Showing papers on "AC power published in 2006"
TL;DR: In this article, real and reactive power management strategies of EI-DG units in the context of a multiple DG microgrid system were investigated. And the results were used to discuss applications under various microgrid operating conditions.
Abstract: This paper addresses real and reactive power management strategies of electronically interfaced distributed generation (DG) units in the context of a multiple-DG microgrid system. The emphasis is primarily on electronically interfaced DG (EI-DG) units. DG controls and power management strategies are based on locally measured signals without communications. Based on the reactive power controls adopted, three power management strategies are identified and investigated. These strategies are based on 1) voltage-droop characteristic, 2) voltage regulation, and 3) load reactive power compensation. The real power of each DG unit is controlled based on a frequency-droop characteristic and a complimentary frequency restoration strategy. A systematic approach to develop a small-signal dynamic model of a multiple-DG microgrid, including real and reactive power management strategies, is also presented. The microgrid eigen structure, based on the developed model, is used to 1) investigate the microgrid dynamic behavior, 2) select control parameters of DG units, and 3) incorporate power management strategies in the DG controllers. The model is also used to investigate sensitivity of the design to changes of parameters and operating point and to optimize performance of the microgrid system. The results are used to discuss applications of the proposed power management strategies under various microgrid operating conditions
1,531 citations
TL;DR: In this paper, a new direct power control (DPC) strategy for a doubly fed induction generator (DFIG)-based wind energy generation system is presented, which is based on the direct control of stator active and reactive power by selecting appropriate voltage vectors on the rotor side.
Abstract: This paper presents a new direct power control (DPC) strategy for a doubly fed induction generator (DFIG)-based wind energy generation system. The strategy is based on the direct control of stator active and reactive power by selecting appropriate voltage vectors on the rotor side. It is found that the initial rotor flux has no impact on the changes of the stator active and reactive power. The proposed method only utilizes the estimated stator flux so as to remove the difficulties associated with rotor flux estimation. The principles of this method are described in detail in this paper. The only machine parameter required by the proposed DPC method is the stator resistance whose impact on the system performance is found to be negligible. Simulation results on a 2 MW DFIG system are provided to demonstrate the effectiveness and robustness of the proposed control strategy during variations of active and reactive power, rotor speed, machine parameters, and converter dc link voltage
731 citations
TL;DR: In this paper, a simple doubly fed induction generator (DFIG) based wind turbine model was developed for real and reactive power production in which the power converter is simulated as a controlled voltage source, regulating the rotor current.
Abstract: Due to its many advantages such as the improved power quality, high energy efficiency and controllability, etc. the variable speed wind turbine using a doubly fed induction generator (DFIG) is becoming a popular concept and thus the modeling of the DFIG based wind turbine becomes an interesting research topic. Fundamental frequency models have been presented but these models are often complex with significant numerical overhead as the power converter block consisting of power control, rotor side and grid side converter control and DC link are often simulated in detail. This paper develops a simple DFIG wind turbine model in which the power converter is simulated as a controlled voltage source, regulating the rotor current to meet the command of real and reactive power production. This model has the form of traditional generator model and hence is easy to integrate into the power system simulation tool such as PSS/E. As an example, the interaction between the Arklow Bank Wind Farm and the Irish National Grid was simulated using the proposed model. The model performance and accuracy was also compared with the detailed model developed by DIgSILENT. Considering the simplification adopted for the model development, the limitation and applicability of the model were also discussed in this paper.
711 citations
TL;DR: Adapt virtual output impedance is proposed in order to achieve a proper reactive power sharing regardless of the line impedance unbalances and can be properly shared due to the addition of a current harmonic loop in the control strategy.
Abstract: In this paper, a method for the parallel operation of inverters in an ac-distributed system is proposed. This paper explores the control of active and reactive power flow through the analysis of the output impedance of the inverters and its impact on the power sharing. As a result, adaptive virtual output impedance is proposed in order to achieve a proper reactive power sharing, regardless of the line-impedance unbalances. A soft-start operation is also included, avoiding the initial current peak, which results in a seamless hot-swap operation. Active power sharing is achieved by adjusting the frequency in load transient situations only, owing to which the proposed method obtains a constant steady-state frequency and amplitude. As opposed to the conventional droop method, the transient response can be modified by acting on the main control parameters. Linear and nonlinear loads can be properly shared due to the addition of a current harmonic loop in the control strategy. Experimental results are presented from a two-6-kVA parallel-connected inverter system, showing the feasibility of the proposed approach
676 citations
TL;DR: In this article, the authors reviewed the present situation as well as projected future research and development work of advanced vehicular electrical power systems including those of electric, hybrid electric, and fuel cell vehicles (EVs, HEVs, and FCVs).
