Development of an advanced voltage control technique to improve voltage and reactive power characteristics of a large-scale power cable system

The power supply system for a metropolitan area consists of multiple 275-kV power cable systems to supply power to a large number of consumers. Each system has a large charging capacity (capacitive reactive power). When 275-kV power cable systems experience a voltage drop, their charging capacity decreases. However, the reactive power losses increase in the 275-kV overhead transmission lines, which supply large power to power cable systems, thus causing the performance of the power supply system to deteriorate. In this paper, the following three points are reported:

• 1 When the secondary power system of the trunk substation is a large-scale power cable system, new techniques can greatly improve the voltage and reactive power characteristics by controlling the rise of the sending-end voltage at the secondary side of the trunk substations and maintaining the voltage of power cable systems at a constant level.
• 2 In the use of this control technique, it has been demonstrated that controlling by the direct-detecting method of a voltage drop in the primary power system is superior to one that controls by the indirect-detecting method, which increases load power in the cable system.
• 3 The results of simulations obtained by using a 275-kV cable system model and a performance power system model show that the use of this control technique can produce a good effect despite the allowances made for the opposite effect, i.e., a decrease in the capacity of power capacitors resulting from voltage drop at the tertiary voltage of a 500-kV transformer.

This study is carried out to examine the possibility of lightning control using a photoionized plasma produced by a UV laser without an optical air breakdown. As the fundamental experiment, the characteristics of a laser-triggered spark gap (LTSG) are examined, where a laser beam is not irradiated on the surface of the electrodes. In this experiment, the KrF excimer laser is very effective in increasing the plasma density n_e and the reduction ratio p of 50 percent breakdown voltage against the self-breakdown voltage. The relation between n_e and p is increased by generating a long and high-density plasma parallel to the discharge axis. On the other hand, the abnormal discharge process in triggered lightning using a rocket is examined, and it is indicated that the most important condition to trigger a lightning discharge is the production of a plasma channel of length 200 m and density about 10¹⁹ m^?3. It is suggested that such a plasma channel could be produced by a KrF excimer laser with an energy of only about 3.67 J.     

综合考虑负荷增长和多预想故障的静态电压失稳预防控制策略

提出的综合的静态电压失稳预防控制策略以最小控制代价为目标,综合考虑了负荷增长方式和多预想故障条件下的静态电压稳定裕度约束对系统静态电压稳定性的影响。该策略分2步进行:首先考虑负荷增长的影响,若系统在未来运行点不满足静稳指标,则找出系统的薄弱区域和负荷最安全变化方向,在此方向进行合理的无功补偿;其次考虑多预想故障条件下系统的静态电压稳定裕度约束,并引入关键故障集的概念求解计算优化策略,施加控制措施后再进行扫描确定新的关键故障集,循环直至对所有故障都满足裕度要求。IEEE-39节点算例证明了该综合预防控制策略的有效性。     

Preventive voltage control actions to securely face load evolution in power systems

One of the main aims of the System Operator (SO) is to maintain in every moment the system parameters between feasible operational margins. In certain periods of the day the load suffers fast changes which cause, specially when it tends to increase, a generalized voltage decrement and a more stressed condition for many reactive resources. In such cases, many devices may arrive to their operational limits, situation which translates into a weaker system. To avoid this negative effect the control variables should be rescheduled to maintain the normal operation conditions in the foreseeable future. This work proposes a useful tool to assist the SO when determining such actions. The main improvements are due to the implementation of a hybrid method that allows the comparison of different kinds of control variables and the inclusion of the operator background and experience in the algorithm that determines the actions. The performance of the proposed method is tested in both the IEEE 14-Bus and 118-Bus test systems.     

无功电压优化集中控制系统对电网的影响分析

该系统借助调度自动化的SCADA功能,实现对青岛地区全网无功电压的优化和集中自动控制.介绍了系统原理、方法和控制策略,用一个实例来分析了系统的一些重要功能.系统的引入对青岛电网全网各节点的电压合格率有了明显的改善,同时降低了网损,给公司带来了可观的经济效益.     

基于粒子群算法的变电站电压无功综合控制

变电站电压无功综合控制的作用是在负荷和电压波动情况下向用户提供合格的电能,降低网损。近年来已开发出许多电压无功综合控制优化算法。根据负荷预测,全局规划,寻求最优控制策略,是较先进的一种方法。文章阐述在负荷预测精度不断提高的基础上,如何建立变电站电压无功控制的求解模型,利用改进的粒子群算法求取变电站电压无功最优控制策略。对实例的计算结果表明,利用该算法得出的控制策略与传统方法相比控制效果更优,且能提高系统的安全性和经济性。     

Dynamic preventive control for power system using transient stability assessment based on pattern recognition

To maintain power system security, the authors are developing an integrated security monitoring and control (ISMAC) system which consists of the three main functions: security monitoring, preventive control and emergency control. This paper focuses on the dynamic preventive control which deals with the transient stability immediately after the contingency has occurred. The proposed method is based on the transient stability assessment using the pattern recognition with two-dimensional feature space. Therefore, a preventive control strategy can be obtained rapidly. An index which represents the severity of the contingency quantitatively (security index) is defined by the distance from a linear decision surface which divides a feature plane into a stable and an unstable region. Further, this method has also the advantage that it is possible to consider the effect of the control devices or damping to some extent and specify the operator demand for stabilization flexibly. The effectiveness of the proposed method is ascertained through numerical examples for model power systems.     

