Point-of-Common-Coupling and Center-of-Inertia Frequency Based Auxiliary Frequency Control Strategy for Windfarm Frequency Support Improvement

Low inertia is becoming an issue that cannot be avoided as renewable energy sources, represented by wind energy, are increasingly integrated into the power systems. Wind farms have taken on the role of supplying frequency support during system disturbances. In this case, the signal source of wind farm frequency support becomes a critical factor for the control performance. The Center of Inertia (COI) frequency can better reflect the dynamic change of the system frequency after disturbance compared with the Point of Common Coupling (PCC) frequency. However, due to the time delay in signal communication and calculation, the direct utilization of the COI frequency may bring a detrimental influence on the performance of frequency support control, while the PCC frequency is measured locally with a rare time delay. Therefore, how to combine both advantages of the PCC frequency and COI frequency into the auxiliary frequency control signal of wind farms requires specific attention. This paper presents a comparative analysis of the control effect of using two frequency signals. Simultaneously, the effect of different delays of the control signals on the control effect is firstly analyzed. To minimize the detrimental influence of time lag in COI frequency, Long Short-Term Memory (LSTM) neural network is introduced to correct the time lag of the COI frequency. Furthermore, based on the delay-corrected COI frequency signal, an auxiliary frequency control strategy based on the PCC-COI frequency is proposed. This novel strategy aims to combine the advantages of both signals, effectively enhancing the efficiency of auxiliary frequency control. Finally, the efficiency of the suggested control strategy is validated in the modified IEEE 39 bus system.