This paper investigates a frequency coordination control strategy for islanded microgrid. The dynamic process is divided into three levels including the dynamic support, droop control and zero error regulation. The control strategy is classified into primary and secondary frequency regulation. Simulation is performed on DIgSILENT and the results verify the effectiveness of the proposed control strategy and improve the performance of system frequency regulation.

Electric vehicle is an important part of the smart grid. However, when electric vehicle charging station which is with massive application of the power electronic equipments connects to the grid, it will make a lot of power quality problems, especially the harmonic problems. This paper analyses the mechanism of harmonic generation caused by high-frequency charger, proposes to use APF to deal with power quality problems , and verifies the viability and effectiveness.

In this paper, the hyperbolic S-transform (HS-transform) has been generalized with the introduction of the whole time frequency regulation factor and making the HS window function proportional to the square root of the frequency. Meanwhile, combined with the idea of incomplete S-transform, a rapid power quality detection based on generalized HS-transform (GHST) is proposed. Firstly, the fast Fourier transform (FFT) was performed and dynamic measurement was utilized to describe the envelope of power spectrum so as to detect the valid frequency samples of FFT. Then the GHST was specifically performed for these samples and a complex matrix was generated. Finally, these feature vectors extracted from the complex matrix were used to detect the power quality disturbances. Simulation results demonstrate that the proposed method can accurately detect the power quality disturbances with high computation speed and low sensitivity to noise, and it is suitable for practical applications.

The excellent time–frequency resolution of the modified S-transform (MST) makes it an attractive candidate for analysis and detection of harmonic in micro-grid. This paper presents a new approach for micro-grid harmonic detection based on the MST. Firstly, the MST was performed for the harmonic signal, and then the feature vectors were extracted from the resulting time-frequency matrix. Finally, the frequency, amplitude and phase of the harmonic were obtained by analyzing and processing these feature vectors. Simulation results show that the proposed approach can detect the harmonic in micro-grid with high accuracy and strong noise immunity.

In this paper, a new approach for harmonic detection in power signals based on fast modified S-transform (FMST) is proposed, which combines the advantages of the incomplete S-transform and the modified S-transform. Initially, the Fast Fourier Transform was performed and dynamic measurement values were obtained from the envelope of power spectrum, then the valid harmonic frequency points were detected by selecting the dynamic measurement values which were larger than the set thresholds. Further, the FMST was specifically performed on these major frequency points and a complex matrix was generated. The row vectors of the matrix reflected the phase and the time location information of harmonic disturbances, while the column vectors reflected the amplitude-frequency characteristics. And the feature vectors extracted from the complex matrix were used to detect the harmonic amplitude, phase and transient information. Simulation results validate the high accuracy, strong noise immunity and rapidity of the proposed approach.