Showing papers on "Voltage regulation published in 1995"

Electrical Power Systems Quality

Abstract: CHAPTER 1: INTRODUCTION What is Power Quality? Power Quality -- Voltage Quality Why Are We Concerned About Power Quality? The Power Quality Evaluation Procedure Who Should Use This Book Overview of the Contents CHAPTER 2: TERMS AND DEFINITIONS Need for a Consistent Vocabulary General Classes of Power Quality Problems Transients Long-Duration Voltage Variations Short-Duration Voltage Variations Voltage Imbalance Waveform Distortion Voltage Fluctuation Power Frequency Variations Power Quality Terms Ambiguous Terms CBEMA and ITI Curves References CHAPTER 3: VOLTAGE SAGS AND INTERRUPTIONS Sources of Sags and Interruptions Estimating Voltage Sag Performance Fundamental Principles of Protection Solutions at the End-User Level Evaluating the Economics of Different Ride-Through Alternatives Motor-Starting Sags Utility System Fault-Clearing Issues References CHAPTER 4: TRANSIENT OVERVOLTAGES Sources of Transient Overvoltages Principles of Overvoltage Protection Devices for Overvoltage Protection Utility Capacitor-Switching Transients Utility System Lightning Protection Managing Ferroresonance Switching Transient Problems with Loads Computer Tools for Transients Analysis References CHAPTER 5: FUNDAMENTALS OF HARMONICS Harmonic Distortion Voltage versus Current Distortion Harmonics versus Transients Harmonic Indexes Harmonic Sources from Commercial Loads Harmonic Sources from Industrial Loads Locating Harmonic Sources System Response Characteristics Effects of Harmonic Distortion Interharmonics References Bibliography CHAPTER 6: APPLIED HARMONICS Harmonic Distortion Evaluations Principles for Controlling Harmonics Where to Control Harmonics Harmonic Studies Devices for Controlling Harmonic Distortion Harmonic Filter Design: A Case Study Case Studies Standards of Harmonics References Bibliography CHAPTER 7: LONG-DURATION VOLTAGE VARIATIONS Principles of Regulating the Voltage Devices for Voltage Regulation Utility Voltage Regulator Application Capacitors for Voltage Regulation End-User Capacitor Application Regulating Utility Voltage with Distributed Resources Flicker References Bibliography CHAPTER 8: POWER QUALITY BENCHMARKING Introduction Benchmarking Process RMS Voltage Variation Indices Harmonics Indices Power Quality Contracts Power Quality Insurance Power Quality State Estimation Including Power Quality in Distribution Planning References Bibliography CHAPTER 9: DISTRIBUTED GENERATION AND POWER QUALITY Resurgence of DG DG Technologies Interface to the Utility System Power Quality Issues Operating Conflicts DG on Distribution Networks Siting DGDistributed Generation Interconnection Standards Summary References Bibliography CHAPTER 10: WIRING AND GROUNDING Resources Definitions Reasons for Grounding Typical Wiring and Grounding Problems Solutions to Wiring and Grounding Problems Bibliography CHAPTER 11: POWER QUALITY MONITORING Monitoring Considerations Historical Perspective of Power Quality Measuring Instruments Power Quality Measurement Equipment Assessment of Power Quality Measurement Data Application of Intelligent Systems Power Quality Monitoring Standards References Index INDEX

Performance limits of switched-capacitor DC-DC converters

Abstract: The theoretical performance limits of two-phase switched-capacitor (SC) DC-DC power converters are discussed in this paper. For a given number of capacitors k, the complete set of attainable DC conversion ratios is found. The maximum step-up or step-down ratio is given by the k/sup th/ Fibonacci number, while the bound on the number of switches required in any SC circuit is 3k-2. Practical implications, illustrated by several SC power converter examples, include savings in the number of components required for a given application, and the ability to construct SC power converters that can maintain the output voltage regulation and high conversion efficiency over a wide range of input voltage variations. Limits found for the output resistance and efficiency can be used for selection and comparison of SC power converters. >

