Determination method for loss‐minimum configuration considering reconnection of distributed generators

In the field of electrical power system, various approaches, such as utilization of renewable energy, loss reduction, and so on, have been taken to reduce CO₂ emission. So as to work toward this goal, the total number of distributed generators (DGs) using renewable energy connected into 6.6‐kV distribution systems has been increasing rapidly. The DGs can reduce distribution loss by appropriate allocation. However, when a fault occurs such as distribution line fault and bank fault, DGs connecting outage sections are disconnected simultaneously. Since the simultaneous disconnection of DGs influences restoration configuration and normal configuration after the restoration, it is necessary to determine the system configuration in the normal state considering simultaneous disconnection of DGs. In this paper, the authors propose a computation method to determine the loss minimum configuration in the normal state considering reconnection of DGs after simultaneous disconnection by fault occurrence. The feature of determined loss minimum configuration is satisfying with operational constraints even if all DGs are disconnected from the system. Numerical simulations are carried out for a real‐scale distribution system model with 252 sectionalizing switches (configuration candidates are 2²⁵²) and 120 DGs (total output is 38.46 MW which is 23% of total load) in order to examine the validity of the proposed algorithm. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(4): 7–14, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21142     

考虑降损和平抑峰谷的配电网储能电池Pareto优化模型

为发挥储能电池在配电网运行中降损及平抑峰谷的作用,建立了一种考虑降损和平抑峰谷的配电网储能电池Pareto多目标优化模型。该模型以配电系统中有功损耗最小和1天中各时段负荷方差最小为目标函数,以储能电池的充放电功率为控制变量,以罚函数的形式处理电池容量约束和静态安全约束。依据日负荷曲线获取储能电池最佳充放电时段,结合前推回代潮流计算方法和带精英策略的快速非支配排序遗传算法（non-dominated sorting genetic algorithm II,NSGA-II）对多目标模型进行求解。基于最大满意度,在Pareto解集中分别分析了网损最小、削峰填谷效果最优和网损与削峰填谷折中最优3种优化方案,以获取不同的储能电池运行优化方案。最后,以IEEE33配电网系统为例,验证了所提方法的实用性和有效性,并分析了不同决策策略下运行方案的优劣,为配电网经济运行提供决策参考。     

A study on cooperative tap control method for voltage profile maintenance in distribution networks with distributed generators

The introduction of distributed generators (DGs) that can utilize renewable energy is of prime importance to solve the energy and environmental issues. When a distribution network has a large number of DGs, voltage maintenance becomes a serious problem. To solve this problem, we had proposed the ‘voltage profile control method’ using reactive power control of DGs. However, the control is limited to continuous reactive power control so far, and tap control has not been considered. It is important that the conventional voltage control equipment such as the load ratio tap changer (LRT) or step voltage regulator (SVR) is utilized in order to enhance the control efficiency of the voltage profile control method. Therefore, in this paper, we develop a new method that can realize a cooperative work between inverters and tap control of LRT and SVR. The proposed method is tested in 8‐ and 24‐node model systems and its effectiveness is shown. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于有序充电策略的换电站及分布式电源多场景协调规划方法

通过引入电动汽车换电站的有序充电策略,以系统建设运行成本、综合净负荷波动指标以及网络能量损耗最小为目标,提出统筹考虑电动汽车换电站和分布式电源的多场景协调规划方法,并给出满足电动汽车换电需求约束和备用电池存在性约束的备用电池调度方案和最少备用电池计算方法。结合风光电源出力的季节特性,针对IEEE 33节点系统,利用生物地理优化算法进行多场景规划仿真分析,验证了所提规划方法可利用换电站有序充电策略平抑配电网综合净负荷波动,起到了削峰填谷的作用,大幅降低了网络能量损耗,显著提高了风光电源的可规划容量;同时所采用的最少备用电池计算方法,可充分考虑换电站内备用电池在一天中的循环利用,在维持有序充电策略周转的前提下能有效缓解电池储备压力,大幅降低了换电站投资成本。     

