A Comparison of Fixed-Parameter Active-Power-Oscillation Damping Solutions for Virtual Synchronous Generators

An enhanced second-order-consensus-based distributed secondary frequency controller of virtual synchronous generators for isolated AC microgrids

The increasing penetration of inverter-based resources (IBRs) into electric power systems and the retirement of synchronous generators (SGs) both reduce system inertia and challenge frequency stability. This is particularly evident in terms of the rate of change of frequency (ROCOF) measured over short, practically measurable time windows (P-ROCOF). Conventional frequency-constrained unit commitment (FCUC) uses a theoretically idealized ROCOF (T-ROCOF) constraint that underestimates the effect of the fast frequency response (FFR) provided by virtual synchronous generators (VSGs) on P-ROCOF, leading to over-provisioning of generator capacity and higher operating costs. This paper presents a neural network-assisted FCUC (NN-UC) framework that formulates a mixed-integer ROCOF constraint based on an NNtrained to accurately predict P-ROCOF, and introduces a post-solution compensation procedure to correct NN prediction errors.We conducted one-year scenario studies on modified IEEE 9-bus and Japanese EAST 10-machine systems. Results show that NN-UC reduces both total operating cost and committed SG capacity compared to the conventional UC, which uses the T-ROCOF constraint. Even after worst-case compensation for NN’s ROCOF prediction errors, NN-UC still achieves net SG capacity reductions in most scenarios. These findings demonstrate that explicitly modeling the VSG’s FFR in FCUC yields both economic and operational benefits, while the compensation procedure ensures reliable operation.

Decreased system inertia due to Converter Coupled Generation (CCG) is main challenge of future power system operation. This will result in higher Rate of Change Of Frequency (RoCoF) during system disturbance. Either renewable energy sources or independent energy storage devices may contribute to inertia as a solution to frequency instability. Mimicking rotational inertia of Synchronous Generators evolves the concept of Virtual Synchronous Generators(VSG). Real time frequency detection is the important step in VSG implementation. This paper focusses upon potential of VSG to support primary frequency control of power system with precise frequency detection technique called Smart Discrete Fourier Transform (SDFT).

Real-time validation of RoCoF – Enhancing advanced coordinated control strategy for voltage unbalance mitigation implementing demand side management

This paper presents a methodology that aims at identifying virtual inertia (VI) gain limitations from virtual synchronous generators (VSGs) while maintaining the frequency stability considering the delay associated with the frequency measurement process. The phase-locked loop (PLL) is typically used for frequency estimation that is used to calculate the rate of change of frequency (RoCoF) and it drives the VI loop. The PLL is generally accompanied by a low-pass filter that aims to suppress the impact of harmonics. This filter introduces a delay that when used with the VI control loop causes stability issues for high values of VI gain. A comparison of various PLL approaches suggests that certain variants tend to permit higher value of cut-off frequencies which can be utilized to increase the VI gain limit from VSG. This study presents a method by which the upper limit on VI gain can be quantified and related to the cut-off frequency of the PLL low pass filter that is indirectly representing the delay. It is performed using small signal frequency stability analysis on the frequency domain model of the grid with virtual inertia emulating VSG. The effective maximum VI gain from VSG is explored while satisfying the frequency measurement accuracy specification considering harmonics. The results show that the requirements of reaching a stable operation with sufficient stability margins can still be met with a faster PLL-based system and the potential increases in VI support from VSG can be quantified using the proposed method. The study has been first performed on a single machine single inverter bus (SMSIB) system and is generalized to the multi-machine and multi-inverter system.

Synchronous generators (SGs) inherently support grid stability through their physical inertia and capability to tolerate overcurrent conditions during faults. In contrast, inverter-based resources (IBRs), due to the limitations of semiconductor switching devices, lack such overcurrent handling capacity, making them vulnerable during grid disturbances. This paper investigates the low voltage ride-through (LVRT) capability of IBRs employing virtual synchronous generator (VSG) control to enhance their transient response during fault-induced voltage sags. A comprehensive VSG model is developed, incorporating virtual inertia and damping emulation to replicate the dynamic behavior of SGs. The proposed control strategy is validated through time-domain simulations in MATLAB/Simulink under both symmetrical and asymmetrical fault conditions. Simulation results demonstrate that the VSG control effectively enables voltage recovery, sustains stable power output, reduces the rate of change of frequency (RoCoF), and ensures grid code-compliant current injection with acceptable total harmonic distortion (THD). The findings confirm the potential of VSG-based control in fulfilling LVRT requirements and enhancing grid resilience in high-renewable penetration scenarios.

Frequency damping control is a crucial aspect of islanded microgrids utilizing multiple virtual synchronous generators (VSGs). This paper studies the effects of line impedance mismatches and transient frequency out-of-sync leading to frequency interactive oscillation in VSGs. To address this issue, we propose a distributed interactive damping and zero-error control method that utilizes sparse communications. The objective of this method is to effectively suppress frequency oscillation by minimizing the differences in frequency dynamics among all VSGs. By implementing this approach, a low rate of change of frequency (RoCoF), accurate active power sharing, and zero frequency deviation are ensured. Through dynamic performance analysis, frequency characteristic analysis, and stability analysis based on LaSalle’s invariance principle, we demonstrate significant improvements in system stability, as well as dynamic and steady state performances. Finally, simulation and experimental results obtained under load changes, short-circuits, and communication faults validate the effectiveness of the proposed control method.

