Seamless Mode Transition Technique for Virtual Synchronous Generators and Method Thereof

Wang

IEEE Open J. Power Electron.

et al. 2022

This paper addresses the transient stability of gridforming (GFM) inverters when transitioning from the islanded to grid-connected mode. It is revealed that the reconnection of the GFM inverters to the main grid can be equivalent to a step change of the active power reference, whose impact is closely related with the local load, active power reference of GFM inverter, and shortcircuit ratio (SCR) of the grid. Such equivalent disturbance may cause GFM inverters lose the synchronism with the grid. To avoid loss of synchronization, the existence of equilibria of GFM inverter after reconnecting it with the grid is examined, considering the varying SCR. Then, the parametric effects of power controllers on the transient stability are characterized by using phase portraits, which shed clear insights into the controller design for reliably reconnecting GFM inverters with grid. Lastly, all the theoretical findings are confirmed by experimental tests.

Section: Impact Of Q-v Droop Control On the Transient Stabilitysupporting

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Transient Stability Analysis for Grid-Forming Inverters Transitioning from Islanded to Grid-Connected Mode

Wang

IEEE Open J. Power Electron.

et al. 2022

“…The mathematical formula for the controller was established and the closed-loop stability of the system was evaluated using the eigenvalue stability analysis method. The results showed that this approach eliminated the need for PLLs and islanding detection techniques, as well as multiple feedback loops and complex adjustments to proportional-integral regulators [4]. To address how Inverter-based micro-grids (IMGs) maintain stability during various operational modes to support power sharing and voltage/frequency regulation in overloaded micro-grids, Naderi M et al conducted a comprehensive review of IMG concepts, models, and stability analyses.…”

Section: Motivation and Incentivesmentioning

confidence: 99%

Pre Synchronization Control Strategy of Virtual Synchronous Generator (VSG) in Micro-Grid

Wang,

Ramli,

Aziz

2023

IEEE Access

The constant increase of energy demand and the widespread adoption of renewable energy sources have led to the significant interest in micro-grids, which are small-scale power systems that utilize distributed energy resources. However, micro-grids face synchronization challenges in terms of stability and reliability, and virtual synchronous generator technology has become the key to addressing this issue. This study focuses on the pre synchronization control strategy of virtual synchronous generators in microgrids, aiming to solve the potential surge current problem that virtual synchronous generators may generate when switching from off grid mode to grid connected mode through innovative methods. This strategy employs a phase difference acquisition method that eliminates the need for a phase-locked loop. It calculates virtual power by utilizing the output voltage of the virtual synchronous generator and the grid side voltage, and obtains the phase difference through calculation. The resulting phase difference is then used as input for the frequency phase synchronization unit in pre-synchronization. By adjusting the diagonal frequency, the phase difference θ ∆ can be modified to achieve pre-synchronization before connecting the virtual synchronous generator to the power grid. This method notably reduces the dependence on the phase-locked loop and enhances the stability and reliability of the system. The paper has effectively solved the synchronization problem of virtual synchronous generators in micro-grids through innovative pre synchronization control strategies and improved secondary frequency regulation strategies. It is hoped that these research results will provide new ideas and methods for the further development and application of micro-grid technology.

IEEE Trans. Power Electron.

“…The virtual synchronous generator [5]- [6], which controls the inverter to generate an output voltage via embedding the mathematical model of synchronous generators into the controller of the inverter, has been generally studied. Due to the excellent performances, it has been applied to enhance the inertia and damping of the system [7]- [8] and provide the seamless transition between off-grid and grid-interfaced modes of the inverter [9]. The parameter design of power loops is proposed in [10] to ensure the stability and dynamic performance of the VSG.…”

Section: Introductionmentioning

confidence: 99%

Impedance Analysis and Stabilization of Virtual Synchronous Generators With Different DC-Link Voltage Controllers Under Weak Grid

Guo

Chen

Wang

et al. 2021

In recent years, the virtual synchronous generator (VSG) concept has been widely studied to integrate renewable energy sources. However, instability occurs due to the implementation of the dc-link voltage controllers under the weak grid, and its mechanism remains unclear, which is investigated in this paper. At first, the wideband dq-frame impedance models of the VSGs with the dc-link voltage controllers for two cases are established. Then, the stability analyses of the VSGs are compared based on these impedance models. It is revealed that the interaction dynamics between the dc-link voltage loop and the active loop lead to the negative resistor behavior of the q-q channel impedances for both VSGs, which induces the emerging oscillations of the system in a weak grid. Besides, as a useful design guideline, the parameter design of the VSGs is proposed to enhance the system stability. Finally, experimental results obtained from a 100kW prototype system show good agreement with simulated results, validating the impedance models and theoretical analysis.