Modelling and Implementation of Multi-source Isolated Microgrid Using Virtual Synchronous Generator Technology

To improve the living standards,economical efficiency and environmental protection of isolated islands,remote areas and other areas with weak electric power facilities construction,a multi-source independent microgrid system is studied,including diesel generators,photovoltaic power generation system,wind power generation system and energy storage unit.Meanwhile,in order to realize the voltage and frequency stability control of AC bus of multisource microgrid,the virtual synchronous generator technology is introduced into the energy storage unit,and the charge and discharge control of the energy storage battery are simulated as the control behavior characteristics of synchronous motors,so as to provide damping and inertia support for the microgrid.The operation mode and control principle of each energy subsystem are expounded and analyzed.The algorithm principle of virtual synchronous generator and the control method of energy storage unit are given.Then,the working modes of the microgrid system under different environmental conditions are analyzed,and the multi-source microgrid system simulation model is built based on MATLAB/Simulink.The simulation results show that the microgrid system can run stably under different working modes and the energy storage unit using the virtual synchronous generator technology can provide good voltage and frequency support for the microgrid system.Finally,experiments verify the supporting function of energy storage unit on the voltage and frequency of the microgrid system.

Optimal Design of Hybrid Microgrid in Isolated Communities of Ecuador

In rural territories, the communities use energy sources based on fossil fuels to supply themselves with electricity, which may address two main problems: greenhouse gas emissions and high fuel prices. Hence, there is an opportunity to include renewable resources in the energy mix. This paper develops an optimization model to determine the optimal sizing, the total annual investment cost in renewable generation, and other operating costs of the components of a hybrid microgrid. By running a k-means clustering algorithm on a meteorological dataset of the community under study, the hourly representative values become input parameters in the proposed optimization model. The method for the optimal design of hybrid microgrid is analyzed in six operating scenarios considering:(1) 24-hour continuous power supply;(2) load shedding percentage;(3) diesel power generator(genset) curtailment;(4) the worst meteorological conditions;(5) the use of renewable energy sources including battery energy storage systems(BESSs);and(6) the use of genset. A mathematical programming language(AMPL) tool is used to find solutions of the proposed optimization model. Results show that the total costs of microgrid in the scenarios that cover 100% of the load demand(without considering the scenario with 100% renewables) increase by over 16% compared with the scenario with genset operation limitation. For the designs with power supply restrictions, the total cost of microgrid in the scenario with load shedding is reduced by over 27% compared with that without load shedding.

Coordinated Control of Parallel Three-phase Four-wire Converters in Autonomous AC Microgrids

The coordinated control of parallel three-phase fourwire converters in autonomous AC microgrids is investigated in this paper.First,based on droop control,virtual impedance is inserted in positive-,negative-and zero-sequences to enhance system damping and imbalance power sharing.Then,to facilitate virtual impedance design,small signal models of the three-sequence equivalent circuits are established respectively.Corresponding indexes are proposed to comprehensively evaluate the impact of sequence virtual impedance on current sharing accuracy,voltage quality at the point of common coupling(PCC)and system stability.In addition,constraint of DClink voltage is also considered to avoid over modulation when subjected to unbalanced loads.Furthermore,to address the PCC voltage degradation resulting from virtual impedance,a voltage imbalance compensation method,based on low-bandwidth communication,is proposed.Finally,simulation and experimental results are provided to verify the correctness of the theory model,indicating that the proposed method can achieve PCC voltage restoration while guaranteeing the current sharing accuracy with desirable dynamics.

Research and practice of designing hydro/ photovoltaic hybrid power system in microgrid

Small-hydro power station is often used in remote areas beside a river,but it doesn't match electricity demand so well,especially in dry seasons. A photovoltaic (PV) system with battery is a suitable option to complement the electricity gap. In this paper,a new structure of megawatt-class PV system integrating battery at DC-bus (DC: direct current) is proposed to be used in hydro/PV hybrid power system,and 4 main designing considerations and several key equipments are discussed. In 2011,a 2 MWp PV station with the proposed structure was built up in Yushu,China. From stability analysis,the station shows a strong stability under load cut-in/off and solar irradiance's fluctuation.

