Showing papers on "Voltage optimisation published in 2003"
12 Oct 2003
TL;DR: In this article, the authors proposed a hybrid asymmetric nine-level inverter, which consists of a three-phase three-level integrated gate-commutated thyristor inverter (main inverter), with a two-level insulated-gate bipolar transistor H-bridge (subinverter) in series with each phase.
Abstract: In symmetric multilevel inverters, there is a tradeoff between the output quality and the reliability and efficiency of the converter. New asymmetric and hybrid solutions, using different voltages and devices in various parts of the inverter, promise significant improvements for medium-voltage industrial drives. This paper investigates such a hybrid asymmetric nine-level inverter. It consists of a three-phase three-level integrated gate-commutated thyristor inverter (main inverter), with a two-level insulated-gate bipolar transistor H-bridge (subinverter) in series with each phase. To keep the power part simple and the efficiency high, the subinverters have no feeding from the net and can only supply reactive power. This is a very interesting solution in terms of power quality, efficiency, reliability, and cost. But the nonsupplied intermediate-circuit capacitors form an unstable system. This paper proposes a control method to stabilize their voltages. Power balancing is guaranteed by varying the common-mode voltage, using an online nonlinear model-predictive controller. The controller predicts the system evolution as a function of the control inputs. A cost function of system and control quantities is iteratively minimized in real time, to find the optimal control to apply to the system. Simulations and measurements demonstrate stable behavior in steady state and during transients. Precharging of the nonsupplied capacitors is also an issue to consider. This paper proposes a startup method that charges them in parallel with the supplied ones, without any additional equipment. Measurements show its successful application in the proposed drive system.
369 citations
Patent•
24 Jan 2003TL;DR: In this paper, a power supply rail controller operates on an analog component having a signal input, a power input, and a signal output, and provides a control output responsive to the signal output.
Abstract: A power supply rail controller operates on an analog component having a signal input, a power input and a signal output. A voltage controller provides a control output responsive to the signal output. A power supply generates a voltage for the power input, where the voltage is responsive to the control output. The voltage is reduced in magnitude to reduce power dissipation and increased in magnitude to avoid signal distortion.
271 citations
TL;DR: In this paper, the authors introduce the terminology and various issues related to power quality, and explain the interest in power quality in the context of deregulation of the electricity industry, increased customer-demands, and the integration of renewable energy sources.
254 citations
23 Jun 2003
TL;DR: In this paper, the authors present a methodology for evaluating the impact of DG units installation on electric losses, reliability and voltage profile of distribution networks based on a power flow method with the representation of generators as PV buses.
Abstract: This work presents a methodology for evaluating the impact of DG units installation on electric losses, reliability and voltage profile of distribution networks. The losses and voltage profile evaluation is based on a power flow method with the representation of generators as PV buses. The reliability indices evaluation is based on analytic methods modified to handle multiple generations. The methodology may be used to evaluate the influence of the local of installation and the capacity of DG on these system performance characteristics for different generation expansion planning alternatives. The results obtained with the proposed methodology for systems extracted from the literature demonstrates its applicability.
209 citations
TL;DR: In this article, the authors proposed a new compensation scheme capable of reducing transient voltage fluctuations caused by a phase angle change in the installation bus voltage, which was tested by computer simulation and experimental results.
Abstract: This paper discusses control characteristics of line-voltage regulation by a shunt active filter intended for installation on a power distribution system. Since the power circuit configuration of the active filter is the same as a static synchronous compensator (STATCOM), it is possible to regulate the line voltage by means of controlling an adequate amount of a reactive power. In this case, no harmonic voltage affects a feedback controller for the line-voltage regulation, because the active filter eliminates harmonic components from the line voltage at the installation bus. The dynamic performance is also investigated by computer simulation and experimental results. This paper proposes a new compensation scheme capable of reducing transient voltage fluctuations caused by a phase angle change in the installation bus voltage.
172 citations
TL;DR: In this paper, a systematic and an intuitive approach to the analysis of voltage dips due to faults in three-phase systems is presented, based on the decomposition of the three phase voltages in symmetrical components.
162 citations
Patent•
22 Sep 2003TL;DR: In this article, a conditioning circuit that measures operating points of a power supply to deduce therefrom the current-voltage characteristic of the power supply and determine directly the voltage corresponding to its maximum power point, without using any kind of tracking algorithm, is presented.
