Concept Of Virtual Synchronous Generator Research Articles

Control approach for photovoltaic inverters enhancing the primary grid using the virtual synchronous generator concept

This paper presents a control scheme for virtual synchronous generators (VSGs) in PV inverters, designed to enhance grid frequency and voltage. Through the skillful management of active and reactive power, this control scheme enables PV inverters to interact seamlessly with the main grid in response to grid events, including voltage and frequency fluctuations. The VSG controller is implemented using Matlab Simulink, and its effectiveness is rigorously assessed under various scenarios in a case study involves a 50 kVA rated PV inverter, a 50 kW rated PV system, and a 220 V grid phase voltage. In conditions of low power generation from the PV system (solar radiation of 200 W/m²) and high load power (120 kW and 37.5 kVAr), the load voltage drops to 202.4 V. The VSG controller successfully raises the grid voltage by 17.6 V, stabilizing it at 220 V. Conversely, in scenarios of high PV power generation (solar radiation of 1000 W/m²) and low load power (20 kW and 7.5 kVAr), the grid voltage surges by 10 V, reaching 230 V. The proposed control strategy adeptly fine-tunes the voltage, ultimately stabilizing at 220 V. Additionally, when the frequency deviates within ±0.4 Hz from the nominal frequency of 50 Hz, the proposed control effectively restores the frequency to its nominal value.

Utilization of superconducting magnetic energy storage and doubly fed induction generator for enhancing stability of interconnected power system

SummaryAs the share of wind power keeps on increasing, the interaction between synchronous and wind generators pose a challenging issue on power system stability. In order to investigate the impact of wind penetration on stability of power system, appropriate modeling of wind energy conversion systems (WECSs) is necessary. Moreover, it is needed to comprehensively study the impact of wind penetration on power system oscillations. This paper presents a didactic approach for integrating a doubly fed induction generator (DFIG)‐based wind farm from SimPower Systems library to a five‐area 68‐bus power system modeled in Simulink. Inter‐area oscillations with and without wind power penetration are investigated for their characteristics. Renewable energy sources are connected to the grid via power electronics converters at the cost of a reduction in inertia. The concept of virtual synchronous generator (VSG) produces virtual inertia by exchanging active power with the power system. The impact of superconducting magnetic energy storage (SMES) and DFIG on enhancing damping performance of inter‐area is investigated. The increase in damping ratios of inter‐area oscillatory modes verifies the enhancement in small signal stability by connecting SMES and DFIG to the power system. The usage of SMES operating in VSG mode to improve the dynamic stability with highly erratic wind profile is also investigated. The developed MATLAB/SIMULINK‐based DFIG model is simple to use and can be expanded to build efficient controllers. The fidelity of the DFIG model and VSG technology is verified in real time by Opal‐RT (OP4510).

Stochastic unit commitment to determine frequency response ramp rate including wind turbines with synthetic inertia and virtual synchronous generator

In this paper, the dynamic frequency constraints are derived for power systems incorporating full-converter wind turbines. These wind turbines could be equipped with a virtual inertia by either synthetic inertia control or virtual synchronous generator concept. In the former scheme, deviations in the wind turbines rotor speed remain in synchronism with the system frequency. However, the wind turbines start to restore their rotor speed before the system frequency recovery initiation, in virtual synchronous generator scheme. The restriction on the virtual inertia are determined considering a limit variable on wind turbines rotor speed drop. The frequency response requirements are derived in terms of governor’s base power, ramp rate and reserve power. A linear frequency nadir constraint is also proposed for the synthetic inertia strategy. Then, the constraints are integrated into the stochastic unit commitment to be consistently and economically met over 24-hour period. As such, the contingency size management are coordinated with the virtual inertia provision. The unit commitment results of IEEE 118-bus system including multiple wind farms reveal that the virtual synchronous generator concept can be an optimal solution for future low-inertia grid’s challenges. Finally, accuracy of the unit commitment results is validated through time-domain simulations of the detailed system model.

Impedance Model Based Dynamic Analysis Applied to VSG-Controlled Converters in AC Microgrids

The virtual synchronous generator (VSG) control technique has proven to be an attractive solution to power flow control of distributed generation (DG) systems integrated in AC microgrid by using power converters. Thus, this paper presents the influence of Thevenin impedance seen by each DG unit on the dynamic performance of grid-connected converters controlled by using VSG concept. The dynamic analysis is based on a small-signal model suitable for describing the power flow transient characteristics of DG units operating in medium and high voltage networks. Based on this model, the Thevenin impedance parameters influence on the VSG controllers dynamic performance are discussed. The VSG technique performance in different operating scenarios is assessed by means of simulation results. The obtained results reveal the effectiveness of the theoretical analysis performed.

