Generalized Impedance Analysis and New Sight at Damping Controls for Wind Farm Connected MMC–HVdc

Effect of Frequency Coupling on Stability Analysis of a Grid-Connected Modular Multilevel Converter System

“…In general, SCR ≥ 3 denotes a strong system; 2 ≤ SCR < 3 denotes a weak system; and 1 ≤ SCR < 2 indicates a very weak system [39,40]. Then, the stability can be examined by checking the Nyquist plot of Zg(s)YMMC(s), i.e., λ1, λ2, which are obtained as: (27) where:…”

“…Recently, the frequency coupling of MMC admittance/impedance has received considerable attention [21][22][23][24][25][26][27][28][29]. Two-order MMC impedance matrixes are proposed in [21][22][23][24][25][26], where the off-diagonal elements in the matrix capture the frequency coupling in MMC impedance.…”

“…Two-order MMC impedance matrixes are proposed in [21][22][23][24][25][26], where the off-diagonal elements in the matrix capture the frequency coupling in MMC impedance. A three-order impedance model of MMC is derived in [27], and the impedance model includes the coupling among the positive-sequence system, the negative-sequence system, and the DC system. The authors of [28,29] proposed an equivalent SISO impedance model of grid-connected MMC considering its frequency coupling, and the model shows that the frequency coupling makes the MMC impedance be coupled with the grid impedance.…”

“…Although the SISO impedance model provides simplicity and convenience for the stability analysis, some cases exist where the SISO impedance model leads to the wrong stability assessment [30]. To include the frequency coupling effect, [21][22][23][24][25][26][27] apply the MIMO impedance model of MMC in the stability analysis of MMC-HVDC, where the generalized Nyquist criterion (GNC) is inevitably introduced in the stability assessment. However, the stability assessment applied by the GNC is more complicated than the SISO analysis tool.…”

A Novel Hybrid Control Strategy for the Energy Storage Modular Multilevel Converters

“…Nowadays, modular multilevel converters (MMCs) have a rapid development in the high-voltage and high-power applications, e.g., high voltage direct current (HVDC) transmission, reactive compensation, grid integration of renewable energy generation and so on, for their high efficiency and low output harmonic distortion [1][2][3]. On the other hand, large-scale renewable energy generation system usually needs energy storage devices to absorb or release the power and effectively reduce the impact resulted from converters' output fluctuation on the power with the considerations of the intermittent and uncertain characteristics of the renewable energies [4][5][6][7][8].…”