Showing papers on "AC power published in 1987"

Security analysis and optimization

Abstract: An operationally "secure" power system is one with low probability of blackout or equipment damage. The power system control processes needed to maintain a designated security level at minimum operating cost are extremely complicated. They increasingly depend upon on-line computer security analysis and optimization. This on-line technology is still relatively new, with enormous further potential. Since security and optimality are normally conflicting requirements of power system control, it is inappropriate to treat them separately. Therefore, they are slowly becoming coalesced into a unified hierarchical mathematical problem formulation: one that is, however, far too complex to afford anything but an approximate, near-optimal solution. The practical validity of this unifying trend relies on being able to incorporate all significant security constraints within the process. The main two current computational tools in this field are contingency analysis and special operations-oriented versions of optimal power flow (OPF). Contingency analysis identifies potential emergencies through extensive "what if?." simulations on the power system network. OPF is a major extension to the conventional dispatch calculation. It can respect system static security limits, and can schedule reactive as well as active power. Moreover, the advanced versions of OPF include or interface with contingency analysis. This paper reviews present formulations and methods, and tries to point out areas of difficulty that constitute the main challenges for successful practical on-line implementations over the coming years.

What is wrong with the Budeanu concept of reactive and distortion power and why it should be abandoned

Abstract: The Budeanu definitions of reactive and distortion power in circuits with nonsinusoidal waveforms have been widely used for almost 60 years. There have been objections, concerned mainly with the questions of whether these powers should be defined in the frequency domain and whether they can be measured as defined. The main drawbacks of these definitions include the fact that the Budeanu reactive and distortion powers do not possess any attributes which might be related to the power phenomena in the circuit; that their values do not provide any information which would allow the design of compensating circuits; and that the distortion power value does not provide any information about waveform distortion. It is concluded that Budeanu's concept has led the power theory of circuits with nonsinusoidal waveforms into a blind alley.

A Three-Phase Controlled-Current PWM Converter with Leading Power Factor

Abstract: Experimental tests performed on a three-phase bipolartransistor controlled-current PWM power modulator show that it can operate with near-sinusoidal currents at 60 Hz with a 360-degree power angle range. Because of its capability to operate with leading power factor and good waveform, the PWM converter is a promising alternative to the thyristor Graetz bridge. A theoretical method based on the concept of ``local average'' is presented.

Security control system

Abstract: A security and control system for use in a home or building which utilizes a coded audio link between the entry detectors/transmitters and the relay modules, and a digital pulse coded power line communication ("PLC") link between the relay modules and the system controller as well as between the system controller and the various remotely located slave units which control the energization of lamps, appliances, and alarms. The relay modules and controller include constant false alarm rate ("CFAR") receivers for isolating the coded audio signal from background noise and unique exclusion circuitry for decoding the isolated signal. The PLC messages are generated by impressing a pulse code modulated high frequency carrier signal onto the AC line at selected points in the AC waveform. The location of each carrier frequency pulse relative to the 60 Hz AC line cycle determines the digital value of the pulse. Both before and during a PLC message transmission, the controller and relay modules are adapted to check the status of the AC power line for the presence of intelligence or excessive noise levels and delay transmission if either condition is detected. In the security mode, the system has three major states: INSTANT-ARM, ARM-DELAY, and DISARM. In the INSTANT-ARM state, the system responds immediately to the detection of an intrusion event. In the ARM-DELAY state, a 40-second delay is implemented before alarm action is taken to permit an authorized entrant to DISARM the system. Significantly, the 40-second delay is implemented by each of the remotely located slave modules so that destruction of the controller by an intruder within the 40-second period will not defeat the system.

Three-Phase AC/DC PWM Converter with Sinusoidal AC Currents and Minimum Filter Requirements

Abstract: A pulsewidth modulation (PWM) control technique suitable for fully controlled three-phase ac/dc converters is analyzed, which gives sinusoidal input currents and ideally smoothed dc voltage. The technique allows four-quadrant operation and full-range control of the input power factor. An extension to a simplified converter scheme, capable of one-quadrant operation, is also considered. Operation of the converter is analyzed under both ideal and actual conditions. Control implementation and design criteria are discussed and experimental results are reported.

Incorporation of Switching Operations in Power System Corrective Control Computations

Abstract: This paper presents a linear programming based methodology for corrective controls computations. The methodology computes adjustments of unit real power output, VAR source output, transformer tap settings, capacitor/reactor switching, branch switching or line sectionalization, and if necessary, load shedding. A previous publication presented the basic algorithm for computing adjustments of continuous controls such as generator real power, transformer tap setting, etc. This paper addresses the problem of incorporating discrete controls such as capacitor/reactor switching and line switching/sectionalization into the overall procedure. Efficient algorithms are presented for the computation of discrete controls such as capacitor bank and transmission line switching. The methodology is illustrated with typical results obtained with the Georgia Power Company's 500 kV/230 kV/115 kV system. The network representation of this system comprises 981 buses and 1175 circuits.

