A Comparison of Adjustable-Speed Drive Systems: Voltage Source Inverters and Load-Commutated Inverters for High-Power Applications

The current development of adjustable-speed drives (ASDs) has made voltage source inverter (VSI) technology available to high-power applications, such as large axial compressors. Hence, the comparison of VSI technology to the traditional way of controlling large rotating equipment with load-commutated inverters (LCIs) is of interest. This article compares the ASD systems for shaft powers of 20 MW or more. A drive system includes the drive, the supply network connection, and the motor behavior. System reliability and availability are the main drivers, while system efficiency and costs are additional motivations for the technology positioning. In general, the simple scalability of the LCI leads to maximum reliability, especially for very high power. VSI technology comes with a higher degree of flexibility in terms of possible output frequencies, cable lengths, and types of motor.