The permanent magnet semi-direct drive cutting transmission system of shearer is taken as the research object, the non-linear dynamic model of the system is established and the Runge-Kutta method is used to solve it. The statistical processing is carried out to gear stress by rain-flow counting method, and an eight-stage random loading model is established. Combining the nonlinear fatigue damage theory, the dynamic reliability of gear is predicted through the modified stress-strength interference model. Finally, the influence of some parameters on gear reliability is further studied, which provides a reference for the reliability optimization of gear in shearer cutting unit.

Due to changes in the working temperature in a shearer transmission system, it is easy to cause the transmission gear to work abnormally. In this paper, the first gear pair in a cutting transmission system of a permanent magnet semi-direct drive shearer was taken as the research object. The coupling effect of time-varying meshing stiffness, meshing damping, bearing clearance and gear backlash under thermal deformation were fully considered. Then, a three degree of freedom nonlinear dynamic model of the gear pair was established, and a dimensionless analysis was performed. Finally, the Runge-Kutta method was used in the numerical calculations. The motion characteristics of the system were analysed through the gear’s bifurcation diagram of the temperature at different frequencies and the bifurcation diagram of the frequency at different temperatures. The meshing state was analysed at different frequencies and temperatures. For the chaotic motion generated in the system, a periodic resonance excitation was applied to control unstable motion. This study has revealed various specific effects of the temperature on the dynamic characteristics of the system. In addition, the periodic excitation method can effectively control the nonlinear motion in the system and realise the control of the chaos under the temperature effect.

The nonlinear torsional vibration and instability oscillation caused by nonlinear damping in the shearer electromechanical coupling cutting transmission system in shearer driven by the permanent magnet synchronous motor (PMSM) is investigated in this paper. The electromechanical coupling transmission system in the shearer is equivalent to a concentrated mass model for the purpose of establishing the system dynamic model by the Lagrange–Maxwell equation. Then, the Routh–Hurwitz criterion is used to determine the torsional vibration critical point and stability region for the Hopf bifurcation for the cutting transmission system. According to the Routh–Hurwitz stability criterion, the Hopf bifurcation type and the effect of the supercritical Hopf bifurcation in the torsional vibration of the cutting transmission system are analyzed. Furthermore, based on the washout filter, the Hopf bifurcation controller is designed for suppressing the transmission system’s large vibration amplitude and unstable oscillation. In addition, the influences of the linear gain and nonlinear gain on the bifurcation point and the limit cycle amplitude are discussed. Finally, the numerical simulation results indicate the effectiveness of the designed controller. The research achievements can provide a theoretical basis for design or optimize the cutting transmission system of high-reliability shearer driven by PMSM.

The modular multilevel converters become more and more popular in high power applications in recent years. The solution to make the MMC operate well under the submodule failure is a key technology to increase reliability of the MMC-based systems. In this paper, a fault tolerant control method based on the zero-sequence voltage injection is proposed to maintain stable line-to-line voltage under submodule fault conditions. The proposed method can make full use of un-faulty submodules and reduce the negative influences caused by the submodule failure. In addition, the proposed method is with simple implementation and easy to be executed in digital controllers. Comparative analysis between the proposed method and one conventional method is carried out from the aspects of the harmonic characteristics, dynamic-state characteristics. Finally, the effectiveness of the proposed control method is verified by experimental results.