Negative Imaginary Approached High Performance Robust Resonant Controller Design for Single-Phase Islanded Microgrid and Its Voltage Observation on Different Load Condition

This paper presents the design of a high performance robust resonant controller for the islanded single-phase microgrid operation on different loads conditions. The design of the controller is done using the results of Negative Imaginary approach. The performance of the proposed controller has been found much effective to track the instantaneous reference grid voltage. The simulation work has been done with the help of MATLAB/SimPower System toolbox. This shows that the proposed controller provides effective control of voltage against the uncertain load conditions.

Communication-less Management Strategy for Electric Vehicle Charging in Droop-controlled Islanded Microgrids

Adopting high penetration levels of electric vehicles(EVs) necessitates the implementation of appropriate charging management systems to mitigate their negative impacts on power distribution networks. Currently, most of the proposed EV charging management techniques rely on the availability of high-bandwidth communication links. Such techniques are far from realization due to(1) the lack of utility-grade communication systems in many cases such as secondary(low-voltage) power distribution systems to which EVs are connected, rural areas, remote communities, and islands, and(2) existing fears and concerns about the data privacy of EV users and cyber-physical security. For these cases, appropriate local control schemes are needed to ensure the adequate management of EV charging without violating the grid operation requirements. Accordingly, this paper introduces a new communication-less management strategy for EV charging in droop-controlled islanded microgrids. The proposed strategy is autonomous, as it is based on the measurement of system frequency and local bus voltages. The proposed strategy implements a social charging fairness policy during periods when the microgrid distributed generators(DGs) are in short supply by allocating more system capacity to the EVs with less charging in the past. Furthermore, a novel communication-less EV load shedding scheme is incorporated into the management strategy to provide relief to the microgrid during events of severe undervoltage or underfrequency occurrences due to factors such as high loading or DG outages. Numerical simulations demonstrate the superiority of the proposed strategy over the state-of-the-art controllers in modulating the EV charging demand to counteract microgrid instability.

Distributed Event-triggered Control for Frequency Restoration in Islanded Microgrids with Reduced Trigger Condition Checking

For islanded microgrids(MGs),distributed control is regarded as a preferred alternative to centralized control for the frequency restoration of MGs.However,distributed control with successive communication restricts the efficiency and resilience of the control system.To address this issue,this paper proposes a distributed event-triggered control strategy for the frequency secondary control in islanded MGs.The proposed event-triggered control is Zeno behavior free and enables each DG to update and propagate its state to neighboring DGs only when a specific“event”occurs,which significantly reduces the communication burden.Compared with the existing event-triggered control,a trigger condition checking period of the proposed event-triggered control is provided to reduce the computation burden when checking the trigger condition.Furthermore,using the aperiodicity and intermittent properties of the communication,a simple detection principle is proposed to detect and isolate the compromised communication links in a timely and economic fashion,which improves the resilience of the system against FDI attacks.Finally,the control effectiveness of the proposed control scheme is validated by the simulation results of the tests on an MG with 4 DGs.

Optimal Secondary Control of Islanded AC Microgrids with Communication Time-delay Based on Multi-agent Deep Reinforcement Learning

In this paper,an optimal secondary control strategy is proposed for islanded AC microgrids considering communi-cation time-delays.The proposed method is designed based on the data-driven principle,which consists of an offine training phase and online application phase.For offline training,each control agent is formulated by a deep neural network(DNN)and trained based on a multi-agent deep reinforcement learning(MA-DRL)framework.A deep deterministic policy gradient(DDPG)algorithm is improved and applied to search for an optimal policy of the secondary control,where a global cost function is developed to evaluate the overall control performance.In addition,the communication time-delay is introduced in the system to enrich training scenarios,which aims to solve the time-delay problem in the secondary control.For the online stage,each controller is deployed in a distributed way which only requires local and neighboring information for each DG.Based on this,the well-trained controllers can provide optimal solutions under load variations,and communication time-delays for online applications.Several case studies are conducted to validate the feasibility and stability of the proposed secondary control.Index Terms-Communication time-delay,global cost function,islanded AC microgrid,multi-agent deep reinforcement learning(MA-DRL),secondary control.

