Control Strategy Of Generator Research Articles

Improved virtual synchronous generator control strategy for the flexible interconnection system in distribution transformer areas

• An improved virtual synchronous generator control strategy is proposed for the flexible interconnection system. • The DC side impedance small signal model is built. • The stability of the flexible interconnection system is analyzed mathematically. • The controller hardware-in-the-loop experiment is designed for verification. The flexible interconnection system (FIS) in the distribution transformer areas containing high-penetration distributed photovoltaics plays a significant role in balancing the load and improving new energy consumption. This paper proposes an improved virtual synchronous generator (VSG) control strategy for the FIS. Firstly, the impedance small signal model of the FIS is developed for analyzing the influence of the conventional VSG control strategy on the stability margin of the FIS in the case of bidirectional power flow. Then, the improved VSG control strategy is proposed based on the analysis, which can improve the stability of the FIS in the negative power direction. Finally, the controller hardware-in-loop experiments of the FIS verify the effectiveness of the proposed improved VSG control strategy.

Inertial imitation method of MMC with hybrid topology for VSC-HVDC.

A new virtual synchronous generator (VSG) control strategy was researched and proposed for a VSC-HVDC (High Voltage Direct Current Based on Voltage Source Converter) transmission system. It can be applied to half-bridge or full-half-bridge hybrid topology modular multi-level converter (MMC) to improve the stability and reliability of the system. First, it is proposed that the energy stored in the equivalent capacitor of MMC power module was used to imitate the rotor inertial of synchronous generator. It can buffer transient power fluctuations and synchronize autonomously with the grid. Then the impedance characteristics of the proposed control method have been deduced and analyzed. The results show that the VSG control loop mainly improves the low frequency characteristics of the converter. Secondly, the ability to suppress transient fault current is weak. So, a method, that the given values of inner current loop are calculated by grid impedance matrix, was used. A double closed loop control structure composed by a power outer loop based on VSG control and a current inner loop is obtained. The simulation results show that it can effectively improve the current control capability during the transient process for systems with a 1:2 ratio of converter capacity to grid capacity (The grid short-circuit capacity is 60MW and the MMC is 30 MW). Finally, a hybrid MMC simulation model was built based on PSCAD and the steady-state and transient fault ride-through simulations were performed. The power adjustment time of MMC under the proposed VSG control is about 1s, while the adjustment time under the conventional control strategy is greater than 4s.

Research on Control Strategy of Grid-connected Brushless Doubly-fed Wind Power System Based on Virtual Synchronous Generator Control

The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid, which leads to the decline of grid stability. Therefore, a control strategy of brushless doubly-fed reluctance generator (BDFRG) based on virtual synchronous generator (VSG) control is proposed to solve the problem in this paper. The output characteristics of BDFRG based on VSG are similar to a synchronous generator (SG), which can support the grid frequency and increase the system ‘inertia’. According to the mathematical model of BDFRG, the inner loop voltage source control of BDFRG is derived. In addition, the specific structure and parameter selection principle of outer loop VSG control are expounded. The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy. Finally, the effectiveness and feasibility of the proposed strategy are verified in the simulation.

Research on VDG Control Strategy in Hybrid Energy Storage System of Photovoltaic DC Microgrid

With the access to many energy storage devices in the Photovoltaic DC microgrid, energy storage converters are also widely used, which have the characteristic of low inertia. Therefore, there are problems of low inertia in the optical storage DC microgrid system, which contains an energy storage converter, and the instability of the system causes by the fluctuation of micro-source and load mutation. In order to solve the existing problems, the paper proposes a Virtual DC Generator (VDG) control strategy based on the traditional double closed-loop control strategy in the hybrid energy storage system (HESS) of a photovoltaic DC microgrid. Applying this proposed control strategy can make the inertia and damping characteristics introduced into the converters, which provides sufficient inertia support for the optical storage DC microgrid and further improves the voltage quality. The microgrid system is modeled and analyzed based on VDG. The results show that the VDG control strategy effectively reduces power fluctuation of the hybrid energy storage and improves the stability of the microgrid system.

