Showing papers on "Voltage regulation published in 1990"

Voltage stability condition in a power transmission system calculated by sensitivity methods

Abstract: A new method for determining the voltage stability condition in a power system is presented. The method is based on sensitivity techniques, taking into account the limits on reactive power generation capacities. A distance to voltage collapse in terms of MVAr is defined as a measure of system security. Results from calculations on a 480-bus network with 140 generators are presented. The method can be efficiently used for reactive power security evaluation in both system planning and operation. >

Power supply and oscillator for a computer system providing automatic selection of supply voltage and frequency.

Abstract: Disclosed is a power system for use with a computer, the power system having incorporated in its circuitry for automatically varying the supply voltage output to the computer system based upon the magnitude of the current being supplied to the computer by the power system. Also included in the computer system is a variable frequency clock circuit, the frequency of which changes based upon the supply voltage produced by the power system. This permits, during computer system operation where low voltage and low clock speeds will be sufficient to provide the performance needed, achievement of a power saving since both the voltage and frequency at which the system operates is reduced, thereby markedly reducing the power consumption.

On the existence and uniqueness of load flow solution for radial distribution power networks

Abstract: On the basis of voltage level, an electric power system can be viewed as consisting of a generation system, a transmission system, and a distribution system. The steady-state operation of a power system requires that the power supply, transmission losses, and load demand be balanced, as described by the load flow equations. The configuration of a transmission network is that of a loop while the configuration of a distributed network is radial. It is well recognized that the number of load flow solutions for transmission networks, if they exist, are multiple. In contrast, it is shown here that a load flow solution with feasible voltage magnitude for radial distribution networks always exists and is unique. These results demonstrate the weak ability of radial distribution networks to meet load demands in the sense that different patterns of load demand require different power supply from the substation. >

Power supply with improved power factor correction

Abstract: A regulated voltage converter circuit includes a storage inductor and a controlled semiconductor switch connected in series circuit to a pair of input terminals that supply a full wave rectified voltage of a sinusoidal 50 Hz AC input voltage. A power factor amplifier receives a divided part of the rectified voltage and produces an output control voltage V M of a predetermined waveform (Fig. 2c). A comparison circuit compares the control voltage V M with a ramp voltage that is proportional to the current flowing through the semiconductor switch. The comparison circuit supplies PWM pulses to a control electrode of the semiconductor switch so as to regulate the output voltage of the converter circuit. The control voltage (V M ) waveform is chosen so as to produce near unity power factor correction at the input of the converter circuit.

Self powering technique for integrated switched mode power supply

Abstract: A regulator circuit is connected to a transformer. The transformer has a primary winding connected to a rectified D.C. voltage signal and has a feedback winding. A feedback capacitor is coupled across the feedback winding of the capacitor. The regulator circuit includes a high voltage switching transistor, a pulse width modulator which controls the high voltage switching transistor and a high voltage power up transistor. At power up, the high voltage power up transistor connects the single high voltage pin to the feedback capacitor allowing the feedback capacitor to begin charging. When the feedback capacitor has charged past a first threshold voltage the pulse width modulator alternately turns the high voltage switching transistor on and off. When the high voltage switching transistor is turned on, the high voltage pin is connected to ground and current passes through the primary winding of the transformer, and thus current is generated through the feedback winding into the feedback capacitor. Additionally, when the high voltage power up transistor is on, the gate of the high voltage power up transistor is connected to ground turning the high voltage power up transistor off. Once the feedback capacitor has been charged to a second threshold voltage a transistor connects the gate of the high voltage power up transistor to ground thus permanently switching the high voltage power up transistor off.