Voltage control of distribution network with a large penetration of photovoltaic generation using FACTS devices

In recent years, there has been a great deal of interest in distributed generation from viewpoints of environmental problems and energy saving measures. Thus, a lot of distributed generators will be connected to the distribution network in the future. However, increase of distributed generators, which convert natural energy into electric energy, raises concerns as to their adverse effects on the distribution network. Therefore, control of distribution networks using Flexible AC Transmission System (FACTS) devices is considered in order to adjust the voltage profile, and as a result more distributed generations can be installed into the networks. In this paper, four types of FACTS devices— Static Synchronous Compensator (STATCOM), Static Synchronous Series Compensator (SSSC), Unified Power Flow Controller (UPFC) and self‐commutated Back‐To‐Back converter (BTB)— are analyzed by comparison of required minimum capacity of the inverters in a residential distribution network with a large penetration of photovoltaic generations. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 16– 28, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20499     

An overall cost based on optimal power flow control method of dual‐source distribution network with closed‐loop operation using UPFC

Supply reliability can be effectively improved by a normally closed‐loop operation of a distribution network with dual sources, in which there might be large circulating power flow. A unified power flow controller (UPFC) has the powerful capability to adjust the power flow, but it would face a technoeconomic bottleneck when applied to the distribution system. Based on the constant current load model, the power flow distribution of a normally closed‐loop distribution network with dual sources is analyzed, and the relationship between the network loss, the voltage deviation of load nodes, and the compensated voltage is deduced. Then, the optimal power flow control model is presented considering such economic factors as the network loss, the voltage deviation of load nodes, and the cost of the apparatus used to produce the compensated voltage. In order to simplify the problem of multiobjective optimization into a single‐objective optimization model, the fuzzy membership functions and their weight coefficients of the network loss, the voltage deviation, and the UPFC's cost are designed, and the weights are determined according to their contribution in economy. The optimal control model is solved with the global optimal algorithm. Simulation results based on PSCAD prove that this method can ensure overall economy of the system with balancing the power distribution, controlling the node voltage deviation, and decreasing the active power loss of the network effectively. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

利用电动汽车可调度容量辅助电网调频研究

电动汽车既可作为可控性负荷,也可作为分布式电源,能够为电网提供可调度容量,参与调频等辅助服务。但该可调度容量受用户出行需求及电池损耗等因素的制约,不能无限制地调度。基于此,对电动汽车采取"分散接入,集中控制"的管理模式,首先基于用户出行需求及电池使用寿命等约束,对电动汽车可调度容量进行评估。进而建立了计及可调度容量的电动汽车集中管理器充放电静态频率特性模型,以单区域系统为例模拟了电动汽车参与负荷调频的作用效果。仿真结果表明,利用电动汽车可调度容量辅助电网调频,不仅可以快速有效地减小系统频率偏差,提高电能质量,还能减小传统调频机组的备用容量,进而提高电网经济性。研究电动汽车参与调频的作用效果时,用户需求及电池损耗是不容忽视的影响。     

A current sensorless MPPT control method for a stand‐alone‐type PV generation system

In this paper, a current sensorless MPPT control method for a stand‐alone‐type PV generation system is proposed. This control method offers advantages of the simplified hardware configuration and low cost by using only one sensor to measure the PV output voltage. When used as a stand‐alone‐type with a battery load, the experimental results show that the estimated values of PV output current are accurate, and the use of the proposed MPPT control increases the PV generated energy by 16.3% compared to the conventional system. Furthermore, the authors clarified that the proposed method has an extremely high UUF (useful utilization factor) of 98.7%. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 65– 71, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20424     

A fuzzy‐based control method for smoothing power fluctuations in substations along high‐speed railways

