Systematic design method for PI controller with Virtual Resistor-based Active Damping of LCL filter

The Virtual Resistor based Active Damping(VR-AD) is widely employed in converters connected to the grid via LCL filters in order to mitigate the inherent resonance of the filters. Nevertheless, in digitally controlled systems, the PWM and the calculating delays modify the system characteristics in terms of frequency and phase, thus destabilizing the system and degrading the VR-AD performances, mainly in low switching frequencies. Moreover, the stability of the system is greatly affected under weak grid operation characterized by large grid impedance variation. This paper solves these problems by proposing a systematic, robust and optimized design procedure of voltage oriented PI control(VOC) with VRAD. The considered design procedure ensures robust control(sufficient stability margins) and high quality of grid current(reduced steady-state error and minimized THD value) despite the negative impact of digital time delay, grid impedance variation and filter parameters change. Simulation and experimental results are presented to show robustness and efficiency of the suggested design procedure.

A Novel Control Strategy of PWM Rectifier with LCL Filter Under Unbalanced Grid Condition

The paper presents a successful design and good result of grid voltage feed-forward control strategy with no damping regulator of LCL filter applied in Three-phase Pulse Width Modulation( PWM) rectifier under unbalance grid condition for renewable energy processing. It is demonstrated that the closed-loop current control is decoupled with the grid voltage feed-forward control,and good waveform of grid current with low order harmonics is obtained under unbalance grid condition. This novel strategy is simple and reliable,applied with PI regulator but no resonant controller in α,β two-phase stationary frame. Moreover,the results of experiment and simulation are also illustrated to validate the novel strategy well applied in the closed-loop current control system under unbalanced grid condition.

Single Current Feedback Control Strategy for Grid-connected Inverters With LCL Filters

LCL滤波器广泛应用于并网逆变器系统中,其对高次谐波具有良好的衰减作用;但LCL滤波器为低阻尼三阶系统,容易发生谐振。传统的有源阻尼方法,通过对电容电流进行采样并反馈,能够抑制系统振荡,但增加了传感器数量。提出一种单电流反馈控制策略,其采用入网电流两次微分的反馈方法,增加了系统阻尼,从而有效地抑制LCL滤波器的谐振尖峰,保证系统的稳定性;同时其对系统参数不敏感,并且不增加额外的传感器,是一种低成本高可靠性的控制策略。文中推导该控制策略下的系统传递函数,并分析系统的稳定性。最后,通过仿真和实验,验证提出的控制策略的可行性与有效性。

A Control Strategy for Grid-connected Inverters With LCL Filters

把LCL滤波器作为电压源型并网逆变器与电网的接口已受到广泛关注。与单电感L滤波器相比，利用电感值较小的LCL滤波器对入网电流的高次谐波具有显著的衰减效果，特别是在低开关频率的大功率并网逆变系统应用中更具明显优势，但是仅采用直接入网电流控制时，LCL滤波器接口的并网逆变器系统存在稳定性问题。该文采用电网侧电感电流和逆变侧电感电流双闭环控制策略对并网电流进行直接控制，电网侧电感电流作为外环更容易抑制并网电流的谐波因素，且可以直接控制入网电流的单位功率因数，采用逆变器侧电感电流作为内环可以增加系统阻尼，从而可抑制系统振荡，增加系统稳定性。对该方案进行系统建模，并深入分析了滤波器参数、控制器参数及系统稳定性之间的精确量化关系。仿真和实验结果表明，该控制策略既可有效抑制入网电流谐振和实现进网电流的高功率因数运行，同时又具有良好的稳态和动态性能。

Dual-loop Control Strategy for Grid-connected Inverter with LCL Filter

As to the concrete topology of three-phase LCL type grid-connected inverter with damping resistance, mathematical model was deduced in detail, using method of equivalent transformation to the structure diagram, damping resistance was virtualized, mathematical model under the DQ frame that can realize decoupling control was established, a dual-loop control strategy for grid-connected inverter with LCL filter was proposed, the system stability was analyzed and the design method of controller was given. The proposed method overcame the flaws of loss increase, efficiency reduce and cost increase which were caused by damping resistance in LCL type grid-connected inverter, the system efficiency and power supply quality of the output were improved. Feasibility and effectiveness of the new method were validated by simulation and experimental results.

