LCL滤波并网逆变器的控制策略

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。     

Grid synchronization and control of distributed generation unit with flexible load compensation capabilities using multi-output LMS-filter

This paper deals with grid synchronization and control of single-phase voltage source inverter in distributed generation (DG) systems using a multi-output adaptive filter. Besides the active power injection, the proposed control enables the inverter to compensate load harmonic and reactive currents based on the capacity of inverter. The currents to be compensated are obtained using a multi-output adaptive filter structure that operates on the principle of variable step size (VSS) least mean squares (LMS) algorithm. The main objective of VSS-LMS filter is to decompose the load current into harmonic and reactive current components and compute their RMS values. The currents extracted by the VSS-LMS filter are used in developing a flexible compensation based on load compensation factors. The load compensation factors are calculated based on the remaining capacity of the inverter and priority. Harmonic currents compensation is given first priority over the reactive currents. In addition to harmonic currents detection, the same VSS-LMS filter is used in developing a phase locked loop unit for synchronizing the inverter with fundamental point of common coupling (PCC) voltage. Synchronizing the DG inverter with fundamental PCC voltage would make the proposed control algorithm insensitive to grid voltage harmonics and frequency fluctuations. The feasibility and the efficacy of the proposed control algorithm are demonstrated using hardware-in-the-loop (HIL) based experiments.     

并网逆变器中LCL滤波器改进拓扑的对比研究

电压源并网逆变器交流侧通常采用LCL滤波器进行滤波,但LCL滤波器存在对主导次输出谐波抑制不足的问题,文中分析了这一问题,并在此基础上对4种基于LCL滤波器的改进拓扑展开对比研究,通过开环传递函数和波特图的分析,比较了这些拓扑的高次谐波抑制能力,最后通过Matlab/Simulink进行仿真验证,验证了分析结论的正确性。     

LCL滤波的三相并网逆变器电流双环控制策略

对于LCL滤波的三相并网型逆变器系统,电网电压畸变会增加网侧电流总谐波。针对该问题,分析了传统逆变侧电流单环控制策略无法有效抑制电网电压畸变对网侧电流的影响。为了增加网侧电流对电网电压畸变的抗扰性,提出了电流双环的控制策略。内环通过PI控制器实现对逆变侧电流的控制,外环通过PI+PR的控制方案完成对网侧电流的控制。通过推导系统的输出导纳的频率响应,分析了在提出方案下,网侧电流能够更有效地抑制网侧电压畸变的影响。仿真以及100kW样机的实验结果验证了该控制策略的有效性。     

具有精确非线性补偿的三相光伏并网逆变器滑模变结构控制策略

三相并网逆变器中,由于死区效应和开关延时带来的非线性将导致逆变器输出电压的严重失真,以致并网电流的总谐波失真增加。提出了一种新型的具有精确非线性补偿的三相光伏并网逆变器滑模变结构控制策略,以抑制并网电流谐波,并提高其动态响应速度和鲁棒性。该控制策略将d-q坐标变换下的非线性补偿实现于离散积分滑模控制中。分析了逆变器输出电压的非线性,并建立了相应的非线性效应模型。根据此新模型设计了离散积分滑模控制策略。该控制策略既实现了精确的非线性补偿,也保证了整个系统的强鲁棒控制,并在一个100 kW的三相光伏并网逆变器样机上得以证实。仿真和实验结果表明:所提控制策略实现了系统全局稳定性控制、动态响应快速、鲁棒性强以及优良的电流谐波抑制能力。     

An FPGA-based switching photovoltaic-connected inverter topology for leakage current suppression in grid-connected utilizations

This study presents a symmetrical photovoltaic (PV)-connected inverter topology for eliminating the common-state leakage current in grid-connected inverters. A new inverter topology is introduced that minimizes the leakage current, increases efficiency, and is economically viable because it consists of six power switches and two power diodes that, compared with similar ones, consist of the same element numbers. In this inverter, power losses are lower than popular topologies such as H5, H6, and HERIC, and the voltage stresses of the switches are reduced. These features are due to the unique composition of the inverter branches and the location of the switches and diodes and the formation of a suitable freewheeling path for the current. The freewheeling path separates the alternating current (AC) side from the direct current side in the converter and cuts off the PV array leakage current to the AC grid. This will improve network reliability indices and maintain conservation standards. Finally, the content of this method is validated by comparing the proposed inverter with the existing conventional topologies. A prototype has been implemented for the performance analysis of the proposed inverter and results presented.     

有源滤波器在d,q坐标系下的PI-模糊谐振控制

有源电力滤波器(APF)被认为将代替传统LC无源滤波器,用来治理线路上非线性负载及开关器件产生的谐波和无功电流.APF为消除谐波,逆变器必须根据指令输出补偿电流,而谐波电流随时间快速振荡变化,因此电流控制器对谐波电流的跟踪能力决定了APF的性能高低.在此分析了并联型APF的电流控制数学模型,针对并联型APF提出一种简单...     