含风光出力随机性的独立微电网二次频率控制

针对风、光发电随机性的问题,提出一种考虑新能源减载参与二次调频的模型预测控制方法。建立包含随机功率扰动的扩展状态矩阵,采用卡尔曼滤波估算随机未知扰动;依据风、光最大可用功率,建立实时变约束,避免机组功率越限;设置合理的权重系数,优先风、光发电出力参与二次调频;通过求解变约束二次规划问题,获得各个机组的优化调频功率。最后,建立含多个光伏、风电的微电网模型,在不同场景下与常规二次调频方法进行对比仿真。仿真结果表明,所提方法能提高系统频率恢复速度,减小系统频率波动,尤其在风、光发电剧烈波动场景下。

可再生能源高渗透下时滞孤岛微电网的负荷频率控制

针对孤岛微电网系统中大规模接入可再生能源导致的低惯性和开放通信网络中通信延迟对系统稳定运行造成的不可忽略的影响,该文研究变时滞影响下低惯性孤岛微电网系统的负荷频率控制问题。首先,提出一种引入虚拟惯性控制的时滞微电网分层频率控制模型;然后构造一个新的Lyapunov-Krasovskii泛函,它包括时滞乘积项和增广的s-dependent积分项。进而,选取复合松弛积分不等式、二次函数不等式和凸组合等方法与所构造泛函有效配合,得到保守性更低的稳定性判据。最后,通过不同场景的仿真分析验证所提方法在提高孤岛微电网时滞稳定裕度和系统动态性能方面具有更好的效果,并分析了时滞稳定裕度与控制器参数、非线性负载扰动之间的关系。

孤岛微电网的虚拟同步发电机分布式协同二次调频控制

基于孤岛微电网中虚拟同步发电机一次控制存在的频率偏差问题,提出一种基于预定时系统的分布式二次频率控制策略。该策略通过预定时系统对一致性进行改进并适配虚拟同步发电机本体算法,使各逆变器仅依靠相邻单元的通信,即可实现系统有功缺额按容量分配与频率的无差控制。同时,预定时系统通过提前设定一致性的收敛时间,进一步提高频率的恢复速度,并且无需考虑初始容量与协议参数的影响,有利于分布式电源的即插即用,提高运行效率。最后通过仿真验证了所提控制策略的可行性和有效性。

交流微电网谐波功率分布式共享控制策略

交流母线电压的电能质量是微电网分布式控制的关键问题之一,该文将含逆变器接口的分布式发电机连接到微电网母线上,重点研究了含非线性负荷的微电网谐波功率共享问题。为了解决非线性负荷引起的电压畸变,设计了谐波下垂控制器和模型预测电压控制器,替代传统的电压电流双闭环控制。在此基础上,提出了一种基于有限集模型预测控制的分布式协同一致协议,使每个分布式发电单元的谐波功率在公共耦合点均匀分布。该方法可以提高微电网系统的可靠性和灵活性,防止电网扰动和馈线阻抗失配,使谐波功率在分布式发电机组之间精确地按比例分配。仿真结果表明,该控制策略在实现谐波功率共享和改善公共耦合点电压谐波失真方面具有良好的效果。

基于多目标协调的混合储能功率自适应分配方法

混合储能具有良好的功率可控特性,在孤岛微网中常被用作功率缓冲器,补偿分布式电源和负荷多变的功率潮流.围绕储能的功率响应问题,本文设计了混合储能的功率控制方案,并提出了一种基于多目标协调的子单元功率自适应分配方法.首先基于对母线功率供求平衡关系的分析,设计了主从并联型储能功率控制方案.其次利用积分器的“时空调零”特性,实现了子单元的功率自主分配;基于此,考虑了不同荷电状态(SOC)下储能最大充放电功率的差异,设计了子单元的SOC分层管理和多目标功率协调策略.仿真结果表明,所提策略实现的功率分配效果满足子单元的功率响应特性;随着超级电容SOCscn偏移加深,所提策略对SOCscn的优化能力越强,初始SOCscn为97%时能提高10.10%的优化性能,这保障了超级电容作为电压源的功率输出能力;所提策略降低了超级电容常态下的蓄电池的输出深度,蓄电池的最大功率深度降低了46.70%,这提高了蓄电池的使用寿命.

