A New Droop Coefficient Design Method for Accurate Power-Sharing in VSC-MTDC Systems

Abstract

This paper proposes a new droop coefficient design method with the aim of improving the power-sharing accuracy among the converters in a multi-terminal dc (MTDC) system. The proposed droop coefficient design method works by adjusting the droop coefficient and can realize an arbitrary power-sharing ratio among all the converters in an MTDC system. This method does not rely on a communication network and therefore has the potential for higher reliability than the alternative methods. Mitigating the impact of the variation of dc line resistances on the power-sharing is discussed. Simulation of a four-terminal MTDC system is carried out by using PSCAD/EMTDC. The experimental results under a scaled-down four-terminal dc grid platform demonstrate the effectiveness of the proposed method. INDEX TERMS VSC-MTDC system, accurate power-sharing, droop control, dc line resistance. NOMENCLATURE

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

“…In [96] a coordinated control strategy based on voltage margin and voltage droop control has been proposed to maintain the and transient stability of MTDC system and adequate power flow. In [122] a droop coefficient design method has been proposed that can ensure arbitrary power sharing between all converter stations in MTDC system. Such method doesn't require any communication medium.…”

Resistive–Capacitive Output Impedance Shaping for Droop-Controlled Converters in DC Microgrids With Reduced Output Capacitance

“…Within the voltage control bandwidth ω v (i.e., ω < ω v ), T vCL (jω) and T iCL (jω) can be approximately considered as a unit gain. Hence, combining (9) and (12), (14) can be simplified as: To numerically verify the feasibility of the proposed design method, two representative examples of DC/DC DER converters are studied herein: a buck-type converter and a boost-type converter. It should be noted that this design method is generic and it can be also applied to other converters like buck-boost, Cuk, Sepic, and Zeta.…”

“…To suppress the magnitude of output impedance, a straightforward solution is to choose relatively bulky output capacitors for DER converters [12]. By doing so, even at medium frequency, the output impedance is dominated by the output capacitance, obtaining the desired shape.…”

Controller design for MTDC grid to enhance power sharing and stability

“…The study [21] presents a control scheme to dynamically limit the overload on the converter to provide frequency support application. The line resistances in MTDC network are relatively high and will significantly affect the accuracy of the power sharing [22]. Under this situation, the designed control scheme should not only ensure the distribution of power among the converters according to their capacity but also limit the overloading dynamically.…”