Showing papers on "Three-phase published in 1990"

Limits on the performance of the three-phase self-excited induction generators

Abstract: Dependency of the output voltage and frequency of the isolated self-excited induction generator on the speed, load, and terminal capacitance causes certain limitations on its performance. In this study, the performance of the induction generator under a wide range of operating conditions is examined. It is found that the machine operates only in certain element ranges and that all generated currents and voltages are bounded. It is also shown that a combination of these elements exists that is optimal for maximum power generation. >

Solid-state trip device for a protective circuit breaker of a three-phase mains system, enabling the type of fault to be detected

Abstract: The solid-state trip device of a protective circuit breaker of a three-phase mains system comprises a fault type detection circuit comparing the currents flowing in the mains system conductors with a first threshold and a second threshold, higher than the first one. It supplies a signal representative of a certain type of fault, single-phase or two series pole, when a first number of currents are lower than the first threshold and a second number of currents are higher than the second threshold.

Air-conditioning apparatus including an indoor unit and an outdoor unit having its compressor driven by a three-phase AC power supply

Abstract: An air-conditioning apparatus includes a control circuit adapted to detect, from among first to third line voltages of a three-phase AC power supply, the second or third line voltage not synchronizing with a serial signal. The control circuit detects a difference between a phase angle of the detected line voltage and that of the serial signal, compares the difference with set values and determines, by that comparison, whether the three-phase AC power supply is in a positive-phase sequence or in a negative-phase sequence. The operation of a compressor is inhibited when the negative-phase sequence is determined by the control circuit.

System for controlling a PWM inverter having delay time compensation

Abstract: A system is provided for controlling a PWM inverter having three main circuit arms in which free-wheel diodes are connected in parallel to positive and negative side switching elements. The inverter takes three phase alternating current from an intermediate portion of the arms on the basis of a voltage supply of a direct current and an ON and OFF operation of the switching elements. The control system includes a circuit for detecting a zero-crossing point of the three phase alternating current. A wave generating circuit generates a PWM wave at every main circuit arm, which changes the level thereof corresponding to ON and OFF operation of the switching elements and is inverted to each other in the positive and negative sides. An on-delay circuit delays a level change timing from ON to OFF of the PWM wave for a short circuit preventing duration. A compensation circuit compensates the PWM wave width of one phase in which a current opposite to other phases flows by expanding and contracting the width at the rate of two times as the short-circuit preventing duration. The expanded and contracted pulse width is added to the on-delay circuit, thereby controlling the switching elements of the inverter main circuit.

Some implementation aspects of line current reconstruction in three phase PWM inverters

Abstract: A method of motor current reconstruction that can be applied with all pulsewidth-modulation (PWM) schemes is discussed. The method is well suited to implementation with digital signal processors (DSPs) or application specific integrated circuits (ASICs). It is based on system variable identification by means of the least-squares method. It is shown that a sinusoidal current waveform of known frequency can be reconstructed accurately for all operating conditions from data sampled on the DDC bus. In particular, the amplitude and phase shifts of the sinusoidal waveform are obtained by combining information from the DC link current and the switching pattern. A sinusoidal PWM switching scheme is used to test the algorithm. Simulated and experimental results are presented. >

Intelligent power controller

Abstract: A remotely controllable circuit breaker and switch for controlling the flow of current from a three phase AC power source to a three phase load, and usable in either wye or delta configurations. A latching relay controls the current for each phase. Current samples in the three phases are scaled and converted to DC values by scalers and RMS to DC converters. The DC values are converted to digital current values by an analog-to-digital converter which sequentially scans the DC values of the currents in the three phases. A central processing unit monitors the digital current values to detect significant phase imbalances and overcurrents which persist for time periods which exceed allowable limits according to a predetermined time-dependent function, and to initiate opening of the relays in response thereto. The central processing unit also opens and/or resets the relays in response to remote control signals. The relays are opened in a zero-crossover mode when the currents exceed predefined threshold values; and in order to minimize the effects of noise are opened without regard to zero crossover when the currents are below said threshold values. Relay status contacts are employed to reduce power consumption during relay operation by terminating relay coil drive pulses when the relay contacts have achieved the desired state.

