Showing papers on "Power optimizer published in 2012"

A review of energy storage technologies for wind power applications

Abstract: Due to the stochastic nature of wind, electric power generated by wind turbines is highly erratic and may affect both the power quality and the planning of power systems. Energy Storage Systems (ESSs) may play an important role in wind power applications by controlling wind power plant output and providing ancillary services to the power system and therefore, enabling an increased penetration of wind power in the system. This article deals with the review of several energy storage technologies for wind power applications. The main objectives of the article are the introduction of the operating principles, as well as the presentation of the main characteristics of energy storage technologies suitable for stationary applications, and the definition and discussion of potential ESS applications in wind power, according to an extensive literature review.

Power Electronics Converters for Wind Turbine Systems

Abstract: The steady growth of installed wind power together with the upscaling of the single wind turbine power capability has pushed the research and development of power converters toward full-scale power conversion, lowered cost pr kW, increased power density, and also the need for higher reliability. In this paper, power converter technologies are reviewed with focus on existing ones and on those that have potential for higher power but which have not been yet adopted due to the important risk associated with the high-power industry. The power converters are classified into single- and multicell topologies, in the latter case with attention to series connection and parallel connection either electrical or magnetic ones (multiphase/windings machines/transformers). It is concluded that as the power level increases in wind turbines, medium-voltage power converters will be a dominant power converter configuration, but continuously cost and reliability are important issues to be addressed.

Edison Redux: 380 Vdc Brings Reliability and Efficiency to Sustainable Data Centers

Abstract: We are on the cusp of a great technology transition in power distribution from ac to dc at the edge of the grid Data centers are merely one of the first industries to embrace the coming tide The transition on the customer side of the meter is on the order of what happened over the last 40 years with personal computers, the Internet, and cell phones The predominant use of power electronics in almost everything we buy new today makes them natively dc devices As a society, we could be more efficient and sustainable if we were to skip the last ac-to-dc conversion At some point soon, when the majority of the load base is natively dc, we reach a tipping point where ac and hot power converter “bricks” on everything are no longer sustainable Add to this distributed generation, distributed energy storage, and renewable carbon-free power sources that prefer dc, and one can conclude that the transition is not only necessary but inevitable

Wireless power transmission system using solar cell module

Abstract: A wireless power transmission system includes a charging and path controller configured to supply, to a battery module, power generated by a solar cell module, or power generated by an alternating current-to-direct current (AC/DC) converter, based on a control signal; a power converter configured to receive power from the battery module and generate a supply power to be supplied to a target device from power received from the battery module using a resonant frequency; a source resonator configured to receive the supply power from the power converter and transmit the supply power received from the power converter to the target device; and a control/communication unit configured to generate the control signal of the charging and path controller based on an amount of the power generated by the solar cell module and an amount of power that can be output from the battery module.

Dynamic Modeling and Operation Strategy for a Microgrid With Wind and Photovoltaic Resources

Abstract: This paper presents a dynamic modeling and control strategy for a sustainable microgrid primarily powered by wind and solar energy. A current-source-interface multiple-input dc-dc converter is used to integrate the renewable energy sources to the main dc bus. Potential suitable applications range from a communication site or a residential area. A direct-driven permanent magnet synchronous wind generator is used with a variable speed control method whose strategy is to capture the maximum wind energy below the rated wind speed. This study considers both wind energy and solar irradiance changes in combination with load power variations. As a case study a 30-kW wind/solar hybrid power system dynamic model is explored. The examined dynamics shows that the proposed power system is a feasible option for a sustainable microgrid application.

Optimal Power Flow Solution Incorporating Wind Power

Abstract: This paper presents a solution of optimal power flow (OPF) incorporating wind power. A paradigm for modeling the cost of wind-generated electricity from a wind farm is proposed. Based on the Weibull wind speed distribution and wind turbine model represented by function approximation, the frequency distribution of wind farm power output to be the basis for modeling wind generation cost is established via applying Monte Carlo simulation. The proposed wind generation cost model consists of the opportunity cost of wind power shortage and the opportunity cost of wind power surplus, which reflect the cost of dispatching additional reserve capacity and the cost of environmental benefit loss, respectively, and it is integrated into the conventional OPF program. Furthermore, the small signal stability constraints are considered simultaneously as well during optimization. A self-adaptive evolutionary programming method is employed to solve the OPF with wind power involved. A case study is conducted based on the IEEE New England test system (10-Generator-39-Bus) as a benchmark. The simulation results demonstrate the effectiveness and validity of the proposed model and method.

