Commutation Period Research Articles

Traffic Accidents Involving Cyclists Identifying Causal Factors Using Questionnaire Survey, Traffic Accident Data, and Real-World Observation.

The purpose of this study is to clarify the mechanism of traffic accidents involving cyclists. The focus is on the characteristics of cyclist accidents and scenarios, because the number of traffic accidents involving cyclists in Tokyo is the highest in Japan. First, dangerous situations in traffic incidents were investigated by collecting data from 304 cyclists in one city in Tokyo using a questionnaire survey. The survey indicated that cyclists used their bicycles generally while commuting to work or school in the morning. Second, the study investigated the characteristics of 250 accident situations involving cyclists that happened in the city using real-world bicycle accident data. The results revealed that the traffic accidents occurred at intersections of local streets, where cyclists collided most often with vehicles during commute time in the morning. Third, cyclists' behavior was observed at a local street intersection in the morning in the city using video pictures. In one hour during the morning commute period, 250 bicycles passed through the intersection. The results indicated that one of the reasons for traffic accidents involving cyclists might be the combined effect of low visibility, caused by the presence of box-like building structures close to the intersections, and the cyclists' behavior in terms of their velocity and no confirming safety. It was observed that, on average, bicycle velocity was 3.1 m/s at the initial line of an intersection. The findings from this study could be useful in developing new technologies to improve cyclist safety, such as alert devices for cyclists and vehicle drivers, wireless communication systems between cyclists and vehicle drivers, or advanced vehicles with bicycle detection and collision mitigation systems.

Commutation Torque Ripple Reduction Strategy of Z-Source Inverter Fed Brushless DC Motor

Based on the Z-source inverter, this paper proposes a novel commutation torque ripple reduction strategy for brushless DC motor (BLDCM). The proposed strategy employs the same modulation mode in both the normal conduction period and the commutation period, and the commutation torque ripple is reduced by regulating the shoot-through vector and active vector duty cycles. The proposed detection method acquires the end point of commutation by comparing the clamped terminal voltages with reference zero level, and the signal-noise-ratio of the detection is improved by avoiding the attenuation of the terminal voltages. Furthermore, a certain pulse width of the shoot-through vector can not only reduce the commutation torque ripple but also provide a new opportunity to detect the end point of commutation. Moreover, Z-source inverter provides the buck–boost ability for BLDCM drive system, then the dc voltage utilization can be improved, and the safety of the drive system can also be improved. In addition, this paper analyzes the terminal voltages during each vector. The experimental results verify the correctness of the theories and the effectiveness of the proposed approach.

Ripple Reduction in BLDC Motor Based on Cascaded DC-DC Converter

This paper proposes a novel converter topology to reduce the commutation torque ripple in brushless DC (BLDC) motor drives. The proposed topology is composed of a three-level neutral-point-clamped (NPC) inverter, two modified SEPIC (single-ended primary inductor converter) DC-DC converters, and a commutation voltage selection circuit. The torque ripple appears due to stator winding inductance during phase commutation, which prevents the use of BLDC motor in high performance applications due to undesirable vibration and acoustic noise. The three-level NPC inverter is used to reduce the torque ripple during conduction period. To weaken the torque ripple during the commutation period, two modified SEPIC converters are used to adjust the DC bus voltage to the desired value depending upon the BLDC motor rotational speed. A metal oxide semiconductor field effect transistor (MOSFET)-based commutation voltage selection circuit is used to apply the regulated DC bus voltage during the commutation period. Finally, experimental results show that torque ripple can be significantly reduced by the proposed modified SEPIC DC-DC converters with three-level NPC inverter and commutation voltage selection circuit.

