Wound Rotor Research Articles

Optimal low voltage ride through of wind turbine doubly fed induction generator based on bonobo optimization algorithm

The large-scale wind energy conversion system (WECS) based on a doubly fed induction generator (DFIG) has gained popularity in recent years because of its various economic and technical merits. The fast integration of WECS with existing power grids has caused negative influence on the stability and reliability of power systems. Grid voltage sags produce a high overcurrent in the DFIG rotor circuit. Such these challenges emphasise the necessity of the low voltage ride through (LVRT) capability of a DFIG for ensuring power grid stability during voltage dips. To deal with these issues simultaneously, this paper aims to obtain the optimal values of injected rotor phase voltage for DFIG and wind turbine pitch angles for all operating wind speeds in order to achieve LVRT capability. Bonobo optimizer (BO) is a new optimization algorithm that is applied to crop the optimum values of injected rotor phase voltage for DFIG and wind turbine pitch angles. These optimal values provide the maximum possible DFIG mechanical power to guarantee rotor and stator currents do not exceed the rated values and also deliver the maximum reactive power for supporting grid voltage during faults. The ideal power curve of a 2.4 MW wind turbine has been estimated to get the allowable maximum wind power for all wind speeds. To validate the results accuracy, the BO results are compared to two other optimization algorithms: particle swarm optimizer and driving training optimizer. Adaptive neuro fuzzy inference system is employed as an adaptive controller for the prediction of the values of rotor voltage and wind turbine pitch angle for any stator voltage dip and any wind speed.

Enhancement of LVRT Ability of DFIG Wind Turbine by an Improved Protection Scheme with a Modified Advanced Nonlinear Control Loop

One of the problems with the doubly-fed induction generator (DFIG) is its high vulnerability to network perturbations, notably voltage dips, because of its stator windings being coupled directly to the network. As the DFIG’s stator and rotor are electromagnetically mated, the stator current peak occurs during a voltage dip causing an inrush current to the critical converter back-to-back and an overload of the DC-link capacitor. For this purpose, a series of researchers have achieved a linear and non-linear controller with a crowbar-based protection scheme. With this type of protection, the Rotor Side Converter (RSC) is disconnected momentarily, and consequently, its control of both the active and reactive output power of the stator is totally lost, leading to incorrect power quality at the point of common coupling (PCC). In this document, a robust nonlinear controller by Advanced Backstepping with Integral Action Control (ABIAC) is initially employed to monitor the rotor and the network side converters under normal network operations. In the presence of a network fault, an improved protection scheme (IPS) is tacked on to the robust nonlinear control to help enforce the behavior of the DFIG system to be able to overcome the fault. The IPS, which is formed by a crowbar and an RL series circuit, is typically located in the space between the rotor coils and the RSC converter. Compared to a standard crowbar, the developed scheme is successful to limit the rotor transient current and DC-link voltage, also an RSC disengagement to rotor windings can be prevented during the fault. Furthermore, the controllers of both the RSC and the Network Side Converter (NSC) are modified to boost the supply voltage at the PCC. A comparative study is also performed between the IPS without and with modification of the reactive power control loops. The simulation results mean that with the modified controllers during the fault, the amount of reactive power sustainment with ABIAC at the PCC is optimized to 17.5 MVAr instead of 15 MVAr with proportional-integral control (PIC). Therefore, the voltage at the PCC is fort increased in order to comply with the voltage requirements of the farm and absolutely to maintain the connection to the network in case of voltage dip.

