A wind power short-term forecasting method based on discrete wavelet transform and long short-term memory networks (DWT_LSTM) is proposed. The LSTM network is designed to effectively exhibit the dynamic behavior of the wind power time series. The discrete wavelet transform is introduced to decompose the non-stationary wind power time series into several components which have more stationarity and are easier to predict. Each component is dug by an independent LSTM. The forecasting results of the wind power are obtained by synthesizing the prediction values of all components. The prediction accuracy has been improved by the proposed method, which is validated by the MAE (mean absolute error), MAPE (mean absolute percentage error), and RMSE (root mean square error) of experimental results of three wind farms as the benchmarks. Wind power forecasting based on the proposed method provides an alternative way to improve the security and stability of the electric power network with the high penetration of wind power.

The existing studies show that the virtual resistance scheme has positive effects on synchronous resonance suppression but negative effects on transient synchronization stability of virtual synchronous generator (VSG). To address this contradiction, this article proposes a modified VSG control scheme. The basic idea is that the virtual active power at virtual PCC, instead of real active power, is introduced as the power feedback into the control loop. Then, the effect of virtual resistance on transient stability can be equivalent to that of grid resistance, which improves transient stability. Besides, a proportion–integral controller is added at the forward loop to control the real active power to track the power reference. Compared with the existing VSG control methods, the modified VSG control scheme can well solve the conflict caused by virtual resistance between small-signal stability and transient stability. The effectiveness and superiority of the proposed method are verified by control hardware-in-loop experimental results.

This letter addresses the parameters design problem for converter-based virtual synchronous generators (VSGs), which is crucial for stable operation. Existing methods only consider performance optimization based on the small-signal model or qualitative analysis of large-signal stability. However, it remains to be elucidated on how to quantitatively design virtual inertia and damping to ensure transient stability. In this letter, sufficient conditions of VSG control parameters for transient synchronization stability are derived using Lyapunov direct method. Then, a systematic feasible parameters region is obtained that satisfies grid-code-based transient stability and rate-of-change-of-frequency (RoCoF) requirement under large disturbances. As a result, this letter provides a practical reference for control parameters design and engineering application of VSG. Control-hardware-in-the-loop (CHIL) experiment validates the designed control parameters region.

In cascaded-type microgrid, the synchronization and power balance of distributed generators become two new issues that needs to be addressed urgently. To that end, an f-P/Q droop control is proposed in this letter, and its stability is analyzed as well. This new droop control is capable to achieve power balance under both resistive-inductive and resistive-capacitive loads autonomously. Compared with the inverse power factor droop control, its advantage consists in extending the scope of application. Finally the feasibility of the proposed method is verified by simulation results.

Constant power loads (CPLs) are often the cause of instability and no equilibrium of DC microgrids. In this study, we analyze the existence and stability of equilibrium of DC microgirds with CPLs and the sufficient conditions for them are provided. To derive the existence of system equilibrium, we transform the problem of quadratic equation solvability into the existence of a fixed point for an increasing fractional mapping. Then, the sufficient condition based on the Tarski fixed-point theorem is derived. It is less conservative compared with the existing results. Moreover, we adopt the small-signal model to predict the system qualitative behavior around equilibrium. The analytic conditions of robust stability are determined by analyzing quadratic eigenvalue. Overall, the obtained conditions provide the references for building reliable DC microgrids. The simulation results verify the correctness of the proposed conditions.

Parallel VSG systems are emerging as an attractive solution for inertia support and frequency stability enhancement of the power grid. However, the dynamic frequency characteristic is more complicated due to the coupled interaction of line impedance, virtual inertia, and damping coefficient in parallel VSG systems. The problems for frequency stability, dynamic performance, and frequency/power oscillation have raised much more attention. In this paper, a systematic analysis of the influence of virtual inertia and damping coefficient on the dynamic frequency characteristic among parallel VSG systems was presented and a quantitative assessment for dynamic frequency performance based on the 2-norm H 2 was proposed. Furthermore, a coordinated control for virtual inertia and damping was proposed to improve frequency stability and achieve a better dynamic performance of parallel VSG systems. The effectiveness and superiority of the proposed method were verified by simulation and experimental results.