Showing papers on "AC power published in 1986"

Estimating the Voltage Stability of a Power System

Abstract: A method for the online testing a power system is proposed which is aimed at the detection of voltage instabilities. Thereby an indicator L is defined which varies in the range between 0 (noload of system) and 1 (voltage collapse). Based on the basic concept of such an indicator various models are derived which allow to predict a voltage instability or the proximity of a collapse. The indicator uses information of a normal load flow. The advantage of the method lies in the simplicity of the numerical calculation and the expressiveness of the result.

Power Electronics and Ac Drives

Abstract: An integrated treatment of technological advances in power electronics Add this article to private library Remove from private library Submit corrections to this record View record in the new ADS and ac drives is presented. The topics include: power semiconductor devices, ac machines, phase-controlled converters and cycloconverters, voltage-fed inverter drives, current-fed inverter drives, slip powercontrolled drives, control of induction and synchronous machines, and microcomputer control. Both practical and theoretical aspects of the technology are addressed, and numerical examples are given. Bibtex entry for this abstract Preferred format for this abstract

Control Strategy of Active Power Filters Using Multiple Voltage-Source PWM Converters

Abstract: The control strategy of active power filters using switching devices is proposed on the basis of the instantaneous reactive power theory. This aims at excellent compensation characteristics in transient states as well as steady states. The active power filter is developed, of which the power circuit consists of quadruple voltage-source PWM converters. As the result, interesting compensation characteristics were verified experimentally which could not be obtained by the active power filter based on the conventional reactive power theory.

Switching power supply with automatic power factor correction

Abstract: An off-line switching power supply is described which controls the switching transistor of a fly-back circuit in such a fashion as to achieve better than 0.99 power factor control. The technique used for power factor control allows the switching power supply to operate either from AC or DC sources. The power supply operating from an AC source will accept all international voltages and line frequencies as input to produce a well-regulated DC output. The inductor of the fly-back circuit is maintained at the verge of continuous/discontinuous operation by the power factor control circuit to achieve a high efficiency operation and to minimize switching losses. The power factor correction circuit uses pulsewidth modulation and frequency modulation to control the switching transistor and maintain a high power factor under varying line and load conditions. The power supply also includes integral current limiting protection and RFI filtering for safe and quiet operation.

Unity power factor power supply

Abstract: A unity power factor power supply which includes a boost converter connected to the alternating current line which is controlled to draw sinusoidal current from the line by operating as a current regulator having a current reference control signal which tracks the line voltage waveform, thereby to minimize the required input current for a given power output.

An Expert System Assisting Decision-Making of Reactive Power/Voltage Control

Abstract: An expert system is developed to assist in the decision-making of the reactive power/voltage control problem. The knowledge required to perform the task is identified. To alleviate a voltage problem, empirical rules are used to generate appropriate control actions when slight voltage violations occur. Controls such as shunt capacitors, transformer tap changers and generator voltages are utilized. Theoretical justification of the empirical rules is presented. When it is judged that the voltage problem is so severe that empirical judgements may not be reliable, the developed expert system can help in formulating the problem so that an available application software package can be effectively utilized. In this paper, production rules are proposed to perform the above functions. Numerical examples are also presented.

Sparse Reactive Power Scheduling by a Penalty Function - Linear Programming Technique

Abstract: This work presents a linear programming based algorithm to solve reactive power dispatch problems. A mixed set of variables (generated voltages and reactive power injections) and the reactive power model of the fast decoupled load flow algorithm are used to derive linear sensitivities. A suitable criterion is suggested to form a sparse reactive power sensitivity matrix. The sparse sensitivity matrix is in turn modeled as a bipartite graph which is used to define an efficient constraint relaxation strategy to solve linearized reactive power dispatch problems. The penalty function - linear programming technique method is used in a complete reactive power dispatch solution algorithm, the performance of which is discussed by solving a 256-node, 58 control-variable test system.

Power line communication system

Abstract: A low-level, low-power radio frequency (RF) communications system designed to operate as a point-to-point power line communications sytem (PLC) utilizing frequencies from 50 to 600 MegaHertz (MHz) superimposed onto the AC power signal in a building.

