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To improve the robustness of grid-connected inverter against grid impedance in a weak grid an integrated design method of LCL-filter parameters and controller parameters is proposed. In the method the inherent relation of LCL-filter parameters and controller parameters is taken into consideration to realize their optimized match. A parameter normalization scheme is also developed to facilitate the system stability and robustness analysis. Based on the method all normalization parameters can be designed succinctly according to the required stability and robustness. Additionally, the LCL parameter and controller parameter can be achieved immediately by restoring normalization parameters. The proposed design method can guarantee the inverter stability and robustness simultaneously without needing any compensation network, additional hardware, or the complicated iterative computations which cannot be avoided for the conventional inverter design method. Simulation and experiment results have validated the superiority of the proposed inverter design method.

The present paper reports the results of a laboratory experiment that aimed to investigate the residual deformation and stiffness changes of frozen silty clays under cyclic triaxial loading. Two sets of cyclic stress magnitude — namely, low and high level — were applied to the reconstituted artificial frozen soil specimens with identical properties, and the effect of six levels of confining pressure was examined. The results indicate that two distinct development categories of residual axial strain with number of loading cycles are induced by the low- and high-level cyclic stress. The dynamic Young’s modulus derived from each test experiences a significant increase with the number of loading cycles, which is partly attributed to the cyclic densification. A special observation from the tests under high-level cyclic stress along with a confining pressure of 0.3 MPa also indicates that the dynamic Young’s modulus keeps as a relatively constant value when the change of residual volumetric deformation transfers from compression to dilation. The empirical relationships were proposed to properly reflect the development of the residual axial strain and dynamic Young’s modulus with the number of loading cycles.

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