Power Delivery from an Actual Thermoelectric Generation System

Similar to photovoltaic (PV) and fuel cells, thermoelectric generators (TEGs) supply direct-current (DC) power, essentially requiring DC/alternating current (AC) conversion for delivery as electricity into the grid network. Use of PVs is already well established through power conditioning systems (PCSs) that enable DC/AC conversion with maximum-power-point tracking, which enables commercial use by customers. From the economic, legal, and regulatory perspectives, a commercial PCS for PVs should also be available for TEGs, preferably as is or with just simple adjustment. Herein, we report use of a PV PCS with an actual TEG. The results are analyzed, and proper application for TEGs is proposed.     

Engpassmanagement im hoch ausgelasteten Übertragungsnetz von Verbund-Austrian Power Grid

Congestions resp. highly loaded utilities in transmission grids are due to unbalanced regions caused by surplus or deficit of electricity combined with insufficient transmission capacity. In the case of congestion, the transmission system operator has to apply counter measures in order to reduce the bottlenecks. This article describes different possibilities to reduce congestions and illustrates the mode of working on the basis of a simple network model. A distinction is made between congestion measures which are applied by changing the operation of grid devices and those applied by changing generators or loads (market based CM). The application of the described congestion management is shown on the basis of the highly loaded transmission grid of Verbund-Austrian Power Grid AG (APG). To eliminate the congestions in the grid of APG, new 380 kV lines are planned to be put into operation. If the commissioning of these lines is delayed, CM measures which would have to be implemented are described and the disadvantages for the Austrian electricity supply are shown.     

Integration von Energiemarkt und Verteilnetzbetrieb durch einen Flexibility Operator

The growing share of volatile distributed generation in the electric power grids results in increased local network utilisation and challenges the conventional strategies for maintaining the system balance. While grid extensions and smart grid solutions are considered for network utilisation issues, new market mechanisms are in focus for the balancing challenge. It can be expected that distributed generators on one hand will be able to supply only part of their available power to the grid in peak times, and on the other hand will have (potentially changing) contracts with different trans-regional virtual power plants. Against this background it will be necessary to define rules dealing with expected network access conflicts. One strategy also followed in this work is to find market mechanisms that support economically efficient network extension. Such mechanisms will have to include local flexibility markets that allow for compensating network bottlenecks. This work proposes strategies and technical interfaces for coordinating market and grid operation by means of a “Flexibility Operator”. Its integration into a holistic smart grid concept is discussed.     

Interaction between photovoltaic distributed generation and electricity networks

Electricity power systems worldwide have traditionally been designed to a vertically connected scheme characterised by centralised generation. Over the last few decades, several factors have dictated a gradual shift from the central‐control approach to a more distributed layout where distributed generation (DG) technologies are effectively integrated and not just connected (appended) to the networks; amongst others liberalisation of electricity markets, security and quality of supply and environmental issues. Photovoltaic powered distributed generation (PV‐DG), although still having a much lesser impact than other DG technologies, is increasingly being embedded into electricity distribution networks worldwide within the framework of successful regulatory state and marketing programmes. PV‐DG has added values (benefits) for the electricity systems that extend from peak power and load reduction (when deployed close to electricity consumption points) to participation in grid‐supporting or grid‐forming modes of operation. The question arises as to what the present situation of PV technology is for its optimal integration in distribution networks, whether there are still technical barriers to overcome as well as new opportunities for PV in future renewably supplied electricity systems. This paper presents the current state of knowledge concerning these topics from a European perspective with regard to different grid structures. It also discusses existing standards, new opportunities to provide grid services and research and development needs identified to fully exploit the added‐value—and still developing—benefits of PV‐DG. Copyright © 2008 John Wiley & Sons, Ltd.     

