Transient Damping of Virtual Synchronous Generator for Enhancing Synchronization Stability during Voltage Dips

Virtual synchronous generators(VSGs)are widely introduced to the renewable power generation,the variablespeed pumped storage units,and so on,as a promising gridforming solution.It is noted that VSGs can provide virtual inertia for frequency support,but the larger inertia would worsen the synchronization stability,referring to keeping synchronization with the grid during voltage dips.Thus,this paper presents a transient damping method of VSGs for enhancing the synchronization stability during voltage dips.It is revealed that the loss of synchronization(LOS)of VSGs always accompanies with the positive frequency deviation and the damping is the key factor to remove LOS when the equilibrium point exists.In order to enhance synchronization stability during voltage dips,the transient damping is proposed,which is generated by the frequency deviation in active power loop.Additionally,the proposed method can realize seamless switching between normal state and grid fault.Moreover,detailed control design for transient damping gain is given to ensure the synchronization stability under different inertia requirements during voltage dips.Finally,the experimental results are presented to validate the analysis and the effectiveness of the improved transient damping method.

Online Field Current Estimation for Brushless Synchronous Starter/Generator Considering the Rectifier Commutation Mode

The information of the field current is essential for the brushless synchronous starter/generator system,which determines the performance and health status of this system.However,since the field winding of the main machine is installed in the rotor part,the measurement of the field current in this brushless system seem impossible.Considering that,the field current might be affected by the rectifier mode,the field current estimation method in different rectifier mode is studied in this paper.The main exciter(ME)rotor currents were restructured based on the ME flux equations.With these restructured rotor currents,the field current in different rectifier commutation mode is analyzed,then the field current estimation method considering the rectifier mode can be obtained.The experiments in different rectifier modes are carried out to verify the proposed method.

Improved Strategy of Grid-Forming Virtual Synchronous Generator Based on Transient Damping

The grid-forming virtual synchronous generator(GFVSG)not only employs a first-order low-pass filter for virtual inertia control but also introduces grid-connected active power(GCAP)dynamic oscillation issues,akin to those observed in traditional synchronous generators.In response to this,an improved strategy for lead-lag filter based GFVSG(LLF-GFVSG)is presented in this article.Firstly,the grid-connected circuit structure and control principle of typical GFVSG are described,and a closed-loop small-signal model for GCAP in GFVSG is established.The causes of GCAP dynamic oscillation of GFVSG under the disturbances of active power command as well as grid frequency are analyzed.On this basis,the LLF-GFVSG improvement strategy and its parameter design method are given.Finally,the efficiency of the proposed control strategy in damping GCAP dynamic oscillations under various disturbances is verified using MATLAB simulations and experimental comparison results.

An Adaptive Control Strategy for Energy Storage Interface Converter Based on Analogous Virtual Synchronous Generator

In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To address this issue,the application of a virtual synchronous generator(VSG)in grid-connected inverters control is referenced and proposes a control strategy called the analogous virtual synchronous generator(AVSG)control strategy for the interface DC/DC converter of the battery in the microgrid.Besides,a flexible parameter adaptive control method is introduced to further enhance the inertial behavior of the AVSG control.Firstly,a theoretical analysis is conducted on the various components of the DC microgrid,the structure of analogous virtual synchronous generator,and the control structure’s main parameters related to the DC microgrid’s inertial behavior.Secondly,the voltage change rate tracking coefficient is introduced to adjust the change of the virtual capacitance and damping coefficient flexibility,which further strengthens the inertia trend of the DC microgrid.Additionally,a small-signal modeling approach is used to analyze the approximate range of the AVSG’s main parameters ensuring system stability.Finally,conduct a simulation analysis by building the model of the DC microgrid system with photovoltaic(PV)and battery energy storage(BES)in MATLAB/Simulink.Simulation results from different scenarios have verified that the AVSG control introduces fixed inertia and damping into the droop control of the battery,resulting in a certain level of inertia enhancement.Furthermore,the additional adaptive control strategy built upon the AVSG control provides better and flexible inertial support for the DC microgrid,further enhances the stability of the DC bus voltage,and has a more positive impact on the battery performance.