Abstract: The invention relates to a conditioning circuit that measures operating points of a power supply to deduce therefrom the current-voltage characteristic thereof and to determine directly the voltage corresponding to its maximum power point, without using any kind of tracking algorithm that causes the operating point of the power unit to oscillate about the maximum power point The maximum power point voltage VMPP is supplied to a controller which regulates a power cell by slaving it to the input voltage until the output voltage of the supply is equal to the maximum power point voltage V MPP The invention also relates to a solar generator and an associated conditioning method One particular application is to high-power satellites
146 citations
TL;DR: In this paper, two approaches to the mitigation of power quality problems are discussed: load conditioning and line-conditioning, which ensure that the equipment is made less sensitive to power disturbances, allowing the operation even under significant voltage distortion.
Abstract: There are two approaches to the mitigation of power quality problems. The first approach is called load conditioning, which ensures that the equipment is made less sensitive to power disturbances, allowing the operation even under significant voltage distortion. The other solution is to install line-conditioning systems that suppress or counteract the power system disturbances. Among the different new technical options available to improve power quality, active power filters have proved to be an important and flexible alternative to compensate for current and voltage disturbances in power distribution systems. Power filter topologies are discussed including shunt active filter, series active filters, series-shunt active filters, and hybrid active filters. New topologies using multilevel inverters are also discussed.
137 citations
TL;DR: The paper shows that the advanced DC voltage controller (ADCVC), which is a higher hierarchical controller, can meet the targeted voltage margin.
Abstract: Security requires that a system continues to function even when any one subsystem fails. A multiterminal HVDC system consists of N voltage-source converters (VSCs) exchanging power through a DC network. When any one converter is lost, before the surviving (N-1) converters have time to re-establish a new power balance, the excess DC power can produce voltage spikes which are destructive to the power electronic switches. The paper shows that the advanced DC voltage controller (ADCVC), which is a higher hierarchical controller, can meet the targeted voltage margin.
130 citations
TL;DR: In this paper, the authors investigated a new potential application of coordinated secondary voltage control by multiple FACTS voltage controllers in eliminating voltage violations in power system contingencies and proposed a multiagent collaboration protocol, which is graphically represented as a finite-state machine, for the coordination among multiple SVCs and STATCOMs.
Abstract: In order to achieve more efficient voltage regulation in a power system, coordinated secondary voltage control has been proposed, bringing in the extra benefit of enhancement of power system voltage stability margin. This paper investigates a new potential application of coordinated secondary voltage control by multiple FACTS voltage controllers in eliminating voltage violations in power system contingencies. The study is presented by the example New England ten-machine power system with two SVCs and two STATCOMs installed. The coordinated secondary voltage control is assigned to the SVCs and STATCOMs in order to eliminate voltage violations in system contingencies. In the paper, it is proposed that the secondary voltage control is implemented by a learning fuzzy logic controller. A key parameter of the controller is trained by P-type learning algorithm via offline simulation with the assistance of injection of artificial loads in controller's adjacent locations. A multiagent collaboration protocol, which is graphically represented as a finite-state machine, is proposed in the paper for the coordination among multiple SVCs and STATCOMs. As an agent, each SVC or STATCOM can provide multilocation coverage to eliminate voltage violations at its adjacent nodes in the power system. Agents can provide collaborative support to each other which is coordinated according to the proposed collaboration protocol.
116 citations
TL;DR: In this paper, it was shown empirically that the power transfer distribution factors are relatively insensitive to the operating point and the topology of an electric power system, but only for the special case of having reactive compensation sufficient to keep voltages constant at all busses.
Abstract: Power transfer distribution factors depend on the operating point and topology of an electric power system. However, it is known empirically that, for a fixed topology, the power transfer distribution factors are relatively insensitive to the operating point. We demonstrate this result theoretically for systems of arbitrary topology with losses, but only for the special case of having reactive compensation sufficient to keep voltages constant at all busses. We also analyze a power to current distribution factor that more closely relates to thermal constraints. We provide empirical corroboration for the theoretical result.
15 Apr 2003
TL;DR: In this paper, a simple and straightforward method of determining the maximum permissible loading and voltage stability margin of a power system using information about the current operating point is proposed, which simply requires some locally measurable quantities, such as bus voltage magnitude, and active and reactive components of load power.
Abstract: On-line determination of the maximum permissible loading of a power system is essential for operating the system with an adequate security margin. A very simple and straightforward method of determining the maximum permissible loading and voltage stability margin of a power system using information about the current operating point is proposed. The method simply requires some locally measurable quantities, such as bus voltage magnitude, and active and reactive components of load power. The measured data are carefully processed to estimate the maximum permissible loading and voltage stability margin of a system. The proposed method was vigorously tested on the IEEE 14- and 30-bus systems and the simulation results indicated that the method can correctly estimate the maximum permissible loading of the systems at the verge of voltage collapse.
