Abstract
The operation of single-phase Modular Multilevel Converter (MMC) is analyzed in the paper. A mathematical model of the converter is developed and described, based on which the structure and selection of parameters for Classical Control and Optimal Switching State Model Predictive Control (OSS-MPC) are defined. Additionally, the procedure for the determination of circuit parameters, such as submodule capacitance and arm inductance, is described and carried out. The listed control methods are designed and evaluated in Virtual Hardware-in-the-Loop together with single-phase MMC power circuit, regarding three control objectives: AC current control, voltage balancing control and circulating current control. Control methods are evaluated for both steady-state and transient performance and compared based on nine criteria: AC current reference tracking, THD of AC current and voltage, submodule capacitor voltage balancing, total submodule voltage control, circulating current magnitude and THD, number of control parameters and computational complexity. This is the first time that a fair comparison between Classical Control and MPC is considered in literature, resulting in superior performance of both control methods regarding four different criteria and the same performance regarding AC current reference tracking.
Highlights
In accordance with the ever growing energy demands, together with the depletion and combustion problems of fossil fuels, renewable energy sources, especially large offshore wind farms have gained maybe the most significant place in future energy systems
model predictive control (MPC) and classical modular multilevel converter (MMC) control, in addition to listed qualitative differences, which this paper aims to fill
Along with the power circuit, both Classical Control and Optimal Switching State Model Predictive Control (OSS-MPC) algorithms are designed in separate models
Summary
In accordance with the ever growing energy demands, together with the depletion and combustion problems of fossil fuels, renewable energy sources, especially large offshore wind farms have gained maybe the most significant place in future energy systems. The authors of [3] have presented the state of the art of MMCs regarding topologies, modeling and control methods, modulation techniques and applications. A review of operation and control methods for MMCs in unbalanced AC grids is provided in [4], while [5] presents the state of the art in model predictive control of high power MMCs. Considering AC-to-AC applications, the state of the art in relatively new power converter topology—modular multilevel matrix converters has been discussed regarding implementation issues and applications [6]. As stated in listed literature, the MMC is the preferable topology for high power and medium/high voltage energy conversion systems, because it offers modularity, voltage and current scalability, high efficiency with transformer—less operation, redundancy at low expenses and reduced output current ripple. The filter size is reduced, but because of their complexity, MMCs are challenging from the control standpoint
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