Novel Transformerless Grid-Connected Power Converter With Negative Grounding for Photovoltaic Generation System

Abstract: This paper proposes a novel transformerless grid-connected power converter with negative grounding for a photovoltaic generation system. The negative terminal of the solar cell array can be directly connected to the ground in the proposed grid-connected power converter to avoid the transparent conducting oxide corrosion that occurs in some types of thin-film solar cell array. The proposed grid-connected power converter consists of a dc-dc power converter and a dc-ac inverter. The salient features of the proposed power converter are that some power electronic switches are simultaneously used in both the dc-dc power converter and dc-ac inverter, and only two power electronic switches operate at high switching frequency at the same time (one is in the dc-dc power converter and the other is in the dc-ac inverter). The leakage current of the photovoltaic generation system is reduced because the negative terminal of the solar cell array is connected directly to the ground. Finally, a prototype was developed to verify the performance of the proposed grid-connected power converter. The experimental results show that the performance of the proposed grid-connected power converter is as expected.

A survey of maximum PPT techniques of PV systems

Abstract: This paper introduces a survey of different maximum peak power tracking (MPPT) techniques used in the implementation of photovoltaic power systems. It will discuss different 30 techniques used in tracking maximum power in photovoltaic arrays. This paper can be considered as a completion, updating, and declaration of the good efforts made in [3], that discussed 19 MPPT techniques in PV systems, while summarizes additional 11 MPPT methods.

Power oscillation damping supported by wind power: A review

Abstract: As a consequence of technological progress, wind power has emerged as one of the most promising renewable energy sources. Currently, the penetration level of wind energy in power systems has led to the modification of several aspects of power system behaviour including stability. Due to this large penetration, transmission system operators have established some special grid codes for wind farms connection. These grid codes require wind farms to provide ancillary services to the grid such as frequency regulation and reactive power regulation. In the near future, the capability of damping system oscillations will be required. For this reason, the influence of grid-connected wind farms on system oscillations is reviewed in this paper, focusing on the contribution or damping of power system oscillations, and on inner wind turbine oscillations.

Ship to Grid: Medium-Voltage DC Concepts in Theory and Practice

Abstract: Corporate research centers, universities, power equipment vendors, end users, and other market participants around the world are beginning to explore and consider the use of dc in future transmission and distribution system applications. Recent developments and trends in electric power consumption indicate an increasing use of dc-based power and constant power loads. In addition, growth in renewable energy resources requires dc interfaces for optimal integration. A strong case is being made for intermeshed ac and dc networks, with new concepts emerging at the medium-voltage (MV) level for MV dc infrastructure developments.

Requirements of DC-DC Converters to facilitate large DC Grids

Abstract: SUMMARY Two DC grids may be constructed independently. As these DC grids are independently developed, the operating DC voltage, the operating strategy or even the DC topology may be different and hence, these two DC grids cannot be directly connected. Just as AC systems operating at different voltages require transformers to exchange power, DC grids require DCDC converters to exchange power between networks. A group of offshore windfarms may use a high voltage DC, multi-terminal, bulk power transfer scheme to transfer the power to the onshore AC system. At a future stage a new offshore windfarm may be constructed sufficiently remote from the existing scheme or the mainland to merit a DC transmission connection; but at a lower voltage rating than the existing scheme. An economic method of interconnection may, therefore, be the use of an AC-DC converter at the windfarm and a DC-DC converter local to the existing offshore converter in order to use the existing DC grid to bring the power onshore. Many turbines actually generate an AC output from an AC-DC-AC converter. By removing the DC-AC stage within the wind turbine a medium voltage DC collector bus could be used as a common power interconnection between the DC outputs from multiple wind turbines. A DC-DC converter could then be used to raise the DC voltage to a higher voltage for transmission to an onshore DC to AC converter. For many years the possibility has existed of utilising HVDC to supply multiple small loads dispersed over a large geographical area. As each load may only be at a relatively low power the cost of a 3-phase DC-AC high voltage converter may be prohibitive; but a low cost DC-DC converter could be used to reduce the DC bus voltage at each load centre. There are, today, many existing Line Commutated Converter (LCC) HVDC transmission schemes in operation. By using DC to DC converters it may be possible to interconnect these existing DC schemes with new VSC HVDC converter multi-terminal grids increasing the utilisation of existing grids.