Photovoltaic source switching regulator with maximum power transfer efficiency without voltage change

Abstract: For matching the electrical impedance of a photovoltaic power source and a load, a switching regulator circuit has properties especially suited to the conversion of photovoltaic power to electric power. The circuit regulates the source voltage for maximum power output and supplies a load voltage equal to the regulated source voltage. The circuit comprises two branches: one in which a switching transistor (38), a diode (40), and filter components (30) and (42) provide a positive voltage; and the other in which similar components (22, 32, 24, and 44) in a different configuration, provide a negative voltage. The load voltage is the sum of these and is equal to the input voltage. Since the source voltage is substantially constant, the switching regulator in effect converts the photovoltaic power source to a constant-voltage source. The circuit provides improved performance and thus enhances the utility of photovoltaic power sources.

Microprocessor based harmonic elimination in chopper type AC voltage regulators

Abstract: A control strategy for firing instances in pulse-width-modulated (PWM) AC voltage regulators is presented. In this type of regulator, output voltage is controlled by varying the on/off time ratios of a series-controlled switch. Using a microprocessor as a controller makes it possible to vary firing instances at will according to a predetermined timing regime. One of these regimes, proposed here, involves adjusting firing instances so that selected dominant lower-order harmonics can be eliminated. This in turn leads to improved system power factor and efficiency. The theoretical principles used in evaluating firing instances are described, and experimental results verifying the analysis are presented. >

High voltage generating circuit for a semiconductor memory circuit

Abstract: There is provided a high voltage generating circuit including a circuit for sensing a voltage level of a high voltage for erasing and programming operations, a circuit for generating a given reference voltage, a circuit for comparing the sensed high voltage with the reference voltage, a circuit for applying or blocking a pump signal to a high voltage pump circuit according to the compared signal, a circuit for raising the voltage up to a given level under the control of the pump signal, and an EEPROM fuse circuit connected to the circuit for sensing the voltage level of the high voltage or the circuit for generating the given reference voltage and having stored data, whereby the voltage level of the high voltage finally output may be properly maintained and controlled according to the state of the stored data.

Inductor shunt, output voltage regulation system for a power supply

Abstract: High efficiency, post regulation of auxiliary outputs in multiple output-power supplies is provided by connecting a regulating switching device in parallel with a filter inductor connected in the current path from the rectifiers to the output terminal. For minimum output power for that auxiliary output, the switching device is held off at all times. When increased power is required, the switching device is turned on for a short period during each cycle of the inductor voltage. The switching system may be configured to conduct current from the output end of the inductor to the input end of the inductor or vice versa or either one selectively, in accordance with the particular regulation scheme chosen. Efficiency is maximized since current flows in the switching device for only a small portion of the cycle of the inductor voltage.

Analysis of the dynamic and steady-state performance of Cockcroft-Walton cascade rectifiers

Abstract: A detailed analysis, based on digital simulation, of the Cockcroft-Walton rectifier, including transient and steady-state voltages and currents on any component, was performed. It is shown that the numerical solution of the system may be effectively implemented by coupling the modified nodal approach formulation of the circuit equations with companion models and piecewise linear approximations of nonlinear elements. Good agreement between simulated and experimental results confirmed the validity of the proposed model/program. In the transient analysis it was shown that the start-up time of a Cockcroft-Walton rectifier is directly related to the number of stages, increasing as the number of stages increases. The output voltage regulation characteristics are worse for a larger number of stages. A study of the influence of an inductance in series with the voltage source showed that it may be chosen in such a way as to increase the output average voltage and improve its regulation. The analysis of this rectifier fed by a square-wave voltage source showed that, in this case, the output voltage regulation is improved. However, the output voltage overshoots and input current peaks are increased. >

A voltage reduction technique for battery-operated systems

Abstract: Two techniques for voltage reduction are presented, both of which can significantly reduce the power consumption of digital CMOS circuits. The fixed reduction of voltage is applicable to small systems with a low initial consumption, however, the optimum voltage is not reached and the correct operation of the circuit is not guaranteed. The self-adjusted reduction of voltage is adapted to bigger digital systems. The correct operation of the digital circuit is guaranteed, and the supply voltage is near the optimum for the speed requirements. This technique is more versatile, accurate, and reliable than the fixed one. >

