Showing papers on "Voltage regulation published in 1996"

New trends in active filters for power conditioning

Abstract: Attention has been paid to active filters for power conditioning which provide the following multifunctions: reactive power compensation; harmonic compensation; flicker/imbalance compensation; and voltage regulation. Active filters in a range of 50 kVA-60 MVA have been practically installed in Japan. In the near future, the term "active filters" will have a much wider meaning than it did in the 1970s. For instance, active filters intended for harmonic solutions are expanding their functions from harmonic compensation of nonlinear loads into harmonic isolation between utilities and consumers, and harmonic damping throughout power distribution systems. This paper presents the present status of active filters based on state-of-the-art power electronics technology, and their future prospects and directions toward the 21st Century, including the personal views and expectations of the author.

Regulation of a PWM rectifier in the unbalanced network state using a generalized model

Abstract: This study concerns the modeling and control of a pulse-width-modulated (PWM) rectifier in the case of network variations. The aim is to limit and stabilize variations of DC output voltage and line currents in such circumstances. Network variations can result in costly damage to power converters and their loads but a power converter such as the PWM rectifier, using cascade digital control, offers many capabilities to stabilize the system with optimized control. A generalized model of the PWM rectifier is first presented using the Clarke notation in order to separate the positive and negative sequences. The model is also extended to the harmonics. The cases of harmonic disturbance and an unbalanced network are then analyzed and an optimized regulation is presented for the latter case, validating the generalized model. Experimental results are proposed. The line current compensation loop method coupled with identification of network parameters offers a good solution to stabilize the PWM rectifier in an unbalanced network.

Method and apparatus for electronic power control

Abstract: The method of the invention in one aspect involves electronic power control by varying the amplitude of an electrical power supply voltage, independent of frequency, whereby the output frequency will always be the same as the input frequency. An electrical circuit apparatus for accomplishing this function in a preferred embodiment is also disclosed herein. The preferred circuitry of this aspect of the invention uses four solid state switches, such as IGBT's, four diodes, an inductor, input and output filters and novel controlling circuitry. The controller apparatus and methods of the invention may be used to implement all otherwise conventional converter types, buck, boost, and inverting (and duals of these) versions to obtain different regulating characteristics, including galvanic isolation of the output from the input. The inventive methods and devices may be used in power factor correction, voltage and/or current harmonic filtering and neutralization, line and load conditioning, control of power transfer between two power grids, and programmable control of surges, sags, dropouts and most other voltage regulation problems.

An improved voltage control on large-scale power system

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.

Nonlinear-carrier control for high-power-factor boost rectifiers

Abstract: Novel nonlinear-carrier (NLC) controllers are proposed for high-power-factor boost rectifiers. In the NLC controllers, the switch duty ratio is determined by comparing a signal derived from the main switch current with a periodic, nonlinear carrier waveform. As a result, the average input current follows the input line voltage. The technique is suitable for boost converters operating in the continuous conduction mode. Input voltage sensing, the error amplifier in the current-shaping loop, and the multiplier/divider circuitry in the voltage feedback loop are eliminated. The current-shaping is based on switch (as opposed to inductor) current sensing. The NLC controllers offer comparable or improved performance over existing schemes, and are well suited for simple integrated-circuit implementation. Experimental verification on a 240 W rectifier is described.

Voltage control apparatus and method for power supply

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.

Switched-capacitor power supplies: DC voltage ratio, efficiency, ripple, regulation

Abstract: A comprehensive and accurate steady-state analysis of a step-up DC-DC switched-capacitor power converter is performed. No approximations, such as average techniques, are invoked. Parasitic elements such as diode forward voltages, on-resistances of transistors and equivalent-series resistances of capacitors are included into the model. The converter performance functions, i.e. DC voltage ratio, efficiency, output voltage ripple, are expressed in terms of the number of switched-capacitor stages, number of capacitors per stage, values of the capacitors and parasitic elements, switching frequency and load. Design criteria aiming at high efficiency, low ripple and achievable output voltage are formulated. Trade-offs between the efficiency requirement and good regulation capability are discussed.

