Voltage Control Impact on Performance of Virtual Synchronous Generator

The conventional synchronous generator (SG) can regulate the active and reactive power for frequency and voltage stability, when the system fluctuates. In renewable energy generation system (RES), the stability problem of RES can be solved by adding virtual inertia and damping in the control strategy of the grid-connected inverter. The grid-connected inverter and renewable energy system with this kind of control strategy, called as virtual synchronous generator (VSG), acts as a synchronous generator. In this paper, the topology of grid-connected PV array and energy storage system is proposed. The VSG used in grid-connected inverter, is modelled as stator and rotor model by stator voltage equation and rotor motion equation, respectively. Meanwhile, the VSG control mechanism, based on droop control and model of VSG, can be divided as active power-frequency and reactive power-voltage control. Besides, the system stability is analyzed based on small signal model, for the design of inertia and damping. The simulation model is designed by MATLAB/Simulink for the implementation of VSG. In simulation, it is compared that the dynamic regulation performance of VSG with different control coefficient, such as virtual inertia, virtual damping, droop coefficient and integral coefficient. The optimization for regulation performance in simulation provides an appropriate selection method of the control coefficient for VSG.

To make the distributed generation provide better support for microgrid, the idea of virtual synchronous generator (VSG) is proposed. Typically, the VSG consists of the outer power loop and the inner cascaded voltage and current control loops. Due to the three-loop cascaded structure, a voltage loop with higher bandwidth is significant for ensuring good power control performance. Moreover, most loads in the microgrid are variable and nonlinear. So the voltage control scheme must possess strong robustness against load disturbance. A linear active disturbance rejection control (LADRC) scheme based on the improved error feedback control law (IEFCL) is proposed for VSG voltage control. Compared with the traditional EFCL, the proposed IEFCL can effectively improve the gain and compensate phase lag in the midfrequency, thereby increasing the bandwidth of the LADRC based voltage loop. Quantitative analysis demonstrates the proposed scheme can achieve highly decoupled voltage control in dq frame. In comparison with the traditional strategies, the proposed scheme has higher bandwidth and can significantly improve the power control dynamics for VSG in parallel operation. Additionally, it possesses a good capability of harmonic mitigation and strong robustness against load disturbance. Simulations and experiments verify the effectiveness of the proposed scheme.

The technology of Virtual Synchronous Generator (VSG), which can make the inverter connected to distributed generation work like traditional synchronous generator, plays an important role in improving the stability of the power system because of its good voltage and frequency supporting capability. In this paper, an improved VSG control method is proposed, which can ensure seamless transfer between grid-connected and stand-alone modes, and achieve accurate tracking control of active and reactive power. The control topology and mathematical model of VSG are constructed firstly based on the rotation equation and electrical equation of synchronous generator; then, the corresponding VSG active-frequency droop control, reactive-voltage droop control and inner loop voltage-current control are designed, and the influences of key parameters are analyzed through frequency domain method. Finally, two simulations with different operation modes and loads are conducted to verify the effectiveness in Matlab/Simulink environment, and the results show that the performance is well.

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.

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.

This electronic The pan microgrid under the isolated island is a renewable energy with high permeability, yet the lack of inertia and damping characteristics of conventional synchronous generators may lead to frequency and voltage fluctuations, and then may cause instability. In order to suppress these fluctuations, a model predictive control virtual synchronous generator (VSG) is proposed. Which provides inertial support during system transients, enhances the dynamic characteristics of the system voltage and frequency, and avoids the complex parameter adjustment process in traditional voltage and current dual-loop control. By establishing the prediction model of VSG, designing the cost function of frequency and power, calculating the increment of the required active power and reactive power, making corrections to VSG power, reducing the change of grid frequency and voltage, and providing inertial support through energy storage and electric vehicles, the simulation results show that the frequency and voltage are suppressed, verifying the effectiveness and feasibility of the proposed control strategy.

• 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.

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.

In recent years, countries around the world have been vigorously developing new energy and electrifying new energy sources. As a result an increasing number of power electronic devices appear in the grid which makes the power grid develop toward low inertia and low damping. The Virtual Synchronous Generator (VSG) control strategy can simulate the working state of the synchronous generator and provide the grid with inertia and damping, which has become a research hotspot for scholars. Due to the unbalanced load distribution and the random change of power load, the grid voltage may become unbalanced during the actual operation process. The three-phase output current of the VSG would be unbalanced and a fluctuation of output power appears. To solve this problem, a new current and power quality control strategy based on VSG is proposed in this paper, in which the current balancing or constant power is achieved without changing the basic characteristics of the inverters using VSG control strategy.