基于双二阶滤波器的LCL型并网逆变器延时补偿方法

为了抑制LCL型滤波器的谐振尖峰,电容电流反馈有源阻尼被广泛应用于LCL型并网逆变器中。由于数字控制延时带来的不利影响,电容电流反馈有源阻尼的阻尼性能被严重削弱。负阻尼区域出现在f_(s)/6到f_(s)/2之间,减弱了并网逆变器的稳定性和对电网阻抗变化下的鲁棒性。在电容电流反馈通道上插入一个双二阶滤波器来补偿数字控制延时带来的相位滞后,正阻尼范围可以扩展到f_(s)/3,从而实现了对电网阻抗变化的高鲁棒性。选择了合适的离散化方法,分析了补偿后的系统稳定性。提出了一个详细的闭环参数设计流程,以获得良好的控制性能。最后,实验结果验证所提方法的有效性和参数设计流程的可行性。

弱电网下LCL逆变器的有源阻尼控制策略研究

在弱电网中,由于电网阻抗的存在,会导致新能源并网LCL滤波器固有谐振频率发生偏移,传统有源阻尼控制策略则无法保证系统的稳定性。而且随着新能源发电在电力系统中的占比不断提高,如何降低运营成本成为了研究热点。因此本文提出一种基于并网电流和公共耦合电压反馈的新型控制策略,该控制策略不仅提供了有源阻尼以抑制LCL谐振,而且减少了传感器的使用,还能对大范围变化的电网阻抗有较强的适应能力。通过仿真和实验表明,与传统的控制策略相比,在改进的策略下弱电网的实用范围增加,系统的稳定性得到提高,对谐波的抑制能力提升,并网电流质量有了良好的改善。

LCL并网逆变器滤波参数近似计算方法

在高频谐波衰减系数相同的条件下,LCL型滤波器的体积和感量要明显小于L型,但是其约束条件有所增加,参数计算也变得更加复杂,不仅要考虑并网电流的质量,还需要关注逆变器侧电感电流纹波和无功功率等限制条件。为简化计算流程,基于有源阻尼提出一种LCL型并网逆变器滤波参数近似计算法。首先,分析拓扑再利用仿真软件分析逆变器输出电压的谐波含量;其次,对滤波器设计相关约束条件的优先级进行重新排序,以谐振比为关键参数推导出计算公式,以谐振频率为关键参数快速计算出总电感值,再综合各个参数的极限值,给出设计流程图,并进行误差分析;最后,通过流程图输出一组参数进行仿真和实验分析,证明所提出的LCL滤波参数计算方法的合理性和有效性。

基于广义积分器二自由度PID控制的LCL逆变器

传统有源阻尼控制可抑制LCL逆变器谐振,但需要增加额外的电压或电流传感器。为此,提出了一种无需额外传感器的基于广义积分器的LCL并网逆变器单电流反馈二自由度PID控制(GI-2DoF-PID),GI-2DoF-PID比例积分环节实现并网电流无静差跟踪,而基于广义积分器的微分环节则增强LCL逆变器的阻尼特性。推导了控制系统的传递函数,分析了其稳定裕度与动态特性,提出跟踪和抗扰动优化的参数设计原则并选取了合适的控制参数。最后,构建了基于PLECS系统仿真模型,仿真结果表明:基于GI-2DoF-PID控制的LCL并网逆变器可以有效抑制谐振;电网电压严重畸变时,其满载并网电流畸变率仅为3%,远低于国家标准的要求;当系统从半载跳变到满载时,系统超调量低,响应速度快。

