Torque Oscillations Research Articles

Getaran Torsional Sistem Propulsi Kapal Tug Boat

The Torsional Vibration of Propulsion System of the Tug Boat Ship. Vibrations that occur in the ship's propulsion system can cause reduced operating capability and cause damage to the ship's components, one of the vibrations that occur in the ship's propulsion system is torsional vibration. The purpose of this study was to determine the value of torque oscillations in Tugboat Ship propulsion systems and to find out the value of noise radiation following ICES 209 standard with variations of ST 60 steel material, stainless steel, and carbon steel, using analitical methods. The results obtained by the torque oscillation value of the propulsion system from Tugboat Ship BPW 3 with the variation of ST 60 steel material is 0.0004854, while for carbon steel material, the torque oscillation value is 0.0004690 and the propulsion system that uses stainless steel material variation is 0.0004527. The level of noise radiation (SL) that occurs in propulsion systems using variations of ST 60 steel material is 133.22 dB, while for carbon steel material is 133.23 dB and for stainless steel material is 133.25 dB, of the three noise radiation values (SL ) produced, is still included in the ICES 209 noise level standard.

Performance Enhancement of Doubly Fed Induction Generator–Based Wind Farms With STATCOM in Faulty HVDC Grids

In this study, an investigation of different faults for a wind turbine–based doubly fed induction generator (DFIG) system is studied and the performance using a static compensator (STATCOM) is observed. The DFIG network is connected to a voltage source converter high-voltage dc link with a fault occurring near the wind generator network. The ride through capability of DFIG is promising with STATCOM using the proposed control strategy. The ac and dc voltage and torque oscillations are damped effectively, and improved power flow is observed. The low voltage AC grid fault occurs for an HVDC transmission, and the DFIG performance without and with STATCOM is compared, where the DFIG converter control schemes are developed using the proposed improved field-oriented control (IFOC) method. In this, the reference rotor flux value alters to a new synchronous speed value or a slighter value or a standstill depending on the stator voltage dip due to grid disturbance. This speed variation leads to introducing rotor current at that new rotor slip frequency as there is a change in the rotor speed because of the fault, which further decreases the stator flux dc component. Hence, this dc-offset constituent in the stator flux is alleviated and decays rapidly in scheming the divergence of the speed of the rotor to a new orientation speed with decay in the rotor flux. This operation is done in the inner control scheme of the rotor converter, which is quicker in response to the faults. Apart from this, the stator’s real and reactive power also changes accordingly based on the lookup table mechanism–based closed-loop control action of the pulse generator, and this power change is done in the outer loop. The analysis for DFIG and HVDC operation is verified under different faults without and with STATCOM.

Reduction of the Electromagnetic Torque Oscillation during the Direct on Line (DOL) Starting of a 6 kV Motor by Means of a Controlled Vacuum Circuit-Breaker

This article deals with the issue of the reduction of the oscillation of electromagnetic torque in the case of a direct on line (DOL) starting of a 6 kV induction motor. Such engines are used in drive systems where frequent starting may be required. Direct starting in such systems may reduce the mechanical and thermal durability. Therefore, the article presents a method of DOL starting of a 6 kV induction motor with the use of vacuum circuit-breakers and appropriate switching of the voltages supplying the electric machine. To confirm the advantages of the proposed solution, computer simulation and experimental tests were carried out, which are presented and discussed in the article. The obtained results confirm the advantages of the proposed solution, compared to the classic starting known from the literature.

