Full Discrete Modeling, Controller Design and Sensitivity Analysis for High Performance Grid-Forming Converters in Islanded Microgrids

Recent works have shown that state-feedback decoupling of capacitor voltage allows for drastic bandwidth enlarging of current controllers for grid-former converters in islanded microgrids. Furthermore, Smith predictor and lead compensation have been also proved as very effective implementations for compensating the controller delays. These features are key to fulfil demanding requirements in terms of voltage regulation in islanded applications. This work deepens in the discrete-time domain modelling and implementation issues of the abovementioned techniques. A full discrete-time and sensitivity analyses reveal phenomena not properly modelled in previous works, which limits the performance: the presence of high-frequency oscillations due to discrete poles with negative real part. Subsequently, proper design countermeasures (i.e., limit bandwidth) are proposed. Discrete implementation of the voltage controller is also addressed, and design guidelines are provided. Experimental tests in accordance with the high demanding standards for UPS systems verify the theoretical analysis.