Control of an elevator hoisting motor during under voltage conditions in the main power source

Abstract: A method and an apparatus for the control of an elevator a.c. or d.c. hoisting motor driven by a frequency converter unit, or by a rectifier unit, supplied by a three phase power source is disclosed. The voltage of the mains power source is monitored using a voltage measuring unit. The frequency converter or rectifier is supervised by a control unit which selects a speed reference curve, best suited for a run. The controller unit allows the elevator speed to be varied continuously with the mains voltage so that the elevator always travels at the highest possible speed. When an undervoltage condition is detected in the mains power source, the rotational speed of the hoisting motor is reduced without modifying the acceleration so as to avoid an overcurrent if the rectifier or inverter switches. If, in addition, the acceleration is decreased before the maximum speed is obtained, a higher maximum speed may be obtained for a given low level of supply voltage. The solution offered by this invention enables the elevator system to work at undervoltages as low as 60%.

Device to control the speed of two-phase or three-phase motors

Abstract: Disclosed are a device and a method to control the speed of two-phase or three-phase A.C. motors by means of a three-phase converter. The switching-over instants of the switches of the converter for the control of a two-phase motor are computed so that the signals at the common points of each pair of switches are phase shifted with respect to one another and have no low-order harmonic components. The disclosed device and method are applicable to motors driving rotating anodes for X-ray tubes.

A balanced commutator for three-phase switched reluctance motors to minimize torque ripple

Abstract: The balanced commutator method of computing the reference currents for current tracking feedback is presented. For a given switch reluctance (SR) motor, the commutator reduces the peaks and the rate of change of the reference currents. This allows accurate current tracking, and therefore minimum torque ripple, over a wider range of operating speeds. Reference current waveshapes for two different SR motors, and the resulting torque ripples, are compared

A three-phase sine wave inverter system using multiple phase-shifted single-phase resonant inverters

Abstract: Two novel systems for synthesizing three-phase sine waves with a combination of two units, using multiple phase-shifted single-phase resonant inverters, are proposed. The first system has the advantages of both a high-frequency resonant inverter and a high-frequency AC link. The second system has the advantage of a high-frequency resonant inverter. The structure and operating principles of both proposed systems are described and their features are compared with those of a conventional 12-step inverter. The simulated and experimental results show that the proposed systems have excellent characteristics and give high-quality output waveforms. >

Current transformer arrangement for three-wire three-phase systems to detect the actual current value for controlled dc loads powered via power converters

Abstract: In a current transformer arrangement for three-wire three-phase systems, use is made of a single busing transformer (4) arranged on the three-phase side. Two of the total of three phase conductors are pushed through the bushing transformer, specifically either with the same number of turns per unit length and in mutually opposite defined directions or with the same direction and with the ratio of different numbers of turns per unit length of 2:1 or with the same direction and a current flow halved in a phase conductor by a shunt (15). These arrangements prevent the occurrence of a zero resultant magnetic flux. The double secondary voltage produced by a double AW value occurring twice during each period is halved by an electronic correcting circuit. The control commands are derived from suitable control pulses for the thyristors (21-26) of the three-phase bridge circuit (16). Two correcting circuits are specified. The main advantage resides in the considerable saving in current transformer material and thus also in space required.

Method and apparatus for supplying voltage to a three-phase voltage system having a load-carrying neutral conductor with a pulse width modulated three phase invertor

Abstract: To maintain a defined three-phase voltage system at the output terminals of a transformer device TE, for example, a transformer in a delta/wye connection where the primary-side neutral point is unconnected, even when an asymmetrical load is connected to it and to the secondary-side neutral point, single-phase transformers are used, whose primary windings are supplied with voltage by a pulse-width modulated, three-phase invertor in a bridge connection Through the use of voltage regulators, the actual values of the secondary-side line voltages form the control voltages for each bridge-arm pair The closed-loop control circuits of the three phase voltages are broken down in accordance with the structure of the transformer device by means of a break-down element The setpoint values can be calibrated to a synchronizing voltage, and/or a current control for the conductor currents is superposed on the voltage regulators

Ring spinner spindle drive - has three phase synchronous motor with permanently energised rotor for control through switches