Symmetric Resonance Mechanism for Elimination of Parasitic Torque of a Permanent Magnet Generator under Stable Load

Vibration and torque ripple of the permanent magnet generator axis cause excessive wearing up of the generator, noise, efficiency reduction. The article theoretically considers the possibility of eliminating the oscillation of the rotation torque of the permanent magnets generator at constant load due to mutual compensation of the interaction of coils with the field of permanent magnets in the case of certain symmetry of this field. This effect is called pi resonance. For a given class of model functions of the magnetic field density of permanent magnets, it is shown that full compensation occurs with a certain number of coils (Ns) and magnets (Nr), while for other combinations of {Ns, Nr} the interaction is in the nature of oscillations. Pi resonance tables are given for a number of model field density functions represented by Fourier series up to the fifth power. Pi resonance is primarily realized in the case of a small difference in the values of Nr and Ns, which corresponds to the location near the main diagonal of the pi resonance table, as well as at the values of Nr, Ns corresponding to prime numbers. The number of configurations {Nr, Ns} providing pi resonance (compensation of parasitic torques) is the largest for the sinusoidal magnetic flux density and decreases if the magnetic flux density function is approximated by a high-degree Fourier series. It is shown that in the absence of coil cores, pi resonance is possible at Nr = Ns. An additional possibility of pi resonance is shown when placing coils on opposite sides of the rotor. A simplified method of investigating the system (without integrating the equation for the induction current) is substantiated. The results can be used in the design of permanent magnets generators and motors.

Efficiency Enhancements of Wind Energy Conversion Systems Using Soft Switching Multiple Model Predictive Control

The intermittent nature of wind speed imposesa nonlinear behavior on the dynamics of the wind turbine. Consequently, relying on one linear controller tuned to a single specific operating point cannot guarantee a feasible performance in the whole operating region despite providing a fast solution. Besides, wind speed variations cause oscillations in the output power of the wind turbine. To tackle these issues, the Soft Switching Multiple Model Predictive Control (SSMMPC) technique is introduced in which the nonlinear dynamical model of the wind turbine is approximated by defining multiple linear models around various operating points. The gap metric is used as a mathematical tool to construct a bank of multiple linear models that results in a bank of linear controllers. By assuming a relatively small gap threshold value between the neighboring linear models, the soft switching is guaranteed. In this way, there will be no unexpected impulsive behavior in the control input during switching from one MPC to another. The closed loop system stability is studied using Lyapunov theory and a novel switching stability proof based on probabilities is provided. The SSMMPC performance is investigated and compared with a TSR-based controller and a bidirectional control method through simulations using the NREL 10 kW wind turbine model and experimental results on a 7.5 kW wind turbine drivetrain. The results corroborate the improvements that can be attained by using SSMMPC in terms of more captured energy, better maximum power point tracking quality, lower generator torque oscillations, and smoother output power curve.

Acoustic radiation torque of a cylindrical quasi-Gauss beam on a viscoelastic cylindrical shell near an impedance boundary

This work presents a comprehensive analytical formalism to calculate the acoustic radiation torque acting on a viscoelastic cylindrical shell near an impedance boundary, which is exerted by a cylindrical quasi-Gauss beam with an arbitrary incident angle propagating in an ideal fluid. An analytical expression in finite series form for the acoustic radiation torque is derived by applying the partial-wave series expansion method, the image theory and the translational addition theorem. Numerical computations for a viscoelastic cylindrical polyethylene shell immersed in water are provided, with particular emphasis on the effects of the reflecting coefficient of the interface, the shell-boundary distance, the position of the shell, the incident angle and the beam waist. Changing the relative thickness and the interior fluid medium are also considered. It is shown that the cylindrical shell can be rotated counter-clockwise or clockwise, depending on the beam frequency, the shell size, the reflecting coefficient and the incident angle. The periodical oscillation of acoustic radiation torque is also observed as the shell moves away from the boundary. The results of this study can improve our understanding of the acoustic radiation torque behaviors for viscoelastic particles near the boundary, which is commonly encountered in biomedical ultrasound and fluid dynamics.

