Modelling, Implementation, and Assessment of Virtual Synchronous Generator in Power Systems

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

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.

Photovoltaic power generation is mainly connected to the grid by grid-connected inverter. Compared with the traditional synchronous generator, it has the advantages of flexible control and quick response, but there is also lack of inertia and damping. With the increasing of the permeability of the photovoltaic power supply, the rotating spare capacity and the moment of inertia in the power system are relatively reduced, which poses a severe challenge to the safe and stable operation of the power grid. The introduction of photovoltaic virtual synchronous generator makes the grid connected inverter have similar operation characteristics of synchronous generator and improve the stability of power system. In this paper, a hardware in loop simulation test scheme based on RT-LAB is proposed for PV virtual synchronous generator, and a simulation test platform is set up to study the testing method of the performance of the PV virtual synchronous generator. Based on this platform, the characteristics of the PV virtual synchronous generator, such as the inertia and the primary frequency modulation, are carried out. The test results show that the simulation platform is correct.

New energy sources, storage facilities, power electronics devices, advanced and complex control concepts, economic operating doctrines, and cost-optimized construction and production of machines and equipment in power systems adversely affect small-signal stability associated with local oscillations. The objective of the article is to analyze local oscillations and the causes that affect them in order to reduce their negative impact. There are no recognized analyses of the oscillations of modern operating synchronous generators exposed to new conditions in power systems. The basic idea is to perform a numerical analysis of local oscillations of a large number of synchronous generators in the power system. The paper represents the local mode data obtained from a systematic analysis of synchronous generators in the Slovenian power system. Analyzed were 74 synchronous generators of the Slovenian power system, plus many additional synchronous generators for which data were accessible in references. The mathematical models convenient for the study of local oscillations are described first in the paper. Next, the influences of transmission lines, size of the synchronous generators, operating conditions, and control systems were investigated. The paper’s merit is the applicable rules that have been defined to help power plant operators avoid stability-problematic situations. Consequently, boundaries were estimated of the eigenvalues of local modes. Finally, experiments were performed with a laboratory-size synchronous generator to assess the regularity of the numerically obtained conclusions. The obtained results enable the prediction of local oscillations’ frequencies and dampings and will be useful in PSS planning.

The integration of distributed energy resources (DER) generation units based on renewable energy systems into the power system is going on at an unprecedented rate in both bulk power systems and distribution systems globally. However, as the penetration of DER renewables in the power system increases, the system inertia will decline leading to stability issues. As a result, improved converter control methods are required to ensure the high penetration of DERs into the existing power system will not jeopardize the future smart grid. Given that the synchronous generator (SG) has been the bedrock of stable power system operation for over a century, it is desirable for these converter control schemes to emulate the dynamics of the synchronous generator. This idea connotes the virtual synchronous generator (VSG) concept. This paper highlights key findings from recent publications with regard to the VSG concept, by identifying strengths and weaknesses. The inadequacies in some of these literatures are then addressed. A study on the synchronous generator is presented in order to better understand how it controls essential grid parameters. A control technique for an inverter to emulate the SG’s droop control and inertia property is then proposed. For performance evaluation, this control technique is simulated in MATLAB/Simulink using closed-loop control of the inverter.

Pole–zero placement based feed-forward damping control for virtual synchronous generators in power systems with inverter-based resources

• 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.

In the distributed load frequency control (DLFC) scheme, the compromised areas by attackers may endanger the stable and reliable operation of the entire power system. A credibility‐based secure DLFC strategy is in this work proposed to sustain the stable operation of the power system under false data injection attacks. In this secure DLFC method, the gradient‐variation‐based credibility metrics are defined to detect potential attacked measurements. Then, the communication isolation decisions are made based on the adaptive thresholds. To compensate the impact of the communication isolation of misbehaving areas, predictions of future measurements by using the average gradient variation of stored healthy data are feeded back to the area controller. Simulation results of a four‐area power system show the proposed secure DLFC can identify and cut off the communication of the misbehaving areas and still maintain the stability of the power system.

As a typical grid-forming control method, virtual synchronous generator (VSG) control enhances system inertia but introduces frequency oscillation issues. This problem becomes particularly severe in multi-VSG parallel systems when inconsistent virtual inertia exists among power sources, significantly compromising the security and stability of power system operation. Virtual inertia control can directly regulate the rate of change of frequency (RoCoF) under constant torque difference conditions to suppress frequency oscillations, offering faster response characteristics. Therefore, this paper proposes a distributed virtual inertia control strategy for multi-VSG parallel systems. First, a small-signal model of the multi-machine parallel system is established, and its small-signal stability is demonstrated. Second, a neighbor-communication-based distributed virtual inertia coordination control method is proposed. Through neighbor information exchange and local decision-making, this method enables dynamic adjustment of each unit's virtual inertia, driving frequency synchronization among all units in the system. This effectively suppresses post-disturbance frequency oscillations and enhances the dynamic performance of low-inertia power systems. Furthermore, the stability of the proposed control strategy is rigorously proven through the construction of a Lyapunov energy function. Finally, MATLAB/Simulink simulations verify that the proposed virtual inertia control strategy can effectively mitigate frequency oscillations while reducing their settling time.

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

The flexible shaft coupled to the synchronous generator (SG) is critical for the doubly-fed induction generators (DFIG) based wind turbines to improve the ability to suppress system power oscillations. The rigid shaft coupling relationship between the DFIG and SG is analyzed first under the current virtual synchronous generator (VSG) control. To give the power system a vibrational degree of freedom, a novel virtual shaft is added to the VSG emulated by the DFIG-based wind turbine. The power system's two-degree-of-freedom (TDOF) coupled motion model with VSG is then established. The virtual shaft coupling adapted to a DFIG is designed using anti-resonance theory, and the amplitude-frequency characteristic of the TDOF power system is analyzed. With the additional stiffness of the virtual shaft, the power support functions of the VSG, including inertia and damping, are integrated by optimizing the oscillation amplitude at two fixed points in the frequency domain. Finally, on a controller hardware-in-the-loop platform, a typical power system with a high penetration of wind power generation is simulated. The test results demonstrate that by employing virtual shaft coupling, it is possible to suppress system frequency variation and rotor angle oscillation during transient events, significantly improving the reliability of the power support provided by wind turbines.

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.

This study constructs a novel virtual synchronous generator system based on a transfer function, and optimizes the parameters of the model by using the improved whale algorithm to improve the frequency control ability of virtual synchronous generator. Virtual synchronous generator technology helps to solve the problem that the integration of large-scale renewable energy generation into the power system leads to the deterioration of system frequency stability. It can maintain the symmetry of grid-connected scale and system stability. The virtual synchronous generator technology makes the inverter to have the inertia and damping characteristics of a synchronous generator. The inverter has the inertia characteristics and damps to reduce the frequency instability of high penetration renewable energy power system. The improved whale algorithm is efficient to find the best combination of control parameters and the effectiveness of the algorithm is verified by microgrid and power system. The results show that the proposed frequency coordination control scheme suppresses the frequency deviation of power system and keep the system frequency in a reasonable range.

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.

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.