A numerical and experimental study on the performance of a conventional H- Darrieus wind rotor with auxiliary blades

This article presents a numerical and experimental investigation of the performance of a conventional H- Darrieus rotor (Known as H-rotor) equipped with auxiliary blades. The study aims to improve the starting ability and the power coefficient (Cp) of the H- rotor. A numerical model is developed using the computational fluid dynamics (CFD) software ANSYS Fluent to simulate the flow field around the rotor. The model is validated with experimental results obtained from a laboratory-scale test rig. From the pressure contour and flow streamline analysis, it can conclude that the auxiliary airfoil serves as a boundary control device, reducing the amount of flow separation and turbulence around the main blade, which further improves the performance of the H-rotor. From the experimental results, the maximum static torque coefficient (Cts) and Cp of the modified H- rotor were found to be 0.11 and 0.18, which is 84% and 22% higher than the conventional H-rotor, respectively. The study concludes that the use of auxiliary blades can enhance the performance of the H-rotor and make it a more competitive option for harnessing wind energy in low-wind speed regions. The findings of this study could have significant implications for the development of small-scale wind turbines.

Design of a Brushless Doubly Fed Generator With Simplified Three-Phase Wound Rotor

The brushless doubly fed generator (BDFG) shows great potential for the variable speed constant frequency ship shaft power generation applications due to its high reliability and low system costs. The rotor topology, which directly couples two stator magnetomotive forces (MMFs) with different pole pairs, is essential for the BDFG. However, existing rotor topologies cannot have both strong magnetic field coupling ability and simple structure. To address this problem, this paper proposes a simplified three-phase wound rotor that can produce two MMFs with different pole pairs simultaneously. Useless harmonics are also eliminated to achieve strong magnetic field coupling ability. The complete design method of a novel integral-slot single-layer winding acting as a basic unit of the compound wound rotor is presented. Two sets of basic winding units are merged into one according to the principle of Ampere-conductor wave, whose approaches are also thoroughly developed with the design example. The maximum number of winding layers and the coil types are reduced to simplify the winding layout. Steady-state performances of a prototype generator are analyzed by both finite element simulations and experimental tests, which verify proposed design methods and schemes.

Application of aeromagnetic survey to mineral exploration of Jinping, Yunnan, China by using multirotor UAV

Jingping, Yunnan, China, is an unfriendly area for ground survey due to the high altitude, rough terrain and dense vegetation. To detect the concealed magnetite ore bodies in this area, the aeromagnetic survey in a 7.8 km2 region was carried out. The field experiments were conducted to investigate the source and level of the noise. Then, the proton magnetometer was placed 3 m under the multirotor unmanned aerial vehicle (UAV) to decrease the static interference. The inverse distance weighting interpolation algorithm with a nonlinear filter was proposed to suppress the noise and dynamic interference caused by the strong wind. The results show that these methods can alleviate the interference of the UAV rotor and strong wind effectively. The patterns of the data from our aeromagnetic survey agree well with the horizontal distribution of the magnetic strata deduced from the geological background. Furthermore, the concealed mafic magmatic rocks and the titanium magnetite inferred from the aeromagnetic survey are confirmed by 4 drill logs in the study area, which supports the validity of the UAV aeromagnetic survey.

Design Features of the Screw Unit for Processing Bulk Substances

This article is devoted to the description of the multifunctional energy converter (MFEC) design of the screw type. MFEC is an induction motor with an external hollow solid rotor. On the surface of the rotor, which is a steel pipe, the turns of the screw conveyer are welded. When supplying power to the stator winding (which visually resembles the wound rotor of an induction motor), the magnetic field not only causes the rotor to rotate, but also, due to the formation of eddy currents, heats the latter. Thus, the idea of combining several functional components is realized in one device: mixing, heating and transportation along the turns of the screw of bulk material. The specified operations are implemented without the use of an external electric drive, heaters, but only due to the principle of operation of the MFEC. Previously, the two-module design of the MFEC was investigated, but experimental studies indicated certain shortcomings of the chosen approach. In this work, an attempt is made to show an alternative configuration of the MFEC, based on the execution of independent single modules that can be combined into a continuous screw thanks to transitional fasteners. In addition, the approach to the power supply and module management system has been revised. This article is one of a series of works devoted to a detailed description of the design of the MFEC.

