The increasing deployment of offshore wind farms necessitates robust and stable high-voltage direct current networks. Achieving optimal stability, especially in damping oscillations on the DC side, remains a significant challenge. This study focuses on mitigating post-fault converter de-blocking oscillations, a critical issue exacerbated by complex interactions between AC and DC systems, converter dynamics, and system faults. These behavior are governed by nonlinear system dynamics, making traditional control methods less effective in ensuring stability. A comprehensive analysis of DC side oscillations and their interaction with converter dynamics is developed to understand the key factors influencing system stability. The research investigates a DC voltage regulation damping approach, identified as the most effective solution in the literature. Comprehensive parametric sensitivity analysis evaluates system behavior under diverse operational conditions. Addressing current damping method limitations during converter de-blocking, this work proposes an innovative control approach integrating fuzzy logic control and proportional–integral controllers. This approach enhances DC voltage regulation and incorporates a modified circulating current suppression control in the inner loop. The coordinated fuzzy logic control and proportional–integral controller dynamically adjusts to nonlinear system dynamics in real-time, providing a robust framework for improved post-fault recovery. It aims to achieve faster recovery times and reduced overshoot compared to conventional methods. The proposed controller's efficacy is validated through comparative analysis with existing approaches. Electromagnetic transient) simulations using the real-time digital simulator platform demonstrate the controller's performance under realistic operating conditions.

This study investigates the dynamic performance of hybrid power systems, with a focus on Multi-Terminal Direct Current (MTDC) interconnected offshore-onshore systems, under various disturbances. Conventional performance metrics such as Rate of Change of Frequency (RoCoF), commonly used for AC systems, are utilized to assess frequency response. Additionally, a modified Rate of Change of Voltage (RoCoV) metric is proposed to capture DC voltage behavior. The effectiveness of these metrics is evaluated through simulations involving various disturbances, including generator outages, line outages, converter outages, and faults. The results demonstrate the ability of the proposed metrics to effectively capture the impact of disturbances on system response, while also identifying limitations in capturing oscillating responses. Furthermore, the parametric sensitivity of control parameters in the converter’s outer control loop is analyzed to assess their influence on system behavior.

One crucial aspect of Modular Multi-level Converter (MMC)- Bipolar Point-to-Point (BPP) configuration systems is the occurrence and damping of oscillations on the DC side of HVDC networks. These oscillations can arise due to various factors, including the interaction between the AC and DC systems, de-blocking of converters after a fault, and the dynamic behaviour of connected power sources. Various investigations consider damping methods that delve to mitigate oscillatory tendencies and establish stability during Post-Fault (PF) recovery. However, the current research on damping predominantly focus on the impact of AC fault or unbalanced conditions on the DC side. This paper presents an investigation that addresses the gap concerning with sub-synchronous oscillations occurring during the de-blocking of a MMC-BPP within the post-DC fault recovery. The investigation also considers active damping and enhanced current control loop as a combined mitigation measure. A meticulous real-time digital simulation supported parametric sensitivity analysis is conducted on a four-terminal MMC-BPP synthetic power system. Numerical results provide insight into the level of effectiveness that can be achieved by the considered concept of active damping.

High-Voltage Direct Current (HVDC) transmission with Modular Multi-level Converter (MMC) - Bipolar Point-to-Point (BPP) configuration is gaining traction as a solution for integrating renewable energy sources into future power grids. However, one critical challenge associated with MMC-BPP systems is the occurrence and mitigation of oscillations on the DC side. These oscillations can arise due to various factors, including interactions between the AC and DC systems, converter de-blocking after fault events, and the dynamic behavior of connected power sources. The research work presented in this paper addresses a gap by investigating and mitigating oscillations specifically occurring during post-fault converter de-blocking. An enhanced active damping method is proposed that achieves a substantial reduction of these oscillations, ensuring improved system stability during this critical phase. Furthermore, a meticulous parametric sensitivity analysis is conducted on a four-terminal MMC-BPP test system using a real-time simulator to extract valuable insights into the damping method’s effectiveness under various operating conditions.