基于智能整流技术的电网电流谐波补偿方法研究

目前用于电网电流谐波补偿的电器设备,主要以PWM整流器为主。基于PWM整流器的电源产品只能被动地减小自身向电网输出的谐波电流,而对电网中业已存在的电流谐波污染束手无策。为了解决电网中电流谐波污染以及相关联的电压波形失真问题,采用基于SRM(智能整流模块)技术对电网电流谐波进行补偿。仿真结果表明,基于SRM的电力电子装置在从电网吸取电流并在向负载供电的同时,还能对电网电压的波形进行补偿,使电网电压波形接近正弦波形。     

Grid current regulation of a three-phase voltage source inverter with an LCL input filter

Many grid connected power electronic systems, such as STATCOMs, UPFCs, and distributed generation system interfaces, use a voltage source inverter (VSI) connected to the supply network through a filter. This filter, typically a series inductance, acts to reduce the switching harmonics entering the distribution network. An alternative filter is a LCL network, which can achieve reduced levels of harmonic distortion at lower switching frequencies and with less inductance, and therefore has potential benefits for higher power applications. However, systems incorporating LCL filters require more complex control strategies and are not commonly presented in literature. This paper proposes a robust strategy for regulating the grid current entering a distribution network from a three-phase VSI system connected via a LCL filter. The strategy integrates an outer loop grid current regulator with inner capacitor current regulation to stabilize the system. A synchronous frame PI current regulation strategy is used for the outer grid current control loop. Linear analysis, simulation, and experimental results are used to verify the stability of the control algorithm across a range of operating conditions. Finally, expressions for ""harmonic impedance" of the system are derived to study the effects of supply voltage distortion on the harmonic performance of the system.     

Experience with PV‐diesel hybrid village power systems in Southern Morocco

In October 2002, under the auspices of Spanish Cooperation, a pilot electrification project put into operation two centralised PV‐diesel hybrid systems in two different Moroccan villages. These systems currently provide a full‐time energy service and supply electricity to more than a hundred of families, six community buildings, street lighting and one running water system. The appearance of the electricity service is very similar to an urban one: one phase AC supply (230 V/50 Hz) distributed up to each dwelling using a low‐voltage mini‐grid, which has been designed to be fully compatible with a future arrival of the utility grid. The management of this electricity service is based on a ‘fee‐for‐service’ scheme agreed between a local NGO, partner of the project, and electricity associations created in each village, which are in charge of, among other tasks, recording the daily energy production of systems and the monthly energy consumption of each house. This register of data allows a systematic evaluation of both the system performance and the energy consumption of users. Now, after 4 years of operation, this paper presents the experience of this pilot electrification project and draws lessons that can be useful for designing, managing and sizing this type of small village PV‐hybrid system. Copyright © 2007 John Wiley & Sons, Ltd.     

Renewable Energy Systems With Photovoltaic Power Generators: Operation and Modeling

A substantial increase of photovoltaic (PV) power generators installations has taken place in recent years, due to the increasing efficiency of solar cells as well as the improvements of manufacturing technology of solar panels. These generators are both grid-connected and stand-alone applications. We present an overview of the essential research results. The paper concentrates on the operation and modeling of stand-alone power systems with PV power generators. Systems with PV array-inverter assemblies, operating in the slave-and-master modes, are discussed, and the simulation results obtained using a renewable energy power system modular simulator are presented. These results demonstrate that simulation is an essential step in the system development process and that PV power generators constitute a valuable energy source. They have the ability to balance the energy and supply good power quality. It is demonstrated that when PV array- inverters are operating in the master mode in stand-alone applications, they well perform the task of controlling the voltage and frequency of the power system. The mechanism of switching the master function between the diesel generator and the PV array-inverter assembly in a stand-alone power system is also proposed and analyzed. Finally, some experimental results on a practical system are compared to the simulation results and confirm the usefulness of the proposed approach to the development of renewable energy systems with PV power generators.     

