Impedance measurement is an effective method to obtain the impedance characteristic of the renewable power generator (RPG). According to the measurement results, the equivalent transfer function of the impedance can be obtained for stability analysis by fitting algorithm. For accurate impedance measurement and model fitting, existing studies have proposed design methods for the amplitudes, frequency bins and phases of the wideband perturbation signal. However, the wideband signal with excessive peak value may result in over-modulation of the RPG under measurement, leading to inaccurate measurement results, which is not considered in the above methods. In order to fill this gap, this paper proposes a comprehensive design method for frequency bins, amplitudes and phases considering peak-value constrain. The evaluation method for over-modulation risk is proposed to judge whether the peak value of designed signal is excessive. The method can ensure the accuracy of impedance measurement and model fitting while using wideband signal for impedance measurement. Finally, the experiments based on Control-hardware-in-Ioop (CHIL) are conducted to verify the effectiveness of proposed method.

The transient stability of grid-following (GFL) converters is very important for power systems. This article combines the dynamics of DC-link voltage control (DVC) and phase-locked loop (PLL), and establishes a large-signal model for GFL converters. Considering bidirectional power flow, the existence and stability of the equilibrium point (EP) in the system are analyzed, and the power transmission range that enables the system to have a stable equilibrium point (SEP) is obtained. The analysis results indicate that DVC significantly alters the distribution characteristics of the EP in the system, resulting in bidirectional differences in the system's capacity to transmit power. Even if the power is within the power transmission range, the system may still lose synchronization with the power grid due to sudden changes in power. In addition, when power flows from the power grid to the converter, it may generate a “negative capacitance effect”, causing the original SEP to become unstable and weakening the power transmission capacity of the system. As a result, guidelines for designing control parameters that prevent the “negative capacitance effect” are proposed.

Generally, the measurements of modern industries are collected from different sources, which indicates that the traditional multivariate statistical process monitoring methods cannot be directly used in the multirate systems if one aims to utilize the complete multirate measurements. Hence, a set of multirate factor analysis models is developed for process modeling and fault detection purpose in the multirate processes. In the proposed model, the cross correlations are described and bounded by the common factors and the model parameters are calibrated using the expectation-maximum algorithms. Also, the proposed models are further discussed both from theoretical and geometric perspective. Finally, the proposed fault detection methods are tested by a simulated Tennessee-Eastman process and a real R2S anaerobic reactor unit in the wastewater treatment process.