Virtual Synchronous Generator Technology Research Articles

Dynamic Stability Study of Grid-Connected Inverter Based on Virtual Synchronizer under Weak Grid

The power grid has the characteristics of a weak grid with an increase in new energy penetration in the power system. Power electronic-based renewable generation brings issues that weaken the entire system, including the loss of inertia. Low inertia and weak damping cause system oscillation. Virtual synchronous generator (VSG) technology gives power electronic equipment inertia-support capability but increases the complexity of control system parameter design. Many researchers have studied the design method of VSG considering the frequency disturbance of the power grid. The traditional VSG parameter design method ignores the influence of source-side and grid-side fluctuations on the transient stability of the system, resulting in the difference between the actual dynamic and static indicators and the design indicators of VSG in a weak grid. This paper analyzes a small-signal model based on power fluctuations and frequency fluctuations and proposes a control parameter design method that combines the influence of grid impedance to ensure the dynamic stability of the system under a weak power grid. The simulation and experimental results verify the correctness and feasibility of the control method.

An Energy Storage Assessment: Using Frequency Modulation Approach to Capture Optimal Coordination

To reduce the allocation of energy storage capacity in wind farms and improve economic benefits, this study is focused on the virtual synchronous generator (synchronverter) technology. A system accompanied by wind power, energy storage, a synchronous generator and load is presented in detail. A brief description of the virtual synchronous generator control strategy is given. The capacity allocation is based on different optimization goals and the optimal energy storage capacity configuration of the coordinated frequency modulation (FM) control strategy. The detail of the dual-loop control strategy is carried out by establishing the grid-connected transfer function model of the synchronverter energy storage and a theoretical model of life cycle cost is established. The optimal control strategy of coordinated FM for wind storage is implemented using MATLAB software. The simulation showed that the proposed strategy provided the energy storage capacity at high wind speed, which is configured to be 5.9% of the installed capacity of the wind turbine, marking a reduction of 26% compared with the 8% capacity required for independent support. In addition, the proposed method has improved the energy storage capacity configuration of the coordinated FM control strategy.

Coordination of adaptive virtual resistance controller and flux-coupling-type fault current limiter for LVRT fulfillment of virtual synchronous generator

The virtual synchronous generator (VSG) technology equips power inverters with virtual inertia and damping to access generation and storage more friendly. However, the VSG's weak performance to withstand fault current inrush and fulfill low-voltage ride-through (LVRT) operation should be carefully addressed. This paper presents an innovative method to coordinate adaptive virtual resistance controller (AVRC) and flux-coupling-type fault current limiter (FC-FCL). First, the theoretical modeling and transient characteristics of the VSG are illustrated. Then, the implementation of the coordinated AVRC and FC-FCL is done, with an elaboration of the coordination philosophy and the proposed approach's parameter design rules. Further, simulation validations are performed in MATLAB/Simulink. Different severities and types of faults are imitated, and the comparisons of the proposed method against the traditional VSG strategy, the single AVRC or FC-FCL, the inner current control, and the virtual voltage control are conducted. The results prove that: i) the proposed approach offers superior abilities to repress the fault current, alleviate the terminal voltage fluctuation and keep the VSG power balance. ii) the proposed approach can handle different severities and types of faults in the VSG. A satisfactory LVRT is obtained for the VSG with favorable frequency stability and power angle stability.

Power‐frequency oscillation suppression algorithm for AC microgrid with multiple virtual synchronous generators based on fuzzy inference system

In the microgrid, virtual synchronous generator technology can significantly enhance the anti-interference characteristics of the system frequency and bus voltage, as well as solve the problems of insufficient damping and low inertia. However, the system frequency and active power oscillation caused by power fluctuations and grid faults threaten the stable operation of the grid seriously. Therefore, for an alternating current (AC) microgrid multi-virtual synchronous generator (VSG) parallel system, an improved virtual synchronous generator control algorithm based on a fuzzy inference system is proposed, which adjusts the values of virtual inertia and damping coefficient dynamically through fuzzy logic rules to realize the coordinated control of the two. The enhanced VSG algorithm described in this research has a substantial influence on power-frequency oscillation suppression, decreases active power and frequency overshoot, shortens the adjustment time, and improves system frequency stability active power, according to simulation and experimental findings.

