On the Efficiency of Voltage Source and Current Source Inverters for High-Power Drives

The energy performance of various types of voltage-source and current-source converters is examined. For fairness and completeness, efficiency is calculated for three major battleground scenarios. The first is a low dynamic nonregenerative group of applications such as pumps, fans, and compressors. This group represents 85% of high power (2 MW) industrial applications where energy savings are usually a primary consideration justifying investment. The second scenario considers applications requiring good dynamic response and regenerative braking. Finally, the third group considers very high power applications (over 20 MW). The evaluation presented takes into account semiconductor switching and conduction losses, losses in the medium voltage feeding transformer (determined per IEEE Standard C57.18.10-1998), and the losses in ac and dc filters. For purposes of analysis, computer simulations validated against measurements taken on a 1-MW voltage source inverter (VSI) and a 1.4-MW current source inverter (CSI) were used. The results of the first scenario show competitive efficiencies for VSI and CSI drives, whereas voltage source-based solutions are more energy efficient in the second scenario considered. For the last group, the current source load-commutated inverter exhibits the best performance.

I. Introduction

Recent advancement in power semiconductors technology has seen insulated gate bipolar transistors (IGBT) and integrated gate commutated thyristors (IGCT) rapidly replace gate turn-off thyristors (GTO) in high-power applications [1]–[3]. IGBTs and GCTs presently have a voltage blocking capability of up to 6 kV, with saturation voltages ranging between 3 and 4.5 V and 2 and 3 V, respectively. Thus, they can switch at frequencies up to 1 kHz, enabling their usage in high power medium-voltage adjustable speed drives (ASD) in numerous industrial processes [4].