A novel method for the generalised analysis of variable speed drive systems

The authors describe a generalised linear model for variable speed drives. The powerful techniques developed in normal control theory can then be applied to this model so as to determine the modes of the system. These modes reveal whether a system is stable, close to the stability limit, or unstable. Further by transferring to the equivalent s domain, details of the frequency of the mode can be determined. By examining the participation matrix of the model, the relationship between the modes and the states can be surmised. It was noted that due to the formation of the model, as the fundamental period of the inverter changes, so does the sampling period of the model. Thus special precautions need to be taken when converting from the q discrete model to the continuous time model. Additionally the Δ space and associated δ discrete model was introduced to simplify the analysis