High Frequency Torque Research Articles

A VSFPWM strategy for high frequency torque ripple control of PMSM based on stator flux ripple prediction

A VSFPWM strategy for high frequency torque ripple control of PMSM based on stator flux ripple prediction

Experimental investigation of a Wells turbine under dynamic stall conditions for wave energy conversion

Marine energy still plays a marginal role in the current global energy scenario, despite the incessant effort by research for more than thirty years in the exploitation of the so-called blue energy. Among the wide range of marine technologies, wave energy harvesting can play a significant role in view of its potential and Oscillating Water Column (OWC) systems, coupled with Wells turbines, can be considered among the most mature wave energy technology. Due to the oscillating nature of the flow rate in this kind of applications, Wells turbines are affected by dynamic stall, which has significant effects in terms of performance, fatigue, noise and structural integrity of the turbine.Actually, during dynamic stall, the Wells turbine experiences evident high frequency torque fluctuations which overlay on the typical hysteresis loop, mainly during flow deceleration. The amplitudes of these fluctuations are damped as the flow rate decreases toward reattachment. Often these fluctuations are not evident because hysteresis loops are usually provided with phase-averaged data, which can significantly smoothen or even conceal them. Indeed, it is difficult to find in the literature high frequency torque measurements able to show these fluctuations. With the aim to better investigate how the stall triggers this phenomenon, a monoplane Wells turbine has been manufactured in 3D printing and tested in the open wind tunnel of the Polytechnic University of Bari, Italy. The interest of the experimental campaign has been mainly focused on the effects of main parameters of the oscillating inlet flow rate (mean flow rate, amplitude and period of the oscillations, modifying the controlling parameters of the inverter driving the squirrel cage blower) on the performance of the machine. The machine has been firstly investigated under steady state inlet flow conditions, then under dynamic stall conditions. As a result, unsteady torque fluctuations occur during the flow deceleration till the flow reattachment. After the stall, the investigated Wells turbine experiences a drastic reduction of the torque coefficient of about 90%. Moreover, the torque coefficient shows a number of peaks during deceleration phases ranging from 2 to 4. Specifically, the case with the maximum period of the flow rate under investigation (i.e., T = 20 s) shows a greater number of peaks (4) than those related to the other cases (3). Moreover, it has been found that this unsteady behavior is due neither to the mass flow rate crossing the turbine, nor to the stagnation pressure drop, nor to the rotational speed control, which is correctly performed keeping the rotational speed within 1% of the target value. Hence, detecting these oscillations can be relevant in the turbine design phase to enhance the structural strength of the turbine.

High Frequency Torque Pulsation Suppression Strategy for Dual Winding Permanent Magnet Synchronous Motor Sensorless Control Based on Dual High Frequency Square Wave Injection Method

High Frequency Torque Pulsation Suppression Strategy for Dual Winding Permanent Magnet Synchronous Motor Sensorless Control Based on Dual High Frequency Square Wave Injection Method

ROBUST CONTROL OF LOW-COST DIRECT DRIVES BASED ON INTERIOR PERMANENT MAGNET SYNCHRONOUS MOTORS

Torque ripple compensation problem is considered for electrical drives, based on low-cost direct drive interior perma-nent magnet synchronous motors. Robustness properties of the speed and position control systems have been studied using time scale separation properties of the current, speed and position control loops. It is shown that system closed-loop dynamics according to new controller design has cascaded properties with speed and position control loops con-nected in series and therefore has potential of high frequency torque ripple compensation by increasing controllers gains. Experimental results are presented for two motors with similar rated data but significantly different level of the torque ripple. It is shown that despite of significand difference in parasitic torque amplitude, the similar position con-trol performance can be achieved. It makes proposed control algorithms suitable for both high dynamic performance and low-cost direct drive applications with medium performance requirements. References 13, figures 7.

