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Due to the independent controllability and fast power regulation capability, the High Voltage Direct Current (HVDC) system could be a prospective technology to provide multiple ancillary services to the system besides conventional bulk power transmission. However, with the increase of False Data Injection Attacks (FDIAs) on PMU data, the HVDC system could have the wrong response once the collected data that the HVDC system relied on is attacked, thus threatening the system operating security. How to ensure the security of the PMU-based HVDC ancillary service control become an urgent issue. To mitigate the risk, this paper proposed an HVDC attack-defense control based on the FDIAs detection method. Firstly, the Squeeze-Excitation based Double Convolutional Neural Networks (SE-DCNN) is proposed to realize fast identification of the attacking frequency type based on the time and frequency domain signals. The duration time of FDIAs is detected by the local outlier factor. Then, utilizing the results from SE-DCNN, HVDC ancillary service control framework is reorganized and an HVDC attack defense control is proposed for suppressing the potential influence of various types of FDIAs on the HVDC system ancillary service. Different experiments results demonstrate that the proposed method has the ability to significantly mitigate the frequency deviation and oscillation under the FDIA. [ABSTRACT FROM AUTHOR]

• A novel generalized admittance criterion is proposed, significantly reducing the requirement for synchronous phasor measurements. • Harmonic contribution evaluation is simplified based on the proposed generalized admittance criterion. • The fluctuation characteristic of harmonics is considered for the harmonic admittance estimation. • The proposed method has comprehensive applicability and high harmonic source location accuracy. The widespread integration of various nonlinear power electronic devices in modern power systems has made harmonic distortion more serious than ever before. Given the urgent need to improve power quality, the harmonic contribution evaluation (HCE) is of great importance since it can provide a strong basis for harmonic mitigation measures. However, the conventional HCE methods are not effective due to the lack of synchronous voltage and current phasor information in real-field practice. To overcome the phasor limitation, an HCE method based on a generalized admittance criterion (GAC) is proposed in this paper. The proposed GAC aims to determine the dominant harmonic source at the point of common coupling (PCC) from the utility side and customer side. Compared to the conventional method, the developed method only needs the RMS values of the PCC voltage, current, and phase angle difference. Therefore, the synchronous phasor information of voltage and current is no longer required. Meanwhile, a threshold to determine the dominant harmonic source is established by using the equivalent admittance ratio on both sides of PCC. The evaluation process of the proposed method is significantly simplified by comparing the generalized admittance limit with the proposed threshold, which also greatly improves the method evaluation accuracy. Moreover, the interference of background harmonic fluctuation is excluded by using the linear calibration-based harmonic admittance estimation method. Finally, multiple scenarios with various admittance characteristics were simulated to verify the performance of the proposed criterion, and the real-field measurement is also used to demonstrate the accuracy and validity of the proposed method. [ABSTRACT FROM AUTHOR]