High-temperature superconducting DC networks

High-temperature superconducting DC networks are studied as a feasible alternative to AC power transmission systems. The DC network operates at generation voltages allowing direct connection of the generators to the rectifiers, eliminating the need for high-voltage insulation and transformers. The DC system is based on a mesh-connected low-voltage high-current superconducting DC transmission network supplied by unit-connected generators. The DC system feeds many small inverters that pass controlled levels of real and reactive power to AC loads. This paper presents an overview of superconducting low-voltage DC transmission systems, starting with a discussion of the DC system. This discussion is followed by an overview of the operation of AC distribution systems connected to the superconducting DC mesh and then inverter topologies and control strategies required for interfacing the AC distribution systems to the DC mesh. The paper presents a conceptual overview of the operation of the system based on simulation studies     

Moving power through the northeast corridor

Most urban utilities in the northeast and midAtlantic regions lack sufficient generation to meet their peak loads, and in the summer rely on daily imports in the hundreds of megaWatts from other utilities with power to sell. Since extensive transmission networks mean more reactive power losses, utilities are increasingly turning to capacitor banks, which can be installed close to inductive loads, to supply reactive power. Another side effect of long-distance transmission across grids, called wheeling, is caused by a basic law of alternating current networks: the paths over which current is going to flow cannot be chosen for all practical purposes; rather, they are determined by electrical characteristics, namely, the relative voltages, phase angles, and reactance of various points in the network. This results in parallel power flows where part of the power flows into areas that do not want it. A solution to this problem is the phase-angle regulator, a transformerlike device that lets dispatchers change the relative phase angle between two system voltages, thereby helping them control real power transfers between the two systems     

Reliability analysis of capacity and voltage constrained, optimallyoperated, electric power systems

A method for reliability evaluation of capacity and voltage constrained bulk power systems is suggested based upon contingency analysis. For each contingency and consumer load demand situation assumed, the optimal operation of the power system is established that minimizes the total system consumer curtailment cost. Consumer demands at different nodes may be treated as synchronous or as mutually uncorrelated quantities, depending on the data available. The method uses a version of the decoupled power flow network model that makes its possible to determine optimal generation of both real and reactive powers for the system sequentially. This property makes the method superior to other available approaches for bulk power system reliability analysis. An illustrative example is included     

Power control and channel allocation for real‐time applications in cellular networks

The next‐generation packet‐based wireless cellular network will provide real‐time services for delay‐sensitive applications. To make the next‐generation cellular network successful, it is critical that the network utilizes the resource efficiently while satisfying quality of service (QoS) requirements of real‐time users. In this paper, we consider the problem of power control and dynamic channel allocation for the downlink of a multi‐channel, multi‐user wireless cellular network. We assume that the transmitter (the base‐station) has the perfect knowledge of the channel gain. At each transmission slot, a scheduler allots the transmission power and channel access for all the users based on the instantaneous channel gains and QoS requirements of users. We propose three schemes for power control and dynamic channel allocation, which utilize multi‐user diversity and frequency diversity. Our results show that compared to the benchmark scheme, which does not utilize multi‐user diversity and power control, our proposed schemes substantially reduce the resource usage while explicitly guaranteeing the users' QoS requirements. Copyright © 2007 John Wiley & Sons, Ltd.     

Development of a robust anti-islanding algorithm for utility interconnection of distributed fuel cell powered generation

In this paper, a robust anti-islanding algorithm for distributed fuel cell powered generation (DFPG) is proposed. Three different islanding scenarios are explored and presented based on analysis of real and reactive power mismatch. It is shown via analysis that the islanding voltage is a function of real power alone, whereas its frequency is a function of both real and reactive power. Following this analysis, a robust anti-islanding algorithm is developed. The proposed algorithm continuously perturbs (/spl plusmn/ 5%) the reactive power supplied by DFPG while simultaneously monitoring the utility voltage and frequency. If islanding were to occur, a measurable frequency deviation takes place upon which the real power of DFPG is further reduced to 80%; now a drop in voltage positively confirms islanding, and the DFPG is safely disconnected. This method of control is shown to be robust, able to detect islanding under resonant loads, and fast acting (operable in one cycle). Possible islanding conditions are simulated and verified with analysis. Experimental results on a 0.5 kW fuel cell inverter connected to 120 V 60 Hz utility are discussed.     

Analytical performance evaluation of downlink beamforming with power control by transmit power limited channel inversion

We investigate the transmission performance of a downlink BPSK transmission system which uses beamforming combined with cross-polarised antenna arrays and power control in a Rayleigh fading environment to fulfil QoS requirements of real time services. A power control method termed “power control by transmit power limited channel inversion” is applied in the system. Power limitation in the downlink and the effect on the bit error rate performance is especially interesting for mobile stations at the cell borders of a cellular communication system. For this non-linear transmit model we derive analytical formulas for the average transmit power and the bit error rate performance. The exact validity of the results is verified by Monte-Carlo simulations. We also show the interaction of power control and beamforming, and the dependency of the gain in transmit power from the SNR, an effect that is not visible without transmit power limited power control.     