Cooperative Primary Control of a Hybrid AC/DC Microgrid Based on AC/DC Virtual Generators

This article presents a dynamic control strategy for a hybrid AC/DC Microgrid (MG). To allow a high penetration of renewable energies, provide an increased system reliability during islanding and reduce the dependency on the mains, Energy Storage Systems (ESSs) are included in both the DC and AC grids. The MG is composed by DC grid, with connection to the mains and a central battery ESS, and a flexible number of AC subgrids coupled to the DC bus through AC/DC 3-phase Interlinking Converters. The paper presents three main contributions: 1) A DC bus regulation scheme is proposed based on DC virtual generators and P/V DC droop that allows to adapt the participation in the power sharing for DC bus regulation and provides with an automatic transition between grid-connected and islanding modes; 2) In order to provide a cooperative operation between the different AC subgrids, allowing the automatic power sharing between them through the DC bus, a Hybrid AC/DC Virtual Generator control scheme is proposed based on the Virtual Synchronous Generator concept, for its implementation in the interlinking converters; 3) an AC voltage and frequency compensator suitable for systems with high resistive line impedance. The discussion is supported with small signal analysis, simulations and Hardware-in-the-loop.

Fuzzy based virtual inertia emulation in a multi-area wind penetrated power system using adaptive predictive control based flywheel storage

The concept of virtual synchronous generator (VSG), which imitates the behaviour of a real synchronous generator, is considered as a solution for lack of inertia caused due to integration of renewable sources. Unlike most of the existing VSG techniques, which are based on the idea of infinite energy, this paper takes into consideration the energy level of energy storage. This paper proposes a fuzzy based VSG topology to adjust VSG parameters according to the magnitude of perturbation while addressing the constraints on key operational parameters of energy storage. The proposed fuzzy logic controller (FLC) provides set point to an adaptive predictive controller, which in turn provides reference power command to energy storage. Particle swarm optimization (PSO) is employed so that flywheel energy storage system (FESS) tracks any random reference signal. To facilitate VSG operation while addressing operational limits, adaptive predictive controller for FESS is implemented. The FESS speed and converter power rating constraints are directly stated in the supervisory controller development, which are mostly included in an ad hoc way. For various disturbances, the efficacy of the controller is validated in MATLAB/Simulink as well as in real-time by means of the OPAL-RT (OP4510) device. The real-time simulations validate the superior performance of the proposed VSG technique.

Virtual inertia provision through data centre and electric vehicle for ancillary services support in microgrid

The proposal focuses on the role of data centres (DCs) and electric vehicle (EV) energy storage systems (ESSs) for frequency regulation and it provides a new opportunity for different resources to participate in the power sector. Frequency fluctuations are introduced with the emergence of inverter-dominated renewable energy sources (RESs) as it does not provide rotational inertia to the grid, such as synchronous generators. In this study, the virtual synchronous generator (VSG) controlled inverter compensates for the lack of inertia. Particularly, this research work analyses the involvement of DC and EV batteries as ESSs in designing an integrated technical virtual power plant (VPP) to support frequency variations using the VSG concept. Microgrid (MG) simulations are performed in MATLAB/ Simulink platform. Case studies are carried out to validate the grid export and grid import performance of the model by using variations in the load and the solar irradiance of the MG. It is verified that bidirectional power flow takes place between the proposed VPP components and the grid that enables the grid with high penetration of RESs. The work provides a conceptual framework for future contributions towards the smarter usage of assets such as ESS and a greener future.

Optimal allocation of inverter connected DGs: An objective function to minimize deterioration of transient stability of power system

While renewable energy resources have provided more flexibility in operation of power system, it may threaten the security of the power system during transient phenomena. Previous investigation on the power system with high penetration of inverter based connected (IBC) distributed generations (DG) reveal that this type of DG has negative influence on the transient stability margin of the power system (Seungchan et al., 2018). An optimization framework is proposed in this paper, in which the negative effects of IBC type of DGs on the transient stability margin of the power system is minimized. More specifically, this paper proposes a new objective function (OF) to distribute the IBC type of DGs that have minimum deterioration of transient stability margin. To such aim, an improved index based on the kinetic energy is introduced which considers IBC type of DGs based on virtual synchronous generator concept. To calculate index, equal area criterion (EAC) and sensitivity analysis are respectively used for extracted critical kinetic energy (CKE) and consequently to take into account the effect of fault trajectory. The IBC type of DGs in this investigation includes photovoltaic and electrical vehicles. The proposed framework is applied on the IEEE 14-bus and 30-bus test system and further discussed during several contingencies and fault conditions.