Reducing noise and vibrations in wind power plants with DFIG and planetary gearbox through improved rotor current control

Planetary gears in wind power plants transmit force excitations to the mechanical structure due to alternating tooth meshes. Structure-borne sound is generated and proceeds to tower and nacelle where it is radiated to the environment and may be a noise pollution to residents. In addition, unwanted vibrations can decrease the durability of the gearbox. So far, structural vibrations are being avoided by constructive measures or active absorbers. In contrast to this, our approach is to reduce gear mesh excitations only with the existing electric generator. Therefore, the rotor current control of the machine is enhanced to inject high frequency oscillations so that the wind power generator produces a specific oscillating torque. This anti-noise torque ripple is transmitted via the shaft to the gear stage and minimizes the gear mesh orders so that less force excitations are exposed to the mechanical structure at the bearings. In our knowledge this anti-noise torque approach using the electric generator and its current control is completely new in the field of wind power plants. Simulation is performed using a multi-body-model of the drivetrain to identify an optimal torque oscillation. Afterwards a control circuit model of the generator and the power converter for the rotor circuit is shown. Hence, it is possible to calculate the behavior of the system in high level of detail on the mechanical and the electrical side. Resulting bearing forces are analyzed to prove that excitation can be reduced significantly. No additional hardware, especially no additional actor is needed.

Impedance modelling and stability assessment for grid‐connected dual‐PWM adjustable speed drives with motor torque oscillations

The grid-connected dual-PWM adjustable speed drives (ASDs) modulate the energy of the motor torque oscillation and inject it into the power system, potentially causing low-frequency oscillation (LFO) in the grid. In this study, considering the motor torque oscillation and harmonic common-modulation of the both-side converters, the precise sequence impedance models are derived for dual-PWM ASDs using the harmonic linearisation method. Based on the derived impedance of dual-PWM ASD, the torque oscillation, which is equivalent to the time-varying impedance, causes a series of discontinuities at the torque-oscillation-related frequencies on its amplitude-frequency curve. Moreover, these discontinuous drops make it more likely to intersect with the amplitude-frequency curve of the grid impedance, which may lead to LFO of the grid. Then, by applying the proposed impedance model and Bode plot, the stability of the grid-ASD cascade system with motor torque oscillation is assessed. The conclusions of stability analysis demonstrate the exact mechanism that the mechanical system oscillations lead to the grid-converter cascade system instability through the common-modulation and coupling of the dual-PWM ASD. Finally, experimental results on a 3 kW ASD system in the laboratory and measured results on the distribution grid in the Shanghai Yangshan Deepwater Port area verify the correctness and effectiveness of the proposed model and stability assessment.

Robust adaptive direct speed control of PMSG-based airborne wind energy system using FCS-MPC method

Electricity generation using airborne wind energy system (AWES) tends to be more efficient than that of conventional wind turbines due to their ability at extracting higher speeds from wind at higher altitudes by the tethered kite generator system (TKGS). The speed regulation of a permanent synchronous machine (PMSM) attached to a kite to maximize harvested power from wind is the topic of the present research. To track the optimal speed produced by TKGS, a finite-control-set model predictive control (FCS-MPC) with a new cost function is directly employed to generate appropriate gate signals for a 3-level neutral point clamped (3-L NPC) inverter that drives a PMSM. A novel adaptive algorithm is also provided for adjusting the weight coefficients of the cost function to improve the system’s performance across a wider range of change in the operating conditions. Moreover, a terminal sliding mode disturbance observer (TSMDO) is designed to estimate the load torque. A terminal sliding mode speed controller (TSMSC) is also used to produce the current reference for the optimizing algorithm in FCS-MPC. The proposed control scheme eliminates the need for a cascade structure while significantly reduces current deformation and torque oscillations. Additionally, the controller operates as fast as a traditional direct speed controller without the use of a cascade structure and is more robust against parameter uncertainties. To illustrate the success of the suggested controller, the results of simulations are presented in MATLAB/SIMULINK® software. The performance of the proposed technique is evaluated in three situations which simulates a grid-connected PMSM fed by a back to back 3-L NPC. In the first scenario, it is demonstrated that the suggested technique performs well when the system’s operational conditions vary. The performance of the adaptive tuning mechanism of the cost function weight factors is investigated in the second scenario, which takes into account model parameter uncertainty. The impacts of the disturbance observer (DO) on the system performance are explored in the final scenario, and it is discovered that the disturbance observer may increase the speed response and DC link voltage tracking performance. All of the simulation results show that the new technique outperformed the traditional FSC-MPC.