Abstract: There is a clear trend in the automotive industry to use more electrical systems in order to satisfy the ever-growing vehicular load demands. Thus, it is imperative that automotive electrical power systems will obviously undergo a drastic change in the next 10-20 years. Currently, the situation in the automotive industry is such that the demands for higher fuel economy and more electric power are driving advanced vehicular power system voltages to higher levels. For example, the projected increase in total power demand is estimated to be about three to four times that of the current value. This means that the total future power demand of a typical advanced vehicle could roughly reach a value as high as 10 kW. In order to satisfy this huge vehicular load, the approach is to integrate power electronics intensive solutions within advanced vehicular power systems. In view of this fact, this paper aims at reviewing the present situation as well as projected future research and development work of advanced vehicular electrical power systems including those of electric, hybrid electric, and fuel cell vehicles (EVs, HEVs, and FCVs). The paper will first introduce the proposed power system architectures for HEVs and FCVs and will then go on to exhaustively discuss the specific applications of dc/dc and dc/ac power electronic converters in advanced automotive power systems
648 citations
TL;DR: In this article, the optimal AC-DC power generation for a rectified piezoelectric device was investigated under steady-state operation, and the harvested power depends on the input vibration characteristics (frequency and acceleration), the mass of the generator, the electrical load, the natural frequency, the mechanical damping ratio and the electromechanical coupling coefficient.
Abstract: Power harvesting refers to the practice of acquiring energy from the environment which would be otherwise wasted and converting it into usable electric energy. Much work has been done on studying the optimal AC power output, while little has considered the AC–DC output. This article investigates the optimal AC–DC power generation for a rectified piezoelectric device. In contrast with estimates based on various degrees of approximation in the recent literature, an analytic expression for the AC–DC power output is derived under steady-state operation. It shows that the harvested power depends on the input vibration characteristics (frequency and acceleration), the mass of the generator, the electrical load, the natural frequency, the mechanical damping ratio and the electromechanical coupling coefficient of the system. An effective power normalization scheme is provided to compare the relative performance and efficiency of devices. The theoretical predictions are validated and found to be in good agreement with both experimental observations and numerical simulations. Finally, several design guidelines are suggested for devices with large coupling coefficient and quality factor.
624 citations
28 Mar 2006
TL;DR: 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.
Abstract: DC power flow is a commonly used tool for contingency analysis. Recently, due to its simplicity and robustness, it also becomes increasingly used for the real-time dispatch and techno-economic analysis of power systems. It is a simplification of a full power flow looking only at active power. Aspects such as voltage support and reactive power management are possible to analyse. However, such simplifications cannot always be justified and sometimes lead to unrealistic results. Especially the implementation of power flow controlling devices is not trivial since standard DC power flow fundamentally neglects their effects. Until recently, this was not an issue as the application of power flow controlling devices in the European grid was limited. However, with the liberalisation of European electricity market and the introduction of large wind energy systems, the need for real power flow control has emerged and therefore, the use of these devices has been reconsidered. Several phase shifting transformers (PST) are being installed or planned in order to control flows. Therefore, it is important to fundamentally re-validate the fast, but less accurate, DC power flow method. In this paper the assumptions of DC power flow are analysed, and its validity is assessed by comparing the results of power flow simulations using both the DC and AC approaches on a modified IEEE 300 bus system with PSTs.
400 citations
01 Jan 2006
TL;DR: This work examines the validity of prior adhoc approaches to understanding power breakdown and quantify several interesting trends important for power modeling and management in the future, and introduces Mantis, a nonintrusive method for modeling full-system power consumption and providing real-time power prediction.
Abstract: The increasing costs of power delivery and cooling, as well as the trend toward higher-density computer systems, have created a growing demand for better power management in server environments. Despite the increasing interest in this issue, little work has been done in quantitatively understanding power consumption trends and developing simple yet accurate models to predict full-system power. We study the component-level power breakdown and variation, as well as temporal workload-specific power consumption of an instrumented power-optimized blade server. Using this analysis, we examine the validity of prior adhoc approaches to understanding power breakdown and quantify several interesting trends important for power modeling and management in the future. We also introduce Mantis, a nonintrusive method for modeling full-system power consumption and providing real-time power prediction. Mantis uses a onetime calibration phase to generate a model by correlating AC power measurements with user-level system utilization metrics. We experimentally validate the model on two server systems with drastically different power footprints and characteristics (a low-end blade and high-end compute-optimized server) using a variety of workloads. Mantis provides power estimates with high accuracy for both overall and temporal power consumption, making it a valuable tool for power-aware scheduling and analysis.