基于虚拟导纳的LCL型并联有源电力滤波器鲁棒电流控制

基于电网电流和逆变侧电流的双环电流控制策略因其固有的有源阻尼作用而成为LCL型并联有源电力滤波器的研究热点,但控制回路中不同有源阻尼共存将导致系统特性难以确定。对此,通过虚拟导纳模型准确评估了系统的阻尼特性,发现其有源阻尼区域会随电网阻抗波动而变化,最大接近1/3采样频率;考虑LCL初始谐振频率处于不同的频率范围情况,利用开环极点及鲁棒性分析得到适用于不同情况的统一稳定性约束条件,并对应提出了一套鲁棒控制参数设计方法,从而充分保证电网阻抗波动下并联有源电力滤波器的稳定运行。在一台380V、45A的实验样机上验证了所提理论及控制策略的有效性。

并网逆变器分裂电容型LCL滤波器参数优化设计

现有并网系统中传统LCL滤波器有效解决了电流谐振问题,而分裂电容型LCL滤波器则进一步降低了阻尼电阻的功率损耗。针对分裂电容型LCL滤波器的参数配置繁琐、计算密集、准确性低等问题,提出一种基于NSGAⅢ多目标优化算法来设计滤波器的参数,并给出了滤波器参数寻优的实现流程。仿真结果表明,该方法不仅改善了滤波性能和系统稳定性,还降低了功率损耗,大大降低了设计过程对经验的依赖,滤波器参数设计更加具有普适性。

应用于光伏发电的LCL型并网逆变器设计仿真

为提高并网逆变器输出电能的稳定性,建立双环控制策略模型,同时采用无源阻尼法中电容串联电阻的方法抑制LCL型滤波器的谐振尖峰问题。利用MATLAB/Simulink,搭建了光伏并网逆变器系统模型进行仿真验证。结果表明,该方案抗干扰能力强,并网电流和电网电压基本同相,实现单位功率因数并网,具有良好的稳定性。

Optimized damping for LCL filters in three-phase voltage source inverters coupled by power grid

The application of LCL filters has become popular for inverters connected to the power grid due to their advantages in harmonic current reductions. However,the power grid in a distribution system is non-ideal, presenting itself as a voltage source with significant impedance. This means that an inverter using an LCL filter may interact with other grid-connected inverters via the nonideal grid. In this paper, damping optimization of LCLfilters to reduce this interaction is studied for a three-phase voltage source inverter(VSI). Simulation results show that resonant oscillation occurs in a distributed power grid, even if the VSI with an LCL filter is well designed for standalone applications. A small-signal analysis is performed to predict this stability problem and to locate the boundary of the instability using an impedance approach. Based on these analytical results, optimized damping of the LCLfilter can be designed. The oscillation phenomena and optimized damping design are verified by simulations and experimental measurements.

基于改进无源性控制的三相LCL并网逆变器输出导纳重塑方法

基于能量函数的无源性控制(PBC)被广泛研究并用于并网变换器以获得更好的控制性能.然而,传统的PBC方法依赖并网变换器的精确数学模型,且已有研究较少考虑数字控制的延迟效应以及电容性电网或复杂弱电网下电网阻抗的不确定性对系统稳定控制的影响.鉴于此,针对三相LCL并网逆变器提出一种改进PBC方法以实现导纳重塑,通过增加电容电流前馈将系统无源区域扩展到奈奎斯特频率,在电网阻抗宽范围变化下实现LCL谐振频率的有源阻尼控制,并提出改进PBC控制参数设计方法.在3 kW并网逆变器样机平台上开展仿真和实验研究,验证了理论分析的正确性.

