CN111865057A - 一种分频段输出阻抗塑造的并联逆变单元控制方法 - Google Patents
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Abstract
本发明公开了一种分频段输出阻抗塑造的并联逆变单元控制方法,并联逆变单元采用LCL型输出滤波器,采样LCL型输出滤波器电容电压信号、逆变器侧电感电流信号和负载侧电感电流信号;采用电容电压外环和逆变器侧电感电流内环的双闭环控制方案,其中逆变器侧电感电流内环采用比例控制,电容电压外环采用并联的以基波和多个奇次谐波为中心频率的谐振控制器,并在各个谐振控制器的电压基准上引入负载侧电感电流前馈。本发明采用阻抗重塑思想对LCL型并联逆变单元进行分频段输出阻抗塑造,重塑LCL型滤波逆变单元的基波和谐波输出阻抗,使其在各频段内满足实际并联的阻抗特性需求,从而实现了良好的环流抑制和波形质量控制效果。
Description
技术领域
本发明属于电力电子变换器控制技术领域,特别涉及了一种并联逆变单元控制方法。
背景技术
逆变器是将直流电变换为交流电的电能变换装置,在应急供电、不停电电源、变频电源、独立微电网及新能源并网发电等领域广泛应用。逆变电源并联技术可以实现二个或多个逆变单元并联运行,实现并联扩容、提高冗余性,得到了广泛的研究和应用。
逆变器并联技术的关键是实现并联逆变单元的有功和无功功率均分,避免并联逆变单元间的环流,包括基波环流、低次谐波环流和高次谐波环流,保证并联逆变系统的工作稳定性和输出电能质量。输出阻抗重塑和下垂控制等技术是无互连线逆变器并联控制的常用技术,但现有技术仍然存在一定的缺陷。由于逆变器的基波输出阻抗通常不是纯感抗,基于有功-频率、无功-电压的简单解耦下垂控制功率分配效果不理想,虽然在解耦控制策略中可以考虑线路电阻的影响,但改进的解耦下垂控制较复杂且效果也受限。阻抗重塑可以根据并联系统的性能要求将并联逆变单元输出阻抗塑造为期望的阻抗值,进而提高下垂控制性能,但传统的输出阻抗重塑只能重塑逆变器控制带宽内的阻抗,只能控制控制带宽内的环流,难以控制控制带宽外的环流,如开关频率次及其附近频率的谐波环流。
针对应急供电、不停电电源、变频电源及独立微电网等离网应用场合,借鉴并网应用领域广泛采用的LCL滤波并网逆变器,在离网并联系统中采用LCL滤波的逆变单元代替传统的LC滤波并联逆变单元,以增大逆变模块等效输出阻抗,尤其是高频处等效输出阻抗,可以更好地抑制高频环流,同时,LCL滤波逆变单元的负载侧电感也改变了逆变器等效输出阻抗角,便于采用简单解耦的下垂控制的实现。然而,如果采用滤波电容电压反馈控制,在离网运行时,基于LCL滤波的并联逆变单元的输出电压质量容易受到负载的影响,尤其是非线性负载产生的谐波电流在负载侧电感上会产生较大的谐波电压,使输出电压出现较大的谐波畸变,因此难以保证并联系统的输出电压质量。采用负载电压反馈控制方法可以让并联逆变系统的输出特性变硬,从而提高波形质量,但是这种控制方法使得输出阻抗很小,导致逆变器间因输出幅值、相位差异引起的环流难以抑制,而且全频段低阻抗的输出特性使这种并联系统难以实现解耦的下垂控制。因此常规控制方法下LCL型滤波逆变单元在环流抑制和电压波形控制两方面难以兼顾,使得离网应用场合难以使用LCL型滤波逆变单元。
发明内容
为了解决上述背景技术提到的技术问题,本发明提出了一种分频段输出阻抗塑造的并联逆变单元控制方法。
为了实现上述技术目的,本发明的技术方案为:
