基于虚拟惯性频率调节的VSC-MTDC系统自适应下垂控制策略

在传统附加频率控制策略下,多端柔性直流（VSC-MTDC）系统调节交流侧频率易引起较大的直流电压波动。文章提出一种基于虚拟惯性频率调节的VSC-MTDC系统自适应下垂控制策略。首先,通过虚拟惯性频率调节控制,建立直流侧电压与交流侧频率的联系,使VSC-MTDC系统为交流电网频率提供惯性响应,提高系统频率稳定性。其次,考虑换流器的调节裕度,并引入直流电压影响因子,使下垂系数随着直流电压偏差实时变化,由此建立有功功率、直流电压和交流侧频率三者之间的耦合关系,实现VSC-MTDC系统对频率提供惯性支撑,同时保障直流电压稳定。最后,基于PSCAD/EMTDC电磁暂态仿真平台建立四端VSC-MTDC输电系统,并选取交流电网负荷减少、负荷增加和发生瞬时短路故障3种工况,验证了所提控制策略的可行性和有效性。     

双馈风电机的虚拟惯性控制优化策略

电力系统在面对不同扰动时,双馈风力电机采用传统虚拟惯性控制不能充分利用转子动能参与调频,提出一种改进的虚拟惯性控制策略。对现有的风机传统虚拟惯性控制方法中的控制增益进行改进,即将控制增益与频率偏差建立耦合关系,使双馈风力电机根据系统频率偏差实时调整调频增发功率,减缓频率跌落速度,提高频率最低点。基于EMTP-RV仿真平台搭建含高比例风电渗透率的电力系统模型,验证改进方法的有效性。仿真结果表明,提出的改进虚拟惯性控制方法在不同扰动下均可大幅改善频率稳定性,且随扰动增大,改善效果越明显。     

双馈风电场有功频率分层控制

风电场有功频率控制是风电场接入电网运行的关键技术。在分析双馈风力发电机组减载运行控制策略及超速法下双馈风力发电机组的减载运行调节能力的基础上,提出了提高双馈风电场的有功调节能力及接入电网后系统频率稳定性的有功频率分层控制策略。该策略根据不同风速区风电机组的减载运行调节能力差异,设计了风电场层分配策略及风电机组层控制策略,在满足有功控制要求的前提下,尽可能提高风电场对电力系统暂态频率稳定的支持。仿真结果表明,该控制策略在系统稳定运行时尽可能存储转子动能,当出现功率扰动后,能够通过快速释放转子存储的动能响应系统频率变化,从而提高了双馈风电场接入电网后的系统频率稳定性。     

基于VSG的风电机组虚拟惯量控制策略

针对永磁同步风电机组通过全功率变流器并网导致机组功率和电力系统频率解耦,机组不具备惯量响应特性的问题,综合考虑风轮、发电机、变流器特性构建"原动机-直流发电机-网侧变流器"的新型永磁同步风电系统控制模型,提出一种基于虚拟同步发电(VSG)的风电机组功率控制策略以实现机组惯量响应,提高机组电网频率支撑能力。网侧变流器基于VSG模拟传统同步发电机惯量响应特性,将系统频率变化转化为直流母线电压变化,机侧变流器利用机组风轮惯性通过发电机转矩控制实现直流母线电压的稳定。在PSCAD中基于1.5 MW永磁同步风电机组的仿真结果表明,基于VSG虚拟惯量控制策略能有效抑制电力系统频率变化,从而有效提高大规模风电场接入后系统的频率稳定性。     

考虑虚拟惯性的VSC-MTDC改进下垂控制策略

针对多端柔性直流(简称多端柔直)系统用于异步互联时各交流电网的频率稳定问题,提出了一种考虑虚拟惯性的多端柔直系统改进下垂控制策略。该控制策略以提高整个系统的惯性水平为目标,利用直流电压建立起交流电网频率和换流站传输的有功功率之间的联系,使得在单个交流电网因故障而产生频率偏差时,其余交流电网可以提供一定的频率支援能力,在保证直流电压稳定性的前提下改善故障交流电网的频率响应特性。最后,在PSCAD/EMTDC仿真平台上搭建三端柔直系统以验证所提控制策略的有效性。     

风电高渗透虚拟同步电力系统的功角暂态稳定性分析

首先,建立互联系统接入变速风电机组后的动态模型,推导虚拟同步电力系统的暂态能量函数,分析表明在不同振荡阶段,惯性控制对暂态能量转换过程的影响不同;其次,提出两区域协同变惯性控制策略,改善含虚拟惯性互联系统的功角稳定性。最后,搭建风电高渗透的四机两区仿真系统,验证所提控制策略能够兼顾频率调节功能,并改善系统的动态稳定性。     

