Optimized coordinated control of LFC andSMES to enhance frequency stability of areal multi-source power system consideringhigh renewable energy penetration

With rapidly growing of Renewable Energy Sources (RESs) in renewable power systems, several disturbances influence on the power systems such as; lack of system inertia that results from replacing the synchronous generators with RESs and frequency/voltage fluctuations that resulting from the intermittent nature of the RESs. Hence, the modern power systems become more susceptible to the system instability than conventional power systems. Therefore, in this study, a new application of Superconducting Magnetic Energy Storage (SMES) (i.e., auxiliary Load Frequency Control (LFC)) has been integrated with the secondary frequency control (i.e., LFC) for frequency stability enhancement of the Egyptian Power System (EPS) due to high RESs penetration. Where, the coordinated control strategy is based on the PI controller that is optimally designed by the Particle Swarm Optimization (PSO) algorithm to minimize the frequency deviations of the EPS. The EPS includes both conventional generation units (i.e., non-reheat, reheat and hydraulic power plants) with inherent nonlinearities, and RESs (i.e., wind and solar energy). System modelling and simulation results are carried out using Matlab/ Simulink® software. The simulation results reveal the robustness of the proposed coordinated control strategy to preserve the system stability of the EPS with high penetration of RESs for different contingencies.     

Adaptive H∞ event-triggered load frequency control in islanded microgirds with limited spinning reserve constraints

Using an islanded microgrid (MG) with large-scale integration of renewable energy is the most popular way of solving the reliable power supply problem for remote areas and critical electrical users. However, compared with traditional power systems, the limited spinning reserves and network communication bandwidth may cause weak frequency stability in the presence of stochastic renewable active outputs and load demand fuctuations. In this paper, an adaptive event-triggered control (ETC) strategy for a load frequency control (LFC) system in an islanded MG is proposed. First, a bounded adaptive event-triggered communication scheme is designed. This not only saves on network resources, but also ensures that the control center has a sensitive monitoring ability for the MG operating status when the frequency deviations have been efectively damped. Secondly, by fully considering the spinning reserve constraints and uncertain communication delays, the LFC system is described as a nonlinear model with saturation terms. Design criteria for ETC parameters are strictly deduced based on Lyapunov stability theory. Finally, an ETC parameter optimization algorithm based on random direction search is developed to reconcile the bandwidth occupancy and control performance. The efectiveness of the proposed method is verifed in an MG test system.     

Comparative framework for AC-microgrid protection schemes: challenges, solutions, real applications, and future trends

With the rapid development of electrical power systems in recent years, microgrids (MGs) have become increasingly prevalent. MGs improve network efficiency and reduce operating costs and emissions because of the integration of distributed renewable energy sources (RESs), energy storage, and source-load management systems. Despite these advances, the decentralized architecture of MGs impacts the functioning patterns of the entire system, including control strategy, energy management philosophy, and protection scheme. In this context, developing a convenient protection strategy for MGs is challenging because of various obstacles, such as the significant variance in short-circuit values under different operating modes, two-way power flow, asynchronous reclosing, protection blinding, sympathetic tripping, and loss of coordination. In light of these challenges, this paper reviews prior research on proposed protection schemes for AC-MGs to thoroughly evaluate network protection''s potential issues. The paper also provides a comprehensive overview of the MG structure and the associated protection challenges, solutions, real applications, and future trends.     

基于交替方向乘子法的分布式负荷频率控制策略

负荷频率控制(load frequency control, LFC)是维持电力系统安全稳定运行的基础。对于多区域互联电力系统,由于描述动态过程的微分方程组相当复杂,这给负荷频率控制器的设计带来了困难。在此背景下,针对多区域互联电力系统,提出基于交替方向乘子法 (alternating direction method of multiplier, ADMM) 的分布式最优负荷频率控制器设计方法,以取得良好的控制性能,同时具备较高的计算效率。首先,介绍了负荷频率控制问题的微分方程模型。之后,基于二次多项式和矩阵稀疏化构建了分布式最优LFC策略的数学模型,并采用ADMM求解。最后,以三区域互联电力系统为例对所提方法进行了验证。仿真结果表明,针对负荷扰动和时变参数,所提方法能够把各区域的频率偏差和区域间联络线上的功率偏差控制到0。     