Static power conversion and apparatus having essentially zero switching losses

Abstract: A high efficiency power converter is achieved utilizing a resonant DC link between a DC source, such as a converter rectifying power from an AC power system, to a variable frequency voltage source inverter. A resonant circuit composed of an inductor and capacitor is connected to the DC power supply and to a DC bus supplying the inverter and is caused to oscillate stably at a high frequency to provide a uni-directional voltage across the DC bus which reaches zero volts during each cycle of oscillation of the resonant circuit. The switching devices of the inverter are controlled to switch on and off only at times when the DC bus voltage is zero, thereby eliminating switching losses in the inverter. The resonant circuit can be caused to oscillate utilizing pairs of switching devices in the inverter or a separate switching device across the capacitor, which again are caused to switch on and off only at times of zero voltage on the DC bus. For AC to AC conversion, enabling bi-directional power flow, the switching devices of the power source which converts AC power to DC power may have switching devices which are also switched only at the times of zero voltage so that switching losses in these devices is also minimized.

Simultaneous Active and Reactive Power Control of Superconducting Magnet Energy Storage Using GTO Converter

Abstract: By using GTO's (Gate Turn-Off Thyristor) in place of ordinary thyristors in a conventional six pulse Greatz bridge converter, forced commutation is possible, so in the usage of ac-dc power conversion the reactive power of not only lagging but also leading phase can be absorbed. This feature enables superconducting magnet energy storage (SMES) to control reactive power in the wide range between lagging and leading phases. By virtue of this control ability , SMES will be applicable for a power system stabilyzer. A GTO converter which mainly consists of six GTO's was developed and tested. In this GTO converter, the energy stored in leakage inductances of the transformer is handled by voltage clipper circuit. Then, by using two sets of these GTO converters, we carried out some experiments of simultaneous active and reactive power control of SMES. The experiments on the developed control system were successfully performed and the ability of controlling reactive power in the wide range between lagging phase and leading phase was verified.

Lighting system for normal and emergency operation of high intensity discharge lamps

Abstract: A lighting system is provided having a central power supply which includes an AC to DC converter. The DC power is distributed to a plurality of ballast circuits for discharge lamps. Each ballast circuit includes an inverter circuit for inverting the DC power to AC power of sufficient voltage to operate the associated lamps. Should the AC input power for the central power supply fail, batteries may be provided to supply the DC power continuously without interruption. The inverter circuits are operated at high frequency to reduce audible noise and eliminate noticeable strobing. The inverter circuit includes a switching circuit controlled by a pulse train. The duty cycle of the pulse train is controlled in accordance with a composite feedback signal which is the product of signals representative of the lamp operating voltage and lamp current.

Active filter for reactive power and harmonics compensation

Abstract: This paper describes a three-phase active filter aimed at the compensation of reactive power and current harmonics of a symmetrical load. The filter employs an inductor for energy storage and a two-quadrant PWM bridge converter.

An AC-to-DC Converter with Improved Input Power Factor and High Power Density

Abstract: A novel single-phase switch-mode rectifier (SMR) structure is proposed and analyzed. The proposed converter structure employs a synchronous front-end rectifier (SFER) stage which provides high-quality input characteristics with small input filtering. Consequently the proposed converter structure exhibits high power density and has low implementation cost.

Assessment of Real-Time Optimal Voltage Control

Abstract: This paper reports the results of a detailed study of on-line voltage/var control performed on the Ontario Hydro system. The first part of the study is an assessment of active transmission loss savings obtained by optimizing generator voltages and transformer taps with an Optimal Power Flow program using data from a state estimator. In the second part of the study, the question is addressed of how frequently the generator voltages and transformer tape should be optimized in order to achieve a large percentage of the loss savings indentified in the first part. The study showed that the reduction in active losses is sufficient to justify further effort toward implementing voltage control. The results of the second part showed that for the load curve studied, most of the savings could be achieved with voltage control cycle times of about one hour. A new quadratic programming-based optimal power flow algorithm is also presented which exhibits execution times suitable for real-time applications. Sample execution times are given for various systems which confirm that exact optimal power flow solutions can be obtained in a fraction of the control cycle times suggested in the second part of the study.