Dynamic Performance Analysis of a Five-Phase PMSM Drive Using Model Reference Adaptive System and Enhanced Sliding Mode Observer

This paper aims to evaluate the dynamic performance of a five-phase PMSM drive using two different observers: sliding mode (SMO) and model reference adaptive system (MRAS). The design of the vector control for the drive is firstly introduced in details to visualize the proper selection of speed and current controllers’ gains, then the construction of the two observers are presented. The stability check for the two observers are also presented and analyzed, and finally the evaluation results are presented to visualize the features of each sensorless technique and identify the advantages and shortages as well. The obtained results reveal that the de-signed SMO exhibits better performance and enhanced robustness compared with the MRAS under different operating conditions. This fact is approved through the obtained results considering a mismatch in the values of stator resistance and stator inductance as well. Large deviation in the values of estimated speed and rotor position are observed under MRAS, and this is also accompanied with high speed and torque oscillations.

Enhanced control and operation for brushless doubly-fed induction generator based wind turbine system under grid voltage unbalance

This paper presents an enhanced control and operation for brushless doubly-fed induction generator (BDFIG) based wind turbine system under grid voltage unbalance by considering the controls of machine side converter(MSC) and grid side converter(GSC) together. The MSC is controlled to eliminate torque oscillations and realize decoupling control of power winding(PW) average active and reactive power while the GSC is controlled to eliminate oscillations in the total output active power. A single current closed-loop controller composed of a positive sequence current controller in the positive synchronous reference frame and a negative sequence current controller in the negative synchronous reference frame is designed for both MSC and GSC. To achieve decoupling control and improve system dynamic response, in current loops, all the disturbances and cross-coupling terms are derived and used for feedforward control. A fast sequence decomposition algorithm is employed to reduce the considerable time delays of using notch filers. In order to validate the effectiveness of proposed control, simulations for a 2WM BDFIG based wind generation system were carried out, the results demonstrated that the proposed control can effectively eliminate oscillations of BDFIG torque and total output active power, and has good dynamic and stable performance.

Stability Analysis of Open-Loop V/Hz Controlled Asynchronous Machines and Two Novel Mitigation Strategies for Oscillations Suppression

Asynchronous machines are always widely used in most industrial applications due to their reliability, flexibility, and manoeuvrability. To achieve variable speed operations, the quite simple open-loop V/Hz control is largely utilized. Under open-loop V/Hz control, the nonlinear interaction is well known to cause current and torque oscillations while operating at low to medium speeds under light loads. This article presents the stability analysis of induction motors at low–medium frequencies under no-load conditions with the V/Hz control. A system representation in the form of state space is discussed, and the region of instability is plotted against the V/f plane. Two novel and refined methods for the mitigation of oscillations in the region of instability are presented. The two proposed algorithms are finally tested and validated through simulation on an inverter-fed induction motor drive system.

Symmetrical Resonance Mechanism of Elimination of Parasitic Torques of the Permanent Magnets Generator when Starting and Idling