Non-iterative vortex-based smearing correction for the actuator line method

The actuator line method (ALM) is used extensively in wind turbine and rotor simulations. However, its original uncorrected formulation overestimates the forces near the tip of the blades and does not reproduce well forces on translating wings. The recently proposed vortex-based smearing correction for the ALM is a correction based on physical and mathematical properties of the simulation that allows for a more accurate and general ALM. So far, to correct the forces on the blades, the smearing correction depended on an iterative process at every time step, which is usually slower, less stable and less deterministic than direct methods. In this work, a non-iterative process is proposed and validated. First, we propose a formulation of the nonlinear lifting line that is equivalent to the ALM with smearing correction, showing that the results are practically identical for a translating wing. Then, by linearizing the lifting line method, the iterative process of the correction is substituted by the direct solution of a small linear system. No significant difference is observed in the results of the iterative and non-iterative corrections, in both wing and rotor simulations. Additional contributions of the present work include the use of a more accurate approximation for the velocity induced by a smeared vortex segment and the implementation of a free-vortex wake model to define the vortex sheet, which contribute to the accuracy and generality of the method. The results presented here may motivate the adoption of the ALM by other communities, for example, in fixed-wing applications.

Simple and Robust MPPT Current Control of a Wound Rotor Synchronous Wind Generator

In the search for efficient non-permanent magnet variable-speed wind generator solutions, this paper proposes a maximum power point tracking (MPPT) current-control method for a wound rotor synchronous wind generator. The focus is on direct-drive, medium-speed wind generators. In the proposed method, the currents of the wound rotor synchronous generator (WRSG) are optimally adjusted according to the generator speed to ensure maximum power generation from the wind turbine without needing information on wind speed. The design, modeling, and simulation of the MPPT current controllers are done in Matlab/Simulink with the WRSG in the synchronous reference frame. The controller is put to the test using different wind speed profiles between cut-in and rated speeds. The simulation results indicate that the proposed current control method is simple, effective, and robust, suggesting its practical implementation. To validate the simulation results, experimental work on a 4.2 kW WRSG prototype system is presented to demonstrate the stability and robustness of the MPPT current control method in operating the turbine at or near the maximum power point.

A Rotor Ground Fault Protection Method Based on Injection Principle for Variable Speed Pumped Storage Generator-Motor

Three-phase AC excitation is adopted in the variable speed pumped storage generator-motors, which is different from the DC excitation in traditional synchronous generators. The special rotor winding structure makes the existing rotor ground fault protection methods no longer applicable. Therefore, a rotor ground fault protection method for variable speed pumped storage generator-motor is proposed in this paper. Considering that there is no precondition for additional installation of the injection device at the rotor winding neutral point, the rotor ground fault protection scheme is proposed by connecting the injection device through current limiting resistors outside the rotor winding terminals. The key parameters of injection source, band-pass filter, and current limiting resistance are analyzed and calculated. Then, the online calculation methods of grounding resistance and grounding current are proposed based on the injection equivalent circuit. On this basis, the composite protection criterion considering grounding resistance and grounding current is constructed, and the protection outlet mode is clarified. Simulation and experiments verify the effectiveness of the proposed method.

Sensorless Starting Control of the Brushless Synchronous Starter/Generator by Using the Main Exciter as a Quasi-Resolver at Low Speed

The main generator (MG) and the main exciter (ME) are mounted on the same shaft in the brushless synchronous starter/generator (BSSG). Besides, the internal high-frequency signals, caused by the rotating rectifier, exist in the rotor windings of ME. These mechanical and electrical features of BSSG indicate that the sensorless starting control of MG could be conducted with ME. However, the existing research of this strategy is limited to extract rotor position information from the steady-state characteristics of the rotor currents of ME and consequently has not fully exploited the potential. In this paper, a dynamic sensorless starting control method of MG by using ME as a quasi resolver is proposed. Firstly, the injection mechanism of the excitation signals in the rotor of ME and the characteristics of the induced back electromotive force (EMF) in the stator of ME in different commutation modes are analyzed to clarify the dynamic operating principle of the quasi resolver. Then, back EMF estimation based on extended state observer is presented and an envelope extraction method is proposed. According to the envelope features of the back EMF, a software-based resolver to digital conversion method is proposed. Finally, the effectiveness of this method is verified by experiments.

