Control of Stacked Power Electronics Systems

Abstract

Series-connected power electronics converters are commonly used in applications where low-distortion multilevel waveforms are needed or the overall system voltage exceeds the ratings of the individual converter. Two notable use-cases are modular multilevel converters and solid-state medium-voltage transformers. In such systems, control is traditionally tackled via a centralized controller that communicates with each converter in the stack. Given the large number of converters in such a system, these approaches entail significant complexity and communication limits resilience to failures. In this paper, we introduce distributed controllers that can be executed on each converter and can be used to address challenges for both distortion mitigation and power-sharing among the converter stack. The first controller we consider operates at the switching timescale and utilizes a sample-and-hold operation and a basic proportional controller that yields automatic distortion minimization. Analysis demonstrates robustness from to limited sensor bandwidth and other practical issues. The second controller considered here is designed for decentralized synchronization and power sharing among the cascaded converters. This architecture allows for each unit in the stack to process non-uniform power if necessary and deliver power into a medium-voltage grid a near-unity power factor. After covering relevant models for both controllers, we conclude with experimental results.