Operating point optimization of wind turbine generators for provision of inertial response and frequency control

Inertial and frequency control approaches for wind turbine generators have proven to be effective in mitigating the frequency control and stability problems inherent to power systems and microgrids with high penetration levels of wind generation. This paper proposes an optimization formulation to determine the operating point of de-loaded wind turbines in order to improve the mechanical dynamics of the wind turbine-generator set. Such operating point optimization reduces the speed deviation magnitude and settling time of the wind turbine caused by the action of inertial and frequency control. The optimization approach is integrated into a combined inertial and frequency control approach for type-4 wind turbine generators. The optimized control approach, based on the concept of virtual synchronous generator, may extend the inertial response and frequency control capabilities of type-4 wind turbine generators, thus improving the transient and steady-state frequency performance of high wind penetrated power systems.

Performance Tuning for Power Electronic Interfaces Under VSG Control

Renewable generation, such as solar PV and wind power, is commonly integrated into the power grid through inertialess power electronic interfaces (PEIs). Due to the increasing penetration of renewable generation, the frequency stability of the current power system deteriorates. In order to sustain the desired level of the overall inertia, the virtual synchronous generator (VSG) algorithm has been proposed. The concept of VSG is to enable the PEIs to emulate the external properties of traditional synchronous generators (SGs), such as inertia and primary frequency responses. By exploitation of the well-established knowledge system of conventional SG-based power grids, the VSG can also be implemented with the capabilities of primary, secondary, and tertiary frequency control in multiple temporal stages. This paper focuses on parameter tuning for VSG-PEIs by performance indices. The emulation strategies are completed with the capability of secondary and tertiary frequency regulation. The transfer functions of the dynamic systems of PEIs are simplified and referred to the control theory. The composite influences of different parameters on performance indices are analyzed. The methods of the parameter tuning are proposed according to the temporal sequences of the control stages. By typical performance standards, the proposed method is verified through simulation.

A novel VSG model suitable for the analyses of static/transient stability and rated power/energy capacity of energy storage system

AbstractThis 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.

Research on Virtual Synchronous Generator Control for Vehicle-to-Grid System

This paper investigates the concept of Virtual Synchronous Generator (VSG) and analyses the working principle of common VSG control technology. With the promotion of Vehicle-to-Grid(V2G) technology, large-scale power electronics devices will be connected to the grid. Consequently, the stability of the grid will be influenced by the lack of mechanical inertia and system damping within these power electronic devices. The extant normal control methods are difficult to cope with this issue. Accordingly, a VSG control technology is proposed by this study, which can be applied to V2G system. Moreover, the mathematical analysis of this control method is also suggested in this research. This control method provides mechanical inertia and system damping, which is similar to synchronous generators. It also can achieve the accurate control of power. The original P/Q-U-I three-loop control is simplified to P/Q-I dual-loop control in the condition of not losing the inertia of the converter. Ultimately, the simulation examines the accuracy and effectiveness of the control method.

Control Method of Self-Frequency Recovery and Active Power Sharing for an Isolated Microgrid Based on VSGs

The concept of virtual synchronous generator (VSG) is emerging as an attractive solution for renewable energies to enhance the microgrid inertia and damping property by emulating the essential behaviors of conventional synchronous generators. However, in the isolated microgrid based on VSGs, there will be a frequency deviation when the power demand varies because of the droop characteristic of the VSG in active power–frequency regulation. In this paper, a control method for VSGs to implement self-frequency recovery and active power sharing in isolated microgrid is proposed. With this method, the VSGs regulate their power baseline values over multiple iterations through local-feedback of the frequency deviation until the microgrid frequency restores to normal value, and simultaneously share the power demand variation according to the ratio of their power baseline values. Compared to the previous studies, the proposed method can eliminate the output power and frequency oscillations in secondary control, and additionally, reduce the dependence of the microgrid on communication system, which is beneficial to enhance the robustness of the microgrid operation. Simulation results proved the proposed method to be effective.

Frequency support in a micro‐grid using virtual synchronous generator based charging station

This study focuses on the role of electric vehicle (EV) charging station (CS) to support the frequency of the islanded micro-grid (MG). Frequency deviation is a common issue in islanded MGs due to the intermittent nature of renewable energy sources (RES). This issue can be minimised by providing the inertia to the system. However, RES have low or no rotational mass and therefore, they are not able to provide the inertia to the system. In this study, the concept of virtual synchronous generator (VSG) mechanism using a CS is proposed to provide the inertia to the system, where a fleet of EVs parked in CS acts as an energy storage system for MG. Simulations have been performed in Matlab Simulink on the data taken from the MG on the island Kythnos in Greece. Case studies have been carried out to verify the frequency support of MG using VSG mechanism. In these case studies, irradiation level of the photovoltaic array and load of the MG system have been changed arbitrarily to induce the power mismatch in the system. Through simulation results, it has been verified that the frequency of the system can be supported by the bidirectional flow of power between the CS and MG using VSG control mechanism.