This paper presents an effective method, which can address the existing dc-link double-line-frequency voltage ripples in single-phase grid-connected PV inverters, to improve the grid-connected current. The instantaneous power pulsations at grid side cause double-line-frequency fluctuations of the dc-link voltage in single-phase grid-connected PV systems. A PI controller is generally used to regulate the dc-link voltage and its output is used to generate the grid-connected current reference. Since the PI controller cannot effectively attenuate the double-line-frequency components, the generated grid-connected current reference suffers from harmonic components. As a consequent, the actual current injected to the grid also contains the undesirable harmonic components, which leads to a high total harmonic distortion (THD). To improve the grid-connected current, an adaptive filter, which can filter the double-line-frequency voltage ripples, is inserted into the dc-link voltage feedback control loop in this research work. In this way, the generated grid-connected current reference can be free from the negative effects of dc-link double-line-frequency voltage ripples. The principle of the proposed approach is presented in detail, and the simulation as well as the experimental results corroborates the theoretical analysis.
Furong Xiao, Lei Dong, X. Liao
The 27th Chinese Control and Decision Conference (2015 CCDC)