Equilibrium mechanism between dc voltage and ac frequency for ac-dc interlinking converters

Abstract

The equilibrium between dc bus voltage and ac bus frequency (Udc-f equilibrium) is the algorithm core of unified control strategies for ac-dc interlinking converters (ILCs), because the equilibrium implements certain mechanism. However, what the mechanism is has not been explicitly explored, which hinders further studies on unified control. This paper reveals that the state-space model of a Udc-f equilibrium controlled ILC is highly similar to that of a shaft-to-shaft machines system. Hence a detailed mechanism is discovered and named "virtual shaft-to-shaft machine (VSSM)" mechanism. A significant feature of VSSM mechanism is self-synchronization without current sampling or ac voltage sampling.

A unified droop control of AC microgrids under different line impedances: Revisiting droop control and virtual impedance method

“…However, due to the use of virtual power for droop feedback, accurate power-sharing cannot be achieved. Then, some other power-sharing control methods have been proposed for AC microgrids with low-voltage highly-resistive line characteristics, including active power-amplitude (P-V) droop and reactive power-frequency (Q-ω) droop control strategies (Tuladhar et al, 2000;Yu et al, 2010), power angle droop (Majumder et al, 2009;Majumder et al, 2010), intelligent algorithm-based droop control (Bevrani and Shokoohi, 2013), and decoupling-based droop control (Wu et al, 2015;Guan et al, 2016;Shi et al, 2022). However, there is no unified droop control strategy that can ensure stable system operation under arbitrary line characteristics, achieve accurate active power sharing among micro-sources, and realize satisfactory dynamic performance.…”

Adaptive Inertia and Damping Coordination (AIDC) Control for Grid-Forming VSG to Improve Transient Stability

“…Increasing the virtual damping coefficient can enlarge the positive virtual damping effect and enhance transient stability. However, the value of the virtual damping coefficient is often designed fixed and restricted by the frequency regulation requirement of the grid code [31]. It is also reported in [32] that droop control performs better than VSG control in transient stability enhancement for the hybrid power system.…”

Analysis and synchronization controller design of dual-port grid-forming voltage-source converters for different operation modes

“…T he modern power system is envisioned to integrate more and more voltage source converters (VSCs) to provide various critical services [1][2][3][4][5][6] . As illustrated in Figure 1, a grid-tie VSC can operate in an AC-dominant, a DC-dominant, or a balanced mode when an external stiff voltage source is applied on the AC bus, DC bus, or both, respectively [4,5] .…”

“…T he modern power system is envisioned to integrate more and more voltage source converters (VSCs) to provide various critical services [1][2][3][4][5][6] . As illustrated in Figure 1, a grid-tie VSC can operate in an AC-dominant, a DC-dominant, or a balanced mode when an external stiff voltage source is applied on the AC bus, DC bus, or both, respectively [4,5] . A voltage source is defined to be "stiff" when it has a low series impedance internally, meaning that when the current flowing into or out of it changes, the voltage will change very little [4] .…”