通信延迟下的分布式孤岛微电网有限时间二次频率控制

针对孤岛微电网中存在通信延迟的频率恢复问题,研究了孤岛式微电网的分布式二次频率控制,提出了一种最优分布式控制策略。该策略的显著特征在于考虑了所设计的控制器中存在通信延迟的情况,通过在最优分布式控制中加入延迟补偿项,进一步降低了对通信网络的依赖。与传统控制方法相比,所提策略在有限时间内消除了频率偏差并实现了有功功率分配,系统的可靠性得到了进一步提高。最后在MATLAB/Simulink环境下构建了由4个分布式电源(distributed generator,DG)单元组成的孤岛微电网测试系统仿真模型,仿真结果验证了所提策略的有效性。

Control strategy for seamless transition from islanded to interconnected operation mode of microgrids

Microgrids can operate either interconnected to the utility grid or disconnected forming an island. The transition between these modes can cause transient overcurrents or power oscillations jeopardizing the equipment safety or the system stability. This paper proposes a local multi agent control method for a seamless transfer between the islanded and interconnected modes of operation with agents implemented into the microgrid central switch(MCS) and into the microsources inverters. The MCS agent supervises the grid status and controls the switch for the transition of the microgrid through the different operation modes, while it communicates locally with the inverter agents of the microsources. The inverter agents undertake the synchronization process in case of reconnecting and change the inverter control mode depending on the grid status. Simulation and experimental results are presented to show the performance and feasibility of the proposed strategy.

基于虚拟阻抗自适应的孤岛型微电网并联逆变器下垂控制策略

当前微电网并联逆变器下垂控制机制一般设定为独立式,控制的范围较难扩展,导致控制补偿差增加。为此,提出对基于虚拟阻抗自适应的孤岛型微电网并联逆变器下垂控制策略的设计与实践。先进行下垂控制特性提取,采用交互的方式,扩大控制的范围,设计交互控制机制。在此基础上,构建虚拟阻抗自适应微电网并联逆变器下垂控制模型,采用补偿核验的方式确保下垂控制效果。针对选定的5个测试逆变器,经过2个周期的测定得出的控制补偿差被较好地控制在1.05以下,说明此次在虚拟阻抗自适应原理的辅助下,所设计的微电网并联逆变器下垂控制方法更为高效,具有实际的应用价值。

基于双人零和博弈的孤岛微电网有界L2增益负荷频率控制

针对含不确定建模误差和新能源接入的孤岛微电网,提出了一种结合有界L2增益基线控制和扰动补偿的综合负荷频率控制(LFC)方法。首先,推导了微电网的全驱模型,将建模误差和新能源的影响总结成一个综合扰动。为提高系统的鲁棒性,该综合扰动被定义成控制信号的对手玩家。进一步,关于扰动抑制的有界L2增益问题被等价成求解综合扰动和控制信号的零和博弈Nash均衡,由此推导出有界L2增益基线控制器。为改善频率的二次控制,设计了基于五阶广义积分观测器的扰动补偿控制,并在此基础上引入了一种针对发电速率约束(GRC)的新型抗发电速率约束(anti-GRC)措施。最后,搭建了16 MW的新能源-柴油混合微电网仿真模型,并在多种工况下对所提出的综合LFC方法进行测试,验证了其有效性。

计及下垂曲线与储能的孤岛微电网分级调度策略

目前国内孤岛微电网运行调度中分布式发电(distributed generation,DG)电源被统一处理为传统发电机的PQ模型,与微电网实际情况不一致,同时较少有文献考虑电压潮流约束,为此,考虑下垂控制DG静态模型,计及潮流非线性约束,提出含可再生能源出力、储能充放电的孤岛微电网分级调度策略;同时,考虑DG下垂特性与潮流非线性约束,上级孤岛微电网经济、安全运行调度依靠集中优化控制器进行,控制下级DG各类静态参数及各储能装置充放电功率;下级依靠传统下垂控制在上级控制参数下实时调整有功、无功出力,维持系统频率、电压稳定。上述模型采用YALMIP+IPOPT程序进行求解,以14节点系统为例开展模拟仿真。仿真结果证明:所提模型及其求解方法可以有效求解孤岛微电网经济及安全运行调度模型,在稳定并提高系统电压水平、降低孤岛微电网运行费用方面具备显著优势。

独立直流微网电压动态轨迹神经网络优化控制策略

为解决独立直流微网功率扰动下电压过渡过程动态偏差大的问题,该文提出一种优化电压动态轨迹的神经网络控制策略。分析下垂控制及其改进方法的控制特性,提出独立直流微网最优电压动态轨迹,并以此为基础,采用神经网络生成参考电压,通过非线性控制实现公共直流母线动态电压偏差最小化。基于向量空间同构原理,提出神经网络降维状态反馈构建方法,并根据系统源荷不平衡功率变化范围提出神经网络控制边界。考虑动态电压偏差及其运动趋势,构建电压扰动分层奖励函数,静态层奖励引导神经网络减小电压偏差,动态层奖励加强神经网络对电压运动趋势的修正,实现电压动态轨迹全过程优化控制。最后,利用MATLAB/Simulink进行算例验证,结果表明所提策略可有效抑制由功率不平衡导致的动态电压偏差,保证公共直流母线电压的快速稳定。

