Fast Dynamic Control of Stacked Low Inertia Converters

This paper explains control challenges of stacked low inertia converters (SLIC) in detail and presents a novel control method called model prediction based priority switching control (MPPS) for such converters. Low inertia converters, which feature smaller dc storage, either dc-link capacitor or inductor, dramatically reduce cost, size, and weight compared to conventional power converters. However, due to the absence of the large de-link buffer, the decoupling between input and output is reduced, leading to significant control challenges. The control becomes even more challenging when these converters are stacked for high voltage applications, which brings up coupling between the modules besides the coupling within each module. The paper discusses this multi-objective, multi-degree of freedom control problem and points out challenges of employing conventional control, such as PI, to achieve fast and stable operation of the stacked low inertia converters. A control method called model prediction based priority switching (MPPS) control is proposed. The proposed MPPS control and PI control applied to modular soft-switching solid-state transformer (S4T), a representative of the stacked low inertia converters, are compared to verify the effectiveness of the proposed control method.