A New Approach for Minimizing Power Losses and Improving Voltage Profile

Abstract: This paper presents a new method for minimizing transmission line losses and improving voltage profile in a given system by adjusting control variables, i.e., tap position of transformers and reactive power injection of VAR sources. Transmission losses are considered as a function of voltage increments. The control variables and voltage increments are related by a modified Jacobian matrix. Linear Programming (LP) is used to calculate the voltage increments which minimize the transmission losses, and the adjustments of control variables are obtained by a modified Jacobian matrix. Since this method does not need any matrix inversion, it will save computational time and memory space.

Characteristics of a Controlled-Current PWM Rectifier-Inverter Link

Abstract: Two controlled-current pulsewidth-modulated (PWM) converters have been integrated into rectifier-inverter links of variable-speed ac motor drives. The authors focus on developing a mathematical model of the rectifier-inverter link and presenting experimental justification of the model. The characteristics of the rectifier-inverter system and the constraints imposed by the voltage feedback loop and dc link voltage are discussed. The rectifier-inverter system is made to drive a "selfcontrolled" synchronous motor, thus forming a system for which both the utility and the motor currents are near sinusoidal. The optimized power conversion capability of the motor is now matched by unity power factor operation on the rectifier side. Fast reversal from motoring to regenerative braking capability is demonstrated experimentally.

Uninterrupted power supply system

Abstract: A power supply system for providing uninterrupted AC power includes a first input port to which to couple AC input power at a specified RMS voltage level from a primary power source, a second input port to which to couple DC input power at a specified voltage level from a backup power source, and an output port to which to connect a device to be powered. A fullwave rectifier generates a first direct current from the AC input power, and up-converter generates a second direct current from the DC input power at an RMS voltage level approximately equal to that of the AC input power, and a switching arrangement couples a selected one of the first and second direct currents to the output port according to whether the AC input power is stabilized or interrupted, so that the flow of current to the output port is periodically reversed thereby generate AC output power. Switching may by synchronized with each zero crossing of the AC input power. A microprocessor in one form of the invention generates a reference waveform, compares it to the waveform of the AC input power, and selects one of the first and second direct currents according to whether the AC input power is interrupted or stabilized.

Power supply system having improved input power factor

Abstract: A circuit and method using a low frequency active switch for improving input power factor in power supplies utilizing a full wave rectifier and capacitor filter for supplying a filtered DC voltage from an AC power source. A switch control activates and deactivates an active switching once in each half cycle of the alternating voltage input. The switch control is connected to the active switching for operating the circuit providing high power factor.

Microprocessor-Controlled SIT Inverter for Solar Energy System

Abstract: A microprocessor-controlled static induction transistor (SIT) inverter is proposed to link a solar battery with a utility ac power line. The main control objectives are to optimize the power flow from the solar battery to the utility power line and to compensate the reactive power, including harmonic distortion. The performance is well realized by the experimental setup.

Optimal Reactive Power Allocation

Abstract: A systematic procedure is developed to locate reactive power devices in a power system based on a set of indices, that are based on overall system conditions. After identifying the desired locations, the cost of installation and number of reactive power devices, subject to any required practical and real economic constraints, are minimized. Existing controllers are fully utilized before adding any new devices. Linearized sensitivity relationships of power systems are used to obtain an objective function for minimizing the cost of installation. The constraints include the limits on dependent variables (reactive powers of the generators, load bus voltages) and control variables (generator voltages, tap positions, switchable reactive power sources). A parametric linear programming technique based on active set analysis is proposed to solve the reactive power allocation problem.

Modeling and Control Design for Wind Energy Power Conversion Scheme using Self-Excited Induction Generator

Abstract: This paper deals with dynamic modeling of self-excited induction generator connected to a supply system through a de link (converter-line commutated inverter) and digital control design for regulating the power transfer through the link. Using different sampling rates for the converter and inverter control loops, the proposed design ensures reduced reactive power burden on the induction generator. Results of implementation on a laboratory system are given.

