Coordinative frequency-constrained unit commitment model for HVDC interconnected AC systems

Considering the increasing penetration of renewable energy resources (RES) and the higher capacity of HVDC system that responsible for RES transition, our paper proposes a coordinative frequency-constrained unit commitment (FCUC) model to manage the frequency stability after credible contingency with bulk power loss. The robust enhanced emergency frequency control strategy is proposed in this paper, wherein the transient overload capabilities of HVDC system are exploited to provide inertial response when ensuring the effectiveness and speed. Afterwards, the AC-DC primary response model considering the descent rates of HVDC is derived for the first time. This HVDC decline induces an extra steady-state power rescheduling procedure in this model, based on day-ahead schedule and emergency control procedures, the optimized AC-DC secondary response solution in power rescheduling further promotes the model economic benefits. In view of the max-min structure of emergency control problem and the solution domain formation of power reschedule problem, an improved threelevel algorithm combining the features of Benders decomposition and C&CG method is developed to solve the problem. After applying the proposed coordinative FCUC model on two scales of asynchronous systems with parallel HVDC lines interconnection, it is validated that by formulating the multi-speed response services among procedures coordinately, the flexibility of operation scheme is further excavated.