Virtual Synchronous Generator Control Method Research Articles

A virtual synchronous generator control method in microgrid with vehicle-to-grid system

Abstract The inertia in power systems plays a very important role in stabilizing the power system. With the growth of distributed generation (DG)/renewable energy source (RES) penetration in the power grid, there has been a concern about the lack of inertia in the power system. One of the solutions to solve the problem is to use the Virtual Synchronous Generator (VSG) control method. For energy storage, the Vehicle-to-grid (V2G) storage system can replace the traditional hybrid energy storage which consists of batteries and supercapacitors. This application will be implemented in Microgrid. The article will focus on simulating the Microgrid with the V2G system and solar energy as a renewable energy source, the inverters are controlled by the method of VSG control. The models will be simulated and the results will be shown on MATLAB/SIMULINK software.

Analysis of voltage and frequency stability of electric power system network with photovoltaic-based generation penetration

The operation of Distributed Generation (DG) with renewable energy sources integrated with distribution networks through microgrids poses challenges in terms of operation and control. If this is left unchecked, it can have a negative impact on system security and reliability in terms of voltage and frequency stability that will be disrupted because of frequent variations in power production and loading levels. This study investigates voltage and frequency stability in microgrids because of the penetration of DG with photovoltaic (PV) renewable energy sources in the power system using the Virtual Synchronous Generator (VSG) control technique. The VSG is a control alteration that enhances the capabilities of the power system so that voltage and frequency stability can be preserved and improved. The VSG control method with additional damping controllers that increase inertia with additional virtual inertia is used to simulate the speed of restoration of voltage and frequency stability of the power system due to the penetration of PV-based power plants. The simulation results show that at the time of penetration of PV-based power plants in the power system, there is a momentary instability in voltage and frequency, but it is immediately dampened by VSG control and can be quickly restored so that the stability of voltage and frequency is maintained.

Power decoupling control of paralleled virtual synchronous generators based on virtual complex impedance

With the high ratio of distributed generation (DG) linked to power system via converters, power system stability is degraded in terms of inertia and damping. In recent years, the virtual synchronous generator (VSG) has become a potential solving method to deal with these issues. However, the power coupling problem exists in the traditional VSG control method, which severely impacts the VSG power control performance. The impedance characteristics of the transmission line are closely related to the effect of the power decoupling control of VSGs. To solve the voltage sag and poor robustness issues resulting from traditional virtual impedance control, a virtual complex impedance power decoupling and sharing control strategy for VSGs based on coordinate transformation is proposed. Combining the characteristics of traditional virtual impedance control and virtual power control, the power coupling mechanism in parallel VSGs caused by line impedance is analyzed. The virtual complex impedance control loop is introduced in VSG control to realize the matching of the equivalent line impedance and the precise decoupling of VSG power output. Then the load can be accurately allocated in the light of the proportion of VSG capacity.

Adaptive VSG control strategy considering energy storage SOC constraints

The virtual synchronous generator (VSG) control strategy is proposed to mitigate the low inertia problem in the power system brought about by the high percentage of distributed generation connected to the grid and the application of power electronic devices. In order to maximize the effectiveness of the advantages of the flexible and adjustable parameters of VSG control, an adaptive VSG control strategy considering SOC constraint of the energy storage unit is proposed in this paper. Considering the significant loss of service life by operating the energy storage unit at its limit state, based on the rate and degree of change in system frequency, the adaptive control strategy realizes the online adaptive adjustment of the inertia factor and damping factor under different perturbation conditions by adaptively adjusting the control parameters when the system frequency oscillates. Finally, the effects of this adaptive VSG control method and conventional VSG control method are compared by simulation in PLECS. Hardware-in-the-loop (HIL) experimental platforms and semi-physical simulation experiments are constructed on RTBOX, and the feasibility and validity of this adaptive VSG control strategy are verified.