Aerodynamic analysis of a 2-stage elliptical-bladed Savonius wind rotor: Numerical simulation and experimental validation

ABSTRACT The Savonius rotor is a type of vertical-axis wind turbine that utilizes drag to generate power. Its design simplicity and ability to self-start at low wind speeds make it an attractive option for small-scale wind energy generation. Previous research has focused on optimizing the geometric configuration of a 1-stage, 2-bladed rotor with semicircular blade profiles to improve its performance and mitigate negative torque. However, limited research has been conducted on 2-stage, 2-bladed Savonius rotors with elliptical blade profiles. The present investigation aims to fill this research gap by evaluating the aerodynamic characteristics of a 2-stage, 2-bladed Savonius rotor with elliptical profiles. 3D unsteady simulations using the SST k-ω turbulence model in ANSYS Fluent are conducted to evaluate the performance coefficients over a range of tip speed ratios. The numerical results are validated through wind tunnel experiments. The results show that the CPmax (maximum power coefficient) for the 1-stage rotor is 0.19 and 0.12 for numerical and experimental analyses, respectively. For the 2-stage rotor, the CPmax is 0.21 and 0.17 for numerical and experimental analyses, respectively. These findings suggest that the 2-stage rotor with elliptical profiles has the potential to efficiently harness wind energy.

Research on coupled dynamic characteristics of Floating Wind Turbine under complex environment

The fully coupled aerodynamic-hydrodynamic-mooring numerical model of floating offshore wind turbine(FOWT) has been established. The complex conditions such as second-order wave force, full-field turbulent wind, and mooring break have been taking into account. Using OrcaFlex and FAST to calculate the dynamic response of FOWT under the combined action of wind, wave and current. The time-domain response of floating foundation, mooring tension, blade root contact force, aerodynamic power, and wind rotor thrust are obtained. And the effect of the turbulent wind and mooring break at different positions on the FOWT are studied. The results show that compared with the platform motion and mooring tension, the aerodynamic power and rotor thrust are more sensitive to the turbulent wind, and there are fluctuations in amplitude and multiple peaks in the frequency spectrum. Compared with the leeward side, the mooring break on the windward side is a more dangerous situation, and it is easy to cause the collapse of platform and the break of the remaining mooring. The mooring break on the leeward side is relatively safe, and it will produce a drift in the sway direction, and have little impact on the safety of the wind turbine.

High-Frequency Signal Injection-Based Sensorless Control for Dual-Armature Flux-Switching Permanent Magnet Machine

The new topology of the dual-armature flux-switching permanent magnet machine (DA-FSPM) leads to new characteristics and issues in the control of the machine, of which the mutual inductance of the two sets of armature windings is the most important one. This paper proposes a novel position–sensorless control method based on high-frequency injection (HFI) for DA-FSPM. The high-frequency model of the machine is derived, and the theory of the position estimation method is proposed. Different from the conventional HFI-based position estimation method, the proposed method utilizes the mutual inductance of the DA-FSPM rather than the machine saliency. Meanwhile, because the extracted position information based on the mutual inductance is more obvious, the proposed method also has better steady and dynamic performance. Then, the position observer based on the phase lock loop and the initial position detection method for the DA-FSPM is proposed. The experiments are executed on a DA-FSPM prototype with three-phase stator windings and five-phase rotor windings to prove the effectiveness and superiority of the proposed method.

