摘要
电网电压不平衡下,星形级联H桥STATCOM的三相直流电压通常被控制为相等。然而,为了应对电网的负序电压,三相调制波会变得不平衡。不平衡的调制波会减少STATCOM输出电压的阶梯数,同时还会使得三相直流电压的二次脉动不平衡,由此增加了输出电流的高频与低频的谐波含量。不仅如此,输出电流中还需要注入负序分量用来重新分配三相有功功率实现三相直流电压均衡,由此不利于电网的电能质量。为了提高电流的质量,在电网电压不平衡下将三相直流电压调节为不相等值,从而保证三相调制波的平衡且三相调制最大。基于这个思想,通过正负序分离,在满足电流平衡的前提下推导出三相直流电压参考值。同时,为了维持三相直流电压的稳定,推导了由三相直流电压偏差所产生的输出零序电压,由此分析STATCOM三相输入的功率流,发现由负序电压和零序电压产生的功率相互抵消,这就意味着STATCOM的三相直流电压可以自稳定,无需注入额外的负序电流用来实现三相直流电压稳定。最后,搭建400 V/±5 kvar的星形级联H桥STATCOM样机,验证了提出方法的可行性与有效性。
Under unbalanced grid voltage,the three-phase DC voltages of a star-connected cascaded H-bridge static synchronous compensator(CHB STATCOM)are usually controlled to be equal.However,to deal with the negative-sequence voltages,the three-phase modulation wave will become unbalanced,resulting in fewer steps of staircase voltages from the STATCOM and unbalanced second-order ripples in the three-phase DC voltage.Therefore,the content of highand low-frequency harmonics in the output current will increase.In addition,the negative-sequence components are required to be injected into the output current so as to redistribute the three-phase active power and thus realize the threephase DC voltage balance,which degrades the power quality of grid.To improve the current performance under unbalanced grid voltage,three-phase DC voltages are regulated to be different values in this paper,thus ensuring the balance of three-phase modulation waves and maximizing the three-phase modulation.Based on this idea,the reference values of three-phase DC voltage can be derived by decomposing the positive-and negative-sequence components under the premise of satisfying the current balance.Meanwhile,to maintain the stability of three-phase DC voltage,the zero-sequence voltage output due to the three-phase DC voltage shift is derived to analyze the three-phase power flow input to the STATCOM.It is found that the powers induced by the negative-and zero-sequence voltages offset each other,meaning that the three-phase DC voltage in STATCOM can realize self-stabilization without injecting additional negative-sequence current.Finally,a star-connected CHB STATCOM of 400 V/±5 kvar was built,and experimental results verified the feasibility and effectiveness of the proposed method.
作者
华明
管松敏
朱永亮
HUA Ming;GUAN Songmin;ZHU Yongliang(Nanjing Research Institute of Electronics Technology,Nanjing 210039,China)
出处
《电源学报》
CSCD
北大核心
2020年第4期165-171,共7页
Journal of Power Supply
关键词
级联H桥STATCOM
不平衡电网电压
谐波特性
三相直流电压自稳定
cascaded H-bridge static synchronous compensator(CHB STATCOM)
unbalanced grid voltage
harmonic performance
three-phase DC voltage self-stabilization