Step-up DC power supply based on a switched-capacitor circuit

Abstract: A new step-up DC-to-DC power converter with high power density is presented. It contains no inductors or transformers. The controlled energy transfer from an unregulated voltage source to a regulated output voltage is realized through a switched-capacitor circuit. The operation of the switches in the power stage is dictated by a PWM-type feedback circuit. The new regulator is simulated by using an averaged state-space approach. The transient and steady-state waveforms, as well as the AC small-signal input-to-output and control-to-output transfer functions are obtained by both simulation and experiments. The power supply, implemented for a nominal power of 15 W, and input-to-output voltage ratio of 5/12, features high efficiency for this class of powers, small output voltage ripple, continuous input current, low weight and small size. >

DC-DC converter design for battery-operated systems

Abstract: This paper describes performance, design and optimization of DC-DC converters for energy limited, battery operated systems. Variable-frequency operation is used to achieve voltage regulation and high efficiency for an extremely wide range of load currents. An experimental 15 W, 3.3 V buck converter has been constructed to demonstrate design and optimization techniques. The converter employs synchronous rectification to reduce conduction losses, and discontinuous, variable-frequency, current-mode control with optimum peak current to maximize efficiency for a wide range of loads. Applications include portable computers, hand-held instruments, and telecommunications. >

Voltage regulator that operates in either PWM or PFM mode

Abstract: A switching voltage regulator achieves high efficiency by automatically switching between a pulse frequency modulation (PFM) mode and a pulse-width modulation (PWM) mode. Switching between the modes of voltage regulation is accomplished by monitoring the output voltage and the output current, wherein the regulator operates in PFM mode at small output currents and in PWM mode at moderate to large output currents. PFM mode maintains a constant output voltage by forcing the switching device to skip cycles when the output voltage exceeds its nominal value. In PWM mode, a PWM signal having a variable duty cycle controls the switching device. A constant output voltage is maintained by feedback circuitry which alters the duty cycle of the PWM signal according to fluctuations in the output voltage.

High precision voltage regulation circuit for programming multilevel flash memory

Abstract: A voltage regulation circuit (45) that includes a sample and hold circuit (501) for sampling an input voltage (Vin). The sample and hold circuit (501) includes a capacitor (C1, 515) that holds the reference voltage. The voltage regulation circuit (45) also includes a regulator circuit (503) coupled to the capacitor (C1) of the sample and hold circuit (501). The regulator circuit (503) outputs an output voltage using the reference voltage supplied by the capacitor (C1). The voltage regulation circuit (45) may be used to provide a high precision programming voltage for programming memory cells having two or more analog states.

Reactive power/voltage control in a distribution substation using dynamic programming

Abstract: The reactive power/voltage control in a distribution substation is investigated. The purpose is to properly dispatch the shunt capacitors and onload tap changers at the distribution substation based on the forecast hourly loads of a main transformer and its primary bus voltage such that the reactive power flows through the main transformer, and the transformer secondary bus voltage deviations from the desired values can be minimised. Practical constraints on secondary bus voltage limits and the maximum allowable number of switching operations in a day for the onload tap changers are taken into account. An approach based on dynamic programming is presented to reach the desired dispatching schedule. To demonstrate the usefulness of the proposed approach, reactive power/voltage control in a distribution substation within the service area of Taipei City District Office of Taiwan Power Company is performed. It is found that a proper dispatching schedule for the shunt capacitors and onload tap changers can be reached by the proposed method.

Speed control of interior permanent magnet synchronous motor drive for flux weakening operation

Abstract: A novel flux-weakening scheme for an interior permanent magnet synchronous motor (IPMSM) is proposed. It is implemented based on the output of the synchronous PI current regulator-reference voltage to PWM inverter. The onset of flux weakening and the level of the flux are adjusted inherently by the outer voltage regulation loop to prevent the saturation of the current regulator. Attractive features of this flux weakening scheme include no dependency on the machine parameters, the guarantee of current regulation at any operating condition, and smooth and fast transition into and out of the flux weakening mode. Experimental results at various operating conditions including the case of detuned parameters are presented to verify the feasibility of the proposed control scheme.