Abstract: Drive system, esp. as an individual spindle drive has a three-phase synchronous motor (1) with a permanently energised rotor. Controlled switches (S1,S2,S3) are operated by the drive control (3) so that, with the required high torque in the start-up and shut-down phase, all three phases are switched through from the frequency converter (2) to the three-phase coils (W1,W2,W3) in a star or delta configuration. To increase the working with the required low torque on normal operation, one of the three phase coils is disconnected from the corresp. phase after the required working speed has been achieved. Rotor is radially permanently energised to increase the holding action when the motor is at rest, and the holding action can be reinforced by applying DC to the three-phase coils. Frequency and amplitude of the phase voltage from the frequency converter (2) are varied for the three-phase system on start-up, shut-down, acceleration or braking of the motor, and they can be adjusted by the drive control (3). Short circuit is applied to the three-phase coils (W1,W2,W3) by the switches (S1,S2,S3) to stop the motor (1). USE/ADVANTAGE - For the workstation of a ring spinner. Mechanism gives a controlled drive for the spindle, with detection of drive faults, and prevents uncontrolled rotation when the spindle is at rest.

Two-sided induction generator with both stator and rotor windings connected in parallel

Abstract: An induction generator is disclosed wherein both the stator and rotor windings are utilized to generate power with the three phase winding of the stator and rotor each connected in parallel with a delta connected capacitive network connected therebetween. The electrical output may thus be increased by a factor of four over a conventional generator of the same size.

A microprocessor-based firing circuit for thyristors working under a three-phase variable-frequency supply

Abstract: A microprocessor-based firing scheme for controlling antiparallel-connected thyristors working under a three-phase variable frequency supply is presented. The firing angle is controlled by microcomputer software. The desired firing angle is given to the microprocessor and is then kept constant irrespective of supply frequency. This is achieved by measuring the frequency of one-phase (or line-to-line) voltage at every supply voltage cycle and accordingly adjusting the required time delay to get the desired firing angle for the thyristors of each phase. The required hardware is considerably reduced by using a zero-crossing detector for only the one-phase (or line-to-line) voltage of the three-phase supply. The firing instants of the thyristors connected to the other two phases are adjusted relative to the calculated instant of firing for the thyristors connected to the measured phase. The hardware and software used to implement the firing scheme are described. >

Power supply systems for neon lights

Abstract: A main power supply device uses single phase, or three phase R, S, T; through rectification and filtration; each phase produces a different D.C. voltage so as to supply a respective voltage transforming device. The rectifier output of a step-down supply of the S, T, phase, in addition to supplying an astable square wave oscillator, so as to control signal outputs via a driving circuit, also supplies a tripping device, so as to control the high A.C. output from the high-voltage transformer of the transforming device. Any abnormal load can be detected by a detecting transformer and a protective circuit, so as to control cut-off of a transistor of a switching loop. A plurality of transforming devices are of the modular plate type; trouble-shooting can be performed easily, and the speed of maintenance is increased; the working safety is also enhanced.

Three-Phase Voltage Fed Type PWM Power Converter by means of Power Factor Control

Abstract: Recently, the voltage fed type PWM converters have been investigated from ideal and inherent properties as DC power source. But, the current control system generally used may be somewhat complicate due to the DC voltage detection.In this paper, we propose the simple control system of the PWM converter by means of power factor control in which the DC voltage detection is not always needed. In this system, the DC voltage is given by the line voltage and the modulating index of the PWM converter.The principle of the PWM control system is shown at first. From the simplified circuit model and its phasor diagrams, some basic relations of the PWM converter system are obtained and some fundamental characteristics are shown. From these investigations, it is seen that the phase control region is restricted to a certain angle, which depends on the setting power factor, the modulating index of the PWM and the load. Under the operating condition of unity power factor, it is given by ±π/4 for both the converting and inverting operations. The system can be operated over the all control range of the modulating index by restricting the angle to this critical value for the angle over this control range.The ideal operating characteristics as DC power source can be verified by some experimental results such as the operating waveforms of line current, the steady state characteristics and the transient responses between both operations of the converter and inverter.The features of the system are in the simple construction of the control circuit and some inherent and excellent characteristics as a voltage fed type DC power source.This control system may be applicable to any types of PWM converter used now.

Three-phase voltage-source convertor with controlled DC current for the minimisation of filter capacitance

Abstract: The paper presents a novel control strategy for the output DC current in a three-phase AC/DC convertor using diodes, combined with a boost-type DC chopper. This contributes to the suppression of the output voltage ripples so that the size of the filter capacitor can be minimised. The steady-state characteristics and transient response of the system, with a digital proportional-integral (PI) controller, which has a variable proportional gain to allow stable steady-state operation, are invetigated in the paper.