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

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

SOC Balanced Power Distribution Control Strategy of a DC–DC Converter with Virtual Synchronous Generator

The DC microgrid does not need to consider frequency when accessing distributed energy, but the distributed energy access port does not have inertia and damping characteristics, so there are problems of voltage instability and power fluctuation. In this paper, the bidirectional DC–DC converter is the main object; based on the virtual synchronous generator (VSG) control strategy, the inertia regulation is added to adjust the bus voltage dynamically. In addition, a balancing strategy is proposed to ensure the balanced distribution of the state of charge (SOC) and power for multiple batteries. Finally, a simulink is built to prove the viability and availability of the VSG control strategy.

Control Strategy of Doubly-Fed Induction Generator under Zero Voltage Fault of Power Grid

For improving the zero-voltage ride through the capability of a doubly fed induction generator in high proportion new energy grid in extreme faults, a coordinated control scheme of hardware and optimal control strategy is proposed. A high-temperature superconductive-fault current limiter suppresses stator fault current, adaptive virtual impedance control and active dynamic reactive power support control act on the back-to-back converter of wind turbines as optimal control strategies. Optimizing the control strategy without changing the controller structure is beneficial to engineering implementation. After mathematical derivation and simulation verification, the coordinated control strategy adopted in this paper can effectively avoid the rotor current and voltage exceeding the limit when the wind turbine is facing extreme faults, actively provide reactive power support for the busbar, realize zero voltage ride through and reduce the risk of high voltage failure at the point of failure. The control effect is obviously better than the traditional virtual impedance control.

A Comprehensive Review on a Virtual-Synchronous Generator: Topologies, Control Orders and Techniques, Energy Storages, and Applications

In recent years, the penetration of renewable power generations into the electrical grid has substantially increased. Continuous deployment of power electronic-based distributed generations and the reduction of traditional synchronous machines with their essential dynamics in modern power networks are very critical in this change. The use of power electronic inverters leads to the dissociation of sources and loads and lowering the power system inertia. Under power imbalance, this drop causes an elevated rate of change in frequency and frequency divergences, which has a notable impact on the system’s frequency stability. As a result, enhanced control techniques for grid-tied electronic converters are required to secure the power system’s stability and support. The virtual-synchronous generator (VSG) control is used to mimic the dynamics of a rotating synchronous generator and improve the power system’s stability. In this article, the problems of such low-inertia power systems, as well as the VSG technologies, are explored. This research also looks at different control orders and strategies for virtual-synchronous generators (VSG). In addition, the utilization of energy storage and critical matters in VSG and further research recommendations are explained.

Adaptive Virtual Synchronous Generator Based on Model Predictive Control with Improved Frequency Stability

With the massive integration of renewable energy into the grid, grid inertia and its stability continue to decrease. To improve inertia and facilitate grid restoration, a control strategy for radial basis function virtual synchronous generators based on model predictive control (MPC-VSG-RBF) is proposed in this paper. In this method, virtual synchronous generator (VSG) control strategy is introduced into the model predictive control (MPC), so that the reference value of the inner loop current can vary with the grid voltage and frequency. Using the radial basis function (RBF) neural network to adjust the VSG virtual inertia online can solve the large fluctuation of frequency and power caused by excessive load fluctuation. The simulation model was built based on MATLAB and compared and analyzed with the MPC control method. The simulation results show that: when the output power of the inverter changes, the model predictive control of the adaptive virtual synchronous generator can increase the inertia and stability of the power grid; by adjusting the moment of inertia, the system damping ratio is improved to effectively suppress the transient process overshoot and oscillation in medium power.

Application of MMC-RPC in High-Speed Railway Traction Power Supply System Based on Energy Storage

In order to effectively improve the power quality and utilize railway regenerative braking energy in high-speed railway traction power supply system, this paper adopts the Modular Multilevel Converter type Railway Power Conditioner (MMC-RPC) with distributed super-capacitor (SC) energy storage (ES) scheme. Firstly, the single-phase MMC mathematical model is established, and the power compensation characteristics of MMC-RPC are derived. Secondly, the Virtual Synchronous Generator (VSG) control strategy is adopted to provide inertial support. Compared with the double closed loop (DCL) control, it has better anti-disturbance and dynamic performance. Then, based on the VSG control, a two-stage circulating current suppression strategy is proposed, in which Quasi-Proportional Complex Integral (QPCI) control is used to suppress the bridge arm circulating current, and integrated Proportional Integral-Quasi Proportional Resonant (PI-QPR) control is an improvement of the VSG control to further suppress the circulating current inside the VSG. Furthermore, the virtual DC motor (VDCM) strategy was proposed to control the charge and discharge of the distributed SC connected to MMC-RPC to recycle railway braking energy. Finally, simulation results of the VSG small signal model and the MMC-RPC simulation model on the Matlab/Simulink platform verify the effectiveness, stability of VDCM and improved VSG controls in the MMC-RPC.

