Showing papers on "AC power published in 1980"

The generalised transformer: A new bidirectional, sinusoidal waveform frequency converter with continuously adjustable input power factor

Abstract: A new frequency converter design is proposed The new converter is capable of sinusoidal waveforms at both input and output ports, bidirectionality, continuously controllable input power factor and reactive power generation The converter operation does not require any reactive element

On the Definition of Reactive Power Under Non-Sinusoidal Conditions

Abstract: A new method of defining reactive power under non- sinusoidal conditions is proposed. It consists of sub- dividing the current into components which would have the same waveform as the current in a resistance and either an inductance or a capacitance when the voltage is applied to them, and into a residual component. An instrument for subdividing and measuring each current component and its corresponding power is described. The method permits the power system operator to determine if the possibility of improving the power factor by means of a shunt capacitance or inductance exists and to easily identify the proper value required to realize the maximum benefit.

Network Constrained Reactive Power Control Using Linear Programming

Abstract: The use of linear prograrming (LP) in power system reactive power control calculations is presented in this paper. Ihe method incorporates the usual reactive power control devices and is particularly successful in rescheduling tap-changing transfornmers. Solutions are constrained within limits set by busbar voltage levels and network reactive power flows. Results are given which indicate a high degree of reliability and versatility, with solution times which are suitable for real-time applications on large systems.

Reactive Power in Nonsinusoidal Situations

Abstract: Reactive power is interpreted as a time-domain reciprocating flow of energy, with a formulation that is valid for any periodic waveforms It is shown that the current can be resolved into orthogonal components, and that the current and power components can be measured with practical instrumentation

Characteristics of Static, Thyristor-Controlled Shunt Compensators for Power Transmission System Applications

Abstract: The operating and performance characteristics of two basic types of static, thyristor-controlled shunt compensators, one with a fixed capacitor bank and the other with synchronously switchable capacitor banks, are presented with regard to power transmission system applications. The operating principles, and the similarities and differences between the performance of the two schemes are discussed in the areas of steady-state voltage versus VAR characteristic, behavior under small and large system disturbances, harmonic generation, and loss versus output VAR characteristic.

Harmonic Pollution on Power Systems - A Change in Philosophy

Abstract: Static power converters have increased in number and uses in the past decade, and there has been an increased use of static power capacitors for improving power factor. These two trends have set, the stage for possibly uncontrolled harmonic resonances on industrial power systems. Some example of some problems are given and some practices are recommended, in line with a new IEEE standard, that will minimize the chance of harmful resonant conditions.

Electrical aircraft engine start and generating system

Abstract: This invention relates to electrical aircraft engine start and generating system for use in an aircraft having an engine driven torque converter coupled to an alternator which provides AC power for conversion to DC and AC power. The system includes a reversible AC to DC converter controllably electrically coupled to the alternator and a controller unit to provide DC power in a generating mode. The reversible AC to DC converter is capable of receiving externally supplied DC power to be converted to AC power to drive the alternator as a motor in a start mode. A DC to AC converter is controllably electrically coupled to the controller unit and the DC power output during the generating mode. The reversible DC to AC converter in the start mode is mutually controllably electrically coupled to the externally supplied DC power. The controller unit and the alternator cooperate to provide a controlled AC power output to be delivered to the alternator to bring the alternator operating as a motor up to operating speed, whereupon the reversible DC to AC converter responds to the external DC power and is electrically coupled to the alternator to drive the alternator as a motor to deliver rotary power through the torque converter to start the aircraft engine.

Frequency shift inverter for variable power control

Abstract: A variable frequency AC power source drives a gas discharge lamp which is connected in parallel with the capacitance of a series resonant circuit. The polarity of the voltage applied to the resonant circuit is commutated at such times as the rate-of-change of current flow in the resonant circuit is below an adjustable threshold value. The setting of a threshold adjusting circuit determines the brightness of the lamp. The polarity is also commutated at such times as the current flow from the source reaches a predetermined level. Lamp current is thus independently and variably controlled in the variable power mode.

