Showing papers on "Voltage regulation published in 1993"

Power system voltage stability

Abstract: Voltage stability is a major concern in the planning and operation of electric power systems. This book provides a clear, in-depth explanation of voltage stability, covering both transient and longer-term phenomena and presenting proven solutions to instability problems. The book describes equipment characteristics for transmission, generation, and distribution/load subsystems of a power system, together with methods for the modelling of equipment. Readers will find static and dynamic computer simulation examples for small equivalent power systems and for a very large power system, plus an account of voltage stability associated with HVDC links. They will also get helpful planning and operating guidelines, computer methods for power flow and dynamic simulation, and descriptions of actual voltage instability incidents.

Stabilizing a multimachine power system via decentralized feedback linearizing excitation control

Abstract: A new controller for the generator excitation system is described that uses a combination of feedback linearizing and the observation decoupled state space. This creates a controller that can be realistically implemented using only local measurements, and whose performance is consistent with respect to changes in network configuration, loading and power transfer conditions. The control differs in this respect from linear constant-gain controllers such as power system stabilizers, whose characteristics can vary significantly with changes in operating conditions. The design is well-suited to a multimachine setting, in that it is not based on an infinite-bus approximation. Simulations were performed on a 38-bus reduced modelof the Northeast Power Coordinating Council system and benchmarked against simulations in which automatic voltage regulators with power system stabilizers were substituted in place of the nonlinear controls. >

Transient stability enhancement and voltage regulation of power systems

Abstract: Improvement of the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed. The dynamical model of the system is described. A design strategy for nonlinear controllers is considered, and the design of a nonlinear variable-structure excitation controller is described. Simulation results obtained using the nonlinear excitation controller are given, and a new nonlinear coordinated controller is proposed. Simulation results obtained by using the nonlinear coordinated controller are presented. >

The three-level ZVS-PWM DC-to-DC converter

Abstract: A novel high-frequency DC-to-DC power converter for high voltage and high power is introduced which features zero voltage switching (ZVS), operation at constant frequency, regulation by pulse width modulation (PWM), and low RMS current stress upon power switches. Its greatest attribute, in comparison with the full-bridge (FB-ZVS-PWM) converter, is that the voltage across the switches is half of the input voltage, This property is achieved due to the use of a three-level leg in place of the conventional two-switch leg. Operation, analysis, design procedure and example, and simulation are presented. A prototype operating at 100 kHz, rated at 600 V input voltage, and 1.5 kW output power and 25 A output current has been fabricated and successfully tested in the laboratory. The measured efficiency at full load was 93%. >

Technique for decoupling the energy storage system voltage from the DC link voltage in AC electric drive systems

Abstract: An ac electric drive system includes a bidirectional power semiconductor interface between a battery, or an auxiliary energy storage device, and a power inverter for boosting an input do voltage and for decoupling the dc link voltage from the input dc voltage such that the dc link voltage is substantially independent of the input dc voltage and the parameters of the battery or energy storage device. The input dc voltage is controlled to maximize efficiency along predetermined torque envelopes.

Voltage converting circuit and multiphase clock generating circuit used for driving the same

Abstract: A voltage converting circuit of the charge pump step-up type includes a first circuit means for charging each of first and second capacitors with the voltage of a voltage source at a first timing. A second circuit operates to serially connect the charged first capacitor between a positive electrode of the voltage source and a positive voltage output terminal at a second timing so that a positive voltage which is a double of the voltage source voltage, is supplied from positive voltage output terminal. A third circuit operates to the charged first and second capacitors in series between a ground terminal and a negative voltage output terminal at a third timing so that a negative voltage which is a double of the voltage source voltage, is supplied from the negative voltage output terminal. Since the positive voltage and the negative voltage are generated independently of each other, a voltage variation on one of the positive and negative voltage output terminals caused by an external load causes no voltage variation on the other of the positive and negative voltage output terminals.

High power factor boost rectifier apparatus

Abstract: A power supply for providing a single level dc output voltage, with input power factor correction, from a wide range of ac input voltages commonly available worldwide. The power supply rectifier circuit can be configured as a full wave bridge for high line voltage inputs and as a voltage doubler for low voltage inputs. Output voltage regulation and power factor correction are accomplished by a high frequency boost circuit having two inductors connected in parallel for the low input voltage configuration and in series for the high input voltage configuration. The high frequency switching semiconductor components are connected in a series circuit which limits their voltage requirement to one-half the output voltage.

