CN112886844A - 一种考虑子模块电压传感器噪声的mmc建模方法 - Google Patents

一种考虑子模块电压传感器噪声的mmc建模方法 Download PDF

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CN112886844A
CN112886844A CN202110032441.XA CN202110032441A CN112886844A CN 112886844 A CN112886844 A CN 112886844A CN 202110032441 A CN202110032441 A CN 202110032441A CN 112886844 A CN112886844 A CN 112886844A
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徐雷
周欣
张育粱
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Changsha University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
    • H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation

Abstract

本发明公开了一种考虑子模块电压传感器噪声的MMC建模方法。该方法在MMC开关模型下计算子模块电压传感器噪声表达式，并结合选择的子模块电压传感器等效电路，可得到电压传感器采样噪声与占空比、寄生电阻、寄生电容之间的关系。而在MMC的平均值模型中，无法准确求得子模块电压传感器的采样噪声，因此，在忽略转换器产生的开关频率分量的情况下，构建MMC平均值模型，将噪声单元集成到子模块采样电路中，在子模块电容电压中叠加噪声分量。仿真结果也说明，在子模块电压传感器噪声较大时，受桥臂环流中的谐波分量影响，在子模块电容电压上产生谐波电压分量，影响系统安全运行。

Description

一种考虑子模块电压传感器噪声的MMC建模方法
技术领域
本发明专利涉及柔性直流输电中一种考虑子模块电压传感器噪声的MMC建模方法，属于电力技术领域。
背景技术
模块化多电平转换器(MMC)作为新一代的电压源型换流器已广泛运用于各种中压和高压领域，如海上风电场，高压直流输电和交流输电系统等应用中。与其他电源转换器相比，MMC具有易于扩展，高压质量，较小的滤波器尺寸等显著优势。
MMC在拥有众多优势的同时，对模型的精准度要求也非常高。现如今，MMC模型主要分为开关模型和平均值模型两种。在开关模型中，对子模块中的功率元器件进行详细排列描述。由于模型没有简化，开关模型具有良好的准确性，并且还可以描述与开关相关的问题。但是，代价是模型复杂，导致仿真时间过长。为了节省计算资源，提高仿真速度，通过忽略切换细节提出了平均值模型。子模块由受控的电压和电流源组成，其状态在每个开关周期中仅计算一次。在子模块数量较多的MMC系统中，平均值模型已得到了研究验证。
近年来，具有改善的开关性能的新型功率半导体迅速发展。同时，紧凑的子模块设计对于增加功率密度是有积极作用的。然而，由于紧凑的子模块设计，在较高的dv/dt和di/dt下具有更强的噪声源以及更紧密的耦合，噪声问题变得更加严重。本发明着重研究子模块电压传感器噪声(SVSN)对MMC建模的影响，而在以前的MMC模型中尚未考虑过。针对于本发明提出的问题，SVSN可能导致产生子模块电容电压波动和桥臂电流谐波。这些噪声谐波分量会影响MMC的输出质量甚至系统的安全运行。鉴于此，有必要对考虑子模块电压传感器噪声MMC系统进行建模。
发明内容
针对于模块化多电平换流器在运行过程中因子模块电压传感器噪声对MMC建模精准性的影响，本发明提出了一种考虑子模块电压传感器噪声的MMC建模方法。该方法在MMC开关模型下计算子模块电压传感器噪声表达式，并结合选择的子模块电压传感器等效电路，可得到电压传感器采样噪声与占空比、寄生电阻、寄生电容之间的关系。而在MMC的平均值模型中，无法准确求得子模块电压传感器的采样噪声，因此，在忽略转换器产生的开关频率分量的情况下，构建MMC平均值模型，将噪声单元集成到子模块采样电路中，在子模块电容电压中叠加噪声分量。仿真结果也说明，在子模块电压传感器噪声较大时，受桥臂环流中的谐波分量影响，在子模块电容电压上产生谐波电压分量，影响系统安全运行。
本发明提供了一种考虑子模块电压传感器噪声的MMC建模方法，包括：
步骤S1：子模块电压传感器等效电路构建与子模块电压波形叠加环节，根据MMC开关模型下子模块电压传感器的等效电路，通过寄生电阻和电容间耦合得到的噪声同电容电压的叠加，得到考虑采样噪声下的子模块电容电压波形示意图。
步骤S2：子模块电压传感器噪声计算环节，根据电容电压波形示意图，通过积分运算得到MMC开关模型下子模块电压传感器噪声表达式。
步骤S3：平均值模型噪声集成环节，由于平均值模型中无法准确得到采样噪声，将采样噪声单元集成到MMC平均值模型中。
有益效果
在MMC的子模块中，SVSN通过分压器和SM中点之间的寄生电容耦合。噪声幅度取决于占空比的变化。考虑到SVSN，通过在开关模型中添加寄生耦合电容器和在平均模型中添加噪声单元，可以改善开关模型和平均模型。提出的切换模型和平均模型与实验结果相符。所提出的模型可以描述SM电压不平衡和臂电流谐波。