The use of superconducting magnetic energy storage (SMES) for smoothing power fluctuations in a railway substation has been discussed. This paper proposes a smoothing control method based on fuzzy reasoning for reducing the SMES capacity at substations along high‐speed railways. The proposed smoothing control method comprises three countermeasures for the reduction of the SMES capacity. The first countermeasure involves modification of rule 1 for smoothing out the average electric power to its average values. The other countermeasures involve the modification of the central value of the stored energy control in the SMES and revision of the membership function in rule 2 for the reduction of the SMES capacity. The SMES capacity in the proposed smoothing control method is reduced by 49.5% compared to that in the nonrevised control method. Computer simulations confirm that the proposed control method is suitable for smoothing out power fluctuations in substations along high‐speed railways and for reducing the SMES capacity. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 35–43, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21175     

A novel variable frequency modulation technique to improve light‐load efficiency for multiphase synchronous rectified VRM

A novel variable frequency modulation technique for multiphase synchronous rectified voltage regulator module (VRM) is proposed in this paper. The proposed technique provides zero voltage switching (ZVS) for high‐side and low‐side power switches under both light‐ and heavy‐load conditions, thereby increasing the efficiency as compared to the conventional approach. The dependency of switching frequency on the load condition for the proposed modulation technique and the related conduction loss are analyzed. It will be shown that the frequency increases for light‐load condition in order to retain ZVS and decrease the conduction loss. Although the switching loss will slightly increase due to the increase of switching frequency, the analysis and experimental results will show that the contribution of frequency increasing can cover this additional loss. Experimental results derived from a single‐phase and an eight‐phase synchronous rectified VRM show that the proposed modulation technique is superior to the conventional one and compared to conventional constant switching frequency techniques with 250 and 550thinspacekHz, the efficiency can be increased up to 17 and 5% for single‐phase VRM and 8 and 4% for eight‐phase VRM under various load conditions. Even an off‐the‐shelf controller with an additional simple and cheap control circuit comprising one switch, two operational amplifiers and several resistors is used to realize the proposed technique, that is, a very low cost and small circuitry is attached to gain the significant benefit. Copyright © 2011 John Wiley & Sons, Ltd.     

A new high‐frequency voltage injection method for sensorless drive of permanent‐magnet synchronous motors with pole saliency

This paper proposes a new sensorless vector control method for salient‐pole permanent‐magnet synchronous motors. In regard to rotor phase estimation, the sensorless vector control method is characterized by a new high‐frequency voltage injection method distinguished from the conventional ones by a unique ellipse shape of the spatial rotation, and by a new PLL method whose input is a high‐frequency current autocorrelated signal. The new vector control method established by two innovative technologies can have the following high‐performance and attractive features: (1) it can allow 250% rated torque at standstill; (2) it can operate from zero to the rated speed under the rated motoring or regenerating load; (3) it accepts instant injection of the rated load even for zero‐speed control; (4) it accommodates a load with huge moment of inertia; (5) phase estimation is very robust against inverter dead time; (6) the computational load for estimating rotor phase is very small, would be the smallest among the methods with comparable performance. This paper presents the new vector control method by focusing on two innovative technologies from its principles to design rules. Usefulness of the new vector control method is verified through extensive experiments. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 62–77, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20632     

Smoothing of PV system output by tuning MPPT control

A PV system's power output is not stable and fluctuates depending on weather conditions. Using a battery is one feasible measure to stabilize a PV system's power output, but it requires additional costs and results in additional waste of used batteries. In this paper, we propose a new measure for smoothing the short‐term change in a PV system's power output, which is performed by tuning the characteristics of Maximum Power Point Tracking (MPPT) control without additional equipment. In our proposed measure, when the insolation increases rapidly, the operation point of MPPT control changes to a new point where the maximum power is not generated with the current insolation, so that the rate of increase in the PV system's power output is limited to a certain value. In order to evaluate the effect of the proposed measure on the operation of electric power systems, we evaluated the required capacity of generators for load‐frequency control (LFC). It was revealed that the additional LFC capacity is not required even in the case where penetration of PV systems reaches 5% of the utility system's total capacity if the proposed measure is applied to all PV systems. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 10–17, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20106     

