In recent years, environmental and energy issues have gained global significance, leading to the expanded integration of renewable energy sources. In battery energy storage systems (BESS), equipping grid-following (GFL) inverters with fast frequency response (FFR) control has attracted attention as an effective means to mitigate grid frequency deviations. These deviations are caused by fluctuations in power output from increasing renewable energy and the reduction of power system inertia due to a decrease in synchronous generators.

The performance of FFR fundamentally depends on the response time and accuracy of frequency measurement. The interpolated discrete Fourier transform (IDFT) method, while offering high accuracy in steady-state conditions and excellent tracking performance during frequency sweeps, suffers from reduced measurement accuracy due to interference from three-phase imbalance and harmonic distortion in the grid voltage. Furthermore, waveform disturbance caused by phase jumps in the grid voltage can result in frequency estimation errors exceeding 1 Hz.

This paper proposes an improved frequency measurement algorithm based on IDFT. The improvements consist of utilizing a moving average filter (MAF) to eliminate interference from negative-sequence components and harmonic distortion, and employing a specific window function in the pre-FFT signal processing to avoid waveform disturbance caused by phase jumps. Due to the operating principles of IDFT, the delay time introduced by the MAF does not affect the overall delay of the measurement algorithm, which is maintained within 40 ms.

To evaluate the performance of the proposed algorithm, simulations were conducted using MATLAB/Simulink 2022b. The simulation time step was set to 100 μs, with an IDFT window width of 40 ms and an update period of 10 ms. In the analysis, the GFL inverter is connected to an infinite bus through a filter reactance (X=8.0%) and line impedance (Z=10%, R:X=1:7). The measurement results were observed under conditions of 10% negative-sequence components, harmonic distortion, and phase jumps within a range of ±90 deg at the infinite bus. To investigate the impact of phase jumps, simulations were performed at various time intervals (20 ms and 1.7 ms increments) to account for the impact of the jump timing on the FFT sampling results.

The simulation results confirmed that negative-sequence components and harmonic distortion were successfully eliminated, leading to enhanced frequency measurement accuracy. It was also verified that frequency estimation errors due to phase jumps were suppressed to within ±0.1 Hz.

Future work will involve model-in-the-loop (MIL) simulations or hardware-in-the-loop (HIL) tests using actual inverter equipment to evaluate noise immunity, measurement accuracy, and response speed, thereby examining the overall impact on the FFR performance of BESS.