岛礁风光柴储多能源独立微电网建模分析

岛礁多能源独立微电网是解决远海岛礁供电难题,确保岛上军民用电稳定及提高岛礁自然资源利用率的关键技术。传统岛礁独立微电网建模电源种类不够完备,交流母线应用较少。为此,建立了风、光、柴、储4种电源数学模型,在电力电子变换器中使用了基于扰动观察法的Boost升压电路与基于电网电压定向的矢量控制方式。系统模型中风、光、柴、储4种电源汇入交流母线,整体功率、电压趋于稳态。仿真结果表明:所构建的岛礁多能源独立微电网模型较为科学合理,可为开展岛礁多能源微电网健康管理等研究打下坚实基础。

基于动态事件触发的微电网分布式协调控制策略

在孤岛交流微电网电压和频率的协调控制中,存在着依赖周期通信、通信负担大等问题.为此,提出了一种基于动态事件触发的分布式协调控制策略,在微电网中运用多智能体系统理论,将频率和电压作为追踪同步目标.通过评估事件触发条件,从根本上摆脱了分布式电源DGs的连续通信和Zeno行为.并引入与系统偏差和反馈有关的动态变量,合理调整触发阈值和反馈增益.此方案提高了通信效率,降低了控制更新频率,保持了良好的控制性能.并且在Matlab/Simulink环境中验证了所设计控制策略的正确性和有效性.

一种基于多目标优化的独立微电网容量配置方法

针对独立型微电网容量配置存在经济成本和供电可靠性难以实现同时最优的问题,提出一种实现经济成本和供电可靠性最优的独立型微电网容量多目标优化配置方法。根据独立型风光储微电网系统中各分布式电源的机理构建风机、光伏、磷酸铁锂电池的数学模型,以等年值投资成本为评估指标构建独立微电网经济成本模型,功率偏差为评估指标构建出基于层次分析法的独立微电网可靠性模型,使用非支配排序的多目标粒子群算法求解系统最优容量配置。算例结果表明,该方法对独立型微电网容量配置在同时实现供电可靠性和经济性上更有优越性。

Control strategy for microgrid under three-phase unbalance condition

Microgrid(MG) is generally developed at utility terminal which contains lots of unbalanced loads and distributed generations(DGs). The interaction between MG and the unbalance loads or DGs will degrades the control performance of interfaced inverter in MG and dramatically leads to MG voltage unbalance. In this paper, a negative-sequence compensation based three-phase voltage unified correction strategy is proposed. While MG operates in islanded mode, a positive virtual impedance control is used to eliminate the negative voltage resulted from the negative-sequence current,and then a positive-sequence voltage control loop and negative-sequence control loop are used to improve the inverter control performance. While MG operates in grid-tied mode,the inverter operates as a negative-sequence current source to compensate the negative-sequence currents of loads to guarantee the point of common coupling(PCC) voltage balance.By using the proposed strategy, the voltage control performance of inverter can be improved;the MG power quality can be enhanced significantly. Simulation and experimental results verify the effectiveness of the proposed method.

不同类型新能源接入对微电网频率的影响

为建设新型能源体系与构建以新能源为主体的新型电力系统,不同类型的新能源加入到电力系统中,高比例新能源的加入对电力系统的影响日益显现。基于国家大力发展新能源的时代背景,结合广东山区具有发展小水电和风电的区位优势,运用理论、仿真等研究方法,对光伏、风电、小水电等不同种类新能源组成的多能互补微电网孤岛初期频率变化规律问题展开研究。首先,研究小水电、风电及光伏发电分别作为单独的分布式能源接进微电网孤岛运行幅频变化情况,发现只有光伏微电网具有较好的孤岛运行稳定性。接着,探讨小水电和光伏分别加入对风电微电网在孤岛初期幅频变化的影响,发现光伏对风电微电网全工况都有支撑作用,而小水电在特定工况下支撑作用较大。最后,分析风光水多能互补微电网孤岛初期幅频变化的影响,研究结果表明风光水多种新能源在一定配比下具有较好的运行稳定性。

