Harmonic measurement and analysis system for characterization of adjustable speed drives

Abstract

Variable speed drives, commonly employed for motor speed control, incorporate electronic converters that emit harmonics to both the power grid and the motor-load system. These harmonics can have adverse effects on the motors, necessitating the experimental measurement of their diverse and unpredictable harmonic content. To perform these measurements on the input side of the drives or power grid, commercial quality analyzers are available, but they are not prepared to perform these measurements on the motor-load or output side of the drive. The outputs of the drives generate a significant harmonic and interharmonic content across a wide range of low and high frequencies, coupled with variable fundamental frequencies. Consequently, the development of a specialized measurement system tailored to these signal characteristics becomes imperative. This paper presents a harmonic measurement and analysis system specifically designed for frequency inverter’s output signals, which adheres to international standards that standardize measurements and includes new features to evaluate converter signals not available in commercial meters. By utilizing this system, frequency groupings and distortion rates are obtained to comprehensively analyze the power quality of commercial drives under realistic operating conditions, thus enabling the early detection of potential failures and the implementation of preventive measures.