Low Motor Speed Research Articles

Suppression of the Capacitor Voltage ripple in Modular Multilevel Converter for Variable-Speed Drive Applications

The modular multilevel converters (MMC) utilization has brought about a transformative impact on high voltage direct current (HVDC) transmission relying on voltage-sourced converters (VSC). However, their application in medium-voltage (MV) variable-speed motor drives has not achieved broad acceptance due to the substantial voltage fluctuation in the capacitor, especially at lower frequencies. The present study introduces a hybrid MMC (HMMC) aimed at markedly limiting capacitor voltage fluctuations, particularly during low motor speeds. Vector control was used to achieve the required motor speed. The proposed HMMC validity was confirmed through the MATLAB/ SIMULINK environment. The results were compared with conventional MMC from the standpoint of the capacitor voltage fluctuation at low frequencies.

Высокодинамичная компенсация «мертвого времени» в электрических приводах на базе сигнальной адаптации

The article discusses the analysis and synthesis of a system of highly dynamic "dead time" compensation in the current loop of motors powered from transistor pulse-width converters. The first part of the paper provides a brief analysis of existing technical solutions, whose algorithms do not imply changes or additions to the power part of the drive and therefore are implemented exclusively by software. It is shown that the most modern methods of adaptive compensation can be considered using reference models of the control object. A non-search adaptive dead-time compensation system is proposed in the paper which provides signal self-tuning in the motor current loop, and dead-time compensation is based not on linearization or correction of nonlinear effects and delays of a pulse-width converter, but on parrying disturbing influences caused by the negative effects of “dead time”. Particular attention is paid to the practical orientation of the proposed solution; therefore, the considered algorithm is based solely on the basic principles of the control theory proven by practice. This approach allows us to ensure not only the transparency of the theoretical arguments presented in the article, but also reduce the time spent on the analysis and synthesis of the current loop, the purpose of which, ultimately, is the optimization of high-precision drives. With the absence of iteration methods of mathematics, the resources of microprocessor control units are minimized, which makes this method even more attractive in low-budget drives that do not claim to "exclusivity of integrated circuitry. The proposed algorithm was integrated into the existing current loop of an asynchronous electric drive with vector control, which proved the high efficiency of static and dynamic compensation of not only the “dead time” of the converter, but also of the non-linear effects associated with it that are difficult to analyze. The adaptive "dead time" compensation increased the efficiency of the electric drive at low motor speeds, compared to voltage boost compensation, by approximately four percent, and also reduced the motor torque ripple by about seventeen percent. An oscillogram of the phase current of a real drive with "dead time" compensation is given according to the principle of parametric voltage addition, which is the most common in practice, as well as a waveform of current with adaptive compensation action according to the principle considered in this article.

Preparation and characterization of rare earth element nanoparticles for enhanced photocatalytic degradation

The present work focuses on the photocatalytic degradation of methylene blue (MB) on erbium ion (Er3+) doped TiO2 under visible light. Pure TiO2 nanoparticles and erbium (Er3+) doped TiO2 nanocomposite (Er3+/TiO2) NCs were synthesized using the sol–gel method. The synthesized (Er3+/TiO2) NCs were characterized using Fourier transform infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HR-SEM), elementary dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS), specific surface area (BET), zeta potential, and particle size. Different parameters were used to study their efficiency for the photoreactor (PR) and the synthesized catalyst. These parameters include pH of the feed solution, the rate of flow, the presence of an oxidizing agent (aeration pump), different ratios of nanoparticles, the amount of catalyst, and the concentrations of pollutants. An example of an organic contaminant was the dye methylene blue (MB). The result achieved using the synthesized nanoparticles (I) under ultraviolet light pure TiO2 was found to have degraded by 85%. For (Er3+/TiO2) NCs under visible light, dye removal increased with pH to a maximum of 77% degradation at pH 5. Furthermore, photocatalytic efficiency improves to 80% at 40 rpm (3 l/h) low motor speed. The degradation efficiency decreased to 70% when the MB concentration was increased from 5 to 30 mg/L. When oxygen content was increased using an air pump, and deterioration reached 85% under visible light, it improved performance.