Compensation strategies for shunt active-filter control

Compensation strategies for control of shunt active filters are compared in the paper. It is shown that the strategy based on unity-power factor control is appropriate when the supply voltage waveform of the plant where the active filter is connected shows significant distortion. As voltage distortion increases, this strategy provides compensated line current having lower harmonic distortion and RMS value with respect to the strategy generally used. This contributes to diminish the current and voltage distortion in networks. The unity-power factor compensation strategy conditions the current flowing in the plant where compensation is realized to fit the voltage waveform, thus reaching a unity power factor. Hence, the line current RMS value is minimum. The comparison of the strategies is performed by both Monte Carlo and ATP simulation     

中低压配电网规划中的问题及解决措施

在电力企业日常的运营过程中,中低压配电网规划是十分重要的一部分工作。同时,电力也是人们日常工作生活中必不可少的一部分。为了让所有的居民都可以得到用电需求的满足,就要使中低压配电网规划工作可以顺利进行。这一项工作也对整个电网规划有着直接的影响作用。     

一种基于移相控制的电压补偿器研究

电力系统在负载较重,供电距离较远的情况下,受电网参数的影响,远端供电品质会出现下降。文中针对这种现象提出了一种基于移相控制的电压补偿装置,在电网电压波动时使负载端电压保持恒定并具有良好的谐波滤除能力。     

基于微网并网的智能电网用户用电福利研究

考虑需求侧响应的微网并网运行机制能够引导用户合理用电,对研究智能电网用户用电福利具有重要意义。综合光伏、风能发电的不稳定性,提出微网并网运行机制下需求侧响应策略,以微网运行成本最小和需求侧用电效用最大为目标,建立了考虑需求侧响应的微网并网运行福利模型。仿真结果表明所建立的模型可达到用户最大用电福利,且有利于削峰填谷,降低供电压力,提升用户参与建设微网的积极性。     

Suppression of line voltage related distortion in current controlled grid connected inverters

The influence of selected control strategies on the level of low-order current harmonic distortion generated by an inverter connected to a distorted grid is investigated through a combination of theoretical and experimental studies. A detailed theoretical analysis, based on the concept of harmonic impedance, establishes the suitability of inductor current feedback versus output current feedback with respect to inverter power quality. Experimental results, obtained from a purpose-built 500-W, three-level, half-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding an output current total harmonic distortion (THD) some 29% lower than that achieved using output current feedback. A feed-forward grid voltage disturbance rejection scheme is proposed as a means to further reduce the level of low-order current harmonic distortion. Results obtained from an inverter with inductor current feedback and optimized feed-forward disturbance rejection show a THD of just 3% at full-load, representing an improvement of some 53% on the same inverter with output current feedback and no feed-forward compensation. Significant improvements in THD were also achieved across the entire load range. It is concluded that the use of inductor current feedback and feed-forward voltage disturbance rejection represent cost-effect mechanisms for achieving improved output current quality.     

SVC动态无功补偿在安钢1780mm热连轧当中的应用

阐述了安钢热连轧为降低在轧钢过程当中由于负荷变化而造成电网电压电流畸变对设备产生影响而采用的无功补偿装置（SVC）。通过分析SVC工作原理以及运行中的无功补偿装置对电网电能质量的改变,得出了投入使用后的SVC系统对于抑制电网波动、抑制谐波电流、提高功率因数等起到了明显的改善作用。     

Discrete Frequency Tuning Active Filter for Power System Harmonics

Severe voltage distortion, due to power system harmonic resonance, has been reported in recent years. This issue becomes more significant in high penetration of a photovoltaic (PV) network. A conventional voltage detection active filter operates as similar conductance for all harmonic frequencies to resolve this problem whether in a fixed conductance command or in an automatic gain adjustment control. However, its filtering capability is impeded by the mismatch between the active filter and the radial line, and the voltage distortion may still be significant. This paper proposes a discrete frequency tuning active filter to suppress power system harmonics. The active filter operates as variable conductance for each individual harmonic frequency. Each harmonic conductance is dynamically adjusted according to the corresponding harmonic voltage distortion of the active filter installation point in response to increase or decrease of nonlinear loads, or variation of resonant frequency in the power system. The mismatching problem between the feeder impedance and the active filter can be avoided effectively. Therefore, harmonic voltage distortion can be maintained at an allowable level throughout the feeder with lower peak current and lower rms current of the active filter, and loads installed at various locations of the power system receive more uniform voltage waveform.     

