Showing papers on "Power optimizer published in 2010"

A Novel Control Strategy for a Variable-Speed Wind Turbine With a Permanent-Magnet Synchronous Generator

Abstract: This paper presents a novel control strategy for the operation of a direct-drive permanent-magnet synchronous-generator-based stand-alone variable-speed wind turbine. The control strategy for the generator-side converter with maximum power extraction is presented. The stand-alone control is featured with output voltage and frequency controller that is capable of handling variable load. The potential excess of power is dissipated in the dump-load resistor with the chopper control, and the dc-link voltage is maintained. Dynamic representation of dc bus and small-signal analysis are presented. Simulation results show that the controllers can extract maximum power and regulate the voltage and frequency under varying wind and load conditions. The controller shows very good dynamic and steady-state performance.

A DC-DC multilevel boost converter

Abstract: A DC-DC converter topology is proposed. The DC-DC multilevel boost converter (MBC) is a pulse-width modulation (PWM)-based DC-DC converter, which combines the boost converter and the switched capacitor function to provide different output voltages and a self-balanced voltage using only one driven switch, one inductor, 2 N -1 diodes and 2 N -1 capacitors for an Nx MBC. It is proposed to be used as DC link in applications where several controlled voltage levels are required with self-balancing and unidirectional current flow, such as photovoltaic (PV) or fuel cell generation systems with multilevel inverters; each device blocks only one voltage level, achieving high-voltage converters with low-voltage devices. The major advantages of this topology are: a continuous input current, a large conversion ratio without extreme duty cycle and without transformer, which allow high switching frequency. It can be built in a modular way and more levels can be added without modifying the main circuit. The proposed converter is simulated and prototyped; experimental results prove the proposition's principle.

T-S Fuzzy Maximum Power Point Tracking Control of Solar Power Generation Systems

Abstract: This paper presents maximum power point tracking (MPPT) control for stand-alone solar power generation systems via the Takagi-Sugeno (T-S) fuzzy-model-based approach. In detail, we consider a dc/dc buck converter to regulate the output power of the photovoltaic panel array. First, the system is represented by the T-S fuzzy model. Next, in order to reduce the number of measured signals, a T-S fuzzy observer is developed for state feedback. Then, a fuzzy direct MPPT controller is proposed to achieve asymptotic MPPT control, in which the observer and controller gains are obtained by separately solving two sets of linear matrix inequalities. Different from the traditional MPPT approaches, the proposed T-S fuzzy controller directly drives the system to the maximum power point without searching the maximum power point and measuring insolation. Furthermore, when considering disturbance and uncertainty, robust MPPT is guaranteed by advanced gain design. Therefore, the proposed method provides an easier implementation form under strict stability analysis. Finally, the control performance is shown from the numerical simulation and experimental results.

A STATCOM-Control Scheme for Grid Connected Wind Energy System for Power Quality Improvement

Abstract: Injection of the wind power into an electric grid affects the power quality. The performance of the wind turbine and thereby power quality are determined on the basis of measurements and the norms followed according to the guideline specified in International Electro-technical Commission standard, IEC-61400. The influence of the wind turbine in the grid system concerning the power quality measurements are-the active power, reactive power, variation of voltage, flicker, harmonics, and electrical behavior of switching operation and these are measured according to national/international guidelines. The paper study demonstrates the power quality problem due to installation of wind turbine with the grid. In this proposed scheme STATic COMpensator (STATCOM) is connected at a point of common coupling with a battery energy storage system (BESS) to mitigate the power quality issues. The battery energy storage is integrated to sustain the real power source under fluctuating wind power. The STATCOM control scheme for the grid connected wind energy generation system for power quality improvement is simulated using MATLAB/SIMULINK in power system block set. The effectiveness of the proposed scheme relives the main supply source from the reactive power demand of the load and the induction generator. The development of the grid co-ordination rule and the scheme for improvement in power quality norms as per IEC-standard on the grid has been presented.

Power system with power converters having an adaptive controller

Abstract: A power system having a power converter with an adaptive controller. The power system is coupled to a load and includes a power system controller that receives a signal indicating a system operational state of the load and selects a power converter operational state as a function thereof. The power system also includes a power converter with a power switch that conducts for a duty cycle to provide a regulated output characteristic at an output thereof. The power converter also includes a controller that receives a command from the power system controller to enter the power converter operational state and provides a signal to control the duty cycle of the power switch as a function of the output characteristic and in accordance with the command, thereby regulating an internal operating characteristic of the power converter to improve an operating efficiency thereof as a function of the system operational state.

