Abstract: A generalized theory of instantaneous reactive power for three-phase power systems is proposed in this paper. This theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal, balanced or unbalanced, three-phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. A three-phase harmonic distorted power system with zero-sequence components is then used as an example to show reactive power measurement and compensation using the proposed theory.

Abstract: To achieve a better voltage-VAr control in the electric power transmission system, different facilities are used. Generators are equipped with automatic voltage regulators to cope with sudden and random voltage changes caused by natural load fluctuations or failures. Other devices like capacitors, inductors, transformers with on load tap changers are installed on the network. Faced with the evolution of the network and operating conditions, electricity utilities are more and more interested in overall and coherent control systems, automatic or not. These systems are expected to co-ordinate the actions of local facilities for a better voltage control (more stable and faster reaction) inside different areas of the network in case of greater voltage and VAr variations. They afford a better use of existing reactive resources. Also, installation of new devices can be avoided allowing economy of investment. With this in mind, EDF has designed a system called Co-ordinated Secondary Voltage Control (CSVC). It is an automatic closed loop system with a dynamic of a few minutes. It takes into account the network conditions (topology, loads), the voltage limits and the generator operating constraints. This paper presents improvements which allow the CSVC to control the voltage profile and different kinds of reactive means on a large-scale power system, Furthermore, this paper presents a solution to spread out investment costs over several years, considering a deployment gradually extended.

Abstract: This article presents voltage sag measurements and their analysis, which were performed in two industries for a period of 17 months. Voltage sags are caused by faults in the utility's transmission system, since both industries are fed by a 115 kV line, but from different circuits. Even faults in 230 or 400 kV lines are felt by the industries' entrance substation as voltage sags. These events cause interruptions in important continuous processes because the adjustable speed drives (ASDs) involved are sensitive to voltage variations. It is shown that, with the measurements made, ASDs are more sensitive to voltage sags than data processing equipment, according to the tolerance curve shown in C51. Also identified were ASDs that tripped more frequently with voltage sags. This allowed the selection of problem areas in both industrial plants, requiring a more detailed analysis in order to select some type of power line conditioning equipment.

Abstract: A voltage control apparatus which is robust against disturbances such as variations in solar radiation amount around a solar cell, and has quick response, has a voltage detection unit (4) for detecting the voltage value of a battery power supply (1), a power conversion unit (2) for performing predetermined conversion of electric power supplied from the battery power supply, and supplying the converted electric power to a load or a commercial AC system (3), an output setting unit (5) for setting the output value of the power conversion unit on the basis of the voltage detection value, and a control unit (6) for controlling the power conversion unit on the basis of the output setting value. The output setting unit is constituted by a target voltage setting unit (51) for setting the target voltage value of the battery power supply, and an output calculation unit (52) for calculating the output setting value on the basis of the deviation between the voltage detection value and the target voltage value.

Abstract: In high power factor AC-to-DC applications, boost power converters operating on the boundary of continuous mode and discontinuous mode switch with variable frequency and draw high peak input currents. A method is presented to parallel two or more of these power converters to reduce the high peak input currents. Each power converter continues to operate on the boundary of continuous mode and discontinuous mode and maintains the benefits of zero-voltage switching.

Abstract: In this paper a new configuration for an active line conditioner is proposed to correct dynamically voltage unbalances in a three-phase AC system. In the proposed system it is shown that the injection of a correction voltage V/sub inj/ in one phase is sufficient to nullify the negative sequence voltage component in the incoming three phase supply. The resulting three phase voltages at the load terminals are essentially positive sequence voltages and hence are balanced. It is further shown that the kVA requirement of the proposed active line conditioner is small, typically 3% for a ten percentage unbalance in the input supply. The dynamic cancellation of the negative sequence voltage component by the proposed scheme drastically improves the performance of induction motor loads connected to a weak AC system. A thorough analysis of the scheme along with the suitable design guides are presented. Finally selected experimental results on a laboratory prototype active line conditioner are detailed.