Three-phase voltage stiff convertor

Abstract: A three-phase voltage stiff converter (SR) has two six-pulse converters (SR1, SR2). The alternating voltage terminals of the partial converters are connected to a transformer (TR) with the aid of which the resultant alternating voltage of the converter is formed as the difference between the alternating voltages of the partial converters. Each partial converter has a separate direct voltage source (C1, C2). The converter has control members (SD) which control the two partial converters with a mutual phase displacement alternating between +150° and -150°.

Microcomputer-based single-phase to three-phase cycloconverter

Abstract: A microprocessor application for a single-phase to three-phase cycloconverter is presented. An algorithm is formulated for the cosine-wave modulation method so that it requires only one reference wave (RW) to generate the trigger pulses for all three phases. The method is implemented on an 8085 microprocessor system with output frequencies that are integer submultiples of the input frequency. The operating principle of the cycloconverter is reviewed. A complete software design of the scheme is given, and test results are presented for an induction motor load. The difference between the experimental and the calculated values of the firing angle is in the range of 0 to 0.51 degrees for the selected step size of 1 degrees . This can be reduced further by reducing the step size from 1 degrees to some lower value. Output voltage and current waveforms for an induction motor load approach sinusoidal. >

Three-phase 200 kVA UPS with IGBT consisting of high power factor converter and instantaneous waveform controlled HF PWM inverter

Abstract: A description is given of a three-phase 200 kVA UPS (uninterruptible power supply) In this UPS, both the input converter section and the output inverter section utilize an IGBT (insulated gate bipolar transistor) as a main semiconductor switching device Compared with the conventional type of UPS using bipolar junction transistors, this UPS provides an equivalent efficiency in spite of having an approximately 10 times higher switching frequency As a result, the new UPS is of a compact, lightweight, low-acoustic noise, and high performance design, resulting in reduced input harmonic current (less than 5% THD) and also a reduced output voltage distortion (less than 8% THD) under a nonlinear load >

Reduced length rotating rectifier assembly

Abstract: The disclosed rotating rectifier assembly (12) has a reduced axial length thereby achieving the goal of reducing the overall axial length of a brushless generator (10) which includes a rectifier assembly disposed along its axis (26) for developing DC output power from three phase AC power supplied by a three phase rotor armature (14) also contained within the generator (10). A typical rotating rectifier assembly is comprised of plates and diodes arranged in a stack clamped axially along the axis of rotation with a diode sandwiched between each adjacent pair of plates. The reduction of the axial length of the rectifier (12) is achieved by positioning a stack (67) of diodes (19) and plates (52 through 64) perpendicular to the axis of rotation (26) while providing the necessary electrical conductors to define a rectifier circuit.

Three phase high frequency DC-DC convertor

Abstract: A three phase system in a high frequency DC-DC convertor is proposed. Potential advantages of such an implementation include smaller magnetic parts, much lower output and input ripple, higher transformer utilisation factor and efficiency, and lower AC voltages for the same DC output voltage. There are also some disadvantages. More switchers and rectifying diodes are required. A three phase transformer and master oscillator at high frequencies are also necessary.

Suppression of converter introduced harmonic currents using a forced-commutated cycloconverter

Abstract: A method of current harmonic suppression through application of a modified forced-commutated cycloconverter is described. The cycloconverter is operated using current-error control with hysteresis. Advantage is taken of the multiple source voltage switching choices available with the cycloconverter to produce corrective harmonic current injection that tracks the command with minimum error. A numerical simulation of the filter is made with a three-phase, six-pulse rectifier load. The results are presented in the forms of both harmonic residual components and Fourier spectra. >

Induction motor performance when fed from single to three phase converters

Abstract: The most popular single-to-three-phase converter consists of a capacitor connected between the motor's third phase and either the live or neutral of the single-phase supply. Proper voltage balance at any one given operating point is obtainable with the autotransformer-capacitor converter (ACC), while proper balance over the entire operating range is obtainable with a variable-inductor-variable-capacitor converter (LCC). The appropriate vector diagrams of the above-mentioned converters are developed to provide insight into their operation. An assessment of the derating necessary in the presence of unbalanced voltages and currents is presented. A technique for the measurement of the negative sequence voltage is discussed. Measured results for the case when an induction machine starts directly off a three-phase supply and off the above converters are included. >

