Isolation Techniques for Medium-Voltage Adjustable Speed Drives: Drive Topologies for Maintaining Line-Side Performance

Abstract

Compression and pumping applications represent a majority of all rotating machinery in modern industrial plants. In the past two decades, electric motors have been replacing turbines as the prime mover of choice for large rotating equipment at an increased rate. The use of electrically driven equipment is widespread even for critical applications. As semiconductor technology evolves, adjustable speed drives (ASDs) gain favor as the best option for both motor starting and speed control. Volume, pressure, and flow are adjusted by varying the speed of electric motors, even in motors that are larger than 50,000 hp. Multiple medium-voltage (MV) ASD topologies exist today that offer excellent motor performance. One of the key topics of discussion among specifiers and end users concerns the effects of ASDs on the utility line. Several methods for improving line-side performance use incoming isolation transformers, but some do not. It is often not clear when drive isolation transformers (DITs) should be used and which converter topology should be employed. This article is a guide to drive isolation techniques and major types of converters for various topologies of MV ASDs. It briefly explores the theory, advantages, and disadvantages of each configuration and application with considerations for selecting the optimal drive isolation technique.