Characteristics Of Synchronous Generator Research Articles

Electromechanical Characteristics Analysis under DSISC Fault in Synchronous Generators

This paper studies the electromechanical characteristics of synchronous generators under dynamic stator interturn short circuit (DSISC). First, the air gap magnetic flux density (MFD) of the generator under normal and DSISC fault was obtained. Then, the expression for the phase current and the electromagnetic torque (EMT) were obtained. After this, the phase current and EMT were analyzed by finite element analysis (FEA). Finally, the measured electromechanical characteristics of the CS-5 generator under different conditions were analyzed in accordance with theory and simulation. It was shown that with the occurrence, and deterioration, of DSISC, the amplitude of the first harmonic, third harmonic and fifth harmonic of the phase current became more affected by the pulse. Meanwhile, the even-numbered harmonics components of EMT increased.

Prescribed Performance-Based Adaptive Terminal Sliding Mode Control for Virtual Synchronous Generators

Due to the lack of inertia and damping in the distributed power system with power electronic devices as interface, the stability of the power system will be adversely affected when the distributed power system is connected to the grid. In order to solve the problem of low inertia and improve stability, an adaptive terminal sliding mode control method based on the electromagnetic transient characteristics of virtual synchronous generators is proposed. During the design process, projection operators and parameter adaptive law control methods are introduced to compensate for parameter errors caused by environmental interference. Furthermore, by utilizing a prescribed performance function, the terminal sliding surface of the system will have the desired dynamic response, and variations of the system tracking error can be restricted. Simulation results show that the proposed controller has improved control accuracy and response speed, frequency stability, and power response.

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

The large-scale access of renewable energy generation has caused weak grid and a series of instability issues. Virtual synchronous generators (VSG), which can support the voltage and frequency, are gaining increasing applications. At present, there are two main types of VSG. One is single-loop VSG containing only a power control loop. The other is multi-loop VSG containing not only a power control loop, but also a voltage inner loop and a current inner loop. Although both VSGs exhibit the external characteristics of synchronous generators, there are still some differences between them. However, there are few studies on this issue, which makes it difficult to choose which type VSG to use in practical application. This paper analyzes the differences between the two VSGs in terms of broadband stability and current distortion suppression capabilities, so as to provide a reference for related applications.

Adaptive Control Strategy with Threshold of Virtual Inertia and Virtual Damping for Virtual Synchronous Generator

Virtual Synchronous Generator (VSG) control strategy can provide inertia and damping support for the power system by simulating the operating characteristics of synchronous generator, and improve the frequency response of the power system. First, analyse the influence of various parameters on the output characteristics of the system by establishing a mathematical model of VSG. Secondly, to fully utilize the flexible and controllable characteristics of VSG control strategy, the basic principle of VSG parameter adaptation is obtained through the analysis of the angular frequency oscillation characteristics of synchronous generators, and an adaptive control strategy of virtual inertia and virtual damping parameter is proposed, which can better track changes in frequency, and set the action threshold for adaptive control. Finally, compare the frequency and active power response between the traditional VSG control strategy and the adaptive one and verify the effectiveness of the proposed control strategy.

Stability Assessment and Damping Optimization Control of Multiple Grid-connected Virtual Synchronous Generators

The virtual synchronous generator (VSG) control has been widely used in grid-connected inverter to effectively increase the equivalent inertia of power system. However, the active power oscillation similar to electromechanical transient characteristics of conventional synchronous generator (SG) is introduced to power grid, especially under the condition of multi-virtual synchronizer. In this paper, the dynamic stability of the multiple grid-connected voltage source converters (VSC) controlled by VSG is studied. Firstly, the system linearization model is established to analyze the oscillation risk. In order to improve the damping characteristics of multi-VSG grid-connected systems, an additional power system stabilizer (PSS) method is proposed. Then considering the influence of controller installation location and control parameters on the dynamic stability of the system, the design methods of multi-VSG damping controller based on residue index and hybrid particle swarm optimization algorithm are proposed respectively. Finally, the effectiveness of the damping controller design method is verified through the simulation and test cases of the multi-VSG grid-connected system.

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).

