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Showing papers on "Power optimizer published in 2005"


Journal ArticleDOI
TL;DR: In this article, a new methodology is presented which quantifies the reserve needed on a system taking into account the uncertain nature of the wind power, and the reliability of the system is used as an objective measure to determine the effect of increasing wind power penetration.
Abstract: With wind power capacities increasing in many electricity systems across the world, operators are faced with new problems related to the uncertain nature of wind power. Foremost of these is the quantification and provision of system reserve. In this paper a new methodology is presented which quantifies the reserve needed on a system taking into account the uncertain nature of the wind power. Generator outage rates and load and wind power forecasts are taken into consideration when quantifying the amount of reserve needed. The reliability of the system is used as an objective measure to determine the effect of increasing wind power penetration. The methodology is applied to a model of the all Ireland electricity system, and results show that as wind power capacity increases, the system must increase the amount of reserve carried or face a measurable decrease in reliability.

795 citations


Proceedings ArticleDOI
12 Jun 2005
TL;DR: In this article, the authors analyze the assumptions of DC power flow, and make an attempt at quantifying these using indexes, and answer the question of how low the X/R ratio of line parameters can be, and what is the maximal deviation from the perfect flat voltage which still allows DC Power Flow to be acceptably accurate.
Abstract: In recent days almost every study concerning the analyses of power systems for market related purposes uses DC power flow. DC power flow is a simplification of a full power flow looking only at active power flows. Aspects as voltage support and reactive power management are not considered. However, such simplifications cannot always be justified and might sometimes be unrealistic. In this paper authors analyze the assumptions of DC power flow, and make an attempt at quantifying these using indexes. Among other, the paper answers the question of how low the X/R ratio of line parameters can be, and what is the maximal deviation from the perfect flat voltage which still allows DC power flow to be acceptably accurate.

391 citations


Journal ArticleDOI
TL;DR: The paper shows that the application of this novel sensorless current flyback inverter to an MPPT-operated PV system exhibits satisfactory MPPT performance similar to the one exhibited by the system with a dc current sensor as well.
Abstract: This paper presents a flyback inverter controlled by sensorless current maximum power point tracking (MPPT) for a small photovoltaic (PV) power system. Although the proposed system has small output power such as 300 W, a few sets of small PV power systems can be easily connected in parallel to yield higher output power. When a PV power system is constructed with a number of small power systems, the total system cost will increase and will be a matter of concern. To overcome this difficulty, this paper proposes a PV system that uses no expensive dc current sensor but utilizes the method of estimating the PV current from the PV voltage. The paper shows that the application of this novel sensorless current flyback inverter to an MPPT-operated PV system exhibits satisfactory MPPT performance similar to the one exhibited by the system with a dc current sensor as well. This paper also deals with the design method and the operation of the unique flyback inverter with center-tapped secondary winding.

359 citations


Patent
28 Jan 2005
TL;DR: An inverter for use in connecting a DC power source to the utility grid includes a single DC-DC conversion stage, maximum (source) power tracking, and current control based on feed-forward compensation as a function of an input power commanding voltage, rectified utility line voltage, and either a scaled and squared inverse or a scaled inverse of RMS voltage as discussed by the authors.
Abstract: An inverter for use in connecting a DC power source to the utility grid includes a single DC-DC conversion stage, maximum (source) power tracking, and current control based on feed-forward compensation as a function of an input power commanding voltage, rectified utility line voltage, and either a scaled and squared inverse or a scaled inverse of RMS utility line voltage. Various embodiments also include over-voltage, over-current, under-voltage, and over-temperature protection, and a stand-by battery with its battery management control, while others adapt a multiple-channel front-end distributed power system with distributed maximum power tracking to serve as a single DC power source input to the inverter system downstream with controllers, emergency or auxiliary loads, and alternative current feedback control systems for providing an in-phase output current with respect to the utility grid voltage while absorbing maximum power available from the DC power source and minimally utilizing the stand-by battery for maximal system reliability.