Implementation of conservation voltage reduction at Commonwealth Edison

Abstract: The implementation of a conservation voltage reduction program is described. Such a program involves the calibration of substation voltage-regulating equipment so that distribution system voltages are maintained at as low a level as possible within the standard acceptable range. Initial distribution system voltmeter data were used to estimate potential voltage reductions. Program results show that an average reduction of 1.6 V was achieved. Comparison of this result with the initial estimate indicates that the feasibility of additional voltage reductions depends on the definition of acceptable service quality. >

Regulated chopper and inverter with shared switches

Abstract: An improved inverter AC power supply includes a chopper providing a DC voltage from an AC source voltage and an inverter providing from the DC voltage a high frequency AC voltage to a load. The chopper incorporates a pair of first and second switching elements operating to turn on and off for obtaining a periodically interrupted AC voltage which is rectified and smoothened to provide the DC voltage to the inverter. The inverter is arranged to share the first and second switching elements in common to the chopper, and operates to drive the same switching elements for switching the DC voltage in order to provide a desired AC voltage to the load. The power supply is provided with an input power sensor monitoring an input power supplied to the chopper and an output power sensor monitoring an output power from the inverter to the load. A power controller is included for varying at least one of a switching frequency and a duty ratio for the first and second switching elements in accordance with the monitored chopper input power and inverter output power for equalizing the input and output powers.

Battery pack including electronic power saver

Abstract: A housing (11) of a battery pack (10) contains in addition to standard power cell elements (14-16) a voltage converter (75). The voltage converter (75) is interposed between the power cell elements (14-16) and external output contacts (29, 30, 100) of the housing (11). The voltage converter (75) regulates the output voltage applied to the output contacts (29, 30, 100) of the battery pack (10), such that the supply voltage of the battery pack (10) remains at a predetermined value which is independent of the voltage supplied by the power cell elements (14-16) to the voltage converter (75) and does not vary over the discharge cycle of the power cell elements (14-16). Excess battery voltage available particularly during the initial portion of the discharge cycle of the power cell elements (14 - 16) is efficiently converted to the predetermined output voltage value which reduces the overall current delivered by the power cells (14-16) to extend the useful life of the battery pack (10) between charges.

Single phase ac power conversion apparatus

Abstract: A power conversion apparatus (20) circuit includes pairs of rectifying devices (48,49) connected together at a first node, a pair of capacitors (50, 51) connected together at a second node, and pairs of controllable switching devices (53,54) connected together at a third node, each of the pairs being connected in parallel by DC bus lines (58,59). The AC power source (21) is connected between the first and second nodes and the output voltage to a load (22) is provided between the first and third nodes. The switching devices (53,54) are controlled to switch on and off at proper times to provide a controllable output voltage to the load (22) which is at the same frequency as the input voltage and which may be controlled from zero to substantially twice the peak-to-peak input voltage. The output voltage waveform provided to the load can be filtered to provide a substantially sinusoidal waveform to the load. The power conversion apparatus (20) can also function as an uninterruptible power system by connecting an energy storage device, such as a large capacitor (140 ) or a battery (146) across the DC bus lines (58,59), and by controlling the charging of the energy storage device when power is available for the source and discharging the storage device when the power source fails.

Identifying electrically weak and strong segments of a power system from a voltage stability viewpoint

Abstract: Voltage instability leading to collapse appears to be due to the inability of networks to meet a demand for reactive power at certain critical (or weak) buses. Practical control algorithms to prevent voltage collapse should identify the critical buses in the network and maintain control on voltages at these buses in particular. Two methods are proposed for identifying the weak buses and segments in power transmission networks. Both methods employ a technique presented earlier for determining the static voltage stability limit in multimachine power systems. The first method is based on the relative change in the bus voltages going from an initial operating state to the voltage stability limit. The second method is based on the sensitivity parameters computed at the voltage stability limit.