Evaluation of neural network based real time maximum power tracking controller for PV system

Abstract: This paper presents a neural network based maximum power tracking controller for interconnected PV power systems The neural network is utilized to identify the optimal operating voltage of the PV power system The controller generates the control signal in real-time, and the control signal is fed back to the voltage control loop of the inverter to shift the terminal voltage of the PV power system to its identified optimum, which yields maximum power generation The controller is of the PI type The proportional and the integral gains are set to their optimal values to achieve fast response and also to prevent overshoot and also undershoot Continuous measurement is required for the open circuit voltage on the monitoring cell, and also for the terminal voltage of the PV power system Because of the accurate identification of the optimal operating voltage of the PV power system, more than 99% power is drawn from the actual maximum power >

Fast assessment methods for voltage sags in distribution systems

Abstract: Based on a simple voltage divider model, a relation is derived between the load sensitivity to voltage sags (expressed as a critical voltage) and the exposed area (expressed as a critical distance). The critical distance increases about linearly with voltage level. The relation found is remarkably similar to relations found in power quality surveys. An equivalent expression is found for the critical distance as a function of the critical phase-angle jump. Realizing that faults downstream of a transformer do not significantly influence the expected number of sags, it is possible to estimate the number of sags at a specific load location. The method is extended to some nonradial systems: simple subtransmission loops, local generation, feeding from two substations, and operating with a normally open breaker.

Design considerations for single-stage isolated power-factor-corrected power supplies with fast regulation of the output voltage

Abstract: The paper introduces a new family of single-stage isolated power-factor-corrected power supplies with fast regulation of the output voltage, and discusses the most-important design issues, including all of the following: storage-capacitor voltage, dual-range and wide-range operation, device RMS currents, and line harmonic currents. In addition to the theoretical analyses, experimental data are also provided. >

A novel on-line UPS with universal filtering capabilities

Abstract: A novel line-interactive uninterruptible power supply (UPS) is proposed that offers the characteristics of an "on-line" or "inverter-preferred" UPS (which incorporates a pulse-width modulation (PWM) rectifier) at a reduced cost. This new UPS is based on the combination of two full-bridge VSI converters: one in series with the input and the other in parallel with the load. The UPS acts as a line conditioner and output-voltage stabilizer in the presence of input power while charging the battery at a controlled rate. In case of loss of input power, the UPS can make a seamless transition to backup mode while supplying the load with a controlled sinusoidal voltage, drawing power from the battery. The series converter sees only a small percentage of the input voltage (typically, 10%-20%) while carrying the input current and therefore has a small kilovoltampere rating. The parallel converter supplies the load during blackout and hence determines the total kilovoltampere rating of the UPS. The reduced kilovoltampere rating of the series converter results in reduced system cost compared to conventional on-line systems without sacrificing any desirable characteristics. A laboratory version of the proposed UPS has been built to demonstrate the claimed capabilities, and both simulation and experimental results are included in the paper.

Secondary voltage control: analysis, solutions and simulation results for the Spanish transmission system

Abstract: Secondary voltage control was introduced in some European countries as a means to improve voltage security and operation. It is a closed loop system dedicated to keep the voltage of some load buses called pilot buses constant. In this paper, a new approach covering all the main aspects of secondary voltage control; pilot buses and control generators selection, the control law and the decentralization problem, is presented. This approach has been applied to the Spanish power system. Some of the results obtained are also presented.

A new approach to enhance power quality for medium voltage drives

Abstract: A new approach to medium voltage, variable frequency, static AC motor drives offers improvements in power quality. Harmonic current injection into power lines is below the most severe requirements of IEEE 519-1992. The power factor of this new type of drive exceeds 94% at full load and is above 90% at 10% load. Motor voltage and current waveforms are improved so that torque pulsations are reduced. Peak voltage stress on motor insulation does not exceed peak input line voltage, and no zero sequence voltage is imposed. Drive efficiency exceeds 96%. This paper describes the new approach, and some of the results achieved.

