A Resonant Controller With High Structural Robustness for Fixed-Point Digital Implementations

This paper presents a new resonant (R) controller. The proposed R controller is input-output equivalent to the conventional R controller but it is internally nonlinear. Its internal state variables are the transformed versions of the conventional R controller into the polar coordinates. It is, thus, given the name of polar form resonant (PFR) controller. While the PFR is totally equivalent to the R controller in continuous-time domain, it offers a much higher structural robustness when it comes to digital implementations. Particularly, it is shown in this paper that the PFR resolves the well-known structural sensitivity of the R controller for applications that need high sampling frequency and have word length limitations. Such a structural sensitivity is conventionally resolved by resorting to the delta-domain realizations. The PFR offers an alternative method to the delta-domain realization technique with even higher degree of robustness and easier stage of adjustment. Moreover, the PFR can easily be enhanced to accommodate frequency variations, a feature that is not easily attainable using the delta-domain method. Feasibility of the PFR controller is verified using a laboratory prototype of a single-phase uninterruptible power supply system operating at high sampling and switching frequencies where the control system is implemented on a field programmable gate array board.