Showing papers on "Three-phase published in 1980"

Optimum Voltage and Harmonic Control PWM Techniques for Three-Phase Static UPS Systems

Abstract: Pulsewidth modulation (PWM) is frequently employed with static ac power supplies to control the amplitude and harmonic content of load voltage However, published work on the subject of PWM techniques has mainly dealt with variable-speed ac drive applications Consequently, PWM techniques compatible with constant frequency and constant (load) voltage applications, such as uninterruptible power supply (UPS) systems, have been largely ignored Several known and novel PWM techniques suitable for three-phase static UPS systems are analyzed, and attempts are made to evaluate them Optimum techniques are subsequently selected on the basis of the low-order harmonic attenuation obtained with each technique and the number of thyristor commutations (per cycle) required to implement each technique

Load state control for an asynchronous machine fed by a converter

Abstract: A control unit for regulating an asynchronous motor supplied with power from a three phase network by a line-controlled power converter which is DC coupled to a self-commutated inverter has a function generator and a current regulator which controls the stator current of the motor by the controlling rectifier valves in the inverter. Control of the stator current is a function of a predeterminable value of flux fed into the function generator. In a parallel control system, an actual-value computer and a load state control regulate the stator frequency by generating a signal for controlling the self-commutating converter as a function of the actual values of the stator current, the stator voltage, and a value calculated from the function generator input variable. The computer forms signals corresponding to the amplitude of the flux vector, and to a stator current component perpendicular to the flux vector. A variable derived from the predeterminable variable is applied to the load state control as a reference value. Fall-out-proof, low oscillation, speed control is effected from low angles to nearly 90°.

Electronic three-phase watt-hour meter

Abstract: An electronic multiphase watt-hour metering system containing time-division multiplying circuitry. A duty cycle modulator and a switching device are provided for each phase of interest, the output signals of which are combined and conducted to a current-to-frequency converter. The output frequency of the current-to-frequency converter is responsive to the rate of electrical power consumption from a multiphase transmission system. In one embodiment, the current-to-frequency converter is coupled at its output to an accumulating counting system for recording the total energy supplied to a load. There may further be provided an indicator responsive to the frequency of the current-to-frequency converter for providing a visual indication of the instantaneous rate of power usage.

Three phase power-factor control system for A.C. induction motors

Abstract: A three-phase power factor control system for an AC induction motor (10) monitors the power factor of a first-phase motor winding and produces a rectangular-wave pulse power-factor signal (f) which is used to directly control the duration of "on" time of each cycle of input power to the first-phase winding and to indirectly control the "on" time of each cycle of input power to second- and third-phase windings. To provide a signal for controlling the power to second- and third-phase windings the power-factor pulse signal is synchronized with a square-wave oscillator (30) whose frequency is three times that the power-factor pulse signal. Each second and third positive pulse (38 and 40) of the square-wave oscillator (30) is used to control the "on" time of each cycle of input power to the second- and third-phase windings. A current sampler (72) for monitoring current flowing through the first-phase winding samples voltage across a triac and thereby avoids unduly loading the first-phase winding with a resistor as was done in the prior art. The current sampler (72) is coupled to following circuits through an optical isolator (74) for producing pulses corresponding to current phase.

Earth contact monitoring device for a polyphase three-phase filter circuit

Abstract: A monitoring system for detecting earth contact of at least one phase of a polyphase network. Each of the phases in the network is connected by a capacitive-inductive filter to a neutral node which is connected to earth. In one embodiment of the invention, the current flowing from the neutral node to earth is detected by an induction current transformer which provides a signal responsive to said earth current. The output signal of the induction current transformer is conducted through at least one low pass filter for suppressing harmonics, and rectified to produce a direct current voltage signal, the amplitude of which is proportional to the amplitude of the fundamental frequency component of said signal. A fault indicating signal is produced when the direct voltage signal exceeds a predetermined value.

Three-Phase Energy Transfer Circuit with Superconducting Energy Storage Coils

Abstract: The operation and circuit analysis of a three-phase inductor converter bridge (ICB) is described. The ICB is used to transfer energy between two superconducting coils and may find application in future tokamak fusion power reactors and large particle accelerators. This circuit provides an efficient, controllable, and reversible means for energy transfer.