. “Sticking” and vibrations of the stator of permanent magnet generators cause their increased wear, noise; also, their operation efficiency decreases. The article theoretically considers the possibility of eliminating the starting torque and oscillation of the rotation torque of the generator with permanent magnets without load due to mutual compensation of the interaction of coils with the field of permanent magnets at a certain symmetry of this field. The mentioned pheno-menon is called pi-resonance. For the specified class of model interaction potentials of the field of permanent magnets and coils, it has been shown that full compensation occurs with a certain number of coils (Ns) and magnets (Nr), while for other combinations of {Ns, Nr} the interaction is in the nature of oscillations. The corresponding tables for various classes of potentials are given which can serve as a basis for making design decisions when developing generators. Pi-resonance more probably takes place in the case of even number of stator coils and odd number of magnets, as well as with an increase in the number of stator coils. The cases of both one-sided and two-sided arrangement of the stator relative to the rotor are considered. Numerical modelling has shown that the pi-resonance is easily destroyed if the placement of magnets or coils is inaccurate, as well as by the magnet field potential symmetry breaking. An error in the angular arrangement of the coils of 1° can result in the appearance of a significant “cogging” of the rotor with energy of the order of the interaction energy of an isolated magnet – coil pair. A distortion of the symmetry of the potential yields a result similar in scale which is equivalent to the adding of a rump function with the amplitude of 10 % of the amplitude of the symmetric periodic potential. The patterns that have been discovered can be used in the design of efficient generators with reduced level of noise and vibration.

Spin Transfer Torque Oscillation in Orthogonal Magnetization Disks

We numerically demonstrated the spin transfer torque oscillation (STO) in a magnetic orthogonal configuration by introducing a 90° magnetic coupling. In our model, the multilayer consists of a top layer with in-plane magnetic anisotropy, a nonmagnetic spacer, and a bottom layer with perpendicular magnetic anisotropy. The advantage of utilizing the orthogonal configuration is the high efficiency of spin transfer torque but it is difficult to stabilize STO. By introducing 90° magnetic coupling into the trilayer of FePt/spacer/Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> , or Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> or Ni, a stable STO in an orthogonal configuration was realized. When the top layer was Ni with low levels of saturation magnetization, a small damping constant, and a small anisotropy, it exhibited high frequency and low amplitude. This indicates the possibility of controlling the STO frequency. Moreover, the STO frequency was increased by enhancing the 90° coupling. The combination of the orthogonal magnetization structure and 90° magnetic coupling is an effective approach to obtain a stable spin transfer torque oscillator with high frequency.

Failure analysis of a high-speed induction machine driven by a SiC-inverter and operating on a common shaft with a high-speed generator

Due to ongoing research work, a prototype test rig for testing high speed motors/generators has been developed. Its design is quite unique as the two high speed machines share a single shaft with no support bearings between them. A very high maximum operating speed, up to 80,000 rpm, was required. Because of the need to minimise vibration during operation at very high rotational speeds, rolling bearings were used. To eliminate the influence of higher harmonics of supply voltage and current on the formation of torque oscillations on the shaft and excessive losses in the form of heat, a voltage source inverter with high switching silicon carbide (SiC) power transistors characterizing high precision of the output voltage generation with a fundamental harmonic frequency of several kilohertz has been used. During the first start-ups, it turned out that the system was not stable, and a failure occurred. The paper presents the consequences that may arise when a machine operating at a speed of about 70,000 rpm fails. The article contains pictures of a generator failure that occurred at a high rotational speed.

Software in-the-Loop Simulation of an Advanced SVM Technique for 2ϕ-Inverter Control Fed a TPIM as Wind Turbine Emulator

An appropriate modulation scheme selection ensures inverter performance. Thus, space vector modulation (SVM) is more efficient and has its own distinct advantages compared to other pulse width modulation (PWM) techniques. This work deals with the development of an advanced space vector pulse width modulation (SVM) technique for two-phase inverter control using an XSG library to ensure rapid prototyping of the controller FPGA implementation. The proposed architecture is applied digitally and in real time to drive a two-phase induction motor (TPIM) for small-scale wind turbine emulation (WTE) profiles in laboratories with minimum current ripple and torque oscillation. Four space voltage vectors generated for the used SVM technique do not contain a zero vector. Hence, for an adequate adjustment of these four vectors, a reference voltage vector located in the square locus is determined. Considering the asymmetry between the main and auxiliary windings, the TPIM behavior, which is fed through the advanced SVM controlled-two-phase inverter (2ϕ-inverter), is studied, allowing us to control the speed and the torque under different conditions for wind turbine emulation. Several quantities, such as electromagnetic torque, rotor fluxes, stator currents and speed, are analyzed. To validate the obtained results using both Simulink and XSG interfaces, the static and dynamic characteristics of the WTE are satisfactorily reproduced. The collected speed and torque errors between the reference and actual waveforms show low rates, proving emulator controller effectiveness.