Analysis and Implementation of a High Boost Ratio DC-DC Converter for Minimizing Commutation Torque Ripple in Brushless DC Motor

Brushless dc motor still suffers from commutation torque ripple, which primarily depends on transient line current in the commutation interval. In order to control the incoming and outgoing phase currents to change at the same rate during commutation, this paper presents a novel high boost ratio DC-DC circuit topology in the front end of the inverter. With a suitable closed loop control scheme, the proposed high boost ratio DC-DC converter is operated with two different duty ratios one during commutation period and the other during non commutation period. The cause of commutation ripple is analyzed, and the way to adjust the duty ratio for obtaining the desired dc link voltage is introduced in detail. Finally, simulation and experimental results show that, compared with the existing dc–dc converter topologies, the proposed method can obtain the desired voltage much faster and minimize commutation torque ripple more efficiently

Measurements of armature current in the brush collector unit of a direct current motor during the commutation period

The operating conditions of locomotives determine the special technical state requirements of individual units and aggregates. Traction dc motors are the most heavily loaded and vulnerable objects as far as the work of commutators and their influence on the commutation processes in a motor are concerned. Analysis of the effects of a brush collector unit shows that the split-type-brush-based method for finding the technical state of a dc machine is not sufficiently informative about the commutation process. The current measurement of a short-circuited section of the armature winding during the commutation period was made using two parts of a split-type brush and a proper measurement scheme was proposed. A test bench for the research of the commutation processes in a dc motor was designed, which provided the description of the transition processes in a commutator of a dc machine at the use of a brush consisting of two parts. The current distribution in a short circuited coil and separate parts of a brush was obtained. The measurement scheme of the armature current at a commutator is presented and the experimental results are provided in the form of oscillograms of the characteristics of a real motor.

Switching technique for minimisation of DC‐link capacitance in switched reluctance machine drives

A switched reluctance (SR) machine drive has many advantages over other competing drive technologies in terms of reliability and fault tolerance, which make it particularly attractive for safety critical applications in more electric aircraft technologies. However, an SR machine drive requires a large DC-link capacitor to buffer the de-fluxing magnetic energy during a phase commutation period and to filter out AC harmonic currents from contaminating the DC supply. This study describes a switching technique for minimisation of the DC-link capacitance in SR machine drives and presents experimental results from a laboratory demonstrator. The proposed switching method aims to maintain a constant average DC-link current over a switching cycle, thus eliminating commutation-induced low-frequency current harmonics. Consequently, the DC-link capacitance can be minimised. The effectiveness of the proposed technique is assessed through filter design and demonstrated by experiments with a dSPACE control platform.

Harmonic state-space modelling of a controlled HVdc converter

In this paper a harmonic state-space (HSS) model of a 6-pulse HVdc converter with constant current control is presented. The HSS provides a linear time-invariant (LTI) environment for modelling system harmonics under both steady-state and transient conditions. Although nonlinear and time-variant in nature, the HVdc converter can be linearised around an operating point described by fixed thyristor switching instants. The effect of varying switching instants, both through control and commutation period dynamics, is modelled. The HSS model is implemented in MATLAB and it is validated against a purely time domain model built in PSCAD/EMTDC. It is shown that the combination of frequency coupling through the converter and closing the current control loop can result in high frequency resonances dominating low frequency transient performance. The approach can be generalised to many switching converters, and the HVdc converter example shows how the mechanism behind problems involving non-characteristic frequencies can be identified.

Approach for torque ripple reduction for brushless DC motor based on three‐level neutral‐point‐clamped inverter with DC–DC converter

This study proposes a novel topology for reducing commutation torque ripple in a brushless DC motor (BLDCM) drive system using a three-level neutral-point-clamped (NPC) inverter combined with single-ended primary-inductor converter (SEPIC) converters. In the BLDCM, current ripples arise because of the influence of stator winding inductance, which generates torque ripples. The torque ripple that is generated in the commutation period prevents the use of BLDCM in high-precision servo drive systems. In this study, two-stage converters are proposed to reduce the torque ripple. The first stage consists of two SEPIC converters to obtain the desired commutation voltage according to motor speed. A dc-link voltage selection circuit is combined with the SEPIC converters to apply the optimised voltage during the commutation interval. To reduce the torque ripple further, a three-level NPC inverter is used to apply a half dc-link voltage across the motor winding and this effectively reduces the torque ripple. Experimental results show that the proposed topology is able to reduce commutation torque ripple significantly under both low-speed and high-speed operation.

