Showing papers on "Three-phase published in 1988"

A three-phase soft-switched high power density DC/DC converter for high power applications

Abstract: Three DC/DC converter topologies suitable for high-power-density high-power applications are presented. All three circuits operate in a soft-switched manner, making possible a reduction in device switching losses and an increase in switching frequency. The three-phase dual-bridge converter proposed is shown to have the most favorable characteristics. This converter consists of two three-phase inverter stages operating in a high-frequency six-step mode. In contrast to existing single-phase AC-link DC/DC converters, lower turn-off peak currents in the power devices and lower RMS current ratings for both the input and output filter capacitors are obtained. This is in addition to smaller filter element values due to the higher-frequency content of the input and output waveforms. Furthermore, the use of a three-phase symmetrical transformer instead of single-phase transformers and a better utilization of the available apparent power of the transformer (as a consequence of the controlled output inverter) significantly increase the power density attainable. >

Analysis and design of a three-phase offline DC-DC converter with high-frequency isolation

Abstract: Single-phase offline switch mode rectifiers (or offline DC-DC converters) face severe component stresses in higher than 10kW applications. The authors show that in three-phase, switch-mode rectifier (SMR) topologies' component stresses are reduced, and performance is improved substantially. These improvements include faster response times, reduced switching stresses of the power semiconductor devices, and reduced size and ratings of associated reactive components. The authors also present an analysis and design approach for three-phase SMR converters under large-input voltage and load variations. Output voltage control is achieved by varying the duty cycle of the inverter power semiconductor switches. Theoretical results are verified experimentally. >

Electric, variable damping vehicle suspension

Abstract: An electric, variable damping suspension for a motor vehicle comprises a three phase rotary electric alternator, a ball screw and nut apparatus connecting the sprung and unsprung masses and driving the alternator in alternating rotary directions as the sprung and unsprung masses oscillate relative to each other, a rectifier bridge for converting the three phase alternator output to a single DC current, an electric load, and a switch for controlling the application of the DC current to the electrical load. Circuits determine the times of consecutive zero crossings of each phase and update therefrom a signal indicative of the magnitude of rattle space velocity. The circuits further determine, from the identities of the alternator phases of successive zero crossings of any phase compared with stored expected consecutive phase identities, the direction of the rattle space velocity. A chopping control circuit is responsive to the magnitude and direction signals of rattle space velocity to control the switch in a variable duty cycle operation to vary the average current through the electric load and thus the damping force of the suspension. An additional circuit may be responsive to the current through the electric load to generate a signal indicative of the actual damping force of the suspension.

Analysis of three-phase AC-DC converters under unbalanced supply conditions

Abstract: A three-phase AC-DC converter is analyzed, and the performance of the converter under balanced conditions is evaluated. It has been observed that the level of unbalance plays a significant part in the converter characteristics, especially at the lower output voltage range. >

Vector control system for induction motors

Abstract: A vector control system for an induction motor driven by a power converter which generates three phase ac currents containing harmonics. In the system, an exciting current command value and a torque current command value in a rotating magnetic field coordinate system are applied, induction motor primary currents in a stator coordinate system is detected at a period which is the same or integral multiple of that of the harmonic components by integration operation, the detected value of the integrated primary currents is subjected to definite integration over the same time interval as the period thereof thereby detecting fundamental wave components of the primary currents without the harmonic components, the fundamental wave components are transformed in the form of rotating magnetic field coordinate system thereby detecting an exciting current component and a torque current component, a deviation between the exciting current command value and the detected actual exciting current component and a deviation between the torque current command value and the detected actual torque current component are detected respectively, and producing and applying to the power converter three phase ac voltage command values in the stator coordinate system tending to reduce the deviations to zero.

A half-wave rotary rectifier assembly

Abstract: In a brushless synchronous generator having a three phase, WYE connected exciter armature (18) providing current which is rectified by a half-wave rectifier before energizing a field (26) of a main generator (24), a conductor is required to couple a neutral lead (42) of the exciter armature (18) to a negative input terminal (41n) of the main generator field (26). In order to overcome the foregoing problem, a rotary rectifier assembly (22) for a brushless synchronous generator is disclosed. The rotary rectifier assembly (22) comprises a housing (44), three diodes (D1, D2, D3), three resistors (R1, R2, R3), wherein the diodes (D1, D2, D3) and the resistors (R1, R2, R3) are interconnected to form a three phase half-wave rectifier bridge within the housing (44), and a neutral conductor (43) coupled between the neutral output lead (42) and the negative lead (41n) and carried within the housing (44).

