Research on control strategy of double terminal converter station in UHVDC transmission system based on virtual synchronous generator

Under the traditional control strategy, UHVDC transmission system is lack of inertia and damping characteristics, so it can't effectively adjust the frequency of AC system dynamically. Virtual synchronous generator (VSG) technology can simulate the operation characteristics of traditional synchronous generator, making the converter have inertia and damping characteristics, so as to slow down the frequency change of AC system, but it belongs to differential frequency modulation method. To solve the above problems, in this article, we propose a two-terminal converter station control strategy for UHVDC transmission system based on VSG technology. Two key parameters of synchronous generator rotational inertia and damping coefficient are retained in this method. Meanwhile, the calculation method of frequency in virtual rotor is improved, and secondary frequency regulation is added. Aiming at the situation of load mutation, a two terminal VSG system model is built in Matlab/ SIMULINK for simulation. The results show that the control strategy has the characteristics of inertia and damping, which can reduce the amplitude, speed and overshoot of frequency fluctuation, suppress the voltage fluctuation of DC system, and realize secondary frequency modulation.