Sensorless Optimal Control Strategy of PMSG in Wind Energy Conversion System

This paper presents a sensorless optimal control strategy of Permanent Magnet Synchronous Generator (PMSG) used in Wind Energy Conversion System (WECS). An approach to develop a simple reduced speed observer for PMSG is developed. The speed and rotor position estimation of the PMSG are obtained by only measuring phase voltage and current. Maximum wind energy extraction is achieved by running the wind turbine generator in variable-speed mode. The rotor speed is allowed to vary in sympathy with the wind speed by maintaining the tip speed ratio to the value that maximizes aerodynamic efficiency. Advantages of this mechanical sensorless control strategy for maximum power estimation are demonstrated by digital simulation of the WECS.

Control Strategy and Corresponding Parameter Analysis of a Virtual Synchronous Generator Considering Frequency Stability of Wind Power Grid-Connected System

The doubly-fed induction generator (DFIG) based on the control strategy of constant parameter virtual synchronous generator (VSG) can cause problems of sharp frequency variations in the grid-connected system, long adjustment times, and large overshoot of the active power output from the DFIG. Aiming at dealing with the above-mentioned problems, a VSG control strategy with an independent flexible link (IFLVSG) is proposed in this paper without changing the parameters and structure of the VSG, so that the moment of inertia and damping coefficient can be flexibly adjusted according to the change of the system frequency, so as to improve the system frequency stability. To form a complete selection scheme for control parameters in IFL, the state space equation including IFLVSG control is established, and the advantages of exponential IFL are highlighted by using the sensitivity calculation method. At the same time, in order to improve the analysis efficiency, the main control parameters affecting the frequency stability of the system are selected according to the sensitivity value. Finally, the root locus analysis method is used to reveal the influence law of the main control parameters on the frequency stability of the system. The formed scheme provides a theoretical basis for the selection of control parameters.

Comparative Study of Three Types of Controllers for DFIG in Wind Energy Conversion System

An improved Doubly-Fed Induction Generator (DFIG) control strategy for the Wind Energy Conversion System (WECS) is presented in this paper. To produce the best aerodynamic torque and enhance the WECS's dynamic performance, a robust Super-Twisting (STW) sliding mode control for variable speed wind turbines is developed. To maximize power extraction, the proposed control directly tracks the DFIG's electromagnetic torque. The STW control strategy is contrasted with conventional Sliding Mode (SM) and Proportional-Integral (PI) controllers in terms of performance and efficiency. Chattering reduction, a finite convergence time, and robustness to changes in parameters and system disturbances are among the intriguing characteristics of the proposed STW algorithm.

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.

A novel software applications rollout and monitoring strategy for enabling the transition to electromobility in future smart grids

The ongoing transition from fossil fuels-powered transportation to electromobility is expected to create new challenges for electrical power system operators, especially in the distribution level. Secondary substations in medium voltage grids and its distribution grid transformers can be considered as the first bottleneck that needs to be overcome. In particular, operating limits and the utilization of resources must be taken into account. Thus, technical solutions are required in order to adapt the permissible charging power in grid-critical situations, including local power generation control strategies, demand-side management and power quality monitoring. Within the scope of this research study, a concept for the automated integration of flexible automation systems will be discussed. The focus is on the development of an engineering process based on the IEC 61850 standard and the virtualisation of smart grid services for the flexible rollout of smart grid systems.