Abstract: Power system reactive power planning requires the computation of the reactive power margin from the point of voltage collapse in the steady-state in order to quantify the adequacy of the level of installed reactive power plant. This reactive margin is the difference between the maximum reactive load distributed across selected power system nodes and the reactive load at the planned system operating point. The margin can be estimated by applying an optimisation method using the total reactive load as the objective, with the load flow equations as equality constraints, whilst including system limits such as generator reactive capability limits as inequality constraints. This paper describes a full AC formulation of the optimisation problem. It is solved using an interior point implementation of the Newton method developed for the optimal power flow. This avoids potential difficulties in identifying the binding inequality constraints.

Abstract: An SRAM memory cell (10) is provided a boosted voltage by a charge pump (56) to reduce the soft error rate within the SRAM (10) and to improve bit cell stability. A voltage regulator (58) is coupled to the charge pump (56) to regulate the operation of the charge pump (56) and its outputted boosted voltage. The voltage regulator (58) regulates the boosted voltage over three operating states: low supply voltage, steady state operation, and burn-in.

Abstract: In this paper, design considerations for twelve-pulse diode rectifier systems operating under utility voltage unbalance and pre-existing harmonic voltage distortion are discussed. For a twelve-pulse diode rectifier system connected in parallel to feed a common DC link via an interphase transformer, it is shown that a small amount of impedance mismatch, utility voltage unbalance or pre-existing voltage distortion drastically affects the current sharing capability of the rectifier bridges. This, in turn, generates additional uncharacteristic and characteristic harmonics thereby increasing the THD. In order to mitigate these effects and ensure proper operation of diode rectifiers, specially designed line reactors termed harmonic blocking reactors (HBRs) are introduced. Analysis and design procedures for HBRs are discussed. Simulation results illustrate improved performance. Experimental results from a laboratory prototype system show close agreement with theory.

Abstract: Power supplied from a battery power supply to a load through a power conversion unit is maximized with a relatively simple arrangement and a small processing load. In addition, an output command value for controlling the power conversion unit is detected, a set voltage for which the output command value is maximized is calculated with reference to a past or present set voltage, as needed, and set as the next set voltage such that the maximum output is supplied to the load without any erroneous operation in the case of variation in solar radiation. In this case, a plurality of voltages are sequentially set for a relatively short period. Output command values for the respective set voltages are fetched while setting the same voltage at the start and end of the operation. A variation in output command value caused by the fetching difference for the same set voltage is detected. The output command value for calculating the next set voltage is corrected in accordance with this variation.

Abstract: The APLC (active power line conditioner) is a type of active power filter that compensates voltage waveform distortion caused by harmonics in power systems. This paper presents a new approach, based on optimization theory, to investigate the determination of locations and sizes of APLCs. The objective is to minimize the new APLC injection currents and the voltage distortion while satisfying the harmonic standard. The test results for an 18-bus distribution system show the applicability of the proposed method.

Abstract: This paper presents a new approach using fuzzy set theory for voltage and reactive power control of power systems. The purpose is to enhance voltage security of an electric power system. The violation bus voltage and the controlling variables are translated into fuzzy set notations to formulate the relation between voltage violation level and controlling ability of controlling devices. A feasible solution set is first attained using the minimum operation of fuzzy sets, then the optimal solution is quickly determined employing the maximum operation. A modified IEEE 30-bus test system is used to demonstrate the application of the proposed approach. Simulation results show that the approach is efficient and has good flexibility and adaptability for voltage-reactive power control.