377 citations
13 Jul 2006
TL;DR: In this article, the authors present a model of a single generator with three phases and a series of parallel circuits, and show that the three phases are connected by resistive heuristics.
Abstract: Preface. 1. The Physics of Electricity. 1.1 Basic Quantities. 1.1.1 Introduction. 1.1.2 Charge. 1.1.3 Potential or Voltage. 1.1.4 Ground. 1.1.5 Conductivity. 1.1.6 Current. 1.2 Ohm's law. 1.2.1 Resistance. 1.2.2 Conductance. 1.2.3 Insulation. 1.3 Circuit Fundamentals. 1.3.1 Static Charge. 1.3.2 Electric Circuits. 1.3.3 Voltage Drop. 1.3.4 Electric Shock. 1.4 Resistive Heating. 1.4.1 Calculating Resistive Heating. 1.4.2 Transmission Voltage and Resistive Losses. 1.5 Electric and Magnetic Fields. 1.5.1 The Field as a Concept. 1.5.2 Electric Fields. 1.5.3 Magnetic Fields. 1.5.4 Electromagnetic Induction. 1.5.5 Electromagnetic Fields and Health Effects. 1.5.6 Electromagnetic Radiation. 2. Basic Circuit Analysis. 2.1 Modeling Circuits. 2.2 Series and Parallel Circuits. 2.2.1 Resistance in Series. 2.2.2 Resistance in Parallel. 2.2.3 Network Reduction. 2.2.4 Practical Aspects. 2.3 Kirchhoff's Laws. 2.3.1 Kirchhoff's Voltage Law. 2.3.2 Kirchhoff's Current Law. 2.3.3 Application to Simple Circuits. 2.3.4 The Superposition Principle. 2.4 Magnetic Circuits. 3. AC Power. 3.1 Alternating Current and Voltage. 3.1.1 Historical Notes. 3.1.2 Mathematical Description. 3.1.3 The rms Value. 3.2 Reactance. 3.2.1 Inductance. 3.2.2 Capacitance. 3.2.3 Impedance. 3.2.4 Admittance. 3.3 Power. 3.3.1 Definition of Electric Power. 3.3.2 Complex Power. 3.3.3 The Significance of Reactive Power. 3.4 Phasor Notation. 3.4.1 Phasors as Graphics. 3.4.2 Phasors as Exponentials. 3.4.3 Operations with Phasors. 4. Generators. 4.1 The Simple Generator. 4.2 The Synchronous Generator. 4.2.1 Basic Components and Functioning. 4.2.2 Other Design Aspects. 4.3 Operational Control of Synchronous Generators. 4.3.1 Single Generator: Real Power. 4.3.2 Single Generator: Reactive Power. 4.3.3 Multiple Generators: Real Power. 4.3.4 Multiple Generators: Reactive Power. 4.4 Operating Limits. 4.5 The Induction Generator. 4.5.1 General Characteristics. 4.5.2 Electromagnetic Characteristics. 4.6 Inverters. 5. Loads. 5.1 Resistive Loads. 5.2 Motors. 5.3 Electronic Devices. 5.4 Load from the System Perspective. 5.4.1 Coincident and Noncoincident Demand. 5.4.2 Load Profiles and Load Duration Curve. 5.5 Single- and Multiphase Connections. 6. Transmission and Distribution. 6.1 System Structure. 6.1.1 Historical Notes. 6.1.2 Structural Features. 6.1.3 Sample Diagram. 6.1.4 Topology. 6.1.5 Loop Flow. 6.1.6 Stations and Substations. 6.1.7 Reconfiguring the System. 6.2 Three-Phase Transmission. 6.2.1 Rationale for Three Phases. 6.2.2 Balancing Loads. 6.2.3 Delta and Wye Connections. 6.2.4 Per-Phase Analysis. 6.2.5 Three-Phase Power. 6.2.6 D.C. Transmission. 6.3 Transformers. 6.3.1 General Properties. 6.3.2 Transformer Heating. 6.3.3 Delta and Wye Transformers. 6.4 Characteristics of Power Lines. 6.4.1 Conductors. 6.4.2 Towers, Insulators, and Other Components. 6.5 Loading. 6.5.1 Thermal Limits. 6.5.2 Stability Limit. 6.6 Voltage Control. 6.7 Protection. 6.7.1 Basics of Protection and Protective Devices. 6.7.2 Protection Coordination. 7. Power Flow Analysis. 7.1 Introduction. 7.2 The Power Flow Problem. 7.2.1 Network Representation. 7.2.2 Choice of Variables. 7.2.3 Types of Buses. 7.2.4 Variables for Balancing Real Power. 7.2.5 Variables for Balancing Reactive Power. 7.2.6 The Slack Bus. 7.2.7 Summary of Variables. 7.3 Example with Interpretation of Results. 7.3.1 Six-Bus Example. 7.3.2 Tweaking the Case. 7.3.3 Conceptualizing Power Flow. 7.4 Power Flow Equations and Solution Methods. 7.4.1 Derivation of Power Flow Equations. 7.4.2 Solution Methods. 7.4.3 Decoupled Power Flow. 7.5 Applications and Optimal Power Flow. 8. System Performance. 8.1 Reliability. 8.1.1 Measures of Reliability. 8.1.2 Valuation of Reliability. 8.2 Security. 8.3 Stability. 8.3.1 The Concept of Stability. 8.3.2 Steady-State Stability. 8.3.3 Dynamic Stability. 