A soft actor-critic deep reinforcement learning method for multi-timescale coordinated operation of microgrids

This paper develops a multi-timescale coordinated operation method for microgrids based on modern deep reinforcement learning. Considering the complementary characteristics of different storage devices, the proposed approach achieves multi-timescale coordination of battery and supercapacitor by introducing a hierarchical two-stage dispatch model. The first stage makes an initial decision irrespective of the uncertainties using the hourly predicted data to minimize the operational cost. For the second stage, it aims to generate corrective actions for the first-stage decisions to compensate for real-time renewable generation fluctuations. The first stage is formulated as a non-convex deterministic optimization problem, while the second stage is modeled as a Markov decision process solved by an entropy-regularized deep reinforcement learning method, i.e., the Soft Actor-Critic. The Soft Actor-Critic method can efficiently address the exploration–exploitation dilemma and suppress variations. This improves the robustness of decisions. Simulation results demonstrate that different types of energy storage devices can be used at two stages to achieve the multi-timescale coordinated operation. This proves the effectiveness of the proposed method.     

Frequency control of a wind-diesel system based on hybrid energy storage

Owing to the significant number of hybrid generation systems (HGSs) containing various energy sources, coordination between these sources plays a vital role in preserving frequency stability. In this paper, an adaptive coordination control strategy for renewable energy sources (RESs), an aqua electrolyzer (AE) for hydrogen production, and a fuel cell (FC)-based energy storage system (ESS) is proposed to enhance the frequency stability of an HGS. In the proposed system, the excess energy from RESs is used to power electrolysis via an AE for hydrogen energy storage in FCs. The proposed method is based on a proportional-integral (PI) controller, which is optimally designed using a grey wolf optimization (GWO) algorithm to estimate the surplus energy from RESs (i.e., a proportion of total power generation of RESs: Kn). The studied HGS contains various types of generation systems including a diesel generator, wind turbines, photovoltaic (PV) systems, AE with FCs, and ESSs (e.g., battery and flywheel). The proposed method varies Kn with varying frequency deviation values to obtain the best benefits from RESs, while damping the frequency fluctuations. The proposed method is validated by considering different loading conditions and comparing with other existing studies that consider Kn as a constant value. The simulation results demonstrate that the proposed method, which changes Kn value and subsequently stores the power extracted from the RESs in hydrogen energy storage according to frequency deviation changes, performs better than those that use constant Kn. The statistical analysis for frequency deviation of HGS with the proposed method has the best values and achieves large improvements for minimum, maximum, difference between maximum and minimum, mean, and standard deviation compared to the existing method.     

基于功率跟踪优化的双馈风力发电机组虚拟惯性控制技术

基于电力电子换流器并网的变速恒频风力发电机组对电力系统的惯性几乎没有贡献,这将成为风电场大规模接入电网之后面临的新问题。在分析双馈风电机组运行特性和控制策略的基础上,研究双馈机组的虚拟转动惯量与转速调节及电网频率变化的关系,提出双馈风电机组的虚拟惯性控制策略。该控制策略通过检测电网频率变化来调节最大功率跟踪曲线,从而释放双馈机组"隐藏"的动能,对电网提供动态频率支持。通过对含20%风电装机容量的3机系统的仿真分析,验证该控制策略在系统出现功率不平衡后,能够利用双馈风电机组的虚拟惯量使风电场具备对系统频率快速响应的能力,从而提高了基于双馈风电机组的大规模风电场接入电网后的电力系统频率稳定性。     

