Mathematical Modeling of a Digital Current Control Loop for Electrical Drives

Analysis of a digitally controlled current loop in a drive system is performed by a newly developed z-transform method that serves both the discontinuous and continuous case, and is verified by an interactive computer program based on system modeling. The assumption made is that the drive system has a sufficiently high mechanical inertia so that the current loop responds before the speed has changed. It is shown that under such conditions the transient response in discontinuous conduction can be approximated by a series of rectangular pulses, the heights of which are calculated by assuming that the current-time areas for the actual current increment and the equivalent pulse are equal. The results of the z-transform method agree well with those obtained from ditigal modeling.