Stator Winding Temperature and Magnet Temperature Estimation of IPMSM Based on High-Frequency Voltage Signal Injection

The interior permanent-magnet synchronous motor (IPMSM) has been widely used as the traction motor in electric/hybrid vehicles because of its high torque density and wide operating speed range. During the operation of the IPMSM, the stator winding temperature and magnet temperature should be monitored to prevent winding insulation breakdown and irreversible demagnetization and to improve the torque accuracy. This article devised a method involving the use of a high-frequency (HF) resistance and an HF inductance for estimating these two temperatures at low motor speeds. The relationship between the HF impedance and both temperatures was determined and verified using an experimental setup in which both temperatures could be measured. Based on the relation, the temperature estimation method has been proposed, in this article, and verified by the experimental test. The proposed method was used to estimate the stator winding and the magnet temperatures simultaneously for 6000 s, and the maximum error was 6 °C and 3 °C for the stator winding and magnet temperature, respectively, even when the load and the temperatures varied considerably.

If You Are Old, Videos Look Slow. The Paradoxical Effect of Age-Related Motor Decline on the Kinematic Interpretation of Visual Scenes.

Perception and action are tightly coupled. However, there is still little recognition of how individual motor constraints impact perception in everyday life. Here we asked whether and how the motor slowing that accompanies aging influences the sense of visual speed. Ninety-four participants aged between 18 and 90 judged the natural speed of video clips reproducing real human or physical motion (SoS, Sense-of-Speed adjustment task). They also performed a finger tapping task and a visual search task, which estimated their motor speed and visuospatial attention speed, respectively. Remarkably, aged people judged videos to be too slow (speed underestimation), as compared to younger people: the Point of Subjective Equality (PSE), which estimated the speed bias in the SoS task, was +4% in young adults (<40), +12% in old adults (40–70) and +16% in elders. On average, PSE increased with age at a rate of 0.2% per year, with perceptual precision, adjustment rate, and completion time progressively worsening. Crucially, low motor speed, but not low attentional speed, turned out to be the key predictor of video speed underestimation. These findings suggest the existence of a counterintuitive compensatory coupling between action and perception in judging dynamic scenes, an effect that becomes particularly germane during aging.

Performance Investigation of Indicated Parameters of a Diesel Blended Engine

The significance of the diesel motor for public activity is rising each day. Experience has indicated that the exhibition of interior ignition motor taking a shot at diesel is huge as a camper to some other fuel. The components that are answerable for the smooth working of a motor likewise assume a significant job. This paper investigates the attainability of utilizing four strokes four-chamber diesel motors. The aftereffects of the exhibition of CI Engine by differing the heap are introduced in this paper. The impact of shifting the heap affects execution, outflow, and ignition boundaries. The motor exhibition boundary examined was brake warm productivity, brake explicit fuel utilization, demonstrated force, brake power, volumetric proficiency, energy equilibrium, and wind stream estimation. Results have demonstrated that the brake power increments as the heap’s increments on the four strokes four-chamber motor. The measure of fumes and coolant misfortunes are nearly little at high motor speed and high at low motor speed.

Modular multilevel converter with thyristor DC-link switch for full-torque variable-speed drives

The modular multilevel converter (MMC) is a promising topology for medium-voltage drive applications due to its high-quality output waveforms, low device switching frequency and voltage rating. However, the large cell capacitor voltage ripple is a severe challenge faced by MMC at low motor speeds. Recently, a hybrid MMC (HMMC) topology is proven to be a competitive solution because of its lower cell capacitor voltage ripple and no common-mode voltage (CMV) problem compared with other methods. However, the dc-link switch with IGBT limits HMMC to be applied for high-voltage applications. This paper uses the thyristor instead of IGBT as the dc-link switch. To ensure the thyristor can be softly turned on and safely turned off, a new control scheme is proposed. When using this proposed scheme, HMMC can also tolerate the failure of thyristor's turning-off without shutting down the system, improving the reliability effectively. The cell capacitor voltage ripple analysis is presented considering the effects of the thyristor switching process. In addition, a decoupled energy balancing control is utilized to suppress the fluctuation of dc current. Experimental results obtained from a 380 V/7.5 kW downscaled prototype validate the effectiveness of starting up a motor from the standby mode to rated speed with full-torque.

