WEG Technical Guide: Induction Motors Supplied by PWM Frequency Inverters

This in-depth technical guide from WEG explores the principles, benefits, and challenges of operating low-voltage induction motors with PWM (Pulse Width Modulated) frequency inverters. Covering everything from harmonics and efficiency to cable recommendations and real-world examples, the document is a comprehensive resource for engineers, installers, and operators seeking to optimize motor performance in variable speed drive (VSD) applications.

Key Points

  • Standards Overview: The guide references key standards including NEMA MG1, IEC 60034, and GAMBICA/REMA for inverter-fed motors and system performance expectations.
  • Efficiency Considerations: Discussion on motor efficiency under PWM supply, including the impact of speed variation and switching frequency on energy losses.
  • Bearing Protection: Covers common-mode voltages and methods to mitigate bearing currents, including grounding brushes and insulated bearings.
  • Application Examples: Real-world dimensioning cases in industries like textiles, pumping, and compressors, showing torque, thermal, and electrical evaluations.
  • System Interactions: Detailed analysis of how PWM inverters interact with motors, AC lines, and loads—impacting harmonics, efficiency, and insulation requirements.
  • Insulation Design: Technical explanation of rise time, cable effects, corona discharge, and standards-based insulation design to handle inverter-induced stress.
  • Noise and Vibration: Insight into increased acoustic noise and mechanical vibration from inverter operation, and criteria for mitigation per IEC and NEMA.
  • Cable Recommendations: Clear guidelines for cable types, shielding, and reactor/filter use to reduce EMI and protect motor lifespan.