基于PR控制和谐波补偿的三相光伏并网系统

将电网电压定向矢量控制与比例谐振(PR)控制相结合的控制策略应用于三相光伏并网系统中,实现逆变器的并网控制。该控制策略比传统PI调节器的双闭环电网电压定向控制更简便,不需要复杂的坐标旋转变换和前馈解耦控制。同时,PR控制器可以很方便地实现并网电流低次谐波的补偿。仿真结果验证了该系统的结构和控制策略的有效性,可提高电网的电能质量。     

双馈风电机组转子侧变换器改进优化控制

准比例谐振控制器在静止坐标下能够对特定频率的交流信号实现无静差控制,基于此结合双馈风力发电机的静止αβ坐标系下的数学模型,提出了转子侧变换器PR控制。该方法将电流内环的有功和无功分量转换到静止坐标系下,利用准PR控制器进行跟踪给定信号,实现了有功、无功功率解耦控制。与传统PI控制策略相比,优化的控制策略减少了坐标旋转变换,提高了控制系统的鲁棒性。在PSCAD/EMTDC环境下搭建了仿真模型,仿真结果验证了文章控制策略的有效性和无功在抑制电网电压波动的作用。     

弱电网下海上低频风电系统网侧控制和稳定性分析研究北大核心CSCD

低频交流输电技术广泛应用于海洋风电的输送,但其送出的电流质量和系统稳定性会受到网侧变流器和弱电网线路阻抗的影响。文章针对海上低频风电系统的网侧控制,研究了αβ坐标系下基于虚拟同步机(Virtual Synchronous Generator,VSG)控制方法,并引入虚拟阻抗环节实现VSG的功率解耦,使得网侧变流器能在电网频率突变时自发调频,提高了其并网电能质量和弱电网下的稳定性。考虑到VSG并网系统与弱电网之间的交互作用,利用谐波线性化方法建立了αβ坐标系下VSG并网系统的序阻抗模型,结合阻抗分析法和Nquist稳定判据分析了并网系统在弱电网下的稳定性。最后,通过仿真验证了分析的正确性。     

双馈风电场VSC-HVDC系统接入弱电网的控制研究

由于大型并网风电场有功功率与无功功率的波动导致风电场并网母线及受端弱电网系统的电压和频率不稳定,提出用电压源换流器高压直流输电(VSC-HVDC)的电压与频率控制模型控制风电场并网母线的电压和频率。建立风电场经VSC-HVDC并入大电网的电力系统数学模型,详细设计VSC-HVDC的变流器WFVSC(风电场侧变流器)和GSVSC(电网侧变流器)控制环节,在电压和功率外环及电流内环双环控制的基础上,加入频率控制,以解决电网频率发生改变时,双馈变速风机无法对电网提供频率响应的问题。建立相同条件下高压交流(HVAC)并网的模型进行比较,仿真分析风电场风速波动和风电场出口端三相短路故障两种情况下的并网点(PCC)电压与频率变化,仿真结果验证了该控制模型的正确性和有效性。     

海上风电场柔性直流输电并网系统暂态特性研究

针对基于全功率换流器的直驱式永磁同步风电机组所建海上风电场,通过高压直流输电远距离并网,研究整个系统的暂态特性。全功率换流器和并网VSC-HVDC均实现有功无功独立控制。提出在应对电网故障时新的控制策略,即故障期间换流器站间交互协调控制,遏制VSC-HVDC直流电压上升幅度过大。利用PSCAD/EMTDC平台建立整个风电场并网模型,针对风速变化、风电场集电系统故障、电网故障几种常见情况进行暂态特性分析,对电网故障时是否加入换流器站间交互协调控制系统暂态特性进行比较,研究结果验证了并网系统及相应控制方法的正确性和有效性。     

可调度型光伏并网逆变器直接电流控制策略研究

为实现光伏电站有功功率的平稳输出以及灵活调度,文章提出了一种基于优化型DDSRF-PLL锁相环的直接电流控制方案。该方案将广义二阶积分器(SOGI-QSG)与解耦双同步旋转坐标系锁相环(DDSRFPLL)相结合,并应用于直接电流控制方案中。在Matlab/Simulink软件中对控制策略进行了仿真,结果表明,该控制策略下的光伏并网逆变器可以实现有功功率的平稳输出与灵活调度,动态性能优异,抗干扰能力强。     

电网频率波动时LCL并网逆变器重复控制研究

针对电网频率波动时,并网电流畸变和谐波较大的问题,提出了静止坐标系下LCL并网逆变器的重复控制策略,该策略可有效降低并网电流谐波畸变率;在静止坐标系下,LCL并网逆变器数学模型无耦合现象,省去了复杂的解耦运算,从而该控制策略简单易实现;在确定电路参数的基础上,对重复控制进行了参数设计,并通过仿真试验证明了理论分析的正确性。研究成果对于提高电能质量意义重大。     