Coordination between the reactive power scheduling function and the hierarchical voltage control of the EHV ENEL system

Abstract: The paper presents the control strategies adopted at ENEL (the Italian Electric Power Company) for the automatic voltage regulation and for the short and very short term reactive power scheduling. The advanced project is based upon a three level hierarchical control of voltage and reactive power (primary, secondary and tertiary regulation) and a reactive power dispatch procedure. The three levels are characterized by specific control actions which affect systems of different size and complexity, operating in three steps. In particular, the slowest third level executes the optimal voltage profile defined by the short or very short term reactive power scheduling. The need of an effective co-ordination between the off-line reactive scheduling procedures and the on-line voltage control is pointed out in the work. Besides, the paper presents a computation procedure realized in order to simulate the steady state behaviour of the electric power system submitted to the hierarchical voltage control system and its interaction with the VAr optimisation program. >

Method and circuit for simultaneously programming and verifying the programming of selected EEPROM cells

Abstract: A method and circuit programs and automatically verifies the programming of selected EEPROM cells without alternating between programming and reading modes like prior art methods and circuitry. The circuitry includes a programming circuit and a bit line voltage regulation circuit. The programming circuit further includes a novel sense amplifier which unlike prior art sense amplifiers, is operable during both cell reading and programming modes. Included in the sense amplifier are two current providing circuits. A first circuit provides current to a selected EEPROM cell which is sufficient for reading the programmed state of the cell, and a second circuit which automatically provides additional current when required, for programming the cell. The sense amplifier detects when programming of a selected EEPROM cell has completed and causes programming of that cell to be terminated. The voltage regulation circuitry regulates the bit line voltage to the selected EEPROM cell's drain electrode. The programming circuitry, including the sense amplifier, and voltage regulation circuitry are shown to be shared between a plurality of bit lines through a bit line selection circuit.

Combined deadbeat control of a series-parallel converter combination used as a universal power filter

Abstract: This paper presents the notion of combined control of a system of interconnected power electronic converters. The concept is demonstrated using a three-phase series-parallel active power filter as an example. The described active power filter consists of a series-parallel combination of two full bridge VSIs capable of arbitrarily controlling the input current and the output voltage. The proposed control scheme treats the converter combination as a single unit and uses the inverse system model to generate deadbeat control response for both input current and output voltage. A full order predictive state observer is used to reduce the number of sensors. Simulation results show the excellent disturbance rejection characteristics of the proposed control when compared to the separately controlled converter scheme. >

Lead acid charger

Abstract: A battery charge controller (50) is provided which includes a PWM switch controller (36) that is operable to control a switching regulator to supply current to a battery (10) in either a current regulation mode or a voltage regulation mode. A charge control (40) is operable to control the charging operation such that multiple modes of operation are selectable by an external programmable pin. The three modes provided are: a constant voltage mode, a dual-current mode and a pulse-current mode. The constant voltage mode provides for a conditioning state followed by a bulk charging state followed by a maintenance state. In the bulk charging state, current regulation is provided at a maximum current until a charged condition occurs, at which time the charger is placed in a voltage regulation mode. In the dual-current mode, the system is switched between two current regulation levels, a high current regulation level for fast charging to a substantially fully charged state of around eighty percent of rated full charge after which a low current pulsed operation is maintained during a maintenance mode. In the pulsed-current mode, current regulation is performed at the maximum current until the substantially full charged state is detected, after which the cell voltage is allowed to float until it falls below a nominal cell voltage, at which time rapid charging is again performed at a current regulated level. In this last mode, a substantially fully charged state is determined by examining the gradient of the voltage change of the charging profile to determine when a sustained negative value occurs, this indicating the onset of an increase in the pressure and temperature of the cell.

A low supply voltage high PSRR voltage reference in CMOS process

Abstract: This paper describes a bandgap voltage reference circuit that operates with a 3 V power supply and is compatible with a digital CMOS process. The use of a simple circuit topology results in a small silicon area of 0.07 mm/sup 2/, a power consumption of 1 mW and a high power supply rejection over a wide frequency band. The circuit realizes a temperature coefficient of 85 ppm//spl deg/C and a standard deviation of 20 mV without trimming. >

