Data-driven Small Signal Stability Evaluation And Damping Modulation Strategy Of AC/DC Hybrid Power Grid

The hybrid AC/DC grid is a new stage of chinese energy development and evolution.While meeting the requirements for long-distance and large-capacity transmission of the grid,its operational fragility and coupling characteristics also increase the risk of system instability.The large-capacity power transmission on the tie line of the large interconnected power grid has a negative impact on the stability of the power system with small disturbances.When the power of the tie line section is unbalanced due to faults,the damping level of the system interval oscillation mode is likely to drop significantly,posing a threat to the safe and stable operation of the power grid.In this paper,the random response of the system under natural excitation is used as the data set to evaluate the small disturbance stability of the AC-DC hybrid grid,and formulate a modulation strategy to improve the damping level of the interval mode.The main research contents are as follows:Firstly,based on the traditional eigenvalue analysis method,the small disturbance stability analysis of the AC-DC hybrid grid is carried out.Study the relationship between the AC and DC power ratios of the tie line section and the oscillation damping ratio of the system interval,and design the DC unipolar blocking fault to study the influence of unipolar blocking on the electromechanical oscillation modes of the system,and monitor the power changes on the tie line.The influence of power transfer on the interval oscillation mode of the AC-DC hybrid grid is summarized,which provides a reference for the subsequent data-driven identification of system modal parameters.Secondly,taking the generator’s active power random response under natural excitation as the data set,the modal parameters of the AC-DC hybrid system before and after the DC unipolar blocking are identified by the stochastic subspace identification method（SSI）,and the results obtained by the characteristic method are compared and analyzed.The accuracy of the identification results is verified,and the influence of unipolar blocking on the electromechanical oscillation mode of the system is verified.The simulation results of the improved IEEE4-machine 2-region and IEEE 16-machine 5-region system verify the effectiveness of the SSI identification method for modal parameter identification of the AC-DC hybrid system.Finally,in order to improve the damping level drop in the interval mode caused by DC unipolar blocking,a damping promotion strategy by adjusting the active output of the generator is studied.According to the perturbation of the generator’s active output and the change of the system damping ratio identification result,a fixed-point sliding window perturbation algorithm is proposed to calculate the damping ratio sensitivity of each generator.As a result,sensitive generator sets are selected to participate in the active power redispatches process.The magnitude of the active power modulation is determined by the working state of the generators participating in the redispatches process and the active power output constraints.Multiple active power redispatches is performed to increase the damping ratio of the interval oscillation to meet the requirements of safe and stable operation of the hybrid system.The simulation results of the improved IEEE 4-machine 2-region and IEEE 16-machine 5-region systems verify the effectiveness and applicability of the damping modulation strategy proposed in this paper.