Design of Permanent Magnet Synchronous Generators for Wave Power Generation

In this paper, a design method for ocean wave permanent magnet synchronous generator(PMSG)is proposed with new performance criteria to obtain better output performance at the cost of less permanent magnet material. Besides, a simple equivalent analytical geometry method is put forward to calculate the sizes of permanent magnets. Based on geometric and electromagnetic models, four types of rotor structures are compared, i.e., embedded, tangential, tile surface mount and convex surface mount structures. The designs and comparisons of machine are performed with the same permanent magnet volume. Moreover, the influences of mechanical pole-arc coefficient of tile surface mount PMSG on electrical efficiency, output power, material corrosion, core loss, and torque ripple are investigated. Finite-element analysis method is applied to verify the results using Ansoft/Maxwell.

Adaptive H-infinity control of synchronous generators with steam valve via Hamiltonian function method

Based on Hamiltonian formulation, this paper proposes a design approach to nonlinear feedback excitation control of synchronous generators with steam valve control, disturbances and unknown parameters. It is shown that the dynamics of the synchronous generators can be expressed as a dissipative Hamiltonian system, based on which an adaptive H-infinity controller is then designed for the systems by using the structure properties of dissipative Hamiltonian systems. Simulations show that the controller obtained in this paper is very effective.

The Study of Optimal Structure and Value of Dump Resistance in Direct-Drive Permanent Magnet Synchronous Generators

This paper studied the direct-drive permanent magnet synchronous machine (permanent magnet synchronous generator, PMSG) Chopper optimal topology and resistance value. Compared the different Chopper circuit low voltage ride-through capability in the same grid fault conditions in simulation. This paper computes the dump resistance ceiling according to the power electronic devices and over-current capability. Obtaining the dump resistance low limit according to the temperature resistance allows, and calculating the optimal value by drop voltage in the DC-Bus during the fault. The feasibility of the proposed algorithm is verified by simulation results.

Consensus-Based Distributed Control with Communication Time Delays for Virtual Synchronous Generators in Isolate Microgrid

A consensus-based distributed control method of coordinated VSGs with communication time delays in isolate microgrid is proposed. When time delays are considered in communication, there are some effects on frequency restoration and active power output allocation. In the control structure, only local information exchange is needed, while the final frequency can be controlled to the nominal value and the VSGs can automatically share loads according to their rated values. An AC microgrid with three VSGs and some loads is implemented. The proposed control strategy is verified by MATLAB/ Simulink simulation results.

The Minimum Rotor Rotation Angle for Calculating On-Load Electromotive Force Waveform of Synchronous Generators

为了快速计算同步发电机负载运行时的稳态性能,希望在转子相对定子旋转的角度尽可能小的情况下就能够准确得到电枢绕组电动势波形。根据电机理论,针对分数槽绕组同步发电机负载运行时的气隙磁通密度进行分析,得到了准确计算电枢绕组电动势波形的转子最小旋转角。应用有限元法计算最小旋转角范围内定、转子不同位置下的电磁场,通过对电磁场计算结果进行后处理,得到了定子每个齿磁通在一个或者多个周期的变化波形,从而快速计算电枢绕组电动势波形。对两台不同电枢绕组形式的永磁同步发电机负载电动势波形进行了计算,通过对计算结果进行比较,验证了方法的正确性。在一台电机上进行了实验,计算结果和实验结果较吻合。该方法具有计算准确以及计算量小的优点。

Influence of Design Parameters on Cogging Torque in Directly Driven Permanent Magnet Synchronous Wind Generators

In order to reduce the cogging torque, this paper investigates the influence of some parameters on the cogging torque developed by directly driven permanent magnet synchronous wind generators. Based on the remanent magnetic flux densities, the cogging torque is computed by using finite element method. It is shown that many parameters have influence on cogging torque and the slot and pole number combination has a significant effect on cogging torque. A simple factor has been introduced to indicate the effect of the slot and pole number combination. Some practical experience to reduce the cogging torque was applied to 2 MW three phase permanent magnet synchronous generator at rated speed of 37.5 rpm for wind energy conversion. The simulation and experiment results verify the effect of the proposed method.