In order to improve the friendliness of the grid connection of new energy power generation, the new energy photovoltaic (PV) unit is equivalent to a synchronous generator in the power system and a virtual synchronous generator (VSG)-controlled PV energy storage complementary grid-connected power generation system model is established and studied to analyze the VSG. When power is supplied to the load together with the power grid, the energy storage unit inside the VSG will release and store the electrical energy according to the fluctuation of the PV output, which plays the role of the adjustment of the prime mover; in the case of load power fluctuations, and power grid assume the corresponding active power regulation according to their capacity. The amount of active power adjustment to jointly and maintain the power balance inside the system under the condition of fluctuating load power. The overall system architecture and control strategy of PV grid-connected inverter based on VSG algorithm are proposed. The PV-VSG proposed here not only takes into account the maximum power point tracking control but also has independent participation in the power supply. A series of characteristics of synchronous generators, such as network frequency modulation voltage regulation and inertia damping, can effectively improve the new energy PV power generation system and promote the new energy consumption. The results of system simulation and field demonstration operation fully show the effectiveness and correctness of the proposed control strategy based on VSG algorithm.

A comparative study of single-loop VSG and multi-loop VSG

As an important part of electric multiple units (EMU), the auxiliary power supply system plays an important role in the normal operation of the vehicle. In order to improve the reliability of the auxiliary power supply system, the virtual synchronous generator (VSG) technology is applied to the parallel control system of auxiliary inverter. The essence of VSG technology is to control the inverter to simulate the working principle of synchronous generator, so as to obtain similar operation characteristics of synchronous generator. The auxiliary inverter controlled by VSG technology can avoid the disadvantage of hard external characteristics of power electronic devices. Its rotating inertia can obviously prevent frequency fluctuation, and the system has high stability and reliability. In this paper, the frequency and voltage of the auxiliary inverters are controlled independently with VSG technology, so that the output voltage can be controlled stably and the power quality can be improved. Finally, the MATLAB simulation results show that the parallel control of auxiliary inverter based on VSG achieves the expected goals.

In an islanded microgrid supplied by virtual synchronous generator (VSG) based inverter-based resources (IBRs), inter-IBR oscillations pose a serious threat to frequency stability and power-sharing accuracy. While VSG control enables gridforming inverters (GFMs) to emulate inertia and improve frequency dynamics, it also introduces poorly damped modes. This paper proposes a distributed cooperative control strategy that enhances damping of inter-IBR oscillations without compromising key frequency performance metrics such as the rate of change of frequency (RoCoF) and frequency nadir. The proposed control introduces a dynamic state variable that adjusts the auxiliary frequency reference in real-time based on both local frequency error and a distributed feedback term derived from the mismatch in normalized active power among neighboring inverters, thereby enhancing damping and actively suppressing inter-IBR oscillations. In addition, the control incorporates normalized active power mismatch to achieve proportional load sharing, implemented using a sparse communication topology among neighboring IBRs. An eigenvalue analysis based on small-signal model is conducted for appropriate selection of control gains to achieve system stability. Simulation results under various IBR configurations demonstrate that the proposed control method effectively suppresses inter-IBR oscillations, ensures proportional power sharing, and achieves robustness. Accordingly, the applicability of the proposed control design is validated for both homogeneous and heterogeneous VSG systems.

In recent years, the increasing penetration of distributed generation in microgrids challenges the control and coordination of energy resources. Especially in microgrids with virtual synchronous generator (VSG)-controlled converters and conventional synchronous generators (SG), the inherent inertia difference (i.e., the VSG and SG) results in a poor transient performance when the VSG and/or loads are cut in/out. Thus, this paper explores the transient performance of microgrids with parallel VSG and SG systems. More importantly, a novel pre-synchronization control method is proposed to eliminate the phase jump while meeting the requirements in case of closures or re-closures of generation units. A small-signal dynamic model is presented, and accordingly, the VSG inertia and its damping can be designed considering the capacity ratio of VSG and SG units. In addition, with the power angle stability analysis, an active power provision strategy is introduced to suppress the transient power oscillation due to the inertia difference. Finally, the feasibility of the proposed methods is verified by simulations on a microgrid consisting of parallel VSG and SG units.

A circulating current suppression strategy of VSG based on adaptive virtual complex impedance

As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, the virtual synchronous generator (VSG), in which the power electronic inverter is controlled to mimic the characteristics of traditional synchronous generators, is a promising strategy. In this paper, the representation of the synchronous generator in power systems is firstly presented as the basis for the VSG. Then the modelling methods of VSG are comprehensively reviewed and compared. Applications of the VSG in power systems are summarized as well. Finally, the challenges and future trends of the VSG implementation are discussed.

Virtual synchronous generator (VSG) was a control strategy for inverter generators (IGs) to overcome the shortcomings of small inertia and low damping by simulating the rotor operating mechanism of synchronous generators (SGs). The stability of VSG is very important for its application. At present, the related research mostly focuses on the VSG itself and its application in microgrid. There is few research to explain how VSG effecting the low frequency oscillation in transmission power system. This paper built a small-signal model of VSG-SG interconnected system, which is suitable for the study of low frequency oscillation damping characteristics of the transmission power grid. Based on the model, the effect of VSG on the low frequency oscillation were compared with the effect of SG to reveal the mechanism of how VSG affecting the damping characteristic.