孤岛微电网系统的混合控制策略及动态滤波技术研究

应用于孤岛型微电网以实现频率控制功能的传统控制器多为分数阶PID(fractional order PID,FOPID)控制器及模糊分数阶PID(fuzzy fractional order PID,FFOPID)控制器,二者的控制性能均存在局限性。针对这一问题,设计了一种变论域混合FFOPID控制器,用于提高孤岛微电网的频率控制性能。通过对比FOPID、FFOPID以及变论域混合FFOPID3种控制器作用时的不同效果,证明了变论域混合FFOPID控制器相比其他控制器对于孤岛微电网的频率控制有着更好的控制性能。同时考虑了反馈信号受到测量噪声干扰时对控制器的控制性能产生影响进而使得孤岛微电网频率波动增大的情况,并针对此问题使用了动态数据校正(dynamic datareconciliation,DDR)滤波技术。通过对比时域仿真中FOPID、FFOPID以及变论域混合FFOPID控制器各自作用时孤岛微电网频率偏差的输出结果,验证了DDR滤波技术对孤岛微电网的频率控制的显著效果。

时滞孤岛微电网负荷频率控制系统在采样控制下的指数稳定

孤岛微电网配有开放式通讯网络。通讯信息不可避免存在的延迟,会对系统的稳定造成显著影响。针对变时滞影响下的孤岛微电网负荷频率控制系统的稳定性问题进行了研究。首先,建立了考虑时滞的孤岛微电网负荷频率控制系统模型,并据此推导出含时滞项的系统状态方程。然后,在基于采样的事件触发非周期间歇控制策略下,通过数学推导证明了系统在变时滞的影响下能够实现指数稳定。最后,通过仿真分析,验证了所提控制策略的有效性,并将其与最近提出的基于状态控制宽度的事件触发非周期间歇控制策略进行了对比。结果显示,相较于后者,提出的控制策略在系统稳定性方面表现更为高效,且所需的控制次数更少。

孤岛微电网电流同步U-I下垂控制方法

采用电压-电流(U-I)下垂控制的孤岛微电网系统始终运行于工频频率,避免了传统下垂控制存在的频率偏差及频率越限问题,但电源间易产生环流,功率分配精度差。为此,提出电流同步U-I下垂控制方法,该方法由电流同步控制及U-I幅值下垂控制两部分构成。前者通过调节输出电压相角使各电源输出电流相角一致,以抑制电源间环流;后者依据输出电流的幅值调节输出电压的幅值,使各电源出力依据自身容量分配。在此基础上,建立双端系统的小信号模型,分析电流同步控制环路中控制参数对系统稳定性的影响,为参数设计提供依据。仿真及实验结果表明,相比U-I下垂控制,所提方法的系统环流减小50%以上,电压畸变率改善近10%,电源间功率分配精度及系统电能质量均得到明显提升。

计及电动汽车与飞轮储能单元的孤岛微电网负荷频率控制

针对孤岛微电网惯性和阻尼不足的问题,引入飞轮储能单元,并构建带飞轮储能单元的孤岛微电网负荷频率控制模型,研究了通信时滞对孤岛微电网系统的影响。采用适用的Lyaunov-Krasovskii泛函(LKF),通过广义自由权积分不等式对导数积分项进行界定,从而得到了时滞相关稳定性判据。当考虑电动汽车电池状态对系统增益的影响时,将系统视为参数不确定时滞系统。通过不同的参数设定,进行了仿真实验,结果证明了所提方法的有效性与优越性。

考虑电动汽车的时滞孤岛微电网负荷频率控制

本文研究了考虑电动汽车参与调频的时滞孤岛微电网,重点研究了通讯时滞对孤岛微电网系统的影响,构建了考虑电动汽车的时滞孤岛微电网模型,采用了适用的Lyaunov-Krasovskii泛函(LKF),并通过运用自由权矩阵积分不等式得到了稳定性判据,通过不同的参数设定,进行了仿真实验,结果说明了本文方法的有效性。