Challenges of Grid Integration of Wind Power on Power System Grid Integrity: A Review

Abstract: Wind Energy Conversion Systems (WECSs) exhibit variability in their output power as a result of change in their prime movers (wind speed)This introduces a new factor of uncertainty on the grid and poses a lot of challenges to the power system planners and the utility operators in terms of the power system grid integrity ie power system security, power system stability and power quality This paper discusses the various challenges of wind power when integrated into the grid and identifies different mitigating strategies for its smooth integration This paper therefore enables the specifications for mitigation/integration technologies to be appreciated and quantified

Power Capability Investigation Based on Electrothermal Models of Press-Pack IGBT Three-Level NPC and ANPC VSCs for Multimegawatt Wind Turbines

Abstract: Wind turbine power capability is an essential set of data for both wind turbine manufacturers/operators and transmission system operators since the power capability determines whether a wind turbine is able to fulfill transmission system reactive power requirements and how much it is able to provide reactive power support as an ancillary service. For multimegawatt full-scale wind turbines, power capability depends on converter topology and semiconductor switch technology. As power capability limiting factors, switch current, semiconductor junction temperature, and converter output voltage are addressed in this study for the three-level neutral-point-clamped voltage source converter (3L-NPC-VSC) and 3L Active NPC VSC (3L-ANPC-VSC) with press-pack insulated gate bipolar transistors employed as a grid-side converter. In order to investigate these VSCs' power capabilities under various operating conditions with respect to these limiting factors, a power capability generation algorithm based on the converter electrothermal model is developed. Built considering the VSCs' operation principles and physical structure, the model is validated by a 2 MV·A single-phase 3L-ANPC-VSC test setup. The power capability investigations regarding a sample grid code's reactive power requirement show that 3L-ANPC-VSC results in 32% better power capability than 3L-NPC-VSC at the switching frequency of 1050 Hz. Furthermore, 3L-ANPC-VSC with 57% higher switching frequency (1650 Hz) and 33% smaller switching ripple filter can yield close power capability compared to 3L-NPC-VSC with 1050 Hz.

Mathematical Modelling of Wind Turbine in a Wind Energy Conversion System: Power Coefficient Analysis

Abstract: The world is increasingly going green in its energy use. Wind power is a green renewable source of energy that can compete effectively with fossil fuel as a generator of power in the electricity market. For this effective competion, the production cost must be comparable to that of fossil fuels or other sources of energy. The initial capital investment in wind power goes to machine and the supporting infrastructure. Any factors that lead to decrease in cost of energy such as turbine design, construction and operation are key to making wind power competitive as an alternative source of energy. A mathematical model of wind turbine is essential in the understanding of the behaviour of the wind turbine over its region of operation because it allows for the development of comprehensive control algorithms that aid in optimal operation of a wind turbine. Modelling enables control of wind turbine’s performance. This paper attempts to address part or whole of these general objectives of wind turbine modelling through examination of power coefficient parameter. Model results will be beneficial to designers and researchers of new generation turbines who can utilize the information to optimize the design of turbines and minimize generation costs leading

Classification and comparative evaluation of PV panel integrated DC-DC converter concepts

Abstract: Strings of photovoltaic panels have a significantly reduced power output when mismatch between the panels, such as partial shading, occurs since integrated diodes are then partly bypassing the shaded panels. With the implementation of DC-DC converters on panel level, the maximum available power can be extracted from each panel regardless of any shading. In this paper, different concepts of PV panel integrated DC-DC converters are presented, comparative evaluation is given and the converter design process is shown for the buck-boost converter which is identified as the best suited concept. Furthermore, the results of high precision efficiency measurements of an experimental prototype are presented and compared to a commercial MIC.

Coordinated Control of Cascaded Current-Source Converter Based Offshore Wind Farm

Abstract: Offshore wind farms with cascaded PWM current-source converters (CSCs) at both generator- and grid-side can eliminate the need for bulky central offshore converter platform, which is usually used in a voltage-source converter (VSC) based counterpart. This novel system structure can simplify the system configuration and operation. However, the wind speed inconsistency at each turbine causes different dc-link current requirements for each CSC. This causes a considerable challenge for systems in which each CSC shares equal dc-link current. In order to overcome the problem, a coordinated control scheme for the dc-link current regulation, which considers wind speed difference of each turbine, is proposed. This control scheme enables the system to operate at minimum dc-link current, contributing to a lower operation losses. In the meantime, the independent control capability of each generator is guaranteed (e.g., maximum power tracking to make full utilization of available wind energy). Furthermore, the whole wind farm control strategy, which consists of wind farm supervisory control (WFSC), local wind turbine control and centralized grid control, is investigated and studied, where maximum power tracking and power limitation modes can be easily achieved. Both simulation and experimental verification of the proposed system with use of two permanent-magnet synchronous generators (PMSGs) are provided.