Design and parameter analysis of an improved pre-synchronization method for multiple inverters based on virtual synchronization generator control in microgrid

The microgrid is increasingly important because of the rapid development of renewable energy. Meanwhile, power converter is an important interface, where the stable operation of microgrid need effective inverter control strategy. The virtual synchronous generator technology emulates the synchronous generator’s electromechanical transient characteristics, which has been used in the inverter of microgrid in both the grid-connected and islanded mode. While switching from islanded mode to grid-connected mode, the virtual synchronous generator based microgrid need a pre-synchronization method to avoid voltage distortion and current surge. The previous pre-synchronization methods usually focus on the synchronization of single inverter, which may lead to the dynamic power distribution problem in mode switch. This paper presents an improved pre-synchronization method for virtual synchronous generator based multi-inverter microgrids, which can realize the seamless switching and rational power distribution. In addition, to optimize the performance in mode switch, the influence of pre-synchronization parameters on the pre-synchronization microgrid is analyzed, which provides useful advice to the parameter design. Finally, the experimental platform of microgrid based on dSPACE is built to verify the effectiveness of the proposed control strategy.

Microgrid’s multi-VSGs cooperative control method based on distributed communication

Microgrid is a group of interconnected Distributed Generators (DGs) and loads. As an application of renewable energy, microgrid began to enter people’s vision. The technology of Virtual Synchronous Generator (VSG) is becoming a research hotspot owing to it can supply inertia for distributed generation system. For the oscillation problem in microgrid after using VSG technology, this paper theoretically analyzes the variation in output frequency and power of parallel VSGs after system load fluctuation, and proposes a cooperative control method of multi-VSGs. Through distributed communication network, this method improves the output control of each VSG. In the transient process, applied method alleviates the uneven distribution in the active power of the microgrid, while reducing the difference in the output frequency of each VSG, therefore, it can significantly restrain the oscillation and ameliorate the dynamic characteristics of microgrid. A simulation model is established to prove the validity and advantage of this method at the end of this paper.

Multi-VSG-based frequency regulation for uninterruptible power AC micro-grid with distributed electric vehicles

In view of the energy storage performance of electric vehicles (EVs) can be regarded as backup power sources to provide electric energy for residents in case of power failure in the community. With the aim to improve the dynamic frequency regulation ability of EVs accessed uninterruptible power AC micro-grid, the virtual synchronous generator (VSG) technology is utilized to EV inverter, and a consensus-based cooperative adaptive virtual inertia (CAVI) strategy is designed between VSGs. Meanwhile, according to the time-varying topology switching method, each VSG can select the optimal communication direction based on the real-time system state. Then, a derivative-free cooperative VSG control structure is designed to avoid the noise of frequency derivation in the CAVI strategy. The important feature of CAVI is that the virtual inertia can be regulated by the VSG frequency deviation, and local VSG can sense the state of neighboring VSGs to realize the consensus of the frequency response of multi-VSG with different parameters. The proposed CAVI is completely distributed, it can be implemented on each local VSG with directed communication among neighboring VSG, and avoid the requirement on the central controller. The effectiveness of the proposed control strategy is demonstrated by the Case study.

Frequency Modulation Method and System of Photovoltaic Virtual Synchronous Generator Based on Computer Technology

With people’s attention to environmental protection, clean energy has become an important research and development direction. Among them, photovoltaic power generation has many advantages, such as simple process, no fuel consumption, no noise, no pollution and so on. The power grid capacity is becoming larger and larger, and has a great impact on the environment. Therefore, the grid connection of photovoltaic power generation will cause major problems for the planning, operation and dispatching of power grid. Virtual synchronous generator (hereinafter referred to as VSG) technology can simulate the inertia, primary frequency regulation and voltage regulation characteristics of synchronous generator, which has become an important way to improve the dynamic frequency response ability of the system. Therefore, VSG technology has become an important research technology of photovoltaic grid connected system, among which FM method will also become an important research direction. Firstly, this paper analyzes the VSG algorithm and its basic characteristics. Finally, this paper analyzes the control scheme of overall primary frequency regulation of photovoltaic power station (hereinafter referred to as PPS).

