Review of the Configuration and Transient Stability of Large-scale Renewable Energy Generation through Hybrid DC Transmission

Based on the complementary advantages of Line Commutated Converter(LCC)and Modular Multilevel Converter(MMC)in power grid applications,there are two types of hybrid DC system topologies:one is the parallel connection of LCC converter stations and MMC converter stations,and the other is the series connection of LCC and MMC converter stations within a single station.The hybrid DC transmission system faces broad application prospects and development potential in large-scale clean energy integration across regions and the construction of a new power system dominated by new energy sources in China.This paper first analyzes the system forms and topological characteristics of hybrid DC transmission,introducing the forms and topological characteristics of converter-level hybrid DC transmission systems and system-level hybrid DC transmission systems.Next,it analyzes the operating characteristics of LCC and MMC inverter-level hybrid DC transmission systems,provides insights into the transient stability of hybrid DC transmission systems,and typical fault ride-through control strategies.Finally,it summarizes the networking characteristics of the LCC-MMC series within the converter station hybrid DC transmission system,studies the transient characteristics and fault ridethrough control strategies under different fault types for the LCC-MMC series in the receiving-end converter station,and investigates the transient characteristics and fault ride-through control strategies under different fault types for the LCC-MMC series in the sending-end converter station.

A Nonlinear Coordinated Approach to Enhance the Transient Stability of Wind Energy-Based Power Systems

This paper proposes a novel framework that enables the simultaneous coordination of the controllers of doubly fed induction generators(DFIGs) and synchronous generators(SGs).The proposed coordination approach is based on the zero dynamics method aims at enhancing the transient stability of multi-machine power systems under a wide range of operating conditions. The proposed approach was implemented to the IEEE39-bus power systems. Transient stability margin measured in terms of critical clearing time along with eigenvalue analysis and time domain simulations were considered in the performance assessment. The obtained results were also compared to those achieved using a conventional power system stabilizer/power oscillation(PSS/POD) technique and the interconnection and damping assignment passivity-based controller(IDA-PBC). The performance analysis confirmed the ability of the proposed approach to enhance damping and improve system’s transient stability margin under a wide range of operating conditions.

Coordinated Control of Multi-FACTS to Enhance the Dynamic Stability of the Power System

This article introduces a FACTS coordinated control strategy with impedance/admittance measurement feedback. Then the effectiveness of this method is proved in mathematics with damp torque method. The control strategy effect is verified in a single machine infinite bus system and a four machine power system with PSASP6.26 (Power System Analysis Software Package). This coordinated control strategy has practical significance to improve system dynamic stability and theoretical significance to improve system transient stability.

Transient Stability Analysis of Hu-Liao HVDC and AC Parallel Transmission System

In this paper, transient stability analysis was focused on Hu-Liao HVDC and AC parallel transmission system. The Hu-Liao HVDC project was introduced;Simulation method and mathematic models of AC and DC systems were stu-died as well as corresponding regulators and controllers. The dynamic performance and the interaction between AC and DC systems during serious disturbance were researched by detail time-domain simulation. Comparison was also made under different operation schemes. The research will bring important and significant reference for further operation and stability control of Hu-Liao HVDC and AC system.

Transient Stability Analysis during an Improved Coupling Procedure for an Induction Generator Based Wind Generation System to the Grid

For fixed speed wind turbines, the connection of its squirrel cage induction generator (SCIG) to the grid leads to inrush current which can reach an average of 2 p.u. up to 2.5 p.u. in higher wind speed even by using a soft starter. We propose in this paper a new soft starting of squirrel cage induction generator based wind turbine connected to the grid. Our strategy overcomes such transient instability problems and pinpoints rapidly synchronous speed regardless the wind speed acting on pitch angle. The proposed strategy ensures at least 50% reduction of inrush current and 18% gain of WTG starting time. A state model of the system is given including the wind turbine model and the SCIG model in the synchronous reference frame. Simulation results are analysed and compared to the classic coupling procedure.

