Optimal voltage control in distribution systems using PV generators

Recently, renewable energy technologies such as wind turbine generators and photovoltaic systems have been introduced as distributed generation. The connection of large number of distributed generators causes voltage deviation beyond the statutory range in a distribution system. In this paper, a methodology for voltage control in proposed by using the tap changing transformers and the inverters interfaced with the distributed generators. In the proposed method, information of the voltage and power is collected via a communication network. Based on these information, the optimal reference values are calculated at the control center, and sent to the transformers and the inverters. The proposed method accomplishes a coordinated operation among the control equipments and reduces the voltage deviation. Effectiveness of the proposed method is verified by the numerical simulation results.     

Reactive power control for improving voltage profiles: A comparison between two decentralized approaches

This paper is concerned with a local regulation of the voltage profiles at buses where wind power distributed generators are connected. In particular, the aim of the work is to compare two voltage control methods: the first based on a sensitivity analysis and the second on the designing of a fuzzy control system. The two methods are tested by means of simulations on a real distribution system and the results indicate that both methods allow the voltage profiles to be regulated at the wind generator connection bus within voltage standard limits, by taking into account the capability curves of the wind generators. Nevertheless, the fuzzy method presents more advantage in comparison with the sensitivity method. In fact, (i) it provides a gentler action control with a lower reactive power consumption during control operations as the reactive power profile follows better the voltage variations; (ii) the design of the fuzzy controller is independent from the knowledge of network parameters and its topology.     

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.     

Voltage control settings to increase wind power based on probabilistic load flow

In this paper, network constrained setting of voltage control variables based on probabilistic load flow techniques is presented. The method determines constraint violations for a whole planning period together with the probability of each violation and leads to the satisfaction of these constraints with a minimum number of control corrective actions in a desired order. The method is applied to define fixed positions of tap-changers and reactive compensation capacitors for voltage control of a realistic study case network with increased wind power penetration. Results show that the proposed method can be effectively applied within the available control means for the limitation of voltages within desired limits at all load buses for various degrees of wind power penetration.     

基于灵敏度分析与最优潮流的电网无功/电压考核方法

针对电网的无功/电压水平考核问题,提出了一种综合应用灵敏度分析和最优潮流的实用化考核方法.当供电公司所辖电网内有节点电压越限时,通过计算各负荷节点的注入无功功率对节点电压变化的灵敏度,可以直接根据考核点的电压偏差求得相应的无功功率偏差;当所有节点电压都在规定范围内时,以全网有功网损最小为目标函数进行最优潮流计算,求得各节点的最优无功补偿量.该方法考虑了电网运行的安全性和经济性,考核结果可以为供电公司实施关于无功/电压水平考核的奖惩提供科学的决策依据,同时也可以对供电公司合理进行无功补偿起到指导作用.     

Steady-state analysis of the effect of reactive generation limits in voltage stability

Voltage collapse phenomena are highly affected by reactive power generation limits. Saturation of the reactive power generation limits of a unit may result in a deterioration of the voltage stability. However, in some cases when the power network is operating close to the voltage collapse point, the reactive power generation saturation of a unit can change the system voltages immediately from stable to unstable; thus, a dynamic voltage collapse leading to blackout may follow. This paper presents a steady-state analysis of the immediate instability caused by reactive power generation saturation phenomena. For this purpose, the paper proposes a novel index that evaluates “when” and “why” a reactive power generation saturation will only result in a deterioration of the system voltage stability or, on the contrary, it will make the system voltages immediately unstable.     

黑龙江省电力网电压现状及改善措施

从黑龙江省电网电压实际情况出发，对系统无功功率进行了综合研究，分析了低谷负荷时段产生电压偏高的原因，阐述发电机进相运行调压与机组安全裕度的协调问题，并提出利用综合目标函数进行优化的无功最优潮流计算方法。     

Efficient integration of distributed generation for meeting the increased load demand

Distributed generation (DG) can be integrated into distribution systems to meet the increasing load demand while expansion and reinforcement of these systems are faced by economical and environmental difficulties. This paper presents an efficient methodology for integration of DG power into distribution systems, in order to maximize the voltage limit loadability (i.e. the maximum loading which can be supplied by the power distribution system while the voltages at all nodes are kept within the limits). The proposed methodology is based on continuation power flow (CPF). The effectiveness of the presented methodology is demonstrated in a test distribution system that consists of 85 nodes with integration of different penetration levels of DG power. The proposed method yields efficiency in obtaining more benefits from the same amount of DG power, decreasing the losses and improving the voltage profile.     

靠近电源点的地区电网无功电压分析

靠近电源点的送端系统电压稳定性较好,但对于轻负荷地区电网电压和功率因数会偏高,难以达到电网考核的标准。结合宿迁电网分析了靠近电源点的地区电网无功电压情况,从变压器的配置、无功平衡以及小电厂和用户无功考核等方面指出了目前电网存在的问题,并提出的一些解决措施和建议。     

Voltage unbalance numerical evaluation and minimization

Among a series of parameters, power quality studies are concerned with voltage unbalances, which represent the voltage magnitude and phase deviation from nominal values. In order to determine the influence of the network's parameters on voltage unbalances, and to provide exact solutions to reduce or even eliminate them, the present study develops and presents two methods. First, a sensitivity analysis is used to determine the influence of each parameter, and then analytical solutions are developed in order to provide the changes needed for correction. The quantification index considered is the symmetrical components method.     

配电系统电压控制和无功优化的简化动态规划法

本文应用动态规划法综合求取有载调压变压器分接头，配电站电容器和馈线电容器的控制策略，实现电压控制和无功优化，并满足控制调节次数约束，为了减少计算量，本文提出了一种启发式的简化算法，算例结果表明了算法的有效性及实用性。     

Voltage sag source location based on instantaneous energy detection

Voltage sag is a major power quality problem, which could disrupt the operation of voltage-sensitive equipment. This paper presents the method based on variation components-based instantaneous energy for voltage sag source detection. Simulations have been performed to provide the thorough analysis for system with distributed generation units. The studies show that the presented method can effectively detect the location of voltage sag source.     

Voltage control with on-load tap changers in medium voltage feeders in presence of distributed generation

This paper discusses voltage regulation on medium-voltage feeders with distributed generation (DG) using on-load tap changer (LTC) and line drop compensation (LDC). The analysis shows that LTC is robust against DG, whereas DG can affect the effectiveness of the voltage regulation provided by LDC. However, with proper coordination between DG and LDC, it is possible to ensure voltage regulation without unnecessarily restricting the integration of DG. It is shown that, while lowering the LTC setting can increase the DG integration limit, even higher increase can be obtained by activating the LDC feature, which is present in most LTCs, but often not used. LDC regulation is also compared with other alternatives such as using a DG unit with voltage control capability and installing a line voltage regulator.     

On the appropriate monitoring period for voltage flicker measurement in the presence of distributed generation

Voltage flicker or voltage fluctuations are considered a major power quality problem causing temperature rise, generators and motors overloading and affecting humans through the irritating light flicker. It is expected that the level of voltage flicker will increase due to the increased penetration of distributed generation (DG) in the distribution system. Site monitoring is required to make sure that the level of voltage flicker is within the allowed limit. In order to determine the appropriate monitoring period for voltage flicker measurement while considering DGs, two case studies were considered in the paper; 1 week and 1 day monitoring periods. The results reveal that a monitoring period of 1 week may be very long especially in the presence of DG and it may hide valuable information. On the other hand a 1-day monitoring period is more appropriate in these situations. Therefore it is recommended to use 1-day monitoring period instead of 1 week especially in the presence of DG.