含抽水蓄能电站的互联电网负荷频率自抗扰优化控制研究

针对发电能源结构的多元化发展给互联电网负荷频率的稳定性控制带来较大的挑战,建立含抽水蓄能电站的两区域互联电网多元混合发电的负荷频率控制模型,提出一种基于粒子群优化算法的负荷频率线性自抗扰控制器参数整定优化策略,通过粒子群算法的迭代寻优计算获得最优的线性自抗扰控制器参数。考虑互联电网各区域发生不同的负荷扰动,在抽水蓄能电站的抽水和发电2种工况下,对所提出的控制方法进行系统仿真。仿真结果表明,通过粒子群算法优化的负荷频率线性自抗扰控制器,与传统PI控制器对比,前者具有更强的抗扰动能力和适应性,系统动态稳定性更好。     

计及辅助服务的微电网源荷协同调频优化控制策略

针对含高比例新能源微电网中调频资源缺乏且源荷参与调频意愿较低而导致的系统频率稳定性下降问题,通过辅助服务机制激励风电机组与可控负荷提供调频辅助服务,提出一种计及综合经济效益最优的源荷协同调频优化控制策略。该策略根据双馈异步风电机组调频、可控负荷一次调频、柴油机惯量调频以及一次调频计算提供辅助服务的效益和成本,综合考虑微电网的调频经济效益及调频效果,利用深度信念网络优化双馈异步风电机组的减载率、虚拟惯量、下垂控制及可控负荷的控制参数,实现双馈异步风电机组、可控负荷及柴油机多时间尺度的协同调频。通过搭建高比例新能源微电网模型仿真验证了源荷协同调频优化控制策略的有效性,使源荷提供辅助服务后能获得最优经济效益以及较好的调频效果,可有效挖掘源荷提供调频辅助服务的能力。     

Battery energy storage system for frequency support in microgrids and with enhanced control features for uninterruptible supply of local loads

This paper proposes a battery energy storage system (BESS) to support the frequency control process within microgrids (MG) with high penetration of renewable energy sources (RES). The solution includes features that enhance the system’s stability and security of supply. The BESS can operate connected to MG or islanded and the transition between the two states is seamlessly coordinated by an original method. The BESS active power response is governed by an improved frequency controller on two layers, namely primary and secondary. It responds to frequency deviations by combining a conventional droop control method with a virtual inertia function to improve the system’s stability. The proposed BESS may also compensate the power of the local loads, so that the MG frequency transients can be reduced and, depending on the remaining inverter capacity, voltage support in the point of common coupling with the MG may be provided. If the MG power quality degrades in terms of the voltage and frequency, the BESS and the local load are disconnected from the MG and continue operating islanded. The BESS is reconnected to the MG after a smoothly resynchronization of the local voltage with the MG, without disturbing the local loads supply. Simulation and experimental results assesses the proposed control solutions.     

Superconducting energy storage technology-based synthetic inertia system control to enhance frequency dynamic performance in microgrids with high renewable penetration

With high penetration of renewable energy sources (RESs) in modern power systems, system frequency becomes more prone to fluctuation as RESs do not naturally have inertial properties. A conventional energy storage system (ESS) based on a battery has been used to tackle the shortage in system inertia but has low and short-term power support during the disturbance. To address the issues, this paper proposes a new synthetic inertia control (SIC) design with a superconducting magnetic energy storage (SMES) system to mimic the necessary inertia power and damping properties in a short time and thereby regulate the microgrid (µG) frequency during disturbances. In addition, system frequency deviation is reduced by employing the proportional-integral (PI) controller with the proposed SIC system. The efficacy of the proposed SIC system is validated by comparison with the conventional ESS and SMES systems without using the PI controller, under various load/renewable perturbations, nonlinearities, and uncertainties. The simulation results highlight that the proposed system with SMES can efficiently manage several disturbances and high system uncertainty compared to the conventional ESS and SMES systems, without using the PI controller.     

