Modeling of multi-rate controller with current estimator

In the design of control systems, the control engineers need to compute the controller's frequency-domain model, based on which the openloop frequency response is obtainable when the measurement of the plant's frequency response is ready. Then the control engineers can tune or search the controller's parameters based on the performance indexes given by the desired and the designed openloop bandwidth, phase margin, gain margin, sensitivity function, etc. The recent control technology adopts multi-rate controller with current estimator. However, the frequency-domain model of this controller is not given in the existing literature. Hence this paper aims to model the frequency-domain transfer function of the multi-rate controller with current estimator. This paper applies the model to Hard Disk Drive (HDD) servo systems. The experimental data matches the model responses almost perfectly.

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