TL;DR: In this paper, a market-based solution for managing reactive services by transmission operators is presented, which obligates the generators to provide reactive services in proportion to their active power output, optimizing and integrating reactive procurement with market operation for least-cost solution.
Abstract: The management of reactive resources, in particular the generation facilities under control of transmission operators, plays an important role in maintaining voltage stability and system reliability. The current practice of reactive management relies on heuristics and operators' judgments to procure reactive services. Consequently, it lacks a transparent market process and assurance that the procurement costs are the lowest. This paper presents a practical, market-based solution for managing reactive services by transmission operators. Three distinct features for the proposed solution are: (1) obligating generation facilities to provide reactive services in proportion to their active power output; (2) optimizing and integrating the reactive procurement with market operation for least-cost solution; and (3) taking into account the interactions of active and reactive powers for accurate calculation of the lost opportunity costs of generators. The proposed solution further simplifies the modeling and settlement aspects of reactive management. A model process of reactive power management is presented for use by independent transmission operators. A numerical example is also given to illustrate the application of the proposed solution.
12 Oct 2003
TL;DR: This paper proposes a new concept of interline dynamic voltage restoration (IDVR) where two or more DVRs in different feeders are connected to a common dc link and while one of the DVs compensates for a voltage sag, the other DVs connected to the common dc Link replenish the dc-link energy storage.
Abstract: Voltage deviations, often in the form of voltage sags, can cause severe process disruptions and result in substantial economic loss. The dynamic voltage restorer (DVR), a custom power device, has been proposed to protect sensitive loads from the effects of voltage sags on the distribution feeder. One of the main factors which limits capabilities of a particular DVR in compensating long-duration voltage sags is the amount of stored energy within the restorer. This paper proposes a new concept of interline dynamic voltage restoration (IDVR) where two or more DVRs in different feeders are connected to a common dc link. While one of the DVRs compensates for a voltage sag, the other DVRs connected to a common dc Link replenish the dc-link energy storage. A current-mode control strategy is incorporated into the IDVR system in both working modes, voltage sag compensation and power flow control. The reference voltage for power flow control mode is derived from instantaneous active current calculated using the dc-link voltage error signal. Simulation results are presented for a simple system in order to demonstrate the efficacy of the proposed IDVR system.
12 Oct 2003
TL;DR: In this article, two solutions are presented to prevent sensitive equipment from disruptive operation in the presence of voltage dips, which make use of distributed generation systems to maintain the voltage across the equipment.
Abstract: Voltage dips are often responsible for disrupting the operation of sensitive electronic equipment. In this paper, two solutions are presented to prevent sensitive equipment from disruptive operation. Both solutions make use of distributed generation systems to maintain the voltage across the equipment in the presence of voltage dips. The emphasis of this paper is on the transient response of both solutions to balanced as well as unbalanced voltage dips. Simulations have been carried out to provide a thorough analysis.
TL;DR: In this paper, the authors proposed a new concept of restoration technique to inject minimum energy during DVR compensation, which is based on the definition of voltage tolerance of the load, and some particular disturbances can be corrected with less amount of energy discharge than those of conventional methods.
TL;DR: This work shows how voltage scaling can be scheduled to reduce energy usage while still meeting real-time deadlines.
Abstract: Many embedded systems operate under severe power and energy constraints. Voltage clock scaling is one mechanism by which energy consumption may be reduced: it is based on the fact that power consumption is a quadratic function of the voltage, while the speed is a linear function. We show how voltage scaling can be scheduled to reduce energy usage while still meeting real-time deadlines.
Patent•
3 Feb 2003
TL;DR: In this paper, the authors proposed a digitally controlled multi-phase voltage regulator system providing regulated power to electronic components that have variable power requirements, where the voltage and current information is digitized and provided to a control integrated circuit (IC).
Abstract: Disclosed is a digitally controlled multi-phase voltage regulator system providing regulated power to electronic components that have variable power requirements. Power is supplied by one or more power integrated circuits (IC) each having a high side power switch controlled by pulse width modulated signals and a low side power switch. The power IC senses voltage at the load and has an on-chip current mirror for generating a current that is a ratio of current delivered to the load. The power IC also has current limiting and on-chip temperature sensing components. The voltage and current information is digitized and provided to a control integrated circuit (IC). The control IC receives this digitized information as well as user provided parameters and, in the regulation mode of operation, provides digitized pulse width modulated control signals to the power IC. In an active transient response mode of operation, the control IC provides signals to turn either the high side switches or low side switches ON. Fault detection circuitry identifies over voltage, under voltage, and excessive temperatures. All communications between the control IC and the power IC are digital providing high bandwidth, optimal control frequency response, noise immunity and efficient active transient response.
