Dynamic Resonance Analysis and Oscillation Damping of Multiterminal DC Grids

Voltage-source converter-based multiterminal high-voltage direct current (VSC-MTDC) systems/grids are prone to system instability. This critical issue is overlooked in the literature. In order to improve system stability, this paper proposes an effective active damping method as a remedy to suppress voltage and power resonances in the VSC-MTDC grids by injecting damping signals into the inner current loops of VSC-MTDC stations. With dynamic regulation of the damping current, resonance is suppressed by power converter controllers without any additional current and voltage measurement. In this paper, modeling and stability analysis of the VSC-MTDC system/grid is presented considering the dc-side energy storage components, and control with a droop control structure. Then, single-frequency and multifrequency resonance mechanisms of dc-bus voltage and power in the event of transients are analyzed. Later, the stability effect of the MTDC system/grid inductance and capacitance values to the resonance amplitude and frequency droop coefficients is investigated. A PSCAD/EMTDC platform is developed to conduct dynamic simulations, and a scaled-down four-terminal 20-kW experimental prototype is used to validate the effectiveness of the proposed control methodology.