Method and apparatus for coupling transceiver to power line carrier system

Abstract: A method and apparatus for efficiently coupling a transceiver to an AC power line transmission system. The preferred embodiment of the coupling system comprises a line coupling network and first and second filter ports. The first filter port is connected to a resonant circuit having bandpass filtering characteristics adapted to the specific needs of the transmitter portion of the transceiver. The second filter port is isolated from the low impedance of the AC power line and is connected to a high quality factor filter having bandpass filtering characteristics adapted to the specific needs of the receiver portion of the transceiver.

AC power line signaling system

Abstract: A system for controlling the operation of a load circuit coupled to an AC power distribution circuit includes an encoder which may be mounted in a wall switch box and coupled to a single conductor of the AC power distribution circuit for imposing thereon control signals by lengthening the zero crossings of the AC voltage. A decoder, also connected to the AC power distribution circuit at a remote location, detects the lengthened zero crossings and closes an electronic switch for energizing the load circuit. The encoder may be disconnected from the AC power distribution circuit, in which case the load circuit may be controlled by an external condition responsive device, such as a passive IR sensor. Visible light-responsive means may be provided for disabling the IR sensor during the day. The load circuit and the decoder can be turned off from the encoder location.

Force-Commutated Reactive-Power Compensator

Abstract: A reactive-power compensator (RPC) is a type of static var compensator (SVC) that is used to dynamically correct power factor to prevent voltage variation (flicker) in ac power sources due to large dynamic loads. It also minimizes total source current. Thus the application of an RPC or SVC to a load may allow addition of substantial new load to existing feeders or substations. A reactive-power compensator suited to industrial ratings (1.0-25 MVA) is described. It utilizes a force-commutated current-source bridge to provide both leading and lagging reactive power. The ability to operate both leading and lagging can reduce by 2:1 the ratings of the RPC itself and the capacitors and magnetics associated with it. The characteristics of the power circuit, the means used to control it, and the resulting dynamic performance is described. Speed of response compares favorably to the thyristor-controlled reactors now in common use as SVC's at higher MVA ratings. This RPC is suited to compensate any balanced three-phase dynamic load.

Redistribution of Reactive Power Flow in Contingency Studies

Abstract: During recent years, problems associated with reactive power flow and bus voltages have acquired greater importance. The transmission capacity may sometimes be limited by reactive power considerations. In a few instances collapse of transmission network has been attributed to abnormal reactive power flow patterns. Some recent papers have addressed the question of improving the contingency study techniques for the reactive power flow problem. A commonly used method for contingency analysis is based upon the use of distribution factors. The distribution factor method of contingency analysis is very fast in its execution time, and for this reason is widely used in real time applications as well as planning studies. This technique is known to be particularly suited to the study of real power redistribution following an outage. It is not as accurate in dealing with problems of reactive power flow redistribution and accompanying effects on bus voltages. The inaccuracies are particularly significant when voltage controlled buses are present in the power system. The distribution factors are based on approximating active power injections by current injections under the assumption that voltage magnitudes throughout the system are kept constant. This is an unacceptable assumption for reactive power. This paper develops a new formulation of distribution factors which is suitable for the analysis of the reactive power problem. The new formulation is based on the S-E (complex power - complex bus voltage) representation of a power network instead of the usual I-E (complex current - complex bus voltage) formulation.

Transient ride-through AC inverter

Abstract: A transient protection circuit for an inverter has a rectifier capable of supplying direct current from an alternating current power source, where protection is provided against a voltage transient in the AC power source. A DC bus is fed by the rectifier. A bus capacitor is connected across the DC bus. Solid state switches are connected to the DC bus for supplying alternating current to a load. The DC bus voltage is sensed. In response to a transient rise in the DC bus voltage, a resistor is connected across the bus capacitor to provide a discharge path, the solid state switches are disconnected from the DC bus, and after the transient dies away from the DC bus, the solid state switches are reconnected to the bus and the discharge resistor is disconnected from across the bus capacitor.

