Harmonic content analysis of a soft starting variable frequency motor drive based on FPGA

As the demands for electric vehicles, electric aircrafts, unmanned aircraft systems, and other motor-driven systems increase, high-performance motor drives employing variable frequency control with higher efficiency and reliability are becoming increasingly important parts of the ever-changing technological landscape. This study proposes a Field Programmable Gate Array (FPGA)-based variable frequency soft-starting motor drive for a three-phase induction motor. Variable frequency drive is realized by employing Direct Digital Synthesis (DDS) technique. Gradually increasing the modulation index during the startup enables the soft start of the induction motor to limit the inrush current and controlling the soft-start period enables the reduction of the peak in-rush current. Digilent Arty A7-35T Artix-7 FPGA Development board is used to realize the proposed motor drive. The performance of three different Pulse Width Modulation (PWM) techniques—Sinusoidal PWM, Third Harmonic Injected PWM, and Space Vector PWM are analyzed and compared. The proposed architectures require only a small fraction of the FPGA's resources. The inverter output voltage and the load currents are analyzed for the harmonic contents using MATLAB. In the experimental realization, a four-pole squirrel cage delta-connected induction motor is utilized with a switching frequency of 4 kHz. The current and voltage characteristics of the induction motor are studied under different operating conditions to study harmonic contents and the effect of changing soft-start duration. The findings demonstrate a low-cost, flexible control of the induction motor with improved harmonic performance.