Highly Dynamic Four-Quadrant AC Motor Drive with Improved Power Factor and On-Line Optimized Pulse Pattern with PROMC

Abstract: The power factor and the waveforms of the currents of voltage source inverters can be improved essentially when two-pulse inverters are used?one at the line side and the other at the machine side. Both inverters are controlled by similar current vector controllers. The reference value of the stator current can be calculated by field-oriented control or by decoupling, for example. The reference value of the line current is derived from the actual state of the mains and the machine. Furthermore, on-line optimization of the pulse pattern by programmable read-only memory control (PROMC) is used.

Minimization of reactive power under nonsinusoidal conditions

Abstract: The author extends his earlier paper `Considerations on reactive power in nonsinusoidal situations' (see ibid., vol.IM-34, no.3, p.399-404, 1985) to compensation issues. IT is shown that the shunt LC compensator can minimize the reactive power of an RL load only if one of its parameters, L or C is fixed. A method of capacitance calculation is presented and it is shown that the inductance choice affects the harmonic suppression. The complexity of a compensator for the total compensation of reactive power is calculated and a method of synthesizing such a compensator is presented.

Drive system and vehicle for use therewith

Abstract: An electrical drive system is controlled by a microprocessor-based, electronic control unit which is coupled to operator-generated input signals and various feedback signals to individually control the major components of the drive system including a turbine engine, a three-phase alternator, power control units and their respective synchronous AC motors and gearboxes A combat vehicle which utilizes the drive system includes a vehicle bed on which right and left sets of three wheels are mounted on opposite sides of the centerline of the vehicle in driving engagement with their respective gearboxes Each of the wheels includes a hollow hub in which its gearbox and its synchronous AC motor is mounted A torsilastic suspension system supports the wheels on the vehicle bed The turbine engine drives the alternator which comprises a brushless, synchronous device having a variable three-phase power output Each of the power control units first rectifies the three-phase output power, then controls the resulting DC power and finally converts the controlled DC power to variable frequency AC power to independently control the speed and torque of its motor The vehicle turns by electrically slowing the motors on one side of the centerline of the vehicle and electrically speeding up the motors on the other side so that the vehicle turns about the wheels whose motors are electrically slowed (ie regenerative skid steering)

Unity power factor single phase power conditioning

Abstract: This work presents the results of a detailed theoretical and experimental analysis of an elementary switched power conditioning system with unity power factor. The line current stays sinusoidal and in phase with the bus voltage while its amplitude can be varied within a wide range. The introduction of a Penalty Factor (cents/kWh) enabled to define the most cost effective operation in the context of a given resistive load and maximum allowable amplitude of the ripples in the line current.

Optimum impedance system for coupling transceiver to power line carrier network

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 bandpath filtering characteristics adapted to the specific needs of the receiver portion of the transceiver.

Resonant DC-DC converter

Abstract: Disclosed is a resonant DC-DC converter which comprises an inverter for converting DC power into AC power, a rectifier connected to the AC output of the inverter through a resonant transformer for rectifying AC output power of the transformer to obtain DC power to be applied to a load, means for determining respective operation phases of a first, a second, a third and a fourth switching elements constituting the inverter in accordance with set signals indicating a voltage and a current to be supplied to the load, and a phase control circuit for controlling the respective operation phases of the first, second, third and fourth switching elements on the basis of an output signal of the phase determining means in a manner so that the first and second switching elements are alternately turned on with a phase difference of 180 degrees with respect to an operation frequency of the inverter, the third and fourth switching elements are alternately turned on with a phase difference of 180 degrees with respect to the operation frequency of the inverter, while varying a phase difference from turn-on of the first switching element to turn-on of the fourth switching element and a phase difference from turn-on of the second switching element to turn-on of the third switching element to thereby control or feed-back control the DC power to be supplied to the load.

A study of active power filters using quad-series voltage-source PWM converters for harmonic compensation

Abstract: An active power filter using quad-series voltage-source PWM converters is used to suppress ac harmonics by injecting PWM modulated currents to the ac side. In this paper, the calculation circuits for the harmonic currents to be injected, the compensation characteristics, and the capacity of the dc capacitor are discussed. A new control circuit for the dc capacitor voltage is proposed. These discussions focus on transient states and are on the basis of the instantaneous reactive power theory. Finally, a passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the ac side. Some experiments to illustrate the details of the study are shown.

Reactive power compensation device

Abstract: A reactive power compensation device for a system including an AC power source and a load. The device comprises a first detection circuit for detecting reactive power in the load; a first reactive power compensation circuit, having a reactor, a thyristor and a capacitor, the thyristor being controlled based on the detected reactive power in the load; a second detection circuit for detecting total reactive power in the load and the first compensation circuit; a second reactive power compensation circuit having a self-commutated power converter connected in parallel to the load. The second compensation circuit is controlled to minimize the detected total reactive power in the load and the first compensation circuit.