基于序贯蒙特卡洛模拟法的孤岛微电网可靠性评估

为评估孤岛型微电网的可靠性以及分析储能装置对系统可靠性的影响,提出基于序贯蒙特卡洛模拟法的孤岛微电网可靠性评估方案。首先,以孤岛型风柴储混合微电网系统作为研究对象,搭建分布式电源等关键设备的出力模型;其次,制定可靠性评估指标体系、不同的储能运行策略及负荷削减策略,在此基础上提出基于序贯蒙特卡洛模拟法的孤岛风柴储微电网可靠性评估算法;最后,通过对改进的RBTS Bus 6 F4孤岛系统进行仿真,量化分析了储能装置的运行策略、储能容量、容量配置对系统可靠性水平的影响。结果表明:合理的储能策略、适当增大储能容量以及适宜的储能系统配置方案等均可提高系统可靠性。

Optimal economic operation of isolated community microgrid incorporating temperature controlling devices

With the increasing connection of controllable devices to isolated community microgrid,an economic operation model of isolated community microgrid based on the temperature regulation characteristics of temperature controlling devices composed of wind turbine,micro-gas turbine,energy storage battery and heat pump is proposed.With full consideration of various economic costs,including fuel cost,start-stop cost,energy storage battery depletion expense and penalty for wind curtailment,the model is solved by hybrid particle swarm optimization(HPSO)algorithm.The optimal output of the micro-sources and total operating cost of the system in the scheduling cycle are also obtained.The case study demonstrates that temperature adjustment of temperature controlling devices can adjust the power load indirectly and increase the schedulability of the isolated community microgrid,and reduce the operating cost of the microgrid.

Attack-resilient Distributed Control for Islanded Single-/three-phase Microgrids Based on Distributed Adaptive Observers

This paper investigates the power sharing and voltage regulation issues of islanded single-/three-phase microgrids(S/T-MGs)where both sources and loads are unbalanced and the presence of adversarial cyber-attacks against sensors of distributed generator(DG)units is considered.Firstly,each DG unit is modeled as a heterogeneous linear dynamic agent with disturbances caused by sources and loads,then the problem is formulated as a distributed containment control problem.After that,to guarantee satisfactory power sharing and voltage control performance asymptotically achieved for the S/T-MGs,an attack-resilient distributed secondary control approach is developed by designing a distributed adaptive observer.With this approach,the effect of the cyber-attacks can be neutralized to ensure system stability and preserve bounded voltage synchronization.Simulation results are presented to demonstrate the effectiveness of the proposed control approach.

一种光柴储孤岛微电网的控制策略

光柴储孤岛微电网是偏远地区电能供应的一种高效经济的方案。目前光柴储孤岛微电网面临系统储能配置需求过大、各类电源的下垂曲线难以配合以及过于依赖准确的光伏和负荷预测等问题。首先建立了光柴储孤岛微电网模型,然后划分柴发负载率分区,并提出以储能为短时功率支撑、以柴发安全经济运行为核心目标的光柴储孤岛微电网控制策略,最后搭建了电磁暂态仿真模型进行验证。仿真结果表明,所提控制方法能够在柴发负载率进入安全运行区和紧急运行区时,控制柴发负载率进入经济运行区间,保障系统的安全经济运行。所提策略易于在孤岛微电网中实施和应用,为偏远地区的供电提供了快速解决方案。

集成VSG频率调节与经济调度的微网分布式优化

在通信受限的情况下如何对低惯量孤岛运行的微网同时进行频率调节和综合经济调度,是目前需要解决的难点。建立了含多类型电源虚拟同步机(VSG)的微网调度控制模型,提出了一种集成频率调节与综合经济调度的分布式优化算法,来同时实现微网中的频率调节和经济调度。在综合考虑各类电源VSG成本和收益以及微网整体惯量和备用容量需求的基础上,提出了一个分布式经济调度问题,该问题最小化了各类型VSG参与频率调节所产生的综合成本并提高了微网在扰动下频率的稳定运行能力;在考虑微网逆变器的动态特性的基础上重构优化问题,利用事件触发通信在线感知和补偿供需失衡,解决了最优调度问题。仿真结果表明,所提方法能够避免跨时间尺度的层间协调,提高系统的惯量、调频能力以及经济性,并增强对短期通信故障的鲁棒性。

