Modeling and Control of DC Machines

The brushed DC machine, which derives its excitation flux from a field winding or permanent magnets, remains commercially relevant in the field of drives and it is prudent to consider the modeling and control of these machines. From a didactic perspective, there is decided merit in examining the brushed drive concept first. This approach provides the opportunity to introduce and demonstrate some basic modeling and control aspects, which are also highly relevant for AC drives that utilize rotating field machines. The introduction of an extended space vector based current source model of the machine, which builds on the simplified model given in the previous chapter, is both novel and helpful in the quest for building a field-oriented machine concept. The inversion of the current source field-oriented model, an approach which is one of the cornerstones of this book, is initially demonstrated for a brushed DC drive. In addition, attention will be given to the development of control strategies which ensure that drive operation is kept within the drive envelope dictated by voltage or current constraints. In this context, field weakening strategies for separately excited machines are introduced.