AC motor drive apparatus

Abstract: An AC motor drive apparatus of this invention is constituted by an AC power source (SUP), a first circulating current type cycloconverter (CC-1) having an output terminal coupled to the AC power source, a phase-advanced capacitor (CAP) coupled to an input terminal of the first cycloconverter, a second circulating current type cycloconverter (CC-2) having an input terminal coupled to the phase-advanced capacitor, and an AC motor (M) coupled to an output terminal of the second cycloconverter. The first cycloconverter (CC-1) controls a current (IR, IS, IT) supplied from the AC power source (SUP) to be a sine wave (ea, eb, ec) in the same phase as that of the power source voltage, so that a voltage crest value (Vcap) of the phase-advanced capacitor (CAP) becomes substantially constant. The second cycloconverter (CC-2) supplies a sine wave current (Iu, Iv, Iw) of a variable frequency (0 to several hundred Hz) to the AC motor.

Losses in high-power bipolar transistors

Abstract: The calculation of power losses in high-power bipolar transistors is examined for several of the commonly encountered types of power circuits. The magnitude of switching and conduction losses is dependent on the type of circuit in which they are used, the type of load, switching frequency, and characteristics of the transistor itself. Curves, based on computer simulation and mathematical analysis, are presented to aid in the calculation of these losses. Parameters taken into account are dynamic saturation voltage, load power factor, effect of snubbers, and recovery characteristics of circuit associated diodes.

Surge suppressor for coax cable and AC power lines

Abstract: A voltage surge suppressing apparatus for connecting electronic equipment to AC power and coaxial antenna lines. The surge suppressing apparatus includes two surge suppression circuits, one for the coaxial antenna line and other for the AC power line, both mounted within a single housing.

Low power, leakage current switching circuit

Abstract: A low power switching circuit for delivering electrical power to a load includes a rectifier network connected between the hot leg of the AC utility supply and the earth ground of the utility supply. A neon lamp interposed in the rectifier supply limits the current drawn through the rectifier to less than the 500 μa code limit for current flow to ground. A high sensitivity, dual coil, bistable relay is connected between the hot leg of the AC supply and the load, which is connected to the neutral leg of the same supply. A capacitor network is connected to the DC output of the rectifier to store sufficient power to operate the relay, and a transistor switching network is connected to deliver the power from the capacitor network to the relay upon receipt of a trigger signal. A "smart" switch such as an area occupancy sensor may be connected to the transistor switching network to provide the trigger signal to cause the relay to switch AC power to the load.

High voltage power supply particularly adapted for a twt

Abstract: A power supply for helix and collector electrodes of a traveling wave tube is driven by an AC power source having a frequency of at least 500 KHz. The helix supply includes plural, stacked voltage doubler AC to DC modules responsive to the 500 KHz source. The collector supply includes plural AC to DC modules, each having a diode full wave rectifier bridge, connected in stacked relation. Each of the modules includes a transformer with a ferrite, toroidal core dimensioned so that it is not driven into saturation by the 500 KHz source. Each module also includes inexpensive, signal switching diodes having a recovery time of approximately 4 nanoseconds. The ratio of the collector to helix DC voltages is maintained constant by threading a common lead through the apertures of the toroidal cores of the helix and collector modules. A separate common lead threaded through the apertures of the toroidal cores in the collector modules is connected directly to the 500 KHz power source. A feedback circuit responsive to the helix-cathode voltage of the TWT controls the helix power supply voltage precisely.

Cost-Constrained Power Factor Optimization with Source Harmonics Using LC Compensators

Abstract: A method is presented for finding the optimum LC combination for power factor compensation at linear loads in the presence of voltage source harmonics while the total voltamperes of the compensator capacitor and reactor is constrained. The end product is displayed in graph form where for any given compensator voltampere rating or cost, the maximum possible power factor and corresponding LC combination can be found. Examples are included showing that the cost of such an LC compensator may be less than that of a purely capacitive optimum compensator achieving the same power factor.

Optimum Shunt Capacitor for Power Factor Correction at Busses with Lightly Distorted Voltage

Abstract: The goal of this paper is to determine the effect of time variation of system impedances and voltage harmonics on the value of optimum capacitor for power factor correction at busses with nonsinusoidal voltage. Two types of 24 hours time-variation of voltage harmonices and Thevenin impedance are assumed. The equivalent load impedance is also considered time variable and assumed to contain a large proportion of induction motors. The daily energy losses are computed and graphed in function of the shunt capacitance used for power factor correction. The results of this study indicate that in order to avoid resonances and to find the optimum capacitor the time variation of harmonics and system impedances must be known as precise as possible.