A virtual synchronous generator control method for remote island power system considering dynamic voltage stability

Remote island power systems are difficult to install renewable energy sources (RES) because of the small system capacity and the large impact of intermittency of RES. Virtual synchronous generators (VSG) can equip inverters with the inertia of synchronous generators and can suppress frequency and voltage fluctuations. This paper proposes a VSG control method for dynamic voltage stability in remote island power systems. In conventional VSG control methods, the command of active and reactive power is determined by the Droop characteristics of frequency and transmission line voltage. However, the command are not based on dynamic voltage stability indices. Therefore, the compensation amount of active and reactive power is inappropriate. The proposed method determines the command of active and reactive power based on dynamic voltage stability indices. The dynamic voltage stability index considers the critical boundary index (CBI). The CBI is defined as the distance between the operating point of active and reactive power flowing through a transmission line and the stability limit curve calculated from the power flow between two bus lines. The proposed method improves dynamic voltage stability by determining power command so that the operating points of active and reactive power are closer to the origin direction. Simulation verification is performed for load increase and three-phase ground fault. In the three-phase ground-fault simulation, FRT requirements are considered to verify continued operation and the case of gate blocking. The conventional Droop control and the proposed method are compared for the case of continued operation with FRT requirements during load increase and ground fault. Simulation verification results show that the proposed method improves the dynamic voltage stability compared to the conventional method. Furthermore, it is shown that the proposed method is capable of stable continuous operation of the system even after a transmission line failure considering the FRT requirement.

A distributed VSG control method for a battery energy storage system with a cascaded H-bridge in a grid-connected mode

With the high penetration of renewable energy, new challenges, such as power fluctuation suppression and inertial support capability, have arisen in the power sector. Battery energy storage systems play an essential role in renewable energy integration. In this paper, a distributed virtual synchronous generator (VSG) control method for a battery energy storage system (BESS) with a cascaded H-bridge converter in a grid-connected mode is proposed. The VSG is developed without communication dependence, and state-of-charge (SOC) balancing control is achieved using the distributed average algorithm. Owing to the low varying speed of SOC, the bandwidth of the distributed communication networks is extremely slow, which decreases the cost. Therefore, the proposed method can simultaneously provide inertial support and accurate SOC balancing. The stability is also proved using root locus analysis. Finally, simulations under different conditions are carried out to verify the effectiveness of the proposed method.

Enhancing Diesel Generator Fuel Efficiency by Operating in Optimum Variable-Speed Combined with Vienna Converter

Diesel engine generators are commonly used in refinery systems to provide electrical power. The engines are generally Constant Speed Diesel Wound Rotor Synchronous Generator (CSD-WRSG) type and are operated in parallel with ones. In this study, a Variable Speed Diesel Wound Rotor Synchronous Generator (VSD-WRSG) system is proposed, combined with additional AC-to-DC and DC-to-AC converters, in order to meet the low load condition and save the fuel. The Diesel Generator's current rotation, which is set at a constant speed, is then changed to the optimum speed. It varies depending on the load demand. The electrical frequency is controlled through the converters. This research focuses on a single diesel generator with a capacity of 880 kW for supplying 343 kW average load demand. The AC-to-DC converter employs a Vienna Rectifier with hysteresis control. In order to enable smooth power transmission during load changes, a DC-to-AC converter is used with a Virtual Synchronous Generator control method. All the simulations are completed using MatLab/Simulink. The simulation results indicate that the proposed model is effective. When daily load data is employed, the VSD-WRSG system can save up to 5.3% or 121 liters of fuel per day if compared to the CSD-WRSG system.

Intelligent Fault-Tolerant Control for AC/DC Hybrid Power System of More Electric Aircraft

This paper presents a novel intelligent fault-tolerant control method for a kind of more electric aircraft AC/DC hybrid electrical power system, in order to ensure the safe operation of the engine and improve the power supply quality. The more electric aircraft electrical power system was combined with an aircraft engine, two generators, two AC/DC rectifiers, two DC/AC inverters, DC loads, and AC loads. A multi-objective optimization intelligent sliding mode fault-tolerant controller was obtained for aircraft engine with actuator faults. Each of AC/DC rectifiers is 12-pulse autotransformer rectifier unit with active power filter. Active power filter was used to realize the desired performance of DC bus. Intelligent fractional order PI controller is presented for AC/DC rectifier by considering multiple performance indexes. In order to guarantee the AC-side has satisfying voltage, current, and frequency, no matter the sudden change of AC load that happens or DC/AC fault that occurs, the virtual synchronous generator control method was used for DC/AC inverters. Simulation results verify the effective of the proposed more electric aircraft AC/DC hybrid electrical power system.