基于转矩极限的改进风电机组虚拟惯量控制策略

为解决大规模风电并网带来的系统频率稳定性降低问题,风电机组通过虚拟惯量控制可为系统提供短期频率支撑,然而惯性响应期间风电机组转速收敛缓慢,导致一部分转子动能被无故浪费;转速恢复阶段的有功突变易造成频率二次跌落。为此,提出基于转矩极限的改进风电机组虚拟惯量控制策略,实现在释放较少动能的前提下提供与传统策略相同的频率响应服务;并在频率步入准稳态时,借助时变功率函数开始转速恢复,实现转速快速恢复的同时缓解二次频率跌落。基于EMTP-RV仿真软件搭建包含风电场的电力系统模型,验证了所提策略的有效性。     

基于储能惯性响应的电网紧急频率控制方法

针对特高压直流闭锁等原因造成的受端电网频率严重跌落问题,提出一种储能紧急频率控制策略。首先,建立储能参与紧急频率控制的数学模型。其次,对于大功率缺额后发电机组惯性响应不足问题,提出了改进的频率变化率（rate of change of frequency,RoCoF）下垂控制策略以提高储能的惯量支撑,根据储能比例分配系数实时调节储能虚拟惯性及下垂控制出力;惯性响应阶段以RoCoF下垂控制为主、虚拟惯性控制为辅,抑制系统频率变化率;结合频率调节需求和储能系统出力特点提出不同区域的调频策略,并通过模糊控制量化处理区域控制偏差及荷电状态不确定性,提高储能系统频率控制的精度。最后,以某电网实际算例仿真验证了所提方法的有效性和工程实用性。     

双馈风机虚拟惯量控制策略研究

双馈风机由于其转子转速不能像传统同步机一样保持与电网频率的一致性,导致风机的机械惯性不能参与电网频率调节。针对常规虚拟惯量控制策略通过释放转子"隐藏"的动能,为电网提供转动惯量,参与频率调节,但只能为电网提供短暂的频率支撑,频率恢复过程中,还有可能导致频率二次下跌的问题。文章提出了利用储能系统协同风电场为电网补偿惯量的控制策略,在Matlab/simulink中搭建仿真模型,仿真结果表明,在电网负荷发生突变时,虚拟惯量协同控制策略能够为电网提供较长时间的频率支撑,并有效防止频率二次下跌,提高电网频率稳定性。     

全功率变频风力发电机组惯性响应控制

针对频率波动时全功率变频风电机组不能对电网提供频率支撑的问题,文章将虚拟惯性调节和下垂调节相结合,利用全功率变频风电机组的惯性控制技术参与电网调频,将风机有功出力设定在低于最大功率追踪,使其有足够空间进行有功调节,以及惯性环节结束后发电机转子转速快速恢复。仿真结果证明了文章控制策略的有效性。     

A novel method for obtaining virtual inertial response of DFIG‐based wind turbines

This paper investigates virtual inertia control of doubly fed induction generator (DFIG)‐based wind turbines to provide dynamic frequency support in the event of sudden power change. The relationships among DFIGs' virtual inertia, rotor speed and network frequency variation are analysed, and a novel virtual inertia control strategy is proposed. The proposed control strategy shifts the maximum power point tracking (MPPT) curve to the virtual inertia control curves according to the frequency deviation so as to release the ‘hidden’ kinetic energy and provide dynamic frequency support to the grid. The calculation of the virtual inertia and its control curves are also presented. Compared with a PD regulator‐based inertial controller, the proposed virtual inertia control scheme not only provides fast inertial response in the event of sudden power change but also achieves a smoother recovery to the MPPT operation. A four‐machine system with 30% of wind penetration is simulated to validate the proposed control strategy. Simulation results show that DFIG‐based wind farms can provide rapid response to the frequency deviation using the proposed control strategy. Therefore, the dynamic frequency response of the power grid with high wind power penetration can be significantly improved. Copyright © 2015 John Wiley & Sons, Ltd.     

考虑动态频率响应的风光水互补发电短期优化调度模型

针对风光并网会降低系统惯量、削弱系统调频能力的问题,综合考虑水电机组同步惯量、风电场和光伏电站的虚拟惯量和下垂控制作用,提出含风光水的多机系统动态频率响应模型,推导系统频率变化率约束、最低点频率偏差约束和准稳态频率偏差约束。基于此,为实现清洁能源利用最大化,以弃风、弃光、弃水最小及水库调度期末蓄能最大为目标,兼顾梯级水电、风电、光伏和发电系统的多种运行约束,构建风光水互补发电系统短期优化调度模型,并使用混合整数线性规划方法进行求解。最后通过算例仿真验证所提模型的有效性和适用性。     

风电机组惯量响应与一次调频能力研究

目的  风电大规模接入电网给电网运行的稳定性尤其频率稳定带来极大挑战。为改善大规模风电接入电网导致的调频能力不足,提升风电并网频率适应性能力,风电机组亟须具备调频功能及响应及时性。 方法  文章采用基于转子动能和桨距角备用的调频系统方案,在电网频率变化时可快速精确地为电网提供有功支撑。首先,在对惯量响应和一次调频算法逻辑进行理论分析的基础上,进行主控算法设计;然后,在联合仿真平台进行功能性验证;最后,在某项目进行实测。 结果  仿真和测试结果表明：基于转子动能和桨距角备用的调频系统方案可应对多种电网频率变化,快速提供有功支撑。 结论  风电机组的调频系统方案可在多种频率变化工况下进行快速地惯量响应（响应时间小于500 ms）和一次调频响应（响应时间小于5 s）,并为电网提供稳定的有功支撑,有助于辅助电网频率恢复,有效提升风电机组的频率适应性。     