8.3.4 Voltage Stability. 8.4 Power Quality. 8.4.1 Voltage. 8.4.2 Frequency. 8.4.3 Waveform. 9. System Operation, Management, and New Technology. 9.1 Operation and Control on Different Time Scales. 9.1.1 The Scale of a Cycle. 9.1.2 The Scale of Real-Time Operation. 9.1.3 The Scale of Scheduling. 9.1.4 The Planning Scale. 9.2 New Technology. 9.2.1 Storage. 9.2.2 Distributed Generation. 9.2.3 Automation. 9.2.4 FACTS. 9.3 Human Factors. 9.3.1 Operators and Engineers. 9.3.2 Cognitive Representations of Power Systems. 9.3.3 Operational Criteria. 9.3.4 Implications for Technological Innovation. 9.4 Implications for Restructuring. Appendix: Symbols, Units, Abbreviations, and Acronyms. Index.
348 citations
TL;DR: In this paper, an optimized dispatch control strategy for active and reactive powers delivered by a doubly fed induction generator in a wind park is proposed, which exploits a combination of pitch control and control of the static converters.
Abstract: This paper proposes an optimized dispatch control strategy for active and reactive powers delivered by a doubly fed induction generator in a wind park. In this control approach, wind turbines are supposed to operate over a deloaded maximum power extraction curve and will respond to a supervisory wind farm control after a request from a system operator for adjusting the outputs of the wind park. The definition of the active and reactive powers operating points, for each wind turbine, is defined from an optimization algorithm that uses the primal-dual predictor corrector interior point method. The control strategy used at the wind generator level exploits a combination of pitch control and control of the static converters to adjust the rotor speed for the required operation points. A small wind park is used to illustrate the effectiveness of the developed approach.
340 citations
TL;DR: A control method is proposed that fully exploits the inherent fast response of the inverters while also ensuring voltage balance even with extreme load imbalance and it is shown that circulating currents are avoided during steady state and transients.
Abstract: Inverters are a necessary interface for several forms of distributed generation (DG) and where they form a microgrid they have the potential to offer high power quality. The challenge is to coordinate the actions of a group of inverters so that they offer the level of power quality known to be possible from fast local control of a single inverter. The case examined here is a power park of several inverter-based DG in relatively close proximity. A basic requirement is that the inverters regulate the grid voltage and share the real and reactive power demands according to their ratings. In small girds with high proportions of nonlinear and unbalanced loads it is also important to actively control the waveform quality in terms of harmonics, transient disturbances, and balance. Further, it is important that these duties are shared equally between the units rather than having one master unit taking the lead in the voltage control function. A constraint faced in designing a sharing system is the limited bandwidth of signal communication even over distances of a few meters. A control method is proposed that separates the control tasks in the frequency domain. Power sharing and voltage regulation are controlled centrally and commands are distributed through a low-bandwidth communication link. Waveform quality functions are controlled in high bandwidth controllers distributed to each local inverter. Experimental tests on a grid of three 10-kVA inverters are used to show that the method fully exploits the inherent fast response of the inverters while also ensuring voltage balance even with extreme load imbalance. It is shown that circulating currents are avoided during steady state and transients
TL;DR: In this article, a unified power quality conditioner with the distributed generation is proposed, which consists of a series inverter, a shunt inverter and a distributed generator connected in the dc link through a rectifier.
