Frequency-domain transfer function of digital multirate controller with current estimator

A multirate controller with a current estimator is a recent but useful control technology. This scheme has less phase loss due to a zeroth-order-hold (ZOH) and controller discretization in comparison to the continuous form as compared to the single-rate scheme. This brief presents the modeling of the frequency-domain transfer function of a multirate controller with a current estimator. Based on this model, the control engineer can evaluate the open-loop response in terms of phase margin, gain margin, open-loop gain crossover, and so on. This brief applies the model to a hard disk drive (HDD) servo control. The experimental data accurately match the model responses.