一种分频段输出阻抗塑造的并联逆变单元控制方法,并联逆变单元采用LCL型输出滤波器,采样LCL型输出滤波器电容电压信号、逆变器侧电感电流信号和负载侧电感电流信号;采用电容电压外环和逆变器侧电感电流内环的双闭环控制方案,其中逆变器侧电感电流内环采用比例控制,电容电压外环采用并联的以基波和多个奇次谐波为中心频率的谐振控制器,并在各个谐振控制器的电压基准上引入负载侧电感电流前馈。
进一步地,所述谐振控制器的表达式如下:
上式中,GPR为控制器增益,Kp为比例增益,Kr为谐振系数,ωc为剪切频率,s为拉氏变换微分算子,ωok为k次谐波频率,k表示谐波次数,n为最大谐波次数,k=1时表示基波。
进一步地,所述谐振控制器采用不同的控制基准,其中,基波的控制基准为所需的基波电压值,3,5,7,…,n次谐波的控制基准为0。
进一步地,所述负载侧电感电流前馈的前馈系数为sL2,其中,s为拉氏变换微分算子,L2为负载侧电感值。
进一步地,所述负载侧电感电流前馈仅作用于各次谐波谐振控制器,不作用于基波谐振控制器。
进一步地,所述并联逆变单元采用逆变器有功、无功解耦下垂并联控制策略,按逆变单元的需要分配有功和无功功率,由有功功率决定逆变单元的基准基波频率,由无功功率决定逆变单元的基准基波幅值。
采用上述技术方案带来的有益效果:
(1)本发明实现了LCL型并联逆变单元在宽频率范围的阻抗塑造,其中基波频段呈现小感抗、低频谐波段呈现零阻抗、高频段呈现高感抗,基波频段的小感抗有利于采用简单的有功无功解耦并联环流控制,低频谐波零阻抗可保证非线性负载下的电压波形质量,高频段的高感抗可有效抑制开关频率相关的高频谐波环流;
(2)本发明无需增加额外硬件电路,便能够实现并联逆变单元的输出阻抗重塑,实现较为简单;
(3)本发明采用本发明控制方法的LCL滤波并联逆变单元结合简单的有功-电压、无功-频率解耦下垂控制策略就能实现较好的有功和无功分配控制效果。
附图说明
图1是本发明提供的LCL型滤波并联逆变单元的分频段输出阻抗塑造方法的方法流程图;
图2是本发明所述的LCL滤波并联逆变单元的滤波器结构图;
图3是本发明并联逆变单元控制方法中未加入负载侧电流前馈时的控制框图;
图4是图3所示控制策略下并联逆变单元例子的输出阻抗伯德图;
图5是在图3所示控制框图的基础上加入了负载侧电感电流前馈的并联逆变单元的控制框图,即本发明的并联逆变单元的控制框图;
图6是不采用谐波谐振控制器的LCL型滤波并联逆变单元带非线性(整流型)负载时的滤波电容电压及负载电流实验波形图;
图7是采用图3所示控制框图的LCL型滤波并联逆变单元带非线性(整流型)负载时的输出电压电流实验波形图;
图8是采用本发明的逆变并联单元控制方法的并联逆变系统的示意图;
图9是本发明控制方法结合下垂控制下的逆变单元二台并联系统的二个逆变单元的滤波电容电压、输出电流及二个单元间的环流实验波形图。
具体实施方式
以下将结合附图,对本发明的技术方案进行详细说明。
本发明设计了一种分频段输出阻抗塑造的并联逆变单元控制方法,如图1所示。
本实施例的LCL滤波逆变单元的功率电路参数如表1所示,逆变桥采用为T型中点钳位(T-NPC)拓扑,输出LCL型滤波器如图2所示,图中L为逆变器侧电感,L2为负载侧电感,C为滤波电容。
表1逆变器主电路参数
对所述LCL型滤波逆变单元中的滤波电容电压信号和逆变器侧电感电流信号进行采样,采样得到的电压和电流信号用于逆变单元的闭环控制。LCL滤波并联逆变单元采样电容电压外环和逆变侧电感电流内环的双闭环控制方案,其中电流内环使用比例控制,电容电压外环采样并联的以基波和3、5、7次谐波为中心频率的多个谐振控制器。
在本实施例中,所述谐振控制器如下:
