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.

As wind power reaches a high penetration in power systems, inertia control is required in grid codes to improve the system frequency dynamics. This supplemental control will couple the mechanical system of wind turbines (WTs) with the electrical system, causing torsional vibration in drivetrains. However, the impact of inertia control on this torsional vibration can be rarely seen in literature. This article studies the mechanism of this impact and the impact rule of different parameters. A small-signal model of a DFIG-based WT with inertia control is first proposed to study the interaction between the inertia control and WT's torsional vibration. The differences between controls in DFIG-based WTs are considered in this model. Through the model, interaction paths can be obtained to help explain the impact mechanism from a general perspective. On the basis of analyzing the interaction paths, the impact rules of different parameters on the damping of torsional vibration in drivetrain are investigated in detail. Finally, time-domain simulations are performed to demonstrate the correctness of the analyses.

This paper establishes an instantaneous voltage model to illustrate the dynamic characteristics of grid voltage in electromagnetic time scale affected by power-electronic interfaced voltage regulatory devices with two typical categories of control systems, i.e., power-current cascading control and power synchronization control, exemplified by the STATCOM and virtual synchronous condenser (VSCON) respectively. In this paper, a linearized instantaneous voltage model is firstly established to analyze the impact paths of control loops in the STATCOM and VSCON. Based on the model, the dynamic process of grid voltage is divided into three stages. Various factors on the dynamic process of grid voltage are analyzed, especially cascading control loops prior to the functioning of AC voltage control. Moreover, stiffness characteristic is proposed to evaluate the effects of power electronic interfaced voltage regulatory devices with different control structures. In addition, the effectiveness of the stiffness compensation based on the VSCON is validated by the study cases.

Synchronization is the key of AC power system operation, but its mechanism becomes unclear with the large-scale integration of voltage-source converters (VSCs). As an important feature distinguishing VSCs from synchronous generators (SGs), the current-source characteristics of VSCs have hardly been focused from the perspective of synchronization. In this letter, a synchronization mechanism between power-synchronized voltage-source (VS) and PLL-controlled current-source (CS) is clarified. Based on this mechanism, negative damping oscillations of SGs caused by VSCs are disclosed.

In conventional wisdom, the function of the phase-locked loop (PLL) is to synchronize with the grid and provide a coordinate reference for the control system. It is usually not easy to understand the role of PLL from the perspective of system stability. This letter reexamines the function of PLL and proposes that PLL can be regarded as a natural power system stabilizer (PSS).

The process, in which the internal voltage with time-varying amplitude and frequency (A/F) regulated by equipment generates the electric network’s terminal power variations, plays a critical role in the system dynamic. For the system dynamic analysis, the relationship between the time-varying A/F and the power response, as well as its characteristics, is required. However, this subject has yet to be emphasized and thoroughly studied due to insufficient attention to the fact that the frequency is time-varying. In traditional power system analysis, since the network’s time constant is often fast enough compared to synchronous generators, the electric network is generally depicted by the static relationship with the assumption of constant frequency, although it is not consistent with the practice of frequency time-varying. Moreover, in the present renewable generation scenario, the fast A/F dynamics of internal voltages can impact the power response, and further the system dynamics. So that adequate investigations around the electric network’s power response in relation to the time-varying A/F are more urgent. Motivated by these considerations, this paper studies the network’s original relationship between the internal voltage’s A/F stimulation and the active/reactive power response, which contains the oscillatory integral problem in math. By using the method of integration by parts, an explicit expression of this relationship is given. Further, a simplified relationship is presented to help understand the dynamic characteristics of the network. Several unusual observations, including the composition and consumption on the line of the active/reactive power in relation to the time-varying A/F, are obtained.