Power Management System for Online Low Power RF Energy Harvesting Optimization

Abstract: For many years, wireless RF power transmission has been investigated as a viable method of power delivery in a wide array of applications, from high-power space solar power satellites to low-power wireless sensors. However, until recently, efficient application at the low sub-milliwatt power levels has not been realized due to limitations in available control circuitry. This paper presents a “smart” microcontroller-based power management system with online power stage efficiency optimization and maximum power point tracking (MPPT). The system is experimentally evaluated using a new, more accurate four-quadrant rectenna model and circuit realization that enables rigorous testing of the power management system for a wide range of rectenna arrays and power characteristics. Hardware results are presented with online optimization over a converter input power range from 10 μW to 1 mW. Results are also shown based on the application of harvesting RF power from a nearby cellular tower, where the power management system collects up to seven times more energy when compared to a direct battery connection.

Analysis and Design of an Offshore Wind Farm Using a MV DC Grid

Abstract: This paper outlines the design of an offshore wind farm using a dc offshore grid based on resonant dc-dc converters. Multiphase resonant dc-dc converters are studied to step up the dc voltage from individual wind generators to a Medium Voltage (MV) dc bus, and from the MV bus to an HVDC line that will connect the wind farm to shore. Compared to an equivalent ac grid-based wind farm, a dc grid-based wind farm has slightly higher losses, but the weight of the magnetic components and cables is substantially lower. The analysis of operating permanent-magnet synchronous generators at variable and constant dc voltages shows that a fixed dc voltage has marginally higher efficiency than a variable dc voltage. However, using a variable dc voltage gives lower harmonics at the generator facing the voltage-source converter and the dc-dc step-up converter. An aggregated model of multiple parallel connected wind generators is developed and shown to accurately approximate a detailed PSCAD model during varying wind conditions and transients.

An Efficient Wind–Photovoltaic Hybrid Generation System Using Doubly Excited Permanent-Magnet Brushless Machine

Abstract: With ever-increasing concerns on energy issues, the development of renewable energy sources is becoming more and more attractive. This paper first reviews both the wind power and photovoltaic (PV) power generation techniques and their maximum-power-point tracking (MPPT) methods. Then, a new stand-alone wind-PV hybrid generation system is proposed for application to remote and isolated areas. For the wind power generation branch, a new doubly excited permanent-magnet brushless machine is used to capture the maximum wind power by using online flux control. For the PV power generation branch, a single-ended primary inductance converter is adopted to harness the maximum solar power by tuning the duty cycle. The experimental results confirm that the proposed hybrid generation system can provide high efficiency with the use of MPPT.

Review on frequency control of power systems with wind power penetration

Abstract: The increasing penetration of wind power may influence the frequency stability of power systems. Therefore, new control schemes are necessary for wind turbines and power systems to support the frequency control. Currently, most of the published control methods can be classified into 3 levels, i.e., wind turbine level, wind farm level and power system level. The wind turbine level control enables wind turbines, particularly the variable speed wind generators, to provide dynamic response and power reserves for the primary frequency control by implementing the inertial, droop or deloading controller. The wind farm level control distributes the central control command from the system to the local wind turbines and energy storage units for the desired generation. The power system level control coordinates wind farms with conventional power plants for the secondary control to recover the frequency to the reference value faster than for the no coordination control case. This paper presents a review on the latest studies in relation to the 3-level frequency control of power systems with wind power penetration.

Electric power from offshore wind via synoptic-scale interconnection

Abstract: World wind power resources are abundant, but their utilization could be limited because wind fluctuates rather than providing steady power. We hypothesize that wind power output could be stabilized if wind generators were located in a meteorologically designed configuration and electrically connected. Based on 5 yr of wind data from 11 meteorological stations, distributed over a 2,500 km extent along the U.S. East Coast, power output for each hour at each site is calculated. Each individual wind power generation site exhibits the expected power ups and downs. But when we simulate a power line connecting them, called here the Atlantic Transmission Grid, the output from the entire set of generators rarely reaches either low or full power, and power changes slowly. Notably, during the 5-yr study period, the amount of power shifted up and down but never stopped. This finding is explained by examining in detail the high and low output periods, using reanalysis data to show the weather phenomena responsible for steady production and for the occasional periods of low power. We conclude with suggested institutions appropriate to create and manage the power system analyzed here.