A novel method of harmonic assessment generated by three-phase AC-DC converters under unbalanced supply conditions

Abstract: A three-phase converter is fully analyzed, and the performance of the converter is evaluated under both balance and unbalanced supply situations. It is observed that the level of imbalance in the supply voltage increases the harmonic content of the input current and decreases the power factor of the converter. This situation worsens toward the lower output region of the converter. The nature of the analysis has been kept very general so that future related work can be incorporated. >

The three-phase bridge rectifier with a capacitive load

Abstract: The 3-phase bridge rectifier supplying a capacitive load is significantly more difficult to analyse than the inductive load case. The authors examine how the ideal behaviour of such a system is affected by the following circumstances: (i) a supply impedance which includes resistance; (ii) less than infinite link capacitance; (iii) an unbalanced 3-phase supply. The authors derive results for a digital simulation (CAD) package, which conveniently illustrates the rectifier trends.< >

Starting performance of saturable three-phase induction motors

Abstract: The starting currents and torques (at slip S=1) are determined as a function of the terminal voltage of saturable three-phase induction motors from numerical magnetic field solutions. In order to obtain a first approximation for the stator and rotor currents, the unsaturated stator and rotor leakage reactances and resistances are calculated based on the conventional approach. The equality of the fundamentals of the stator and rotor current sheets along the circumference of the machine is used to compute the currents in the rotor bars as a function of the stator current. For this first approximation of the stator and rotor slot currents, the magnetic field and its associated reluctivity distribution within one pole pitch are determined based on the finite-difference formulation. The calculated (frozen) reluctivity distribution is then used to recalculate saturated stator and rotor leakage reactances, which provide a basis for a first and second approximation for the current distributions at starting. Both the measured stator currents and the associated torque agree well with the numerically determined values. >

A three-phase neutral point clamped inverter for motor control

Abstract: A microprocessor-controlled PWM (pulse-width-modulated) inverter has been developed in which the neutral point at a star-connected load is clamped in potential. In addition to PWM waveforms, the inverter can generate six-step or eight-step waveforms in response to the appropriate software, using the MC68000 microprocessor. Operation takes places in the PWM model for 1-40 Hz and in a step mode for 40-100 Hz. The inverter used 12 power switches compared with the customary six switches in a standard inverter. Darlington power transistors were used in a laboratory prototype rated at 6 kW. A design feature is that power to the drive circuits of the twelve switches come directly from the DC supply, eliminating the need for individual power supplies. The root-mean-square value of the fundamental line voltage is 0.64 V DC compared to 0.5 V DC for conventional PWM operation with a six-switch inverter. >

Automatic overvoltage protection circuit

Abstract: An automatic overvoltage protection circuit is provided for an electrical power supply of the type comprising a variable speed three phase alternator (50) having a permanent magnet rotor and three stator output windings (51, 52 and 53), a gated three phase rectifier bridge (60) connected to the three stator output windings and producing a d.c. output voltage, and a control circuit (120) for supplying gating signals at controlled firing angles to the gated three phase rectifier bridge. The control circuit includes first, second and third reference circuits (73, 74 and 75) each including a resonant LRC circuit and connected to a respective one of the three stator output windings, a gating logic circuit (135) connected to the first, second and third reference circuits and providing six outputs, feedback means (122) connected to receive the d.c. output voltage for generating an error voltage, and comparator and isolation means (140 and 145) connected to the gating logic circuit and to the feedback means for generating firing signals for the gated three phase rectifier bridge. The automatic overvoltage protection circuit limits the firing angle of the firing signals at high speed of the alternator to ≅59° while allowing the firing angle of the firing signals at low speed to be ≅0°. This is accomplished by deliberately selecting the Q and resonant frequency of the reference circuits to achieve this beneficial result.