Small-signal modeling and stability analysis of grid-connected offshore wind power based on virtual synchronous generator control

With the increasing installed capacity of offshore wind power, the grid-connected of offshore wind power technology based on virtual synchronous generators (VSG) control can simulate the inertia and damping characteristics of synchronous generator, which is helpful to improve the networking ability and inertial supportability of grid-connected inverter. However, VSG control also inevitably causes system oscillation, endangers the safe and stable operation of the power grid. Hence, the main circuit and control circuit of offshore wind power grid connection are firstly modeled, and the small-signal model of offshore wind power grid-connected inverter based on VSG control is obtained. Then the correctness of the model is verified by Matlab/Simulink software. Finally, the root trajectory method is used to identify the effects of VSG control parameters and line parameters on the system stability. The results show that VSG control has a significant influence on the stability of the grid-connected system, and reasonable design parameters are needed to ensure the safe and stable operation of the power grid.

Electromagnetic Analysis and Experimental Study to Optimize Force Characteristics of Permanent Magnet Synchronous Generator for Wave Energy Converter Using Subdomain Method

This paper presents an electromagnetic analysis and experimental verification to optimize the noise, vibration, and harshness (NVH) characteristics of a permanent magnet synchronous generator (PMSG) for wave energy converters (WECs). WECs applicable to breakwater installed in island areas require a wider operating range and a robust design for maintenance compared with wind-turbine systems. Owing to the use of a permanent magnet with a high energy density, the PMSG has a higher power density than other types of generators; however, strong electromagnetic excitation forces that affect the NVH characteristics are generated. Therefore, in this study, the electromagnetic forces are analyzed through an electromagnetic-field analysis using a subdomain analytical method. Based on the analytical solution, electromagnetic forces were determined. Four electromagnetic excitation forces were classified, and the methods for reducing electromagnetic excitation forces are presented here. Finally, a method for evaluating the system resonance through electromechanical analysis is presented. The proposed analysis, optimization, and experimental study are validated through comparison with finite-element analysis and experimental results.

Multi-VSM based fuzzy adaptive cooperative control strategy for MVDC traction power supply system

This paper studies the control of a medium-voltage DC (MVDC) traction power supply system for rail transit (RT). In order to optimize the ability of DC voltage fluctuation and frequency regulation of rail trains, a fuzzy adaptive cooperative secondary control strategy based on improved virtual synchronous machine (VSM) is proposed. Firstly, the improved VSM control strategy is adopted in the traction substations (TSSs), which makes the RT trains have the external characteristics of synchronous generator and have certain inertia and damping support capacity, so as to improve the ability of the RT traction system to cope with traction network transient changes. Secondly, the virtual inertia and virtual damping can be dynamically adjusted by the system frequency deviating from the nominal steady-state frequency, and the dynamic fuzzy adjustment can be carried out by the fuzzy logic system to slow down the frequency fluctuation. Then, due to the different power supply distances and parameter settings between multiple TSSs, cooperative control is used to coordinate local TSS perceptions of information between adjacent TSS to achieve consistency of frequency response of multiple TSSs under different parameters. Besides, a time-varying switching topology handoff method is considered to select the optimal communication topology between adjacent base stations. Finally, simulation results verify the effectiveness of the proposed control strategy.

Low voltage ride-through control strategy for virtual synchronous generators based on virtual self-inductive flux linkage

Virtual synchronous generators (VSGs), with the operational characteristics of synchronous generators (SGs), have been employed in renewable energy generation grid-connected systems to solve the problem of insufficient equivalent inertia, which is caused by the high permeability of distributed generation systems in the grid. However, a VSG does not possess low voltage ride-through (LVRT) capability. A novel LVRT control strategy for a VSG based on virtual self-inductive flux linkage is proposed in this paper. First, the electromagnetic transient response mechanism of a SG under grid faults is analyzed in detail. Then, a memory and retention strategy are proposed to simulate the effect of the switch law. Furthermore, the virtual q-axis armature self-inductance is introduced into the VSG and a virtual self-inductive magnetic chain is utilized to block the change of the transient fault current. This helps the inverter adjust the output voltage quickly. In addition, under the premise of meeting the reactive power margin, the reactive power compensation strategy is optimized to achieve a quick response in terms of the reactive power compensation of grid faults, which is helpful for realizing the LVRT of a VSG. Finally, the feasibility and effectiveness of the proposed LVRT method are verified by thorough simulation results.