附图说明
图1是本发明提供的MMC拓扑结构图；
图2是本发明提供的电压传感器等效电路图；
图3是本发明提供的叠加子模块噪声的子模块电压波形图；
图4是是本发明提供的MMC平均值模型子模块电压等效图。
具体实施方法
图1所示的MMC拓扑由6个桥臂组成，每个桥臂包含有多个并联电容器的半桥子模块和一个串联的桥臂电抗器，每个子模块单独控制，可以插入或旁路电容器。6个桥臂共同输出所需的电压，以实现交流侧和直流侧之间的功率交换，并处理转换器的内部能量平衡。图中，idc为直流侧电流；Vdc为直流母线电压；ipj,inj分别为上桥臂和下桥臂电流；upj,unj分别为上桥臂和下桥臂电压；ij为交流测输出电流；uj为交流测输出电压；L0,Lt分别为桥臂电感和交流测电感；R0，Rt分别为桥臂电阻和交流测电阻。
根据图1定义的电流方向，相电流，环流与上下桥臂电流的关系式为
Figure BDA0002891103080000031
式中，idiffj为j相环流。
在理想条件下，MMC交流测输出的相电流ij，相电压uj可以表示为
Figure BDA0002891103080000035
式中，Uj，Ij分别为相电压幅值和相电流幅值；ω基波角频率；
Figure BDA0002891103080000032
为输出电流相位。
利用式(2)中相电压uj的表达式，可以得到上下桥臂调制信号sp_n(j)的表达式为
Figure BDA0002891103080000033
式中，m为j相电压调制比。
综合式(1)和式(3)，可以得到桥臂子模块电压和的表达式为
Figure BDA0002891103080000034
式中，Carm为桥臂电容之和。
当MMC系统处于高电压等级多子模块串联的工作状态运行时，子模块电容的电压传感器的噪声会对子模块电容电压平衡造成影响，特别是处于dv/dt较高的情况下，考虑传感器噪声的MMC建模显得尤为重要。本文采用通用电压传感器等效模型，如图2所示。其中Cfoll为寄生电容；Rfoll为寄生电阻。
电压传感器的DC端连接到另一个半桥子模块的dv/dt高点，使得电压传感器同MMC子模块经历相同的dv/dt。在处于dv/dt较高的环境下，电压传感器的噪声通过寄生电容Cfoll与电阻Rfoll间的耦合影响MMC的运行性能。电容Cja,Cjb的充放电状态受到子模块功率器件关断的影响，当上部IGBT打开而下部IGBT关闭时，电容充电；而当上部IGBT关闭而下部IGBT打开时，电容放电。
MMC逆变端的三个输出电压ua,ub,uc可以通过将三角波形与每个相的期望平均输出电压进行比较来生成，所需的输出电压通常在一个开关周期内保持恒定，从而减少了次谐波的产生。采样噪声波形示意图如图3所示，除直流分量和基频分量外，以二倍频为主的谐波分量也会被包含在子模块电容电压中，并且子模块电容电压被控制在纹波波动不超过10％的可控范围内。但在dv/dt较高的多子模块串联的情况下，电压传感器的采样噪声会改变子模块电容电压的幅值大小，影响系统的正常运行。
图3中，vPWM是理想情况下的输出的PWM方波；vsm是第n至n+1周期内的子模块电容电压。在第n个周期内,v(n,1)至v(n+1,1)中的子模块噪声主要受环流成分中的谐波电流分量影响，在子模块电容电压上产生谐波电压分量；在第n+1个周期内,子模块电容电压上产生谐波电压分量可分为v(n+1,1)-v(n+1,2)，v(n+1,3)-v(n+1,4)和v(n+1,5)-v(n+2,1)三个部分，其中v(n+1,2)-v(n+1,3)和v(n+1,4)-v(n+1,5)中的突降与突增是电容电压传感器中的寄生电容与电阻耦合引起的。在第n+1个周期内，采样噪声可以表达为
Figure BDA0002891103080000043
式中，vsvsn,n+1是第n+1个周期的采样噪声；T为采样周期；τ为时间常数。由上式可以发现，单个个周期内的采样噪声由周期内子模块电容采样电压的起始点和结尾点决定。vn+2,1又可以表示为:
Figure BDA0002891103080000041
其中Dn+1为第n+1个周期的占空比。
当时间常数τ大于采样周期T时，使用泰勒级数对bDn+1进行线性逼近，可以得到b的表达式为
Figure BDA0002891103080000042
由于exp(-T/τ)小于1，从式(6)中可以得到，采样噪声主要由占空比决定。固对式(6)进行省略化简可以得到采样噪声更新后的表达式
Figure BDA0002891103080000051
而在MMC的平均值模型中，无法直接从传感器等效电路中增加寄生电容引入噪声影响，固考虑将噪声单元集成到子模块的采样电路中，如图4所示
在两种MMC模型下，考虑SVSN后上下桥臂电容电压之和表达式就可以表示为
Figure BDA0002891103080000052
通过以上的几个构想的环节，我们可以通过考虑子模块电压传感器噪声的影响，建立新的MMC模型和子模块电容电压表达式，从而更加合理调控MMC电容电压以达到更好的控制效果。
以上所述仅为本发明的实施例而已，并不用以限制本发明，凡在本发明精神和原则之内，所作任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (4)

