Investigation of the accuracy of VFD analog output data and the energy performance of different voltage controls in a VFD-motor-belt-fan system

Abstract Variable frequency drives (VFDs) are widely applied on induction motors to reduce electrical power by adjusting power frequency. Meanwhile VFDs also adjust power voltage based on different voltage controls, including a linear ratio, a squared ratio and a flux optimizer. Moreover, VFDs measure motor operating data, such as frequency, current, voltage and power, and provide them through their analog outputs. However, it is not clear whether the VFD analog output data are accurate and how the different voltage controls impact the drive system performance. The purpose of this paper is to investigate the accuracy of VFD analog output data and the energy performance of different voltage controls through an experiment conducted on a VFD-motor-belt-fan system. First the operating data provided by the VFD and measured by a power analyzer were compared, then the efficiencies of the motor-belt, VFD, and drive system among different voltage controls were measured and evaluated. The experiment results show that the VFD provides accurate frequency and current but inaccurate voltage and power. The squared ratio results in the highest drive system efficiency, 2–12% higher than the linear ratio and 0–2% higher than the flux optimizer, as the frequency varies from 35 to 20 Hz.