单相LCL并网逆变器电流控制综述

并网逆变器采用LCL滤波器方式的高频滤波效果优于单电感滤波器,但是由于电容支路的引入,将明显增加控制难度.就采用LCL滤波器的并网逆变器基本控制策略而言,可以大体分为三种:采用逆变器侧电感电流反馈的间接电流控制策略,采用电网侧电感电流反馈的直接电流控制策略,以及采用部分逆变器侧电感电流和部分电网侧电感电流反馈的混合控制...     

基于多谐振电网电压前馈的并网逆变器相位补偿算法研究

在传统比例前馈并网逆变器中,使用多谐振控制能够有效抑制电网背景谐波,提高适应性。但是在弱电网情况下,电网电感会使得系统的相位裕度大幅降低并出现多谐振环节的谐振峰与0 dB线相交的问题。因此提出了一种多谐振控制器与相位补偿器的组合控制策略。首先通过在电网电压前馈回路增加多谐振控制器以抑制电网背景谐波的干扰。其次,为了解决加入多谐振控制器后系统相位裕度不足的局限性,在逆变桥PWM传递函数处增加参数自适应的相位补偿器以提升系统相位裕度。仿真与实验结果证明了提出的控制策略能够有效地提升系统的相位裕度,增强对高次谐波的抑制能力。     

不平衡情况下光伏多电平逆变器的控制策略研究

电网发生不对称故障时,电网电压中存在的负序分量会对光伏并网控制造成影响。为了消除逆变器交流侧电流和直流侧电压的谐波,采用了正、负序独立旋转坐标系的控制方法,做了基于光伏三电平逆变器的电网不平衡情况下的并网控制策略仿真。仿真结果表明采用正、负序独立旋转坐标系的控制方法,逆变器交流侧电流和直流侧电压的谐波得到有效抑制。     

带LCL滤波的SAPF电流控制点选取的研究

通过理论分析提出带LCL滤波的无源阻尼并联型有源电力滤波器(SAPF)双环控制系统电流控制点的选取方法。与传统的内外环反馈电流均取自电网侧相比,当内环反馈电流取自逆变器侧,外环反馈电流取自电网侧时,使系统稳定的阻尼电阻和比例增益取值范围较大,稳态精确度在高次谐波处略有降低,由于一般高次谐波含量较少,这种降低几乎可以忽略不计。因此,只需要较小的阻尼电阻,就可使系统达到稳定以及获得很好的稳态精确度,这样可以减小阻尼损耗,以及减小设备发热隐患;由于使系统达到稳定的比例增益值取值范围较大,可以通过适当增大比例增益的方式来提高系统的稳态精度,同时加快系统的响应速度。仿真结果验证了所提控制系统反馈电流选取方法的正确性和有效性。     

基于滤波电容电流补偿的并网逆变器控制

在并网逆变器中,LC滤波器因容易控制和具有良好的高频衰减特性而应用广泛。分析了输出滤波电容对采用LC滤波的并网逆变器并网电流幅值、相位和低次谐波的影响,提出一种采用滤波电容电流补偿和电网电压前馈的数字PI控制策略,给出了离散时间域下控制器参数的设计方法,并从电网谐波阻抗角度分析了控制器抑制电网电压扰动的能力。理论分析和实验证明,该方案能有效降低并网电流的谐波畸变率(THD),提高并网逆变器输出电能质量。     

Design and implementation of a new four-switch modified quasi Z-source inverter with improved space vector control method

This paper proposes a novel cost-effective feature as a three-phase four-switch inverter utilizing a modified quasi Z-source (MQZs) network. This inverter exploits a pulse-width modulation (PWM) control strategy based on developed space vectors to provide balanced three-phase output voltages and currents. It also has many applications such as the three-phase induction motor (IM) with adjustable speed drive (ASD) fed by a DC and/or rectified AC supply. Unlike some other similar four-switch inverters or converters, which can only work in step down (buck) mode or step up (boost) mode, this inverter can operate in both modes that depend on switching signals and due to adjusting the zero shoot-through (Zsh-th) duty cycle. It also decreases the total harmonic distortions (THD) of output voltages and currents. The MQZs inverter reduces the switching losses and the cost of topology in comparison with the conventional six-switch topologies. The utilized control strategy can work well without any extra filtering circuit in DC side to eliminate the effect of the DC-bus voltage ripples on the inverter output currents and voltages. The experimental results are found closely analogous and confirm the aforementioned features of the proposed topology compared with other traditional topologies, although the inverter output filter is a conventional LC filter.     

An Advanced Universal Power Quality Conditioning System and MPPT method for grid integration of photovoltaic systems

A photovoltaic system usually produces power quality pollutions to the interfaced power systems without a proper functioning of active filters. At present, available active filters are unable to fully suppress power grid harmonics and distortions, worsening power quality conditions within the interfaced system. This paper presents an Advanced Universal Power Quality Conditioning System (AUPQS) to interface photovoltaic systems to a power grid. In the interfaced system, an improved series active filter is designed to generate output voltages to compensate all the source voltage deficiencies and to highly suppress the grid-end current harmonics and distortions, even under unbalanced non-linear load conditions. Also, an independent single-phase inverter is suggested at the load side instead of the source side to regulate the DC-link voltage. Hence, the distortions and harmonics generated by this single-phase inverter are absorbed by the shunt filter of the AUPQS. Finally, a hybrid maximum power point tracking (MPPT) approach is proposed for effective operation of photovoltaic systems even under sudden light intensity changes and solar cells temperature variations. The overall interfaced system is designed and developed using Matlab/Simulink software. The effectiveness of the proposed AUPQS and MPPT method is further validated by simulation results.     

