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The rapid detection of grid voltage faults is crucial to achieve grid voltage fault ride-through. However, conventional grid voltage detection methods, including Fourier transform, dq axis transform, wavelet transform, and voltage peak methods, generally yield varying degrees of distortions in the detection results of short-time disturbances in grid voltage. To address this, this paper proposes an approach for quickly detecting short-time disturbances in grid voltage. Leveraging the distinctive high harmonic content present in grids, the suggested strategy involves a transformation of grid voltage calculated using the Fourier transform method, known for its robust anti-interference performance, into high-frequency signals through coordinate conversion. The integration of the rolling sliding window method addresses the extended calculation time issue associated with the Fourier transform, enabling the detection of grid voltage disturbance signals within a single high-frequency signal cycle using this method. The simulation experiment results demonstrated the wide applicability of the proposed method compared with other methods. It is not only effective for short-time grid voltage disturbances, but also suitable for long-time grid voltage disturbances. Regardless of whether high-frequency harmonics are present or absent in the grid voltage, this method allows for the rapid detection of grid voltage disturbances (within about 2 ms). Moreover, its accuracy in detecting grid voltage amplitudes aligns with requirements in engineering applications.

At present, most of China's onshore wind farms use doubly-fed induction generators (DFIG) with small-capacity and and low-cost converters, but generally, these DFIGs can only operate within the slip rate range of ±30%, and can not be connected to the grid normally under low-speed conditions. In order to improve the output of DFIGs under low-speed conditions, the paper proposes a dual-mode grid-connection control scheme. The author first established an asynchronous mathematical model for stator shorting of doubly-fed motor to finally identify the value range of short-circuit resistance, and then put forward the dual-mode flexible switching strategy, that is, units operate in the asynchronous mode when the speed is low, and in the conventional doubly-fed mode when the speed is high, thus realizing power generation operation at low speed. The simulation results show that, at low speed, in the asynchronous mode, the rotor current distortion rate can be reduced by 50% and the power control accuracy is higher, with the power fluctuation amplitude controlled within 3 kW, compared with those in the doubly-fed mode, and after the flexible switching strategy is adopted, the transient impulse current can be reduced by more than 36% and the new steady state can be reached in only 150 ms. This verifies the validity and feasibility of the dual-mode grid-connection control strategy for DFIGs.

In the operating environment of power system with weak grid characteristics, the traditional current source converter control mode is prone to vibration, which increases the crossing difficulty and off-grid probability of wind turbines. Based on virtual synchronous generator (VSG) technology, a novel control strategy of voltage source converter is designed in this paper, and the voltage source converter control mode and current source converter control mode are studied. Under normal grid-connected operation conditions, voltage source converter control mode is adopted. Active power control increases active power compensation through VSG, and reactive current is injected into the front end of reactive power control. Under start-stop and high & low-voltage ride-through conditions, the current source converter control mode is adopted. The control strategy combines the advantages of voltage source converter control mode and the current source converter control mode. It has not only the frequency support characteristics, but also the fast active and reactive power response capability. The simulation and prototype experiments on the grid-connection process, active and reactive power response and high & low-voltage ride-through process of the full-power wind power converter are carried out. The results show that the proposed control scheme can achieve good control effect under each operating condition of the wind power converter, so that the wind power units have good steady-state and dynamic performance, and can well adapt to the demands of new energy grid-connection.

At present, the installed capacity of new energy power generation equipment shows a trend of rapid growth. A higher proportion of new energy generation will make the power grid show the characteristics of high impedance, low inertia, weak damping and low short circuit ratio. However, traditional double-fed wind power converter usually adopts current source control mode, which is difficult to adapt to the increasingly harsh operating environment of power grid. Therefore, this paper studies a voltage source control mode of double-fed wind power converter, compares its performance with current source converter control mode, and proposes a switching method between voltage source converter control mode and current source converter control mode in the case of high voltage ride-through and low voltage ride-through. Through real-time network voltage monitoring, the converter control modes of voltage source and current source can be smoothly switched. Simulation results show that the proposed control scheme has good steady-state and dynamic performance, and can adapt to the requirements of new energy grid-connection.

Brevibacillus laterosporus is a strain of probiotic bacteria that has been widely used in pest control, cash crop, and other production areas. However, few studies have been conducted on its use as a feed additive in animals. Therefore, the probiotic potential of B. laterosporus PBC01 was evaluated by characterizing hydrophobicity, auto-aggregation activity, bile salt and simulated gastrointestinal fluid tolerance, bienzymatic, and antibacterial activity. Antibiotic susceptibility, hemolysis assays, and supplemental feeding of mice were also performed to evaluate safety features. Our results showed that B. laterosporus PBC01 had moderate hydrophobicity, high auto-agglutination ability. Meanwhile, B. laterosporus PBC01 had good tolerance to bile salt and simulated gastrointestinal fluid. It had the ability to secrete protease, cellulase, and to inhibit various pathogens. In addition, B. laterosporus PBC01 was sensitive to many antibiotics, and did not produce hemolysin. In the safety assessment of mice, it did not cause any deaths, nor did it affect the cell components of blood, antioxidant capacity, and reproductive health. The study indicated the great probiotic characteristics and safety of B. laterosporus PBC01. This may provide a theoretical basis for the clinical application and development of probiotic-based feed additives., (© 2024 Federation of American Societies for Experimental Biology.)