The Application of the Current Comparator in Instrumentation for High Voltage Power Measurements at Very Low Power Factors

Abstract: A current-comparator technique is applied to several auxiliary instruments which enables accurate high voltage power measurements to be made at very low power factors using precision wattmeters and precision bridges. The instruments include a high-voltage active-divider with a nominal output voltage of 100 V, a high-voltage inductive-quadrature-current reference source with current output ranges of 1 mA, 2 mA, and 10 mA, and a high-voltage high-capacitive-quadrature-current reference source with current output ranges of 0.1 A, 0.5 A, and 1 A. The current comparator is used in a feedback loop to correct the magnitude and phase of the associated outputs of these instruments to an accuracy of better than ±10 ppm (parts per million) and ±10 ?rad respectively.

A Computation Algorithm for Assessing Voltage Stability at AC/DC Interconnections

Abstract: A new method for the analysis of ac voltage stability problems at HVDC terminals, when imbeded in large networks, is presented. The method can be used to evaluate the effects of dc modes of operation, ac system operating conditions and VAr compensation schemes on the combined system voltage stability. Dynamic properties of both ac and HVDC systems are incorporated in the solution algorithm. A step-by-step technique is developed for integrating the new algorithm with available load flow programs. Examples are given to demonstrate the performance of a new control strategy for HVDC converters connected to weak ac systems and the results are compared to classical solutions.

Photovoltaic power control system

Abstract: There is disclosed a photovoltaic power control system equipped with at least one inverter for inverting an output of a solar cell array to AC power, and having charge-and discharge control means for charging a surplus portion with respect to the power for expected use of the output of the solar cell array to a storage battery and discharging shortage portion with respect to the power for expected use of the output of the solar cell array from the storage battery by detecting the surplus or shortage produced between the output of the solar cell array and AC power for expected use inverted by the inverter, the improvement comprising weather fluctuation pattern selection means for selecting one weather pattern out of various kinds of weather patterns preset based on weather information at a time point when the weather is forecasted on the day when the power is generated by the solar cell array; and workable pattern selection means for selecting one actuation pattern of the inverter corresponding to the weather pattern selected by the weather fluctuation pattern selection means out of various actuation patterns of the inverter preset corresponding to the weather pattern.

Reactive power compensation apparatus

Abstract: of the Disclosure A reactive power compensation apparatus for compen-sating for voltage fluctuation of an AC power supply system includes a first arithmetic circuit for synthe-sizing a positive-phase fundamental wave voltage signal from voltages of the AC power supply system, a second arithmetic circuit for synthesizing negative-phase voltage signals from the voltages of the AC power supply system, a third arithmetic circuit, coupled to the first and second arithmetic circuits, for synthesizing current instructions from the positive-phase fundamental wave voltage and the negative-phase voltage signals, and a circuit, coupled to the third arithmetic circuit, for generating a reactive power corresponding to the current instructions.

Flywheel power source apparatus

Abstract: A flywheel power source apparatus of the invention can be additively used in a power source apparatus for a load such as computer, which is weak to momentary service interruption or large voltage variation and therefore requires the countermeasure. The flywheel power source apparatus comprises main circuit having a converter for converting AC power source output into DC output and a first inverter for converting the DC output of the con­verter into AC output and supplying it to a load, a flywheel device supplied with power from the main circuit and driven for rotation, and a compensation circuit for supplying the stored energy based on the rotational force of the flywheel device to the first inverter of the main circuit. The flywheel power source apparatus is composed of a chopper circuit for controlling voltage of the compensation circuit, a second inverter circuit for controlling frequency of the compensation circuit, and first and second comparators for comparing outputs during outage of the power source and at normal state with reference values respectively and controlling the chopper circuit.