Abstract: This paper describes analysis results of a combined operation of the unified power quality conditioner with the distributed generation. The proposed system consists of a series inverter, a shunt inverter, and a distributed generator connected in the dc link through a rectifier. The proposed system can compensate voltage sag and swell, voltage interruption, harmonics, and reactive power in both interconnected mode and islanding mode. The performance of proposed system was analyzed using simulations with power system computer aided design/electromagnetic transients dc analysis program, and experimental results with the hardware prototype. The proposed system can improve the power quality at the point of installation on power distribution systems or industrial power systems.
Patent•
13 Dec 2006
TL;DR: In this paper, a motor for rotating a drill is connected to an AC power source through a motor control unit, a current detector, and a power switch, which rotates the motor on the basis of a signal sent from a main control unit according to a state in which a motor start switch is on.
Abstract: A drilling device prevents recurrence of an overload condition after occurrence of the overload condition, thereby improving operability and safety in the drilling device. A motor for rotating a drill is connected to an AC power source through a motor control unit, a current detector, and a power switch. A magnet is also connected to the AC power source through the power switch and a full-wave rectifier. The motor control unit rotationally drives the motor on the basis of a signal sent from a main control unit according to a state in which a motor start switch is on. The main control unit controls the motor control unit to gradually reduce a supply voltage to the motor when the motor becomes overloaded, to gradually increase the voltage to the normal power supply condition when the overload condition is vanished, and to stop power supply to the motor if the overload condition continues for a predetermined period.
TL;DR: The analysis and software implementation of a robust synchronizing circuit, i.e., phase-locked loop (PLL) circuit, designed for use in the controller of active power line conditioners, and it is shown that the PLL can fail in tracking the system voltage during startup under some adverse conditions.
Abstract: This paper presents the analysis and software implementation of a robust synchronizing circuit, i.e., phase-locked loop (PLL) circuit, designed for use in the controller of active power line conditioners. The basic problem consists of designing a PLL circuit that can track accurately and continuously the positive-sequence component at the fundamental frequency and its phase angle even when the system voltage of the bus, to which the active power line conditioner is connected, is distorted and/or unbalanced. The fundamentals of the PLL circuit are discussed. It is shown that the PLL can fail in tracking the system voltage during startup under some adverse conditions. Moreover, it is shown that oscillations caused by the presence of subharmonics can be very critical and can pull the stable point of operation synchronized to that subharmonic frequency. Oscillations at the reference input are also discussed, and the solution of this problem is presented. Finally, experimental and simulation results are shown and compared
TL;DR: A photovoltaic power conditioning system (PCS) with line connection with high performance such as an almost-unity power factor, a power efficiency of 94%, and a total harmonic distortion (THD) of 3.6% is proposed.
Abstract: A photovoltaic (PV) power conditioning system (PCS) with line connection is proposed. Using the power slope versus voltage of the PV array, the maximum power point tracking (MPPT) controller that produces a smooth transition to the maximum power point is proposed. The dc current of the PV array is estimated without using a dc current sensor. A current controller is suggested to provide power to the line with an almost-unity power factor that is derived using the feedback linearization concept. The disturbance of the line voltage is detected using a fast sensing technique. All control functions are implemented in software with a single-chip microcontroller. Experimental results obtained on a 2-kW prototype show high performance such as an almost-unity power factor, a power efficiency of 94%, and a total harmonic distortion (THD) of 3.6%
TL;DR: In this article, a current-source ECaSS (CS-ECS) is proposed, which consists of EDLC, bi-directional DC-DC converter, and current source inverter.
Abstract: Utilization of renewable energy are coming up from view points of environmental conservation and depletion of fossil fuel. However, the generated power from renewable energies is always fluctuating due to environmental status. Energy storage system is indispensable to compensate these fluctuating components. Energy capacitor system (ECaSS) connected an electric double-layer capacitor (EDLC) with power-electronics devices is useful for the compensation of fluctuating power since one is capable of controlling both active and reactive power simultaneously. This paper proposes the current-source ECaSS (CS-ECS), which consists of EDLC, bi-directional DC-DC converter, and current-source inverter. We have presented the control system for the active/reactive power control of CS-ECS, and have shown the effectiveness of CS-ECS through computer simulations for case of wind power generation system.
01 Aug 2006
TL;DR: In this paper, an overview of the active methods used for islanding detection is presented, and the reported algorithms are carefully analyzed in their advantage and drawbacks and the considerations are validated by tests results obtained in accordance with the IEEE Std. 929-2000 procedure.
