Research Article Controlling Transformer Magnetizing Offset Current in Isolated Phase-Shift Full-Bridge Converters Using a Luenberger Observer -Angelika Neumann, Sönke Meynen, Ahmad Rahmoun, Daniel Ziegler, Thomas Kirchartz---Karlsruhe University of Applied Sciences, Karlsruhe, Germany

Controlling Transformer Magnetizing Offset Current in Isolated Phase-Shift Full-Bridge Converters Using a Luenberger Observer Angelika Neumann, Sönke Meynen, Ahmad Rahmoun, Daniel Ziegler, Thomas Kirchartz 

Abstract This paper proposes a flexible digital control scheme for isolated phase-shift full-bridge (PSFB) converters. The required transformer suffers from inevitable imbalance of magnetic flux resulting in an increased magnetizing DC-offset current that threatens system reliability due to saturation effects. The paper addresses two major issues of the occurrence of a magnetizing DC-offset current. First, caused by the change of duty cycle due to output power regulation and second caused by initial manufacturer tolerances of devices. In contrast to common methods the novel control scheme uses a Luenberger observer to estimate the magnetizing current requiring only simple measurement of transformer voltages without additional and lossy auxiliary networks. The observer model, in combination with a PI-controller, directly interventions the duty cycle and removes any DC-offset current resulting from both issues. A detailed deviation of the state-space model of the transformer and a subsequently design of the observer are presented. Simulation and experimental results on a PSFB prototype verify the principal functionality of the proposed control scheme to prevent transformer saturation. 

 International Transactions on Electrical Energy Systems Volume 2022, Article ID 9243429, 15 pages https://doi.org/10.1155/2022/9243429 

ORIGINAL LINK: https://onlinelibrary.wiley.com/doi/10.1155/2022/9243429 

Single-Stage Multi-Port Solid-State Transformer (SST) Based Medium-Voltage DC (MVDC) Interconnection System and Coordinated Control Strategies - Di Zhu, Chuang Liu, Jingyue Wang, Zhongchen Pei*, Chao Liu, Heyang Sun, Yu Jiang Northeast Electric Power UniversityDalian University of Technology

Single-Stage Multi-Port Solid-State Transformer (SST) Based Medium-Voltage DC (MVDC) Interconnection System and Coordinated Control Strategies Di Zhu, Student Member, IEEE, Chuang Liu, Member, IEEE, Jingyue Wang, Zhongchen Pei, Chao Liu, Member, IEEE, Heyang Sun, Yu Jiang 

Northeast Electric Power University

Dalian University of Technology

Abstract—Decentralized integration of distributed generation (DG) units and loads are increasing in the modern distribution grid. Maintaining the power flow and power quality within their accepted limits is a challenging task. This paper proposes a medium-voltage DC (MVDC) interconnection system based on the single-stage multi-port solid-state transformers (SST). First, the single-stage multi-port SST's coordinated control strategies and energy management method are discussed, aiming at the flexible power flow control between the utility grid, MVDC grid and the low-voltage AC/DC microgrid. Secondly, the MVDC controller parameters and SST passive components are optimized based on the impedance interaction characteristics between the two SSTs' MVDC ports, thereby enhancing the stability margin of the interconnected system. Then the operation modes of the interconnected system are defined. Finally, the effectiveness of the proposed operation modes and control strategy is verified through a 1-MW simulation platform, while a 1-kW scaled-down experimental prototype is built to further validate the single-stage multi-port SST and the MVDC interconnected system.

ORIGINAL LINK: https://orbit.dtu.dk/en/publications/single-stage-multi-port-solid-state-transformer-sst-based-medium-/ 

Bidirectional Grid-Forming Converter with Modified Voltage Control for Enhanced Power Dynamics Dos Santos Serra, Amiron Wolff; Nascimento, Khristian Augusto Freitas; De Matos, José Gomes; De Souza Ribeiro, Luiz Antonio; Savaghebi, Mehdi; Oliveira, Hércules Araújo Department of Engineering Technology and Didactics Federal University of Maranhão

Abstract— This paper proposes a control strategy for a bidirectional grid-forming converter, operating as a virtual synchronous generator, based on an improved voltage controller to enhance the dynamics of the active and reactive power loops. The theoretical analysis and real-time simulation results demonstrate the enhanced disturbance rejection of the proposed strategy, which is based on disturbance input decoupling. Furthermore, virtual impedance is used to limit the current injected by the converter during grid transitory situations.

ORIGINAL LINK: https://orbit.dtu.dk/en/publications/bidirectional-grid-forming-converter-with-modified-voltage-contro/ 

Green & Black-starting HVDC-connected Offshore Wind Power Plants: Grid forming control, Energization transients and Islanding capabilities - Anubhav Jain

 

Summary

 Green energy transition is the most urgent need of the hour to curb the rising impact of global warming. The carbon-neutral energy system of the future will have electricity as its backbone, which requires a domination of renewable sources and long distance interconnections. However, such a transformation brings forth a massive penetration of power electronic converters to allow for flexibility in operation that is essential for efficient and cost-effective grid usage. This paradigm shift will make future power grids very different from the current system resulting in a highly dynamic environment that poses a risk to power system stability. Coupled with the declining strength of the network, it has the potential to increase the impact of severe network disturbances and give rise to challenges for the containment of voltages and frequency excursions, ultimately triggering wide-area blackouts. Since conventional synchronous generation is being phased out, the responsibility to maintain power system stability and provide network restoration services must be taken up by alternate sources of generation. Being one of the fastest growing renewable energy sources in the world, offshore wind is deemed a prime candidate.

ORIGINAL LINK: https://orbit.dtu.dk/en/publications/green-amp-black-starting-hvdc-connected-offshore-wind-power-plant/ 

A Multi-Loop Control for Grid-Forming Converters with Enhanced Dynamics Amiron Wolff Dos Santos Serra, Luiz Antonio De Souza Ribeiro, Mehdi Savaghebi-Institute of Electrical Energy Federal University of Maranhão São Luís – MA, Brazil-Department of Engineering Technology Technical University of Denmark (DTU)-

 

A Multi-Loop Control for Grid-Forming Converters with Enhanced Dynamics Amiron Wolff Dos Santos Serra, Luiz Antonio De Souza Ribeiro, Mehdi Savaghebi Department of Engineering Technology and Didactics

 2024 Energy Conversion Congress & Expo Europe - Darmstadt, Germany Duration: 2 Sept 2024 → 6 Sept 2024

 Abstract This paper proposes a control strategy for grid-forming converters based on a cascade control scheme with current and voltage controllers and an outer loop to control the injected active and reactive power. The analysis demonstrates the increased disturbance rejection capability of the current controller, and the improved loop gain in the low-frequency region of the voltage controller from the concept of disturbance input decoupling. Simulation results prove the effectiveness of the proposed strategy. 

ORIGINAL LINK: https://orbit.dtu.dk/en/publications/a-multi-loop-control-for-grid-forming-converters-with-enhanced-dy/