A RTDS Model for Simulating HVDC Transient Valve Voltage during Commutation Period

This paper presents a RTDS model applied to simulate periodic commutation impulse voltage of HVDC convent valve. The model’s main configure and basic parameters are matching to a typical monopole system which include 12-pulse converters of rectifier and inverter, convert-transformers, DC transmission line, DC filters and AC equivalent power network. Among the system model, the valve components of rectifier are User-Define-Component (UDC) model with RC branch for describing detail valve internal. And also, discrete time step apply 2.5μS non real-time of RTDS for complying with high frequency transient. The validation test is carried out and the result show that the model can simulate accurately valve voltage waveform.

The Research on Suppression Strategies for Electromagnetic Torque Ripples of Brushless DC Motors

Despite of its remarkable active performances, brushless DC motors, which are widely used in mechanical engineering, have an obvious disadvantage in its high electromagnetic torque ripples. In the paper, a ripple suppression method based on predictive controls of stator currents is proposed according to analysis of causes electromagnetic torque ripples generate in commutation periods of brushless DC motors. First of all, a relative accurate prediction is acquired through DC motor on-line parameter corrections based on generalized predictive control algorithms. Then rolling optimizations make tracking errors and control qualities optimized for best control effects. And finally, minimum electromagnetic torque ripples are achieved. The simulation results show that torque ripples can be suppressed effectively with improved reliabilities by using the method proposed.

Implementation of an improved power supply with simple inverters for arc welding machine

Summary The paper provides a simple control, energy recovery inverter without voltage spike. The proposed inverter can be used for arc welding machines. The output of the inverter has two inductors and two switches. These components are in charge of processing positive and negative cycle of alternating current (AC) load current, respectively. They are able to keep the load current continuous to avoid generating voltage spikes during commutation period. Besides, the energy in the inductors can be stored by switches. The stored energy can provide high slope current to avoid arc extinction during commutation. Besides, the energy stored in inductors can be released to improve the conversion efficiency in the next transferring cycle. The operations and design procedures of the circuit are verified. Also, the experimental results of the proposed inverter are measured to demonstrate that the scheme is effective to drive a 100 A AC arc welding machine. Copyright © 2014 John Wiley & Sons, Ltd.

Cycle to cycle adaptive control of simulated moving bed chromatographic separation processes

The simulated moving bed (SMB) technology is increasingly applied in various fields, ranging from the food to the pharmaceutical sectors, for the chromatographic separation of fine (bio)chemicals. In this study, an adaptive controller acting on the fluid flow rates and commutation period is used to regulate the spatial location of the adsorption and desorption waves, and in turn the purity and productivity of the raffinate and extract effluents. This controller is based on a simple discrete-time model of the concentration fronts movement, derived from wave theory. A simple parameter adaptation scheme makes this controller robust to parameter uncertainties and drifts, and allows process start-up with minimum a priori knowledge of the separation parameters. In this study, the performance of the controller is demonstrated for two different applications: the separation of fructo-oligosaccharides (linear isotherms) and cyclopentanone–cycloheptanone (competitive Langmuir isotherms). Different plant/sensor configurations are also examined, indicating the potential of the control strategy even with reduced measurement information.

A novel energy‐retaining inverter for AC arc welding machines

SUMMARYA novel energy‐retaining power supply for AC arc welding machines is proposed in this paper. In this kind of power supply, current‐steering diodes connected across the output chokes keep the inductor current continuous and retain the energy during the commutation period, hence reducing the commutation time to ensure a better welding performance. In addition, the stored energy can be released in the next energy transfer cycle to raise the conversion efficiency. The circuit operations and design procedures are likewise examined thoroughly. Experimental results on a prototype inverter for driving a 100‐A AC arc welding machine are recorded to validate the effectiveness of the presented scheme. Copyright © 2010 John Wiley & Sons, Ltd.