Abstract: For pt.I see ibid., p.420-5 (2006).This paper offers an overview of the active methods used for islanding detection. The inverter control algorithm is based on the use of harmonic compensators in order to create ideal working conditions (i.e. the PV-system produces a sinusoidal current and reject grid harmonics). This condition is the indispensable starting point to implement active islanding detection methods. In fact these methods are based on the perturbation of the ideal conditions (e.g. the injection of active/reactive power, the injection of current harmonics, or the insertion of an external capacitor). All the reported algorithms are carefully analysed in their advantage and drawbacks and the considerations are validated by tests results obtained in accordance with the IEEE Std. 929-2000 procedure
TL;DR: In this article, a joint-phase redundancy control for flying capacitor multilevel inverters (FCMIs) has been proposed to improve capacitor voltage balancing under a wide range of power factors and modulation indices.
Abstract: Recent research in flying capacitor multilevel inverters (FCMIs) has shown that the number of voltage levels can be extended by changing the ratio of the capacitor voltages. For the three-cell FCMI, four levels of operation are expected if the traditional ratio of the capacitor voltages is 1:2:3. However, by altering the ratio, the inverter can operate as a five-, six-, seven-, or eight-level inverter. According to previous research, the eight-level case is referred to as maximally distended (or full binary combination schema) since it utilizes all possible transistor switching states. However, this case does not have enough per-phase redundancy to ensure capacitor voltage balancing under all modes of operation. In this paper, redundancy involving all phases is used along with per-phase redundancy to improve capacitor voltage balancing. It is shown that the four- and five-level cases are suitable for motor drive operation and can maintain capacitor voltage balance under a wide range of power factors and modulation indices. The six-, seven-, and eight-level cases are suitable for reactive power transfer in applications such as static var compensation. Simulation and laboratory measurements verify the proposed joint-phase redundancy control.
TL;DR: In this article, a maximum power point tracking algorithm for single-stage converters connecting photovoltaic panels to a single-phase grid is presented, which is based on the application of the "ripple correlation control" using as perturbation signals the current and voltage lowfrequency oscillations introduced in the PV panels by the single phase utility grid.
Abstract: A maximum power point tracking algorithm for single-stage converters connecting photovoltaic (PV) panels to a single-phase grid is presented in this paper. The algorithm is based on the application of the "ripple correlation control" using as perturbation signals the current and voltage low-frequency oscillations introduced in the PV panels by the single-phase utility grid. The proposed control technique allows the generation of sinusoidal grid currents with unity power factor. The algorithm has been developed to allow an array of PV modules to be connected to the grid by using a single-stage converter. This simple structure yields higher efficiency and reliability when compared with standard solutions based on double-stage converter configurations. The proposed maximum power point tracking algorithm has been numerically simulated and experimentally verified by means of a converter prototype connected to a single-phase grid. The results are presented in the paper, showing the effectiveness of the proposed system.
30 Nov 2006
TL;DR: In this article, the static compensator (STATCOM) with hybrid battery energy storage (BES) has great potential to fulfil this role, though considerable advances in the control of this system are still to be made.
Abstract: A large penetration of wind generation info the power system will mean that poor power quality and poor stability margins cannot be tolerated from wind farms This requires that methods to improve power qualify and stability for such systems be found The static compensator (STATCOM) with hybrid battery energy storage (BES) has great potential to fulfil this role, though considerable advances in the control of this system are still to be made From an economic point of view, rating the STATCOM for steady-state power-quality improvement duty is appropriate Rating the STATCOM to absorb large amounts of additional power in excess of its transient overload capability during network faults is inappropriate A hybrid of BES and braking resistor is therefore proposed A new hybrid STATCOM–BES control technique is developed and discussed in the context of improving the stability and power quality to fixed speed, induction generator, wind turbines The variation of the network voltage, active and reactive power with the fluctuation of the wind generation is studied A wind generation system with a STATCOM battery energy storage unit and the new control was simulated and the results demonstrate that both power quality and the stability margin can be improved significantly for wind farms
TL;DR: In this article, the authors investigate how power phenomena and properties of three-phase systems are described and interpreted by the Instantaneous Reactive Power (IRP) p-q Theory.
Abstract: This paper investigates how power phenomena and properties of three-phase systems are described and interpreted by the Instantaneous Reactive Power (IRP) p-q Theory. This paper demonstrates that this theory misinterprets power properties of electrical systems or provides some results that at least defy a common sense or meaning of some notions in electrical engineering. For example, it suggests the presence of an instantaneous reactive current in supply lines of purely resistive loads and the presence of an instantaneous active current in supply lines of purely reactive loads. Moreover, it suggests that line currents of linear loads with sinusoidal supply voltage contain a nonsinusoidal component. This paper shows, moreover, that the IRP p-q Theory is not capable to identify power properties of three-phase loads instantaneously. A pair of instantaneous values of p and q powers does not allow us to conclude whether the load is resistive, reactive, balanced, or unbalanced. It is known that a load imbalance reduces power factor. However, the IRP p-q Theory does not identify the load imbalance as the cause of power factor degradation.
