A single-phase grid-connected PV inverter with improved grid-connected current

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.