MMC front-end for klystron modulators: an augmented modulation scheme for arm balancing

Jankovic, Marija and Costabeber, Alessando and Watson, Alan James and Clare, Jon C. and Aguglia, Davide (2018) MMC front-end for klystron modulators: an augmented modulation scheme for arm balancing. IEEE Transactions on Plasma Science . ISSN 0093-3813

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Abstract

This paper discusses the control of a Modular Multilevel Converter (MMC) used as a grid-interface for the klystron modulators in the Compact Linear Collider (CLIC). The converter has a DC side load which takes short-duration power pulses, causing high DC side power fluctuations that are not tolerable if seen by the AC grid. The DC-AC power decoupling capability of the MMC enables mitigation of the power ripple on the AC side, guaranteeing compliance with power quality requirements. However, the pulse repetition rate of the CLIC modulators is synchronised the the 50 Hz AC grid and this induces permanent power imbalance in the arms of the MMC, causing voltage deviation and over-modulation unless appropriate balancing strategies are implemented. Unlike existing arm balancing methods that control 50 Hz circulating currents to balance the arm powers, the method proposed in this paper introduces an augmented modulation strategy where modulation signals are redistributed among arms based on the demand from a balancing controller. The resulting controller has lower complexity and its simple structure enables an easier design of the balancing loop, which guarantees predictable dynamics in operation. The effectiveness of the method has been demonstrated in simulation for the full scale CLIC converter ratings and experimentally on a 7kW MMC prototype operating with a 3.3 kA pulsed DC load.

Item Type: Article
RIS ID: https://nottingham-repository.worktribe.com/output/936942
Additional Information: © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Keywords: Arm balancing control; Grid-connected converter; Pulsed power; Modular multilevel converter; Modulation strategy, Klystron Modulator
Schools/Departments: University of Nottingham, UK > Faculty of Engineering > Department of Electrical and Electronic Engineering
Identification Number: https://doi.org/10.1109/TPS.2018.2837619
Depositing User: Burns, Rebecca
Date Deposited: 14 Jun 2018 10:08
Last Modified: 04 May 2020 19:39
URI: http://eprints.nottingham.ac.uk/id/eprint/52371

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