Hybrid Back-to-Back MMC System for Variable Speed AC Machine Drives

Modular multilevel converter (MMC) has drawn great attention in variable-speed machine drives. However, a challenge exists that the voltage ripple of sub-module capacitors in MMC would be very large at low motor speed. In this paper, a novel back-to-back (BTB) MMC system is introduced which can effectively limit the capacitor voltage ripple. The grid-side MMC is a hybrid structure which uses full-bridge sub-modules in the upper arm whereas half-bridge sub-modules in the lower arm. The DC-link current is controlled to be constant thus the motor-side MMC with half-bridge sub-modules can reduce its DC-link voltage at low frequencies so as to absorb less energy variation and limit the capacitor voltage ripple. The operating principle of this hybrid BTB MMC system and the corresponding control strategies are discussed. The effectiveness has been validated by simulation and experimental results.

A Low Glutamate Diet Improves Cognitive Functioning in Veterans with Gulf War Illness

Abstract Objectives The objective of this research was to investigate a novel low glutamate dietary intervention for Gulf War Illness (GWI), a chronic multi-symptom disorder that includes cognitive dysfunction. Methods Forty GW veterans with GWI were recruited from across the US. As part of a larger clinical trial, participants completed computerized cognitive testing and the Adult ADHD Self-Report Scale (ASRS) using CNS Vital Signs® (CNSVS) software. Before diet initiation, subjects received intensive dietary counseling. Post-diet assessments were completed after 1 month on the diet, and then participants were randomized to a 2-week double-blind placebo-controlled crossover challenge with glutamate (MSG)/placebo administered over 3 days of each week. The CNSVS battery was administered again on the 3rd day of each challenge week. The challenge data have not yet been un-blinded, and therefore will not be included in this abstract. Pre-post testing (t-test or Wilcoxon Signed Rank test) was conducted for each domain in the CNSVS battery, including an overall marker of neurocognitive function (NCI) and the ASRS. Results Several cognitive domains were significantly improved after 1-month on the low glutamate diet, including NCI (P &amp;lt; 0.01), executive functioning (P = 0.01), cognitive flexibility (P &amp;lt; 0.05), motor speed (P &amp;lt; 0.01), processing speed (P &amp;lt; 0.05), and psychomotor speed (P = 0.001). However, reaction time was slower at post-diet testing (P = 0.01). ADHD symptoms were also significantly improved at post-diet (P &amp;lt; 0.0001). Conclusions Veterans with GWI showed major improvements in cognitive function after 1-month on a low glutamate diet, including improvement in overall neurocognitive status. Upcoming analysis of the double-blind placebo-controlled crossover challenge data will provide additional information on which cognitive domains are directly affected by challenge with glutamate relative to placebo. Funding Sources The US Army Medical Research Acquisition Activity, 820 Chandler St, Fort Detrick MD 21,702–5014 is the awarding and administering acquisition office. This work is supported by the Office of the Assistant Secretary of Defense for Health Affairs through the Gulf War Illness Research Program. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the Department of Defense.