上式中,GPR为控制器增益,Kp为比例增益,Kr为谐振系数,ωc为剪切频率,s为拉氏变换微分算子,ωok为k次谐波频率,k表示谐波次数,n为最大谐波次数,k=1时表示基波。
谐振控制器采用不同的控制基准,其中,基波的控制基准为所需的基波电压值,3,5,7,…,n次谐波的控制基准为0。控制框图如图3所示,图中C为滤波电容,KPWM为逆变桥增益,GI(s)为电流内环增益,io为负载侧电感电流,iref为电流环基准,uref为电压环基准,L为逆变器侧电感,r为逆变器侧电感寄生电阻,iL为逆变器侧电感电流。通过电容电压多比例谐振控制降低了逆变器在滤波电容端口的基波和谐波处输出阻抗,其阻抗伯德图如图4所示。
采样逆变器的负载侧电感电流io。在各次谐波谐振控制器的电压基准上引入前馈系数为sL2的负载侧电流前馈,其控制框图如图5所示,引入此前馈量后相当于在基准上补充了输出电压在负载侧电感上的电压降,即相当于在各谐波处建立了大小为sL2虚拟负阻抗,从而在谐波处抵消了负载侧电感,使逆变器在负载端口的谐波处输出阻抗接近于0,而基波处的负载端口阻抗为负载侧电感感抗(sL2),呈现纯感性,有利于基于简单的解耦控制策略实现有功和无功功率的控制均流控制的实现。另外,图6和图7的对比可以看出本发明控制方法可以极大改善LCL型逆变器带非线性负载时的电压畸变问题。
将上述控制方法结合简单的有功-频率、无功-电压解耦下垂控制策略应用于如图8所示的基于LCL滤波逆变单元的逆变器并联系统,即逆变单元的基准电压幅值和基准电压频率由下述公式给出:
ωi=ω*-kPωPi
Ui=U*-kQUQi
其中,ωi为采样电压频率,Ui为采样电压幅值,ω*为基准电压频率,U*为基准电压幅值,kPω为有功下垂系数,kQU为无功下垂系数,Pi为采样有功功率,Qi为采样无功功率。得到实验波形如图9所示,其中iH为并联环流。实验结果验证了本发明的并联逆变单元控制方法能够实现并联系统的各频段环流的有效抑制,并联系统在带非线性负载时也能保证高品质的输出电压波形。
实施例仅为说明本发明的技术思想,不能以此限定本发明的保护范围,凡是按照本发明提出的技术思想,在技术方案基础上所做的任何改动,均落入本发明保护范围之内。
Claims (6)
1.一种分频段输出阻抗塑造的并联逆变单元控制方法,其特征在于:并联逆变单元采用LCL型输出滤波器,采样LCL型输出滤波器电容电压信号、逆变器侧电感电流信号和负载侧电感电流信号;采用电容电压外环和逆变器侧电感电流内环的双闭环控制方案,其中逆变器侧电感电流内环采用比例控制,电容电压外环采用并联的以基波和多个奇次谐波为中心频率的谐振控制器,并在各个谐振控制器的电压基准上引入负载侧电感电流前馈。
3.根据权利要求2所述分频段输出阻抗塑造的并联逆变单元控制方法,其特征在于:所述谐振控制器采用不同的控制基准,其中,基波的控制基准为所需的基波电压值,3,5,7,…,n次谐波的控制基准为0。
4.根据权利要求1所述分频段输出阻抗塑造的并联逆变单元控制方法,其特征在于:所述负载侧电感电流前馈的前馈系数为sL2,其中,s为拉氏变换微分算子,L2为负载侧电感值。
5.根据权利要求1所述分频段输出阻抗塑造的并联逆变单元控制方法,其特征在于:所述负载侧电感电流前馈仅作用于各次谐波谐振控制器,不作用于基波谐振控制器。
6.根据权利要求1所述分频段输出阻抗塑造的并联逆变单元控制方法,其特征在于:所述并联逆变单元采用逆变器有功、无功解耦下垂并联控制策略,按逆变单元的需要分配有功和无功功率,由有功功率决定逆变单元的基准基波频率,由无功功率决定逆变单元的基准基波幅值。
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