Data-driven energy models for existing VFD-motor-pump systems

Efficiency deterioration and inappropriate control can degrade the energy performance of motor-driven pump and fan systems. Since variable frequency drives (VFDs) are widely applied, variable frequency and voltage power makes the motor power calculation more complicated. Simple and accurate energy models are essential to identify the efficiency deterioration and develop the optimal control of these motor-driven systems. The purpose of this paper is to develop and validate simple energy models for existing VFD-motor-pump (VMP) systems driven by actual operating data to determine the system input power using either the VFD output frequency or motor shaft power along with the pump flow rate and head. First, two drive system efficiency models are simplified for VMP systems by consolidating correlated VFD output frequency, voltage, and motor shaft power; and then the developed energy models are calibrated and validated using measured operating data in an existing VMP system with the rated motor load of 15kW. The experimental data shows that the VFD output frequency was exactly correlated to the VFD output voltage and approximately correlated to the motor shaft power in the studied system. Moreover, the developed energy models can accurately determine the system input power with a standard deviation of 0.11kW.