A New Approach to Reactive Current and Reactive Power Measurement in Nonsinusoidal Systems

Abstract: A simple converter for resolving current or voltage into two orthogonal components-active and reactive-is suggested. It enables the direct measurement of reactive power as defined by Fryze. The converter can be easily extended to a three-phase system.

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

A solid state transformer

Abstract: This paper describes a solid state step up/down transformer system which also provides AC output voltage regulation. It uses PWM AC power switching to achieve high efficiences and uses no large inductive components. Its performance has been verified by extensive computer simulation of the entire system and breadboard testing of several of the key circuits.

Operation control apparatus for AC motors

Abstract: An apparatus for controlling the operation of an AC motor wherein braking energy at the time of a reduction in motor speed is disposed of by regenerative braking. The apparatus includes a rectifier which is connected to the AC power source, a DC link which includes smoothing capacitors and a regenerative transistor bridge circuit, a variable voltage-variable frequency inverter. Further provided are a diode which is connected between the rectifier and the transistor bridge circuit and which is biased in the reverse direction at the time of regenerative braking, and a firing control circuit for detecting the reverse bias voltage of the diode to control the firing of each transistor in the transistor bridge circuit, the braking energy being fed back to the AC power source when the AC motor undergoes a reduction in speed. The apparatus, which provides stable regenerative operation, can be constructed simply and inexpensively, and reduced in size.

System for transferring a load between two power sources without interruption of power to the load

Abstract: A system for transferring a load from a first to a second AC power source, including a monitor for sensing both power sources and producing an output signal when the differences in voltage, frequency, and phase between the two sources are within prescribed limits. Contacts close, in response to the monitor output signal, to connect the second power source to both the first power source and the load. Other contacts open, to disconnect the first power source from the second power source and load, but only after the second power source has been connected to the first power source and the load. The contact arrangement may include an automatic transfer switch and separate contacts in parallel with one or both sets of transfer switch contacts, or it may involve two independently operable contactors, or it may involve a four position switch.

Induction motor control system

Abstract: A variable frequency power supply device supplies an AC power to a squirrel-cage motor through an AC parameter control. The control receives a command active current resulting from a command torque and a command exciting current to generate a resultant current and its phase. The command torque is produced from the actual and command motor speeds and the exciting current is caused from the actual motor speed. The control also receives a command frequency determined by the actual motor frequency and a command slip frequency also resulting from the command torque. The control controls the firing phases of thyristors in the power supply device in response to the command current, phase and frequency. The control may generate a voltage for supplying the active current and an exciting voltage to similarly control the firing phases of the thyristors. In the latter case, the exciting voltage may be added with its differential to compensate for a rapid change in active current.

Power Factor of AC Controllers for Inductive Loads

Abstract: A general relationship for the input power factor of ac controllers with inductive loads is derived in this paper. Its simplified form is given for the phase angle, integral cycle, and symmetrical pulsewidth modulated controllers. The latter may or may not have a freewheeling path for the load.

Coordination of Surge Protectors in Low-Voltage AC Power Circuits

Abstract: Surge protectors can be installed in low-voltage ac power systems to limit overvoltages imposed on sensitive loads. Available devices offer a range of voltage-clamping levels and energy-handling capability, with the usual economic trade-off limitations. Coordination is possible between low- clamping-voltage devices having limited energy capability and high-clamping- voltage devices having high energy capability. The paper gives two examples of coordination, as well as additional experimental results on surge propagation.

Synchronous data transmission system utilizing AC power line

Abstract: A data transmission system utilizing a power line transmits a data signal of a plurality of bits in a serial fashion in synchronism with the cycles of the alternating current of a power supply. A start signal, channel section signal, control data signal and end signal are sequentially generated to transmit the control data to a selected receiver to control a desired output. Each cycle is divided into at least two phase sections, the one being used for a busy signal and the other being used for a data signal. The data transmission system includes a plurality of transmitters and a plurality of receivers coupled to the power line. Each of the transmitters comprises a receiving circuit for receiving a busy signal from other transmitters, a transmitting circuit for transmitting a data signal, a key input switch for operation, a selecting switch for selecting a channel which receives the transmitted data signal, and a memory for storing the key input signal. The transmitting circuit generates a data signal in response to the key input signal stored in the memory and to a non-busy signal. One embodiment of the transmission system of the present disclosure enables information to be transmitted over multiple-phase power lines.

