Aimed at the issue of DC offset injection to the grid when the topology of a quasi-Z-source grid-connected inverter without isolation transformer is adopted, a DC offset suppression strategy based on an observer under weighted average current control is proposed in this paper. First, the topology of the quasi-Z-source inverter and the causes of DC offset are analyzed. Second, the order of an LCL filter is reduced from the third-order to first-order by weighted average current control, thus simplifying the system model and eliminating the resonance problem. Then, a disturbance observer is utilized to observe the DC offset of inverter output voltage in realtime, the DC offset disturbance is dynamically compensated by feedback, and its stability is analyzed. Finally, the proposed strategy was validated by experiments. Experimental results show that the proposed strategy can effectively reduce the DC offset of grid-connected current, meet the grid-connected DC offset requirement of less than 0.5%, and ensure good steady-state and dynamic performances of the inverter.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |