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Under the traditional line protection approach, the problem of external faults not being addressed by the Peterson principle is resolved by solving the voltage and current fluctuation equations that satisfy the boundary conditions derived from the transmission line equations, this allows for the derivation of closed analytical solutions for the measured point voltages for different fault locations. In this paper, according to the threshold of the protection criterion, the pre-estimation of the fault point resistance and the fault pole selection are realized, a hybrid three-terminal DC line cooperative control and protection strategy based on estimated fault characteristics is proposed. Firstly, a start-up criterion considering estimated fault characteristics is constructed to achieve reliable start-up during high-resistance faults. Secondly, a ratio braking transverse differential protection is proposed to identify forward and reverse faults reliably. The control strategy is chosen based on the estimated fault characteristics, resulting in a comprehensive approach to cooperative control and protection of lines. The proposed method can quickly suppress the fault current by introducing a phase shift and negative input of converter voltage when a metallic fault occurs in the line. In the case of high resistance faults, the control system intentionally delays taking the action and waits for the control strategy to be corrected based on the results of the opposite end in the process. Multiple simulation scenarios show that the protection method is reliable and can quickly identify the line faults. The proposed method has effectively resolved the problem of high resistance in line protection through the process of “pre-estimation-correction”.

High-speed traveling wave acquisition devices often use a mutation start algorithm with a low threshold value, which can collect a large number of interference clutters. If the devices automatically screen out a flashover fault traveling wave from a massive traveling wave, the traveling wave fault location performance could be improved. In this paper, a fault and interference classification method based on the random forest algorithm, which uses a convolutional neural network as a supervised feature extractor of traveling wave data, is proposed. First, one-dimensional traveling wave data are mapped to a two-dimensional matrix by dividing the information section, and a gray image is used to characterize it. Next, a two-dimensional convolution neural model of traveling wave data is constructed to realize the self-learning of traveling wave data characteristics, and the waveform feature sequence of traveling wave data is obtained. Then, on this basis, a random forest algorithm is used to realize automatic identification and screening of flashover fault traveling waves. Finally, a large number of tests on the simulation and measured data show that the proposed combined algorithm based on the feature extraction and classification of stochastic forest algorithm has better recognition effect of fault and interference than the traditional support vector machine, single stochastic forest algorithm, and convolutional neural network.

The emerging energy technologies, such as wind energy and photovoltaic (PV), will gradually replace the traditional synchronous generator in wide-area power system. As the wind, PV and energy storage equipment are all controlled by power electronic inverters, which are decoupled from the system and cannot provide effective inertial support to the power system with new energy (PS-NE), resulting in stability problems caused by the low inertia of the PS-NE. In particular, this paper investigates the inertia response of synchronous generator and PS-NE, and the inertia model of PS-NE considering with high renewable penetrations. Then the relation between inertia and frequency of PS-NE with high renewable penetrations are explored in this paper. Besides, the real-time inertia of the PS-NE is estimated by using the statistical algorithm based on the historical data of the PS-NE, and the range of the inertia and synchronous generator start-up capacity of the PS-NE can be estimated by using the statistical algorithm based on the renewable penetrations when we cannot obtain the historical data of the PS-NE. In addition, IEEE39 system of PS-NE is used to verify the relation between inertia and frequency of PS-NE with high renewable penetrations, and the inertia estimation of PS-NE with high renewable penetrations is analyzed in this paper.

As the development of photovoltaic (PV) power generation continuously accelerated the total installed capacity of PV, the traditional static load model is difficult to meet the needs of the power grid with the increasing penetration of PV. And the dynamic model of grid-connected PV power generation is complicated and there are plenty parameters need to be identified, so the dynamic model of grid-connected PV power generation are extremely challenging to apply in wide-area power system. In this paper, a discrete-time equivalent model of PV (PDEM) is established based on the third-order dynamic differential equation of the PV power generation system and the parameters of the PDEM are identified using the least squares (LS) and the bat algorithm (BA). Besides, the dynamic characteristics of the PV power generation grid connected system with different permeability and the fitting residuals of the two methods is analyzed in the IEEE14-bus system incorporated into the PV system. The applicability of the PDEM is verified by setting short circuit grounding fault and changing the PV permeability and voltage dip. The simulation results demonstrate that the PDEM has a strong adaptability and good applicability in the case of high PV permeability with a wide application. And the applicability of the BA in identification of PDEM are given in this paper.

With the proposal of the carbon peak goal, a multi-terminal flexible DC grid containing various renewable energy becomes the one of main ways of renewable energy power transmission. Thus, it is increasingly important to improve its transmission reliability and stability. This paper proposes a single-ended protection principle based on the analysis method of transient power change for the “mesh structure” ring-shaped flexible direct current (DC) grid. Based on the propagation characteristics of voltage, current, and anti-traveling waves during fault periods, the transient power variation coefficient based on SOD transformation is introduced to distinguish the internal and external faults. Besides, simulation based on the PSCAD/EMTDC platform within the Zhangbei four-port network verifies the effectiveness of the proposed protection principle under various fault conditions. Meanwhile, the protection criterion is designed according to the difference in the change coefficient of the transient power SOD within and outside the fault time zone. Moreover, the setting value of the start of protection is obtained by analyzing the simulation results, thus a set of fast and reliable single-ended protections for the same-side short-time transient power window of an enhanced flexible straight power grid is developed via combining it with the starting criterion of a sudden voltage change.