Patent•
24 Jul 2003TL;DR: In this paper, a power factor correcting power supply includes an input stage power converter and an output stage power converter, and the output voltage is provided on a DC rail for a load of the power factor correction power supply.
Abstract: A power factor correcting power supply includes an input stage power converter and an output stage power converter. The input stage power converter includes a plurality of series connected boost switches and a power factor correction controller. The power factor correction controller may direct the operation of the boost switches with series interleave phasing to perform power factor correction and voltage regulation. The boost switches are supplied input voltage and input current from a power source. The input voltage is converted to a DC boost voltage by high frequency series interleaved switching of the boost switches. The DC boost voltage is converted to a DC output voltage by the output stage power converter. The DC output voltage is provided on a DC rail for a load of the power factor correcting power supply.
TL;DR: In this paper, potential problem areas in using RMS values in power quality assessment are identified and discussed, as well as potential solution areas for using root mean square mathematical operations for power quality analysis.
Abstract: The root mean square mathematical operation is widely used in power engineering. The process has a frequency response characteristic and an associated time constant which is important especially for short term signals. Potential problem areas in using RMS values in power quality assessment are identified and discussed.
19 Feb 2003
TL;DR: In this article, a new two-stage structure is proposed for DC/DC transformers, where the leakage inductor combined with the resonance is used to achieve a simple, high efficiency isolation stage.
Abstract: In this paper, a new two-stage structure is proposed. For the first stage, a concept of energy transfer by the leakage inductor combined with the resonance is used to achieve a simple, high efficiency isolation stage. Application of this concept leads to the discovery of a family of simple, high efficiency DC/DC transformers. In order to achieve optimal system performance, the intermediate bus voltage is also investigated. Finally, The experimental results are provided.
TL;DR: In this paper, the authors proposed a shunt active filter that minimizes the third, fifth, and seventh harmonic voltage components at the point of filter coupling to compensate the pantograph voltage form factor, and provide reactive power to maintain the feeder voltage.
Abstract: AC railway traction systems are particularly susceptible to harmonic distortion. They are weak single-phase networks often loaded with severely distorting SCR-based locomotive drives which continually change their point of physical connection to the network. For a public distribution system the total harmonic distortion is a clear measure of supply quality. However, for a traction system the more important parameter is the voltage form factor, which is directly related to the maximum power a locomotive can deliver. To minimize this form factor, this paper proposes the use of a shunt active filter that minimizes the third, fifth, and seventh harmonic voltage components at the point of filter coupling. It is shown that the filter is effective in both compensating the pantograph voltage form factor, and providing reactive power to maintain the feeder voltage. The results are confirmed by detailed simulation using the EMTDC package.
Patent•
29 Apr 2003TL;DR: In this paper, a power management system includes a voltage booster in combination with a voltage regulator to provide a regulated output voltage, which is used to selectively enable/disable the doubling functionality of the voltage booster to increase power conversion efficiency.
Abstract: A power management system includes a voltage booster in combination with a voltage regulator to provide a regulated output voltage. The voltage provided to the voltage regulator is used to selectively enable/disable the doubling functionality of the voltage booster to increase power conversion efficiency.
1 Sep 2003
TL;DR: A novel emergency control scheme capable of predicting and preventing a voltage collapse in a power system, that is modelled as a hybrid system incorporating nonlinear dynamics, discrete events and discrete manipulated variables is presented.
Abstract: This paper presents a novel emergency control scheme capable of predicting and preventing a voltage collapse in a power system, that is modelled as a hybrid system incorporating nonlinear dynamics, discrete events and discrete manipulated variables. Model Predictive Control in connection with the Mixed Logical Dynamical framework is used to successfully stabilize the voltage of a four bus example system.
2 Nov 2003
TL;DR: Two control strategies to improve the dynamic performance of the static series compensator are proposed, each based on vector control, which uses a fast technique for separating positive and negative sequence components of the supply voltage.
Abstract: The static series compensator (SSC) is suited to protect sensitive loads against voltage dips. Because most of the power system faults are single- or double-phase, the control algorithms of the SSC should be adapted for unbalanced dips. This paper proposes two control strategies to improve the dynamic performance of the SSC. The first strategy uses a fast technique for separating positive and negative sequence components of the supply voltage, which are then controlled separately. Thus, two controllers are implemented for the two sequences, each based on vector control. The second strategy is based on using only a positive sequence controller and increasing the switching frequency. Consequently, the negative sequence due to the unbalanced dip is transformed into variations in the positive sequence. As the switching frequency increases, the ability of the controller to follow those variations improves. The validity of the proposed strategies is demonstrated through PSCAD/EMTDC simulation, when the grid is subjected to unbalanced three-phase voltage dips.