Rechargeable back-up battery system including a number of battery cells having float voltage exceeding maximum load voltage

Abstract: A back-up battery system for a switching equipment load in a telephone central office wherein the back-up battery system includes one or more rechargeable batteries having cells floated at a given float voltage and of a number such that when the batteries are switched in circuit across the load, the voltage of the batteries exceeds a minimum load voltage for a preselected period, and further being of a number such that the float voltage of the batteries exceeds a maximum load voltage.

High frequency quasi-resonant DC voltage notching inverter for AC motor drives

Abstract: A high-frequency quasi-resonant DC voltage notching inverter derived from a resonant DC link inverter is discussed. The quasi-resonant link circuit provides a DC voltage with resonant notches to the inverter such that inverter switches can switch at zero voltage crossing. Compared to resonant DC link inverters, the size of passive components is reduced. Compared to traditional pulse-width modulation (PWM) inverters, the efficiency and performance are largely improved because high-frequency switching occurs at zero voltage crossing. The resonant voltage notches can be created at any instant, which permits the inverter to operate at standard or optimized PWM control. A least current error square method is proposed to incorporate the quasi-resonant DC voltage notching inverter, resulting in minimum output current ripples. For regenerative-type AC drive operation, a bidirectional current initialization is included in the circuit. The complete system was simulated using PC-SIMNON and fabricated as a laboratory prototype. >

Zero-voltage resonant transition switching power converter

Abstract: A single-ended DC-to-DC power converter which is operative at very high switching frequencies with zero-voltage resonant transition switching. A single magnetic element functions as both a storage inductor and a transformer. A charging capacitor is switched to induce a reversal current through the inductor for providing the zero-voltage switching function. Control to output characteristics are identical to those of conventional buck and buck-boost converters. The invention provides efficient, high-frequency operation and isolation of the output from the input power source with minimal component volume. The control system is adaptable to constant frequency pulse width modulation for voltage regulation.

New challenge: Voltage stability

Abstract: Line and transformer thermal limits have become less restrictive as our networks have become more dense. Static VAR systems (SVSs) and excitation stabilizers have raised transfer limits in stability limited systems. The resulting transmission capacity is being used to ship economy purchases among neighbors, and to support new generation remote from load centers. Today, the average transmission line is loaded more heavily than ever before, and this has given rise to a new problem, voltage instability. The author discusses the problem of voltage instability. Techniques to improve voltage stability are presented.

Steady-state modeling, analysis, and performance of transistor-controlled AC power conditioning systems

Abstract: Steady-state modeling, analysis, and solution of transistor-controlled systems are developed and experimentally verified over a wide range of operation. General features of the system performance and the effects of the chopping frequency on the performance parameters and harmonic generation are thoroughly investigated. Over most of the control range, and for chopping frequencies in the order of several hundred hertz and higher, it is demonstrated that the harmonic contents of the load current are almost negligible, providing highly desired operating conditions for many applications where the fundamental current is the only useful component. >

Controllable power distribution system

Abstract: A user operable power distribution system that is suitable for supplying switched power to an individual workstation, or to an entire office, is expandable to accommodate additional loads. The system includes a user command device, such as a touch panel, for supplying low voltage command signals and a connection device, which responds to the low voltage command signal to interconnect a load with a supply voltage, such as an AC power outlet. The connection device further responds to the low voltage input command signal by producing a low voltage output command signal which may be applied to another connection device to cause that particular connection device to connect another load with a source of supply voltage. In this manner, the connection devices may be ganged in an indefinite number.

Semiconductor memory operating with low supply voltage

Abstract: The present invention is intended to operate a semiconductor device at high speed with low voltage. A circuit configuration is used in which the transfer impedance between a common I/O line and a data line is changed depending on whether information is to be read or written. A current/voltage converter is provided which includes a MISFET different in conduction type to a select MISFET. Thus, the speed of reading information is increased. An intermediate voltage generator having high driving capability is provided. Thus, the circuit has sufficient driving capability for an LSI having large load capacitance. A voltage converter is provided which converts a data line supply voltage or word line supply voltage to a higher voltage. Therefore, stabilized signal transmission is ensured.