Abstract: A circuit for determining and reporting the energy consumed by an electronic device having a microprocessor and power supply lines for supplying power to the device is disclosed. The circuit comprises a voltage divider connected for sensing the voltage across the power supply lines and generating a voltage signal indicative of the sensed voltage. A current sense resistor is connected in series with a power supply line for sensing the current passing through the power supply lines and generating a current signal indicative of the sensed current. An analog multiplier is connected for receiving and computing the product of the voltage and current signals, and for generating a power signal indicative of the product of the voltage and current signals, the power signal being indicative of the power consumed by the device. A proportional voltage-to-frequency converter is connected for receiving the power signal and for generating primary signal pulses at a frequency proportional to the voltage level of the power signal, each of which pulses is indicative that a predetermined quantity of energy has been consumed by the device. An opto-coupler, connected to the converter, is responsive to generation of the primary signal pulse for reporting to the microprocessor a secondary signal pulse indicating that a predetermined quantity of energy has been consumed by the device.

Abstract: This paper describes recent work on the theoretical and algorithmic enhancements of the MIT method for power system steady-state voltage monitoring and control. Under the conditions that no dynamic voltage problems are present, the method is intended primarily: to monitor steady-state voltage and reactive power conditions; to identify potential problem situations; and to make decisions regarding their severity. The developed method utilizes various reactive power resources on the power system to remedy voltage violations. The corrective actions suggested are either in the order assigned by the operator or according to efficiency criteria, determined by this algorithm. The corrective actions ensure minimum possible voltage deviations from a given desired voltage profile. Corrective actions are considered to be optimal in this sense. The method has the unique feature of identifying minimum number of most effective corrective actions so that voltages are maintained within the given limits. The method does not solve the exact load flow equations, and therefore it avoids inversion of a full system size matrix. Reactive power scheduling is computed so that the resulting load voltages, are within pre-specified target values. The computational time does not increase significantly with increase of power system size, since no inversion of a system size matrix is needed. Numerical tests on a small and large scale electric power system (IEEE 39 and New England 1726) are presented and analyzed.

Abstract: A voltage source type power converting apparatus having voltage source type power converter units and phase-shifting transformers. The transformers have either a common multiple-phase primary winding or a group of parallel connected multiple-phase primary windings, either of which being connected in parallel or series to a multiple-phase AC system. The transformer further include a group of multiple-phase secondary windings with phase differences with respect to each other and which are connected to voltage source type power converter units. The voltage source type power converter units are operated with the phase differences. Accordingly, the construction of the multiplexing phase-shifting transformer is simple, and fundamental electric variables can be controlled by a simple phase controlling operation. In addition, a higher harmonic defect of the AC system can be reduced, and the DC voltage can be easily raised.

Abstract: Regulation of load voltage in single-phase applications is becoming an important issue for critical loads. This paper proposes a method to regulate a single-phase AC source by using a series connected auxiliary voltage source. A voltage source inverter, connected in series with the AC supply through a transformer, is used to compensate the input voltage variations to achieve a regulated load voltage. Input power factor improvement can also be obtained, when operating with reactive load, by phase-shifting the compensating voltage with respect to the input voltage. The operation of the compensator in all four quadrants allows the compensation of any voltage drop, and not only the reactive voltage drop within the same path. The total kVA rating for the system is a fraction of the load total power, and is determined by the maximum allowable line voltage variations. The use of a series connection associated with a high-performance modulation technique results in a high-quality output with a small size filter. This paper includes a description of the proposed method, implementation principles, design equations and a design example. Steady-state performance features are investigated. Simulated and experimental results confirm the concept and feasibility of the proposed system.

Abstract: A generalized theory of instantaneous reactive power for three-phase power systems is proposed in this paper. This theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal, balanced or unbalanced, three- phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. With this new reactive power theory, it is very easy to calculate and decompose all components, such as fundamental active/reactive power and current, harmonic current, etc. Reactive power and/or harmonic compensation systems for a three-phase distorted power system with and without zero-sequence components in the source voltage and/or load current are then used as examples to demonstrate the measurement, decomposition, and compensation of reactive power and harmonics.