Dual voltage generator system

Abstract: A system for providing a regulated low voltage DC source and a regulated higher voltage AC source at a preselected frequency, such as 60 Hz from the same windings of an alternator rotated at variable speeds including a phase WYE connected engine driven alternator providing three output posts and a neutral post and having a field circuit, a half-wave rectifier connected to each of the output posts of the alternator providing a low voltage DC source, a cycloconverter having a three phase input connected to the posts of the alternator and providing a single phase output at the preselected frequency, a resonating transformer having the primary connected to the output of the cycloconverter and having a capacitor in the secondary providing a resonant frequency at the desired AC frequency, such as 60 Hz, and a clock circuit providing an AC control voltage at a preselected frequency, such as 60 Hz, the clock being connected to the cycloconverter for control of the cycloconverter to provide the selected input frequency to the resonating transformer The secondary of the resonating transformer providing the AC voltage source at the preselected frequency and a regulator circuit controlling the field current of the AC generator for regulating the AC voltage output of the resonating transformer

Method of and apparatus for driving three-phase D.C. brushless motor

Abstract: A three-phase D.C. brushless motor having a rotor and stator windings of three phases can be driven by alternately switching to the step of causing currents to flow through stator windings of only two phases among the stator windings of three phases or to the step of causing currents to flow through the stator windings of all the three phases each time the rotor rotates 30 degrees in terms of an electrical rotational angle, whereby torque fluctuation can be reduced.

Converter system for coupling two high voltage three-phase networks

Abstract: The converter system couples two high voltage three-phase networks. Two converter transformers are associated with each network to be coupled. Each transformer has secondary windings. One secondary winding associated with a first network is Y-connected while the other is delta-connected. The converter transformers operate on a three-phase full wave rectifier with twelve semiconductor rectifier components. The arrangement of valve towers, a stacking of semiconductor components, is designed to keep a base area or a so-called valve housing in which the valve towers are accommodated as small as possible. The semiconductor components are arranged in uniform modular assemblies and may be stacked as modular components having insulating spacings between components which are also uniform. A tower of uniform modules is formed in association with each of the phases of the three-phase secondary windings of the converter transformers. The number of modules defines the number of stories of the tower. The number of modules is varied in accordance with the desired power throughput. The system provides DC short couplers for asynchronous networks of different powers while uitilizing the same basic design concept so that a power match can be made by a corresponding number of modules forming a tower with the same insulating spacings in a standardized design.

Method and apparatus for measuring the resistance of the winding of a converter-fed single- or three phase machine during operation

Abstract: A method and apparatus for measuring the resistance of a winding of a converter-fed single- or three-phase machine during operation by means of a d-c measuring current. The firing instant of at least one up-commutating valve of a maching converter is delayed by a predetermined variable setting angle for generating d-c measuring currents in the phase currents, whereby the current conduction time of the up-commutating valve is shortened and the current conduction time of a valve commutating down with the valve which is commutating up with delay, is lengthened. The generated d-c measuring current is filtered out of the measured machine current and the generated interlinked d-c measuring voltage is filtered out of a measured terminal voltage of the single- or three-phase machine, and the winding resistance is determined from the linked d-c measuring voltage and the d-c measuring current by forming a quotient. Thus, it is possible to measure a winding resistance in a converter-fed three-phase machine during operation without using a nonlinear resistance circuit in a connecting lead.

A fast-response current controller for microprocessor-based SCR-DC motor drives

Abstract: An LSI firing circuit, in conjunction with a high-speed digital signal processor (DSP), has been developed to adjust the thyristor firing angle between 0 and 180 degrees for both positive and negative current control in a dual antiparallel-connected three phase power converter connected to a DC motor. A fast-response current controller is obtained by using feedforward techniques and a variable-structure proportional-integral (PI) compensator to produce an optimal current response under both continuous and discontinuous current conduction. Theoretical derivations and practical results of a predictive control strategy are shown. The main objective of this control scheme is to analyze the mathematical behavior of the system and use this knowledge to advantage in the control of armature current. >

A three-phase to three-phase series-resonant power converter with optimal input current waveforms. I. Control strategy

Abstract: A control strategy for multiphase-input multiphase-output AC to AC series-resonant (SR) power converters is presented. After reviewing some basics in SR power converters, a hierarchy of control mechanisms is presented, together with their respective theoretical backgrounds and practical limitations. The respective controllers are then presented in a simulation context. The control scheme fully exploits the capabilities of high-frequency power converters and facilitates the extraction of currents at a unity power factor from the supply side, even under transient conditions. The control scheme takes into account losses and inaccuracies in the control electronics without deteriorating the intended waveforms. Through computer simulation, it has been shown that, in particular, the input current wave-shapes are greatly improved compared to the best-available operating data. >