1.一种考虑子模块电压传感器噪声的MMC建模方法，其特征在于：
步骤S1：子模块电压传感器等效电路构建与子模块电压波形叠加环节，根据MMC开关模型下子模块电压传感器的等效电路，通过寄生电阻和电容间耦合得到的噪声同电容电压的叠加，得到考虑采样噪声下的子模块电容电压波形示意图。
步骤S2：子模块电压传感器噪声计算环节，根据电容电压波形示意图，通过积分运算得到MMC开关模型下子模块电压传感器噪声表达式。
步骤S3：平均值模型噪声集成环节，由于平均值模型中无法准确得到采样噪声，将采样噪声单元集成到MMC平均值模型中。
2.根据权利要求1所述的考虑子模块电压传感器噪声的MMC建模方法，其特征为步骤S1中的桥臂子模块电压和的表达式为：
Figure FDA0002891103070000011
式中，Carm为桥臂电容之和；m为j相电压调制比；ω基波角频率；
Figure FDA0002891103070000012
为输出电流相位；idiffj为j相环流；ij为交流测输出电流。
子模块电压传感器噪声会对电容电压产生影响，基于此，绘制电压传感器的等效电路，方便后文中对采样噪声的计算处理。
3.根据权利要求1所述的考虑子模块电压传感器噪声的MMC建模方法，其特征为步骤S2中的子模块电压传感器噪声计算环节为：
在第n+1个周期内，采样噪声可以表达为
vsvsn,n+1＝∫vsvsn(t)dt/T
＝[(vn+1,1-vn+1,2)+(vn+1,3-vn+1,4)+(vn+1,5-vn+2,1)]τ/T
＝(vn+1,1-vn+2,1)τ/T
式中，vsvsn,n+1是第n+1个周期的采样噪声；T为采样周期；τ为时间常数。由上式可以发现，单个个周期内的采样噪声由周期内子模块电容采样电压的起始点和结尾点决定。vn+2,1又可以表示为:
Figure FDA0002891103070000013
其中Dn+1为第n+1个周期的占空比。
当时间常数τ大于采样周期T时，使用泰勒级数对bDn+1进行线性逼近，可以得到b的表达式为
Figure FDA0002891103070000021
由于exp(-T/τ)小于1，从式(6)中可以得到，采样噪声主要由占空比决定。固对式(6)进行省略化简可以得到采样噪声更新后的表达式
Figure FDA0002891103070000022
4.根据权利要求1所述的基于考虑子模块电压传感器噪声的MMC建模方法，其特征为步骤S3中的考虑SVSN后上下桥臂电容电压之和表达式为：
Figure FDA0002891103070000023
式中，Rfoll是耦合电阻，vsmj为第j个子模块的当前电容电压，Dn为第n个周期的占空比。
将噪声单元集成于MMC平均值模型中，考虑SVSN影响的子模块拓扑如图4所示。
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