基于VSC-HVDC风电并网系统风电场侧故障下系统低电压穿越能力研究

针对经柔性直流输电(VSC-HVDC)并网的风电场,风电场侧故障易造成风机脱网的问题,提出了一种新型无功控制策略。该策略能充分利用故障两侧的无功源,即双馈风力发电机(DFIG)与VSC-HVDC风电场侧变流器(WFSVSC)来提供无功支持,实现低电压穿越。采用DIgSILENT软件进行仿真,仿真结果表明该控制策略能有效减小故障恢复期间的电压波动,缩短故障恢复时间,具有更好的低电压穿越能力。     

直接驱动型风电系统谐波抑制技术研究

研究一种改进的直驱风电系统谐波抑制控制策略,针对电网电压畸变或不平衡引起的低次(5、7次等)电流谐波及负序分量,提出采用在同步坐标系下电流环PI调节器并联多谐振控制器的改进控制策略,以消除并网变流器电流谐波为目标,从而改善机组并网电能质量,同时也有效抑制功率波动。采用该改进谐波抑制控制策略无需进行复合坐标系下序列分解及谐波分离滤波器,不影响基波电流控制。实验结果表明:该控制策略可有效抑制谐波电流且易于实现数字控制,具有较好的实用价值。     

微网双向变流器的解耦控制策略研究

在微电网中,双向变流器作为核心组网装置,起到稳定接入点电压,降低网损率和提高功率因数的作用。但是在同步旋转坐标系下,双向变流器是一个强耦合、非线性的系统,因此需要对其进行解耦控制,以保证并网电流能够快速无差地跟踪给定信号。研究双向变流器的解耦控制策略,对其在同步旋转d-q坐标系下的数学模型进行了推导和分析,在此基础上采用PI控制和前馈控制相结合的解耦控制方法,将原系统进行线性化解耦,消除了有功与无功电流的耦合,实现系统的解耦控制。实验结果表明,所提解耦控制策略能够降低稳态跟踪误差和总谐波失真,具有较好的控制性能。     

Coordinate control strategy for stability operation of offshore wind farm integrated with Diode-rectifier HVDC

Due to low investment cost and high reliability, a new scheme called DR-HVDC (Diode Rectifier based HVDC) transmission was recently proposed for grid integration of large offshore wind farms. However, in this scheme, the application of conventional control strategies for stability operation face several challenges due to the uncontrollability of the DR. In this paper, a coordinated control strategy of offshore wind farms using the DR-HVDC transmission technology to connect with the onshore grid, is investigated. A novel coordinated control strategy for DR-HVDC is proposed based on the analysis of the DC current control ability of the full-bridge-based modular multilevel converter (FB-MMC) at the onshore station and the input and output characteristics of the diode rectifier at the offshore. Considering the characteristics of operation stability and decoupling between reactive power and active power, a simplified design based on double-loop droop control for offshore AC voltage is proposed after power flow and voltage–current (I–V) characteristics of the offshore wind farm being analyzed. Furthermore, the impact of onshore AC fault to offshore wind farm is analyzed, and a fast fault detection and protection strategy without relying on communication is proposed. Case studies carried out by PSCAD/EMTDC verify the effectiveness of the proposed control strategy for the start up, power fluctuation, and onshore and offshore fault conditions.     

VSC-HVDC在海上风电输电系统的应用研究

海上风电须进行远距离传输,大规模风电场采用直流输电技术的运营费用比交流输电技术低。为保证风能质量和电网稳定性,提出了应用VSC-HVDC直流输电技术,重点研究该直流输电系统的控制技术特点。在VSC-HVDC稳态数学模型的基础上,提出了用于该系统的闭环PI控制器,并辅以PSCAD/EMTDC建模仿真。仿真结果表明,该控制器简便有效,能够满足稳定运行的需求。     

Control of a grid-connected direct-drive wind energy conversion system

This paper investigates the current control for a grid-connected direct-drive wind energy conversion system (DDWECS) with a permanent magnet synchronous generator (PMSG), which utilizes a back-to-back pulse width modulation (PWM) converter. For the machine-side, the controller adopts a current vector control method based on the rotating reference frame (RRF) and the maximum power extraction (MPE) is realised through the tip speed ratio (TSR) method. For the grid-side, a novel controller is proposed for the first time to be successfully used for the DDWECS, which combining a proportional complex integral (PCI) current inner loop based on stationary reference frame (SRF) for regulating the grid-side current with a dc voltage outer loop for stabilizing the dc bus voltage and compare with the proportional resonant (PR) controller. A system simulation model is established by using the Matlab/Simulink to simulate the performance of the DDWECS and a prototype system has been build and tested to verify the validity of the developed control methods for both machine-side and grid-side and the excellent performance of the DDWECS.     

