Bilateral Primary Frequency Support and AC Voltage Regulation of LCC-HVDC Systems for Asynchronously Interconnected Systems

Modern power systems require significant grid flexibility. As the AC transmission lines are passive and cannot be controlled, grid flexibility in the transmission system can only be provided by actively controlling High-Voltage Direct Current (HVDC) systems, particularly the dominant LCC-HVDC systems. Although grid-flexibility support using LCC-HVDC has been studied, existing methods fail to achieve bidirectional frequency support while maintaining AC voltage. Therefore, a coordinated control method is proposed for the LCC-HVDC system to achieve bilateral frequency support (BFS) and AC voltage regulation (AVR) for asynchronously interconnected systems. The level of frequency support and the coupled dynamics of sending-end (SE) and receiving-end (RE) system frequencies are quantified by the developed low-order frequency response model, different from frequency models in previous research for only one end of the system. With the developed model, the control parameters of the proposed method are analytically calculated. This ensures an appropriate level of primary frequency support without jeopardizing the frequency response of the system at the remote end. The effectiveness of the proposed method is demonstrated through real-time simulation.