Digital communications for the control of modular multilevel converters

Abstract

Invented in 2001, the Modular Multilevel Converter (MMC) marked a leap in the technology for converting and controlling the electrical energy in high voltage levels. The MMC has gained much attention in both academy and industry ever since, and it has been widely studied. Nevertheless, the number of works that explore the use of digital communications in this application domain is limited. The digital communication employed to implement an internal control network simplifies the converter assemblage and maintenance; it also brings several benefits, such as the ability to adopt new control strategies or to parameterize the cells during operation. In this work, we investigate several aspects of high-speed digital communications for MMCs. It starts with a review of the operating principles and particular control characteristics of the Modular Multilevel Converter and the state-of-the-art of communication solutions for power electronic converters. We also discuss how the MMC and the internal network interact and influence both the design and operation of each other. Next, a codesign strategy for the control and communication makes possible to operate Ethernet-based ring networks with quasi-optimum Minimum Cycle Time, allowing the control algorithms to execute at the necessary high rates, what is especially difficult in converter with hundreds of cells. Following, we investigate the internal delay of Ethernet nodes and propose hardware accelerators for implementation in Field Programmable Array technology that can minimize the latency during the reception of packets. Finally, a model-based predictor compensates for the loop delay and overcome some of the limitations caused by the introduction of the network. We explain the predictor in mathematical terms, assess the influence of parameter variations, and present simulation and experimental results to demonstrate its effectiveness. After all, the thesis intends to make relevant contributions to the use of high-speed digital communications in Modular Multilevel Converters with a high number of cells, allowing at the same time all the benefits of such implementation without compromising the high performance of the system control