An adaptative control strategy for interfacing converter of hybrid microgrid based on improved virtual synchronous generator

Inertial support for hybrid AC/DC microgrid systems is provided by the virtual synchronous generator (VSG). However, the fast performance of the system is neglected while enhancing the stability of the system. To address this problem, an adaptive virtual inertia control strategy based on VSG technology is proposed. This control approach adaptively adjusts the system virtual inertia when the system operation deviates from the nominal value, by slowing down the rate of change of AC frequency and DC voltage and improving the deviation of AC frequency and DC voltage. Meanwhile, when the AC frequency and DC voltage restore back to the rated value, the rate of change of AC frequency is accelerated and the DC voltage fluctuation is reduced by dynamically adjusting the virtual inertia of the system. The proposed adaptive virtual inertia control method combines the advantages of large and small inertia to effectively improve the dynamic response of the system voltage and frequency in both rectifier and inverter modes. Finally, the simulation and experimental results verify the effectiveness of the proposed control algorithm.

An integrated control algorithm of power distribution for islanded microgrid based on improved virtual synchronous generator

Virtual synchronous generator technology can effectively improve the anti-interference characteristics of the system frequency and bus voltage in the microgrid, and solve the problems of insufficient damping and low inertia of the system. However, in an islanded microgrid with multiple distributed generation, the difference in line impedance will cause local voltage deviations, which in turn leads to a series of problems, such as reducing power distribution accuracy and increasing bus voltage drop. Therefore, for the island-type microgrid multi-inverter distributed power generation parallel system, in order to solve the problem of low power distribution accuracy and large frequency oscillation caused by system parameters in virtual synchronous generator control, an improved virtual synchronous generator control algorithm based on adaptive droop coefficient is proposed in this paper, which not only eliminates the resistance component of the line impedance, makes the system impedance characteristic present a purely inductive nature, but also realises real-time adjustment of active and reactive power. While maintaining the stability of the bus voltage and system frequency, it maintains high power distribution accuracy and improves the dynamic performance and operational stability of the power grid system.

VSG-Based Parameter Adaptive Control Strategy

As a large number of converters composed of power electronic devices are connected to the grid, power system has gradually decreased stability. How to increase dynamic response of the converter has become one of the research hotspots. Virtual synchronous generator technology (VSG) can endow the converter with moment of inertia and damping characteristics, thereby enhancing dynamic response, but the traditional VSG technology cannot achieve the optimal control effect. To solve this problem, an adaptive control strategy is proposed, which takes logical combination of system angular velocity and frequency change as the real-time change condition, with exponential function as the change expression. Finally, this paper uses MATLAB / Simulink to compare the method in this paper with several existing typical control strategies.

Cooperative Control Strategy of Multiple VSGs in Microgrid Based on Adjacent Information

As an interface between distributed power source and large power grid, microgrid has attracted more and more attention. Due to the lack of inertial support for the power system, the virtual synchronous generator (VSG) technology that can simulate the external characteristics of synchronous generators came into being. Aiming at the problem of power and frequency oscillation in microgrid after the introduction of VSG technology, this paper conducts small-signal modeling of multiple VSGs in parallel, analyzes their operating characteristics, and proposes a multiple VSGs cooperative control strategy based on adjacent information. Depend on the adjacent information, the strategy optimizes the output control of each VSG, which makes each VSG tend to the same output frequency at any time. Therefore, the proposed strategy can suppress the power and frequency oscillation, and improve the dynamic characteristics of the system. In this paper, the stability of the proposed control strategy is studied by Lyapunov stability theory, and the effectiveness of the proposed control strategy is verified by simulation.

