Inertia and damping are the core index of the estimation of power system stability. Existing analysis to the support of inertia and damping are focused on the improvement of system stability as well as parameters tuning of virtual inertia and virtual damping but rarely involved in the quantitative calculation of level of inertia and damping under a certain condition. Based on this background, this article puts forward a unified calculation method to identify the equivalence of inertia and damping under various ratios of R_g / X_g . In addition, the quantity of improved inertia and damping support enabled by virtual inductance control are estimated by the derived calculation model of equivalence. The calculated mathematical model of equivalence of inertia and damping is well verified by the overlapped eigenvalues distribution. Besides, the negative synchronous power will inevitably influence the aperiodic loss of synchronization (ALoS) of power system caused by the large virtual inductance. Therefore, a solution should be derived to make a compromise between oscillation damping and ALoS by tuning the value of virtual inductance. Finally, the simulation and experiment results in various cases verify the effectiveness of the proposed equivalent damping and inertia calculation method as well as virtual inductance control.

Frequency stabilization is the premise of guaranteeing grid-friendly integration of virtual synchronous generator (VSG). Based on that premise, this article, focused on frequency stability, establishes the small signal model of grid-forming VSG system. At first, the mechanism of frequency oscillation occurring in system of active- and reactive-power coupling is analyzed by the defined feedback effect factor in this article. Besides, a new dynamic model is established for identifying dynamic interaction of voltage magnitudes and frequency by means of feedback effect. The analytical results of established models agree with that of eigenvalue analysis. Furthermore, a new virtual inductance control strategy is proposed to mitigate the unstable oscillation of frequency and powers, enhance damping performance, and improve stability margins. Unlike the conventional virtual inductance control, which is reliable on dual-loop control framework, the proposed virtual inductance control in this article is based on principle of energy conservation and can be applicable for the grid-forming inverter without inner dual-loop control structure. Finally, the proposed modeling as well as virtual inductance control method is experimentally verified.

In conventional HVDC systems where the harmonic filters and shunt capacitors are installed at the ac grid side, the converter transformers inevitably suffer the detrimental impacts caused by harmonic penetration. In this paper, combined with an inductive filtering method, a parallel delta-connected filtering winding scheme for 12-pulse converter transformer units is proposed to reduce the harmonic currents flowing through the transformers and, thus, to attenuate the harmonic effects on them. This paper describes the presented transformer configuration in terms of the wiring scheme of the 12-pulse converter transformer unit and corresponding flowing paths of different harmonic currents with the orders of 3,6n ± 1(n=1,3,5,.. .),11 and 13 in the filtering winding circuit. Then, the mechanism of the proposed scheme on harmonic suppression to the converter transformers is explained theoretically. In an attempt to validate the theoretical analysis, simulations based on PSCAD/EMTDC and experiments in a laboratory prototype system are performed to evaluate the harmonic eliminating performance of the proposed scheme.

This study focuses on microgrid systems incorporating hybrid renewable energy sources (HRESs) with battery energy storage (BES), both essential for ensuring reliable and consistent operation in off-grid standalone systems. The proposed system includes solar energy, a wind energy source with a synchronous turbine, and BES. Hybrid particle swarm optimizer (PSO) and a genetic algorithm (GA) combined with active disturbance rejection control (ADRC) (PSO-GA-ADRC) are developed to regulate both the frequency and amplitude of the AC bus voltage via a load-side converter (LSC) under various operating conditions. This approach further enables efficient management of accessible generation and general consumption through a bidirectional battery-side converter (BSC). Additionally, the proposed method also enhances power quality across the AC link via mentoring the photovoltaic (PV) inverter to function as shunt active power filter (SAPF), providing the desired harmonic-current element to nonlinear local loads as well. Equipped with an extended state observer (ESO), the hybrid PSO-GA-ADRC provides efficient estimation of and compensation for disturbances such as modeling errors and parameter fluctuations, providing a stable control solution for interior voltage and current control loops. The positive results from hardware-in-the-loop (HIL) experimental results confirm the effectiveness and robustness of this control strategy in maintaining stable voltage and current in real-world scenarios.

Low-frequency oscillation (LFO) in the train- network interaction system would easily lead to traction blockades and seriously threaten the normal operations of high-speed railway systems. This paper proposes a notch filter-based active damping (NFAD) control method to suppress the LFO. First, a small-signal model of the train-network interaction system is developed to investigate the LFO mechanism. By sensing and feeding back the input current of four-quadrant converter, NFAD control method is then formulated to emulate a virtual resistance in order to increase the system damping. Furthermore, a fundamental notch filter is designed to mitigate the damping influence of virtual resistance on the fundamental component. Finally, simulation and experimental results are employed to demonstrate reliability and effectiveness of the proposed method.