弱电网下LCL并网逆变器新型复合有源阻尼策略

为抑制并网逆变器LCL滤波器在弱电网中产生的谐振,提出一种基于二阶滤波器的有源阻尼控制策略,对参数进行设计,在减少高精度传感器使用数量、考虑控制延迟的情况下,有效抑制谐振。为了进一步提高由于电网阻抗的增加引起的下降的相位裕度,引入超前相位补偿,构成新型复合有源阻尼策略,有效提高逆变器并入弱电网系统的稳定性和鲁棒性。最后,在MATLAB/Simulink仿真平台和MWINV-9R144三相桥式逆变器实验平台对该策略进行验证。结果表明,当电网阻抗较大时,采用新型复合有源阻尼策略依旧能有效提升逆变系统稳定性,在弱电网中具有较强的适应能力。

LCL电压型整流器模型预测优化控制

传统的LCL整流器模型预测控制需要附加有源阻尼算法MPC-AD(model predictive control-active admping)来消除LCL滤波器引起的谐振问题,此时由于网侧电流由整流器侧电流间接控制,导致其控制性能不佳。为此提出了一种基于LCL滤波的电压型整流器VSR(voltage source rectifier)有限控制集模型预测优化控制策略。利用模型预测控制中多变量控制的特性,通过构建单个代价函数同时控制网侧电流矢量、滤波电容电压矢量以及整流器侧电流矢量(MPC-i_(1)i_(2)u_(c)),无需状态变量反馈有源阻尼,然后通过所构造的代价函数J来选取下一时刻最优开关状态作用于系统。为验证所提出方法的可行性,进行仿真实验并搭建测试样机。通过与传统的MPC-AD控制方法进行比较,验证了所提优化控制策略的可行性与优越性。

LCL-resonance damping strategies for grid-connected inverters with LCL filters: a comprehensive review

Grid-connected LCL-filtered inverters are commonly used for distributed power generators. The LCL resonance should be treated properly. Recently, many strategies have been used to damp the resonance, but the relationships between different damping strategies have not been thoroughly investigated. Thus, this study analyses the essential mechanisms of LCL-resonance damping and reviews state-of-the-art resonance damping strategies.Existing resonance damping strategies are classified into those with single-state and multi-state feedback. Singlestate feedback strategies damp the LCL resonance using feedback of a voltage or current state at the resonance frequency. Multi-state feedback strategies are summarized as zero-placement and pole-placement strategies, where the zero-placement strategy configures the zeros of a novel state combined by multi-state feedback, while the poleplacement strategy aims to assign the closed-loop poles freely. Based on these mechanisms, an investigation of single-state and multi-state feedback is presented, including detailed comparisons of the existing strategies. Finally,some future research directions that can improve LCL-filtered inverter performance and minimize their implementation costs are summarized.

弱电网下LCL换流器谐振的自适应抑制研究

LCL型换流器因其体积小,滤波性能好等优点广泛地应用于并网系统。但其自身的谐振问题不可忽略,电容电流反馈有源阻尼是常用的谐振抑制方法。在实际应用中,电网阻抗能够对LCL滤波器谐振产生影响。基于此,提出一种基于遗传算法优化RBF神经网络的自适应谐振抑制方法,该方法依据遗传算法对RBF神经网络进行初始参数的优化,利用RBF神经网络自身的辨识能力对PI控制器的参数进行识别,实时修正PI控制器参数和有源阻尼系数,从而实现LCL型换流器在电网阻抗变化时保持系统稳定。最后分别采用传统无参数优化方法、RBF神经网络优化方法以及所提方法进行实验,通过仿真结果的分析,验证了该方法的有效性。

含LCL滤波的全桥变流器参数设计与改进控制策略

分布式电源通过电力电子装置并网引发的谐波问题日益凸显,采用滤波环节去除电网侧高次谐波成为重要解决方案。其中,LCL滤波是一种有效的滤波结构,但其高阶特征使系统控制策略更加复杂。为提高LCL滤波器接入后并网变流器的谐波抑制能力和运行稳定性,推导了LCL滤波全桥变流器运行控制数学模型,提出了LCL滤波结构设计和参数计算方法,设计了基于准比例谐振控制和比例积分控制的电压-电流双闭环控制策略,提出了基于带通滤波器和信号限幅环节的控制策略改进方案。算例测试表明,本文方法能够基于LCL滤波器实现精准的谐波抑制,同时避免高阶滤波器谐振问题,改善了LCL滤波并网变流器在复杂运行环境下的谐波抑制能力和控制稳定性。