Study on a Frequency Fluctuation Attenuation Method for the Parallel Multi-VSG System

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.

Coordinated Damping Control Design for Power System With Multiple Virtual Synchronous Generators Based on Prony Method

With more renewables integrated into power grids, the systems are being transformed into low inertia power electronic dominated systems. In this situation, the virtual synchronous generator (VSG) control strategy was proposed to deal with insufficient inertia challenge caused by the reduction of synchronous generation. However, as the VSG control method emulates the dynamic behavior of traditional synchronous machines, the interaction between multiple VSG controllers and synchronous generators (SGs) may cause low-frequency oscillation similar to that caused by the interaction between multiple SGs. This paper reveals that the system low-frequency oscillatory modes are affected by multiple VSGs. Then Prony analysis is utilized to extract the system mode information which will be subsequently used for VSG controller design, and a decentralized sequential coordinated method is proposed to design the supplementary damping controller (SDC) for multiple VSGs. The system low-frequency oscillation is first analyzed based on a modified two-area system with a linearized state-space model, and a further case study based on a revised New England 10-machine 39-bus system is used to demonstrate the effectiveness of the proposed coordinated method for multiple VSGs.

Inertia Response Improvement in AC Microgrids: A Fuzzy-Based Virtual Synchronous Generator Control

The absence of rotational masses from synchronous generators in converter-interfaced microgrids leads to a lack of inertia. Consequently, the system exhibits steeper frequency variations and higher frequency nadir, which may degrade the dynamic performance and challenge the operation of sensitive equipment such as protective relays in the grid. Virtual synchronous generator is introduced as an effective solution to increase the inertial response of converter interfaced renewable energy sources. This article proposed a fuzzy controller, which is augmented on the virtual synchronous generator topology to damp the perturbation during transients by increasing the inertia of the system. The proposed fuzzy control adds a correction term to the governor's output power that increases the system inertia during transients. In order to compare the inertial response improvement, a comparison between proposed fuzzy control technique and cost function based inertia and damping coefficient optimization is done on a virtual synchronous generator platform. It is shown that online measurement based adaptive methods have a better inertial response against other time-consuming techniques. To further verification, a number of experiments are done, which confirm the merits of the proposed fuzzy based virtual synchronous generator control method.

A Unified Modeling Method of Virtual Synchronous Generator for Multi-Operation-Mode Analyses

To provide inertia support for the grid, virtual synchronous generator (VSG) control of inverter-interfaced distributed generators (IIDGs) becomes a focus of worldwide attention. However, a VSG-based IIDG behaves differently in the grid-connected (GC) mode, the islanded-single-DG mode, and the islanded-multi-DG mode, whereas the mathematical and physical interpretations of this phenomenon are not well studied. In this article, we propose a unified modeling method of VSG-based IIDG to analyze its different dynamic performance in each operation mode. The proposed unified formulas can obtain the state-space models of the islanded-single-DG and islanded-multi-DG modes from that of GC mode for any VSG control method. With the obtained models, for several different types of VSG control in different operation modes, we analyze the distribution and sensitivity of the closed-loop poles and investigate the step responses both analytically and experimentally. These analyses reveal the intrinsic differences and correlations of the dynamics of VSG-based IIDG between each operation mode. These intrinsic features are valid independent of the applied VSG control scheme; thus, a test method to evaluate the parameters and performance of an unknown IIDG is derived. The findings of this article provide important instructions for engineers to model and design and test multi-operation-mode distributed generators.