Cooperative Control Strategy of Virtual Synchronous Generator Based on Optimal Damping Ratio

Wind power, photovoltaics and other new energy sources are connected to the grid on a large scale. The power electronic interface cannot provide inertia and damping support for the microgrid. The virtual synchronous generator technology is introduced into the inverter control system. Unlike the synchronous generator, its parameters are flexible and adjustable, which can enhance the robustness of the microgrid. This paper firstly analyzes the influence of the moment of inertia and damping on the system, it is based on the equivalent relationship between the three-phase inverter and the synchronous machine, combined with the VSG rotor motion equation, and conducts stability analysis based on the small signal model and root locus. Based on the existing control strategy, a virtual synchronous generator cooperative control strategy based on the optimal damping ratio is proposed. Finally, the VSG collaborative control model is built in MATLAB/Simlink, the experimental results show that the proposed control strategy effectively improves the transient performance of the VSG, the system active power overshoot is reduced from 5% to 0, and the frequency deviation peak is lowered from 0.174 Hz to 0.115 Hz, which confirms the effectiveness of the proposed control strategy.

Presynchronous Grid-Connection Strategy of Virtual Synchronous Generator Based on Virtual Impedance

The virtual synchronous generator (VSG) technology of inverter is widely used to provide the inertia and damping support for power system. However, an additional measurement device PLL (phase-locked loop) is required in the virtual synchronous generator grid connection to track the voltage phase, amplitude, and frequency, which restricts the flexible output of the distributed power generation system. To tackle this challenge, a method for grid-connected control of virtual synchronous generator based on virtual impedance is proposed. It is assumed that there is a virtual power exchange between the synchronous machine and the power grid when the virtual synchronous generator is off-grid, the virtual impedance is developed to calculate the virtual current, and when the virtual current is zero, the output voltage of the VSG can be synchronized with the voltage of the power grid, thereby seamlessly switching between off-grid and grid-connected VSG. A semiphysical simulation platform is built based on RT-LAB; simulation and experimental results show that the proposed grid synchronization control strategy of the VSG can achieve seamless transform between different VSG modes, which is simpler than the conventional synchronization control, while having a good active and reactive power tracing performance.

Renewable Energy System on Frequency Stability Control Strategy Using Virtual Synchronous Generator

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.

A novel ramp-rate control of grid-tied PV-Battery systems to reduce required battery capacity

This paper proposes a novel ramp-rate control of PV-battery systems in microgrids, including the coordination and control of time-varying loads. The power consumed by the loads is part of regulation strategy and participates in mitigating the overall ramp-rate of the controlled PV system and the loads. The control strategy is grid-friendly as the power fluctuation of the loads is also considered besides that of the PV system. Furthermore, this control strategy economizes on the number and size of auxiliary batteries that tipically are considered combined with PV system, since a part of the required active power is now borrowed from the loads. Combined to the load control a ramp-rate control, based on the virtual synchronous generator technology, is originally proposed to further reduce the use of the batteries and to provide innovative ancillary service. Finally numerical simulations on a test microgrid indicate the effectiveness of the proposed ramp-rate control. The test cases also demonstrate that this control strategy succeeds in reducing the battery capacity and the number of (dis)charge cycles as well as in offering frequency support to the microgrid.