Dynamic and static voltage stability enhancement of power systems

Abstract: The static voltage stability and the dynamic voltage stability are integrated. To consider a shunt compensator and/or a more general load which is dependent on voltage, a modified criterion for the static voltage stability is developed and the system is controlled to satisfy this static stability criterion. For an accurate analysis of the dynamic voltage stability, the system model includes excitation systems, tap-changers, capacitors and power system stabilizers in addition to network equations. A parameter optimization technique with a modal performance measure is developed to determine optimal control parameters for dynamic voltage stability enhancement. >

Microprocessor control of multiple peak power tracking DC/DC converters for use with solar cell arrays

Abstract: A method and an apparatus for efficiently controlling the power output of a solar cell array string or a plurality of solar cell array strings to achieve a maximum amount of output power from the strings under varying conditions of use. Maximum power output from a solar array string is achieved through control of a pulse width modulated DC/DC buck converter which transfers power from a solar array to a load or battery bus. The input voltage from the solar array to the converter is controlled by a pulse width modulation duty cycle, which in turn is controlled by a differential signal comparing the array voltage with a control voltage from a controller. By periodically adjusting the control voltage up or down by a small amount and comparing the power on the load or bus with that generated at different voltage values a maximum power output voltage may be obtained. The system is totally modular and additional solar array strings may be added to the system simply be adding converter boards to the system and changing some constants in the controller's control routines.

Switching converter with open-loop input voltage regulation on primary side and closed-loop load regulation on secondary side

Abstract: An isolated switching dc-to-dc converter is provided with a novel open-loop input voltage regulation on the primary side and the full regulation and independent protection of each of multiple outputs on the secondary side using an auxiliary circuit comprising a current bidirectional switch Q a and a capacitor C a on the primary side in a series circuit connected in parallel with a main current bidirectional switch Q to assure a continuous conduction mode for operation of the primary boost-like converter, and consequently preserves the simplicity of open-loop input voltage regulation for all loads from no load to full load. The auxiliary switch Q a is very efficient with only a fraction (5% or less) of the losses of the main active switch Q. The ideal dynamic response approaching theoretical limits is achieved for both line and load transients together with a high efficiency (85%) and record power density (20 W per cubic inch) for multiple output converters. Finally, the whole power supply needs isolation only at the main power transformer, since the need for isolation in the open-loop input and closed-loop output regulation control and drive circuitry is completely eliminated.

Wide load range three-level ZVS-PWM DC-to-DC converter

Abstract: A new three-level ZVS-PWM DC-DC converter operating in a wide load range is introduced. It is used for high-voltage and high-power applications and has as its main features: zero-voltage-switching (ZVS) from no load up to full load, operation at constant frequency, regulation by pulse-width modulation (PWM), and low RMS current stress upon power switches. Its greatest attribute is that the voltage across the switches is half the value of the input voltage. A prototype operating at 100 kHz, rated at 600 V input voltage, 1.5 kW output power, and 25 A output current, has been fabricated and successfully tested in the laboratory. The principle of operation, theoretical analysis, design procedure, and an example, along with experimental results, are presented. >

Soft-switching converter DC-to-DC isolated with voltage bidirectional switches on the secondary side of an isolation transformer

Abstract: A soft-switching dc-to-dc converter for providing regulated voltage to a load combines the functions of loss-less soft switching at zero voltage and at a constant switching frequency on the primary side and soft switching at zero current on the secondary side of an isolation transformer for all load currents from full load to no-load and PWM output voltage regulation on the secondary side. This is made possible by using voltage bidirectional switching element in series with a low-pass filter on the secondary side and current bidirectional switching element on the primary side driven at close to 50% duty ratio with adjustable dead time between switching. The adjustable dead-time is realized by sensing voltages across paired primary side current bidirectional switching element in order to enable alternate turn ON of said pair only at zero voltage, thereby eliminating or greatly reducing switching losses under all load current conditions. The output voltage is regulated by PWM control of the voltage bidirectional switching element comprising one of the following: a bipolar transistor, or a MOSFET in series with a diode, or preferably a saturable reactor in series with a diode to form a magnetic amplifier on the secondary side.