321 citations


Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, a high boost converter with a voltage multiplier and a coupled inductor was proposed to boost low input voltage to high voltage output with low duty cycle, and the secondary voltage was rectified using voltage multiplier.
Abstract: With the increasing demand for renewable energy, distributed power included in fuel cells have been studied and developed as a future energy source. For this system, a power conversion circuit is necessary to interface the generated power to the utility. In many cases, a high step-up DC/DC converter is needed to boost low input voltage to high voltage output. Conventional methods using cascade DC/DC converters cause extra complexity and higher cost. The conventional topologies to get high output voltage use flyback DC/DC converters. They have the leakage components that cause stress and loss of energy that results in low efficiency. This paper presents a high boost converter with a voltage multiplier and a coupled inductor. The secondary voltage of the coupled inductor is rectified using a voltage multiplier. High boost voltage is obtained with low duty cycle. Theoretical analysis and experimental results verify the proposed solutions using a 300 W prototype.

262 citations


Proceedings ArticleDOI
24 Oct 2005
TL;DR: In this article, different concepts of DC circuit breakers are presented and compared for different voltage levels and all solutions are compared under technical and economical aspects under both technical and economic aspects.
Abstract: The development of advanced transmission and distribution technologies is steadily gaining interest. Especially the large number of wind farms leads to a demand for new and innovative solutions. Considering the interconnection of offshore wind farms, new technologies must be investigated. One promising solution for an interconnection is a DC distribution system which is also discussed for new (onshore) medium-voltage distribution systems. Beside the advantages of DC distribution (low losses, no reactive power), DC has major disadvantages concerning control and switching actions. Since present circuit breakers are not able to switch large DC currents, new solutions must be found. After a brief introduction of the fundamental principles for switching DC currents, different concepts of DC circuit breakers are presented and compared in this paper. Furthermore, this analysis is accomplished for different voltage levels and all solutions are compared under technical and economical aspects.

239 citations


Patent
05 Jan 2005
TL;DR: A variable speed wind turbine employing a rotor (103) connected to a multiplicity of synchronous generators (106 - 112) with wound field or permanent magnet rotors is used for power transfer back to the grid.
Abstract: A variable speed wind turbine employing a rotor (103) connected to a multiplicity of synchronous generators (106 - 112) with wound field or permanent magnet rotors. A passive rectifier (114 - 120) and an inverter (136 - 142) are used for power transfer back to the grid. A Turbine Control Unit (TCU) (132) commands a required generator torque based on rotor speed and power output of the turbine inverters. Torque is controlled by regulating the DC current by control of the inverter. A main-shaft-damping filter is provided by measurement of the DC bus voltage. In high winds the turbine remains at a constant average output power through a constant torque command and a varying pitch command to a rotor pitch servo system (102). A set point is fixed at the inverter output such that output VAR load is minimized running the turbine at very nearly unity power factor. Dynamic VAR and power factor control is provided by a separate VAR apparatus.

210 citations


Patent
12 Jul 2005
TL;DR: In this article, the authors proposed a system for providing power from solar cells whereby each cell or cell array is allowed to produce its maximum available power and converted by an operatively connected DC/DC converter.
Abstract: The present invention is a system for providing power from solar cells whereby each cell or cell array is allowed to produce its maximum available power and converted by an operatively connected DC/DC converter. Each cell or cell array has its own DC/DC converter. In one form the system for providing power from solar cells includes one or more solar generators wherein each of said solar generators has one to nine solar cells; a maximum power tracker operatively associated with each solar generator, each of said maximum power tracker includes a buck type DC/DC converter without an output inductor, each of said maximum power trackers are operatively connected in series with each other; an inductor operatively connected to the series connected maximum power trackers; and means for providing electrical power from the inductor to load means, wherein each of said maximum power trackers is controlled so that the operatively associated solar generator operates at its maximum power point to extract maximum available power.