Analysis of Performance Improvement of Passenger Car Synchronous Homopolar Generator with the Addition of Ferrite Magnets

Electric machines with hybrid excitation have increased torque density while maintaining a wide range of speed control. This article presents the results of the optimal design of a synchronous homopolar generator (SHG) with ferrite magnets on the rotor and excitation winding on the stator for passenger cars. The use of ferrite magnets on the rotor of a synchronous homopolar generator makes it possible to use the stator surface more efficiently, which in turn increases energy efficiency and reduces the dimensions of the generator. At the same time, the excitation winding on the stator provides a reliable brushless design and the ability to control the excitation flux. The problem of long-time calculation of the three-dimensional SHG structure, which is especially relevant when using multi-iterative computer optimization, is solved by using the computationally efficient Nelder-Mead method and a simplified SHG model using two-dimensional finite element analysis. It is also clear that the low torque ripple of SHG with ferrite magnets with two stator-rotor stack combinations (SRSC) is largely provided by the fact that the torque ripples of individual SRSCs are in antiphase. The problem of considering the magnetic properties of magnetic core sections made of structural low-carbon steel is discussed. It has been found that with an increase in both the saturation level of the magnetic circuit and the magnetomotive force (MMF) of the SHG excitation winding, resistance to irreversible demagnetization of ferrite magnets on the rotor can be increased by increasing their height. In addition, it is shown that there is a significant increase in performance when using the hybrid excitation, in comparison with the conventional SHG design without magnets.

New Two-BWT Blade Aerodynamic Design and CFD Simulation

Due to reduced manufacturing, transportation, and installation costs, the two-blade wind turbines (Two-BWT) are a viable option for offshore wind farms. So far, there is no mature design model for offshore Two-BWT. This paper proposes an aerodynamic design method for offshore Two-BWT blades using the blade element momentum (BEM) theory. This method calculates the power coefficient of the Two-BWT by analogy with the three-blade wind turbines (Three-BWT), and then determines the wind rotor diameter. Then, the airfoil, chord length, and twist angle are taken as the key design factors. Furthermore, the piecewise combination method (PCM) for airfoil distribution, the three-point sine method (Three-PSM) for chord length distribution, and the two-point sine method (Two-PSM) for torsion angle distribution are adopted, respectively. Subsequently, the minimum rotational speed, under the rated wind speed and rated power, is taken as the optimization objective to establish the optimization model. The global flow field of Two-BWT is constructed based on CFD technology, and the characteristics of wind speed distribution and blade pressure distribution in the flow field are investigated. Finally, the CFD results are compared with the results of the BEM theory, and the consistency of the results also shows the feasibility of the design method.

Motor driving force of bridge-type crane lifting mechanism under real operating use

Introduction. The requirement for modelling the dynamic processes of a hoisting mechanism in real operating situations has been revealed. The necessity of increasing the accuracy of moving effort description for the most common types of crane hoist drive control has been determined.Materials and Methods. The operation of a single-speed electric motor with squirrel-cage rotor without speed control, with a phase rotor and additional resistors in the rotor winding and with a squirrel-cage rotor and control by a frequency converter has been considered. The static characteristic of the electric motor is taken as the initial function. The Clauss formula with the corresponding values of the parameters synchronous speed, critical force and critical slip was used to take into account the driving force of the motor for frequency control and for relay-contactor control and a motor with a phase-rotor and additional resistances in the rotor circuit.Results. The dependences for the motor driving force with the most common methods of speed control of the crane hoisting mechanism drive are presented. In the case of the frequency control system, the form of the motor driving force is given in the case of steady-state motion and in the case of transient starting/braking processes when the corresponding algorithms are implemented by a frequency converter. Experimental and theoretical graphs of the load lifting processes for the cases of lifting with pickup in the relay-contactor control system and with elastic pickup in the frequency control system are given.Conclusion. The conclusion about applicability of static mechanical characteristic for description of electric motor operation in crane drives is given. The presented dependences provide an opportunity to model the full working cycle of the hoisting mechanism. The dependences are valid both during steady motion of the mechanism and during transients. It is concluded about the use of the dynamic model taking into account the presented form of the motor driving force for practical purposes for the analysis of the crane operation with regard to the effect of the lifting capacity limiter.