A New Interconnecting Method for Wind Turbine/Generators in a Wind Farm and Basic Performances of the Integrated System

Abstract: A new interconnecting method for a cluster of wind turbine/generators is proposed, and some examples of the basic characteristics of the integrated system are shown. This method can be achieved with a wind turbine generating system using a shaft generator system. A group of wind turbine/generators can be interconnected easily with the proposed method, and high reliability and electric output power with high quality are also expected. Moreover, since this method enables transmission of the generated power through a long-distance dc transmission line, the optimum site for wind turbines can be selected so as to acquire the maximum wind energy.

Converter Systems for Fuel Cells in the Medium Power Range—A Comparative Study

Abstract: Inverter systems that feed electrical power from fuel cells into the grid must convert the direct current of the fuel cell into the alternating current of the grid. In addition, these inverters have to adapt the different voltages of the fuel-cell system and the grid to each other. In this paper, different topologies of appropriate inverter systems in the medium power range of 20 kW and higher are presented briefly. The inverter operating behavior, power rating, and efficiency are compared. The power rating and efficiency are compared using an analytical calculation of the semiconductor losses. The study includes transformerless inverters as well as two-stage inverter systems with high-frequency transformers (dc/dc converter combined with an inverter). This paper compares converter systems using insulated-gate bipolar transistors (IGBTs), e.g., a boost converter in series with a voltage-source inverter (VSI), current-source inverter, and z-source inverter or converter systems using superjunction MOSFETs, such as voltage- and current-fed full-bridge converters or a boost converter with an autotransformer. The MOSFET-based dc/dc converters must be connected in series to a VSI with IGBTs to feed into the three-phase grid. The presented converters were tested in the laboratory. Some characteristics of their laboratory performance are shown.

Photovoltaic power plant output

Abstract: A method and system for reducing power output rate change variability. A photovoltaic power output is received from a photovoltaic array. The rate of change of the photovoltaic power output is measured. An auxiliary power source output is adjusted to limit a plant power output rate of change to within a power output rate change band when combined with the photovoltaic power.

Thin-film photovoltaic power element with integrated low-profile high-efficiency DC-DC converter

Abstract: A photovoltaic device includes at least one photovoltaic cell and a DC/DC converter electrically coupled to the at least one photovoltaic cell. The at least one photovoltaic cell and the DC/DC converter are integrated into a photovoltaic package.

Soft-Switching Converter With HF Transformer for Grid-Connected Photovoltaic Systems

Abstract: In this paper, the design, realization, and performance evaluation of a single-phase 3-kW dc/ac power converter, using an active-bridge dc/dc converter and a full-bridge dc/ac, are introduced, presenting a novel solution on the industrial scenario for the considered application. Control algorithms, including the maximum power point tracking, paralleling to the grid, and converter switching signals, are digitally implemented on a standard microcontroller.

A hybrid smart AC/DC power system

Abstract: Recently, a smart grid has been attracted attention from the background of the introduction promotion of natural energy. At present, a smart grid based on AC grid has been proposed. However, no paper or article has been presented or published on a smart grid based on DC grid. This paper presents a AC/DC hybrid power system. The system has advantages on both DC and AC grid. The power system consists of wind generators and controllable loads. The controllable loads have different capacities. Therefore, by applying power consumption control under the droop characteristic, the DC bus voltage are maintained in the acceptable range. As the controllable loads, electric water heater and electric vehicles are used. The effectiveness of the proposed method is performed by using MATLAB/POWER SYSTEM® environment.

Wind energy power conversion system reducing gearbox stress and improving power stability

Abstract: A wind energy power conversion system includes a gearbox, a generator, an AC to DC power converter, a DC link, and a DC to AC power converter, and at least one ultracapacitor module connected in parallel on the DC link. A method of reducing stress on a wind turbine gearbox can be performed by obtaining an unwanted frequency of the wind energy power conversion system gearbox; determining an input torque value on the input shaft of the gearbox as a function of time; determining a frequency of the input torque value; and adjusting a torque on the output shaft of the gearbox based on the unwanted frequency.

Dynamic operation and control of a hybrid wind-diesel stand alone power systems

Abstract: This paper presents the dynamic operation and control strategies of a hybrid wind-diesel-battery energy storage based power supply system for isolated communities are investigated. Control strategies for voltage and frequency stabilization and efficient power flow among the hybrid system components are developed. The voltage and frequency of the hybrid wind-diesel system is controlled either by a load side inverter or by diesel generation depending on the wind conditions. During high penetration of wind, the wind turbine supplies the required power to the load. A battery energy storage system is connected to the dc-link to balance the power generated from the wind turbine and the power demand by load. Under low wind conditions, a diesel generator is used with wind energy conversion system to generate the required power to the load. A power sharing technique is developed to allocate power generation for diesel generator in low wind conditions. Results show that the control strategies work very well under dynamic and steady state condition to supply power to the load.