单相PWM整流器控制方法及谐波分析

传统二极管不控整流或晶闸管相控整流,对电网注入大量谐波及无功功率,造成电源污染.PWM整流器采用全控型开关器件取代二极管或半控型器件,并将PWM控制技术引入整流器,在稳定直流电压输出同时,使交流侧电源电流接近正弦波,实现能量的双向流动.通过介绍单相PWM整流器的控制方法,利用Matlab/Simulink搭建仿真模型,比较分析不同控制方式下PWM整流器运行时电压波形及输入电流的谐波频谱.     

三相单级式光伏并网控制策略仿真

根据单级式光伏并网系统的拓扑结构及工作原理,建立了基于电网电压定向的矢量控制的并网逆变系统.该系统控制部分采用了最大功率跟踪、电压外环、电流内环的控制策略,保证光伏系统最大功率输出,实现并网电流与电网电压同频同相,高功率因素运行.     

Three-Phase Low-Frequency Commutation Inverter for Renewable Energy Systems

The connection of distributed power sources with the utility grid generally needs an electronic power converter for processing the locally generated power and injecting current into the system. If the source provides a dc voltage, the converter must be able to produce a low-distortion high-power-factor ac current. The same aspects related with the voltage and current distortion produced by nonlinear loads can be considered for the injection of power into the grid. In the absence of a specific standard, this paper takes as a reference the limits for current harmonics given by international standards. The justification for this approach is that, from the resulting line voltage degradation, there is no difference between injected and absorbed currents. This paper presents a three-phase inverter using low-frequency commutation. An auxiliary circuit is added to the inverter topology to reduce the output voltage distortion, thus improving the current waveform. The main advantages of this approach are the minimization of the switching losses and the elimination of the electromagnetic interference, which avoids high-frequency filters necessary in high-frequency commutation inverters     

Analysis Results of Output Power Loss Due to the Grid Voltage Rise in Grid-Connected Photovoltaic Power Generation Systems

This paper describes the connected photovoltaic (PV) power generation system's grid overvoltage protection function and summarizes the occurrence of the output power loss due to the grid voltage rise. Power injection from the PV system will raise the voltage at the power distribution line. A power conditioning subsystem (PCS) needs to regulate its output if the voltage becomes higher than the upper limit in order to avoid the overvoltage at the power grid. Thus, a PV system cannot generate electricity under the high grid voltage. There are 553 residential PV systems installed in Ota, Japan, for the demonstration research project of clustered PV systems. Measurement data of these 2.1-MW grid-connected PV systems are used for the analysis. Only the limited number of PV systems experienced a significant amount of output energy loss due to the high grid voltage in a particular day, whereas the other system's outputs also raise the grid voltage. The causes of this maldistribution of the output energy loss are the difference of the line impedance, the difference of the starting voltage of the PCS's grid overvoltage protection function, and the imbalance of the load in single-phase three-wire power distribution systems. The present control of the PCS successfully avoids the overvoltage on the grid but cannot share the loss.     

基于dsPIC的PV逆变器的一种改进结构及其实现

针对目前PV光伏并网发电系统的核心逆变器的现状、结构和控制方法进行了详细的分析,从电网、PV系统及用户的需求出发,指出传统的单级全桥逆变器普遍具有不能处理较宽的输入PV电压,且需要重型工频升压变压器等缺点。在此基础上,本文创新设计并实现了一种基于单级全桥逆变器的并联耦合改进结构。实测证明这种并联耦合反激结构可以有效地减小通过大容量输入电解电容的纹波电流的RMS,从而延长电容的寿命;还可减小输出电流的纹波,从而降低输出电流的THD（谐波失真）;还可适应较宽的输入电压,减小交流纹波,减小磁芯,同时可以提供较高的额定输出电流等优点。