Current Commutation Research Articles

A singular perturbation approach to sensorless control of a permanent magnet synchronous motor drive

For most surface mounted permanent magnet synchronous motors, the electrical time constant is relatively small due to its large air gap. This has been exploited with small parameter perturbation techniques to develop observers for the position and speed using measurements of currents. In this paper, a singular perturbation algorithm is experimentally evaluated for both current commutation and closed loop speed control of a permanent magnet synchronous motor drive. An improved algorithm is then proposed and related implementation issues are presented.

1997-1998 Survey of Potential North American Applications for Emerging Diesel Multiple Unit Technologies

The results of a survey done in the United States and Canada in 1997 and 1998 are presented. The survey was done to determine the level of interest among current and potential commuter rail operations in applying emerging technologies for self-propelled, diesel multiple unit (DMU) rail passenger cars. Interest in DMU rail passenger cars is waxing across the continent as commuter rail grows in popularity as a transit mode and operators search for possible alternatives to push-pull diesel equipment. The survey team contacted representatives of 58 operators, regional transit agencies, planning agencies, state departments of transportation, and other agencies. Twenty-eight of the respondents currently operate or oversee commuter or regional rail service and 30 do not. The principal survey was conducted in 1997 with follow-on surveys of selected jurisdictions in 1998. Of the 58 potential operators, 19 do not foresee DMU use, 8 currently operate DMUs, 2 are actively implementing DMU plans, and the remaining 29 are considering DMUs for future applications in their jurisdictions. At least 14 potential operators have hosted DMU demonstrations. Two sections are presented: ( a) a summary of findings and observations with a summary table of survey results, and ( b) details on each jurisdiction surveyed covering current operations, plans, and orientation toward DMU applications.

Zero-voltage- and zero-current-switched PWM DC-DC converters using active snubber

A novel active snubber soft-switched method is proposed to achieve zero-voltage and zero-current switching (ZV-ZCS) for pulsewidth modulation (PWM) DC-DC power converters. The unique location of the snubber capacitor and inductor ensures low current stress and commutation losses in the auxiliary circuit. A boost converter adopting this technique is presented as an example, to illuminate its operation principles and derive the design procedures. Simulation and hardware implementation of a 350-W 150-kHz boost converter have been made to validate the operation and the efficiency improvement. Some other basic PWM DC-DC topologies with the proposed snubber are also been given.

A Novel Three-Phase Current-Fed ZCS-PWM Converter Incorporating A Single Resonant DC Link Soft Commutation Snubber

This paper presents a novel prototype three-phase current-fed PWM converter with switched-capacitor type resonant DC link commutation circuit operating with a new optimum PWM pattern strategy under a design consideration of low-pass filter, which can operate on the basis of the principle of zero current soft-switching commutation.In the first place, the steady-state operating principle of this converter with a new resonant DC link snubber circuit is described in connection with the equivalent operating circuit, together with the practical design procedure of the switched-capacitor type resonant DC link circuit. In the second place, the three-phase current-fed PWM converter with the switched-capacitor type resonant DC link circuit is discussed from a theoretical viewpoint on the basis of a design example for high-power applications. The actively delayed time correction method to compensate distorted currents due to a relatively long resonant commutation time is newly implemented in the open loop control scheme so as to acquire the new optimum PWM pattern. Finally, the experiment of set-up in laboratory system of this converter is concretely demonstrated herein to confirm a zero current soft-switching commutation of this converter. The comparative evaluations between current-fed hard-switching PWM and soft-switching PWM converters are carried out from a viewpoint of their PWM converter characteristics.

Numerical simulation method for the slip power recovery system

A numerical simulation method for the slip power recovery system is presented. The dq induction-machine model, using flux linkages as state variables is used. This leads to a simple and efficient computer program. The diode bridge rectifier is modelled using three switching functions that are determined by the sign of the corresponding AC currents. The model obtained is very simple, and accurately represents the three-phase diode bridge rectifier including the current commutation process. To merge the models of the induction machine and the diode-bridge rectifier, no difficulties arise when a direct-voltage intermediate circuit is present. When a direct-current circuit is used in the intermediate circuit a model of the whole ‘induction machine and diode-bridge rectifier’ must be used. Park's variables can be used in this case, also. The operations performed to model the system are equivalent to assuming that the diode bridge rectifier and the DC circuits are transformed into a nonlinear circuit connected to the rotor terminals. MATLAB/simulink is used to integrate the equations. Experimental and simulated results are presented and compared showing good accuracy.

Erosion resistance of composite Ag’MCaF2 contacts

The erosion resistance of composite Ag’MCaF2 contacts in the communitation of constant currents I=1–10 A was studied. With the aid of metallographic analysis it was shown that in comparison with cast silver contacts, composite contacts even at I=1 A show a stronger tendency to change the direction of mass transport, which increases with increase of the current to I≤4 A. In this range of commutation currents there is a small loss of material, accompanied by the removal of a considerable part of Ag’MCaF2 particles from the working zone to the periphery of the contacts, which promotes their improvement. The laws revealed in the work allowed us to recommend the composite Ag’MCaF2 contacts for use in relay technology. Tests in microswitches confirmed the high erosion resistance of composite contacts in the range I=1–3 A.