Analysis of the Passivity Characteristics of Synchronous Generators and Converter-Interfaced Systems for Grid Interaction Studies

The concept of passivity has been used previously by researchers for avoiding adverse interactions between converter-interfaced devices and the lightly damped oscillatory modes of the electrical network (“grid resonances”). The earlier approaches for achieving this objective involve passivating specific devices like voltage source converters around the resonant frequencies of the network. However, the applicability of passivity for the stability analysis of a wider class of devices and a wider spectrum of transients has not been explored in depth so far. To address this issue, theoretical investigations pertaining to the generalized application of passivity to grid-interaction analysis have been carried out in this paper. The investigations cover aspects like the preservation of passivity under transformations, passivity characteristics of low and high frequency models of synchronous generators and converter-interfaced devices, and the effect of typical real and reactive power control strategies. The results of the investigations are illustrated using case studies. The application of the frequency scanning technique for numerical passivity evaluation of complex, converter-interfaced devices is also presented. The prospects for the practical application of passivity as a generalized grid connectivity criterion are analysed in the light of the presented results.

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.

An inertial droop control based on comparisons between virtual synchronous generator and droop control in inverter-based distributed generators

The adoption of the droop control provides a feasible scheme for the distributed generation connected to the utility grid. Nevertheless, it does not contribute to the inertia and damping factor necessary for power systems. In order to achieve increased stability of microgrids, some scholars simulate the operating characteristics of traditional synchronous generators through control equations, thus virtual synchronous generator control (VSG) was developed. Firstly, the small signal models of inverter based on droop control and VSG control are built in grid-connected (GC) state and stand-alone (SA) state to compare the dynamic response when load transition and power reference change. And we can deduce that in terms of dynamic response neither of these two control strategies can simultaneously satisfy the stringent requirements of different modes of operation. Then, by integrating the advantages of the traditional droop control and VSG control, inertial droop control is introduced in this paper. The presented inertial droop control not only features virtual inertia but also adds compensators to the output power part of the active power control loop to ensure the dynamic response of the system. In the GC state, inertial droop control helps to restrain power oscillations, shorten power adjustment time, and minimize frequency fluctuations to maintain frequency stability. In the SA state, the inertial droop control enables to achieve high enough inertia and damping properties. Finally, this paper demonstrates the superiority of the inertial droop control by means of simulation results.

Research on frequency modulation control of photovoltaic power generation system based on VSG

Abstract 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.

Characteristics of a Sinusoidally-Distributed Cylindrical-Rotor Self-Excited Single-Phase Synchronous Generator

The small-scale power systems favor the installation of self-excited synchronous generators due to their simple construction. Many configurations were reported in the literature but there have been always two issues: voltage regulation (VR) and total harmonic distortion (THD) of the output voltage. This paper presents an experimental investigation to improve the performance of single-phase, self-excited, synchronous generator (SPSESG) in terms of the VR and THD. The applied modification is the implementation of sinusoidally-distributed stator windings which implies a different number of turns in each slot. A typical lab single-phase synchronous machine was rewound with the proper number of turns in each slot and then tested against resistive, resistive-inductive, resistive-capacitive, and dynamic loads (induction motor). The experimental results proved that the modified generator performance has significantly improved in terms of the VR and THD. The worst VR was recorded in the case of dynamic load and it was 6.5 %. While the highest THD was 4.5 %, at no load. These figures are much better than other configurations reported in the literature.