09 Jan 2006
TL;DR: In this article, the power flow through a plasma actuator is divided into four sinks: reactive power losses due to inadequate impedance matching of the power supply to the actuator, dielectric heating of actuator insulating materials, power required to maintain the atmospheric pressure plasma, and power coupled to the neutral gas flow by ion-neutral collisions.
Abstract: Electrohydrodynamic plasma actuators have proven effective for flow attachment in internal and external aerodynamics, and for modification of the lift, drag, and stall angle of airfoils. The performance of plasma actuators has been studied with such classical aerodynamic tools as wind tunnels, drag balances, Pitot tubes, smoke flow visualization, and fluid dynamic modeling programs. However, the physical processes and power flows that occur in plasma actuators, before the plasma ions transfer their momentum to the neutral background gas, are those of an electrical device. Optimization of such actuators needs to include the methods of electrical engineering and plasma physics, including classical electrical discharge physics. To implement a program of optimization, we have conceptually divided the power flow through a plasma actuator into the following four sinks: 1.) Reactive power losses due to inadequate impedance matching of the power supply to the actuator; 2.) Dielectric heating of the actuator insulating materials; 3.) Power required to maintain the atmospheric pressure plasma; and 4.) Power coupled to the neutral gas flow by ion-neutral collisions. These four power flows can be, and usually are, of comparable magnitude. In this paper, we review our progress in understanding and minimizing the first three power flows, and maximizing the fourth by adjustment of the actuator geometry and materials, as well as such plasma parameters as the RF frequency and RMS voltage.
TL;DR: In this paper, the impact of the interface control strategy of inverter-based DGs on islanding detection is examined and the Nondetective Zone (NDZ) is derived analytically for each interface control and validated by simulation.
Abstract: Islanding detection of Distributed Generation (DG) is considered as one of the most important aspects when interconnecting DGs to the distribution system. With the increasing penetration and reliance of the distribution systems on DGs, new interface control strategies are being proposed. Aside from its main task of supplying active power, the DG could provide voltage support, improve the power factor, or mitigate other power quality problems. This paper examines the impact of the interface control strategy of inverter based DGs on islanding detection. The Nondetective Zone (NDZ) for over/under voltage and over/under frequency is derived analytically for each interface control and validated by simulation.
TL;DR: This paper deals with the performance analysis of a static compensator (STATCOM)-based voltage regulator for self-excited induction generators (SEIGs) supplying nonlinear loads and shows that SEIG terminal voltage is maintained constant, even with nonlinear balanced and unbalanced loads, and free from harmonics using STATCOM-based Voltage regulator.
Abstract: This paper deals with the performance analysis of a static compensator (STATCOM)-based voltage regulator for self-excited induction generators (SEIGs) supplying nonlinear loads. In practice, a number of loads are nonlinear in nature, and therefore, they inject harmonics in the generating systems. The SEIG's performance, being a weak isolated system, is very much affected by these harmonics. The additional drawbacks of the SEIG are poor voltage regulation and that it requires an adjustable reactive power source with varying loads to maintain a constant terminal voltage. A three-phase insulated-gate-bipolar-transistor-based current-controlled voltage source inverter working as STATCOM is used for harmonic elimination, and it provides the required reactive power for the SEIG, with varying loads to maintain a constant terminal voltage. A dynamic model of the SEIG-STATCOM feeding nonlinear loads using stationary d-q axes reference frame is developed for predicting the behavior of the system under transient conditions. The simulated results show that SEIG terminal voltage is maintained constant, even with nonlinear balanced and unbalanced loads, and free from harmonics using STATCOM-based voltage regulator
Patent•
09 May 2006
TL;DR: In this paper, an improved light-emitting device for an AC power operation is presented, which employs a variety of means by which light emission time is prolonged during a ½ cycle in response to a phase change of an AC Power source and a flicker effect can be reduced.
Abstract: Disclosed is an improved light-emitting device for an AC power operation. A conventional light emitting device employs an AC light-emitting diode having arrays of light emitting cells connected in reverse parallel. The arrays in the prior art alternately repeat on/off in response to a phase change of an AC power source, resulting in short light emission time during a ½ cycle and the occurrence of a flicker effect. An AC light-emitting device according to the present invention employs a variety of means by which light emission time is prolonged during a ½ cycle in response to a phase change of an AC power source and a flicker effect can be reduced. For example, the means may be switching blocks respectively connected to nodes between the light emitting cells, switching blocks connected to a plurality of arrays, or a delay phosphor. Further, there is provided an AC light-emitting device, wherein a plurality of arrays having the different numbers of light emitting cells are employed to increase light emission time and to reduce a flicker effect.