考虑疲劳均衡的海上风电场主动尾流控制研究

海上风电场运行维护成本高,而其尾流效应影响更加突出,不但会影响风电场的发电效率,还会增大风电场内机组的疲劳载荷,增加运维成本。文章针对基于疲劳均匀的海上风电场主动尾流控制展开研究,通过GH-Bladed软件计算建立了风电机组在典型控制工况下关键零部件的疲劳损伤量数据库。其中的工况包括最大功率追踪、桨距角控制和偏航控制3种,并引用了量子粒子群算法,通过变桨和偏航两种方法进行优化控制,以实现海上风电场发电量提升和风电机组疲劳均匀的多目标主动尾流优化控制策略,降低海上风电场运维成本。仿真结果表明了所提出控制方法的可行性。     

超导储能对并网型风电场运行性能影响的仿真分析

采用超导储能(SMES)可以改善风电场并网运行的稳定性,针对风电系统中出现的联络线短路故障和风电场的风速扰动,提出利用超导储能安装点的电压偏差信号作为超导储能有功控制器的控制策略。为了验证这种策略的有效性,建立了风电机组和超导储能装置的数学模型,并利用MATLAB/Simulink软件搭建了风电场接入电网后的仿真模型。仿真结果表明,采用该控制策略不仅可以在网络故障后有效地提高风电场的稳定性,而且能够在快速的风速扰动下平滑风电场的功率输出,降低风电场对电网的冲击。     

Centralised power control of wind farm with doubly fed induction generators

At the moment, the control ability of wind farms is a prime research concern for the grid integration of large wind farms, due to their required active role in the power system. This paper describes the on-going work of a research project, whose overall objective is to analyse and assess the possibilities for control of different wind farm concepts. The scope of this paper is the control of a wind farm made up exclusively of doubly fed induction generators. The paper addresses the design and implementation issues of such a controller and focuses on the ability of the wind farm control strategy to regulate the wind farm power production to the reference power ordered by the system operators. The presented wind farm control has a hierarchical structure with both a central control level and a local control level. The central wind farm control level controls the power production of the whole farm by sending out reference power signals to each individual wind turbine, while the local wind turbine control level ensures that the reference power signal send by the central control level is reached. The performance of the control strategy is assessed and discussed by means of simulations illustrated both at the wind farm level and at each individual wind turbine level.     

Multi-pole permanent magnet synchronous generator wind turbines' grid support capability in uninterrupted operation during grid faults

Emphasis in this paper is on the fault ride-through and grid support capabilities of multi-pole permanent magnet synchronous generator (PMSG) wind turbines with a full-scale frequency converter. These wind turbines are announced to be very attractive, especially for large offshore wind farms. A control strategy is presented, which enhances the fault ride-through and voltage support capability of such wind turbines during grid faults. Its design has special focus on power converters' protection and voltage control aspects. The performance of the presented control strategy is assessed and discussed by means of simulations with the use of a transmission power system generic model developed and delivered by the Danish Transmission System Operator Energinet.dk. The simulation results show how a PMSG wind farm equipped with an additional voltage control can help a nearby active stall wind farm to ride through a grid fault, without implementation of any additional ride-through control strategy in the active stall wind farm.     

基于PSCAD/EMTDC的直驱式风力发电接入系统建模与仿真

针对频率可变的多极直驱式同步风力发电机接入系统,该文在考虑风力机大转动惯量的情况下,采用电网电压矢量定向和双闭环控制技术,实现了基于背靠背VSC换流器的有功无功独立控制。研究了不依赖于风速测量的直驱式机组最大功率追踪策略,桨距角控制器设计以及变风速下风电机组对电网的无功支持问题。最后通过PSCAD/EMTDC搭建了该接入系统模型,阶跃和随机风速下的仿真结果验证了该模型的合理性及控制策略的有效性。     

Wind farm non-linear control for damping electromechanical oscillations of power systems

This paper deals with the non-linear control of wind farms equipped with doubly fed induction generators (DFIGs). Both active and reactive wind farm powers are employed in two non-linear control laws in order to increase the damping of the oscillation modes of a power system. The proposed strategy is derived from the Lyapunov Theory and is independent of the network topology. In this way, the strategy can be added to the central controller as another added control function. Finally, some simulations, showing the oscillation modes of a power system, are presented in order to support the theoretical considerations demonstrating the potential contributions of both control laws.