Abstract
It is a common practice that one converter controls DC voltage and the other controls power in two-terminal voltage source converter (VSC)–based high voltage DC (HVDC) systems for AC gird interconnection. The maximum transmission power from a DC-voltage-controlled converter to a power-controlled converter is less than that of the opposite transmission direction. In order to increase the transmission power from a DC-voltage-controlled converter to a power-controlled converter, an improved virtual impedance control strategy is proposed in this paper. Based on the proposed control strategy, the DC impedance model of the VSC–HVDC system is built, including the output impedance of two converters and DC cable impedance. The stability of the system with an improved virtual impedance control is analyzed in Nyquist stability criterion. The proposed control strategy can improve the transmission capacity of the system by changing the DC output impedance of the DC voltage-controlled converter. The effectiveness of the proposed control strategy is verified by simulation. The simulation results show that the proposed control strategy has better dynamic performance than traditional control strategies.
Highlights
With the development of power electronic devices, voltage source converter (VSC)–high voltage DC (HVDC) systems have been widely applied to AC grid interconnection because of their independent decoupling control of active and reactive power [1,2,3]
Virtual impedance in the DC voltage control loop can suppress the DC-side oscillation of a VSC–HVDC transmission system and improve its stability margin and the transmission capacity of the system [24,25]
This paper investigates the stability of VSC–HVDC operation in a bidirectional power flow mode
Summary
With the development of power electronic devices, VSC–HVDC systems have been widely applied to AC grid interconnection because of their independent decoupling control of active and reactive power [1,2,3]. An Impedance-based approach can be adopted to analyze the influence of VSC–HVDC systems with different directions of transmission power on stability [13]. Active methods suppress resonance by introducing voltage and current feedback control in a controller to improve the impedance of the source converter or load converter. It can be introduced to suppress DC-side oscillation [24,25], to limit output current for voltage controlled inverters during overloads or faults [26,27], to improve the stability of a grid-connected inverter by change its input admittance [28], and to enhance the small-signal stability of a modular multilevel converter (MMC) based DC grid [29]. Virtual impedance in the DC voltage control loop can suppress the DC-side oscillation of a VSC–HVDC transmission system and improve its stability margin and the transmission capacity of the system [24,25].
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