Fault diagnosis of inter-turn short circuit in turbogenerator rotor windings based on vibration-current signal fusion

The inter-turn short circuit of rotor winding is a common fault of turbogenerator, and fault diagnosis in the early stage is of great significance to ensure the safe and reliable operation of turbogenerator. In this paper, an inter-turn short circuit fault diagnosis model based on vibration-current fusion is proposed by using the real-time state data collected by the distributed control system (DCS) of turbogenerators. Firstly, Pearson correlation coefficient (PCC) analysis method is used to analyze the correlation characteristics between the square of generator excitation current and the shaft radial vibration when the inter-turn short circuit occurs in the rotor winding of the turbogenerator. Then, the method of cooperative gain transformation is adopted to fuse current-vibration correlation coefficient which can amplify the weak correlation between the square of the excitation current and the vibration signal during the early defect, and the residual between the measured and predicted excitation current is combined to further calculate the cooperative gain residual, and an early warning signal can be issued when cooperative gain residual exceeds threshold. Finally, the model is verified by the historical DCS data of a 600 MW large turbogenerator. The results show that the proposed model can sensitively and accurately diagnose the early defects of inter-turn short circuit in turbogenerator rotor windings and ensure the safe operation of the generator.

ON THE REPRESENTATIVE SPACE PHASOR CONCEPT FROM THE DYNAMIC MODEL OF THE THREE-PHASE INDUCTION MACHINE

In the paper, based on the linear dynamic behavior models of the electrical and magnetic subsystems of the induction machine with three-phase symmetrical stator winding and polyphase rotor winding (cage type) in short circuit, the values ​​are represented, in the complex plane confused with the cross-sectional plane of the machine and the instantaneous polar angular positions of the amplitudes of the progressive (spinning) plane waves of the instantaneous resultant solenations of the machine windings, and correspondingly, the spatial phasors representative of the instantaneous electrical circuit scalar quantities of the stator phase windings and rotor equivalents of the machine are defined. The metric (length and orientation) of these representative spatial phasors allows their physical significance to be revealed.

Analisis Penstabilan Tegangan Output Generator Induksi 3 Fasa

One of the alternative generators in supplying electrical energy is a 3-phase generator made from a 3-phase slip ring induction motor, after which the rotor winding is supplied with a DC source and rotated using a prime mover. The problem arises because of the large % voltage regulation of a 3-phase generator when it is under load. This is because the induction generator has a relatively larger voltage loss when loaded with a certain load compared to a 3-phase synchronous generator. To overcome these conditions, there are several ways that can be used to stabilize the voltage from the generator, namely: setting the excitation current from the generator, setting the connection on the rotor windings (using 2 windings or using 3 rotor windings) and a combination of the two steps above. . Based on the results of experiments that have been carried out, it is known that the method of stabilizing the output voltage by setting the rotor winding connection is less effective than setting the excitation current because it turns out that the results of changing the output voltage are not too significant compared to changing the generator excitation current. In addition, it is also known that the stabilization of the output voltage from an inductive load will require a DC voltage that is greater than when under a resistive load because of the large difference in losses.

A Parameter-Free Method for Estimating the Stator Resistance of a Wound Rotor Synchronous Machine

This paper presents a new online method based on low frequency signal injection to estimate the stator resistance of a Wound Rotor Synchronous Machine (WRSM). The proposed estimator provides a parameter-free method for estimating the stator resistance, in which there is no need to know the values of the parameters of the machine model, such as the stator and rotor inductances or the rotor flux linkage. In this method, a low frequency sinusoidal current is injected in the d axis of the stator current to produce a sinusoidal flux in the stator. In this paper, it is shown that the phase difference between the generated sinusoidal flux and the injected sinusoidal current is related to the stator resistance mismatch. Using this phase difference, the stator resistance is estimated. To validate the proposed model-free estimator, simulations were performed with Matlab Simulink and the results were compared with the extended Kalman filter observer. Finally, experimental tests, under different conditions, were performed to estimate the stator resistance of a WRSM.