星形级联H桥STATCOM直流侧电容容值设计

The Direct Current Link Capacitance Design Consideration for Star Cascaded H-bridge STATCOM

为降低成本与提高功率密度,星形级联H桥静止同步补偿器(STATCOM)的直流电容设计越来越小。然而,小容值将会增加直流电压的二次纹波,二次纹波又将通过调制影响STATCOM的输出电压。因此,输出电压的范围发生变化,同时改变STATCOM的输出补偿电流能力。因此,为了保证STATCOM的正常工作,在设计电容时需要考虑直流电压二次纹波对容量的影响,这一点是传统的电容设计方法没有考虑到的。为解决该问题,此处根据基尔霍夫定律,在考虑直流电压二次纹波的前提下建立了 STATCOM可输出的电流范围与直流电容容值的关系。基于此关系,提出一种新的电容设计方法,据此,在保证输出容量不变时,可以设计出最小的直流电容容值。由此,系统可以在正常运行的同时降低系统成本且提高系统的功率密度。最后,搭建400 V/7 kvar的星形级联H桥STATCOM样机验证所提推导的关系与电容设计方法。

To achieve low cost and high power density , direct current link capacitance is preferred in the star cascaded H-bridge static synchronous compensator(STATCOM).However, low capacitance will result in the increase of direct current secondary ripples, which will cause voltage harmonics through modulation.Hence, the changing of the output voltage range of STATCOM will cause the compensation of current, leading to affect the output capacity of STATCOM. Thus, to guarantee operation range of STATCOM, system capacity should be a key design consideration in the design of direct current link capacitance , which has not been taken into consideration in the conventional methods.To address this issue, the relationship between the range of compensable current and the direct current link capacitance based on the Kirchhoff' s law is established. Based on this relationship, a new design consideration is proposed to achieve the minimum direct current link capacitance, which is as small as possible under certain capacity of STATCOM. Meanwhile ,the designed capacitance is small enough to achieve low cost and high power density.A 400 V/7 kvar STATCOM prototype is built to verify the derived relationship and the proposed design method.