Dynamic preventive control strategies for power systems considering transient and midterm stabilities

This paper proposes a new dynamic preventive control strategy to maintain power system security, in terms of both transient and midterm stabilities. While the authors have already presented preventive control strategies for transient stability, a new problem has arisen in midterm instability in which some generators lose synchronism after 10 seconds or more from a fault clearance. It is clear that the cause of the instability is mainly post-contingency dynamic steady-state instability. This paper first shows a preventive control strategy for improving midterm stability using a dominant eigenvalue of post-contingency equilibrium point. This paper also presents a unified dynamic preventive control algorithm that can maintain both stabilities together. In this algorithm, the time domain for each stability problem is considered appropriately and the difference between the classical model and the detailed model is analyzed in detail. The effectiveness of the proposed method is examined with numerical examples for a model system.     

Transmission capacity of longitudinal power systems and SVC voltage control

Power transfer between systems is important due to uneven distribution of generating plants. This paper investigates the relation between the transfer capacity of a longitudinal power system and voltage control of static var compensators. The transfer capacity is basically limited by the thermal capacity of transmission lines. However, the practical systems, it is much restricted by stability and the power transfer level is considerably lower than the thermal capacity. In this paper, we consider a basic case in which SVCs are applied to all buses except generator terminals. In this case, it is possible to transfer power up to the reciprocal of the transmission reactance. Two modifications are then applied to the basic case. One is removal of SVCs on the high-voltage sides of the generator transformers. In this case, generator damping torques deteriorate, and the local oscillation mode becomes unstable. The other is removal of SVCs at intermediate buses on the trunk system. In this case, the shapes of the oscillation modes change greatly, and the global mode becomes unstable. The voltage control of SVCs maintains the generator damping torques and prevents deformation of mode shapes. By investigating different system sizes and transmission circuits, we show that the system transfer capacity is determined by the capacities of the individual transmission lines. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(3): 49–60, 1997     

基于多智能体协调的电网自动电压控制系统研究及应用

针对如何对电力系统的电压调节设备进行实时自动协调控制,实现电网安全、优质和经济运行,利用多智能体系统(MAS)技术,建立电网电压调节设备的协调自动控制系统,并将此系统应用于安徽电网实际运行,取得良好的效果.     

基于电压稳定性对电压无功控制的改进

介绍变电站电压无功控制(VQC)的调节原理。从电压稳定性的角度出发,分析电力系统在扰动情形下VQC对变压器有载调压分接头(OLTC)的控制及对电压稳定的负面影响。结合广域测量系统(WAMS)和宽域网(WAN),对基于计算机监控系统的VQC提出改进方案。     

变电站电压无功综合控制(VQC)装置的应用

电力系统的负荷需要消耗大量的无功功率,而无功功率平衡要满足众多的接点电压,这就需要分级分层就地平衡。地区电网的电压无功控制．主要是控制其管辖范围内的各级变电站,使电网的电压合格,并实现无功就地平衡．降低网损,节约能源。这样,就要大力推动电压无功综合控制装置（VQC）在变电站的广泛应用,为此．对电压无功综合控制装置的实现方式、控制原理、控制方式以及控制策略进行了阐述,并提供了在变电站实际应用的工程方案。     

Influence of AC-DC parallel interconnection on voltage stability of AC systems

The static and dynamic characteristics of power supply to each node in a hybrid ac-dc power system are analyzed by means of static and transient P-V curves. Three kinds of dc transmission control scheme are compared. DC transmission systems are more effective in delivering power to inverter nodes. The constant firing angle, constant current control techinque provides more power to inverter nodes than the conventional constant current, constant voltage and constant power, constant extinction angle techniques. Transient digital simulations indicate that dc interconnection improves voltage stability to both the opening of a dc interconnected line and one-line opening of ac double-circuit interconnected lines.     

电压无功控制系统在从化电网中的运行分析

根据目前从化电网所用的几种电压无功综合控制装置或系统(VQC)情况,分析比较其各自的特点和优缺点,并对VQC运行存在的一些主要问题进行了分析和探讨。     

江门地区电网电压无功优化控制系统的实施

电压质量对电网稳定及电力设备安全运行具有重大影响,而无功潮流又是影响电压质量的一个重要因素。为了适应高速发展的经济对电能质量日益提高的要求,配合国家城市电网“十五”规划关于电能质量原则要求的贯彻实施,提高电压无功调节的自动化水平和调节效能成为供电调度发展的一个主要方向。为此,在江门地区建立了区域电压无功优化控制系统(VarCS系统,以下简称优化控制系统),利用高效稳定的计算机算法在调度中心集中对电网电压进行调控,达到了预期的控制效果,为进一步的应用扩展奠定了良好基础。     

Decentralized voltage control in multiarea power system

This paper discusses the feasibility of a decentralized voltage control scheme for large-scale power systems. The algorithm is intended to apply to a reactive normal operating state from an emergency state caused by illcondition and also to keep the operating state away from approaching unstable boundaries in preventive control. The procedure for releasing voltage deviation (over/under voltage) is formulated as a multistage decision process over a certain time interval. The optimization problem is transformed into a two-point boundary value problem using the discrete maximum principle and is solved easily by using the discrete Riccati equation. For a large-scale power system, control values must be computed from a large number of state variables, and this inevitably prolongs the slow dynamics with controllers. The centralized control system in a large-scale system cannot be justified from the economical and technical viewpoints. To resolve the foregoing problems, a decentralized voltage control system incorporating slow voltage dynamics is presented.     

无功电压优化集中控制系统在青岛电网的应用

阐述基于调度自动化系统的“四遥”功能,实现地区电网无功电压优化运行集中控制的原理、方法和控制策略等。介绍无功电压优化集中控制系统在青岛电网的应用状况,探讨系统应用中应注意的问题。实际应用表明,该系统可有效提高全网各节点的电压合格率,减少网损,能产生较好的经济和社会效益。     

基于电压定向直接功率控制的光伏并网逆变器

将基于电压定向直接功率控制用于光伏并网逆变器的控制策略,引入电网电压和瞬时功率的估算概念,并将并网逆变器输出的瞬时有功功率和无功功率作为被控量进行功辜的直接闭环控制.系统无需检测输入变压器二次侧的电网电压,省去了电网电压传感器,从而不仅克服了电流控制方案的不足问题,还降低了成本,而且系统具有鲁棒性好、控制结构简单等优点.分析了电压定向直接功率控制的原理,设计了并网逆变器的具体参数,并给出了仿真和实验结果.     

基于PSS/E的大电网静态电压稳定裕度计算

阐述了一种基于电力系统仿真软件PSS/E求解静态电压稳定裕度的方法。该法通过PSS/E提供的函数模块,采用内嵌的PYTHON语言进行编程。由于包含了对3绕组变压器和潮流初值回存的处理语句,使其能应用于大规模电网静态电压稳定裕度的求解。几个IEEE标准算例和一个大型电网静态电压稳定裕度的求解验证了所提方法的有效性和可行性。     

The stability of voltage oscillation modes in longitudinal power systems with SVC

In this paper, we investigate the stability of voltage oscillation modes in longitudinal power systems equipped with static var compensators (SVC). These modes are usually stable, so they do not appear without external force. The conventional harmonic resonance is a phenomenon in which an oscillation mode is excited with a harmonic source. Hence, it is solved by removing the source with a harmonic filter. For this reason, an SVC is equipped with several filters. However, there is a possibility that an oscillation mode itself may become unstable. If a mode is unstable, it can have a large amplitude without any harmonic source. Since it needs no harmonic source, its frequency is not limited to a harmonic frequency, but can have any value. The harmonic instability in direct‐current transmission systems is an example of such phenomena. The PLL (phase‐locked loop) is considered to be effective to suppress harmonic instability with an SVC. However, no theoretical reason has been shown as yet. This paper clarifies the effectiveness of PLL based on a stability condition for the voltage oscillation modes. Frequency responses of a thyristor‐controlled reactor (TCR), a component of the SVC, are largely influenced by the presence of the PLL. If a PLL exists, the stability condition is always satisfied, and all modes are stable. Lastly, we perform numerical simulations to show the validity of our investigation. © 2001 Scripta Technica, Electr Eng Jpn, 137(2): 8–17, 2001     

分布式电压无功全局优化控制系统的研制与应用

分析了目前广州电网电压无功控制存在的不足,介绍了由广东省广电集团有限公司广州供电分公司自主开发的分布式电压无功全局优化控制系统的结构原理、研制过程、技术难点及应用情况。该系统已在广州鹿鸣电网挂网运行,运行良好。系统由主站系统、变电站电压无功实时控制子系统(VOC)和通信子系统构成。各子站系统的电压和无功控制范围通过全网离散无功优化计算获得,可实现对电网电压无功全局优化和分布式实时控制。