一种考虑电力系统频率安全的新能源并网限值评估方法

提出一种考虑电力系统频率安全的新能源并网极限评估方法。该方法推导了可再生能源接入后的系统最大频率偏差表达式,并给出一种电网频率偏差极值点近似求解方法;基于近似结果评估了新能源装机容量变化的情况下,电网最大频率偏差随惯性及等效调节常数的变化情况。建立了频率安全约束模型,并以此作为新能源穿透极限的刚性约束。在2个测试系统上对近似模型进行了测试,并与仿真结果进行了比较。仿真结果表明,该方法所确定系统最大新能源穿透水平具有较高准确性,能够保证系统稳定性和可靠性。     

基于双馈风电机组有效储能的变参数虚拟惯量控制

双馈风电机组采用电力电子变流器控制使得机械部分与电气部分解耦,大规模风电并网后电力系统总有效转动惯量下降,增加了系统的调频压力。文中通过对双馈风电机组运行及控制特性的分析,研究给出了反映机组有效储能的等效虚拟惯性时间常数的计算方法,提出了基于双馈风电机组有效储能的变参数虚拟惯量控制策略。该控制策略通过检测电网频率变化以及动态识别机组运行状态,修改控制参数控制机组有功输出,释放或吸收机组有效动能,对电网提供动态频率支撑。在理论分析基础上进行时域仿真验证,仿真结果表明,双馈风电机组变参数虚拟惯量控制在机组各种运行工况下实现了对系统频率的有效支撑,提高了电力系统频率稳定性,且保证了机组调频过程中自身运行的稳定性。     

Coordinated control of conventional powersources and PHEVs using jaya algorithmoptimized PID controller for frequencycontrol of a renewable penetrated powersystem

In renewable penetrated power systems, frequency instability arises due to the volatile nature of renewable energy sources (RES) and load disturbances. The traditional load frequency control (LFC) strategy from conventional power sources (CPS) alone unable to control the frequency deviations caused by the aforementioned disturbances. Therefore, it is essential to modify the structure of LFC, to handle the disturbances caused by the RES and load. With regards to the above problem, this work proposes a novel coordinated LFC strategy with modified control signal to have Plug-in Hybrid Electric Vehicles (PHEVs) for frequency stability enhancement of the Japanese power system. Where, the coordinated control strategy is based on the PID controller, which is optimally tuned by the recently developed JAYA Algorithm (JA). Numerous simulations are performed with the proposed methodology and, the results have confirmed the effectiveness of a proposed approach over some recent and well-known techniques in literature. Furthermore, simulation results reveal that the proposed coordinated approach significantly minimizing the frequency deviations compared to the JAYA optimized LFC without PHEVs & with PHEVs but no coordination.     

Adaptive coordination control strategy of renewable energy sources, hydrogen production unit, and fuel cell for frequency regulation of a hybrid distributed power system

The ‘mismatch losses’ problem is commonly encountered in distributed photovoltaic (PV) power generation systems. It can directly reduce power generation. Hence, PV array reconfiguration techniques have become highly popular to minimize the mismatch losses. In this paper, a dynamical array reconfiguration method for Total-Cross-Ties (TCT) and Series–Parallel (SP) interconnected PV arrays is proposed. The method aims to improve the maximum power output generation of a distributed PV array in different mismatch conditions through a set of inverters and a switching matrix that is controlled by a dynamic and scalable reconfiguration optimization algorithm. The structures of the switching matrix for both TCT-based and SP-based PV arrays are designed to enable flexible alteration of the electrical connections between PV strings and inverters. Also, the proposed reconfiguration solution is scalable, because the size of the switching matrix deployed in the proposed solution is only determined by the numbers of the PV strings and the inverters, and is not related to the number of PV modules in a string. The performance of the proposed method is assessed for PV arrays with both TCT and SP interconnections in different mismatch conditions, including different partial shading and random PV module failure. The average optimization time for TCT and SP interconnected PV arrays is 0.02 and 3 s, respectively. The effectiveness of the proposed dynamical reconfiguration is confirmed, with the average maximum power generation improved by 8.56% for the TCT-based PV array and 6.43% for the SP-based PV array compared to a fixed topology scheme.     

