Abstract : This paper mainly explains the significant improvement in power factor achieved by using AC variable frequency drives (VSDs), while simultaneously reducing the further investment required for power factor compensation devices. Keywords : VSD; motor; power factor 1 Introduction AC asynchronous motors are commonly used in industrial production and tooling. However, compared to other types of loads, their power factor is relatively low, resulting in higher line current, which ultimately leads to additional heating of the line cables and transformers. The power factor is particularly low in applications involving very large motors operating under light loads. Using a VSD to control the motor speed can improve the power factor, thus reducing power losses in transformers and lines. In this way, AC drives can help managers save on the investment in power factor compensation devices. This paper mainly introduces the reasons why the input current is less than the output current after using a VSD, and compares the similarities and differences between AC drives and other speed control methods such as constant speed drives or DC drives. [b]2 Power Factor and Variable Frequency Drives 2.1 Differences between Power Factor and Cos[/b] Power factor (PF) is an important measurement indicator in electrical systems. It is defined as the ratio of actual power consumption (in kW) to the apparent power of the total system (in kVA). [b][align=center]For more details, please click: A Brief Discussion on the Effect of AC Variable Frequency Drives on Improving Power Factor[/align][/b]