To address the inefficiency of the traditional artificial potential field method in complex environment for obstacle avoidance, the basic potential field function of the traditional artificial potential field method is improved, and the traditional spherical potential field is proposed to be improved to ellipsoidal potential field, and the improved algorithm is compared and simulated in MATLAB. The results show that the improved artificial potential field method satisfies the UAV to have high efficiency of safety and passability in obstacle avoidance trajectory planning in complex 3D environment.

Permanent magnet synchronous motor (PMSM) is a nonlinear system. When the control system operates with external interference, it will obviously affect the operating characteristics of the system, and will also make the torque ripple of the system larger. To solve these problems, the zero voltage vector is introduced to suppress the torque ripple in the traditional control mode. In order to further reduce the torque ripple and speed ripple control process, improve the adaptability and stability of the system, the traditional PI controller is replaced with a Super-twisting sliding mode controller and the function sigmoid(s) in a quasi-sliding mode is used to replace the symbol function sign(s). The torque ripple of the PMSM is studied with MATLAB/Simulink simulation software. The simulation results show that in the traditional direct torque control, the super-twisting sliding mode controller has smaller torque ripple than the PI controller and improves the system robustness.

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Background: Over the past few years, the subsynchronous oscillation (SSO) caused by the grid-connected wind farm has a bad influence on the stable operation of the system and becomes a bottleneck factor restricting the efficient utilization of wind power. How to mitigate and suppress the phenomenon of SSO of wind farms has become the focus of power system research. Methods: This paper first analyzes the SSO of different types of wind turbines, including squirrel-cage induction generator based wind turbine (SCIG-WT), permanent magnet synchronous generator based wind turbine (PMSG-WT), and doubly-fed induction generator based wind turbine (DFIG-WT). Then the mechanisms of different types of SSO are proposed with the aim to better understand SSO in large-scale wind integrated power systems, and the main analytical methods suitable for studying the SSO of wind farms are summarized. Results: On these bases, using additional damping control suppression methods to solve SSO caused by the flexible power transmission devices and the wind turbine converters. Conclusion: Finally, the last section summarizes the current development direction of the SSO of large-scale wind farm grid-connected systems, and puts forward the current challenges and recommendations for future research and development.

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