Magnet Segmentation for Commutation Torque Ripple Reduction in a Brushless DC Motor Drive

We present a new brushless DC motor (BDCM) design based on a model elaborated from a finite-element method associated to controller circuit equations represented in a Matlab-Simulink environment. The simulation model takes into account the commutation period effect and is based on the true system design implementation. The simulation results show that there is an effect between this commutation (a major source of torque ripple) and appropriate permanent-magnet segmentation design, particularly when the angle of advance between the back-electromotive force (EMF) and the current is adequately set. Current control strategies are found limited and may require complex implementation. Concentration on back-EMF and ultimately on permanent-magnet design are interesting aspects of torque ripple as well as rotor losses over wide speed range. After validation of the simulation model using an experimental kit set for the purpose, we perform an optimization procedure based on an indirect coupled field circuit approach that has led to an optimal design for which the torque ripple is minimal (less than 6%). An analytical design provided support for the study. The new design shows a lower cogging torque. Overall, the new design helps to provide a low-cost BDCM system for many applications using a simple square wave circuit controller.

Multi-year hourly PM 2.5 carbon measurements in New York: Diurnal, day of week and seasonal patterns

Multi-year hourly measurements of PM 2.5 elemental carbon (EC) and organic carbon (OC) from a site in the South Bronx, New York were used to examine diurnal, day of week and seasonal patterns. The hourly carbon measurements also provided temporally resolved information on sporadic EC spikes observed predominantly in winter. Furthermore, hourly EC and OC data were used to provide information on secondary organic aerosol formation. Average monthly EC concentrations ranged from 0.5 to 1.4 μg m −3 with peak hourly values of several μg m −3 typically observed from November to March. Mean EC concentrations were lower on weekends (approximately 27% lower on Saturday and 38% lower on Sunday) than on weekdays (Monday to Friday). The weekday/weekend difference was more pronounced during summer months and less noticeable during winter. Throughout the year EC exhibited a similar diurnal pattern to NO x showing a pronounced peak during the morning commute period (7–10 AM EST). These patterns suggest that EC was impacted by local mobile emissions and in addition by emissions from space heating sources during winter months. Although EC was highly correlated with black carbon (BC) there was a pronounced seasonal BC/EC gradient with summer BC concentrations approximately a factor of 2 higher than EC. Average monthly OC concentrations ranged from 1.0 to 4.1 μg m −3 with maximum hourly concentrations of 7–11 μg m −3 predominantly in summer or winter months. OC concentrations generally correlated with PM 2.5 total mass and aerosol sulfate and with NO x during winter months. OC showed no particular day of week pattern. The OC diurnal pattern was typically different than EC except in winter when OC tracked EC and NO x indicating local primary emissions contributed significantly to OC during winter at the urban location. On average secondary organic aerosol was estimated to account for 40–50% of OC during winter and up to 63–73% during summer months.

Reduction of speed ripple and vibration for switched reluctance motor drive via intelligent current profiling

This study presents the speed ripple and vibration reductions for a switch-mode rectifier (SMR) fed switched reluctance motor (SRM) drive via intelligent current profiling approach. Firstly, the SRM drive with a boost-type SMR front-end is established, which possesses well-regulated DC-link voltage and good AC line drawn power quality. Secondly, the speed ripple generating process of a SRM is explored. Accordingly, a robust and intelligent speed ripple reduction approach is proposed, wherein the leading edge of winding current command is modified by adding a compensating component, which is automatically generated from the DC-link negative stroke spikes caused by non-ideal commutation. Thirdly, a robust current error cancellation control scheme is designed to yield closer current waveform tracking response, and thus the smoother motor developed torque. In outer loop, a robust speed ripple cancellation control scheme is employed to directly reduce the speed ripple. Finally, the commutation shift is applied to further improve the torque sharing characteristics between phases during commutation period and thus reduce the speed ripple and vibration. In addition, the commutation shift also leads to the improved torque per ampere capability of a SRM. Validity of all the proposed control approaches is demonstrated experimentally.