提升海上风电经柔直联网系统频率稳定性的协调控制策略

针对大规模海上风电经柔直联网引起的受端电网惯量降低、频率调节能力下降等问题,提出了海上风电与柔直主动支撑系统频率的协调控制策略。在惯量支撑方面,利用直流电容能量主动支撑系统惯量,并通过直流电压建立风机转速与频率的耦合关系,提出了基于差异化转子动能调节的风电场惯量支撑协调控制策略,以提升受端电网惯量水平。在频率偏差调节方面,根据本地直流电压偏差量,提出了基于风机变速控制与桨距角控制的风电场一次调频策略,并设计了基于附加桨距角控制的风电场二次调频策略,以提高系统的频率稳定性。最后,设计了多时间尺度频率支撑控制策略的协调配合流程,并基于RT-LAB OP5600实时数字仿真平台验证了所提策略可有效提升系统的频率支撑能力。     

高风电渗透率下变速风电机组参与系统频率调整策略

考虑负荷波动、风电有功输出的随机性,针对电力系统对大规模风电并网时电能质量、经济性、负荷支撑和快速响应等多方面的需求,提出了一种高风电渗透率下变速风电机组参与系统频率调整的多时间尺度协调优化策略。根据变速风电机组运行特性,制定不同风速工况下风电机组的减载控制,并在不同时间尺度对机组间的调频出力进行协调,使惯性与一次调频相结合,实现频率调整优化。结果表明该策略下变速风电机组不仅能够有效地为系统提供惯性支撑,并且具备灵活、可控的静态频率响应特性。     

考虑系统频率安全稳定约束的风储联合频率响应控制策略

为提升风-储联合运行系统的动态频率稳定性能,针对目前调频控制策略未充分发挥风电机组频率调节能力、无法适应负荷扰动过大情况以及转子转速恢复阶段存在频率二次跌落的问题,提出一种考虑系统频率安全稳定约束的风储联合频率响应控制策略。在惯量响应阶段结合转速约束和频率指标自适应调整虚拟惯量和下垂控制系数,在转子转速恢复阶段利用负指数函数动态调整转速恢复过程中功率参考值,避免频率的二次跌落。将风电机组与储能电池结合,引入频率稳定域概念,利用储能电池扩展频率稳定域边界,进一步提升风储联合系统的抗负荷扰动能力和频率稳定性。最后对风储联合调频策略进行仿真,结果表明在不同风速和不同负荷扰动下,所提控制策略能充分发挥风电机组频率响应控制能力的同时,避免了频率二次跌落,提升了电网频率安全稳定性。     

考虑风速分区的风-储系统短期频率响应协同控制策略

在高风电渗透率电力系统中,针对双馈感应风电机组的转子转速与电网频率解耦所造成的机组惯性与频率响应能力缺失的问题,提出了基于模糊逻辑控制的风—储系统协同运行控制策略。该控制策略通过在风—储控制系统中嵌入模糊逻辑控制器来决策风—储系统响应电网频率波动的总有功出力和风力机转子动能的调频参与系数。基于此,根据不同风速下的风电机组运行特性将风速分区,并针对各风速区间构建了适应该区间转速—功率特点的风—储系统运行策略,使风—储系统具备能适应多种风况的短期频率响应能力。仿真结果表明:文中所提出的风—储系统协同运行控制策略能有效提升风—储系统的惯性以及短期频率响应能力,不仅能使风—储系统的短期频率响应能力适应多种风况,还可避免风电机组退出调频造成的频率二次跌落问题,同时改善了高风电渗透率电力系统的频率稳定性。     

基于不动点映射的多微网与配电网主从博弈定价策略及均衡求解方法

随着配电侧微电网接入数量的逐年提升和市场化改革的推进,开展多微网与配电网的协同优化定价问题具有重要意义。针对该问题,本文提出基于不动点映射的主从博弈定价策略,并分析系统博弈均衡状态的求解方法。首先,建立含多微网接入的配电网二阶锥最优潮流模型,并推导其等价的对偶模型以获得准确的节点边际电价。其次,考虑储能、分布式光伏和弹性负荷的协调,建立基于价格响应的微网群运行优化模型。最后,基于不动点理论描述含多微网的配电系统定价策略,利用基于外推改进的最佳响应算法进行求解实现博弈均衡,并基于压缩映射定理证明所提算法的收敛性。基于改进IEEE-33节点配电系统案例的仿真结果表明,所提方法能够有效求解多主体博弈问题并获得均衡解,且具有更高的求解效率。