A fault warning for inter-turn short circuit of excitation winding of synchronous generator based on GRU-CNN

Synchronous generators are important components of power systems and are necessary to maintain its normal and stable operation.To perform the fault diagnosis of mild inter-turn short circuit in the excitation winding of a synchronous generator,a gate recurrent unit-convolutional neural network(GRU-CNN)model whose structural parameters were determined by improved particle swarm optimization(IPSO)is proposed.The outputs of the model are the excitation current and reactive power.The total offset distance,which is the fusion of the offset distance of the excitation current and offset distance of the reactive power,was selected as the fault judgment criterion.The fusion weights of the excitation current and reactive power were determined using the anti-entropy weighting method.The fault-warning threshold and fault-warning ratio were set according to the normal total offset distance,and the fault warning time was set according to the actual situation.The fault-warning time and fault-warning ratio were used to avoid misdiagnosis.The proposed method was verified experimentally.

Maximum Power Point Tracking in Variable Speed Wind Turbine Based on Permanent Magnet Synchronous Generator Using Maximum Torque Sliding Mode Control Strategy

The present study was carried out in order to track the maximum power point in a variable speed turbine by minimizing electromechanical torque changes using a sliding mode control strategy. In this strategy, first, the rotor speed is set at an optimal point for different wind speeds. As a result of which, the tip speed ratio reaches an optimal point, mechanical power coefficient is maximized, and wind turbine produces its maximum power and mechanical torque. Then, the maximum mechanical torque is tracked using electromechanical torque. In this technique, tracking error integral of maximum mechanical torque, the error, and the derivative of error are used as state variables. During changes in wind speed, sliding mode control is designed to absorb the maximum energy from the wind and minimize the response time of maximum power point tracking(MPPT). In this method, the actual control input signal is formed from a second order integral operation of the original sliding mode control input signal. The result of the second order integral in this model includes control signal integrity, full chattering attenuation, and prevention from large fluctuations in the power generator output. The simulation results, calculated by using MATLAB/m-file software, have shown the effectiveness of the proposed control strategy for wind energy systems based on the permanent magnet synchronous generator(PMSG).

Difference between grid connections of large-scale wind power and conventional synchronous generation

In China, regions with abundant wind energy resources are generally located at the end of power grids. The power grid architecture in these regions is typically not sufficiently strong, and the energy structure is relatively simple. Thus, connecting large-capacity wind power units complicates the peak load regulation and stable operation of the power grids in these regions. Most wind turbines use power electronic converter technology, which affects the safety and stability of the power grid differently compared with conventional synchronous generators. Furthermore, fluctuations in wind power cause fluctuations in the output of wind farms, making it difficult to create and implement suitable power generation plans for wind farms. The generation technology and grid connection scheme for wind power and conventional thermal power generation differ considerably. Moreover, the active and reactive power control abilities of wind turbines are weaker than those of thermal power units, necessitating additional equipment to control wind turbines. Hence, to address the aforementioned issues with large-scale wind power generation, this study analyzes the differences between the grid connection and collection strategies for wind power bases and thermal power plants. Based on this analysis, the differences in the power control modes of wind power and thermal power are further investigated. Finally, the stability of different control modes is analyzed through simulation. The findings can be beneficial for the planning and development of large-scale wind power generation farms.

Predictive control of a chaotic permanent magnet synchronous generator in a wind turbine system

This paper investigates how to address the chaos problem in a permanent magnet synchronous generator（PMSG） in a wind turbine system. Predictive control approach is proposed to suppress chaotic behavior and make operating stable;the advantage of this method is that it can only be applied to one state of the wind turbine system. The use of the genetic algorithms to estimate the optimal parameter values of the wind turbine leads to maximization of the power generation.Moreover, some simulation results are included to visualize the effectiveness and robustness of the proposed method.

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.

Performance analysis of 20 Pole 1.5 KW Three Phase Permanent Magnet Synchronous Generator for low Speed Vertical Axis Wind Turbine

This paper gives performance analysis of a three phase Permanent Magnet Synchronous Generator (PMSG) connected to a Vertical Axis Wind Turbine (VAWT). Low speed wind condition (less than 5 m/s) is taken in consideration and the entire simulation is carried in Matlab/Simulink environment. The rated power for the generator is fixed at 1.5 KW and number of pole at 20. It is observed under low wind speed of6 m/s, a turbine having approximately1 mof radius and2.6 mof height develops 150 Nm mechanical torque that can generate power up to 1.5 KW. The generator is designed using modeling tool and is fabricated. The fabricated generator is tested in the laboratory with the simulation result for the error analysis. The range of error is about 5%-27% for the same output power value. The limitations and possible causes for error are presented and discussed.

