To satisfy the low sampling frequency, low computational cost and high accuracy requirements of renewable energy generation systems in the grid voltage detection link, a high-precision discrete-time frequency-locked loop (FLL) which does not need to call trigonometric functions is proposed. First, the open-loop transfer function of discrete-time reduced-order generalized integrator (d-ROGI) is derived according to the expression of voltage based on complex numbers under the static coordinate system. Then, a d-ROGI with a low approximation error is derived according to the relationship between the unknown parameter of the open-loop transfer function and frequency. On this basis, the FLL for estimating the unknown parameter is constructed, the second-order small-signal model of the FLL is established, and the corresponding parameter tuning method is given. Finally, experimental results show that the FLL has a higher detection accuracy at a low sampling frequency than the most commonly used third-order numerical integrator discretization method. At the same time, it has a lower computational cost and requires less storage according to the comparison of computation cost.
| 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 |