Abstract: An amplifying circuit according to the present invention has an amplifying unit for amplifying an input signal to produce an amplified signal, a battery for generating a constant voltage (a first voltage), a step-up converter for always generating an increased voltage (or a second voltage) by increasing the constant voltage, and a selection changing circuit for supplying the increased voltage to the amplifying unit as an electric source voltage when a level of the amplified signal is higher than the constant voltage and supplying the constant voltage to the amplifying unit as the electric source voltage when a level of the amplified signal is lower than the constant voltage. Therefore, because the electric source voltage supplied to the amplifying unit is changed according to the level of the amplified signal, a loss occurring in an electric power consumed in the amplifying unit can be reduced. Also, because the increased voltage is always generated by the step-up converter as compared with a prior art in which any increased voltage is not always generated, even though the increased signal is a high frequency signal, the electric source voltage can reliably change with the level of the amplified signal, so that any distortion of the amplified signal can be prevented.

Abstract: An object is to provide a power supply technique which is optimum when the source voltage range of a signal driver is different from that of a scan driver. A power supply unit supplies a source voltage group of V11, VC1 and V12 of the same polarity having a narrower source voltage range to the signal driver and another source voltage group of V10, VC2 and V15 of the same polarity having a wider source voltage range to the scan driver. The center voltages VC1 and VC2 within these source voltage ranges are equal to each other. The power supply unit has a means for adjusting the source voltages. A control signal and other signals from a control unit are transformed in level by a potential transforming unit. When it is desired to accomplish the display-off function, the outputs of the signal and scan drivers are set to be equal to VC level. Thus, the adjustment of liquid-crystal driving voltages can be accomplished by a simplified adjustment device while maintaining the accurate ratio of voltage division.

Abstract: It has been observed that the presence of DC bias currents/fluxes in power transformers generates harmonic currents and voltages with an associated increase in reactive power (kVAr) demand resulting in a voltage drop. Such DC biases can occur: in transformers near high-voltage DC (HVDC) terminals; due to imperfect or half-controlled rectification resulting in DC, even and odd harmonics; because of geomagnetically induced currents; as a consequence of nuclear explosions changing the Earth's magnetic field; and due to rectifiers working in a normal (e.g., half-wave) mode. The actual network conditions causing such kVAr demand and its suppression, canceling, or mitigation are not very well understood, particularly for transformers with three legs. This article explains for the first time this kVAr demand and its suppression based on experimental data. Tests were performed for three-phase power transformers with three legs, with or without the influence of a magnetic tank.

Abstract: A power-generating voltage outputted from a vehicle synchronous power generator is adjusted to a first voltage for charging a battery under the control of a field current. Further, a leading phase current that leads a phase voltage is supplied to each of multiple armature windings and the field current is supplied to the field winding, whereby the power-generating voltage can be adjusted to a second voltage higher than the first power-generating voltage. Owing to the above construction, a voltage higher than the normal voltage can be generated by supplying each leading phase current from the vehicle synchronous power generator; hence power can be supplied to a high-voltage load based on the generated high voltage.

Abstract: A control system for an automatic shutdown of a power supply constructed with a switching mode power supply (SMPS) receiving an AC voltage and converting the AC voltage into a DC voltage; a main board receiving the DC voltage output from the switching mode power supply; and a control circuit controlling and maintaining the supply of power from the switching mode power supply to the main board until a shutdown process is performed when power is turned OFF, wherein the control system enables the automatic shutdown of a power supply while preventing a file or a system from being damaged by automatically cutting off power after performing the shutdown process by the power control system even though the power switch is turned OFF due to the carelessness of the user or an external factor.

Abstract: An integrated power supply device and a power supplying method for controlling power supply to a computer system having a main computer body and a monitor. The integrated power supply device includes a wake-up sensor for generating a wake-up signal when the computer system is in use; a power supply controller responsive to said wake-up sensor to control the power supply to the monitor and the main computer body; a power input unit connected to an external power source to transform an alternating current voltage received from the external power source into a constant direct current voltage; a monitor power supply unit responsive to the power supply controller to transform the constant direct current voltage output from the power input unit into a first predetermined voltage and to supply the first predetermined voltage to the monitor for operation; a main body power supply unit responsive to the power supply controller to transform the constant direct current voltage output from the power input unit into a second predetermined voltage and to supply the second predetermined voltage to the main computer body for operation; and a subsidiary power supply unit coupled to the power input unit to transform the constant direct current voltage output from the power input unit into a third predetermined voltage and to supply the third predetermined voltage to the power supply controller for controlling the power supply to the monitor and the main computer body to minimize power consumption.

