Variable Frequency Drive Working Principle

VFD Drive Technology Overview

Variable frequency drive technology is now mature and widely used in AC motors. Our variable frequency drives are versatile and provide a high degree of motor control, with motor speeds that can be precisely varied from zero rpm to over 100% of rated speed, while torque can be adjusted to suit.

Variable Frequency Drive Working Principle

Although there are many variations in variable frequency drive designs, they all provide the same basic function of converting an incoming fixed frequency and voltage power source to a variable frequency and variable voltage output to a motor with corresponding changes in motor speed and torque. Motor speed can vary from zero rpm to typically 100-120% of its full rated speed, while up to 150% of rated torque can be achieved at reduced speeds. The motor can run in either direction.

Variable frequency drives applied to AC motors are by far the most common. The basic variable frequency drive design consists of four elements:

1. Rectifier: A rectifier works by converting incoming alternating current (AC) power into direct current (DC).

2. Intermediate circuit: The rectified DC power supply is then conditioned in an intermediate circuit, usually through a combination of inductors and capacitors. Most VFDs on the market today use a fixed voltage DC link.

3. Inverter: The inverter converts the rectified and regulated DC power back to an AC power source of variable frequency and voltage.

4. Control unit: The control unit controls the overall operation of the inverter; it monitors and controls the rectifier, intermediate circuit, and inverter to provide the correct output in response to external control signals.

Variable frequency drives are typically 92-98% efficient, with 2-8% losses due to extra heat dissipation due to high-frequency electrical switching and extra power required by the electronics.

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