An IPAVSG Control Strategy for Microgrid With Multi-Parallel VSG System

Virtual synchronous generator (VSG) is widely used in various distributed power generation systems due to great simulated inertia and damping support performance. However, when the microgrid (MG) composed of multi-parallel VSG is in both grid-connected and islanded modes with various large disturbances, the control strategy with fixed parameters cannot guarantee the stable operation of the MG under all disturbances. To this end, an improved parameter-adaptive virtual synchronous generator (IPAVSG) control strategy is proposed in this paper to ensure that the virtual inertia and damping are adaptively optimized with the system operating state during the disturbance process. Therefore, the dynamic performance of the power frequency regulation and transient stability are significantly improved. Meanwhile, in order to realize the output active power of each VSG is distributed among the loads according to the ratio of its rated capacity, the active power decoupling control is designed to eliminate the influence of the virtual damping on the output active power of the VSG in islanded MG. The effectiveness and practicability of the proposed control strategy are verified through several experiments.

Microgrid Inverter Control Strategy Based on Virtual Synchronous Generator

Study the control strategy of distributed power supply grid-connected based on virtual synchronous generator. Establish the mathematical model of the inverter grid connection and the mathematical model of the virtual synchronous generator control scheme. Study the grid-connected active and reactive power regulation scheme, and analyze the influence of inertia and damping parameters on grid-connected power tracking in detail. A self-synchronous control strategy without phase-locked loop is designed, which simulates the characteristics of synchronous generator’s speed regulation system and excitation system and can seamlessly switch between two operating states of off-grid and on-grid, which is conducive to the improvement of micro-grid stability. Finally, a simple microgrid system is built on the Matlab/Simulink platform. It is verified that the proposed control strategy has good power tracking characteristics and can enable the distributed power supply to switch quickly in different operating modes.

Inertia-enhanced method for active distribution network based on hierarchical control structure

With the increasing penetration of renewable energy, converters need to help enhance the stability and rigidity of the power system. This paper proposes an inertia-enhanced method with the hierarchical control scheme for active distribution network to support inertia for the utility grid. The paper first analyzes the mechanism and influence of inertia in power systems and quantifies the inertia which an active distribution network can supply. Then, two-layer control structure is designed for favorable control performance. At the primary control layer, a virtual synchronous generator control strategy is adopted for instant inertia support under frequency fluctuation. The objective of primary control is to track the control references rapidly and accurately. At the secondary control layer, the objective is to coordinate the active and reactive power output of distributed generators to keep voltage deviations and power loss of internal distribution network operating at a comparatively appropriate level. The secondary control strategy is based on model predictive control method, which can consider the physical and control constraints of distributed generators and find the optimal reference signals for all the primary controllers to track. The inertia of power system is apparently enhanced with the hierarchical inertia-enhanced scheme. Finally, simulation based on Matlab/Simulink is carried out, and the feasibility and validity of proposed control strategy are verified.

Distributed cooperative automatic generation control and multi-event triggered mechanisms co-design for networked wind-integrated power systems

The participation of wind energy brings new challenges to the networked power systems. Now, more network nodes compete for limited communication resources. Considering the utilization efficiency of network transmission resources, a novel multi-event triggered mechanisms based distributed cooperative automatic generation control scheme is investigated for networked wind-integrated power systems (NWIPSs). The multi-event triggered mechanisms based distributed wind-integrated power systems modeling method is proposed. By utilizing the Lyapunov-Krasovskii functional method, the sufficient conditions for system asymptotical stability are obtained. Concerning the previous event-triggered method the proposed multi-event triggered method widespread considered the coupling relationship between interconnected subsystems and make full use of each subsystem state information. The numerical example shows that the proposed scheme is feasible and the design of multi-event triggered mechanisms based distributed cooperative automatic generation controller provides less conservatism and stronger robustness.

Results from the FOCAL experiment campaign 1: turbine control co-design

This paper summarizes the scaling approach and results from the first experimental campaign of the Floating Offshore-wind and Controls Advanced Laboratory (FOCAL) Experimental Program, which is focused on developing public data sets to support the validation of numerical models for floating wind control co-design. A 1:70 Froude-scale performance-matched model of the IEA Wind 15-MW reference turbine was designed, built, and characterized on a fixed base. The National Renewable Energy Laboratory’s Reference Open-Source COntroller (ROSCO) was integrated into the scale testing to examine the impact advanced turbine and generator control strategies have on turbine performance and loads, enabling validation of control strategies for floating wind design optimization.