A PC-based simulation and DSP-based control for an improved high frequency resonant DC link inverter induction motor drive

Abstract: An 80386 PC-based simulation of an improved high-frequency resonant DC link inverter induction motor drive is presented. The resonant circuit was systematically analyzed to establish the criteria for initial current selection, and a new circuit was proposed to establish the bidirectional initial current. The current initialization scheme was modeled and simulated using PC-SIMNON. A three-phase 3 kW insulated-gate-bipolar-transistor (IGBT)-based 50 kHz resonant link inverter was constructed and successfully tested with an induction motor drive. The speed control system was implemented using two microprocessors: the TMS320C25 for computation and the Intel 80386 for monitoring and user interface. The simulation and experimental results show the superior operation of the improved resonant DC link inverter drive. >

Distribution of power from a six phase powerline to one- and three- phase loads

Abstract: Apparatus and method are provided for distributing electrical power from a six phase powerline to both single phase and three phase loads. The invention provides for improved power transmission efficiency, and offers compatibility between an installed base of single and three phase loads and a new six phase distribution wiring system that is configured to reduce fringing electric and magnetic fields.

Two phase power control of a three-phase load circuit

Abstract: A three-phase transformer is supplied by a three-phase AC line voltage. Two phases are connected via switches comprising head-to-tail connected thyristors. The third phase is connected directly to the transformer. The switches are of the zero voltage switching type. Under steady state conditions, the start of each series of cycles is obtained by closing in a fixed order a first switch at a time near the zero-crossing of the voltage across it (alternating between series of cycles the sign of the derivative of the voltage across it immediately before it is closed) and then the second switch approximately 90° after the first switch. The duration of a series of cycles if 570° plus a null or integer number of periods of the AC line voltage. This is achieved by counting thyristor firing command signals from pulse transformers driven by monostables.

Arrangement for converting two single-phase alternating currents into a symmetric three-phase current

Abstract: In order with a low degree of equipment complexity to convert two alternating-currents of 16 2/3 Hz of two separate single-phase generators (G1, G2) of approximately the same power into a three-phase current with 50 Hz, the single-phase generators are connected via a SCOTT transformer (Tr1) to a rectifier (SR1) of a converter with a direct-voltage intermediate circuit (3-6). The direct current transmitted through the direct-voltage intermediate circuit is transformed into three-phase current by two inverters (SR2, SR3) connected in series, and supplied to a national power system (10) via power transformers (Tr2, Tr3). The two single-phase generators (G1, G2) are controlled by one generator voltage controller (42) in each case, which affects the excitation of the single-phase generators (G1, G2) via a field rectifier (43), at the same amplitude of their generator voltages (u1, u2). Moreover, the single-phase generators (G1, G2) are controlled at a phase shift of their generator voltages (u1, u2 ) of 90°el by a load angle controller as a function of the load angles (δ1, δ2). For this purpose, desired-value signals (P1s, P2s) are formed by a turbine balance controller in order to control the fuel supply of turbines (Tu1, Tu2), which drive the single-phase generators (G1, G2).

Apparatus for detecting missing phase of three-phase power source

Abstract: PURPOSE:To make the apparatus compact and to improve reliability by comparing the output voltage from a detecting circuit for three-phase currents with a present constant reference voltage value, and comparing the voltage with a proportional reference voltage value which is present in correspondence with an output voltage value and the like. CONSTITUTION:Of output lines 1a, 1b and 1c of a three-phase power source 1, it is assumed now that a current detector 4 is connected to the V-phase output line 1b. The detector 4 supplies the output voltage to first and second comparator circuits 5 and 6 in correspondence with the detected current value. In the circuit 5, the output from the detector 4 is compared with the constant reference voltage level from a lowest-level setting circuit 7. The output of the result of the comparison is supplied to an OR circuit 8. The output of a frequency controller 24 in an inverter circuit 2 is supplied to a missing-phase-judging-level output circuit 9, and the proportional reference voltage value corresponding to the output frequency of the inverter is guided out and supplied to the circuit 6. When the output of either of the circuit 5 or 6 is introduced into the circuit 8, the OR circuit 8 guides out and supplies an operation stopping signal C for the circuit 2.