Effect of Wind Speed on Wind Turbine Power Converter Reliability

Abstract: Wind turbine power converter system (WTPCS) is a crucial device in a wind energy conversion system. This paper presents the new failure rate models and a reliability evaluation technique for the (WTPCS) considering effects of wind speeds, which can be named by the multistate probability analysis method. The case studies on the WTPCS of a 2 MW wind turbine with a permanent magnet synchronous generator are conducted using wind speed data at Lauwersoog and Valkenburg wind sites in Holland. The results indicate that reliability of the WTPCS is affected significantly by variations of wind speed and the rated wind speed of wind turbine. The effectiveness of the proposed method is demonstrated by examples.

A DC/DC Boosting Technique and Power Management for Ultralow-Voltage Energy Harvesting Applications

Abstract: With the increasing use of low-voltage portable devices and growing requirements of functionalities embedded into such devices, efficient dc/dc conversion and power management techniques are needed. In this paper, an architecture for boosting extremely low voltages (about 100 mV) to the typical supply voltages of current integrated circuits is presented which is suitable for power harvesting applications too. Starting from a 120-mV supply voltage, the converter reaches an output voltage of 1.2 V, providing an output current of 220 μA and exhibiting a maximum power efficiency of about 30%. Along with the dc/dc converter, a power management circuit is presented, which can regulate the output voltage and improve the overall efficiency. A test chip was fabricated using a United Microelectronics Corporation 180-nm low-threshold CMOS process.

High-efficiency bidirectional dc-dc converter with high-voltage gain

Abstract: The aim of this study is to develop a high-efficiency bidirectional dc-dc converter for a power storage system. The proposed converter can boost the voltage of an energy-storage module (e.g. battery) to a high-voltage-side dc bus for the load demand. When the high-voltage-side dc bus has excess energy, this energy-storage module can be charged by the dc bus. In this study, a coupled-inductor bidirectional converter scheme utilises only three power switches with the properties of voltage clamping, synchronous rectification and soft switching. As a result, the objectives of high-voltage gain, high-efficiency power conversion and bidirectional power control can be achieved. Some experimental results via a 48/360 V kW-level prototype are given to verify the effectiveness of the proposed converter in practical applications.

A Transformer-Less High-Power Converter for Large Permanent Magnet Wind Generator Systems

Abstract: The power conversion systems for large wind turbines are facing a great challenge as today's wind turbine power outputs approach 5 MW and above. The conventional low voltage power conversion system will suffer from a high transmission current, which significantly increases losses and cost of the cables as well as voltage drop. This paper proposes a modular, medium voltage, high-power converter topology for the large permanent magnet wind generator system, eliminating the grid-side step-up transformer, which is desirable for both onshore and offshore wind turbines. The converter modules are cascaded to achieve medium voltage output. Each converter module is fed by a pair of generator coils with 90 phase shift to get the stable dc-link power. The power factor correction (PFC) circuit enables the generator to achieve unity power factor operation and the generator armature inductance is used as ac-side PFC boost inductance. At the grid-side, H-bridge inverters are connected in series to generate multilevel medium voltage output and the voltage-oriented vector control scheme is adopted to regulate the converter active and reactive power transferred to the grid. Simulation results with a 2-MW wind turbine system and experimental results with a down-scaled 3-kW system validate the proposed topology and control methods. The proposed system can successfully deliver power from the wind generator to the grid.

Dc micro-grid

Abstract: Systems and methods are provided for creating and operating a Direct Current (DC) micro-grid. A DC micro-grid may include power generators, energy storage devices, and loads coupled to a common DC bus. Power electronics devices may couple the power generators, energy storage devices, and loads to the common DC bus and provide power transfer.

Analysis of Inverter-Voltage Influence on Distributed MPPT Architecture Performance

Abstract: More and more distributed maximum power point tracking (DMPPT) architectures, based on a dc-dc converter for every single photovoltaic (PV) panel, are being released and launched to the market as an alternative to traditional MPPT configurations. Ideally, they can solve any mismatching problem, but actually, this is not always feasible. This paper analyzes the static performance of this kind of architectures in order to determine the key factors to bear in mind in the design of the system. Above all, this paper points out the inverter-voltage influence on the overall performance of the PV system.