Model of a disk magnetohydrodynamic channel using pure inert gases and Faraday current commutation

The purpose of this experiment was to find a way to increase the effective conductivity in a nonequilibrium MHD channel. The working material used was inert gas without admixtures of alkali metals. The experiment was carried out in a disk MHD channel coupled to a shock tube, with radial expansion of the gas and an axial magnetic field. An inset was located in a sector of the disk channel with electrodes, to which a load was connected to extract power into an external circuit. Voltage-current characteristics were recorded in this experiment along with the structure of luminous nonuniformities. The results of the experiment showed that as ionization instabilities develop, the effective conductivity of the plasma increases with increasing magnetic induction, and the extracted power density for fields above critical turns out to be roughly 30% higher than that calculated by assuming that the conductivity is a constant.

Experimental study on the characteristics of current distribution in Rutherford cables and parallel strands

The current distribution in a multi-stranded superconducting cable such as Rutherford cable plays an important role in the stability. Rutherford cables consist of many strands which are twisted and electrically contacted together. Because of this complexity, it is hard to know factors that effect to the current distribution and hence to the stability. The most important factors may be interstrand contact resistances and mutual inductances between strands mainly caused by twisting strands. To evaluate the effect of contacting and twisting, we compared the characteristics of Rutherford cables with parallel strands. We have performed experimental studies on these items for parallel strands with and without insulation by heating with a spot heater. The results for insulated parallel strands show very similar behaviors to those obtained in Rutherford cables. From the fact, we came to the conclusion that the contact resistances at the edges are relatively low in comparison with side-by-side ones between two adjacent strands in the Rutherford cable, and then that the current commutation occurs mainly at the edges. Rest of the transport current could not change the steady state current distribution. To clarify this is remained as a future research.

Fast commutation of high current in double wire array Z-pinch loads

A dynamic model of multi-MA current commutation in a double wire array Z-pinch load is proposed and studied theoretically. Initially, the load is configured as nested concentric wire arrays, with the current driven through the outer array and imploding it. Once the outer array or the annular plasma shell formed from it approaches the inner array, the imploded plasma might penetrate through the gaps between the wires, but the azimuthal magnetic field is trapped due to both the high conductivity of the inner wires and the inductive coupling between the two parts of the array, causing a rapid switching of the total current to the inner part of the array.

Measurement of ion parameters during a forced switching off of current in vacuum

This paper presents the results of ion parameters measured during a forced current commutation of a diffuse vacuum arc, aimed at evaluating the role of ions in discharges occurring rarely after the counterpulse commutation process, in a contact arrangement corresponding to a low-voltage vacuum switch. A sinusoidal half-wave current was interrupted near its amplitude of 400 A with a counterpulse of rise velocities 2.4 and 32 A//spl mu/s. In this way, a forced switching off of dc current was modeled. A retarding field analyzer was used for ion parameter measurements at the forced commutation process. Ion potentials up to 100 V were measured at the current zero moment, and the average decay times of ions after current zero were in the range from a few microseconds up to 30 /spl mu/s as a function of observed ion potential. The measured values of decay times show the rather negligible role of ions in the discharge process after the counterpulse commutation in the examined contact arrangement. The rise time of the countercurrent is proposed as a factor in the successful forced current commutation under these conditions, and values up to a few amperes per microsecond of countercurrent rise velocity can be considered as the limit value.

Commutation-caused eddy-current losses in permanent-magnet brushless DC motors

An analytical approach based on a two-dimensional electromagnetic field analysis in polar coordinates is developed to predict the commutation losses in a permanent magnet brushless dc (PMBD) motor. These losses are essentially the eddy-current losses induced in the PMBD motor's rotor magnets and core and are caused by the rotor sweeping of the stationary stator magnetic field before each current commutation due to inverter switching takes place. The approach is applicable to motor constructions with either magnet segments or a magnet ring and able to deal with ill-conditioned cases. The model was applied to an existing motor and good agreement (within 11%) with the finite element method was achieved.

Optimised input filter design and low-loss switching techniques for a practical matrix converter

The matrix converter permits frequency conversion in a single-stage process. The perceived disadvantage of the matrix converter is that conduction losses are high. However, semisoft current commutation and optimal sequence switching can be used to minimise commutation losses so that at high switching frequencies the total losses in the matrix converter can be less than those in a conventional rectifier–inverter combination. The viability of the matrix converter depends to a large extent on the size and cost of the input filter components required to meet international power quality standards. In the paper filter designs are examined and guidelines established. Practical tests have been carried out on a 3.5 kW converter to validate computer models. It is concluded that the matrix converter is viable if the right combination of semiconductor switching techniques and input filter design are employed.