PMSG Control for a Stand-Alone Gas Engine Generator Using Active Rectifier and VSG-Controlled Inverter

The engine generator system with a diode rectifier causes harmonic currents in the generator which can affect generator efficiency and may produce torque oscillations. Using an active rectifier instead of a diode rectifier helps us to improve the current waveforms. In this paper, an active rectifier is used for a stand-alone gas engine generation system with a permanent magnet synchronous generator (PMSG). The generator side converter and the load side converter can be controlled separately to achieve high performance and reliability of the system. In the proposed control framework, the generator side converter is controlled by means of a current vector control method in a cascade structure with the synchronous reference frame (dq- frame). In the proposed control scheme, the dc link voltage is controlled by the generator side converter. For load side converter control, the concept of virtual synchronous generator control method is adopted to support a smooth power transient during the load changes. To verify the usefulness of the proposed control structure, using PSCAD software (version 4.2.1), the system transient responses with both a diode rectifier and an active rectifier are investigated under loading and load removal cases. Moreover, for the system with an active rectifier, the transient response of the system with different vector control strategies of PMSG is also investigated.

Modelling of distributed generation system based on virtual synchronous generator control technique

Virtual synchronous generator (VSG) control method is considered as a suitable solution for controlling distributed generation (DG) system-based inverter, due to its ability to improve the microgrid stability. The VSG control method consists in controlling the power electronic interface-based DG unit to mimic the main dynamic of the conventional synchronous generator. Unlike, conventional synchronous generators, the load angle is not enough small in case of low and medium DG systems, moreover, they are usually connected to the grid through low and medium voltage lines, where the line impedance is not purely inductive, result in a strong coupling between active and reactive powers as well as nonlinearity between active and reactive powers functions and controls variables. This paper proposes a linear model of DG system with VSG controller based on a small signal analysis. The developed model has been investigated and compared with the detailed simulation model of a studied microgrid.

Enhanced Performance of a Stand-Alone Gas-Engine Generator Using Virtual Synchronous Generator and Energy Storage System

Gas engine generators have been recognized as a set of beneficial generating units for producing electric power owing to their high efficiency, low emissions and appropriate fuel price. However, the major drawback of gas engine generators is the weak transient performance during sudden load change. The reason is that the engine's mechanical system cannot quickly respond to the demanded torque. Therefore, a change in load causes a large engine speed deviation, especially in stand-alone mode. If the engine speed deviation exceeds the allowable limits, the system operation will be shut down. To fix this drawback, this paper introduces the virtual synchronous generator control method combined with an additional energy storage system to the stand-alone gas engine generator. In this paper, the applied virtual synchronous generator control scheme is presented. Compared to the constant-voltage constant-frequency control method, the benefit of virtual synchronous generator control method for the gas engine generator is evaluated by simulation study in PSCAD software. The energy-variables-based feedback control structure is adopted for the control of energy storage system. The required capacity of energy storage system is estimated. To verify the effectiveness of proposed control structure, simulation is conducted under load connection and load removal cases. Finally, an experimental study is carried out for the same configuration of simulation model using a real gas-engine generator set up.

A Virtual Synchronous Generator Based Hierarchical Control Scheme of Distributed Generation Systems

Sustainable energy-based generation systems, such as photovoltaic and wind turbine generation systems, normally adopt inverters to connect to the grid. These power electronic interfaces possess the characteristics of small inertia and small output impedance, which create difficulties to stabilize the voltage and frequency of a distributed power source. To deal with this problem, a Virtual Synchronous Generator (VSG)-based inverter control method is presented in this paper by introducing virtual inertia and damping coefficient into the control loop to emulate the dynamic behavior of a traditional synchronous generator. Based on this VSG control method, a three-layer hierarchical control scheme is further proposed to increase the control accuracy of the voltage and frequency in a VSG-based distributed generation system with parallel inverters. The principle of the VSG control method, the system stability analysis, the design process of the hierarchical control structure, and the frequency/voltage secondary regulation processes are all specified in this paper. Finally, some numerical simulations are carried out and the effectiveness of proposed control scheme is verified by the simulation results analysis.