Power failure early warning circuit for microprocessor with CMOS RAM memory

Abstract: A circuit for preventing data transfers to a RAM by a microprocessor when primary ac power fails also puts the RAM in standby after a period adequate to complete any data transfer started. The sequence is provided by providing a first signal to the microprocessor transfer enable line upon loss of primary power. A second signal is provided for the enable line of the RAM after a predetermined delay but before decay of the dc power to the RAM.

Lamp circuit with disconnected lamp detecting device

Abstract: A lamp circuit is provided having a constant current type AC power source and a plurality of isolation transformers connected in series with the AC power source. The secondary circuit of each isolation transformer is connected to an electric lamp. The voltage-time area, which is measured from the rise of the voltage output signal of the power source to the rise of the current output signal of the power source is detected and is compared with a reference predetermined value. Thereby when the detected value exceeds the reference value an alarm signal is generated and the number of the disconnected lamps can be determined and displayed.

Microcomputer-based control apparatus for a load-commutated inverter synchronous machine drive system

Abstract: A load-commutated inverter synchronous machine drive system control apparatus comprises at least one microcomputer for determining optimum or desired values for inverter turn-off time, inverter link current and machine air gap flux from machine drive system voltage and currents. Inverter frequency is regulated in accordance with the difference in magnitude between optimum and actual inverter turn-off time to minimize the inverter turn-off angle irrespective of machine frequency, thereby reducing synchronous machine reactive power. Inverter link current and synchronous machine field current are regulated responsive to the difference in magnitude between optimum and actual inverter link current and the difference in magnitude between optimum and actual machine air gap flux, respectively, thereby assuring machine operation at maximum efficiency.

A Control Strategy for Reference Wave Adaptive Current Generation

Abstract: Speed control of ac motors requires variable frequency, variable current, or variable voltage supply. Variable frequency supply can be obtained directly from a fixed frequency supply by using a frequency converter or from a dc source using inverters.

Power Converters for Feeding Asynchronous Traction Motors of Single-Phase AC Vehicles

Abstract: Asynchronous induction motors are very well suited to powerful traction drives. For electric locomotives and motor coaches with single-phase supply, a power conversion on the vehicle is necessary. Three different types of static power converters for this application are described. Indirect ac converters with direct voltage link have been developed successfully in the past. For indirect ac converters with direct current link some problems are discussed. At last a self-commutated direct ac converter with suppressed dc link is presented.

DC to AC inverter and motor control system

Abstract: This relates to a low cost reliable controller which may be used in conjunction with induction motors or, more generally, to generate AC power from a DC source. The system utilizes a microprocessor in combination with low cost parallel transistors to provide the control function. A feedback module monitors the actual rotor speed and conveys this information back to the microprocessor. A voltage boost module may be used in combination with the microprocessor and switching circuits to optimize the overall efficiency of the system. The microprocessor computes slip and controls the voltage drive in order to further optimize efficiency of the system as a function of motor speed. Both the footfeed voltage and boosted voltage are analog voltages and are applied to an A/D converter. The output of the A/D converter presents a digital representation of the footfeed voltage or boost voltage to the microprocessor.

Power Usage and Electrical Circuit Analysis for Electric Arc Furnaces

Abstract: Power usage in ultrahigh-powered electric arc furnaces requires considerably more investigation into system parameters, furnace secondary circuit analysis, and operating characteristics than previously given to normal powered electric arc furnaces. The power input must be analyzed from the infinite electric utility bus to the arc at the electrode. All interested parties must participate in the analysis to assure a mutual understanding of each other's problems. Various high-voltage systems are compared along with power factor correction applications. An 18-ft (5.5-m) 80-ton (72.6-metric tons (MT)) furnace has been selected for detailed analysis with a 50-MVA furnace transformer. In addition to electrical considerations, the power melting profile and associated refractory erosion is also subjected to analysis in this review. The analysis indicates that with proper application, ultrahigh-powered electric arc furnaces will provide increased production with reasonable refractory erosion.

