Showing papers on "Three-phase published in 1969"

General Analysis of Three-Phase Inverters

Abstract: A method of analysis for three-phase inverters is described. The method is based on Park vectors [1], [2] and predicts the waveforms of inverter quantities under various load conditions. The procedure discussed can be used to determine the commutation sequence of a pulsewidth modulated inverter. The current distribution of the inverter can be obtained from the current vector. The vectors of the inverter voltage and currents are determined for passive R-L and R-C loads. Oscillograms of the current vectors are shown for different loads.

Apparatus for providing the pilot values of characteristics of an asynchronous three phase machine

Abstract: Multipliers produce a signal having a magnitude proportional to the sum of the squares of the rotary flux vectors and the induced three phase voltage vector of an asynchronous three phase machine by first producing signals having instantaneous magnitudes proportional to flux components of voltages induced in two winding axes spaced from each other by 120*. The multipliers multiply each signal magnitude by itself as well as by the other. The resultant products are then algebraically added.

A Digital Model for Three-Phase Induction Machines

Abstract: A digital model for a three-phase induction machine is developed, which is particularly adapted for studying its dynamic performance when fed from an inverter. Conventionally, the induction motor is analyzed in terms of its d-q variables, while the operation of the inverter generally needs continuous monitoring of the state of its phase quantities. Thus in a study of the composite inverter-induction-machine system, one is faced with the problem of matching the two sets of variables. The proposed model overcomes this problem by describing the machine behavior directly in terms of the stator phase variables, at the same time retaining a computational simplicity comparable to that of the d-q equations. Furthermore, it is shown that the machine equations, expressed in terms of the stator terminal variables, can conveniently handle the various terminal conditions, like open phases, that may arise when the machine is fed from an inverter. Detailed equations in a form suitable for digital solution are also presented for possible terminal constraints of this nature, with or without the machine neutral connected to supply.

Analog computer simulation of a three-phase full-wave controlled rectifier bridge

Abstract: This paper establishes analog computer simulations of the widely used three-phase full-wave controlled rectifier bridge. It is shown that when the individual currents in the legs of the rectifier bridge are not developed directly in the simulation, it is possible to avoid the instability and drift problems which have plagued previous investigators. Furthermore, by proper attention to the periodic nature of the operation of the rectifier bridge, the number of computer components may be considerably reduced. In particular, only two electronic switches need be used if the operating range of the delay angle is small. The unique features of the modern high-speed repetitive-operation type of analog computer are utilized throughout the analysis. Computation time is typically reduced by a factor of 300 when compared with existing digital computer routines. The accuracy of the simulation is illustrated by comparing the computer output to recordings taken from an actual system. Good correlation is demonstrated for both transient and steady-state operation.

System for controlling the speed of a motor utilizing pulse width modulation

Abstract: An input voltage is summed with a voltage picked off from a polyphase motor for driving a voltage-controlled oscillator. The frequency of the output signal from the oscillator is dependent on the magnitude of the summed voltage. The pulse width is modified within a predetermined range as a function of the frequency and is converted into three phase signals which are summed and applied to the stator windings of a motor. The signal across the windings has an optimum voltage and frequency ratio which is varied when the speed of the motor is changed.

Three phase regulated d.c. power supply with control for balancing input phase current

Abstract: A POWER SUPPLY SYSTEM HAS A REGULATED DC OUTPUT AND A THREE PHASE AC INPUT INPUT CURRENT IN EACH PHASE IS CONTROLLED BY A SILICON CONTROLLED RECTIFIER (SCR) THREE BLOCKING OSCILLATORS PRODUCE OUTPUT PULSES FOR FIRING THE SCAR''S AT PHASE ANGLES DETERMINED IN RESPONSE TO THE DC OUTPUT VOLTAGE AND CURRENT ADDITIONALLY THE FIRING ANGLES FOR TWO OF THE THREE SCR''S ARE AUTOMATICALLY ADJUSTED TO BALANCE CURRENT AMONG THE THREE PHASES AT THE INPUT THIS IS ACHIEVED BY CIRCUITRY WHICH SENSES AND COMPARES THE POSITIVE AND NEGATIVE INPUT CURRENT IN TWO OF THE PHASES AND PRODUCES DIFFERENCE SIGNALS WHICH DRIVE TWO FO THE BLOCKING OSCILLATORS TO ADJUST THE FIRING ANGLES OF TWO OF THE SCR''S UNTIL PHASE CURRENT IS EQUALIZED

Wide-Range Speed Control of Three-Phase Squirrel-Cage Induction Motors Using Static Frequency Converters

Abstract: An equipment is presented for speed control of three-phase squirrel-cage induction motors supplied through a thyristor converter directly from the mains (the European 50-Hz system) by controlling the frequency and voltage magnitude. Thus a continuous speed control system is achieved, corresponding to a frequency range of from 2.5 to 85 Hz. Speed control is at a constant torque, up to the motor frequency rating (50 Hz), and at a constant power over this frequency. The system configuration is described, a brief analysis of the control loop parameter adjustment is given, and the experimental results are discussed. Finally, the general characteristics of the method are presented.