Abstract: A power generator using a piezoelectric element is provided which generates electric power at a high efficiency. It has been determined that the efficiency of power generation varies as a function of the ratio of an initial unloaded value of the power generator to a prescribed voltage of the input of an electric power system. A high power generation efficiency can be obtained when the voltage ratio is in the range of approximately two to twenty. In particular, when the voltage ratio is in the range of approximately four to six, a maximum power generation efficiency can be obtained. The invention provides a small-sized, high performance power generator which can be used in practice in portable electronic devices or the like.

Abstract: The superconducting LHC accelerator requires high currents (12.5kA) and relatively low voltage (~10V) for its magnets. The need to install the power converters underground is the driving force for reduced volume and high efficiency of the power converters. Moreover, the machine will require a very high level of performance from the power converters, particularly in terms of DC stability and dynamic response. To meet these requirements switch-mode techniques will be used. This paper gives a survey of current switch-mode converter topologies for high DC current output. The presentation is primarily focused on the various methods for low-loss switching in DC power converters operating with high switching frequency (20 50 kHz). A modular concept is being studied, using several current sources in parallel, to adapt to the various circuits and also provide redundancy.

Abstract: PROBLEM TO BE SOLVED: To minimize the drop of power factor to be caused by a load and the effect to be caused by higher harmonics on a system side, and also to make it possible for a system to be automatically changed over to a self-supporting operation if a system power source is in trouble. SOLUTION: The system voltage and current of a system side are fed back from a load 5 to a power conditioner 21, to control power factor and the suppression of higher harmonics. Also, the abnormality of a system power source 4 is detected, based on the voltage of the system. If there is any abnormality, an electromagnetic contactor 22 is automatically opened, while a relay 14 is automatically closed to change over to an operation supported by non-utility power supply. When the system power source 4 restores its normal condition, the electromagnetic contactor 22 is automatically closed and the relay 14 is opened to change over to an interconnected operation.

Abstract: Voltage sags are more and more being considered as a severe power quality problem. However, stochastic prediction tools for voltage sags are rare. The few methods that have been proposed assume a rectangular voltage sag. This assumption is no longer true in many industrial power systems with large induction motor loads. A simple induction motor model has been developed to describe the extra current taken by the motor during the re-acceleration after a short circuit. This model has been incorporated in the method for reliability/power quality analysis of industrial power systems, as described in a previous paper. Simulations are presented to show the influence of the post-fault voltage sag due to motor re-acceleration on the reliability/power quality of the supply. The simulations result in a table with the expected number of interruptions of plant operation for different load sensitivities.

Abstract: A static CMOS component is operated in a power-down state at the lowest possible voltage that maintains register and internal state levels of the component. A method of operating the static CMOS component includes the steps of selectively supplying a reference voltage at two voltage levels including an operating voltage level and a low reference voltage level, detecting an idle state of the static CMOS component and controlling the selectively supplying step to supply the low reference voltage in response to detection of the idle state. The low reference voltage level is substantially lower than the operating voltage level but is sufficient in voltage amplitude to maintain register and internal state levels of the static CMOS component. An electronic system which performs this method includes a programmable power supply source which selectively supplies an operating voltage and a low voltage which is substantially lower than the operating voltage. The system further includes a static CMOS component which is connected to the programmable power supply source by a power line carrying the selected alternative voltage. The system also includes a system controller connected to the programmable power supply by a power control line which selects the voltage applied to the static CMOS component and by a status line indicative of component status.