考虑车网互动的配电网可靠性评估

作为一种兼具移动储能特性的新型负荷,电动汽车的大规模接入将会对配电网可靠性产生影响。在传统配电网可靠性评估方法的基础上,提出一种考虑车网互动的配电网可靠性评估方法。首先,通过分析电动汽车的出行行为,建立了电动汽车充放电的时空分布模型;其次,利用蒙特卡洛法模拟配电网故障,充分考虑电动汽车的出行需求,得到配电网故障时电动汽车的放电容量和失负荷情况;然后,结合分布式电源的出力,建立孤岛启发式负荷削减模型求取配电网的故障影响结果;最后,通过改造的IEEE-RBTS Bus-6测试系统验证本方法的可靠性与实用性,分别研究电动汽车渗透率、充电模式以及电动汽车电池容量对配电网可靠性的影响。     

Computation of locational and hourly maximum output of a distributed generator connected to a distribution feeder

Recently, the total number of distributed generation such as photovoltaic generation systems and wind turbine generation systems connected to a distribution network has drastically increased. Distributed generation using renewable energy can reduce the distribution loss and emission of CO₂. However, the distribution network with the distributed generators must be operated while maintaining the reliability of the power supply and power quality. In this paper, the authors propose a computational method to determine the maximum output of a distributed generator under operational constraints [(1) voltage limit, (2) line current capacity, and (3) no reverse flow to bank] at arbitrary connection points and hourly periods. In the proposed method, a three‐phase iterative load flow calculation is applied to evaluate the above operational constraints. The three‐phase iterative load flow calculation has two simple procedures: (Procedure 1) addition of load currents from the terminal node of the feeder to root one, and (Procedure 2) subtraction of voltage drop from the root node of the feeder to terminal one. In order to check the validity of the proposed method, numerical simulations are performed for a distribution system model. Furthermore, the characteristics of locational and hourly maximum output of a distributed generator connected to a distribution feeder are analyzed using several numerical examples. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 38–47, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20610     

Multiple roles coordinated control of battery storage units in a large‐scale island microgrid application

In order to build a large‐scale island microgrid with 100% penetration intermittent photovoltaic power generation as the only power source, a structure with multiple role battery energy storage systems (BESSs) is proposed in this paper based on the analysis of energy storage demand in the island microgrid and performance comparison of two types of batteries. The storage system in the proposed structure is composed of three types of functional BESSs. In detail, the master control units (MCUs) with LiFePO4 batteries are responsible for the voltage and frequency stability and instantaneous power balance, slave storage units (SSUs) with lead‐acid batteries are responsible for daily energy storage, and multi‐function units (MFUs) with LiFePO4 batteries are used for short‐time energy regulation. A hierarchical control structure is adopted in the system. At the local level, the converters of the MCUs are controlled as the voltage sources in paralleled mode as grid‐forming units, and those of SSUs and MFUs are controlled in the current source mode as grid‐feeding units. At the system level, a real‐time power balance coordinated control strategy is proposed, which has the capability of efficient and orderly operation of different types of BESSs. Simulation and practical operation analysis of the Qumalai 7.023 MW microgrid demonstrate the practicality and effectiveness of the research methods of the island microgrid. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