Sensorless Control for SynRM Drives Using a Pseudo-Random High-Frequency Triangular-Wave Current Signal Injection Scheme

This article proposes a pseudo-random high-frequency triangular-wave current signal injection (PR-HFTCI) based sensorless control scheme for synchronous reluctance motor (SynRM) drives at zero-low speed domain to suppress the high-frequency (HF) loss and the HF audible noise which are introduced by the significant nonlinearities of SynRMs and the traditional constant amplitude HF square-wave voltage injection method. The pseudo-random HF triangular-wave current signal with random frequency and random phase is injected to eliminate the discrete spectrum of the current power spectra density (PSD) and the corresponding current PSD analysis is performed to evaluate it. In addition, the HF component amplitude of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis voltage reference can be adjusted adaptively with the variation of load to maintain the HF current amplitude constant, it is easy to implement and does not require any extra regulator and signal processing. Hence, the HF loss and the HF torque ripple can be effectively reduced under the heavy load. Finally, the effectiveness and the correctness of the proposed PR-HFTCI based sensorless control scheme are validated with experiments on a 1.5-kW SynRM drive platform.

Theoretical analysis on the VSC instability caused by PLL in weak system

The mechanism of voltage sourced converter's (VSC) instability caused by phase-locked-loop (PLL) in weak system is revealed in a simplified and efficient way. Based on the key-variables small signals model, the PLL's impact to VSC stability is described by the defined low frequency torque and high frequency torque. The low frequency torque decides the characteristic of VSC in low frequency domain, and supplies synchronous ability and low frequency damping to VSC, while the high frequency torque decides VSC's high frequency characteristic and supply high frequency damping. The two torques impact factors are researched and their influences are revealed. It is found that to keep system stable, sufficient torques are needed. Because weakening system strength will decrease both torques, the mechanism of the instability caused by PLL in weak system is actually lack of sufficient torques. The simulation based on PSCAD software is implemented to validate the theory and matches well with the proposed theory.

Minimization of Additional High-Frequency Torque Ripple for Square-Wave Voltage Injection IPMSM Sensorless Drives

The high-frequency (HF) square-wave voltage injection sensorless control method will bring additional HF torque ripple to interior permanent magnet synchronous motor (IPMSM). Focused on this problem, this article analyzes the relationship between the HF response current and the HF torque ripple resulting from HF square-wave voltage injection. It is concluded that when the fluctuation direction of HF response current is vertical to the stator current vector direction at the maximum torque per ampere (MTPA) operating point, the resulting HF torque ripple reaches its minimum. Based on this conclusion, a novel HF square-wave voltage injection sensorless control method is proposed in this article, which can realize the sensorless control and minimize the HF torque ripple at the same time. The injection angle of HF square-wave voltage in the estimated synchronous rotating reference frame is adjusted in real time according to the operating conditions, so that the HF response current always fluctuates along the vertical direction of the stator current vector at the MTPA operating point. Besides, the corresponding demodulation method of the rotor position estimation error is illustrated. Finally, the experiments are performed on a 20-kW IPMSM platform and the results verify the effectiveness of the proposed method.

Rotor Position Estimation for Aviation Three-Stage Starter/Generators in the Low-Speed Region Without High-Frequency Signal Injection

The changeable magnetic saliency of main machine (MM) in aviation three-stage stator/generator (ATSG) makes it difficult to implement the sensorless starting in the low speed region by the machine saliency-based methods. To estimate the rotor position of ATSG (which is also the rotor position of MM), a novel rotor position estimation method based on the harmonic currents in the main exciter (ME) stator windings produced by the rotating rectifier is proposed in this article. The sine and cosine functions on the rotor position without time delay are extracted from the ME stator currents by a constant frequency signal sampling method. Then, the estimated ME rotor position can be obtained by processing the sine and cosine functions through a phase-locked loop. As the ME and MM are mounted on the same shaft, the rotor position of MM can be obtained by the pole ratio between ME and MM. High-frequency (HF) signal injection is not required in the proposed method, so the HF torque ripple and HF loss caused by the injected HF signal can be avoided. The good performance of the proposed method is verified by the experimental results.