PD23-04 AN EXPERIMENTAL COMPARISON OF AUTONOMOUS ROBOTIC AND MANUAL LAPAROSCOPIC SUTURING

You have accessJournal of UrologySurgical Technology & Simulation: Instrumentation & Technology II (PD23)1 Apr 2020PD23-04 AN EXPERIMENTAL COMPARISON OF AUTONOMOUS ROBOTIC AND MANUAL LAPAROSCOPIC SUTURING Michael Hsieh*, Hamed Saeidi, Michael Kam, Shuwen Wei, Justin Opfermann, Simon Leonard, Jin Kang, and Axel Krieger Michael Hsieh*Michael Hsieh* More articles by this author , Hamed SaeidiHamed Saeidi More articles by this author , Michael KamMichael Kam More articles by this author , Shuwen WeiShuwen Wei More articles by this author , Justin OpfermannJustin Opfermann More articles by this author , Simon LeonardSimon Leonard More articles by this author , Jin KangJin Kang More articles by this author , and Axel KriegerAxel Krieger More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000873.04AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The inconsistency and difficulty of suturing in minimally invasive surgeries stem from the limitations in tool motion and visualization. In pelvic surgery, difficulty is amplified since the tool access is restricted by anatomy. Using an open surgical approach, we previously demonstrated superior suture precision and retention via the smart tissue anastomosis robot (STAR) guided by near infrared (NIR) and 3D imaging systems that reconstruct bowel. Here we demonstrate extensions to laparoscopic conditions in preparation for preclinical studies. METHODS: A KUKA LBR Med lightweight robot was equipped with a motorized commercial suture tool with pitch and roll controls. NIR and 3D cameras were used to reconstruct the 3D model of the tissue and enable robotic suture planning. We tested the STAR in two tasks, i) suturing on a 4-cm straight line on suture pads assuming a static target tissue with a one-time suture planning (STAR-S, n = 5), ii) and a vaginal cuff closure on synthetic tissues with 5 cm diameter and 5 mm wall thickness under dynamic motion and deformation and replanning after each stitch (STAR-D, n = 2). STAR-S/STAR-D includes 1/1 knot at the beginning and 3/10 running stitches. Based on the number of stiches and tissue size, a high-level planner determines ideal suture locations. A similar task as STAR-D but in a manual mode was completed by a surgeon in laparoscopic trainers (Manual, n= 4). RESULTS: Standard deviation between consecutive sutures, and suture bite was 0.42mm/1.03mm (p < 0.005), and 0.84mm/1.63mm (p = 0.19) for STAR-S and STAR-D, respectively. STAR-S is 2.45 times more consistent in suture spacing since it represents an easy suturing task while STAR-D is closer to the clinical cases due to continuous deformations and irregular tissue shapes. The standard deviation between consecutive sutures and bite size for Manual are respectively 2.75 mm (STAR-D is 2.67 times more consistent, p <0.05) and 3.17 mm (STAR-D is 1.94 times better, p < 0.05). However, average task completion time for STAR-D is 719.5clip_image002.png">12.5 sec (p < 0.001). This happened due to low motor speeds of the suture tool and safety velocity limits imposed on the robot by the control algorithms. CONCLUSIONS: Autonomous robotics is a promising solution for ensuring consistent laparoscopic suturing in spatially constrained surgeries. Using 3D imaging and improved planning methods, STAR performs laparoscopic suturing with higher consistency than an expert surgeon. Speed can be improved by relaxing safety speed limits. Future work will consider tests in preclinical studies on porcine animal models. Source of Funding: NIH R01EB020610 © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e465-e465 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Michael Hsieh* More articles by this author Hamed Saeidi More articles by this author Michael Kam More articles by this author Shuwen Wei More articles by this author Justin Opfermann More articles by this author Simon Leonard More articles by this author Jin Kang More articles by this author Axel Krieger More articles by this author Expand All Advertisement PDF downloadLoading ...

Approaching the Ideal BLDC Motor: A Novel Electronic Speed Controller System for a Generator-Converted BLDC Motor with Field Weakening Feature

The concept of an ideal Brushless DC (BLDC) motor which has adjustable rotor magnetic field offers an opportunity for wider BLDC area of implementation as a very versatile electric powerhouse especially in variable load areas such as on electric vehicle or other people movers. Characterized by its high-efficiency level, low maintenance and long service duration, the lack of physical commutation brush like in regular DC motor dictates the requirement of an electronic control system to regulates its commutation.&#x0D; &#x0D; An electronic control system equipped with rotor field control capability in a collaboration with an ideal BLDC motor, is believed to offers wider implementation opportunity. Unlike a normal BLDC motor which has a standard power curved characterized with maximum power is only achievable in one specific speed, if properly controlled will have an adjustable maximum power in a wide range of rotational speed. &#x0D; &#x0D; This study proposes a novel approach to an ideal BLDC implementation through novel electronic speed controller with rotor field control in addition to normal standard motor power control. As there is no such thing as an ideal BLDC motor at the current moment, an automotive generator which has an electromagnetic rotor is converted to become a BLDC motor as an effort to approach the ideal BLDC motor concept. Field weakening, the term used for adjusting rotor magnetic field in induction motor control, is adopted as the term for adjusting the BLDC rotor field in operation. Further, a novel an electronic control system is developed which special features to also control the rotor magnetic field.&#x0D; &#x0D; The converted generator has been found to able to function like an ideal BLDC motor, by adjusting the electromagnetic rotor in its operation. It has been found to be able to provides maximum motor power within a wide range of rotational speed. Through rotor field adjustment, the converted generator provides a real-time versatile capability of allocating its power to either the high torque at low motor speed or to a very high speed at minimum torque. 39% to 81% operational efficiency levels have been achieved during the experiment, rendering the performance level of the converted generator and controller way above brushed DC motor and in par with most of standard BLDC motor.&#x0D; &#x0D; The Field Weakening control has also been found to be useable for speed control. Further, a Proportional &amp;ndash; Integral close-loop speed regulation has also been developed for both motor and rotor control and was found to be able to works subsequently with seamless transition between each other.