提高系统暂态稳定性的VSC-HVDC有功无功联合附加控制策略

依据基于电压源型换流器的高压直流输电(VSC-HVDC)对系统暂态稳定性的影响机理,提出一种提高系统暂态稳定性的VSC-HVDC有功无功联合附加控制策略。从VSC-HVDC功率特性与系统等值功角的关系出发,建立含VSC-HVDC有功无功附加量的交直流混联系统暂态稳定分析数学模型。针对数学模型的非线性,采用精确反馈线性化进行坐标变换,并采用滑模控制利用反映系统暂态特征的等值功角变化速度与加速度设计切换面,结合设计的有功无功配合方式,确定了VSC-HVDC有功无功附加量随系统暂态特征量实时调节的控制律,其参数设计与计算过程简便。仿真结果表明所提控制策略充分利用了换流站的功率调节能力,有效降低了系统等值功角首摆幅度,加快系统恢复稳定。

区域新能源并网暂态功角稳定分析与紧急控制策略优化

随着新型电力系统发展和新能源机组不断投产,南方区域将形成多区域新能源与邻近常规电源联合集中接入系统的场景。新能源集中接入常与常规电源共用输电通道,将影响区域系统暂态稳定特性及输送通道的传输能力,使南方区域系统的安全稳定运行和风险防控面临了前所未有的挑战。为深入研究区域新能源送出的稳定特性建立了区域新能源交流集中送出的等值系统模型,分析了新能源并入对区域系统对暂态稳定特性影响的主要机理。基于等面积法则对区域送出系统暂态过程的加、减速面积进行了定量分析,提出了紧急控制切机策略的协调优化方法,实现区域送出传统机组与新能源机组紧急控制切机量及控制代价的最小化的切机策略配置。最终,基于广东区域海风火电打捆送出系统为例,对分析结果的正确性进行了验证。

电化学储能参与电网暂态功角稳定控制研究

针对电网传统紧急控制资源的日益匮乏,利用电化学储能功率控制的快速性与双向控制能力,研究将其应用于电网暂态功角稳定控制。首先推导了计及电化学储能的双机等值模型,基于扩展等面积定则分析了储能改善电网暂态稳定裕度的原理。其次,提出了一种考虑设备保护与系统保护动作时序差异的储能电站有效工作时长计算方法,改善了紧急控制储能的工作效率。提出了计及储能的基于性能代价比多类措施协调控制策略制定方法,兼顾紧急控制的安全性与经济性,为电网暂态紧急控制提供在线辅助决策支撑。进一步提出了储能电站全景监控系统架构,为实现储能电站与电网紧急控制系统的交互提供了技术实践思路。最后西北电网实际算例验证了所提方法的有效性与合理性。研究结论可为规模化储能与高比例新能源电网第二道防线的扩展与建设提供理论参考。

自同步型直驱风电机组暂态稳定分析

随着大规模风电的接入,电网面临系统变弱及调频能力变差的问题.直驱风电机组采用自同步控制,在有效提升设备自身的小扰动稳定性和对电网的支撑能力的同时也带来了复杂的暂态稳定问题.为此,针对2种典型的控制结构(功率自同步和直流电压自同步)分别建立风机系统暂态模型,揭示机侧动态及直流电容动态对暂态特性的影响.针对功率自同步型风电机组,分析频率跌落下风机系统的同步失稳风险;结果表明,机侧动态会降低风机系统在电压跌落下的稳定裕度.针对直流电压自同步型风电机组,揭示暂态下直流电容动态导致的直流电压崩溃失稳风险.总结对比储能和风电机组的暂态特性差异,讨论直驱风电机组的暂态控制设计思路.基于Matlab/Simulink的时域仿真模型验证理论分析的正确性及控制的有效性.