Comparison of an analytical study and EMTP implementation of complicated three-phase schemes for reactor interruption

Abstract: When small inductive currents are interrupted by High Voltage circuit breakers current chopping will generally occur and will induce overvoltages. This paper describes a comparison between an analytical study and EMTP (= ElectroMagnetic Transient Program) implementation for calculation of such overvoltages in three-phase inductive circuits. Capacitive and/or inductive couplings between phases are included in schemes with grounded and non-grounded neutrals. If the time steps for numerical integration are small enough the EMTP calculation gives reliable and even more detailed and complete results than the analytical approach could do. Complete listing of input files for the EMTP program is given in the appendix. Kalasek, V.K.I. Comparison of an analytical study and EMTP implementation of complicated three-phase schemes for reactor interruption. Faculty of Electrical Engineering, Eindhoven University of Technology, The Netherlands, 1988. EUT Report 88-E-204 Address of the author: Or. ire V.K.I. Kalasek, Electrical Energy Systems Group, Faculty of Electrical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven. The Netherlands

Three-phase current output circuit with temperature compensating function

Abstract: A three-phase current output circuit for driving a three-phase brushless motor, the output circuit having a first current source and a second current source with positive temperature coefficients which are provided so as to negate a negative temperature coefficient which causes undesirable reduction of motor torque.

Power converter assembly for coupling two kinds of high-voltage three-phase networks together

Abstract: Converter system for coupling two high-voltage three-phase networks In a known converter system of this type (DC short coupling), two converter transformers assigned to a network, one of whose secondary windings are connected in a star and the other in a triangle, work on a three-phase full-wave rectifier with twelve Semiconductor rectifier components. In order to keep the base area for the so-called valve hall, in which the valve towers are housed, as small as possible, the arrangement of the valve towers is such that each of the semiconductor assemblies assigned to the four secondary windings of the converter transformers form a valve tower. This known arrangement is not suitable for a modular design of the valve towers. The new systems are intended to enable valve towers to be constructed from a number of levels stacked on top of one another as a module, with the same insulation spacing, according to the required throughput capacity. The rectifier bridge branches assigned to each secondary-side three-phase phase (R, S, T) of each three-phase transformer (TR1 to TR4) form a separate tower (VT1 to VT12), which consists of a power-dependent number of levels (18) which are arranged one above the other with the same insulation spacing and which consist of modular ones Function groups (15, 16, 17) are formed. The system designed in this way offers the possibility of constructing short couplings for different outputs according to the same design concept, so that the respective output adaptation can be carried out using a corresponding number of modules forming a tower with the same spacing in a standardized design.

Method for controlling a three-phase current consumer through PWM with a sinusoidal evaluation

Abstract: The subject of the invention is a method for controlling three-phase current consumers through PWM with a sinusoidal evaluation of three phases (PH1, PH2, PH3) shifted in each case 120 DEG with respect to one another. By contrast with the previously known methods, in which all three phases are always clocked, the invention proposes to clock only two phases (PH1, PH2) in each case, while the third phase (PH3) remains unclocked. After a sixth of the period, the control of the phases (PH1, PH2, PH3) is cyclically interchanged. Since the sinusoidally evaluated pulse widths are repeated every 60 DEG , the control of the three-phase current consumers can be substantially simplified. A device for carrying out the method is a further subject of the application. Substantial advantages of the invention reside above all in the fact that the program runtime of a microcomputer required to control three-phase current consumers can be reduced, together with the operating frequency, by a third.

Three phase alternator with common neutral leads

Abstract: A stator of a vehicle mounted alternator having a rotor and a rectifier includes an armature core formed in an inner periphery thereof with a plurality of slots and three-phase armature coils wound in respective slots, coil lead terminals and a neutral lead terminal of the armature coils for each phase being arranged in a limited area so that connections thereof to said rectifier of the alternator are facilitated. The neutral leads for three phases are derived directly at a position between the coil leads, and at least one metal binder for bundling and electrically connecting the neutral leads together at the point is provided, from which a neutral lead terminal to be connected to the rectifier is derived.

Quasi-periodic oscillations in a three phase ferro-resonant circuit.

Abstract: When a three-phase voltage is applied to ferro-resonant circuits connected in a Y-connection, the third harmonics voltage can be obtained in the zero-phase-sequence circuit.Usually, the waveform of this voltage is almost sinusoidal and the oscillation is stable, but under some conditions the voltage changes to a state of quasi-periodic oscillations. This paper deals with the analysis of the mechanism of the quasi-periodic oscillations in a three-phase ferro-resonant circuits.