江苏电网侧电池储能电站建设运行的启示

2018年7月18日,中国首批101 MW/202 MW·h分布式电网侧电池储能电站在江苏镇江投运,在夏季迎峰度夏时段充分发挥电池储能系统调峰、调频、应急响应的作用,解决了镇江仿晋分区夏季负荷供电缺口,有效增加了电网的调节手段和调节能力,有助于电网安全稳定运行。投运至今,该储能电站已多次向电网提供自动发电控制(AGC)功率响应、调峰调频等辅助服务。首先分析了镇江电网侧储能电站建设的背景和内在动因,接着从电池选型、一/二次架构等方面介绍其集成方案,并对其AGC控制、应急响应控制以及一次调频控制分别进行了介绍与分析,最后从储能并网相关技术标准制定、储能并网检测工作开展、储能参与辅助服务市场、分布式储能应用研究等方面,深入探讨了江苏电网侧储能电站投运对中国储能技术发展与应用的启示和建议。     

直流微电网电池储能系统串并联结构分散控制

电池储能系统BESS(battery energy storage system)串并联结构可以实现小容量低电压等级储能系统接入直流微电网的应用,可以提高端电压且实现储能系统扩容。针对直流微电网BESS的串并联结构,提出一种基于电池荷电状态SOC(state of charge)的分散控制方法。该方法可以实现反下垂控制分配串联模块间电压与下垂控制分配并联模块间功率的目标,且反下垂特性不影响下垂外特性。通过低带宽通信将所有电池SOC信息上传到中央控制单元得到每个BESS的下垂系数与反下垂系数,可以有效实现不同BESS间按容量精确分配功率的目的,消除电池差异延长寿命,避免过放。通过建立小信号模型,分析系统稳定性;通过搭建Simulink仿真模型,验证分散控制的可行性与有效性。     

用于平抑间歇性负荷的混合储能系统优化分频定容技术

配电网中鱼塘、水泵等间歇性负荷导致的功率峰谷相差10倍左右,影响配电网的安全运行.含功率型储能器件与能量型储能器件的混合储能系统(HESS)可以用于平抑间歇性负荷功率波动.为此,重点研究了HESS设计过程中的分频定容技术:采用经验模态分解与希尔伯特频谱变换相结合的方法,对间歇性负荷特性进行频域分析;根据能量混叠最少原则...     

Potential estimation of hourly blank storage space and charge loads of EVs using road traffic census and vehicles status

If both EVs (Electric Vehicles, includes plug‐in hybrid electric vehicles) and renewable energies spread in large quantities, it is possible to control the supply fluctuation of renewable energies using the storage battery of EVs. This research sought to show the charge load potential of EVs based on the state of the Japanese passenger car using traffic census results, etc. Furthermore, it tried to show the trend of the storage battery capacity according to time. From the estimated results: (1) the charge electricity of low and middle distance gets a majority of the total charge demand, (2) charge load changes according to time several times, and the minimum load is the number of gigawatt‐hours at early morning, (3) if night charge is assumed, the standby charge demand of noon will reach tens of gigawatt‐hours, it may have sufficient scale for supply fluctuation control of PVs. Although the present EV is not suitable for long‐distance running, these are expected to be 30 or less percent of the total charge demand. The estimated storage capacity potential in this research will not change numbers of times. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(3): 30–38, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22352     

基于数据驱动的有源配电网实时调度降损策略

农村配网通常接入有较大容量的小水电等分布式电源,在向上级电网反送电能的过程中造成了大量的线损,因此本文提出了一种实时调度策略旨在降低配电网的线损。首先,考虑分布式电源的有功无功控制以及有载调压分接头的控制,基于支路潮流模型建立了配电网调度降损模型;进一步,通过构造高维随机矩阵,从配电网运行时间序列数据中提取能够表征运行状态的特征作为输入,对配电网历史调节策略进行热编码作为输出;然后利用深度双向长短时记忆网络学习配电网特征与网络降损策略之间的函数映射关系,建立基于数据深度学习驱动的有源配电网实时调度降损模型。最后,基于实际有源配电网系统进行了仿真,仿真结果表明所提出的实时调度算法能在保证小水电上网收益的前提下,优化小水电的出力曲线,提高分布式电能的就地消纳率,从而降低了网损。