Abstract
This paper presents the design and implementation of a digital control system for modular multilevel converters (MMC) and its use in a 5 kW small-scale prototype. To achieve higher system control reliability and multi-functionality, the proposed architecture has been built with an effective split of the control tasks between a master controller and six slave controllers, one for each of the six arms of the converter. The MMC prototype has been used for testing both converter and system-level controls in a reduced-scale laboratory set up of a Multi-Terminal DC transmission network (MTDC). The whole control has been tested to validate the proposed control strategies. The tests performed at system level allowed exploration of the advantages of using an MMC in a MTDC system.
Highlights
Due to the energy challenges the world is facing today, the interest in the integration into the utility grids of renewable energy sources has significantly increased in recent years
A distributed architecture of the controller requires an effective synchronization of all arm controllers, to ensure that the gates signals of all submodules are synchronized
A non-dead band voltage control [37] has been implemented on VSCDELTA and VSCGAMMA converters while the modular multilevel converters (MMC) controls the power injected in the AC grid
Summary
Due to the energy challenges the world is facing today, the interest in the integration into the utility grids of renewable energy sources has significantly increased in recent years. Many technical challenges must be tackled to allow their large-scale use Among these challenges, the lack of a standardized grid code for interconnecting adjacent HVDC systems [10], the DC faults protection management [11,12], the experimental validation of system control strategies to ensure power flow and DC voltage control can be cited. In [22], a hybrid small-scale prototype is proposed for Alternate Arm Converter (AAC) and MMC Considering all these previous studies, it is obvious that, given the large number of submodules used to form the whole structure of an MMC [6], the complex command and control schemes require efficient architectures.
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