A Study on Wear of Brush and Carbon Flat Commutator of DC Motor for Automotive Fuel Pump

In an automotive fuel pump system, a small DC motor is widely used to drive the pump and driven by a automotive battery. Recently a bio-fuel, usually a mixture of gasoline and ethanol has been used due to shortage of gasoline and environmental aspect. It affects strongly the performances of a DC motor, especially commutation phenomena, what kind of fuel is used. Therefore the authors have started to investigate the influence of ethanol on the commutation phenomena. They have been reporting the wear of brush and carbon flat commutator in gasoline and ethanol so far. In this paper commutation period, arc duration, brush and commutator wear are examined in ethanol 50-gasoline 50%. Brush wears are very small compared with the previous results. Namely in the present test a mechanical sliding wear is predominant rather than erosion by arc due to short arc duration. Further, an area eroded by arc is observed to re-appear as a sliding surface. From these results a threshold arc energy between arc erosion and mechanical sliding wear is obtained, and a wear model is proposed to explain the above wear pattern on the sliding surface.

A Simple Nonlinear Logical Torque Sharing Function for Low-Torque Ripple SR Drive

A novel and simple nonlinear logical torque-sharing function (TSF) for a switched reluctance motor (SRM) drive is proposed. This novel scheme using nonlinear TSF manipulates currents in two adjacent phases during commutation, so that efficiency and torque ripple in an SRM drive can be considerably improved. For constant torque generation, the switching of one-phase windings is regulated, and torque reference for the other phase stays at the previous state under the condition of a certain current limit given by the overall drive power rating. Every torque state monitored by the nonlinear logical condition determines a regulated or nonregulated torque control among two phases overlapped in commutation region, where one phase is incoming to produce the majority of torque and the outgoing current in the other phase is decreasingly controlled by the logical condition. Due to the same switching state in a nonregulated phase and the reduction of commutation period by the proposed control method, the switching number can be significantly reduced, and hence, the switching loss can be reduced. In case that one-phase regulation cannot satisfy a proper torque reference required for minimum torque ripple operation, a two-phase regulation mode is employed in the novel nonlinear TSF. In order to include magnetic nonlinearity in torque control and decrease a current tail at the end of commutation, the current of the incoming phase needs to be controlled in an increasing manner, and at the same time, the outgoing phase current tracks on an opposite direction so that torque sharing between two phases can be smoothly achieved with a minimum current crossover. The proposed control scheme is verified by some computer simulations and experimental results.

Arc Reduction of High-Voltage DC-Motor for Automotive Application by Targetwise Parameter Optimization (TPO)

The aim of this work is to determine the optimal design parameter for reduced arc characteristics of the high-voltage direct current (dc) motor due to the increase of the terminal voltage from 14 to 42 V. The main interesting focus is whether the reactance voltage decreases according to kinds of the brush, the magnet and the electroangle of the stator magnet. To limit the coil inductance, the electrographite instead of the metal graphite is applied to the electromagnetic design for the 42-V dc motor as automotive application. Supposing the law of energy conservation during the commutation period, the resistivity of the eletrographite with high value makes the inductance of the rotor coil with low value. As a result, the arc appearance decreases remarkably. It is applicable to the automotive application such as cooling fan for engine with the continuous high current of the 42-V power net. As an extra approach, the elecromagnetic design is optimized with the same models to make low coil inductance upon similar required load. Finally, we verify the appearance of the arc reduction through comparing a few photographs, which show how these approaches play a role as a bridge from 14 to 42 V.

Harmonic analysis of AC/DC systems based on phase-domain multi-port network approach

This paper describes a phase-domain frequency domain technique to the harmonic analysis of a three-phase AC/DC system. The methodology is based on the harmonic multi-port network concept, expressed in terms of an ABCD parameter matrix which links voltage and current harmonics of different orders on both sides of the converter. Since the commutation angles are unknown, the harmonic interactions are computed by a sequential solution of the AC/DC system state variables, related by the ABCD matrix, and the updating of the commutation periods. A set of analytical equations has been derived to compute commutation times taking place in the converter. Test results are presented which demonstrate the effectiveness of the proposed methodology to assess harmonic interactions on both balanced and unbalanced operating conditions. The results are validated to those obtained by a time domain simulation.