Damping Subsynchronous Oscillations in Power Systems Using a Static Phase-Shifter

Abstract: A method for suppressing Subsynchronous Resonance (SSR) in large turbine-generators, as a result of series capacitor compensation of power systems, is presented. This method utilizes a thyristor-controlled phase-shifter to modulate the generator active power by injecting a quadrature phase voltage in the system. The rotor speed deviation from the synchronous speed is used as the control signal. An eigenvalue analysis and the complex torque coefficient methods are used to demonstrate the technical feasibility of a static phase-shifter for damping SSR. The analytical results are verified by a detailed digital computer study on the first IEEE benchmark for SSR studies, using the BPA's Electro-Magnetic Transients Program (EMTP). The simulation results indicate that injection of 2.4% of the system phase voltage in 4 steps of 0.6%, can suppress all torsional modes of the First IEEE benchmark model.

Control device for power converter

Abstract: The invention relates to the control of a power converter in which the AC side is connected through a reactor to an AC power supply while the DC side is connected to a smoothing capacitor and a load and the power rectification and the power inversion are carried out by the pulse width modulation control. The controls performed include (1) the control, whereby the voltage across the smoothing capacitor coincides with a predetermined value and the current flowing through the reactor and the voltage of the AC power supply have a predetermined phase relationship; (2) the DC component compensation control for eliminating the DC component in an AC circuit within a short time interval and (3) the control of the power conversion operation by utilizing a microprocessor while suppressing the higher harmonics in the AC power supply. The control (1) is performed by using an amplitude signal of the voltage on the AC side of the power converter and a phase difference signal relative to the AC power supply voltage. The control (2) is performed by using the amplitude signal and the phase signal on the AC side of the power converter which cause the current flowing through the reactor to have a predetermined phase relationship with the AC power supply voltage and a detected DC component signal flowing through an AC circuit. The control (3) is performed by using the data of degree of modulation and the phase angle data which are fixed value during a certain period of time and the cross point data stored in the storage means.

Simulation and Experimental Study of a Reactively Loaded PWM Converter as a Fast Source of Reactive Power

Abstract: The question of eliminating distorted current waveforms from power networks by active power filters is investigated. If the active current is subtracted from the distorted current, the compensating equipment must be capable of generating the inverse of this difference. Addition of this compensating current to the distorted current then eliminates the distortion. This requires the capability to generate these currents with response times many times less than the fundamental power frequency cycle. This capability is presented by reactively loaded PWM converters. A system configuration with three single-phase PWM converters building a three-phase unit is investigated. The single-phase converter with PWM operation, inductive reactance as load, low-pass input filter, and representative system losses is simulated by state-space techniques. An experimental system of 1 kVA is also constructed for verification. Good correspondence between the simulation and experiment s shown. Starting up the system, compensating the system losses from the supply, and the influence of the control system on the compensating capabilities are investigated. It is concluded that a PWM converter with a reactive load can be used as a fast distortion compensator and that the present state of the art and future development of PWM converter technology will make this technique applicable at least up to 1 Mvar.

AC power supplied static switching apparatus having energy recovery capability

Abstract: A three-phase matrix converter including switches having snubber circuits associated thereto, is provided with a common voltage clamp capacitor for limiting the voltage applied to the snubber capacitor, and energy is accumulated in the clamp capacitor which is controllably dissipated, in particular by providing energy to auxiliary elements of the overall system.

Localized response performance of the decoupled Q -V network

Abstract: In this paper the assumption of a localized voltage response due to reactive power disturbances is analyzed. Conditions on transmission line parameters, given its normal operating point, are stated which explicitly define directions of voltage changes so that the line is subject to the localized voltage response. We show that it is not possible to give an exclusive answer to the question of the localized response (tier-wise) in the decoupled Q - V network. The answer is network and operating point dependent. The operating regions in which this property is satisfied even under large changes in reactive power injections are derived on the SE graph based decoupled Q- V network. We first define a no-gain operating mode of this network and then claim that the power no-gain operating mode always implies a localized voltage response. These results cannot be used to demonstrate a voltage gain. We develop algebraic type statements to show that a system may have response which is system wide. More definite answers on the localized response are established for the echelon structure of a given network.