Influence of Ultrasound on Friction Induced Vibrations during Tightening of Bolted Joints

AbstractThe assembly of bolted joints is often based on the assumption that the joint has been assembled as the design guidelines prescribe. However, during the tightening process, errors can occur, some of which can be affiliated with friction‐induced vibrations. In order to improve the automated tightening process and reduce the influence of friction‐induced vibrations, an additional high frequency torque is applied to the bearing of the bolted joint. This leads to a significant increase in tightening efficiency, lower tightening torque, and lower pretension force increments during the tightening process. (© 2017 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Control of Brushless DC Motor with Direct Torque and Indirect Flux using SVPWM Technique

Background/Objectives: To minimize the high frequency current and torque ripples Space Vector Pulse Width Modulation (SVPWM) technique is applied with the Direct Torque Control (DTC) technique which is the usual control technique applied earlier. Methods/Statistical Analysis: The Space Vector pulse width modulation technique is implemented in MATLAB through SIMULINK library. And for controlling the torque directly and flux indirectly Park’s and Clark’s transformations are used. And the results are verified. Findings: A constant switching frequency DTC based space vector modulation technique has the capability to improve the performance of drive by reducing the disturbances in the torque and stator flux linkages. Application/Improvements: BLDC motors find applications in every segment of the market. Automotive, appliance, industrial controls, automation, aviation and so on. And with Space Vector Pulse Width Modulation technique the current and torque characteristics have improved. And the performance of motor also increases.

Acoustic Noise Reduction of BLDC Motor Drive Using One-Cycle Current Control Strategy

Torque ripple and resulted acoustic noise and vibration are the main disadvantages of brushless DC (BLDC) motor drives. In this study, One-Cycle Control (OCC) is developed for current regulation of brushless DC (BLDC) motor drive as a unified constant-frequency integration control strategy. Employing one-cycle control strategy reduces high frequency torque ripple of conventional hysteresis current controllers leading to lower acoustic noise and vibration in the drive. To enhance reliability and reducing drive cost, an improved rotor position estimation technique is implemented. OCC strategy and sensorless method are realized using a low-cost general-purpose AVR microcontroller (Atmega8). It is shown that torque ripple, acoustic noise and vibration are reduced via OCC method comparing to conventional hysteresis control strategy. Computer simulations and experimental results with a 375W, 16 poles BLDC motor, demonstrate improved behavior of developed sensorless BLDC drive operation.

Vertical torque responses to vestibular stimulation in standing humans

The effects of electrical vestibular stimulation upon movement and perception suggest two evoked sensations: head roll and inter-aural linear acceleration. The head roll vector causes walking subjects to turn in a direction dependent on head pitch, requiring generation of torque around a vertical axis. Here the effect of vestibular stimulation upon vertical torque (T(z)) was investigated during quiet stance. With the head tilted forward, square-wave stimuli applied to the mastoid processes evoked a polarity-specific T(z) response accompanied by trunk yaw. Stochastic vestibular stimulation (SVS) was used to investigate the effect of head pitch with greater precision; the SVS–T(z) cross-correlation displayed a modulation pattern consistent with the head roll vector and this was also reflected by changes in coherence at 2–3 Hz. However, a separate response at 7–8 Hz was unaffected by head pitch. Head translation (rather than rotation) had no effect upon this high frequency response either, suggesting it is not caused by a sense of body rotation induced by an inter-aural acceleration vector offset from the body. Instead, high coherence between medio-lateral shear force and T(z) at the same frequency range suggests it is caused by mechanical coupling to evoked medio-lateral sway. Consistent with this explanation, the 7–8 Hz response was attenuated by 90 deg head roll or yaw, both of which uncouple the inter-aural axis from the medio-lateral sway axis. These results demonstrate two vertical torque responses to electrical vestibular stimulation in standing subjects. The high frequency response can be attributed to mechanical coupling to evoked medio-lateral sway. The low frequency response is consistent with a reaction to a sensation of head roll, and provides a novel method for investigating proprioceptive-vestibular interactions during stance.

Driver steering assistance to avoid unintended lane departure by lane keeping and steering suggestions