A new control algorithm for three-phase PWM buck rectifier with input displacement factor compensation

Abstract: A new control algorithm for the three-phase buck rectifier with an input filter is developed. The algorithm employs a separate control loop for compensation of the input current displacement factor in steady-state, in addition to the standard output voltage regulation loop. The algorithm allows separate design of the input filter and of closed loop output voltage control. The design procedure is explained and illustrated on an example. The algorithm is verified experimentally on an 1-kW, 100-kHz, three-phase isolated buck power converter. >

Critically continuous boost converter

Abstract: In critically continuous boost converters used to achieve high power factor and low input current harmonic distortion, a power FET is driven by a pulse generator whose on time is essentially constant over a single line cycle. Off time is terminated when current in the inductor falls to zero and the voltage on the side of the inductor not connected to the input voltage is less that the input voltage. A delay causes turn on to occur at the minimum of the voltage ring to minimize turn on switching losses. At voltages when the input voltage is less than one half of the output voltage part of the on time, turn on occurs with negative current flowing through the FET power switch and the inductor. Part of the turn on time is used to charge the inductor current back to zero before energy can begin to flow back into the output of the converter. A correction circuit is provided which extends the on time as a function of the input and output voltage to avoid dead time around the zero voltage crossover of the sinusoidal input voltage which when rectified provides the input voltage to the converter.

Automatic current shaper with fast output regulation and soft-switching

Abstract: A new utility-to-DC, harmonic-free interface combines the functions of automatic input current shaping, fast output voltage regulation, and lossless, soft switching in a single power converter. This was made possible through internal energy storage and the discovery of new modes of operation, which together, effectively decoupled the input boost-like part of the Cuk converter from its buck-like output. Experimental results obtained on a 50 W-12 V prototype confirm the fast output regulation (30 kHz bandwidth for 100 kHz switching frequency) simultaneously with low-harmonic line current waveforms. >

Closed loop pulse width modulator inverter with volt-seconds feedback control

Abstract: A closed loop pulse width modulator (PWM) inverter (50) corrects for variations and distortion in the ouput AC voltage (52) waveform caused by non-linearities of the switching devices (S1-S6) or changes in the DC link voltage (3). A signal is generated that is a volt-seconds representation of the voltage error between a voltage command signal (25) and the actual AC output voltage (52) of the PWM inverter (50). The volt-seconds error signal becomes a controlling signal means in the closed loop of the PWM inverter (50) to regulate the output AC voltage (52) of the PWM inverter (50). Another signal that represents changes in the DC link voltage (3) also modifies the voltage command signal (25). The system will compensate for the non-linear behavior of the PWM inverter (50) due to deadtime, minimum on-times and off-times, and DC link voltage (3) variations and voltage drops across the switching devices (S1-S6), and will also allow the operation of the inverter (50) in a linear fashion for the region of operation when one or more of its phases are saturated, i.e., either fully on or fully off.

Large scale integrated circuit with sense amplifier circuits for low voltage operation

Abstract: Disclosed is a one-chip ULSI which can carry out the fixed operation in a wide range of power supply voltage (1 V to 5.5 V). This one-chip ULSI is composed of a voltage converter circuit(s) which serves to a fixed internal voltage for a wide range of power supply voltage, an input/output buffer which can be adapted to several input/output levels, a dynamid RAM(s) which can operate at a power supply voltage of 2 V or less, etc. This one-chip ULSI can be applied to compact and portable electronic devices such as a lap-top type personal computer, an electronic pocket note book, a solid-state camera, etc.

Multiple time-scale power system dynamic simulation

Abstract: A new program, EXSTAB (extended time-scale stability) has been developed for representing a wide variety of power system performance problems, from transient stability through long-term dynamics and voltage instability. The capability of the program includes multiple execution modes and automatic step size selection to address conflicting goals of accuracy and efficiency. The modeling includes a broad range of apparatus to provide the needed time-scale representation (four orders of magnitude). Models for automatic generation control, plant characteristics and control, voltage and reactive power control, static and dynamic loads, and protective relaying for apparatus and system connections are provided. Technologies were developed to perform analysis of voltage stability and prediction of peak power transfer to avoid voltage collapse. >