Three phase regulated supply with ripple current regulation

Abstract: A circuit for use in a multiphase regulated supply to provide regulation of the ripple current contained in the filtered d.c. output signal of the supply. The supply regulates its output voltage and/or current by controlling the conduction time of the switching elements contained in the rectifier portion of the supply. The switching element conduction time is controlled by controlling the generation of firing pulses to the switching elements as a function of an error control signal which is equal to a first error signal. This signal is equal to the amount by which the actual value of said voltage and/or current deviates from a reference value of said parameter. When the ripple regulation circuit is included in the supply, a second error signal is generated which represents the deviation of the d.c. value of the ripple from a predetermined reference. Also included in the ripple regulation circuit is circuitry for selecting the error control signal as equal only to the larger amplitude one of the first and second error signals. The supply therefore regulates only voltage and/or current until the ripple becomes excessive at which point the supply regulates only ripple.

Transient stability enhancement of electric power generating systems by 120-degree phase rotation

Abstract: A method and system for enhancing the transient stability of an intertied three-phase electric power generating system. A set of power exporting generators (10) is connected to a set of power importing generators (20). When a transient cannot be controlled by conventional stability controls, and imminent loss of synchronism is detected (such as when the equivalent rotor angle difference between the two generator sets exceeds a predetermined value, such as 150 degrees), the intertie is disconnected by circuit breakers. Then a switch (30) having a 120-degree phase rotation, or a circuit breaker having a 120-degree phase rotation is placed in the intertie. The intertie is then reconnected. This results in a 120-degree reduction in the equivalent rotor angle difference between the two generator sets, making the system more stable and allowing more time for the conventional controls to stabilize the transient.

Driving circuit of three phase load

Abstract: PURPOSE:To avoid the increase in torque ripple and lowering in motor efficiency, by adjusting the base current of the output transistor so that the neutral voltage of three phase in star connection can be constant. CONSTITUTION:One terminal of the stator coils 4, 5, 6 is connected to the output terminals 11, 12. 13 respectively of the driving circuit 3. The output voltage of the circuit 3 fed to the terminals 11-13 is added at the resistors R3-R6, and at the detecting terminal 14, the addition signal Vn in proportion to the sum of each output voltage is obtained. The signal Vn is fed to the rate unit 15, it is compared with the voltage VR of the reference power supply 16, the error signal is fed to the preamplifier 9, to control the base current of the output transistors T1...T6 so that the signal Vn is in agreement with the voltage VR. In this case, since the signal Vn is proportional to the neutral voltage VR of each stator coil, by controlling the neutral voltage of the three phase load so that it is constant, the increase in the torque ripple and the lowering in the motor efficiency can be avoided.

Vehicle battery charging system - includes error detection stage to identify errors in operation and gives improved generator regulation

Abstract: A battery charging system is designed to provide display of error conditions and to give improved control of the generator. The system is based upon a generator (10) with a three phase winding (12), coupled as a half bridge rectifier. The winding is coupled to a rectifier stage (13). The voltage regulator consists of a control stage (17) and a power stage (18). In addition, an error detection stage (40) is coupled to the control stage to identify errors in operation. One terminal (D-) of the error detector is connected to the minus terminal (also D-) of the voltage regulator (16), and the other terminal (L) leads to an indicator lamp (35) linked to the half bridge rectifier by a decoupling diode (39).

Variable speed driving system for synchronous motor

Abstract: PURPOSE:To prevent the amplitude differece as well as phase difference from emerging between the current command value and the actual value by adjusting through a current command arithmetic unit so that the respective difference of orthogonal two DC component command values and of DC components of the armature current actual value will be zero. CONSTITUTION:In the transvector control system, as for a current command arithmetic unit 4, respective phase armature current ia, ib, ic of a synchronous motor are converted ialpha, ibeta through three phase /alpha.beta axis coordinate converter 517 and are converted into orthogonal DC components i1, i2 through alpha.beta/1.2 axis coordinate converter 528. And the voltage command values e1*, e2* of 1-axis, 2-axis components are put out through the adjusters 529, 530 in the direction that the respective difference of the current command values i1*, i2* and of the actual values i1, i2 will be zero. Each said command value is converted into the voltage command value ealpha*, e* of alpha, beta axis component through 1.2 axis /alpha.beta axis coordinate converter 525 and are converted into the command values ea*, eb*, ec* of each phase voltage through alpha.beta/ three phase coordinate converter 527 to be put out, whereby the amplitude difference and the phase difference between the current command value and the actual value can be removed.