Efficient power conversion

Abstract: In a power conversion scheme, a power conversion apparatus consisting of boost conversion elements for effecting a boost conversion of power originating from a varying voltage source; additional conversion elements for also effecting conversion of power originating from the varying voltage source; and circuitry for selectively configuring the conversion elements with respect to delivery of power to a load to achieve greater conversion efficiency than if all of the power delivered to the load were constrained to flow through the additional conversion elements and at least some of the boost conversion elements In another aspect power is converted from a voltage source having a predetermined source voltage range, and delivered to a load via two sets of power conversion elements, each set for effecting conversion of power from the voltage source, at least one of the sets having an input operating voltage range narrower than the source voltage range The apparatus includes control circuitry for configuring and reconfiguring interconnections of the two sets with the voltage source and the load to provide an input operating voltage range for the apparatus which is greater than the input operating range of the set of power conversion elements having the narrower input operating voltage range In another aspect, the input voltage operating range is enhanced for a power conversion circuit which has two sets of power conversion elements arranged to share power delivered to a load The circuit is selectively configured with the two sets in series or not in series in a manner so that the input voltage operating range of the power conversion circuit is broader than the input voltage operating range of either of the sets of power conversion elements

High Voltage Engineering and Testing

Abstract: Electric power transmission and HV distribution systems HVDC and power electronic systems Insulation systems Transmission systems Overhead lines High voltage cables High voltage bushings Substation design Intelligent monitoring systems Life management of electrical equipment Switchgear fundamentals Transmission switchgear design, development and service Distribution switchgear design, development and service Application of high power testing and measurement technology Design of high voltage power transformers Transformer user requirements, specifications and testing Fundamental aspects of air breakdown Basic measuring and testing techniques Digital measurements: implications for new international standards and procedures High voltage laboratory techniques

Full range soft-switching DC-DC converter

Abstract: A soft-switching DC to DC power converter which minimizes switching losses from a no load condition to a full load condition while operating at fixed frequency. Output voltage control is achieved by controlling the phase angle between the two switching networks. High frequency transformer primaries are always excited with a square wave input voltage equal to ##EQU1## The power converter can be implemented with a single transformer. Moreover, the switch voltage never increases the input DC voltage from no load to full load. The power converter can be used in both low voltage high current applications and high voltage low current applications.

Selection of capacitors for the self regulated short shunt self excited induction generator

Abstract: The self regulating feature of a self-excited induction generator (SEIG) by connecting additional capacitors is examined. A system consisting of both shunt and series capacitors has been analyzed. A methodology has been explained to choose an appropriate set of values of these capacitors for desired voltage regulation. Performance of short and long shunt configurations has been compared which shows the superiority of the short shunt connection. The results of a detailed investigation on a conventional 3.7 kW induction motor operated as a SEIG are presented to illustrate the effectiveness of the proposed method. Close agreement between predicted and test results has been observed, thereby establishing the validity of the analysis carried out and the criterion adopted. >

Improved secondary and new tertiary voltage control

Abstract: In this paper the basic role of a secondary (regional level) voltage control in a multi-regional electric power system is reviewed. Specifically, certain limitations of presently implemented control schemes are described. Next an improved secondary voltage control (ISVC) scheme is proposed. In the second part of the paper, possible enhancements of a multi-regional power system operation by means of scheduled, tertiary voltage control (TVC) interactions are proposed. It is shown that the prime role of a TVC is in managing limits on voltage control devices, such as generators. The theoretical developments are illustrated on two regions of the French electric power network.

A boost DC-AC converter: operation, analysis, control and experimentation

Abstract: This paper proposes a new voltage source inverter referred to as a boost inverter or boost DC-AC converter The main attribute of the new inverter topology is the fact that it generates an AC output voltage larger than the DC input one, depending on the instantaneous duty-cycle This property is not found in the classical voltage source inverter which produces an AC output instantaneous voltage always lower than the DC input voltage Operation, analysis, modulation, control strategy and experimental results are included in this paper The new inverter is intended to be used in UPS design, whenever an AC voltage larger than the DC link voltage is needed, with no need of a second power conversion stage

Voltage dependent reactive power limits for voltage stability studies

Abstract: This paper presents and studies a static model for synchronous generators with voltage dependent reactive power limits due to maximum stator current, maximum and minimum rotor (field) current as well as maximum rotor angle (underexcitation) limiters. The proposed generator model for static voltage stability studies can be included in an ordinary power flow program, and results from studies on a test system with twenty generators are presented. The influence of voltage dependent reactive power limits is compared with fixed (conventional) limits, by use of the minimum singular value of the power flow Jacobian matrix and related submatrices as indicators of the static voltage stability limit. >

