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.
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