基于暂态能量辨识的含规模化储能的新能源电力系统暂态稳定控制方法

风电等新能源的大规模并网严重影响了电力系统的暂态稳定性。针对新能源电力系统暂态稳定问题,提出基于暂态能量辨识的含规模化储能的新能源电力系统暂态稳定控制方法。首先,构建新能源电力系统的线路稳定裕度和系统暂态稳定裕度指标,准确辨识系统暂态稳定性;然后,提出附加线路暂态能量控制的改进储能控制策略,更好提升系统暂态稳定性;最后,在New England10机39节点系统中进行仿真验证。算例分析表明,所提方法能准确辨识系统暂态稳定分布情况,有效改善新能源电力系统暂态稳定性。

面向直流受端新型电力系统暂态电压稳定的紧急控制策略

在直流受端新型电力系统中,新能源电源及直流的接入导致同步机开机减少,动态无功功率相对紧张,暂态电压失稳风险显著增大。为高效快速获取紧急控制策略,即直流电流控制方案,并使其适应不同的电网运行方式和故障场景,尤其是电网拓扑结构的变化,基于图卷积神经网络(GCN)对常规深度强化学习模型深度确定性决策梯度(DDPG)的网络结构进行改造,构建了GCN-DDPG融合模型。在此基础上,引入双评价网络机制和评价网络与动作网络非同步更新策略以提升算法效果。进一步地,在应用方面,基于GCN-DDPG融合模型构建紧急控制模型并将其下达至安控主站,安控主站将依据电网实际运行方式和故障等信息,对紧急控制策略进行在线量化计算,并发送至直流控保系统执行。最后,通过改造的IEEE 14节点系统验证所提方法的有效性和优越性。

计及功率控制型构网变流器接入的交流系统暂态稳定性仿真研究

为研究功率控制型构网变流器接入交流系统后的暂态稳定性演化趋势,基于IEEE 39节点交流测试系统,将发电机分别等容量替换为功率控制型构网变流器与跟网型变流器,并改变其在交流系统中接入数量、并网位置进行电磁暂态仿真,结果表明:功率控制型构网变流器对接入区域的暂态稳定性提升能力更优,尤其当所替换发电机相邻时,提升效果显著;随着功率控制型构网变流器接入系统比例增加,系统暂态稳定性越强;功率控制型构网变流器内部等效惯性系数越大,系统同步稳定性越弱,其内部阻尼系数越大,系统同步稳定性越强。

求解Controlling-UEP新方法的研究

提出一种将Brown算法与重新选择参考点的策略相结合求解电力系统暂态稳定性直接法 分析中主导不稳定平衡点(Controlling-UEP)的新方法。Brown算法相似于高斯消元法的牛顿类 算法,它把每一方程展成泰勒级数,所得到的最新信息(关于变量的最新解)立刻用于下一函数的构 造及求解,是求解病态方程组的好算法。文中将它与参考点的重新选择策略相结合,进一步提高它 求取病态情况下Controlling-UEP的稳定性。算例表明,所提出的新方法在收敛性和计算效率方 面有较好的效果。

提升末端区域电网供电能力的调控方案及稳控策略研究

针对内蒙古某末端区域电网供电能力受同塔双回线路N-2故障及母线故障制约问题,开展安全稳定控制系统(以下简称稳控系统)控制策略研究。首先,基于对典型故障后末端区域电网稳定特性的仿真计算与分析,结合新能源出力、火电机组开机等对切负荷定值的影响,制订预控方案与稳控系统相结合的综合调度控制方案;然后,分析电解铝行业整流变压器负荷转移特性,提出可优先实切负荷量计算方法和适用于末端电网的分档阶梯切负荷原则,对末端区域电网稳控系统的控制策略进行优化。

Distributed Deep Reinforcement Learning-based Approach for Fast Preventive Control Considering Transient Stability Constraints

Preventive transient stability control is an effective measure for the power system to withstand high-probability severe contingencies.It is mathematically an optimal power flow problem with transient stability constraints.Due to the constraints involved for differential algebraic equations of transient stability,it is difficult and time-consuming to solve this problem.To address these issues,this paper presents a novel deep reinforcement learning(DRL)framework for preventive transient stability control of power systems.A distributed deep deterministic policy gradient is utilized to train a DRL agent that can learn its control policy through massive interactions with a grid simulator.Once properly trained,the DRL agent can instantaneously provide effective strategies to adjust the system to a safe operating position with a near-optimal operational cost.The effectiveness of the proposed method is verified through numerical experiments conducted on a New England 39-bus system and NPCC 140-bus system.

