Abstract
Wireless control of modular multilevel converter (MMC) submodules can benefit from different points of view, such as lower converter cost and shorter installation time. In return for the advantages, the stochastic performance of wireless communication networks necessitates an advanced converter control system immune to the losses and delays of the wirelessly transmitted data. This article proposes an advancement to the distributed control of MMCs to be utilized in wireless submodule control. Using the proposed method, the operation of the MMC continues smoothly and uninterruptedly during wireless communication errors. The previously proposed submodule wireless control concept relies on implementing the modulation and individual submodule-capacitor-voltage control in the submodules using the insertion indices transmitted from a central controller. This article takes the concept as a basis and introduces to synthesize the indices autonomously in the submodules during the communication errors. This new approach allows the MMC continue its operation when one, some, or all submodules suffer from communication errors for a limited time. The proposal is validated experimentally on a laboratory-scale MMC.
Highlights
M ODULAR multilevel converters (MMCs) are widely used in high-voltage dc (HVdc) transmission applications as they can be scaled up to high voltage and power ratings using off-the-shelf power semiconductors
The implementation and operation of optical fiber cables might be quite challenging as the ratings and size of the MMC increase
The dimensions of MMC valve halls used in HVdc applications might range hundreds of meters [3]
Summary
M ODULAR multilevel converters (MMCs) are widely used in high-voltage dc (HVdc) transmission applications as they can be scaled up to high voltage and power ratings using off-the-shelf power semiconductors. The packet losses (communication errors) are resolved by decreasing the closed-loop current control bandwidth and using the last received index for modulation during the packet loss interval This treatment works fine for the losses in the range of a few transmission cycles, the submodules are unprotected for longer losses from tens to hundreds of transmission cycles. The proposed method relies on forming the insertion indices of the affected submodules in their own controllers based on the last fundamental period ac-side voltage or current phase angles before the loss instant. The proposed method can adapt to the changes in the received insertion indices in the last fundamental period before the packet loss. It is independent of the operating point of the submodules.
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