Power supply apparatus with a back-up power unit

Abstract: A power supply apparatus with a back-up power unit includes: a plurality of AC-DC conversion units each connected in parallel to a commercial AC power source, and each converting an AC voltage of said power source to a high DC voltage; a plurality of DC-DC conversion units each connected to an output of each AC-DC conversion unit, each converting the high DC voltage to a low DC voltage to be supplied to a load, and each output thereof connected in parallel to said load; and a back-up power unit connected in parallel to the output of each AC-DC conversion unit through a first and second diodes in order to supply the high DC voltage to the DC-DC conversion unit when a failure occurs in the AC power source.

A new technique for voltage stability analysis in a power system and improved loadflow algorithm for distribution network

Abstract: Voltage collapse may occur in a power system due to loss in voltage stability in the system. Therefore voltage stability analysis is important in order to identify critical buses in a power system, i.e. buses which are closed to their voltage stability limits and thus enable certain measures to be taken by the control engineer in order to avoid any incidence of voltage collapse. This paper presents a new technique to determine the static voltage stability of load buses in a power system for a certain operating condition and hence identifies load buses which are close to voltage collapse. A voltage stability index with respect to a load bus is formulated from the voltage equation derived from a two bus network and it is computed using a Thevenin equivalent circuit of the power system referred to a load bus. This index indicates how far the load buses are from their voltage stability limits and hence identifies the critical buses. The performance of this index is tested using a 9 bus radial network and the 24 bus IEEE Reliability Test System for its validity. A comparison is also made between this index and the impedance ratio used by Sterling et al. as the voltage collapse indicator. This paper also presents a new loadflow technique to compute the power flow solution for a radial network which is found to be more superior than the Second Order Newton Raphson and Distflow since it takes less iterations to give a loadflow solution.

E-beam high voltage switching power supply

Abstract: A high power, solid state power supply is described for producing a controllable, constant high voltage output under varying and arcing loads suitable for powering an electron beam gun or other ion source. The present power supply is most useful for outputs in a range of about 100-400 kW or more. The power supply is comprised of a plurality of discrete switching type dc-dc converter modules, each comprising a voltage regulator, an inductor, an inverter for producing a high frequency square wave current of alternating polarity, an improved inverter voltage clamping circuit, a step up transformer, and an output rectifier for producing a dc voltage at the output of each module. The inputs to the converter modules are fed from a common dc rectifier/filter and are linked together in parallel through decoupling networks to suppress high frequency input interactions. The outputs of the converter modules are linked together in series and connected to the input of the transmission line to the load through a decoupling and line matching network. The dc-dc converter modules are phase activated such that for n modules, each module is activated equally 360°/n out of phase with respect to a successive module. The phased activation of the converter modules, combined with the square current waveforms out of the step up transformers, allows the power supply to operate with greatly reduced output capacitance values which minimizes the stored energy available for discharge into an electron beam gun or the like during arcing. The present power supply also provides dynamic response to varying loads by controlling the voltage regulator duty cycle using simulated voltage feedback signals and voltage feedback loops. Circuitry is also provided for sensing incipient arc currents reflected at the output of the power supply and for simultaneously decoupling the power supply circuitry from the arcing load.

High voltage start-up circuit and method therefor

Abstract: The present invention relates to a switchmode power supply (SMPS) high voltage start-up integrated circuit (IC) with output voltage sensing and output current limiting. The high voltage start-up IC allows low voltage pulse width modulated (PWM) controller ICs to operate directly off rectified AC lines of up to 450 VDC. The high voltage start-up IC allows PWM controller ICs to start-up with a start threshold larger than its operating voltage. The output voltage is monitored internally so that the internal high voltage switch turns off when the output voltage decreases below an internally set trip point voltage (V off ). The internal high voltage switch remains off and an external auxiliary voltage is generated and applied to the output voltage. If the output voltage falls below a lower set trip point voltage (V reset ) the internal high voltage switch turns back on. This allows the start-up circuit to reset itself when the PWM controller IC's auxiliary voltage does not power up properly.