CN112152231B - 链式statcom子模块直流电压均衡控制方法 - Google Patents

链式statcom子模块直流电压均衡控制方法 Download PDF

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CN112152231B
CN112152231B CN202010936310.XA CN202010936310A CN112152231B CN 112152231 B CN112152231 B CN 112152231B CN 202010936310 A CN202010936310 A CN 202010936310A CN 112152231 B CN112152231 B CN 112152231B
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陈继开
胡阳
李国庆
王振浩
辛业春
金国彬
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
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Abstract

一种链式STATCOM子模块直流电压均衡控制方法，属于电力系统无功补偿技术领域。本发明的目的是根据H桥子模块数量和等效电容容值来自适应地修正载波频率，以提高链式STATCOM的子模块直流电压均衡能力基于非整数倍载波频率调制的链式STATCOM子模块直流电压均衡控制方法。本发明步骤是：计算第m相H桥子模块直流电压的不平衡度，判断H桥子模块直流电压不平衡度是否超标，启动子模块直流电压均衡控制方法。本发明解决CPS‑SPWM调制（载波相移正弦脉宽调制）导致的链式STATCOM各相H桥子模块直流电压不均衡的问题。

Description

链式STATCOM子模块直流电压均衡控制方法
技术领域
本发明属于电力系统无功补偿技术领域。
背景技术
链式STATCOM是当前主要的动态无功补偿装置之一，其多应用于中高压配网场合，CPS-SPWM载波相移正弦脉宽调制是其主要的调制方法。相比于其他应用在链式STATCOM的调制策略，如阶梯波脉宽调制、消除特定次谐波调制、SVPWM调制等，CPS-SPWM调制易于实现、在等时间内单模块开关次数几乎相等，能够在较低开关频率下获得良好的基波输出。但是由于CPS-SPWM调制本身的局限性，载波的相位差异会引起输入单个H桥子模块的有功功率不相等，导致子模块电容电压出现不均衡问题，，所以改进子模块直流电压控制方法，维持其直流侧电容电压的均衡一直是国内外学者的研究热点。
发明内容
本发明的目的是根据H桥子模块数量和等效电容容值来自适应地修正载波频率，以提高链式STATCOM的子模块直流电压均衡能力基于非整数倍载波频率调制的链式STATCOM子模块直流电压均衡控制方法。
本发明步骤是：
改变载波频率控制各子模块电容电压平衡，使电容电压差异保持在一定范围，具体实施方法如下：
(1)计算第m相H桥子模块直流电压的不平衡度
采集第m相子模块直流电压有效值Udcmi，按照式(1)计算第m相H桥子模块直流电压的不平衡度
Figure BDA0002672052800000011
式中，N为级联H桥子模块数，i为每相子模块的编号；
(2)判断H桥子模块直流电压不平衡度是否超标
Figure BDA0002672052800000012
式中，CT为非链式两电平STATCOM直流侧等效电容，w1和w2为对应权重；
(3)启动子模块直流电压均衡控制方法
一、按照式(3)在整数倍载波频率fc上叠加频移量，获得非整数倍载波频率fmi，表示为：
Figure BDA0002672052800000021
式中，α为调整因子(1≤α≤1.1)，θ为1个基波周期后相邻检测获得的两个相邻载波之间的相位差；
二、利用式(1)调整第m相中N-1个H桥子模块对应的载波频率
STATCOM第m相中保持1号子模块载波频率不变，根据公式(3)调节后续2号～N号子模块的载波频率fmi；返回步骤(1)，若子模块直流电压回复平衡速度低于预期，可改变调整因子α，使其提高电压平衡调整速度。
本发明解决CPS-SPWM调制(载波相移正弦脉宽调制)导致的链式STATCOM各相H桥子模块直流电压不均衡的问题。
附图说明
图1是并网链式STATCOM主电路示意图；
图2是CPS-SPWM三个模块调制示意图；
图3是载波频率为500Hz下各模块直流电压；图3a为三个子模块直流电压；图3b是三个子模块间直流电压差的绝对值；
图4是载波频率为516.7Hz下各模块直流电压；图4a为三个子模块直流电压；图4b是三个子模块间直流电压差的绝对值；
图5是载波频率为483.3Hz下各模块直流电压；图5a为三个子模块直流电压；图5b是三个子模块间直流电压差的绝对值。
具体实施方式
链式STATCOM主电路拓扑如图1所示，三相之间采用星型连接方式，主拓扑为H桥子模块级联，其中usa,usb,usc为三相电网电压，ua,ub,uc为STATCOM三相输出电压，ica,icb,icc为STATCOM三相电流，L为连接电抗，R为连接电感寄生电阻，isa,isb,isc为三相负载电流。
采用CPS-SPWM对链式H桥三模块STATCOM进行调制控制，三个子模块调制电压波形如图2所示。由图2推知，若级联H桥子模块数为N，则相邻H桥子模块的载波初相位依次相差π/N。将H桥电容左右两侧的两个桥臂看做独立整体，左桥臂的调制波为原调制波，，右桥臂的调制波为与原调制波极性相反的调制波，左右桥臂共用一个三角载波，同一桥臂上的两个开关器件开关信号反相。并网链式STATCOM在进行无功补偿时，需要从电网吸收少量的有功功率以补足其正常运行所发生的损耗。但是由图2可知，CPS-SPWM调制会使STATCOM每相内各子模块的触发脉冲存在相位差，交流侧输出电压之间存在相移，从而使相内各模块直流侧电容在单个载波周期内的充放电时间不一致，导致各子模块间电容电压出现不平衡现象。子模块电容电压失衡程度的加剧，不但会导致个别H桥子模块电压过高，增加开关器件承受应力，而且可能导致STATCOM输出谐波电流污染电网。
本发明是解决CPS-SPWM调制(载波相移正弦脉宽调制)导致的链式STATCOM各相H桥子模块直流电压不均衡的问题，提出的基于非整数倍载波频率调制的链式STATCOM子模块直流电压均衡控制方法。从CPS-SPWM调制机理出发，通过改变载波频率控制各子模块电容电压平衡，使电容电压差异保持在一定范围，具体实施方法如下：
(1)计算第m相H桥子模块直流电压的不平衡度
采集第m相子模块直流电压有效值Udcmi，按照式(1)计算第m相H桥子模块直流电压的不平衡度。
Figure BDA0002672052800000031
式中，N为级联H桥子模块数，i为每相子模块的编号。
(2)判断H桥子模块直流电压不平衡度是否超标
根据每相子模块电容容值Cmi和每相子模块数量N，按照式(2)设定子模块直流电压不平衡度标准E，若εm大于E，执行步骤(3)；
Figure BDA0002672052800000032
式中，CT为非链式两电平STATCOM直流侧等效电容，w1和w2为对应权重。
(3)启动子模块直流电压均衡控制方法
一、为了保证三相H桥子模块直流电压均衡，需要保证每个子模块吞吐有功功率均相等，这里按照式(3)在整数倍载波频率fc上叠加频移量，获得非整数倍载波频率fmi，表示为：
Figure BDA0002672052800000033
式中，α为调整因子(1≤α≤1.1)，θ为1个基波周期后相邻检测获得的两个相邻载波之间的相位差。
二、利用式(1)调整第m相中N-1个H桥子模块对应的载波频率
STATCOM第m相中保持1号子模块载波频率不变，根据公式(3)调节后续2号～N号子模块的载波频率fmi。返回步骤(1)，若子模块直流电压回复平衡速度低于预期，可改变调整因子α，使其提高电压平衡调整速度。
算例验证
为了验证本专利所提方法的正确性，基于MATLAB/Simulink搭建仿真模型，仿真参数为：电网电压35kV，电网频率50Hz，载波频率fc＝500Hz，连接电抗L＝5mH，H桥电容C＝4700μF，子模块直流侧参考电压为12kV，H桥级联子模块数量m＝3。
1)整数倍载波频率下子模块直流电压
图3(a)首先展示了载波频率为500Hz下的每相相内各子模块电容电压波形，由于其充放电不一致导致各子模块电容电压的不一致，相内各子模块直流侧电压出现了不平衡现象。图3(b)为载波频率fc为500Hz下的三个子模块之间的电压差值的绝对值，其中|uA1-uA2|、|uA1-uA3|、|uA2-uA3|的最大值分别为173.5V、217.7V、280.5V，平衡度εm＝a＝2.1％。
2)非整数倍载波频率下子模块直流电压
根据式(3)非整数倍载波频率应为516.7Hz或483.3Hz，图4(a)为载波频率改变为516.7Hz下A相各子模块直流侧电容电压，图4(b)为三个子模块之间的电压差值的绝对值，其中|uA1-uA2|、|uA1-uA3|、|uA2-uA3|的最大值分别为83.1V、90.3V、79.3V，相比于500Hz下三个子模块之间的电压偏差分别减少了52.1％、58.5％、71.7％，平衡度εm＝a＝0.7％；图5(a)为载波频率483.3Hz下各子模块直流侧电容电压，图5(b)为载波频率为483.3Hz下的三个子模块之间的电压差值的绝对值，其中|uA1-uA2|、|uA1-uA3|、|uA2-uA3|的最大值分别为85.8V、96.7V、82.9V，平衡度εm＝a＝0.7％，效果与载波频率采用516.7Hz的平衡效果基本一致。
仿真实验结果表明，本发明所提基于非整数倍载波频率调制的链式STATCOM子模块直流电压均衡控制方法能够实现子模块直流电压平衡，并且不用添加任何附加控制器，操作简便。

