Primary frequency support by virtual synchronous generator with precise frequency detection techniques

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.

Renewable power systems dynamic security using a new coordination of frequency control strategy based on virtual synchronous generator and digital frequency protection

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.

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

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.

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

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.

In order to emulate the frequency support characteristics of conventional synchronous generators (SGs), control algorithms based on the virtual synchronous generator (VSG) have been extensively applied to grid-tied converters. However, in the case that a large inertia is used in VSGs, active power oscillations can be introduced in the transients, due to the lack of enough damping effects. To avoid this phenomena, various solutions with additional damping terms have been proposed. This paper analyzes and compares six relevant fixed- parameter active-power-oscillation damping solutions in detail, where responses under set point and phase angle changes, the parameter sensitivity, and capabilities of limiting the rate of change of frequency (RoCoF) and attenuating power ripples are included. The results show the advantages and drawbacks of each solution, leading to the conclusion that extra damping terms may significantly degrade the inertial response of VSGs and have high dependency on the parameter estimation accuracy.

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.

This paper proposes a novel model for the analysis and design of a virtual synchronous generator (VSGs). To enhance the stability in power systems with distributed generators, the concept of VSG has been proposed. The VSG is designed based on the swing equation of a synchronous generator ignoring the dynamics of current flowing through an interconnection reactor. However, responses obtained with actual system are different from those calculated from the model. It implies that the VSG cannot be correctly analyzed and designed by using the conventional model. This paper constructs an accurate VSG model considering the dynamics of current. Moreover, we address the stability analysis of the VSG and reveal a relation between the parameters of VSG controller and the rated power/energy capacity of energy storage systems equipped with the VSG based on the proposed model. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

The high integration of distributed generation (DG) system based on renewable energy sources (RES) in the power system requires changes regarding the control mode of these sources with some urgency. Such changes seek to maintain the stability of the power systems. Thus, there is a demand for using control techniques on DGs/RESs that can mitigate the disturbances caused by low inertia and the lack of control over the dispatched powers. As a solution, one can use virtual synchronous generator (VSG) techniques making the voltage source inverter (VSI) control behave similarly to the traditional synchronous generator (SG). This paper presents a literature review and performance tests for the main VSG topologies used in DGs/RESs: ISE, VSYNC, VISMA and Synchronverter. The implementation of VSG in the DGs/RESs has made possible increase inertia in the grid and, additionally regulate the active and reactive powers separately and bidirectionally. So, it has been possible to meet power system requirements; being able to operation both grid-connected or island-mode, which is ideal for microgrids. The results obtained confirm the literature reports. It was observed that the Synchronverter topology presented advantages over the other VSG topologies.

Adaptive optimization of virtual synchronous generator based on fuzzy logic control and differential evolution

Low frequency oscillation (LFO) is dangerous for power systems secure operation. Over the past decades, installations of power system stabilizer (PSS) on synchronous generator (SG) exciter or flexible AC transmission systems (FACTS) are widely-used methods in electrical power industry to suppress power system oscillation and improve the system oscillation stability. But with the rapid increase of renewable energy sources, more and more power electronic converters with seriously different dynamic characteristics from that of SGs’ are connected and operated in the power system. Thus, the future power system is very likely to generate more complex oscillation phenomenon and system stability problems are maybe more serious than ever before. Under these circumstances, adding supplementary control on these existing power electronic converters is becoming an attractive choice. In this paper, inspired by working principle of the PSS, an improved virtual synchronous generator (VSG) control strategy is presented to damp LFO actively via adaptively adjusting its parameter values of virtual inertia and damping coefficient, according to deviation value and changing rate of its output active power. This idea takes full advantage of flexible adjustability of VSG’s parameters. The effectiveness of the proposed VSG strategy is proved by simulation results, which indicates remarkable performance in fast damping of LFO.

• The paper focuses on optimising Virtual Synchronous Generator (VSG) control in Modular Multilevel Converter (MMC)-based HVDC systems to enhance power system stability and oscillation damping. • It introduces virtual inertia and damping to mimic synchronous generator behaviour, improving frequency and voltage regulation. • The proposed control strategy ensures smooth transitions between grid-connected and islanded modes, suppresses harmonics, and addresses challenges like low inertia and weak grid conditions. • Simulation results validate the effectiveness of the VSG-controlled MMC in maintaining stability during dynamic and transient events, making it suitable for future power systems with high renewable energy integration. This paper discusses the development of a Virtual Synchronous Generator utilizing a Modular Multilevel Converter. The control system employs an internal simulation of the electromechanical swing equation to replicate the inertia and damping characteristics of a synchronous generator, enabling the generation of the necessary frequency and phase angle for MMC control as a VSG. The ac-side management involves cascaded voltage and current controllers operating within a synchronous reference frame defined by the virtual swing equation. Simulation findings validate the performance of the VSG-controlled MMC when connected to an external AC grid and in islanded mode with a resistive load. This paper validates, through experimentation, the effectiveness of controlling a Modular Multilevel Converter (MMC) as a Virtual Synchronous Generator (VSG) designed to deliver virtual inertia and robust frequency stabilization in power systems with low physical inertia. The proposed control structure incorporates a virtual swing equation, cascaded voltage and current regulation loops, reactive power control, and emulated impedance. A 60 kVA MMC model was employed to demonstrate the system’s capabilities. During frequency disturbances such as a drop from 50 Hz to 49.8 Hz, the controller facilitated dynamic power injection up to approximately 35 kW while capping peak currents at 100 A. Frequency deviations were mitigated within 300 milliseconds, and the converter exhibited seamless transitions to islanded operation along with reliable voltage control during load variations. These findings confirm the proposed controller’s effectiveness in maintaining grid stability under diverse operating conditions.

The high penetration of renewable energy sources (RES) results in a low‐inertia, weak power grid. To mitigate this and restore system inertia, it has been widely proposed to operate the inverters of RES units to mimic synchronous generators; this technology is known as a virtual synchronous generator (VSG). In weak grids there is, however, strong coupling between active power () and reactive power (), and any VSG technique therefore requires decoupling in order to operate effectively. This article proposes a new decoupling technique based on the transformation of the power circle of a VSG connected to a weak grid: first, the power circle is translated from its designed position to that of a conventional synchronous generator (SG) connected to a strong grid, achieving partial decoupling. Then, to achieve full decoupling, the authors propose further to modulate the radius of the translated power circle; this is achieved using a series resistance‐capacitance–inductance () circuit which is virtually implemented in the VSG controller. The efficacy of the proposed scheme is validated using a modified synchronverter connected to the weak grid in representative loading scenarios. It is demonstrated that the technique achieves a decoupled control for the synchronverter connected in a weak grid. Moreover, the modified synchronverter is capable of supporting frequency and voltage regulation in the grid without inducing large transient grid currents during mild frequency and voltage variations.