Circuit arrangement for controlling starting and braking of three phase asynchronous motors and method for operating of such circuit arrangement

Abstract: In a circuit arrangement for controlling the starting and braking of three-phase asynchronous motors, at least one phase of the motor current leads (u, v, w) being used for phase control and each phase control device having at least one thyristor, controlled by a control device, a connecting lead being provided between the motor current leads (T1, T2) of two phases (u and/or v and/or w) after at least two phase control devices (11, 12), in which connecting lead there is arranged a switchable semiconductor component having a rectifier effect, in order to achieve a high positioning accuracy it is provided that a speed detecting device (34) has an integration device (40), acting as an actual distance transmitter, connected downstream from it, the output (41) of the latter being connected to a difference- forming device (42), the other input of the difference-forming device (42) being connected to a preset device (43) for presetting the nominal positioning distance after reaching a proximity switch (2), that the output of the difference-forming device (42) producing an actual residual-distance signal has connected downstream from it a preset device (44) for the nominal speed (n) as a function of the residual distance (s), and that the output (45) of this preset device (44) is connected to the input (46) of the speed regulator (37).

Incremental method of pulse width modulation for three-phase inverters

Abstract: A novel pulse-width modulation technique for three-phase voltage-controlled inverters is presented. Description of a microprocessor-based modulator capable of completing in real-time all the computations required for adjustable frequency, magnitude and phase control of the inverter output voltage is provided. Experimental results are given.

A three-phase to three-phase series-resonant power converter with optimal input current waveforms. II. Applications and results

Abstract: For pt.I see ibid., vol.35, no.2, p.263-8 (1988). A 15 kW three-phase prototype series-resonant power converter is constructed. The converter features sinusoidal output voltage and sinusoidal input currents. The control concepts and necessary electronics, as well as the layout of the power circuit, are discussed. Low distortion levels are achieved for both the output voltages and the input currents, and measurements show the very fast (milliseconds) reaction capabilities of this type of equipment. >

Method and circuit arrangement for the control and regulation of three-phase inverters with sequence regulation.

Abstract: The idea of the invention is that one of the switching elements of a specific bridge path of a three-phase, main-circuit converter (8) connected in a bridge is continuously switched on for a specific period and, during this period, servo control is carried out for the switched-on switching element and the two initial voltages associated with the other bridge paths, the respective switched-on switching element and the servo controls implemented for the continuously switched-on switching element and the two initial voltages associated with the other bridge paths being alternated cyclically in a predetermined sequence. The circuit arrangement contains a three-phase reference signal generator (1) whose first output is connected via a decoder (6) to the control input of a logic unit (5), and whose other three outputs are each connected to a servo control unit (2, 3, 4), which on the one hand are connected to the logic unit (5) and on the other hand are each connected to the first output of one of three sensor units (10, 11, 12) which are connected to the logic unit (5) via a control unit (7), the bridge-connected three-phase, main-circuit converter (8) and a three-phase filter unit (9) and, with their second output, form the output terminals of the device.

Study of power system harmonics in an unbalanced system using the three-phase bus impedance matrix

Abstract: The authors study the effect of harmonic current injected at a certain bus on the voltages at the other buses using the three-phase bus impedance matrix of an unbalanced system at normal and abnormal conditions. The effects of the system capacitors (grounded or ungrounded) in the presence of harmonic distortion is also studied. The results show that for both normal and abnormal system conditions, the highest voltage variations occur when the system capacitors are disconnected. The best case (smallest voltage variation) occurs when the system capacitors are grounded. In the case of ungrounded capacitors, the voltage variation falls in between the other two cases. These conclusions apply to higher harmonic orders. It is also found that the buses closest to the source of injected harmonic current are subject to extremely high voltage variation. >

Control apparatus for three phase alternating current load protection

Abstract: Control apparatus for three phase alternating current load protection wherein each of the phases of the load is connected to a corresponding current transformer. When the load is energized by a three phase power supply the transformers induce signals which are applied to a signal detection circuit. The detection circuit controls a relay means. If any of the three power phases is lost the detection circuit is interrupted causing the relay means to drop out, whereby the load, the power supply and auxilliary circuitry, as the case may be, are protected.