Electrical signal supply with separate voltage and current control for an electrical load

Abstract: An electrical signal supply apparatus independently controls and regulates voltage and current in supplying microampere currents to skin tissue of patients. The apparatus enables operators to select a desired voltage level independent of the requirement to maintain current through the skin tissue at a relatively constant level. The apparatus includes a switching regulator in combination with an electric voltage doubling network and potential divider network to enable the supply of increased voltages.

Power factor correction circuit and circuit therefor having sense-FET and boost converter control circuit

Abstract: A power factor correction circuit includes a boost converter, a zero-current detector for detecting a period in which an inductor current is zero, a half-wave rectifier for supplying a power voltage proportional to an output voltage of the boost converter, a control voltage generator for generating a control voltage to control the turn-on time timing of a sense-FET, a turn-on controller for making constant a turn-on duration of the sense-FET, an over current detector for generating a signal when a mirror terminal current of the sense-FET is greater than a predetermined current, an OR gate for performing a logic OR operation of the output signals of the turn-on controller and the over current detector, an output current controller for generating a gate drive signal of the sense-FET, and an under voltage lock out for turning off the power voltage when the power voltage is less than a predetermined voltage. This circuit enables an external pin count to be reduced by having a built-in boost converter controller and a built-in sense-FET in a single package.

New trends in active filters for improving power quality

Abstract: Since their basic compensation principles were proposed around 1970, active filters have been studied by many researchers and engineers aiming to put them into practical applications. Shunt active filters for harmonic compensation with or without reactive power compensation, flicker compensation or voltage regulation have been put on a commercial base in Japan, and their rating or capacity has ranged from 50 kVA to 60 MVA at present. In near future, the term of active filters will cover a much wider sense than that of active filters in the 1970s did. The function of active filters will be expanded from voltage flicker compensation or voltage regulation into power quality improvement for power distribution systems as the capacity of active filters becomes larger. This paper describes present states of the active filters based on state-of-the-art power electronics technology, and their future prospects toward the 21st century, including the personal view and expectation of the author.

A voltage sag study in an industry with adjustable speed drives

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.

Low voltage CMOS logic circuit with threshold voltage control

Abstract: A MOSFET circuit achieving high speed operation and low power consumption for a wide supply voltage range. MOSFET circuits are connected between a low threshold voltage CMOS circuit and a supply voltage and ground, as a power controller for switching power supply in response to sleep/active modes. High threshold voltage MOSFETs in the MOSFET circuits are gate biased by low threshold voltage MOSFETs, thereby preventing a current from flowing across the backgate terminal and the source terminal.

Neural Networks for Combined Control of Capacitor Banks and Voltage Regulators in Distribution Systems

Abstract: A neural network for controlling shunt capacitor banks and feeder voltage regulators in electric distribution systems is presented. The objective of the neural controller is to minimize total I/sup 2/R losses and maintain all bus voltages within standard limits. The performance of the neural network for different input selections and training data is discussed and compared. Two different input selections are tried, one using the previous control states of the capacitors and regulator along with measured line flows and voltage which is equivalent to having feedback and the other with measured line flows and voltage without previous control settings. The results indicate that the neural net controller with feedback can outperform the one without. Also, proper selection of a training data set that adequately covers the operating space of the distribution system is important for achieving satisfactory performance with the neural controller. The neural controller is tested on a radially configured distribution system with 30 buses, 5 switchable capacitor banks and a nine tap line regulators to demonstrate the performance characteristics associated with these principles. Monte Carlo simulations show that a carefully designed and relatively compact neural network with a small but carefully developed training set can perform quite well under slight and extreme variation of loading conditions.