Field detecting system for three=phase machine - produces voltages proportional to magnetic flux components using model circuit to simulate processes in machine

Abstract: The system has a current model circuit (1) receiving voltages proportional to the stator current (i) and magnetisation current and a rotor-position signal. The model circuit simulates those events in the machine that convert the currents into flux components and thereby produces signals describing the flux components. The circuit output signals are passed to a zero-point controller that eliminates the dc component in the difference between the flux component determined at the ac voltage integrator and the output of the model for this component. The advantage lies in the system's functioning at high and low speeds and in having low phase and amplitude errors that are independent of the machine frequency.

Device for transferring high-power electric energy from a higher frequency three-phase supply network to a lower frequency single-phase load network

Abstract: 1. A device for the transmission of electric energy of high power from a three-phase supply network (1) of high frequency into a single-phase load network (3, 4) of low frequency, characterised by a frequency-dividing direct converter (51, 52, 61, 71, 72) which is connected to the supply network (1) and has a threephase output (5, 6, 7), wherein two phase outputs (5, 6) are connected to the load network (3, 4) and also by means of an electronic phase shifter (10, 12) to the third phase output (7) in each case in order to balance the load.

A novel three-phase stepped-wave inverter using eight thyristors

Abstract: The three-phase stepped-wave inverter is based on a new method of synthesizing waveforms The proposed system comprises a 120° conduction type three-phase bridge inverter and a single-phase triple-frequency square-wave inverter The triple-frequency inverter need for wave-shaping is of low power and is used in the neutral circuit of the three-phase inverter A special complementary impulse commutation circuit realizes the above system with only eight thyristors The output voltage waveform has three steps per quarter cycle and has a total harmonic distortion of 151% The kVA ratings of the wound components are derived The experimental results are presented and discussed

Motor control system for multiple textile machines - uses summing device between selected phase connections and three phase supply

Abstract: The drive for a number of textile machines, e.g. two motors for two open ended spinning machines uses a fault protection system with a current summing unit between the machines and the main supply. One connection is taken to one of the phases of one motor and two connections are taken to two phases of the other motor. The remaining connections are made directly with the three phase supply. In an alternative system, three or six motors are used for three false twisting machines. Two phases of each motor or pair of motors are connected directly to three phase supply, and one phases of each is connected through a summing device to the mains.

Run=up circuit for brushless DC permanent magnet motor - employing rotor position sensors and pulse counting circuit for starting control

Abstract: The application is to a brushless dc motor with a three phase stator winding to which the dc supply is switched in rotation by a solid state control circuit. The stator also has a set of sensing coils whose number is chosen such that the number of output pulses per revolution is equal to the product of the number of phases and the number of rotor pole pairs. At the start the pulses from the position sensing coils are fed to a counter which in turn orders the application of current to the next stator phase in succession. At speed, control is transferred to a conventional controller. The arrangement gives a certain and controlled start regardless of the position in which the rotor is when at rest. The direction of run up is also correct although, depending on rotor initial position, the movement through one pole pitch in the reverse direction may occur initially.