201 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss the key issues that confront power system planners and operators when integrating wind power plants into the electric power system and how the variations in wind plant outputs affect the operation of the power system on a daily basis and what the associated costs are.
Abstract: This paper discusses the key issues that confront power system planners and operators when integrating wind power plants into the electric power system. A key question is how the variations in wind plant outputs affect the operation of the power system on a daily basis and what the associated costs are. These costs are lower than initially expected by some utility engineers. The main reason for this is that wind tends to behave more like negative load than traditional firm-block generation, and the power system has been designed to handle significant load variations on a routine basis. This paper summarizes the key results of wind integration studies conducted to date and provides insights from individual studies. The studies present simulations of system operations that employ well-established production-costing and unit-commitment computational tools.

176 citations


Journal ArticleDOI
TL;DR: An inverter for grid-connected photovoltaic systems is presented in this paper, which can globally locate the maximum power point of the panel over wide insolation and feed the solar energy to the grid.
Abstract: An inverter for grid-connected photovoltaic systems is presented in this paper. It can globally locate the maximum power point of the panel over wide insolation and feed the solar energy to the grid. Its structure mainly integrates a previously developed maximum point tracking method and output current shaping function into a buck-boost-derived converter and then inverts the shaped current through a grid frequency bridge to the grid. Instead of having a storage capacitor connecting in parallel with the converter output, series connection is used, so that the required capacitor voltage rating is lower than that in classical inverters. Most importantly, the inverter output current harmonics are less sensitive to the capacitor value. A 30-W laboratory prototype has been built. The tracking capability, inversion efficiency, and large-signal responses at different insolations have been investigated. Detailed analysis on the inverter performance has been performed. The theoretical predictions are verified with the experimental results.

175 citations



Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this article, a hybrid energy system consisting of wind, photovoltaic and fuel cell designed to supply continuous power to the load is proposed, which can be easily adjusted to accommodate different and any number of energy sources.
Abstract: This paper proposes a hybrid energy system consisting of wind, photovoltaic and fuel cell designed to supply continuous power to the load. A simple and economic control with DC-DC converter is used for maximum power point tracking and hence maximum power extraction from the wind turbine and photovoltaic array. Due to the intermittent nature of both the wind and photovoltaic energy sources, a fuel cell is added to the system for the purpose of ensuring continuous power flow. The fuel cell is thus controlled to provide the deficit power when the combined wind and photovoltaic sources cannot meet the net power demand. In worst environmental conditions, when there is no output power from the wind or photovoltaic sources, the fuel cell will operate at its rated power of 10 kW. Hence this system under any operating condition will ensure a minimum power flow of 10 kW to the load. This hybrid system allows maximum utilization of freely available renewable energy sources like wind and photovoltaic and demand-based utilization of hydrogen-based fuel cell. The proposed system is attractive owing to its simplicity, ease of control and low cost. Also it can be easily adjusted to accommodate different and any number of energy sources. A complete description of this system is presented along with its simulation results which ascertain its feasibility.

Patent
Fred Flett1, Lizhi Zhu1, Sayeed Ahmed1, Ajay V Patwardhan1, Roy I. Davis1 
20 Oct 2005
TL;DR: In this article, the authors propose a power converter system topology that consists of a first DC/DC converter to pull a positive rail of a high voltage bus up, while a second DC-DC converter pushes a negative rail of the high voltage buses down.
Abstract: Power converter system topologies comprise a first DC/DC converter to pull a positive rail of a high voltage bus up, while a second DC/DC converter pushes a negative rail of the high voltage bus down. One or both the DC/DC converters may be bi-directional. Such topologies are suitable for use with separate primary power sources, and/or auxiliary power sources. Such topologies may include a DC/AC converter, which may be bi-directional. Such topologies may include one or more auxiliary DC/DC converters, which may be bi-directional. Multiple substrates, including at least one stacked above another may enhance packaging.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a power electronic converter, designed for efficiency, simplicity and ruggedness, for small-scale stand-alone wind energy systems, finding applications in locations where conventional generation is not practical.
Abstract: Small-scale stand-alone wind energy systems are an important alternative source of electrical energy, finding applications in locations where conventional generation is not practical Unfortunately, most of these systems do not capture power at every wind speed-especially low wind speeds which are low in power but can be very common To address this problem, the authors have proposed a power electronic converter, designed for efficiency, simplicity and ruggedness A simple feed forward technique is presented using discrete components and minimal sensors Test data are presented, indicating that the technique eliminates the standard "cut-in" wind speed and expands the operating range of a wind turbine