新型工业变流系统间谐波与次谐波特性分析

通过对新型工业变流系统主电路拓扑结构的分析,利用开关函数法对其整流器和逆变器进行统一调制建模。通过分析其交直流侧的频率变换关系,揭示交流侧谐波、间谐波与次谐波的产生过程,将3者的分析统一起来。通过新型工业变流系统变流器两侧交流系统在直流侧的互调产物,推导间谐波的理论公式及相序特性,以及直流侧的纹波频率特性,揭示新型工业变流系统中间谐波的产生机理。最后通过仿真实验验证上述理论分析的正确性。     

Active Power Injection Control for Power Converters Connected to the Grid Through an L Filter

This paper presents the design, implementation, and evaluation of a model-based controller for a general scheme of transformerless power converters connected to the grid through an L filter. The proposed controller is aimed at active power injection, and consists of a damping term over the current error in addition to a filter parameter estimation scheme. The latter provides estimates of the filter internal resistance and inductance values. It involves the fundamental and quadrature components of the grid voltage to asymptotically compensate for current harmonic peturbations. As a result, the closed-loop system fulfills the active power injection objective. The proposed controller is tested in an experimental setup and its performance is compared to that of the Proportional-Resonant controller. Experimental results are presented for a single-phase H-bridge inverter; however, the control scheme can be used in several other H-bridge based inverter topologies such as H5 and HERIC.     

光伏电源友好并网系统及其仿真研究

为提高主电网电能质量,对光伏电源并网逆变器及其控制方法进行研究和仿真。该逆变器采用DC/DC+DC/AC的双级结构,以三相瞬时无功理论为基础,将光伏并网逆变器与有源滤波器相结合,使得光伏电源不仅可以输出有功功率,还能进行无功和谐波补偿,实现友好并网。其DC/DC部分采用Boost升压电路,通过电导增量法进行最大功率跟踪(MPPT); DC/AC部分采用电压型三相桥式逆变电路和滞环控制方法。最后给出了较详细的仿真结果,验证了所采用方法的可行性。     

弱电网下计及背景谐波的多并网逆变器阻抗重塑谐振抑制方法

弱电网下多逆变器并网系统的谐振问题一直广受关注,当计及背景谐波时,逆变器的电网电压前馈环节引入正反馈通路,将进一步恶化系统的电能质量。鉴于此,提出了一种弱电网下计及背景谐波的多并网逆变器阻抗重塑谐振抑制方法。通过对逆变器的控制环节进行导纳划分,建立基于三分解导纳的多逆变器并网等效模型,并利用模态分析法得到逆变器数量和电网侧阻抗变化时系统的谐振特性。计及电网电压前馈和电容电流反馈环节,对加权电流控制进行改进,并通过公共耦合点并联虚拟导纳对逆变器进行阻抗重塑,以实现对弱电网下系统谐振的抑制。仿真结果表明,所提方法既能极大地减小背景谐波对逆变器输出电流的影响,又能有效地抑制弱电网下多逆变器并网系统的谐振。     

一种改进的LCL并网逆变器控制方法的研究

LCL型滤波器相对于L型滤波器对交流侧电流中的高频谐波有更强的抑制能力,因此也越来越多地被用于逆变器中。研究了在独立工作模式和并网逆变模式间的切换过程中如何做到无扰动切换。在独立和并网逆变两种模式下分别对空载电压和并网电流直接控制。在对比传统电压电流控制情况下,对电压电流控制进行改进。通过MATLAB/Simulink仿真平台,建立了LCL型滤波的逆变器并网模型,仿真分析证明了可行性。     

复杂电网环境下并网逆变器强迫振荡机理分析与抑制

随着现代工业的迅速发展,非线性电力负荷不断增加,电网电压中出现了大量谐波和间谐波,电网环境日益复杂,这对并网逆变器的安全稳定运行提出了新的挑战。文章详细分析了复杂电网环境下由间谐波电压诱发并网逆变器产生振荡的机理,并提出了相应的振荡抑制措施。首先介绍了电网电压中间谐波的特点及其对并网逆变器输出功率的影响,发现间谐波电压会导致逆变器输出有功功率中存在持续性的周期性波动。然后通过一个保留主导特征值的逆变器降阶模型,从强迫振荡的角度揭示了周期性的功率波动诱发并网逆变器振荡的机理与特点。在此基础上发现强迫振荡的幅值和主导特征值的阻尼强相关,并提出了直流电压控制环时间尺度的有源阻尼来抑制强迫振荡。最后通过仿真验证了本文振荡机理分析的正确性和振荡抑制策略的有效性。