Compact low noise low power dual mode battery charging circuit

Abstract: A low noise battery charger includes a rectifier to convert AC line voltage to a rectified sinusoidal voltage that is applied to a primary winding of a transformer. Another rectifier coupled to a first secondary winding applies a charging current to a battery. A switch coupled in series with the primary winding controls current therein. A rectifier coupled to another secondary winding produces a battery condition voltage. An incrementing signal synchronized with the rectified sinusoidal voltage increments a ratchet DAC until its output voltage exceeds the battery condition voltage. A low charging mode signal is produced when the battery condition voltage falls a certain amount below the DAC output voltage. Flow of current through the primary winding is controlled by operating the switch at a relatively high frequency and by producing constant turn off times for the switch which are proportional to the resonant period of the primary winding circuit and also by modulating turn on times for the switch in response to the signal indicative of primary winding current. Maximum power transfer across the transformer is thereby achieved without flyback voltage of the transformer exceeding breakdown voltage of the switch, and zero current switching is achieved.

The control of high-speed variable-reluctance generators in electric power systems

Abstract: This work studies the control of a direct-current (DC) electric power system that is sourced by a variable-reluctance generator. The power system includes the generator and its switching inverter, a filtering capacitor, a distribution network and an electrical load. The network comprises a series resistor and inductor, while the load comprises a parallel resistor, capacitor and power sink. The voltage at the load is regulated by adjusting the rotor angles at which the inverter switches. Both steady-state and transient performance are considered. Simulations are provided to illustrate performance. >

Power supply control circuit for use in IC memory card

Abstract: An IC memory card used in a dual power supply voltage operation system and having a backup function is arranged to prevent destruction of data stored in an internal memory caused by an erroneous access in a non-operation-ensured voltage range between lower and higher operation-ensured voltage ranges Three voltage levels divided from an external power supply voltage by voltage dividing resistors are compared with a reference voltage from a reference voltage generation circuit to determine whether the external power supply voltage is at the lower or upper limit of the lower operation-ensured voltage range or the lower limit of the higher operation-ensured voltage range On the basis of outputs from these comparators, a memory protection signal generation circuit generates a memory protection signal to enable the memory to be protected even in the voltage range between the lower and higher operation-ensured voltage ranges

Soft-switched DC/DC converter with PWM control

Abstract: In this paper, a soft-switched power converter with two variations is discussed. An asymmetrical PWM control scheme is used to control the power converter under constant switching frequency operation. The modes of operation for both variations are discussed. The DC characteristics which can be used in design of the converters are also presented. Two 50 W converters were built to verify the characteristics of the converters. Due to the zero voltage switching (ZVS) operation of the switches and low device voltage and current stresses, the converters have high full load and partial load efficiencies. They are potential candidates for high efficiency, high density power supply applications. >

Isolated multiple output Cuk converter with primary input voltage regulation feedback loop decoupled from secondary load regulation loops

Abstract: A novel isolated, capacitive idling, Cuk switching-mode converter features two separate nonisolated feedback loops, one on the primary side to regulate against input voltage changes and the other on the secondary side to regulate against load current changes only While preserving cost, size and simplicity of conventional multiple output switching-mode converters, the new converter and feedback control approach offers the advantages of simple feedback control implementation due to elimination of isolation requirements in the feedback control circuits, simultaneous regulation of all output voltages from no load to full load, and greatly improved bandwidth and step-load transient response For operation from a rectified ac line, feedback control on the input to the transformer is modified to force the average input current to follow the full-wave rectified ac line voltage for unity power factor (UPF) performance on the input and wide bandwidth voltage regulation on the output Both are demonstrated simultaneously in a single, isolated, multiple ac-to-dc switching-mode power converter The novel decoupled feedback control is shown to be equally applicable to a number of Cuk-type converter topologies featuring capacitive energy transfer from a voltage source to a load

Microwave output stabilizing apparatus of a microwave oven and a method thereof

Abstract: A microwave output stabilizing apparatus for a microwave oven comprises a rectifier circuit for rectifying power from an AC power supply into a constant DC voltage; an invertor circuit for generating a high frequency power supply by controlling the DC voltage at an intermittent output state; a high voltage transformer for stepping up the high frequency power supply; and magnetron drive circuit for rectifying the high frequency power supply and oscillating a magnetron. Also, an inverter control circuit detects the current flowing into the primary winding of the high voltage transformer, converts the detected current into a corresponding voltage, the corresponding voltage with a reference voltage, and controls the inverter circuit according to the results of the comparison. Further included are an anode current detecting circuit for detecting the anode current of the magnetron and converting the detected anode current into the corresponding voltage; and, a reference voltage adjusting circuit for evaluating the anode current and changing the reference voltage of the invertor control circuit in accordance with the results of the evaluation.