Battery tester with power limit detection

Abstract: In an electrical resistive-load battery testing system, apparatus and methods are disclosed for independently monitoring and reacting to both the temperature of the load and the power actually consumed by the load. The signals derived by the temperature and power monitoring aspects of the invention may be used to provide visual and/or audible indicators to alert an operator that the system has exceeded predetermined operating levels. The load may be of a carbon-pile construction, though other loading arrangements are possible. According to the direct load-power monitoring aspect of the invention, electrical circuity is used to generate a signal representative of the power consumed by the load as a function of the voltage applied across the load and the current through by the load during the test, and a function such as an operator alert is performed in response to the power consumed by the load.

Indirect implementations of sliding-mode control law in buck-type converters

Abstract: Some practical methods for implementing the sliding-mode control law to control the buck-type converters are introduced The control equations are derived from the basic sliding-mode control law to accommodate the conventional fixed-frequency PWM control method As a result, the overall feedback control systems can be expressed under a form similar to state-feedback control where the voltage and current of the output capacitor are sensed and controlled With the switching frequency maintained to be constant (not varied over a wide range as in the original law), these control techniques are insensitive to power circuit parameter changes The output voltage errors in these implementations are proven to converge to zero exponentially similarly to the cases implementing the basic sliding-mode control equation These control implementations can be applied to both constant output voltage regulation (as in popular DC-DC converters) and to time-varying output voltage tracking (as in switching power amplifiers)

Piezoelectric transformer driving circuit

Abstract: A piezoelectric transformer driving circuit includes a boosting circuit receiving an input DC voltage to generate an AC voltage for driving a piezoelectric transformer, a frequency control circuit for controlling the frequency of the AC voltage applied to the piezoelectric transformer to control a step-up ratio of the piezoelectric transformer, and a drive voltage control circuit for controlling the voltage of the AC voltage applied to the piezoelectric transformer at a predetermined level, regardless of variation of the input DC voltage.

An active line conditioner to balance voltages in a three-phase system

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.

Voltage regulator with load pole stabilization

Abstract: A voltage regulator with load pole stabilization is disclosed. The voltage regulator consists of an error amplifier, an integrator which includes a switched capacitor, a pass transistor, and a feedback circuit. In one embodiment, the integrator circuit includes an amplifier, a capacitor, and a switched capacitor which is driven by a voltage controlled oscillator. The voltage controlled oscillator changes its frequency of oscillation proportional to the output current. In another embodiment, the switched capacitor is driven by a current controlled oscillator whose frequency of oscillation is also proportional to the output current of the voltage regulator. When the output current demand is large, the controlled oscillators increase the frequency which decreases the effective resistance of the switched capacitor thereby changing the frequency of the zero to respond to the change in the load pole. Conversely, the effective resistance is increased as the current demand is decreased, also to respond to the decrease in load pole. The controlled oscillator may be coupled to a current sensing device that generates a scaled version of the load current and couples to the regulated voltage output. The controlled oscillator is restricted to operating voltages that are related to the regulated output voltage and a control current that is a scaled version of the load current. Consequently, the disclosed voltage regulator has high stability without consuming excess power.

Voltage regulator for regulating an output voltage from a charge pump and method therefor

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.

Gate-control strategies for snubberless operation of series connected IGBTs

Abstract: Increasing the operation voltage and hence the switching power by series connection of IGBT-modules causes transient and static voltage imbalances. To achieve snubberless operation, novel gate-control strategies have been developed. Active gate-controlled voltage balancing and gate-side di/dt-control as well as dv/dt-control are presented in theory and with measurement results.

Voltage sags: effects, mitigation and prediction

Abstract: Customers all over the world experience problems due to power system voltage sags. Computers, industrial control systems, and adjustable-speed drives are especially notorious for their sensitivity. Tripping of high-power adjustable-speed drives is probably the main voltage sag problem. The number of trips depends strongly on the equipment sensitivity. Prediction methods are needed to quantify this aspect of the quality of the power supply. From utility and manufacturer's data, a customer can assess the compatibility between a piece of equipment and the electricity supply.