Impact of Large-Scale Wind Farm Connecting With Power Grid on Peak Load Regulation Demand

Abstract: At present large-scale wind farms are being constructed in China at a fast pace and they will be connected with power grids, it makes the peak load regulation of power grid becoming one of new puzzles in the operation of power grid containing wind farms. Considering the random nature of wind power output and complicated and changeable operation modes of wind farm, by means of simulating annual chronological load time series and chronological time series of wind power output in the planned year, the impacts of large-scale wind farm on power system peak load regulation are analyzed in a new viewpoint. The impacting mechanism of wind power output on difference between peak load and valley load of power grid is analyzed, by way of leading in a new evaluation index system the variation of peak-to-valley difference of equivalent load of power grid with large scale wind farm connected and its distribution are researched in detail. The influencing laws of large-scale wind farm on system peak load regulation under various outward power transmission modes and coordinative system peak load regulation modes are further analyzed. Selecting the wind farm base located in Jiuquan, Gansu province as the object, the wind power planning and the dispatching and operation of Gansu power grid are analyzed and demonstrated, and based on the analysis results some suggestions of generation expansion planning and operation mode for Gansu power grid are proposed.

Uncertainty analysis for wind energy production with dynamic power curves

Abstract: The production of wind energy often involves uncertainties due to the stochastic nature of wind speeds and the variation of the power curve. The latter occurs when a fleet of wind turbine generators (WTG) of the same type are deployed in the wind farm, yet each generator may produce different amounts of powers given the same wind speed. This paper aims to characterize the dynamics of the wind energy production and estimate the power uncertainty when a WTG operates between the cut-in wind speed and the rated wind speed. We propose a probabilistic model to characterize the dynamics of the output power assuming the power follows the normal distribution with a varying mean and a constant standard deviation. Based on that condition, the mean and the variance for the total wind energy production are derived by incorporating the stochastic wind speed and the power dynamics. Both simulations and numerical examples are provided to verify and illustrate the new model, respectively.

Compensating for wind variability using co-located natural gas generation and energy storage

Abstract: Wind generation presents variability on every time scale, which must be accommodated by the electric grid. Limited quantities of wind power can be successfully integrated by the current generation and demand-side response mix but, as deployment of variable resources increases, the resulting variability becomes increasingly difficult and costly to mitigate. We model a co-located power generation/energy storage block which contains wind generation, a gas turbine, and fast-ramping energy storage. Conceptually, the system is designed with the goal of producing near-constant “baseload” power at a reasonable cost while still delivering a significant and environmentally meaningful fraction of that power from wind. The model is executed in 10 second time increments in order to correctly reflect the operational limitations of the natural gas turbine. A scenario analysis identifies system configurations that can generate power with 30% of energy from wind, a variability of less than 0.5% of the desired power level, and an average cost around $70/MWh. The systems described have the most utility for isolated grids, such as Hawaii or Ireland, but the study has implications for all electrical systems seeking to integrate wind energy and informs potential incentive policies.

Photovoltaic power plant with distributed DC-to-DC power converters

Abstract: A solar photovoltaic plant is disclosed where a number of distributed DC-to-DC converters are used in conjunction with a central DC-to-AC converter. Each DC-to-DC converter is dedicated to a portion of the photovoltaic array and tracks the maximum power point voltage thereof. The DC-to-DC converters also boost the photovoltaic voltage and regulate a DC output current for transmission to the central DC-to-AC converter. Five distinct advantages are had over the prior art. First, efficiencies in intra-field power collection are greatly improved by transferring power at higher DC voltages. Second, the number of independent photovoltaic maximum power point trackers in the power plant can be increased, in a cost effective manner, to optimize the overall photovoltaic array energy harvest. Third, each DC-to-DC converter output “looks” like a current source at the input of the DC-to-AC converter and therefore can be easily paralleled. Fourth, the current source nature of the DC-to-DC converter outputs enables the DC-to-AC converter to operate with a minimum, fixed DC bus voltage to provide maximum DC-to-AC power conversion efficiencies. And fifth, each distributed DC-to-DC converter can isolate a faulted portion of the photovoltaic array while the remainder of the array continues producing power.