Analysis of Bicycle Commuter Routes Using Geographic Information Systems: Implications for Bicycle Planning

A geographic information system (GIS) network data base is used to determine the characteristics of 397 routes used by commuter cyclists in Guelph, Ontario, Canada, and to compare them with the shortest-path routes between each origin and destination. The analysis of route data provides useful insight for understanding factors affecting travel behavior and in this case provides quantitative support for many existing assumptions regarding commuter cyclist behavior. Most commuters divert very little from their minimum path (0.4 km on average) and are found to use major road routes. The cyclists tend to avoid grades, grade-separated railway crossings, and high-activity areas, but not road (as opposed to pedestrian) bridges. Cyclists use traffic signals especially for crossing major roadways and turning. The high-quality direct off-road paths are used only infrequently by the commuter cyclists and the lower quality ones even less. The results of this analysis suggest that efforts to accommodate current commuter cyclists should be focused on improving cycling conditions on the road network, such as providing wider curb lanes, or actuated traffic signal detectors that recognize the presence of bicycles. If potential new commuters are similar to the minority of current commuter cyclists in this study who use mainly local roads, paths or trails, then projects that make the network of local roads and pathways more connective and direct may encourage a higher level of commuter cycling.

Current Algebra and Bosonization in Three Dimensions

We consider the fermion-boson mapping in three dimensional space-time, in the Abelian case, from the current algebra point of view. We show that in a path-integral framework one can derive a general bosonization recipe leading, in the bosonic language, to the correct equal-time current commutators of the original free fermionic theory.

A study on brush wear under commutation arcs in gasoline

The dc motor for an automotive fuel pump has a distinctive feature in that its commutation is carried out in a gasoline environment. The study of brush wear under commutation is generally important from the point of view of its reliability and durability. In this paper, the wear of the copper-graphite brush sliding against the copper commutator under commutation arcs in gasoline and air is reported. It was made clear that the brush wear in gasoline was more severe than that in air on both polarities when the commutation current was set to 10 A including arcs. In order to make the influence of arcs clear on the brush wear, we also examined the brush wear with load current but no arcing and the material transfer in switching contacts with arcing, which gave us the information of electrical erosion. In addition, we analyzed worn brush surfaces after these tests with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). As a result, the arc has a serious influence on the brush wear in both environments, but how to erode the brush surface by arcing in gasoline is different from that in air.

Direct control strategies based on sensing inductance in switched reluctance motors

The stator winding current commutation timing is the central subject of switched reluctance motor control. The direct use of coil inductance information for current commutation is introduced in this paper. The drawbacks of position-based commutation, in the presence of drifting electrical parameters, are overcome by using the instantaneous coil inductance information. Algorithms to optimize torque using this approach are also presented in this paper.

Optical investigation of arc spot formation on cold cathodes in noble gas atmosphere

An arc ignited by a high-voltage breakdown in pure argon at atmospheric pressure is blown magnetically against a third so-called commutation electrode (CE) positioned perpendicularly to the arc axis. Cathodic arc spot formation is initiated on this electrode by application of a potential difference between the bulk plasma and the commutation electrode. The first stage of this current transfer is investigated electrically and optically. Comparing high-speed photographs with the starting phase of the commutation current, it turns out that an abrupt current increase is correlated to a plasma ball in front of the cathode, and a precurrent (less than 1 A) is correlated to a luminous layer on the cathode surface and the subsequent formation of a bright channel between the cathode surface and the bulk plasma.

CURRENT COMMUTATION ANALYSIS IN SELF-CONTROLLED DOUBLE STATOR SYNCHRONOUS MACHINES TAKING INTO ACCOUNT SATURATION EFFECT

In the field of high power drives, the double armature synchronous machines constitute an advantageous choice compared to classical synchronous machines, because of the relatively low torque ripple produced. This paper proposes an analytical model of the current commutation and its influence on pulsating torque, in converter fed Double Stator Synchronous Machines (DSSM), taking into account the magnetic saturation with cross-magnetizing effect. A comparative study, between the linear model (saturation neglected) and the proposed one, is developed with the aim of estimating the influence of the magnetic non-linearity on these two phenomena.

The zero voltage switching partial series resonant converter

A new high-frequency dc to dc converter, suitable for application in the kilowatt range, is presented. The topology is based on a half bridge series resonant converter, i.e., having only two switches. Resonance occurs only for a part of each switching cycle, and a discrete energy pulse is transferred to the load every half cycle, rendering a variable frequency controller for controlling the output power. The converter features zero-voltage turn-on, and snubbed turn-off at reduced current for the switching devices, and zero current commutation of the rectifier diodes, making it suitable for IGBT switches operating at a switching frequency higher than 20 kHz. The efficiency of the converter is very high under full load and low load conditions, while the dynamic output voltage range is two times larger than that of the conventional half bridge Series Resonant Converter.

Magnetic loss and B(H) behaviour of non-oriented electrical sheets under a trapezoidal exciting field

The excess loss and hysteresis response of electrical steel are measured and discussed in the case of trapezoidal field excitation similar to the current provided by a current commutation supply of a self-synchronous rotating machine. Three industrial non-oriented SiFe samples of different magnetic grades and thicknesses are tested using an automatic Epstein frame equipment. The losses and the unusual observed B( H) loops are analysed in terms of the rate of change of the field, the diffusion of the induction inside the sheet and by the calculation of the theoretical hysteresis cycles due to the eddy currents.