Three=phase supply for instrument time-base - has phase shift stage with three phases summed to generate square wave reference signal

Abstract: The use of a three phase supply as a time base supply for instrumentation provides reliable operation in the event of dropout of one or two phases The three phase connections (R, S, T) are connected to a summiting stage (S), with one phase signal delayed by a phase shifting stage (P) The generated output is passed via a low pass filter to generate a square wave reference signal

Electric motor vehicle

Abstract: PURPOSE:To reduce the torque variation of an electric motor vehicle due to conversion of triangular wave in frequency by providing a period for providing six times frequency while converting the frequency of the triangular wave from 9 times of sine wave to 3 times. CONSTITUTION:An induction motor 5 for driving an electric motor vehicle is energized through a pantograph 2 and an inverter 3 by a variable frequency and voltage power supply. The frequency f1 of a pulse generated by a pulse generator 6 directly coupled to the motor 5 is converted by a frequency-to-analog converter 7 to analog voltage V1, and a voltage DELTAV corresponding to n times of predetermined slip frequency is added to the analog voltage V1 by an adder 8. Then, the sum from the adder 8 is applied to a voltage oscillator 9 to generate a frequency f2. The frequency f2 is divided by 1/n by a frequency divider 10 to three phases, and sine generator 11 is connected to thereby produce three phase sine wave of f2/n. Triangular wave generators 20-1- 20-5 generate 1-15 times of the sine wave to a triangular wave switching circuit 27, which switch the frequency of the triangular wave as reaquired.

An improved three-phase stepped-voltage inverter

Abstract: The paper Presents an improved method of generating a three-phase stepped-voltage waveform using ten thyristor power switches. In the proposed method, it is possible to generate one step for every 20 ° of the voltage waveform on all the phases. The waveform has a total harmonic distortion of about 10% and the Predominant harmonies are the 17th and 19th. This is possible by a unique method of magneticcoupling betweena 120° conduction three-phase bridge inverter and a triple frequency single phase bridge inverter. The theoretical results are in close agreement with experimental results.

Frequency doubler for three=phase current - has only six thyristors and one three=phase transformer

Abstract: The frequency doubler has a transformer with three limbs each with two windings. Six thyristors (11 etc.) are connected in pairs: one pair to each phase; the thyristors in a pair being connected to opposite ends of primary winding (15 etc.) associated with that phase. The other ends of the two thyristors in each pair are connected directly to a phase line (1-3). Each secondary winding has a tapping which is connected to a shared rail. The three secondary windings (15 etc.) of the transformer are connected to output terminals. Only six thyristors are needed to perform the frequency doubling, and this reduces the cost.

Three-phase frequency multiplier

Abstract: FIELD: frequency changers including transformer-type multipliers. ^ SUBSTANCE: proposed three-phase frequency multiplier that can be used as current supply for 100- and 200-Hz power consumers incorporates provision for affording leading power factor has three-phase transformer each of whose three legs mounts two pairs of primary windings connected to supply mains through transistors, and output winding. Disposed on each leg of three-phase transformer are two pairs of circuits connected in parallel opposition; each circuit is set up of series-connected winding and transistor which function so that only initial part of sine-wave supply voltage is used. Some pairs of circuits disposed on different legs are star-connected to three input leads and other ones of similar circuits are connected in delta to same leads. ^ EFFECT: enhanced power characteristics of three-phase frequency multiplier. ^ 1 cl, 2 dwg

Three=phase motor starter circuit - uses thyristors as starter impedances varying their firing time in dependence on line phase current drawn by stator windings

Abstract: A starter circuit for a three phase a synchronous motor (10) with Squirrel cage rotor comprises a respective pair of thyristors arranged head to tail in series with the respective motor phase windings and controlled at a function of the phase currents by respective firing multivibrators in turn controlled by bistable switches. A synchronisation circuit applies a respective synchronising pulse at the zero crossing of each phase half cycle directly to the respective bistable switch and also controls the application of a sampled integrated signal to the switch. The signal is derived through a rectifier from a current transformer in the phase line. The sampler includes a capacitor charged by the integrator under control of the synchronising pulses and a comparator which applies a setting signal to the bistable switch in dependence on the capacitor charge, the direct synchronising pulses resetting the switch.

Indicating device for airrconditioner

Abstract: PURPOSE:To easily detect the cause of an abnormal state by a method wherein a non-electricity-applied state outside a chamber and an abnormal state caused by an actuation of a protective switch are indicated separately on a bipole or tetrapole indicating means of a compressor. CONSTITUTION:If an S phase or T phase of a three phase power source is missing, an oscillator 33 oscillates, causing a transistor 35 and a relay 31B to turn on and off. Therefore, their contact points 31B1 repeat switching on and off and a lamp 30B flushes. If a phase missing state is restored to the normal state, the lamp 30B is turned off. If either thermostat 11A or 11B is turned off, the lamp 30A is turned on, indicating the tetrapole operation. Further, if a thermostat 2B2 is turned on, the lamp 30A is turned off and the lamp 30B is turned on, indicating the bipolar operation.

