With the increasing integration of renewable generation, many power grids have gradually formed AC-DC hybrid systems. Abnormal operations, such as DC blocking faults and generation trips, have led to several incidents of large frequency deviations. However, current simulation methods result in large errors when estimating the frequency regulation capacity of the system. This paper proposes a generic system frequency-response (SFR) model that can be used to estimate the dynamic frequency behavior of modern large-scale power systems. The limitations of the classical SFR model is first analyzed. Second, a generic SFR model with a more reasonable structure is presented, and the parameter-determination strategy is proposed using both the dynamic and steady-state data. Then, the generic SFR model is built and verified by a simulation case. Finally, a generic SFR model with satisfactory accuracy is established for the power grid in East China based on the measured disturbance data. The results show that the proposed model is promising for broad potential applications.

This study presents an optimisation control strategy for the power control of voltage source converter-based high-voltage direct current transmission under unbalanced grid voltage conditions. To facilitate simple implementation and flexible operation, the current references are derived and synthesised into one generalised equation that introduces two individually adaptable parameters. The two parameters can be adapted to eliminate the oscillations of instantaneous active and reactive power, as well as the currents at the grid side under unbalanced grid voltage conditions. The optimisation method based on particle swarm optimisation algorithm is presented to determine the two parameters. The simulation is conducted with PSCAD/EMTDC. The results show that the proposed strategy is effective and feasible.

No abstract

Recently, with the increased intermittent renewable energy penetration, many power grids have been incorporated into a large-scale long-distance UHV AC-DC hybrid system. In the actual grid, power disturbances, such as DC blocking faults and trip-off of wind turbines, often occur, resulting in power shortages and large frequency fluctuations. However, the existing approaches to assess the system frequency security are not reliable. This paper proposes an analytic formula for the system frequency response based on a generic system frequency-response (SFR) model, which can be applied to modern large-scale power systems. First, a generic SFR model with a reasonable structure is designed according to the parameter determination strategy. Second, according to the transfer function in the model, the time-domain analytic formula of the frequency response is obtained by realizing the inverse Laplace transform. Moreover, four main indexes are established to represent the characteristics of the frequency dynamic process in different periods, and these indexes are qualitatively and quantitatively analysed. Finally, the New England 10-unit 39-bus power system and East China Power Grid are considered to demonstrate the key features of the proposed method. The results show that the proposed analytic assessment method can be effectively adopted in several applications.

To effectively study the dynamics of power systems with large-scale wind farms (WFs), an equivalent model needs to be developed. It is well known that back-toback converters and their controllers are important for the dynamic responses of the wind turbine (WT) under disturbances. However, the detailed structure and parameters of the back-to-back converters and their controllers are usually unknown to power grid operators. Hence, it is difficult to build an accurate equivalent model for the WF using the component model-based equivalent modeling method. In this paper, a transfer function based equivalent modeling method for the WF is proposed. During modeling, the detailed structure and parameters of the WF are not required. The objective of the method is reproducing the output dynamics of the WF under the variation of the wind speed and power grid faults. A decoupled parameter-estimation strategy is also developed to estimate the parameters of the equivalent model. A WF that consists of 16 WTs is used to test the proposed equivalent model. Additionally, the proposed equivalent modeling method is applied to build the equivalent model for a real WF in Northwest China. The effectiveness of the proposed method is validated by the real measurement data.