A Modified Flux Regulation Method to Minimize Switching Frequency and Improve DTC-Hysteresis-Based Induction Machines in Low-Speed Regions

Direct torque control (DTC) suffers from flux droop owing to the long zero-voltage vectors at low motor speeds. Previous studies were able to attain flux regulation by imposing the continuous switching of forward and reverse active-voltage vectors by causing torque overshoots in the torque hysteresis bands (THBs). This led to an excessive increase in the switching frequency and larger torque and current ripples, thus reducing the drive efficiency. In this paper, a modified flux regulation method is proposed for the classical DTC using a single THB when flux droop occurs in a low-rotor-speed range. The proposed method can protect the DTC from flux droops at low speeds by reducing the duration of zero-voltage vectors and minimizing the number of reverse-voltage vectors. In addition, the proposed strategy is efficient in reducing torque and current ripples while operating at low motor speeds. Furthermore, a significant reduction in the switching frequency is obtained. The effectiveness of the proposed strategy is confirmed by simulation and experimental results.

Fast Torque Control and Minimized Sector-Flux Droop for Constant Frequency Torque Controller Based DTC of Induction Machines

In this paper, two simple control methods are proposed for improving direct torque control (DTC) with a constant frequency torque controller (CFTC-DTC) in induction machines. The CFTC-DTC was initially introduced to reduce torque ripple and achieve constant switching frequency in inverters. However, when compared to the original DTC, the CFTC-DTC algorithm suffers from slow torque dynamic response owing to the selection of zero-voltage vectors during torque transient. In addition, when the motor operates at low speed, flux droop occurs at sector transitions, which leads to undesirable current distortions. The problem of flux droop occurs because of short-duty voltage cycles and small radial voltage components at low speeds. This paper has two main contributions-to eliminate zero-voltage vectors during torque dynamics in order to establish a fast torque response in the transient state, and to minimize the flux droop at the sector transitions by applying another triangular carrier and modifying the torque output in order to increase the duty voltage cycles at low motor speeds. A detailed analysis of the problems and proposed methods is presented. Experimental results are provided to validate the effectiveness of both proposed methods.

Study and Comparison of Discontinuous Modulation for Modular Multilevel Converters in Motor Drive Applications

Discontinuous modulation applied to modular multilevel converters is an effective method for reducing the capacitor voltage ripples. In this paper, the discontinuous modulation is adapted and used in a motor drive application. For proper operation of the converter, a new energy controller is presented, which is suitable for operation with nonsinusoidal reference signals. Experimental results comparing the discontinuous modulation with other techniques operating at low motor speeds are shown. The results demonstrate the effectiveness of the discontinuous modulation on reducing capacitor voltage ripples and power losses.

Constant Switching Frequency DTC for Matrix Converter Fed Speed Sensorless Induction Motor Drive

The paper presents a constant switching frequency scheme for speed sensorless Direct Torque Control (DTC) of Matrix Converter fed Induction Motor Drive. The use of matrix converter facilitates improved power quality on input as well as motor side, along with Input Power Factor control, besides eliminating the need for heavy passive elements. Moreover, DTC through Space Vector Modulation helps in achieving a fast control over the torque and flux of the motor, with added benefit of constant switching frequency. A constant switching frequency aids in maintaining desired power quality of AC mains current even at low motor speeds, and simplifies input filter design of the matrix converter, as compared to conventional hysteresis based DTC. Further, stator voltage estimation from sensed input voltage, and subsequent stator (and rotor) flux estimation is done. For speed sensorless operation, a Model Reference Adaptive System is used, which emulates the speed dependent rotor flux equations of the induction motor. The error between conventionally estimated rotor flux (reference model) and the rotor flux estimated through the adaptive observer is processed through PI controller to generate the rotor speed estimate.

A Hybrid Modular Multilevel Converter for Medium-Voltage Variable-Speed Motor Drives

Modular multilevel converters (MMC) have revolutionized the voltage-sourced converter-based high-voltage direct current transmission, but not yet got widespread application in medium-voltage variable-speed motor drives, because of the large capacitor voltage ripples at low motor speeds. In this paper, a novel hybrid MMC topology is introduced, which significantly reduces the voltage ripple of capacitors, particularly at low motor speeds. Moreover, this topology does not introduce any motor common-mode voltage; as a result, there are no insulation and bearing current problems. Additionally, the current stress can remain at rated value throughout the whole speed range; thus, no device needs to be oversized and converter efficiency can be ensured. Operating principle of this hybrid topology is explained, and control schemes are also developed. Validity and performance of the proposed topology are verified by simulation and experimental results.

