电网电压不平衡下电流源并网变换器控制研究

Control of Grid-connected Current Source Converter Under Unbalanced Grid Voltage

电流源并网变换器在电网电压不平衡情况下运行时,电网电压中的负序分量会引起直流侧出现低频脉动,同时导致网侧电流出现低次谐波,影响系统运行。为了解决此问题,首先建立电流源并网变换器系统数学模型,推导出直流侧输出电流和电压关系的表达式,揭示出传统方法存在的问题。然后利用瞬时功率理论设计电流环参考指令,通过控制输入侧有功功率恒定的方式减小输出电压低频脉动。为了进一步提高系统性能,提出一种新型控制策略,通过直接控制输出侧变量消除输出电压低频脉动,同时输入侧电流正弦。最后对3种方法进行对比实验研究,结果验证了提出方法的有效性。

The grid-connected current source converter may operate under unbalanced grid voltage conditions. The negative sequence component of grid voltage would result in the low-frequency ripple at dc side, as well as current harmonics at ac side. And these problems have adverse impacts on the system operation. In order to cope with them, the mathematic model of the grid-connected current source converter was established. The limitation of the conventional control strategy was clarified based on the mathematic equation of dc-side current and voltage. And then the current reference was designed based on the instantaneous power theory. The output voltage ripple can be reduced by controlling the input active power constant. In order to further enhance the system performance, a new control strategy was presented. Instead of input-side control, the proposed solution eliminates the low-frequency ripple from the output-side-control perspective. Finally, the comparison evaluation was carried out, and the experimental results verified the effectiveness of the proposed solution.