Analysis of common mode voltage-"neutral shift" in medium voltage PWM adjustable speed drive (MV-ASD) systems
Additional Document Info
In this paper analysis of common mode voltage or 'neutral shift' in the new emerging voltage source inverter type medium voltage adjustable speed drive (MV-ASD) systems is presented. Both Cascaded Multi-Level (CML) inverter and 3-level NPC inverter topologies are analyzed. An equivalent circuit model to determine the common mode voltage stress is presented. Analysis and simulation results are discussed and worst case common mode voltage excursion is computed for an example 800Hp, 4160V MV-ASD. It is shown that certain system components are excessively stressed and in the MV-ASD system these data are particularly useful in specifying system components and for proper design of the system. Possible effects of common mode voltage and its dv/dt on medium voltage motor bearings are discussed. A new multi-level PWM strategy is introduced which results in zero common-mode voltage. Simulation results are shown to illustrate the effectiveness of these schemes. Finally, experimental results from a 800hp, 4160V, MV-ASD system are presented.
name of conference
30th Annual IEEE Power Electronics Specialists Conference. Record. (Cat. No.99CH36321)