Claims (1)

1.一种链式STATCOM子模块直流电压均衡控制方法，其特征在于：其步骤是：改变载波频率控制各子模块电容电压平衡，使电容电压差异保持在工程设定范围，具体实施方法如下：
(1)计算第m相H桥子模块直流电压的不平衡度
采集第m相子模块直流电压有效值Udcmi，按照式(1)计算第m相H桥子模块直流电压的不平衡度
Figure FDA0003351583530000011
式中，N为级联H桥子模块数，i为每相子模块的编号；
(2)判断H桥子模块直流电压不平衡度是否超标
Figure FDA0003351583530000012
式中，E为子模块直流电压不平衡度标准，Cmi为每相子模块电容容值，CT为非链式两电平STATCOM直流侧等效电容，w1和w2为对应权重；
(3)启动子模块直流电压均衡控制方法
一、按照式(3)在整数倍载波频率fc上叠加频移量，获得非整数倍载波频率fmi，表示为：
Figure FDA0003351583530000013
式中，f0为基波频率，α为调整因子(1≤α≤1.1)，θ为1个基波周期后相邻检测获得的两个相邻载波之间的相位差；
二、利用式(1)调整第m相中N-1个H桥子模块对应的载波频率
STATCOM第m相中保持1号子模块载波频率不变，根据公式(3)调节后续2号～N号子模块的载波频率fmi；返回步骤(1)，若子模块直流电压回复平衡速度低于预期，可改变调整因子α，使其提高电压平衡调整速度。
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