One of the most frequent causes of highway accidents is the unintended out of lane deviation, due to moments of inattention, sleepiness or drowsiness. The enclosed video shows a driver steering assistance that prevents this type of lane departure. For vehicles with conventional steering columns, there are some difficulties in carrying out this type of steering assistance, in closed loop control. These difficulties consist in sharing vehicle control with the driver. The solution presented in this contribution is based on alternating the steering control of the vehicle between the driver and the steering assistance [1].The activation of the steering assistance takes place when the driver has a moment of inattention and the vehicle is going off the lane.• The driver's attention has been taken into account using the driver's torque on the steering wheel. If the driver's steering torque is below a certain threshold, then he is considered to be inattentive. Other driver monitoring systems could be used instead of the driver torque, without changing anything to the assistance.• The vehicle is considered to be going off the lane, when its front wheels have exceeded a central lane strip, called “normal driving” zone.While active, the steering assistance uses an electrical DC motor installed on the steering column. The DC motor provides a steering torque that brings the vehicle back to the centre of the lane and maintains it there until the driver recovers attention.Therefore, the steering torque follows an optimized control law. To design this control law, linear convex optimization methods (LMI) have been used. Three objectives have been taken into account.1. The first objective is to achieve a bounded overshoot of the front of the vehicle with respect to the considered “normal driving” zone.2. The second objective is for the entire vehicle state vector (side slip angle of the tires, yaw rate, relative yaw angle, lateral offset, steering angle and steering angle rate) to be bounded to safe values during the control.3. The third objective is to ensure a smooth response of the steering assistance after the activation, by using a bounded torque input from the DC motor.The deactivation of the steering assistance can take place under two circumstances.1. One is when the driver has recovered attention under the condition that the vehicle had already been driven back to the “normal driving” zone. This activation/deactivation strategy has been chosen considering the switched system: vehicle driven by its driver / vehicle driven by the steering assistance. The switching rules preserve the state boundedness of the switched system through switching in an invariant set.2. The other type of deactivation allows the driver to immediately switch off the system, for safety reasons, by counteracting the assistance, even if the vehicle is outside the “normal driving” zone. In this case, no guarantee for the state boundedness with respect to the switching action is given. Nevertheless, in order to help the driver, a haptic warning is switched on, after the automatic driving had been deactivated. The warning consists in steering suggestions. These suggestions are generated as asymmetric vibrations of the steering wheel. They consist in a DC motor torque, following a modified sinus signal which has a non-zero mean value. This signal indicates which way the driver should turn the steering wheel in order to return to the centre of the lane. However, these vibrations are a high frequency torque in open loop and are not able to keep the vehicle on the lane without the driver's action on the steering wheel.[1] N.Minoiu, M. Netto and S. Mammar, “A switched optimized approach for road departure avoidance'”, Proc. IEEE Conf. Intelligent Transportation Systems, 2006, pp. 133-138.

Constant and High Switching Frequency Torque Controller for DTC Drives

The letter presents a new method of increasing the switching frequency of a direct torque control (DTC) of induction machines. The method simply replaces the hysteresis comparator of the conventional DTC drives with a triangular waveform-based constant switching frequency controller. By synchronizing the digital signal processor (DSP) sampling with a triangular waveform and with an appropriate systematic controller design, a high switching frequency DTC drive is possible without requiring a high-frequency space-vector modulator. The implementation of the controller is simple and operates based on waveform comparisons; in this letter it is implemented using a combination of a DSP and a field programmable gate array device. Simulation and experimental results indicate that the controller both reduces the torque ripple and maintains a constant switching frequency.

Static and dynamic assessment of the Biodex dynamometer

The validity and accuracy of the Biodex dynamometer was investigated under static and dynamic conditions. Static torque and angular position output correlated well with externally derived data (r = 0.998 and r greater than 0.999, respectively). Three subjects performed maximal voluntary knee extensions and flexions at angular velocities from 60 to 450 degrees.s-1. Using linear accelerometry, high speed filming and Biodex software, data were collected for lever arm angular velocity and linear accelerations, and subject generated torque. Analysis of synchronized angular position and velocity changes revealed the dynamometer controlled angular velocity of the lever arm to within 3.5% of the preset value. Small transient velocity overshoots were apparent on reaching the set velocity. High frequency torque artefacts were observed at all test velocities, but most noticeably at the faster speeds, and were associated with lever arm accelerations accompanying directional changes, application of resistive torques by the dynamometer, and limb instability. Isokinematic torques collected from ten subjects (240, 300 and 400 degrees.s-1) identified possible errors associated with reporting knee extension torques at 30 degrees of flexion. As a result of tissue and padding compliance, leg extension angular velocity exceeded lever arm angular velocity over most of the range of motion, while during flexion this compliance meant that knee and lever arm angles were not always identical, particularly at the start of motion. Nevertheless, the Biodex dynamometer was found to be both a valid and an accurate research tool; however, caution must be exercised when interpreting and ascribing torques and angular velocities to the limb producing motion.