间歇式能源发电系统无功补偿技术的研究

针对间歇式能源发电系统的特点和无功需求,提出了将无功补偿与风力并网发电相结合的设计方案,通过计算得出了间歇式能源发电系统中电缆和变压器无功损耗.本文利用Mat-lab/Simulink搭建了具有无功补偿功能的并网变流器的仿真模型,并采用有功无功解耦控制和SPWM控制方法,补偿系统所需无功以及有效抑制动态电压波动.最后,仿真结果验证了风力并网变流器在向电网提供有功功率的同时也能够提供一定容量的无功功率,提高系统功率因数,有效抑制电网电压波动.     

A Secondary Voltage Control Strategy for Transmission Level Interconnection of Wind Generation

This paper addresses implementation issues associated with secondary voltage control in a doubly-fed induction generator based wind farm. The effects of different system parameters on the performance of the control are considered, namely the short circuit ratio of the interconnection and the inherent communication delay between the wind park and the remote bus. In addition, a strategy for allocation reactive power requirements to each of the generators within the wind park is proposed. The system is developed and simulated for a wind park consisting of six wind generators connected to a typical transmission system. The paper proposes an optimal tracking secondary voltage control method developed to achieve effective voltage regulation, enhance the network voltage profile and provide optimal reactive power compensation to the interconnected power system. The performance of the controller is compared with secondary voltage control at one selected bus, primary voltage control and the optimal voltage profile obtained from the optimal power flow analysis. The performance of the controllers is tested for steady state operation and in response to system contingencies, taking into account the impact of communication time delays and short circuit ratio (SCRs). Simulation results are presented to demonstrate the capability of the controllers to provide the desired reactive power compensation and voltage support to the electric power grid.     

考虑微电网并网接入的配电网无功优化

微电网集分布式发电系统、负荷和储能于一体,提高了分布式发电系统的综合利用.微电网的并网接入对配电网的综合无功优化产生影响,因此,配电网的无功优化过程中需要考虑微电网并网接入的影响.本文在充分考虑微电网运行特性的基础上,构建考虑微电网运行特性的配电网综合无功优化,建立以系统有功网损与节点电压为目标的综合无功优化模型,把含微电网的配电网无功优化转化为一多约束的非线性混合优化数学问题,并利用粒子群算法进行求解.通过IEEE 33节点系统的仿真算法分析验证本文提出方法的有效性和正确性.     

基于MSP430的在线远程监测的数据采集系统设计

随着国计民生对供电高可靠性要求的不断提高,高海拔输电线路定期停电试验的预防性维修制度,已远远不能满足现实要求;并且停电试验还间接造成巨大经济损失。因此,以在线监测为基础的维修策略逐步取代预防性维修制度已是必然趋势。文中结合我国西部高海拔输电线路在线远程监测系统的技术条件要求,开发设计一套输电线路在线远程监测的数据采集系统,负责将传感器数据通过GPRS网络实时传送到主站系统,并实现对所有传感设备进行控制,很好地满足了国民经济对供电高可靠性需求。     

Warum Windenergie keine konventionellen Kraftwerke ersetzt und ein leistungsfähiges Übertragungsnetz benötigt

The amount of wind power installed in Austria has tripled over the year 2003. At present 430 MW are in operation and about 1000 MW of further projects are known. At the end of 2004 about 700 MW are assumed to be in operation. Due to the fluctuation of wind, the limited forecast possibilities and the resulting volatile generation, wind power plants cannot replace conventional power plants but may give an ecologically valuable contribution to the existing generation. Regarding the security of supply wind power plants cannot grant ongoing generation and supply all over the time. This results in the need for additional operation of conventional power plants (e.g., pump storage power plants) to provide the necessary real time balance between generation and consumption of electrical energy at any time (balancing energy). A powerful transmission grid is required for this interaction as well as for the transportation of generation surpluses from large wind parks to the consumers. This advantageous combination of a “wind and water” system cannot be fully exploited due to severe bottlenecks within the Austrian transmission grid. This article shall highlight the new challenges in the operation of the transmission grid and the control area of Verbund-Austrian Power Grid due to the wind energy. Furthermore, an integrated planning approach for the energy system, considering all aspects from generation, transmission and distribution is urgently needed.     

Investigation on Active and Reactive Combined Spot Price Integrated with Wind Farm

An active and reactive combined spot price model and the corresponding algorithm are introduced in this paper based on the theory of optimal power flow. Different from the traditional economic dispatch in the field of spot price, the objective function is to minimize generation costs based on pricing reactive power. Then considering the characteristics of wind turbines, processing methods of wind farms in optimal power flow is discussed. Finally, the feasibility of the model and the algorithm is verified through the simulation results of IEEE 30 system.     