基于迁移学习的OMS配网瞬态稳定性控制方法

为了提升一体化控制效果,确保OMS配网的瞬态稳定,研究基于迁移学习的OMS配网瞬态稳定性控制方法。通过迁移学习调整网络中非固定层参数,依据提取的特征训练重构非固定层的网络,构建迁移学习卷积神经网络模型;输入二维电压电流数据图像,输出OMS配网瞬态稳定性预测结果;若OMS配网瞬态失稳,则求解OMS配网内发电机的灵敏度,按照灵敏度生成OMS配网瞬态稳定性一体化控制策略。实验证明,该方法在不同故障下,综合评价指标值较高,一体化控制效果较佳。

Transient Angle Stability of Inverters Equipped with Robust Droop Control

Transient angle stability of inverters equipped with the robust droop controller is investigated in this work.At first,the conditions on the control references to guarantee the existence of a feasible post-disturbance operating point are derived.Then,the post-disturbance equilibrium points are found and their stability properties are characterized.Furthermore,the attraction regions of the stable equilibrium points are accurately depicted by calculating the stable and unstable manifolds of the surrounding unstable equilibrium points,which presents an explanation to system transient stability.Finally,the transient control considerations are provided to help the inverter ridethrough the disturbance and maintain its stability characteristics.It is shown that the transient angle stability is not a serious problem for droop controlled inverters with proper control settings.

直接电压控制构网型变流器控制参数暂态稳定影响分析

目前针对直接电压控制构网型变流器暂态失稳模式的演化和控制参数对暂态稳定的影响机理尚需进一步深入研究。首先,分析了两种常见电流限幅策略对变流器暂态稳定性的影响,归纳总结出3种暂态失稳演化路径。其次,通过极限切除时间、极限切除角揭示了变流器有功环节不同参数对暂态稳定的影响规律,并针对直接电压控制构网型变流器的内电势和并网点电压之间的非线性关系,使用变流器临界势能为指标,揭示了变流器无功环节不同参数对稳定性的影响规律。在此基础上,解释了不同控制环节参数对变流器暂态稳定性的影响出现反常规律的机理。最后,在PSCAD仿真平台上通过算例验证了理论分析的正确性。

多微型逆变器微电网频率暂态稳定综合控制研究

研究多微型逆变器微电网频率暂态稳定综合控制,有效控制微电网频率暂态稳定性,提升控制准确性,缩短调节时间。通过励磁控制与功频控制构建虚拟同步发电机控制方法,实现负荷小扰动下微电网频率暂态稳定控制;利用改进下垂控制方法,实现负荷大扰动下微电网频率暂态稳定控制;通过设计同步电压控制器与双环控制器,完成虚拟同步发电机控制方法与改进下垂控制方法的自由切换,综合控制不同情况下微电网频率的暂态稳定。实验证明,所研究方法在不同负荷扰动下,可有效实现微电网频率暂态稳定控制;在切换离网模式与并网模式时,能够有效切换控制方法,准确控制微电网频率暂态稳定性,缩短调节时间。

计及故障持续时间的电力系统暂态稳定分布式控制

针对电力系统故障持续时间会影响暂态稳定控制的问题,本文提出了一种使系统在固定时间内恢复暂态稳定运行的策略.该策略通过电力系统通信拓扑建模方法为每个发电机建立“邻居发电机”,利用发电机本地信息和其邻居发电机的信息设计分布式控制器,通过控制储能装置作用于受扰动后的系统,使其在固定时间内恢复稳定运行.其次,此控制策略还解决了一些实际挑战,如控制器的输入延时、外部的干扰、储能装置的容量限制等.通过构建李雅普诺夫函数并利用图论知识对该策略展开了稳定性分析,推导出了稳定系统的时间界限.最后,将控制器投入新英格兰39节点测试系统中,并与其它控制器进行比较,仿真结果验证了在低容量储能装置限制下和抗干扰性上控制器性能的优势.