Converter and sync. machine control circuit - uses commutating converter between rectifier and machine with comparison system to control torque

Abstract: The control system for a converter and synchronous machine arrangement ensures a direct control of the operating component of the current and hence of the torque of the machine by the control angle with reduced current flow variation. The machine is connected to the three phase supply by a rectifier and its stator windings fed by a converter. This has thyristors and antiparallel-connected return diodes or reverse conducting thyristors. Between them is an inductance and a smoothing capacitor. A pulse transmitter determines the angle of the rotating field of the machine. The rectifier is controlled by a mains dependent device connected to a current controller operated by the difference between the nominal value from a voltage controller and the actual of the current in an intermediate circuit. The latter is dependent on a main supply indicator.

Three=phase mains phase loss and rotation monitoring - by capacitor charging generation of pulses for each combination of phases, with common connection to negated OR=gate

Abstract: An arrangement for monitoring symmetrical three phase mains without central conductors for loss of a phase and for the direction of rotation consists of a digital device giving immediate indication of the loss of a phase and enables further action, e.g. switching off system components, to be taken. Three pulses signal series are generated using a capacitor between the phases which is charged periodically. The pulses occur when each pair of phases have a maximum and minimum potential simultaneously. Each pulsed signal is fed to an AND gate. The AND gates are interconnected via delay elements with duration greater than one-third of the three-phase periodic duration. The outputs of the delay elements are also input to inputs of a common negated OR gate.

Three-phase single-chain overhead electric line with split phases

Abstract: A three-phase overhead electric line contains split phases (1, 2 and 3), wires (4) of which are mounted on metal spacers (5), those spacers forming, in a plane perpendicular to the axis of the electric line, countours of the cross-sections of the split phases (1, 2 and 3) fixed by means of insulators (7) to the electric line towers whose elements (8) are stretched beyond the space embraced by the split phases (1, 2 and 3) and by air gaps between them. The distances between the neighbouring split phases (1-2 and 2-3) of the electric line are, on the whole, constant throughout the length of their countours, whereas the wires (4) are so situated in the split phases that their charges and currents are close to their mean values, so that the electric field is weakly non-uniform throughout the entire volume of the interphase gaps, the electrical break-down being possible only in a striated form in the case of an overvoltage. The countours of the split phases may be of different configurations: closed, open and combined.

Three=phase static inverter with symmetric output voltages - uses oscillator to produce three reference vectors for three single-phase inverters

Abstract: The 3-phase inverter contains three single-phase static inverters connected in parallel at their inputs to the dc source. The output of each inverter is connected via a low pass filter to a transformer. The output windings of the three transformers are connected in star configuration to give the 3-phase output. Each inverter is controlled by a controller comprising a vector-orientated control circuit and a control unit. A vector oscillator forms a 3-phase, balanced system of reference vectors for the vector-orientated control circuits. The 3-phase output remains balanced under all load conditions. Each control circuit shifts the independent pulse raster of its associated inverter until its output voltage vector has the same phase as the reference vector produced by the vector oscillator. The 3-phase output voltages are symmetric in angle since the oscillator produces symmetric reference vectors.

Three=phase AC motor speed control - uses variable frequency DC=AC converter and voltage control

Abstract: The system is used for regulating the speed of a three-phase asynchonrous motor (1). The motor is connected to an intermediate circuit, and control at high speed is performed by varying the frequency of AC fed to the motor. The system is used for driving a lift or a hoist,control at low speeds is by varying the voltage. The current for the motor is supplied by a DC/AC converter (2) with external control. There is a firing pulse generator (6) connected to a switching circuit (7). The external control signal is fed to a comparator (10) connected to the switching circuit via amplifiers, (8,9) a frequency converter (12) and a computing network (13).