Sensitivity of Low-Voltage Variable-Frequency Devices to Voltage Sags

Abstract

Variable frequency drives (VFDs) are the types of power electronic device commonly used to drive motors with a wide range of industrial and practical applications, especially in power systems. VFDs are sensitive to voltage sag, thereby limiting their application. However, the difficulty in determining the detailed voltage sag tolerance characteristics of VFDs is due to various influencing factors, and the tolerance curve obtained from test results is updated as mainstream low-voltage VFDs change. This paper is the first to perform an in-depth analysis on the influence and operation mechanism of voltage sags on VFDs. Voltage sag types, which are regarded as the important influencing factors, are explored for their different impacts on VFDs from the perspective of energy. Then, eight commonly used low-voltage VFDs with small and medium powers (7.5 and 18.5 kW) are selected as the test objects. The influence of voltage sags on VFDs is tested, and the equipment parameters (protection modes and control modes of VFDs, and load torque and speed) and voltage sag characteristics factors (sag types, voltage magnitude before voltage sag, and harmonics) are considered. Finally, the general tolerance curves of the low-voltage VFDs under different sag types are extracted via comprehensive analyses and processing of more than 13 000 sets of test data. Based on the test data, this paper further explores the influence of voltage sag on the motor by using the permanent magnet synchronous motor (PMSM) as an example, which is used as the load during the tolerance test. Operation performance of the PMSM driven by different VFDs is also discussed.

Keywords

• Variable frequency drive
• voltage sag
• tolerance curve
• PMSM