直驱式风力发电系统中TSMC的研究

分析了将TSMC(双级矩阵变换器)作为直驱式永磁同步风力发电系的全功率变流器,并且分别对TSMC的整流级的PWM调制和逆变级空间矢量调制进行了推导和计算,简要分析了TSMC的换流方法。然后运用MATLAB对整流级和逆变级调制方法和对直驱式风力发电系统的要求进行仿真验证,仿真结果验证了本文的理论分析和调制方法的正确型,说明了TSMC具有调制方法简单、输出电能质量高等优点,同时也说明TSMC非常适合用于直驱式风力发电系统中,并且为进一步地研究TSMC提供了理论基础。     

Power electronics in electric utilities: static VAR compensators

The author deals with dynamic VAR compensation of electric power systems, applying power electronics for reactive power generation and control. After an overview of the emergence and status of modern, solid-state VAR compensators in utility and industrial applications, it is shown how dynamic VAR compensation increased transmittable power by providing voltage support, transient stability improvement, and power oscillation damping in electric power transmission systems. Methods of reactive power generation and control using thyristor-controlled reactors, with fixed and thyristor-switched capacitors or modern gate-turn-off (GTO) power converters that can function without AC capacitors or reactors, are described. A summary is included of the control structure and operation to provide the desired characteristics and performance in power systems applications     

广州换流站交流滤波器投退顺序异常分析及改进措施

直流输电系统运行时需要从交流输电系统吸收容性无功,即对于交流系统而言,换流器总是一种无功负荷。为了补偿无功,通用的做法是在换流站配置无功补偿设备。而交流滤波器作为重要的无功补偿设备,其伴随着系统运行方式的变化进行投退。文中研究了交流滤波器的投退控制,分析了运行中出现的问题。     

固态激光雷达输电线路实时建模及压缩技术北大核心CSCD

输电线路的三维重建是电网巡检的重要任务之一。为实现电路巡检自动化,提出了一种基于固态激光雷达的输电线路实时三维重建及数据压缩技术。首先,针对固态激光雷达的特点对经典激光SLAM框架进行改进,优化其特征提取过程并加入了运动补偿,使用改进的算法对输电线路进行实时建模;然后,使用加入权重因子改进的模糊C均值聚类方法对点云模型进行降噪滤波,去除离群点及噪点;最后,为了降低大型点云数据的储存及传输开销,设计基于时空编码的方法对输电线路模型进行压缩。实验结果表明,该方法可以实现输电线路场景的高精度实时建模,压缩后的模型可以满足储存及传输要求。     

电压骤降下双馈电机撬棒投切时刻对电网的无功功率影响

风力发电机规模和单机容量不断增大,电网对风力发电机之类的可再生能源并网有着极其严格的要求,其中最具挑战性的要求是低电压穿越,即在电网出现跌落时,要求风机在一定时间内不得脱网,直至发电机发出一定的无功功率帮助电网恢复。本文研究在电网出现大幅跌落时,通过控制撬棒投切的不同时刻,来讨论是否其投切时刻影响着系统从电网吸收的无功功功率,最终通过合理的投切时刻来最大程度上减少系统从电网吸收的无功功率,帮助电网更好的恢复。     

An autonomous controller for improved dynamic performance of parallel-connected,single-phase inverters

A new control technique is presented for the parallel connection of distributed generation inverters. The proposed control technique is based on a modification of the power angle droop control method, and uses only locally measured feedback signals. An improvement in transient response is achieved because the real and imaginary components of the output current are used when deriving the power angle droop controller. The method achieves good active and reactive power sharing and minimises circulating current between parallel connected units. Improved transient response is obtained whilst maintaining power sharing precision or output voltage and frequency accuracy. Simulation and experimental results validate that performance is better than that attained with conventional droop-based approaches.     

10kV输电线路的微机继电保护

伴随着电力系统的快速发展和人们对供电的高要求,为了保证输电线路的安全稳定运行,要求对输电线路实施高性能的微机保护。该文基于C8051F021单片机开发出了一套微机继电保护装置,其功能是对实时电流信号的采集并进行相应的保护运算,对电力系统运行进行实时监测,发生故障或不正常运行时能进行相应的分析后可靠性动作或发出信号。主要内容是进行了微机保护硬件电路的搭建,根据线路保护的要求,利用c语言开发工具实施了软件编写以及保护算法编写工作。其中,在对保护算法的编写工作中,以保证对故障或不正常运行时能快速动作或发出信号为目的,选择了用两点乘积算法和差分滤波器来实现。经过反复测试,其性能符合继电保护的要求。     

An approach for handling the nonlinearities of HVDC system forstability analysis

An approach for linearizing the nonlinearities of the high voltage direct current (HVDC) system for analyzing the system stability over wide range of operation is presented. The nonlinearities can be linearized with ±5% error over a wide range of system operation. It is shown that the nonlinearities introduced by the converter, real power, and reactive power equations can be linearized over a wide range by using the integral square error (ISE) method. The results are compared with standard techniques called small signal analysis. It is shown that the stability margin of the system predicted by the new technique is relatively smaller than what is predicted by small signal analysis. The system stability boundaries are determined by the AC voltage and the reactive current control. These two control schemes may provide the same stability margin, provided appropriate controller gains are selected. The power factor control modeling is discussed