Mitigating Current Spikes in VFD Induction Motor by Optimizing Motor Design and Control Parameters

Variable Frequency Drives (VFD) are used extensively in process plants to save energy. While there are advantages in operating pumps using VFD driven induction motors, issues crop up when there is a change in operating conditions. This paper analyzes one such issue that was faced in a hazardous chemical process plant. The currents of a 730 HP, 4-pole VFD driven induction motor-pump system were found to be spiking abnormally when operated at low frequency. To mitigate the problem, the system is tested at various low frequency conditions. Prony and Hilbert methods are used to analyze the current spikes. Intelligent optimization methods like Simulated Annealing, Genetic Algorithm, Particle Swarm Optimization and Artificial Bee Colony are used to redesign the motor so as to achieve sufficient power at low frequency. Using the optimal redesign values obtained thus, the Taguchi method is operated on the control to get the optimal control parameters for the VFD. The results obtained are compared with the practical values recorded in the test conditions. They are found comparable thus validating the optimization methodology used in this paper.