Virtual inertia for variable speed wind turbines

Inertia provision for frequency control is among the ancillary services that different national grid codes will likely require to be provided by future wind turbines. The aim of this paper is analysing how the inertia response support from a variable speed wind turbine (VSWT) to the primary frequency control of a power system can be enhanced. Unlike fixed speed wind turbines, VSWTs do not inherently contribute to system inertia, as they are decoupled from the power system through electronic converters. Emphasis in this paper is on how to emulate VSWTs inertia using control of the power electronic converter and on its impact on the primary frequency response of a power system. An additional control for the power electronics is implemented to give VSWTs a virtual inertia, referring to the kinetic energy stored in the rotating masses, which can be released initially to support the system's inertia. A simple Matlab/Simulink model and control of a VSWT and of a generic power system are developed to analyse the primary frequency response following different generation losses in a system comprising VSWTs provided with virtual inertia. The possibility of substituting a 50% share of conventional power with wind is also assessed and investigated. The intrinsic problems related to the implementation of virtual inertia are illustrated, addressing their origin in the action of pitch and power control. A solution is proposed, which aims at obtaining the same response as for the system with only conventional generation. The range of wind speeds near the power limitation zone seems to be the most critical from a primary response point of view. The theoretical reasons behind this are elucidated in the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamic contribution of variable-speed wind energy conversion system in system frequency regulation

Frequency regulation in a generation mix having large wind power penetration is a critical issue, as wind units isolate from the grid during disturbances with advanced power electronics controllers and reduce equivalent system inertia. Thus, it is important that wind turbines also contribute to system frequency control. This paper examines the dynamic contribution of doubly fed induction generator (DFIG)-based wind turbine in system frequency regulation. The modified inertial support scheme is proposed which helps the DFIG to provide the short term transient active power support to the grid during transients and arrests the fall in frequency. The frequency deviation is considered by the controller to provide the inertial control. An additional reference power output is used which helps the DFIG to release kinetic energy stored in rotating masses of the turbine. The optimal speed control parameters have been used for the DFIG to increases its participation in frequency control. The simulations carried out in a two-area interconnected power system demonstrate the contribution of the DFIG in load frequency control.     

Comparison of the response of doubly fed and fixed-speed induction generator wind turbines to changes in network frequency

Synchronous and fixed-speed induction generators release the kinetic energy of their rotating mass when the power system frequency is reduced. In the case of doubly fed induction generator (DFIG)-based wind turbines, their control system operates to apply a restraining torque to the rotor according to a predetermined curve with respect to the rotor speed. This control system is not based on the power system frequency and there is negligible contribution to the inertia of the power system. A DFIG control system was modified to introduce inertia response to the DFIG wind turbine. Simulations were used to show that with the proposed control system, the DFIG wind turbine can supply considerably greater kinetic energy than a fixed-speed wind turbine.     

双时间尺度下风电主导的微电网频率控制方法

文章提出了利用风电输出特征对微电网进行频率控制的方法.该方法首先对电网一、二次调频的双时间尺度特征进行了阐述,分析了风机虚拟惯性与桨距角调整两种输出控制方法,并讨论了此两种方式在时间尺度上与电网一、二次调频的对应关系.在此基础上,设计了风机虚拟惯性参与系统一次调频,桨距角调整参与二次调频的混合频率控制方法.最后以风、光...     

基于风速预测的风电场虚拟惯量协调控制技术

针对现有风电场虚拟惯量协调控制在风电机组调频辅助功率协调分配方面的研究,提出一种基于风速预测的风电场虚拟惯量响应场级协同分配策略,具体是通过经验模式分解（EMD）和BP神经网络训练风速时序序列获得风速时序模型,预测短时段内的风速,根据实时转速和预测风速计算惯量分配权重因子,根据频率变化计算全场惯量响应值,通过惯量分配权重因子结合变流器容量限值给单机分配惯量响应值。该控制策略成功应用于云南某148.5 MW风电场站级调频测试,验证了算法的有效性。     

虚拟同步发电机自适应转动惯量策略研究

虚拟同步发电机(VSG)可在系统发生功率扰动时减小系统频率变化率和频率偏差,然而固定的转动惯量参数无法保证功率和频率的调节性能,不能使系统发生扰动时的系统频率响应兼具稳定性和快速性。因此,在离网和并网模式两种工况下提出了转动惯量自适应控制策略。首先,介绍了虚拟同步机的工作原理并分析了不同转动惯量对VSG输出频率的影响;其次,依据转子加速区和减速区的概念提出了自适应转动惯量控制策略,并利用李雅普诺夫稳定性理论证明了该算法的稳定性,给出了关键控制参数的取值原则;最后通过Simulink验证了该算法的有效性。