The adoption of the virtual synchronous generator (VSG) has attracted wide attention because of the equivalent operating mechanism as a synchronous generator, providing a feasible scheme for the distributed generation connected to utility grid. However, the delivered power and frequency of the VSG may easily oscillate when the dramatic power fluctuation occurred in the distribution generation system. Fortunately, the oscillation can be damped though adjusting the rotating inertia and damping coefficient. Thus, to investigate the influences of parameters perturbation on the active power and frequency for a VSG, the small-signal model is derived and the dynamic performances are analyzed in detail. Then, based on the results of parameters analysis, an adaptive control strategy is proposed in this paper. And an optimal damping ratio can be maintained throughout the whole process of operation to suppress the oscillation of power and frequency. Therefore, the dynamic performances of the VSG are enhanced since the dynamic indexes such as the response time and overshoots are optimized. In the end, a prototype of single-phase VSG has been built and the proposed adaptive control strategy has been verified through experimental results.

This article presents an improved virtual synchronous generator (VSG) control strategy of doubly-fed induction generator (DFIG) during symmetrical voltage fault. Based on VSG control, DFIG can behave like a conventional synchronous generator (SG), which can support frequency and voltage in grid-connected mode. Moreover, when microgrid disconnects from grid, DFIG can provide voltage and power for local loads. However, during symmetrical voltage fault, the transient components in DFIG cannot be controlled properly by VSG. To solve this problem, the air-gap flux feedback is designed in VSG control to accelerate the decay of transient components, and rotor current limiting method is also introduced in the article. In the proposed method, there is no need to switch the control structure or control targets. DFIG always works in the VSG control. Therefore, DFIG can operate in the standalone mode when the connection to grid is cut off. The decay time constant, the voltage control, current limiting control and parameter variation of the improved VSG control are analyzed in detail. Finally, the simulation and experimental results in both normal and fault grid condition are given to validate the effectiveness of proposed VSG control strategy.

Aiming at the problem that the power supply quality of the microgrid needs to be improved and the large impact of grid connection, a new type of virtual synchronous generator (VSG) control strategy is proposed to control the microgrid inverter. The VSG model based on stator voltage model and rotor motion model is established by deformation and vector decomposition of the hidden-pole synchronous generator second-order equation. The virtual frequency regulation module and the virtual voltage regulation module are also obtained by improving the principle of generator frequency and voltage regulation, and the grid-connected control module with voltage phase angle double feedback is also designed. By constructing relevant models, compare the performance of voltage, frequency and power before and after grid connection. The simulation results show that the VSG control strategy can better adjust load changes under the premise of less impact on the grid, and verify the effectiveness of the proposed control strategy.

Virtual synchronous generator (VSG) is one of the inverter control methods which can provide extra virtual moment of inertia and achieve frequency support by mimicking the output characteristics of a rotating synchronous generator (RSG), which makes VSG particularly suitable for multi-access point applications, or called the multi-VSG system. However, frequency fluctuations may often occur in the case of power variation. In terms of this issue, this study presents the small-signal state-space model of VSG and analyzes the cause of frequency fluctuation, first. And then, a novel VSG control method is proposed for frequency fluctuation attenuation. The proposed method is especially fit for the parallel multi-VSG system because it does not take grid angular frequency into computation so that it can get rid of the ill effect introduced through PLL. The damping power item is reconstrued with a new means to judge whether the system is in a steady state or not. At the same time, the parametric design method of the proposed method is also figured out. Finally, the simulation experiments are performed, and the results verify that the proposed method performs better than the conventional one in terms of dynamic response and power-sharing among the multi-VSG system.

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

For a VSC-HVDC transmission system based on a hybrid topology converter of full-bridge and half-bridge, a kind of virtual synchronous generator (VSG) control strategy which can be applied to modular multilevel converter (MMC) grid-connected structure was researched and proposed. First, based on the conventional VSG control strategy, the energy stored in the equivalent capacitor of MMC power module was used to imitate the rotor inertia of synchronous generator. The characteristics of generator can be simulated during transient frequency fluctuations and it can help relieve the power fluctuations. Secondly, with respect to the structural characteristics of the direct grid connection through the reactor on the AC side of the MMC, which is unlike the microgrid inverter, there are no additional filter capacitors. So, the existing commonly used VSG control strategy of the microgrid inverter and double-closed-loop structure composed of filter capacitor voltage and AC current cannot be directly applied. For this, a method where the given values of inner current loop are calculated by grid impedance matrix was used. So, a double-closed-loop control structure composed of a power outer loop based on VSG control and a current inner loop is obtained. It can effectively improve the current control capability during the transient process. Finally, a hybrid MMC simulation model was built based on PSCAD to verify the correctness and effectiveness of the proposed methods.