Differential termination network for differential transmitters and receivers

Abstract: A system of terminating a differential transmission line is described, where the differential transmitter and differential receiver are supplied by different power sources. The termination circuit comprises an unbalanced voltage divider pair, a connection to the receiver's voltage source, an adjustable threshold voltage, and circuitry to reduce power consumption. An unbalanced voltage divider pair provides matched termination impedances, and prevents undesired receiver output upon loss of transmitter signals. The voltage supplying the unbalanced voltage divider pair provides a voltage differential at the receiver inputs upon loss of the transmitter power source. An adjustable threshold voltage provides the minimum receiver input threshold voltage on which the transmitter signals can be superimposed. Power consumption is reduced through the use of a current limiter, which is coupled with a high pass filter to maintain the characteristic impedance of the transmission line during high frequency transmission. SEP

Full shunt boost switching voltage limiter for solar panel array

Abstract: According to the present invention a bus voltage limiter is connected between a photovoltaic solar panel array and a load to limit the output voltage to a fixed dc reference voltage. The limiter includes a pulse width modulator which controls the duty cycle of a power switch from 0% to 100% to maintain a substantially constant output voltage V ref . A coupled inductor type boost DC to DC converter includes a pair of main windings which cooperate with the duty cycle modulated power switch to provide the output voltage. An auxiliary winding provides input ripple current cancellation in conjunction with a second inductor and a dc blocking capacitor.

Low-to-high voltage translator with latch-up immunity

Abstract: A fast low-to-high voltage translator with immunity to latch-up. The circuit includes a voltage comparator and employs at least one transistor which is used to quickly pull up a node. If further uses another transistor which is capable of limiting the voltage at certain nodes in order to eliminate latch-up if a pumped power supply is provided to the circuit. Latch-up therefore is eliminated during power-up. Other transistors are utilized as voltage drop limiters to limit the voltage drop across other transistors during switching. This provides improved reliability by reducing substrate current and hot carriers.

Methods for on-line assessment of power system voltage security

Abstract: This paper proposes the use of energy methods in an on-line environment to aid in the assessment of system voltage stability, The application of energy methods to voltage stability is first reviewed. A fast algorithm then is presented for determining the low voltage power flow solutions with lowest associated energy measures. The use of these measures to assess voltage security is discussed for use both on-line and in contingency analysis. The technique is demonstrated on a 415 bus system. A paper recommended and approved between the static and dynamic aspects of the problem, along with the modeling detail required for the individual generators, loads, and other network devices (such as load- tap changing transformers and DC transmission lines) has still not been completely ascertained. While more research is still needed into the basic mechanics of voltage collapse, there is, nevertheless, an urgent need to increase the number of tools available to the operator in the on-line environment. The goal of this paper is to demonstrate that energy function methods can provide such an additional tool. It will be shown that energy methods provide an effective means of increasing the operator's knowledge of the system's voltage security. The paper is organized as follows. First, the application of energy function methods to the problem of voltage security is discussed. Second, an algorithm is presented for the rapid determination of the appropriate energy measures in a large scale system. Lastly, the application of energy method techniques to a large scale system is demonstrated, with consideration of both the present and contingent states of the system.

Internal voltage generator for a non-volatile semiconductor memory device

Abstract: The semiconductor device includes a voltage generator for generating selectively a signal of a first level or a second level onto a first supply line, and a voltage converter using voltage signals on the first supply line and a second supply line for producing a signal of the voltage level on the first or the second supply line in accordance with an input signal, and a voltage level shifter for detecting the level of the voltage on the first supply line to shift in voltage level a signal on the second power supply line toward the first level when the voltage on the first supply line approaches the first level. The difference of the voltages on the first and second supply lines can be reduced to improve the break-down characteristics of a transistor included in the voltage converter, resulting in a reliable semiconductor device.

Control circuit responsive to its supply voltage level

Abstract: In an integrated microcircuit device the supply voltage is monitored by a pair of threshold detector logic circuits configured to generate a first control signal when said supply voltage crosses over a minimum level, and a second control signal when said supply voltage crosses over a maximum level. The control signals are used to configure the device into distinct modes of operation, whereby the functions of the device and the voltage level of the power supply applied to them during testing or operation may be controlled by varying the supply voltage.