Coordinated control strategy for a PV-storage grid-connected system based on a virtual synchronous generator

Due to the characteristics of intermittent photovoltaic power generation and power fluctuations in distributed photovoltaic power generation,photovoltaic grid-connected systems are usually equipped with energy storage units.Most of the structures combined with energy storage are used as the DC side.At the same time,virtual synchronous generators have been widely used in distributed power generation due to their inertial damping and frequency and voltage regulation.For the PV-storage grid-connected system based on virtual synchronous generators,the existing control strategy has unclear function allocation,fluctuations in photovoltaic inverter output power,and high requirements for coordinated control of PV arrays,energy storage units,and photovoltaic inverters,which make the control strategy more complicated.In order to solve the above problems,a control strategy for PV-storage grid-connected system based on a virtual synchronous generator is proposed.In this strategy,the energy storage unit implements maximum power point tracking,and the photovoltaic inverter implements a virtual synchronous generator algorithm,so that the functions implemented by each part of the system are clear,which reduces the requirements for coordinated control.At the same time,the smooth power command is used to suppress the fluctuation of the output power of the photovoltaic inverter.The simulation validates the effectiveness of the proposed method from three aspects:grid-connected operating conditions,frequency-modulated operating conditions,and illumination sudden-drop operating condition.Compared with the existing control strategies,the proposed method simplifies the control strategies and stabilizes the photovoltaic inverter fluctuation in the output power of the inverter.

Analysis and Design of Surface Permanent Magnet Synchronous Motor and Generator

This paper presents an analytical method to design the high-efficiency surface permanent magnet synchronous motor(SPMSM)or generator(SPMSG).The air-gap and permanent magnet size can be approximately determined based on our mathematics model,which is the most important part of SPMSM design.From our method,we can know that motor’s power out torque is related to the torque angle that we selected in our design and it affects the air-gap and permanent magnet size.If we choose a low torque angle,the motor or generator’s overload power handing capability will increase.The embrace value has a vital place in designing a motor or generator due to its effects on air gap flux density,cogging torque,efficiency and so on.In order to avoid the knee effect,the working point of the permanent magnet we selected in the design should be bigger than 0.5.The developed 36 slots,4 poles,surface mound permanent generator is proposed.The corresponding finite element analysis(FEA)model is built based on our design method.Structure optimization includes stator and rotor structure size,permanent magnet size,magnetic bridge and air gap length which are analyzed and simulated by ANSYS Maxwell 2D FEA.Thermal analysis is conducted,and the housing of the alternator is designed.The alternator prototype is fabricated and tested based on our design.

Research on Seamless Switching Control Strategy Based on Virtual Synchronous Generator

This paper studies the voltage, phase and current tracking strategy to eliminate voltage and current mutations when the virtual synchronous generator is switching between grid-connected and islanded. By using these strategies the inverter can realize secondary frequency regulation and voltage regulation. If the phase is near 0 or 2π a little disturbance may made the PLL output a big error, so a new PLL is proposed by this paper. A sine module is added in the PLL to avoid this error. In order to verify the strategy proposed by this paper a simulation model is built in Matlab/Simulink. The simulation results show that the control strategy can realize seamless switching.

Electromagnetic and Mechanical Stress Analysis of Wind-Driven Synchronous Reluctance Generator

The investigation explores the mechanical stress and electromagnetic performance for a wind-driven synchronous reluctance generator(SRG).The change in the mechanical stress due to the presence of centripetal force,wind speed,and rotor speed are evaluated for different thickness of tangential and radial ribs.Moreover,the variation in the electromagnetic feature such as the q−and d−axes flux,reactance ratio,inductance,torque and torque ripple are discussed for different thickness of tangential and radial ribs.Increasing both tangential and radial ribs thickness has an effect on the electromagnetic performance,but it is observed that effect is significantly more with the variation of tangential rib thickness.Similarly,the mechanical stress analysis for rotor design has been explored in this paper.It is observed that high concentration of peak stress on the rotor ribs,which limits the range of rotor speed.