12 Oct 2003
TL;DR: In this paper, a high frequency AC-based microgrid is presented as an interesting step towards integration of renewable energy sources in a distributed generation system using a unified power quality conditioner (UQPC).
Abstract: This paper presents a high frequency AC-based microgrid as an interesting step towards integration of renewable energy sources in a distributed generation system. The successful implementation of an HFAC microgrid depends on the best utilization of the sources and the common bus, which can be accomplished using a unified power quality conditioner (UQPC). The UPQC can compensate for current and voltage harmonics and also for reactive power. Its controller is based on the instantaneous p-q theory and the results obtained so far show that this conditioner can be effectively used to improve the system operation.
Patent•
27 Mar 2003TL;DR: A bus power device includes a connector that is connected to a port of a host apparatus compliant with a predetermined interface standard, a current/voltage detecting unit, and a power assisting unit that assists a current to the bus power line based on a result of comparison between the current detected by the current detecting unit and a threshold current.
Abstract: A bus power device includes a connector that is connected to a port of a host apparatus compliant with a predetermined interface standard; a current/voltage detecting unit that detects a current/voltage supplied from the host apparatus to a bus power line via the port and the connector; and a power assisting unit that assists a current to the bus power line based on a result of comparison between the current detected by the current/voltage detecting unit and a threshold current, and assists a voltage to the bus power line by an amount of shortfalls in the voltage based on a result of comparison between the voltage detected by the current/voltage detecting unit and a threshold voltage.
13 Jul 2003
TL;DR: In this article, simple analytical expressions of voltage profile along radial distribution feeders containing distributed generation (DG) units are derived, where DG active and reactive power generation limits constrained by permissible voltage levels are also expressed as a function of DG location along the feeder.
Abstract: This paper derives simple analytical expressions of voltage profile along radial distribution feeders containing distributed generation (DG) units. The analysis assumes fixed substation voltage by LTC transformer is based on uniformly distributed loads. DG active and reactive power generation limits constrained by permissible voltage levels are also expressed as a function of DG location along the feeder. The method is extended to more practical feeders with concentrated loads and line segments with different conductor size and geometry. The analysis is illustrated by a numerical example that shows that the analytical expressions derived are quite accurate.
1 Jan 2003
TL;DR: In this paper, a wide-area measurement system is proposed to monitor and control voltage as well as frequency stability of power systems and describes their state-of-the-art platform, which is now commercially available.
Abstract: With the emphasis on higher utilization of power systems, monitoring of its dynamics is becoming increasingly important. This requires information with higher accuracy and update rates faster than those usually provided by traditional SCADA systems. In addition, it must be synchronized over a wider geographical area than that provided by traditional protection systems. The introduction of phasor measurement units as well as advances in communication and computational equipment have made it technically feasible to monitor the stability of the power system on-line, using a wide area perspective. This paper outlines the specialized applications to monitor and control voltage as well as frequency stability of power systems and describes their state-of-the-art platform, the wide-area measurement system, which is now commercially available.
9 Jun 2003
TL;DR: In this paper, the authors proposed a direct power control for the three-phase PWM boost rectifier using space vector modulation (DPC-SVM), where the active and reactive power is used as the PWM control variables instead of the 3-phase line currents.
Abstract: The three-phase PWM boost rectifier is an interesting solution thanks to advantages as: bi-directional power flow, low harmonic distortion of line current, regulation of input power factor to unity, adjustment and stabilization of DC-link voltage. This paper proposes a new direct power control for this kind of converter using space vector modulation (DPC-SVM). The active and reactive power is used as the pulse width modulated (PWM) control variables instead of the three-phase line currents ever used. Moreover, line voltage sensors are replaced by virtual flux (VF) estimator. The theoretical principle of this method and the synthesis of the active and reactive power controllers are discussed. The steady state operation, dynamic results and behaviour under distorted and imbalanced line voltage conditions that illustrate the performance of the DRC-SVM are presented. It is shown that the proposed method exhibits several features as: simple tuning procedure of PI power controllers, good dynamic response, constant switching frequency and sinusoidal line current when supply voltage is non ideal. Simulation and experimental results have proven excellent performances and verify the validity of the proposed system.