Spin torque oscillations triggered by in-plane field

We study the dynamics of a spin torque nano oscillator that consists of parallelly magnetized free and pinned layers by numerically solving the associated Landau–Lifshitz–Gilbert–Slonczewski equation in the presence of a field-like torque. We observe that an in-plane magnetic field which is applied for a short interval of time (1 ns) triggers the magnetization to exhibit self-oscillations from low energy initial magnetization state. Also, we confirm that the frequency of oscillations can be tuned over the range ∼25–∼72 GHz by current, even in the absence of field-like torque. We find the frequency enhancement up to 10 GHz by the presence of field-like torque. We determine the Q-factor for different frequencies and show that it increases with frequency. Our analysis with thermal noise confirms that the system is stable against thermal noise and the dynamics is not altered appreciably by it.

Power Consumption Simulation of Servo Motors Focusing on the Influence of Mechanical Vibration on Motor Efficiency

This paper presents a simulation method for the power consumption of servo motors, focusing on the influence of vibrations on the motor efficiency. An apparatus consisting of two servo motors connected through a coupling was specifically designed for this study. The efficiency of the servo motor was experimentally investigated for several torque vibration levels imposed through the selection of the control parameters, and the torque vibration level was quantified through the standard deviation of the torque signal. The efficiency map characteristics for each torque oscillating level were determined. A numerical model of the apparatus clarifying the dependency of the coupling characteristics on the oscillating torque was developed, and the torque oscillation of the system was simulated. A model based on the measured motor efficiency maps and the torque oscillation level was developed to simulate the motor efficiency under several torque vibrating conditions. Finally, the power consumption of the motor was simulated based on the simulated efficiency and mechanical power. A balance of input, output, and loss powers was presented, and the experimental measurements were compared with the simulation results. The power consumption of the motor increased when the torque oscillated owing to vibrations, and the loss of power due to both oscillations and the loss of motor efficiency was quantified.

Buckling pattern formation of the elastic ribbon by twist deformation

A thin elastic object frequently exhibits various pattern formations, such as wrinkles, facets, and loops, under twisting deformation. In the present study, we conduct experimental and numerical analysis for twist deformation of elastic ribbons with various boundary conditions. A sequential pattern transition has been observed from helicoid to local loop through triangular facets in the traction boundary condition. We also observed small oscillations in torque during the development of facets. Isogeometric analysis based on St.Venant-Kirchhoff hyperelastic material reproduced the experimental results.

Robust Deadbeat Finite-Set Predictive Current Control With Torque Oscillation and Noise Reduction for PMSM Drives

This article proposes a unique control strategy for a deadbeat multiple vector finite-set model predictive current control with an embedded integral action (MV-FMPC) for permanent magnet synchronous motor drives. Torque ripple and phase current distortions in permanent magnet synchronous motor (PMSM) drives are minimized with the proposed controller by adopting the multiple vector approach to the finite-set model predictive control. The controller uses a hexagonal co-ordinate system to simplify the location and identification of the virtual vectors created, thereby eliminating the use of large look-up tables and reducing computational burden. When used with the proposed deadbeat prediction model, the overall steady-state performance, system robustness, and quality of disturbance rejection are improved compared to the state-of-the-art finite-set model predictive current control (FS-MPC) methods with pulsewidth modulation. The improvements are due to the modified deadbeat prediction model with integral action, the algorithm used for multiple virtual voltage identification and the retention of the cost function in the proposed method. The proposed deadbeat MV-FMPC method and its improvements over the conventional FS-MPC have been verified through simulation and experiments with an interior-type permanent magnet synchronous machine.