Combination three phase-one phase inverter

Abstract: An inverter having drive change means for converting three phase operation to single phase operation where single phase power is supplied at the same rating as the rating for three phase power. A controlled drive means in a solid state static inverter for the power outputs supplies the outputs 120* out of phase for three phase operation or in phase for single phase operation.

Current converter for transforming three-phase alternating current into direct current

Abstract: A current converter for converting three-phase alternating current into direct current, or vice versa, includes for each phase an AC bus bar, a DC shunt bus bar and a plurality of current converter valves carried by and distributed uniformly along the AC bus bar. The current converter valves are connected electrically in parallel between the AC and DC bus bars of each phase, and the DC bus bars of all three phases are interconnected at each end thereof by conductor paths which have an ohmic resistance (as measured between valve junctions nearest to the associated junction on the DC bus bars associated with two different phases) which is always less than one-fifth of the ohmic resistance of one bus bar (as measured between the outermost positioned valves on the bus bar). Also the distance between the centerline of an AC junction on the AC bus bar and the outermost valve junction thereon (nearest to the direct current terminal structure formed from the interconnection at one end of the DC bus bars) amounts to from 60 to 75 percent of the distance between the two outermost valve junctions on the AC bus bar.

Method and a control device for operating a polyphase electric furnace

Abstract: A control device for operating a three phase electric reduction furnace includes a two-point controller responding to departures of the furnace power actual values from the furnace power nominal values for obtaining from an integral controller variations of the electrode current nominal values. Other two-point controllers compare the varied electrode current nominal values with the electrode current actual values and respond to departures of the varied electrode current nominal values from the electrode current actual values to provide adjustment signals for the output controls for corresponding phases of the furnace transformer. Differential controllers sense the differences between the actual currents flowing through the said electrode and the electrodes disposed nearest thereto on the two sides of it, and additional differential controllers activate the transformer output control drive in response to the adjustment signals for adjusting the furnace transformer phase which lies between the two electrodes having the least sensed current difference.

One-kVA, Three-Phase dc-ac Inverter with Digital Control

Abstract: This paper describes a method of applying digital techniques to the control of a 1-kVA three-phase dc-ac inverter to generate a sinusoidal 400-Hz output, using high-frequency bridge-chopper techniques. The model which was constructed used predominantly off-theshelf digital microcircuits and resulted in a device with an overall efficiency of 85 percent, in a 0.52 cubic-foot package which weighed 19.5 lbs. Sinusoidal output with less than 2 percent harmonic distortion at 115 volts line to neutral was obtained with 28 volts dc input.

Phase shift voltage cancellation system

Abstract: A system for energizing the components of a wire strap heat treating process to prevent unsafe voltage conditions from occurring on the strap wherein heating power and majority voltage cancellation are supplied from a common distributed transformer arrangement and trimming cancellation of voltage is effected in an auxiliary transformer, the latter comprising a phase shift autotransformer arrangement energized from all phases of the three phase power source.

Method of Driving Appliances Supplied with Three-Phase Alternating Current

Abstract: 1,174,025. Control of A.C. motors. INSTITUT FUR SCHIENENFAHRZEUGE. 13 May, 1968, No. 22593/68. Heading H2J. An air-conditioning plant for railway vehicles comprises asynchronous motors 4, 6, driving respectively a fan 5 and compressor 7, as well as an incandescent lamp 9 associated with voltage stabilizer 8. An unregulated directvoltage source 1 is connected through an inverter 2 to the plant, the inverter comprising valves which are ignited by pulses from a unit 3 to provide a desired frequency output. When the motor 4 takes a high starting current, the voltage-drops in the inverter 2 and source 1 increase to reduce the voltage applied to the motor below the value obtaining during normal service. The frequency of the output of the inverter is then reduced in proportion to the input or output voltage of the inverter to maintain the starting torque constant. After the motor has started, the frequency is restored to a constant value, the frequency-increase taking place as a function of time, current, or voltage. The arrangement may be such that the voltage-proportional frequency variation occurs within a predetermined voltage range, and, outside this range, the frequency is kept constant. When the motor 6 is started while the motor 4 is still running, the frequency is again reduced and then restored to its original value, the current consumption of the motor 4 being reduced for a short period.