Thermal Instrument for Measurement of Voltage, Current, Power, and Energy at Power Frequencies

Abstract: The design of an instrument for precision measurement of ac voltage, current, power, and energy is described. It has been developed as a standard for evaluating the performance of instrumentation used in the power frequency range (45-65 Hz). Its accuracy relies on a continuous ac/dc transfer which is achieved by automatically balancing the alternating current derived from the quantity to be measured against the equivalent direct current, both passing alternately through the heater of a thermal converter. Since the instrument can be calibrated with direct voltage and current, its total systematic error is limited by the ac/dc transfer to ±0.0005 percent of full scale for voltage and current, and ±0.001 percent of full scale for power and energy measurements.

Converter Propulsion Systems with Three-Phase Induction Motors for Electric Traction Vehicles

Abstract: Three-phase induction machines have a number of advantages compared with collector type machines which make them particularly suitable for traction purposes. These advantages, which were recognized long before, could only be used in praxis by means of the progress, which the development of static power converters has made in the last decade. Primarily having been used in diesel-electric traction vehicles inverter-fed three-phase induction motors are now going to be applied in large scale to line-fed electric vehicles. In this field of application the induction machine has some additional advantages; e.g., the motor torque versus speed curve declines much less with increasing speed than that of the common series wound ac machine. Consequently, for the first time in history universal electric locomotives can be built, which are equally suited for hauling high-speed passenger trains as well as heavy freight trains. Converter systems are described, which do not drain reactive power from the supply line or even feed reactive power into the line, if necessary, and produce only a small amount of harmonics. Hence these systems are very well suited for high-power electric traction vehicles as well as for smaller vehicles, which are in service simultaneously in one district (e.g., rapid transit vehicles), and for industrial locomotives. Finally, some test and production vehicles with three-phase induction motors, test data, and experiences in service of such vehicles are described.

Steady-State Characteristics of a Current-Source Inverter/Double-Wound Synchronous Machine System for AC Power Supply

Abstract: A detailed steady-state analysis of a novel dc-to-ac conversion system used as an ac power source in dc electric railway coaches is presented. This system consists of a current-source inverter, a double-wound synchronous machine, a position sensor, and a control circuit. An equivalent circuit convenient for predicting the steady-state behavior of the system is first derived. Based on this equivalent circuit, the output voltage waveforms are then examined. It is shown that the voltage waveforms are nearly sinusoidal except that narrow spikes are superposed on them during commutation of the thyristors. As to armature reaction in the double-wound synchronous machine, it is shown that a remarkable direct reaction appears which affects the voltage regulation of the system. Finally, a method for keeping the output voltage and frequency constant is discussed.

Superconductive latch circuit

Abstract: This superconductive latch circuit uses superconductive switching devices and can be powered by the same phase of AC power used to power other circuits with which the latch is used. The latch is comprised of a storage loop including a superconductive switch and an inductor. It is also comprised of another superconductive switch through which an AC gate current can flow and whose state determines whether or not the AC current is delivered to the superconductive storage loop. Information is stored in the loop as the presence and absence of a circulating current of either polarity. In a variation of this latch, an output of the sense circuit which detects the state of the storage loop if fed back as a control signal to the superconductive switch in the storage loop and also as one input to an AND gate to which a SET signal is also applied. AC power is switched to the storage loop when both inputs to the AND circuit are simultaneously present. In another variation, the signal which is fed back from the sense circuit is an input to an OR gate, whose output is the control signal to the switch in the storage loop. This latch reliably holds data when the AC power diminishes to zero, and also when the AC power changes polarity.

Method and apparatus for controlling current or power between interconnected power stations

Abstract: A method and apparatus for controlling a current and/or power between interconnected power stations. A deviation from a base load in an active current or power flowing out of a power station and a deviation from a normal value in the terminal voltage of the power station are measured. A linear function of the ratio of the voltage deviation to the active current deviation is obtained, and a product of the active-current to voltage deviation function and an active current flowing out of the power station is calculated, and thus a reactive current is defined by the product. An internal generation current of the power station is controlled so as to coincide substantially with the sum of the current composed of the active current and the reactive current defined above, and other currents of the power station including the internal load current.