Nondissipative String Current Diverter for Solving the Cascaded DC–DC Converter Connection Problem in Photovoltaic Power Generation System

Abstract: Frequently considered one of the promising solutions for grid connection of the photovoltaic (PV) power generation system, module-integrated converters have been the focus of numerous papers. Most of the proposed approaches thus far have relied on the use of series string of the dc-dc converter to create a high-voltage string connected to the dc-ac inverter. The boost converter is better in this application. However, under inhomogeneous irradiation, the power generated by each PV module and the output dc voltage of each boost become unbalanced so that the output currents of each boost are balanced and equal to the string current. In this case, the boost converter cannot always deliver all the power from a mixture of shaded panels and those delivering full power. In this paper, a nondissipative string current diverter is proposed to overcome this problem. One important feature of the proposed circuit herein is the ability to effectively decouple each converter from the rest of the string, making it insensitive to change in the string current. Hence, it is possible to obtain the maximum power from the PV module with the maximum power point tracking algorithm implemented on each dc-dc converter and to do so at the optimum efficiency. The simulation and experimental results verify that the proposed topology exhibits notable performances despite inhomogeneous irradiation. On the other hand, the string current diverter circuit is very easy to control and does not operate without inhomogeneous irradiation, so the topology efficiency is improved for any type of irradiation.

Reactive power influence on the thermal cycling of multi-MW wind power inverter

Abstract: In this paper the reactive power influence on the thermal cycling of power devices in grid-connected inverter for 10 MW wind turbines is investigated. Restrained by the grid codes, the allowable reactive power ranges in relation to amplitude and phase angle of the load current for a single converter system are first presented at different wind speeds. Furthermore, the interaction between paralleled converter systems in a wind park is also considered and analyzed. By controlling the reactive power circulated among paralleled converters, a new concept is then proposed to stabilize the thermal fluctuation of the power devices during wind gusts. It is concluded that the reactive power may change the thermal distribution of power devices. By properly controlling the reactive power, it is possible to achieve a more stable junction temperature in the power devices during the fluctuation of wind speed, and thereby could provide a new way to improve the reliability of the wind power conversion system.

Power flow control in DC transmission grids using mechanical and semiconductor based DC/DC devices

Abstract: DC power flow can be controlled though N-1 different DC lines/cables in a DC grid having N individual AC/DC converters. A large meshed DC grid can have more DC lines, and since we can not control power in all lines/cables, an overload may result. In this paper, two methods are proposed for DC power flow control through DC lines/cables. The first method involves using extra resistors embedded in series with DC lines/cables and switched by mechanical or semiconductor based DC circuit breakers. The other method includes installing DC/DC converter at one of the DC line/cable ends with the purpose of DC power flow control. It is shown that the first approach suits better for a short transmission line/cable, while the second one is proposed for a long transmission line/cable with high rated current and higher voltage drop. PSCAD simulation results are presented for a half bridge bidirectional DC chopper employed for DC power flow control between two large 370kV DC grids. (6 pages)

Active power control of a flywheel energy storage system for wind energy applications

Abstract: The integration of wind power generation in power systems is steadily increasing around the world. This incorporation can bring problems onto the dynamics of power systems owing to the lack of controllability over the wind and the type of generation used. In this work, a distribution static synchronous compensator (DSTATCOM) coupled with a flywheel energy storage system (FESS) is used to mitigate problems introduced by wind generation in the electric system. A dynamic model of the DSTATCOM/FESS device is briefly presented and a technique to control the active power exchanged between the device and the power system is proposed. The control technique is based on fuzzy logic and a special filter. Tests of the behaviour of the device are analysed when combined with wind generation in the electric system. Results show an overall satisfactory performance of the proposed control technique along with the high effectiveness of the device used to smooth the active power fluctuations of a wind generator.

An Analog Technique for Distributed MPPT PV Applications

Abstract: TEODI is the acronym of a maximum power point tracking (MPPT) technique which has been recently presented in the literature. Such a technique is particularly suitable in distributed MPPT photovoltaic (PV) applications, and it is based on the equalization of the output operating points, of the dc/dc converters dedicated to each subsection of the PV array, in correspondence of the forced displacement of their input operating points. The main advantages of TEODI, its performances in terms of MPPT efficiency and speed of tracking, and the intrinsic capability to attenuate the effect, on the voltages of the PV modules, of the 100/120 Hz disturbances coming from the grid are shown by means of simulation results and experimental findings obtained by using a laboratory prototype developed by means of analog circuitry only.