1.State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources (North China Electric Power University), Beijing 102206, China;2.State Key Laboratory of Operation and Control of Renewable Energy & Storage Systems (China Electric Power Research Institute), Beijing 100192, China

With a large number of renewable energy sources based on the converter-interfaced generator (CIG) connecting to the power grid, the rotational inertia of the system is decreasing. By using the virtual inertia control and the primary frequency regulation control, the capability of renewable energy sources to actively support the frequency of the power grid can be improved. According to the characteristics of the frequency control response of CIG, this paper proposes an equivalent inertia estimation method for CIG considering power response delay compensation. First, the node frequency and the active power of the point of common coupling of CIG are measured, and the node frequency data is adopted to judge whether the frequency regulation control is triggered. Then, by integrating the active power increment in a long time scale after the frequency regulation control is triggered, the coefficient of primary frequency regulation and the time delay of active power response are calculated. Finally, the active power increment after using the virtual inertia control is corrected and the equivalent inertia is calculated. A closed-loop real-time simulation system is established by using the real-time digital simulation (RTDS) system and the frequency controller for wind, photovoltaic, and energy storage. The correctness of the proposed method is verified with different disturbances and different frequency regulation control strategies, and the influence of key parameters of the algorithm on the accuracy of response time delay calculation is analyzed. The simulation results show that the proposed method is suitable for estimating the equivalent inertia of CIG and has high precision.