Proceedings ArticleDOI
12 Jun 2005
TL;DR: In this article, the authors proposed a pitch angle control strategy based on the average wind speed and standard deviation of wind speed, and pitch angle was controlled using a generalized predictive control in all operating regions for wind turbine generator.
Abstract: Effective utilization of renewable energies such as wind energy is expected instead of the fossil fuel. Wind energy is not constant and windmill output is proportional to the cube of wind speed, which cause the generated power of wind turbine generators to fluctuate. In order to reduce fluctuating components, there is a method to control pitch angle of blades of windmill. We have proposed the pitch angle control using minimum variance control in a previous work. However, it is a controlled output power for only rated wind speed region. This paper presents a control strategy based on average wind speed and standard deviation of wind speed, and pitch angle control using a generalized predictive control in all operating regions for wind turbine generator. The simulation results with using actual detailed model for wind power system show effectiveness of the proposed method.

Patent
10 Aug 2005
TL;DR: In this article, a DC-to-AC power converter topology and a novel control method are disclosed for photovoltaic micro-inverter applications, which are very well suited for PV microinverters.
Abstract: An apparatus and method of control for converting DC (direct current) power from a solar photovoltaic source to AC (alternating current) power. A novel DC-to-AC power converter topology and a novel control method are disclosed. This combination of topology and control are very well suited for photovoltaic microinverter applications. Also, a novel variant of this control method is illustrated with a number of known photovoltaic DC-to-AC power converter topologies. The primary function of both control methods is to seek the maximum power point (MPP) of the photovoltaic source with novel, iterative, perturb and observe control algorithms. The control portion of this invention discloses two related control methods, both an improvement over prior art by having greatly improved stability, dynamic response and accuracy.

Journal ArticleDOI
TL;DR: In this article, a deeper understanding of the potential impacts of wind generation facilities on the interaction with the bulk electric power system is provided, with individual wind power plants approaching the output rating of conventional power plants.
Abstract: Large-scale wind generation facilities have become a very visible component of the interconnected power grid in many options of the United States. Only a decade ago, wind generation facilities were viewed by most power engineers as a novelty, and by simple engineering judgement, it could be safely concluded that the effects of these unique but smaller facilities on system reliability would be negligible. Now, with individual wind generation facilities approaching the output rating of conventional power plants, a deeper understanding of their potential impacts on the interaction with the bulk electric power system is needed.

Journal ArticleDOI
TL;DR: In this paper, the authors focus their attention on the system as a whole rather than on individual components, regardless of whether or not the system includes wind generation, and make proper use of wind forecasting and integrate it into our control rooms and our systems.
Abstract: To run the power system most efficiently and effectively, we must focus our attention on the system as a whole rather than on individual components - and this is true regardless of whether or not the system includes wind generation. As larger amounts of wind energy are added to our power systems, we must certainly be aware of the impacts of its variability on the system, but we must also keep in mind that our power systems are already designed to deal with substantial amounts of uncertainty and variability. By making proper use of wind forecasting and integrating it into our control rooms and our systems, we can facilitate the cost-effective use of wind energy as a mainstream component of the energy system.

Proceedings ArticleDOI
12 Jun 2005
TL;DR: In this paper, a variable speed wind turbine with a step-up dc-dc converter is used to track the maximum power output of the turbine by calculating the speed command that corresponds to the maximum output power.
Abstract: This paper discusses a new and simple control method for maximum power tracking in a variable speed wind turbine by using a step-up dc-dc converter. The output voltage of permanent magnet generator is connected to a fixed dc-link through a three-phase rectifier and the dc-dc converter. A maximum power-tracking algorithm calculates the speed command that corresponds to maximum power output of the turbine. The dc-dc converter uses this speed command to control the output power of the permanent magnet generator, such that the speed of generator tracks the command speed. A current regulated PWM voltage source inverter maintains the output voltage of dc-dc converter at a fixed value by balancing the input and output power to the dc-link. In addition, the inverter can improve power factor and inject a current with very low harmonic distortion into the utility grid. The generating system has potentials of high efficiency, good flexibility, and low cost.