Uninterruptible power supply with dual level voltage input

Abstract: An uninterruptible power supply is disclosed having an inverter that operates on either high voltage d.c. supplied by a line-powered power supply or on low voltage d.c. batteries. With line power, the inverter operates as an H-bridge inverter. With battery power, the battery voltage is applied to a smaller portion of the inverter's transformer primary. The changeover from line to battery power is determined by when an intermediate voltage tapped from the transformer drops below the battery voltage.

Source voltage control circuit

Abstract: There is provided a source voltage control circuit including a reference voltage generating circuit with a negative feedback circuit, a source voltage level sensing circuit for increasing the internal source voltage when the external voltage exceeds a given voltage, a first differential amplifying circuit for active operation, and a second differential amplifying circuit for stand-by operation, whereby a stable internal source voltage is produced and the slope of the internal source voltage is readily adjusted when the external source voltage exceeds the given value. The first differential amplifying circuit receives the reference voltage and the internal source voltage, controlled by a first control signal and the output of the source voltage level sensing circuit. The second differential amplifying circuit receives the reference voltage and the internal source voltage, controlled by a second control signal.

Electric power system with line drop compensation

Abstract: An electric power system having line drop compensation includes a controllable electric power source 10 having an output for supplying voltage to a power bus 14, a local voltage regulator 12 for monitoring the output voltage of the power source and for producing a control signal representative of a desired nominal output voltage of the power source, and a remote voltage regulator 20 for sensing voltage on the power bus at a point of regulation located away from the power source. The remote voltage regulator produces a pulse width modulated signal having a duty cycle representative of the voltage at the point of regulation. A pulse width to trim bias converter 26 receives the pulse width modulated signal and produces the trim signal having a magnitude representative of the duty cycle of the pulse width modulated signal. This trim signal is combined with the control signal of the local voltage regulator to produce a modified control signal for controlling the output voltage of the power source to produce a predetermined voltage at the point of regulation.

Method of feedback regulating a flyback power converter

Abstract: A method of providing power regulation in power conversion equipment, where power regulation is implemented on the primary side of a transformer used to provide isolation of a power source from the load. The feedback mechanism utilizes current perturbations which are summed with the primary current in the power transformer. These perturbations are transformed with the load current to the primary side of the power transformer and extracted using signal processing means to regenerate a useful signal which is isolated from the load.

High frequency quasi-resonant DC voltage notching scheme of a PWM voltage fed inverter for AC motor drives

Abstract: A circuit for converting a DC voltage to a pulsating DC voltage useful as a power source for operating an AC machine. The circuit includes means for controlling the amplitude of the pulsating DC voltage as the load changes and means for controlling the duration of the pulses comprising the pulsating DC voltage.

Modular power outlet strip

Abstract: A user operable power distribution system that is suitable for supplying switched power to an individual workstation, or to an entire office, includes a user command module, such as a touch panel, for supplying low voltage command signals and a plug strip, which responds to the low voltage command signal to interconnect a load with a supply voltage, such as an AC power outlet An unregulated power supply is provided in the plug strip and supplies the low voltage requirements for the switching circuit in the plug strip In addition, the unregulated low voltage is supplied to the user command module to provide its low voltage power requirements

Resonant converter controlled by variable capacitance devices

Abstract: A new device called the variable capacitance device is proposed, and its application to the output voltage regulation of resonant converters is discussed. The new device has an independent input terminal for controlling its capacitance. The converters used are the well-known Schwarz circuit and the buck-type current-resonant converter with a resonant switch. By applying the devices to the capacitors in LC resonant tanks, the resonant converters can be regulated with the switching frequency fixed. >