Speed-Sensorless and Motor Parameters-Free Starting Method for Large-Capacity Synchronous Machines Based on Virtual Synchronous Generator Technology

The large-capacity electrically excited synchronous machines are widely applied in modern industrial production, and starting issues have become one of the most concerns of the synchronous motors in practical operation, such as the long starting time, large current shock, and poor adaption to a wide-ranging load. To deal with these starting problems, many starting methods have been proposed in previous studies. Regrettably, high-performance methods depend on specific motor parameters and complex sensorless technology, while simple and low-cost methods are low performance. In this article, a modified back-to-back starting method is proposed for large-capacity synchronous machines based on virtual synchronous generator (VSG) technology, where the cascaded H-bridge converter is controlled as a VSG to replace the prime mover and synchronous generator of the conventional back-to-back starting system. To reduce the current shock, an initial relative-angle regulator is designed. To improve the robustness in the presence of a wide-ranging load, a damping torque branch is adopted. Extra speed sensors are no longer required since the VSG speed is directly applied in the feedback control loop. To validate the effectiveness of the proposed approach, extensive simulation and experimental results are presented. Compared with conventional approaches, the proposed starting method achieves faster response, smaller starting current, and stronger robustness.

Optimization method and stability analysis of MMC grid-connect control system based on virtual synchronous generator technology

Aiming at the issue of how to design controller parameters and analyze system stability when modular multilevel converter (MMC) adopts virtual synchronous generator (VSG) control technology. Firstly, this paper derives the parameter correspondence between the grid-connected MMC system and the synchronous generator (SG) system, and obtains the relationship between the virtual inertia parameter and damping parameter with specific structural parameters of MMC, then the optimization method of key parameters in the main controller of MMC grid-connected system is determined. That is to add the optimized inertia parameters and damping parameters to the active-frequency controller, the flux linkage feedback loop and the reactive differential compensation link to the reactive-voltage controller, the stability of MMC grid-connected system was analyzed by adjusting key parameters, and the optimal inertia parameters and damping parameters of the MMC grid-connected system during stable operation was analyzed. Finally, using MATLAB/Simulink to build a simulation model of MMC grid-connected system based on VSG control, the feasibility and correctness of the proposed optimization method for key parameters were verified, and the stability of the system was analyzed. The results showed that the key parameters of the main controller combined with the MMC unique structure were more suitable for the MMC grid-connected control system, which improved the stability of the system.

Nonlinear Adaptive Robust Control Strategy of Doubly Fed Induction Generator Based on Virtual Synchronous Generator

Doubly fed induction generator (DFIG) may suffer from huge disturbance owing to the uncertainty of generator parameters and load fluctuation during operation process. Hence, in the context of virtual synchronous generator (VSG) technology and its power-frequency control characteristics, this paper presents a VSG-based nonlinear adaptive robust controller (NARC), aiming to enhance the comprehensive regulation performance of DFIG. Firstly, a nonlinear robust adaptive controller with disturbance rejection and uncertainty adaptive learning ability is designed by establishing an improved dynamic model of the rotor motion equation in VSG, so as to achieve the optimal regulation of DFIG with robustness and adaptability. Secondly, in order to realize the fast dynamic response and autonomous synchronization ability in DFIG, a modified control strategy of the grid side converter (GSC) in DFIG is constructed by voltage and current dual-loop control (DLC) and VSG, which not only retains the significant dynamic response ability of the current inner-loop in DLC, but also improves the inertia and damping of the system. Finally, simulation results indicate that the modified control strategy exhibits satisfied dynamic performance and reliability, and reveals the robustness and adaptability of the control strategy in response to external random interferences and internal uncertain parameters.

Parameters analysis and operation area calculation of VSG applied to distribution network

Virtual synchronous generator (VSG) technology is an effective way to realize the coordinated energy supply of active distribution network and comprehensive energy at present. This paper starts from the two perspectives of grid-connected operation mode and island operation modes. Based on the mathematical model of VSG, referring to the existing grid standards, comprehensively considering its active and reactive-power loop stability and dynamic performance, the influence factors of the related control parameters K, D q , J, D p are analyzed. And the selection range of K, D q , J, D p are proposed, which ensures the stability and robustness in grid-connected and island operation modes. In this paper, the method can be used as a reference for the control strategy research and practical engineering application of VSG. Finally, the effects of parameter selection on the stability and dynamic performance of active and reactive-power loops are analyzed by using the zero-pole map and Bode diagram, and the feasibility of the scheme is verified by PSCAD / EMTDC.