A decoupling method based on reference current feedforward for DQ-frame PI current control of grid-connected voltage source converters

Axes cross-coupling in dq-frame will deteriorate the current control performance, especially for applications with low pulse ratios. Decoupling methods based on inductor current state feedback (ICSF) and complex vector PI controllers (cVPI) have been proposed and performed to decouple the axes cross-coupling in dq-frame. In this paper, the axes cross-coupling is analyzed and described with complex-coefficient transfer function. It was pointed out that the dq-frame axes cross-coupling mostly attributes to the lagging phase angle of the plant at the operating frequency. And the closed-loop system with good decoupling performance should present a symmetrical bode diagram with respect to its operating frequency. A new decoupling method based on reference current feed-forward (RCFF) was proposed to deal with the axes cross-coupling. Its decoupling performance was compared with the other two methods (ICSF and cVPI). ICSF, cVPI and the proposed RCFF methods can be considered as three basic types of decoupling methods. The advantages and disadvantages of each decoupling technique were discussed and compared in this paper.