Patent
12 Jul 2005
TL;DR: In this paper, a power and control architecture employing circuitry that sequentially regulates power flows from independent solar-array sources or a mixture of power sources providing power to a common load is presented.
Abstract: A power and control architecture employing circuitry that sequentially regulate power flows from independent solar-array sources or a mixture of power sources providing power to a common load. The device may be used on a satellite with solar-array sources; however it may also be used on ground based systems. Stiff bus voltage regulation is obtained by tightly controlling the most recently activated power-processing channel while keeping the previously activated power-processing channels in the Maximum Power Tracking mode to supply maximum power to a common load. The remaining power-processing channels are turned off or operated in stand-by mode. In an alternative system, with primary design goal of uniform power sharing among solar-array sources, all solar array sources are activated with uniform power sharing at light load and, as load demand increases, sequentially controlled to operate in the Maximum Power Tracking mode one solar array source at a time as necessary.

Proceedings ArticleDOI
19 Sep 2005
TL;DR: In this article, a nonlinear controller has been designed for variable speed wind turbines electric power regulation, and a cascade structure asymptotic output tracking based approach has been applied.
Abstract: A nonlinear controller has been designed for variable speed wind turbines electric power regulation. The efficiency and reliability of wind power is shown to be depending on the applied control strategy of the wind turbine. Up to now, classical regulation is implemented only. However, under sudden wind profile variations, the wind turbine performance decrease which may cause troubles in the electrical network. For the limitation of mechanical loads and rotational speed variations, and to avoid the wind turbine stall above rated wind speeds while controlling the output power, a cascade structure asymptotic output tracking based approach has been applied. Simulations and validation have been performed using the wind turbine modelling and using wind turbine simulator as well. The wind turbine is torque generator controlled. The required performance is met for both

Patent
30 Sep 2005
TL;DR: In this article, a method for controlling power output of a wind turbine generator in response to an anticipated change in wind speed is provided, which includes sensing wind speed at a desired distance from the wind turbines generator in a direction of the wind.
Abstract: A method for controlling power output of a wind turbine generator in response to an anticipated change in wind speed is provided. The method includes sensing wind speed at a desired distance from the wind turbine generator in a direction of the wind. The method further includes controlling pitch of a blade of the wind turbine generator based upon sensed transient wind speed in advance of a change in wind speed at the wind turbine generator.

Patent
20 Dec 2005
TL;DR: In this article, a single stage inverter device for power converters, comprising switching means (M1-M4) capable to periodically connect an energy source (1, in particular a photovoltaic one, to an electric network or grid, was presented.
Abstract: The present invention concerns a single stage inverter device for power converters, comprising switching means (M1-M4) capable to periodically connect an energy source (1), in particular a photovoltaic one, to an electric network or grid (2), the switching means (M1-M4) being controlled by controlling electronic means (10, 20) operating according to a single switching cycle control of the switching means (M1-M4), the operative and circuit device parameters being such to fulfill a series of constraints simultaneously optimising both the maximum power point tracking or MPPT (Maximum Power Point Tracking) and the output power factor or PF-out (Power Factor-output) for one or more operation conditions. The present invention further concerns the related method of controlling and the related method of scaling such device.

Patent
30 Jun 2005
TL;DR: In this paper, a method for controlling variability in power output of a wind farm supplying power to a grid includes monitoring a power output level of the wind farm, compared to a target power output.
Abstract: A method for controlling variability in power output of a wind farm supplying power to a grid includes monitoring a power output level of the wind farm. The monitored power output level is compared to a target power output level. A command is issued to increase or decrease electrical power consumption by an electrolyzer system electrically coupled to the wind farm to maintain a net power output level by the wind farm based upon the comparison.

