Hybrid Damping Strategy for Single-Phase Grid-Connected Photovoltaic Inverter under the Control of PDFI

One of the key operation of the grid-connected PV system is a fast and accurate control of the grid current, but the traditional proportional integral (PI) control of the grid current can not achieve this important goal because of its steady-state error. In addition, after the PV system is incorporated into the grid, the influence caused by grid inductance has a non-negligible effect on the damping strategy of the LCL filter. In order to solve the problems mentioned above, a hybrid damping strategy for single-phase PV grid-connected inverter under the control of PDFI is presented in this paper. This strategy introduces a proportional delay feedback integral (PDFI) control, which is based on the original PI control and can realize the control of the grid current without steady-state error due to the simple feedback circuit. Meanwhile, taking damping coefficient as object, the hybrid damping strategy has a good improvement effect on the grid inductance. The results of the theoretical analysis and Mat lab simulation both show that, under this control strategy, the system can run stably, the grid current can be controlled accurately, and the damping strategy of the LCL filter has good adaptability to the grid inductance.