TL;DR: In this article, the authors developed models of various types of wind turbine generating units (WTGU) used as distributed generation (DG) sources and demonstrated their application for steady state analysis.
TL;DR: In this article, the authors analyze the need for coordinating the control of the DIGs and the HVDC link so that the two topologies can work together, giving system designers and operators a choice that may be useful in some applications.
Abstract: Doubly fed induction generators (DFIGs) are an economic variable-speed solution for large wind turbines while high-voltage dc (HVdc) transmission is being considered for the grid connection of some offshore wind farms. This paper analyzes the need for coordinating the control of the DFIGs and the HVdc link so that the two topologies can work together, giving system designers and operators a choice that may be useful in some applications. It is desired that individual generators be controlled for power tracking in a way similar to that used when they are connected directly to an ac grid, although a grid voltage reference for the DFIG control is no longer available as an independent source in this case. The study shows that machine control should explicitly maintain the flux level, which then allows the HVdc link to regulate the local system frequency and, indirectly, voltage amplitude. Interactions between DFIGs and the HVdc link are investigated and simulations performed to verify the proposed control strategy.
22 Feb 2006
TL;DR: The design and implementation of Pika, a low-power FPGA core targeting battery-powered applications that achieves substantial power savings through a series of power optimizations and is compatible with existing commercial design tools.
Abstract: Programmable logic devices such as FPGAs are useful for a wide range of applications. However, FPGAs are not commonly used in battery-powered applications because they consume more power than ASICs and lack power management features. In this paper, we describe the design and implementation of Pika, a low-power FPGA core targeting battery-powered applications such as those in consumer and automotive markets. Our design uses the Xilinx Spartan-3 low-cost FPGA as a baseline and achieves substantial power savings through a series of power optimizations. The resulting architecture is compatible with existing commercial design tools. The implementation is done in a 90nm triple-oxide CMOS process. Compared to the baseline design, Pika consumes 46% less active power and 99% less standby power. Furthermore, it retains circuit and configuration state during standby mode, and wakes up from standby mode in approximately 100ns.
TL;DR: This work presents a novel current multilevel (CML) inverter topology, named boost CML inverter, and its application on energy processing of single-phase grid-connected photovoltaic (PV) systems, and evidence the feasibility of the application of this new topology on singlephaseGrid-connected PV systems is evidence.
Abstract: This work presents a novel current multilevel (CML) inverter topology, named boost CML inverter, and its application on energy processing of single-phase grid-connected photovoltaic (PV) systems. The structure allows a high power factor operation of a PV system, injecting a quasi-sinusoidal current into the grid, with virtually no displacement in relation to the line voltage at the point of common coupling among the PV system and the loads. The major appeals of using the CML technique are the balanced current sharing among semiconductor switches and the decrease of the current slope in the circuit devices, with a consequent reduction of conducted and radiated electromagnetic interference (EMI). The CML technique also allows adapting or minimizing current waveforms harmonic content. System description, mathematical approach, and design guidelines are presented, providing an overview of the new topology. In order to validate the proposed concepts, experimental measurements, made in a small-scale laboratory prototype, are also presented. The obtained results evidence the feasibility of the application of this new topology on singlephase grid-connected PV systems.
TL;DR: In this article, a new optimal reactive power flow (ORPF) model in rectangular form is proposed, where the Hessian matrices in this model are constants and need to be calculated only once in the entire optimal process, which speed up the calculation greatly.
Abstract: A new optimal reactive power flow (ORPF) model in rectangular form is proposed in this paper. In this model, the load tap changing (LTC) transformer branch is represented by an ideal transformer and its series impedance with a dummy node located between them. The voltages of the two sides of the ideal transformer are then used to replace the turn ratio of the LTC so that the ORPF model becomes quadratic. The Hessian matrices in this model are constants and need to be calculated only once in the entire optimal process, which speed up the calculation greatly. The solution of the ORPF problem by the predictor corrector primal dual interior point method is described in this paper. Two separate prototypes for the new and the conventional methods are developed in MATLAB in order to compare the performances. The results obtained from the implemented seven test systems ranging from 14 to 1338 buses indicate that the proposed method achieves a superior performance than the conventional rectangular coordinate-based ORPF.