Proceedings ArticleDOI
24 Oct 2005
TL;DR: In this paper, a new control scheme for a regenerative AC/DC/AC converter using model based predictive control is presented, which minimizes quality functions, which represent the desired behavior of the converter.
Abstract: This paper presents a new control scheme for a regenerative AC/DC/AC converter using model based predictive control. The control strategy minimizes quality functions, which represent the desired behavior of the converter. At the inverter side, the load current error is minimized, while at the input side, the active and reactive powers are controlled directly. The main advantages of this method are: no need of linear current controllers, coordinates transformations or modulators for converter and inverter. The rectifier operates with sinusoidal input currents and unity power factor, while sinusoidal currents are generated out at the inverter load.

Patent
29 Jul 2005
TL;DR: In this paper, a system and method for power control in wind turbines is presented, which includes switching a plurality of switching devices in a power conversion component of the wind turbine system in a normal switching mode to provide power flow through the power conversion components.
Abstract: A system and method for power control in wind turbines are provided. The method includes switching a plurality of switching devices in a power conversion component of the wind turbine system in a normal switching mode to provide power flow through the power conversion component. The method further includes switching the plurality of switches devices in the power conversion component of the wind turbine system in a short circuit switching mode to prevent power flow through the power conversion component.

Proceedings ArticleDOI
Chad Abbey1, Geza Joos1
24 Oct 2005
TL;DR: In this article, the integration of a short-term energy storage device in a doubly-fed induction generator (DFIG) design was considered to smooth the fast, wind induced power variations.
Abstract: The need to limit power fluctuations resulting from wind turbine generators (WTG) is becoming more important as wind energy reaches higher levels of penetration. This paper considers the integration of a short-term energy storage device in a doubly-fed induction generator (DFIG) design in order to smooth the fast, wind induced power variations. This storage feature can also enhance the low voltage ride through (LVRT) capability. The topology is evaluated in terms of its ability to improve both the steady state and transient performance. The system is modeled in EMTP and a number of cases and configurations are illustrated. Results show that when storage is sized based upon the LVRT requirement, it can provide improved performance both under steady state and during transients when compared with conventional technologies.

Proceedings ArticleDOI
06 Mar 2005
TL;DR: The analysis considers different loss mechanisms and gives out quantitative descriptions of the power losses and useful design criteria and can be extended to other switched-capacitor converters.
Abstract: This paper presents a detailed analysis about the power losses and efficiency of multilevel dc-dc converters. The analysis considers different loss mechanisms and gives out quantitative descriptions of the power losses and useful design criteria. The analysis is based on a three-level multilevel dc-dc converter and can be extended to other switched-capacitor converters. The comparison between the theoretical analysis and the experimental results are shown to substantiate the theory

Proceedings ArticleDOI
14 Dec 2005
TL;DR: In this article, a multiple-input multiple-output DC/DC converter for renewable energy systems is proposed, which can be used to obtain well-regulated output voltage from several power sources, such as wind turbines, photovoltaic arrays, fuel cells, etc.
Abstract: This paper presents a multiple-input DC/DC converter for renewable energy systems. The proposed DC/DC converter can be used to obtain well-regulated output voltage from several power sources, such as wind turbines, photovoltaic arrays, fuel cells, etc. The energy provided by these power sources can be simultaneously transferred into the load. The proposed multiple-input DC/DC converter has the advantages of simple configuration, fewer components, lower cost and high efficiency. The operating principle, theoretical analysis, and design criteria are provided in this paper. A laboratory prototype with two different power sources was successfully implemented and tested. The simulation and experimental results are given to verify the feasibility of the proposed scheme

Patent
Lizhi Zhu1
27 May 2005
TL;DR: A power converter architecture interleaves full bridge converters to alleviate thermal management problems in high current applications, and may, for example, double the output power capability while reducing parts count and costs as mentioned in this paper.
Abstract: A power converter architecture interleaves full bridge converters to alleviate thermal management problems in high current applications, and may, for example, double the output power capability while reducing parts count and costs. For example, one phase of a three phase inverter is shared between two transformers, which provide power to a rectifier such as a current doubler rectifier to provide two full bridge DC/DC converters with three rather than four high voltage inverter legs.