Automatic voltage detection in multiple voltage applications

Abstract: A removable controller card comprised of a plurality of Flash EEPROM devices (24) and a controller device (20) is described. The controller device (20) is further comprised of voltage detection circuitry including a variable voltage detector (28) for determining the system voltage level provided by a power supply within a computer (25) and for appropriately enabling a voltage regulator circuit (30) for dividing the system voltage level to a level suited for operation by the Flash EEPROM devices (24) and applying this operational voltage level to the Flash EEPROM devices (24). Upon determining the system voltage level provided by the power supply to be appropriately suited for operation of the Flash EEPROM devices (24), disabling the voltage regulator circuit (30) and providing the system voltage level to the Flash EEPROM devices (24).

Interpreting recent power quality surveys to define the electrical environment

Abstract: Recent AC power line monitoring projects have enabled a better understanding of the typical electrical environment within which sensitive electronic equipment must be able to operate. Voltage variations caused by utility protective and regulation devices, as well as variations caused by load equipment, contribute to the total power quality picture. Regardless of the origin of these variations, the load equipment must be able to operate with some degree of immunity. This paper presents a combined assessment of data from three of the most recent power quality surveys. Results of this assessment suggest that load equipment with reasonable voltage regulation and interruption ride-through will withstand the majority of recorded power line variations. A detailed analysis of monitor capabilities and limitations is presented, along with a discussion of the interpretation of power line variations recorded at different monitoring locations.

System-area operating margin assessment and security enhancement against voltage collapse

Abstract: The (very) short term reactive power scheduling function, to be adopted by ENEL Spa, takes into account the voltage stability requirements in a preventive application of the security function. In this environment the procedure determines the voltage collapse distance of the global system and of the areas controlled by the secondary voltage regulation (SVR) both in short (24 hours ahead) and in a very short term (few hours or fractions of hour ahead). The procedure also schedules the control actions to be taken in emergency states in a preventive way. Area or system-wise indicators, based on nodal sensitivities and/or eigen (singular) value analysis, provide effective measures of the margins of the system with respect to the risk of voltage collapse and the related corrective actions. Applications of the procedure to the EHV network and to a subtransmission area of the ENEL system are presented in the paper.

A new robust SPMSM control to parameter variations in flux weakening region

Abstract: A new implementation strategy for the flux weakening control of a surface mounted permanent magnet synchronous motor (SPMSM) 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 d-axis current are adjusted by the outer voltage regulation loop to prevent the saturation of the current regulator. The characteristics of this flux weakening scheme include no dependency on the machine parameters, the guarantee of current regulation on any operating condition, and fast transition into and out of the flux weakening mode. Experimental results at various operating conditions including 4-quadrant operation are presented to verify the feasibility of the proposed control scheme.

Single-stage, unity power factor switching converter with voltage bidirectional switch and fast output regulation

Abstract: Ac-to-dc switching converters employ bidirectional voltage switches, preferably magnetic amplifiers in series with a fast recovery diode, as controllable series input switches that couple ac rectifiers to single-stage dc-to-dc converters in order to provide unity power factor operation by control of current through the input inductor achieved by modulating the duty ratio d1 of the bidirectional voltage switch while independent regulation of load voltage is maintained by voltage feedback to modulate the switch duty ratio d of the converter (where d1

Memory modules with voltage regulation and level translation

Abstract: Low voltage DRAMs are used on higher voltage memory modules in a way that requires no modification of the DRAMs. "Bus switch" technology and compact low voltage regulators are used at the module level. The low voltage regulator provides a lowered, regulated voltage to DRAMs. The bus switches are used at the inputs and outputs of the DRAMs and effectively protect the DRAM circuitry from voltage swings that could otherwise be damaging.

An AC-AC power converter for custom power applications

Abstract: A versatile AC-AC converter that can be utilized as a control device for custom power applications is presented. The converter has the ability to regulate bus voltage through voltage sags and overvoltages, and act as a solid state circuit breaker. Performance characteristics under typical conditions are presented along with experimental verification of converter operation. Technical feasibility, protected efficiency and other practical implementation issues are discussed. Operation of the power converter is illustrated using EMTP simulations.