Common-Mode Resonance Suppression in Transformerless PWM Current-Source Drive

Among high-power pulsewidth modulation (PWM) current-source motor drives, the transformerless structure using the integrated dc choke has been widely acknowledged with superior advantages. A typical challenge faced by such transformerless PWM current-source drive systems is the potential common-mode resonance excited by the common-mode voltage (CMV). Since the implementation of power factor compensation (PFC) at low motor speeds may increase the CMV in such drives, the common-mode resonance could be serious and further aggravate the CMV stress on the system. In this paper, the critical factors on the common-mode resonance are thoroughly investigated. Based on the investigation, a solution based on average-value-reduction (AVR) space-vector modulation (SVM) is proposed to suppress the common-mode resonance while maintaining the PFC function. The investigation of common-mode resonance and the effectiveness of the proposed resonance suppression solution are verified through experiments on a transformerless PWM current-source drive system.

Regenerative Cascaded Cell Inverter with Active Filter

In the medium voltage application it is very beneficial to use cascaded inverters. Traditionally, this type of inverter is based on diode front end and bulky phase shifting transformer. Due to the demand of 4 quadrant drives and more severe grid requirement, the cascaded inverters with active front end have been started to emerge in the market. This article introduces regenerative cascade inverter topologies. After a short summary about the topologies, single-phase cell solution with NPC is analyzed in detail. Since one of the most challenging problems is the elimination of low order grid harmonic at low motor speed, the article demonstrates the origin of this harmonics. After the clarification of the harmonic generation phenomenon, a novel harmonic elimination method is introduced. Apart from the description of the new elimination concept, the proper controller structure is described as well. Finally, the performance of the novel method is verified by Matlab simulation.

Experimental Study of Adiabatic Two-Phase Flow in an Annular Channel Under Low-Frequency Vibration

In order to investigate the possible effect of seismic vibration on two-phase flow dynamics and thermal-hydraulics of a nuclear reactor, experimental tests of adiabatic air-water two-phase flow under low-frequency vibration were carried out in this study. An eccentric cam vibration module operated at low motor speed (up to 390 rpm) was attached to an annulus test section which was scaled down from a prototypic boiling water reactor (BWR) fuel assembly subchannel. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm, respectively. The two-phase flow operating conditions cover the ranges of 0.03 m/s ≤ 〈jg〉 ≤ 1.46 m/s and 0.25 m/s ≤ 〈jf〉 ≤ 1.00 m/s and the vibration displacement ranges from ±0.8 mm to ±22.2 mm. Steady-state area-averaged instantaneous and time-averaged void fraction were recorded and analyzed in stationary and vibration experiments. A neural network flow regime identification technique and fast Fourier transformation (FFT) analysis were introduced to analyze the flow regimes and void signals under stationary and vibration conditions. Experimental results reveal possible changes in flow regimes under specific flow and vibration conditions. In addition, the instantaneous void fraction signals were affected and shown by FFT analysis. Possible reasons for the changes include the applied high acceleration and induced void/flow structure changes at certain ports under the specific flow and vibration conditions.

Ship electric propulsion with a sensorless permanent magnet synchronous motor: A simulation study

New general ships powered by electric propulsion always operate at low motor speeds. Popular sensorless vector control methods, including open loop and closed loop methods, are not reliable in this application. This is because the magnitude of back-electromotive force voltage is very small in the low speed region, and the performance of these methods is therefore significantly degraded. To overcome this problem, a high-frequency injection method is introduced in the control of the ship electric propulsion system. The injected periodic signal creates a high-frequency revolving field to act as a carrier. Then the desired information about the position angle of the motor can be retrieved. A simulation model of a ship electric propulsion system is established in Matlab/Simulink. The test results show that the newly proposed control system works stably with various ship operating conditions and robustly against speed variations. Its estimated position error is less than 0.3 rad. Moreover, the proposed sensorless vector control approach has been compared with the closed-loop-based model reference adaptive system. The comparison has demonstrated that the dynamic characteristics of the proposed control system are superior to the latter.