Stability and control of power systems with high penetrations of inverter-based resources: An accessible review of current knowledge and open questions

As power system renewable energy penetrations increase, the ways in which key renewable technologies such as wind and solar photovoltaics (PV) differ from thermal generators become more apparent. Many studies have examined the variability and uncertainty of such generators and described how generation and load can be balanced for a wide variety of annual energy penetrations, at timescales from seconds to years. Another important characteristic of these resources is asynchronicity, the result of using inverters to interface the prime energy source with the power system as opposed to synchronous generators. Unlike synchronous generators, whose frequency of alternating current (AC) injection is physically coupled to the rotation of the machine itself, inverter based asynchronous generators do not share the same physical coupling with the generated frequency. These subtle differences impact the operations of power systems developed around the characteristics of synchronous generators. In this paper we review current knowledge and open research questions concerning the interplay between asynchronous inverter-based resources (IBRs) and cycle- to second-scale power system dynamics, with a focus on how stability and control may be impacted or need to be achieved differently when there are high instantaneous penetrations of IBRs across an interconnection. This work does not seek to provide a comprehensive review of the latest developments, but is instead intended to be accessible to any reader with an engineering background and an interest in power systems and renewable energy. As such, the paper includes basic material on power electronics, control schemes for IBRs, and power system stability; and uses this background material to describe potential impacts of IBRs on power system stability, operational challenges associated with large amounts of distributed IBR generation, and modern power system simulation trends driven by IBR characteristics.

Adaptive control of grid connected inverter based on virtual synchronous machine

In recent years, with the rapid development of distributed generation, virtual synchronous generator (VSG) control technology for distributed generation is proposed. On the basis of droop control, VSG further simulates the inertia and damping characteristics of synchronous generator. Compared with droop control, VSG control technology makes distributed energy have the damping and inertia characteristics of synchronous machine, but it can not guarantee the dynamic regulation performance of frequency and power at the same time. To solve this problem, the adaptive control of VSG is realized by establishing the relationship between the moment of inertia and the damping coefficient. Finally, an experimental platform of VSG adaptive control model is built in Matlab / Simulink. The simulation and experimental results verify the effectiveness and correctness of the proposed control strategy.

Methodology for Tuning MTDC Supervisory and Frequency-Response Control Systems at Terminal Level under Over-Frequency Events

This paper proposes a methodology for tuning a supervisory and frequency-response outer loop control system of a multi-terminal direct current (MTDC) grid designed to transmit offshore wind energy to an onshore AC grid, and to provide frequency support during over-frequency events. The control structure is based on a master–slave scheme and ensures the achievement of frequency response, with specific implementation of the UK national grid code limited-frequency sensitive (LFSM) and frequency-sensitive (FSM) modes. The onshore AC grid is modelled with an equivalent frequency-response model to simulate the onshore AC grid dynamics under frequency deviations. The main innovation of this paper is the development of a methodology for tuning simultaneously two hierarchical levels of a MTDC coordinated control structure, i.e., the MTDC supervisor, given by the active power set point for slave terminal, and the slope of frequency-response functions at onshore terminals. Based on these two hierarchical levels, different strategies are evaluated in terms of frequency peak reductions and change of the frequency order type. Moreover, tuning guidance is given when a different MTDC control structure or different synchronous generator characteristics of the onshore AC grid are considered.

Experimentally Verifying the Generation Characteristics of a Double-Sided Linear Permanent Magnet Synchronous Generator for Ocean Wave Energy Conversion

This paper presents an evaluation system to experimentally verify the performance of a double-sided linear permanent magnet synchronous generator (PMSG) prototype. In general, research on wave power generation systems has concentrated on the optimum design technology of PMSGs, power generation performance analysis technology, loss analysis, and performance evaluation technology. Despite active research in this field, the performance of a system wherein a wave generator and buoy are linked has never been evaluated. Therefore, in this study, a linear PMSG was used in a performance evaluation system to predict a buoy's motion and derive the parameters for optimal power generation under regular and irregular wave conditions.

Research on VSG Control Strategy of Microgrid

In order to solve the low inertia problem and damping effect brought by the large-scale integration of Distributed Generators (DGs) into the grid, the Virtual Synchronous Generator (VSG) control strategy is introduced, The VSG control strategy is applied to the distributed generators grid-connected inverter to make it have the characteristics of synchronous generator, which can provide voltage and frequency support for the grid.Based on the established model, a detailed and complete VSG parameter calculation process is given,and aiming at the problem of seamless switching operation of microgrid based on VSG control, a simplified presynchronization control method is presented, which can simplify the operation and improve the safety and stability of the microgrid. The simulation results based on Real-Time Digital Simulator prove that the proposed method can effectively improve the safety and stability and has good practicability.