Doubly fed induction generator (DFIG) based wind turbines (WTs) occupy a high penetration in power systems and are being required to emulate inertia response as synchronous generators (SGs). Therefore, it is of value to study the impact of inertia control of DFIG-based WT on electromechanical oscillation damping (EOD) of SG. However, relevant studies that are mainly based on eigenvalue analysis method are not enough and general mechanism study is still lacking. This paper studies the impact rules and mechanism of inertia control parameters (proportional constant and time constant) of WT on EOD of SG with a novel approach. Firstly, linearized model of WT under inertia control is derived based on motion equation concept, which can explicitly describe external characteristic of WT. From the model, it is clear that proportional constant determines the inertia characteristic of WT, while time constant has decisive effect on the damping characteristic. Then, by interaction analysis based on motion equation models of both SG and WT, the impact rules and mechanism of inertia control parameters on EOD of SG are explained clearly. Besides, since variable inertia control parameters mean variable inertia and damping coefficients of WT, the impact mechanism can be understood from a general perspective.

The islanded scenarios of voltage source converter (VSC) high-voltage DC (HVDC) directly supplying power to islanded loads or connecting to wind farm are becoming popular, in which some new issues are required to be further addressed. While several control strategies have been studied, to the authors best knowledge, few have investigated the potential capability of VSC HVDC using the typical phase-locked loop (PLL)- synchronized vector control (PLLSynVC) to address islanded operation issues. To explore the potential capability of the typical PLLSynVC in islanded system, this paper proposes a frequency regulation scheme (FRS), including inertia and primary frequency control, for the PLL-synchronized VSC HVDC based on the motion equation concept. By adding the FRS, the VSC HVDC using the PLLSynVC, similar to a synchronous generator from the view of the phase motion equation, not only can self-maintain the frequency stable in an islanded system, but also naturally avoids the transition of control operation modes without changing the basic control structure. Furthermore, based on the developed phase motion equation, the inertia characteristics of VSC HVDC with the FRS is studied, which synthetically considers the impact of different controllers and PLL, and makes VSC HVDCs manifested inertia clear. The effectiveness of FRS and inertia analysis results are verified by time-domain simulations.

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.

Doubly fed induction generator (DFIG) based wind turbine (WT) has a distinct fault current contribution that is critical for the power system analysis. This paper analyzes the mechanism underlying DFIG-based WT’s fault current during low voltage ride through (LVRT) from the perspective of magnetic circuits. The crowding-out phenomenon is discovered and the general relationship between flux linkage and current is depicted with the proposed equivalent inductances. Based on the understanding, a new analytical method for deriving the analytical expressions of fault current is proposed. Compared with the existing methods that rely on solving the ordinary differential equations (ODEs), the proposed method is based on the algebraic operation derived from the magnetic circuits, which makes it appropriate to different fault scenarios. With this method, the stator current is depicted with a series of succinct expressions. The analytical results are verified by experiments and simulations on a 10kW DFIG prototype. The differences of fault current between synchronous generator (SG) and DFIG-based WT are identified. This paper is expected to help understand the regularities of DFIG-based WT’s fault current from a physical perspective. The analytical results are expected to be helpful for rating circuit breakers and studying issues relating to protective relays.