Passivity-based control of grid-connected inverters without phase-locked loop under weak grid

Grid-connected inverters can be greatly affected when operating in weak grid (high-impedance grid), which is due to the fact that in very weak grid, the coupling between the phase-locked loop and the current ring control can lead to harmonic problems in the weak grid and even make the system unstable. When designing an analysis control system, the effects of phase-locked loop are often ignored, which has the effect of unmodeled analysis. In view of this problem, a control strategy was proposed without phase-locked loop, which combines the advantages of vector current control derived from the theory of direct power control. Considering providing more accurate and reliable voltage information for power calculations, a voltage observer based on the principle of second-order generalized integration was used, thus avoiding the use of voltage sensors and phase-locked loop. In addition, in order to make the strategy have better stability and anti-jamming ability under non-ideal conditions, a robust passive controller was designed by the derived current model. Finally, the experimental verification under the condition of high impedance and capacity grid shows that the strategy has enhanced dynamic performance and robustness. © 2022, Harbin University of Science and Technology Publication. All right reserved.