Power oscillation damping with virtual capacitance support from modular multilevel converters

Abstract

Power oscillation damping (POD) is one of the ancillary services expected from high-voltage direct current (HVDC) converters. When providing POD to the ac side, converters draw power from the dc side, which can cause distortion to the dc voltage especially in the case of limited dc capacitance. In meshed/multi-terminal HVDC grids, where dc voltage regulation is distributed using a dc voltage droop control strategy, the distortion due to the POD controller action is propagated to other connected ac grids because of the droop action. This propagation can be reduced by using the inherent energy storage capability of the modular multilevel converter (MMC), which is a common converter topology for HVDC. Different methods to utilise the energy stored in the MMC for the purpose of POD have been proposed in the literature. This study presents a detailed analysis and experimental validation of one of these methods, referred to as virtual capacitance support, which increases the effective dc grid capacitance by using the stored energy of multiple MMCs connected in the same grid. The experiments, which were carried out using power hardware in the loop setup, demonstrated the effectiveness of the method.

MMC Based MTDC Grids: A Detailed Review on Issues and Challenges for Operation, Control and Protection Schemes

“…A flexible model to analyze small signal stability of VSC based hybrid AC/MTDC system is presented in [117] to damp inter area power oscillations. In [118] power oscillations are effectively damped with the support from virtual capacitance of MMCs. The power oscillations are reduced with the help of energy stored in SM of MMC.…”

Guest Editorial: Challenges in Future Grid‐Interactive Power Converters: ControlStrategies, Optimal Operation, and Corrective Actions

“…For Multi‐terminal HVDC grids , paper [21] presents a DC voltage deviation‐dependent voltage droop control method for MTHVDC Systems under large disturbances to ensure the DC grid voltage stability. Paper [22] studies a virtual capacitance support scheme using DC capacitance energy from MMC to mitigate mutual impact of multi‐terminal HVDC converters under droop control.…”

Stability improvement of MMC‐based hybrid AC/DC grids through the application of a decentralized optimal controller

“…These include interactions and stability challenges in multiterminal hybrid AC/DC grids [4][5][6]. Such dynamic interactions, either on the AC-or DC side of the multiterminal grid, can be a source of detrimental oscillations and propagate to the entire network due to the droop control action of the HVDC converters, resulting in stability deterioration, faults, and subsequent blackouts with considerable damages and costs [7,8]. Stability problems with oscillations and harmonic interactions have been reported in several HVDC-dominated grids over the past few years, such as harmonic interactions and high-frequency resonances detected at BorWin1 wind farm [9,10], subsynchronous oscillations observed over a hundred times at Xinjiang wind farm [11], and oscillations reported in several MMC-based HVDC grids in China and Germany [12].…”