独立交流微网中电池储能与柴油发电机的协调控制

在独立交流微网系统内,柴油发电机和电池储能之间的协调控制是保证系统稳定运行的关键。利用电池储能的快速响应特性,提出了柴油发电机和储能电池的协调控制方法。柴油发电机作为主电源时,通过在储能系统传统下垂控制中引入辅助功率控制信号,防止柴油机长时过流引起的系统崩溃,提高了系统稳定性。针对微网内主电源从储能系统转为柴油发电机或者从柴油发电机转为储能系统时的短时停电问题,提出了柴油发电机和储能电池双主电源的无缝切换控制策略。最后利用PSCAD仿真软件对所提方法进行了验证。

风光柴储孤立微电网系统协调运行控制策略设计

在考虑典型风光柴储孤立微电网主要设备运行约束条件的基础上,提出了一种风光柴储孤立微电网系统协调运行控制策略。该策略以保证孤立系统的长期稳定运行、提高系统全寿命周期的经济性为主要设计目标,利用自主研发的微电网准稳态仿真工具对典型实际孤立微电网进行仿真计算,并与美国国家能源实验室(NERL)开发的微电网仿真软件Hybrid2中的相关控制策略进行比较,验证了文中所提出控制策略的正确性和有效性。

基于离散傅里叶变换的孤岛型微电网混合储能优化配置

分析了孤岛型微电网中电源负荷不平衡功率的产生,基于离散傅里叶变换,将不平衡功率分解成日分量和小时分量,分别采用压缩空气储能和钠硫电池平衡该分量,为了使得分解后的日分量和小时分量最优,专门研究了不平衡功率离散傅里叶变换分断点的分断原则。在此基础上,综合计入储能投资运行成本、系统缺电损失费用和弃风惩罚费用等,建立孤岛型微电网混合储能优化配置模型。该模型可以实现离散傅里叶变换分断点和混合储能容量的统一优化,且优化过程中实现了压缩空气储能和钠硫电池两种储能容量优化配置的完全分解,简化了模型的求解复杂性。采用实际微电网系统进行了算例分析,验证了所述模型和方法的正确性。

基于滤波的孤立微网多目标规划设计方法

为实现孤立微网中经济性和污染物排放的整体优化,提出了一种基于滤波的孤立微网多目标规划设计方法。首先,针对当前多目标优化方法中目标权重选取需要主观先验知识,以及结果的选择性和指导性难以兼顾的问题,采用改进非支配排序遗传算法求解孤立微网的多目标优化模型,不需要主观先验知识就可得到多个可选方案,再通过方差最大化决策得到唯一的推荐方案。其次,优化过程中基于滤波调度策略来实现微型燃气轮机和储能优势互补,改善了微型燃气轮机的运行状况。算例结果验证了该方法的有效性。

微电网电源的虚拟惯性频率控制策略

针对微电网孤岛运行时配有储能装置的分布式电源,提出了一种虚拟惯性频率控制策略,使微电网电源具有下垂特性的同时,还具有类似于同步发电机转子的惯性。在扰动发生时,该策略能够支撑微电网的频率,从而提高微电网频率的稳定性。以一个2机系统为例,分析了在微电网中采用这种控制策略时可能引起的功率振荡问题,通过优化主电路和控制器参数抑制了这种振荡。PSCAD/EMTDC的仿真结果验证了该控制策略的有效性。

基于Markov-ELM的独立混合微网分布式电源多目标容量优化配置

以微电网经济性、环保性和能源利用效率综合最优为目标,以系统可靠性为约束条件,构建混合微电网分布式电源(distributed generation,DG)优化配置模型。优化过程中需遍历全年数据进行时序分析,计算量大,运行效率低。针对该问题,采用模糊C-均值(fuzzy c-means clustering method,FCM)算法从风速、光照和负荷8760h的数据中提炼出典型的场景,用随机过程方法建立其对应的Markov模型。引入熵理论确定多目标函数各指标的权重系数,避免了人为定权重的主观性。采用种群移动、自适应变步长、基因变异以及按比例系数缩减搜索空间等方法来改进仿电磁学算法(electromagnetism-like mechanism,ELM)的寻优速度及全局搜索能力。最后将前述建立的Markov模型嵌入改进的ELM中进行优化求解。以广西涠洲岛为背景进行算例分析,验证模型和算法的有效性。结果表明,相较于采用年代数据计算的ELM,采用Markov-ELM的求解方法,在快速性和全局搜索能力等方面更具有优势。