rectifier circuit converts the input AC power into pulsating DC power.
Key Component: Rectifier module.

2. DC (Filtering and Energy Storage)
Process: The pulsating DC power is smoothed by the filter capacitors (and reactors) on the DC bus, becoming stable DC power with less ripple.

Function: Eliminating voltage fluctuations and storing energy.

3. Inversion (DC to Adjustable AC)
Through the inverter (using power switching devices such as IGBTs), under the control of the control circuit, these IGBTs are regularly switched on and off at extremely high frequencies (e.g., thousands to tens of thousands of hertz).

Key Technology: PWM (Pulse Width Modulation) control, simulating a sine wave output by adjusting the switching frequency.

4. Control
Core Control: V/F Control
Maintains a constant voltage-to-frequency ratio, ensuring stable motor flux. Suitable for applications with low precision requirements, such as fans and pumps.
Vector Control
Decomposes the torque and magnetic field components of the motor current using algorithms, achieving precise torque control similar to a DC motor. Suitable for high-precision speed regulation, such as in lifting equipment and machine tools.
Direct Torque Control
Directly controls the motor's torque and flux linkage, offering fast dynamic response and suitable for high-speed impact loads.

Core Components
Rectifier Unit: Converts AC to DC.
DC Bus: Filters and stores energy.
Inverter Unit: Converts DC to variable frequency AC.
Control Unit (CPU): Processes signals and generates PWM waveforms.
Detection Circuit: Monitors voltage, current, temperature, etc.