In this paper, a hybrid transmission system equipped with a speed regulating differential mechanism (SRDM) is proposed for grid-connected wind turbines (WTs) to generate constant-frequency electricity. However, the transmission system is subject to pulsating torque from disturbances in the power grid. Coupled with parameter uncertainties, the speed control accuracy of SRDM and the system stability can hardly be warranted by conventional adaptive or robust controllers. Aiming at the proposed WT, this paper presents a discontinuous projection-based adaptive robust backstepping controller (ARBC) with an extended state observer (ESO) for high-accuracy speed control of permanent magnet synchronous motor (PMSM) in SRDM. The designed control approach, whose global robustness is guaranteed by a feedback robust law, can effectively handle parametric uncertainties and external disturbances together without using the large nonlinear feedback gain and violating any constraints during transient period. Then, the desired tracking performances of ARBC with ESO are verified through comparative experiments in a built platform of the wind turbine with SRDM. Comparative experimental results show that SRDM equipped with the integrated control method can accurately regulate the power frequency to constant under operating conditions of parametric uncertainties, varying wind speeds, sub-synchronous resonance (SSR) and sudden load fluctuation in the power grid.

These years, galloping of bundle conductors has severely threatened the safety of overhead transmission lines and caused enormous losses of economy. So it is noted that the studies on development of effective anti-galloping devices have a great significance for resisting the galloping disaster of power system and for improving the safe and stable operation of the grids. In this paper, a new combined anti-galloping device based on the principles of energy dissipation, restraining the torsion and detuning was developed for ultra-high voltage (UHV below) overhead transmission lines. To perform such analysis, the combined anti-galloping design method was presented and the new device applicable was developed on the rotation-free spacer damper. Then the arrangement of this new anti-galloping device was detailed and the efficiency assessment was carried out for verifying its galloping deterrence effect. Finally, the elastic and damping tests, the high voltage tests as well as the fatigue tests were realized to prove that the device designed satisfies the necessary requirements of overhead transmission lines.

Overhead transmission conductors are prone to wire strands breaking under the conditions of breeze vibration, and many broken strands occur in the vicinity of suspension clamps. In order to research the stress distribution characteristics of the conductor in the vicinity of suspension clamps, a relatively effective Finite Element (FE) model was proposed. Preliminary verification of model rationality through comparative analysis of theoretical calculation and simulation, and use this model to study the mechanical characteristics of the cross-section of the conductor in the key position of the conductor-clamp system. The research conclusions are as follows: a new concept of equivalent bending stiffness and equivalent diameter is proposed, which is used to calculate the alternating bending stress of conductors under breeze vibration conditions. The alternating bending stress of the wire strands follow the bending amplitude (Y _b) increases with increasing. Under the complex load, the Equivalent (Von-Mises) stress of the aluminum wire strands at the Last Point of Contact (LPC) of the conductor and the clamp shows a decreasing trend from the outside to the inside, and the maximum Von-Mises stress occurs at the contact position between the outermost wire strands and the clamp.

For the grid-connected wind turbine, the frequency converter is used to connect the generator and the grid, which makes the power quality weaker than the conventional synchronous generator. To solve such a problem, a continuously variable transmission (CVT) can be connected at the high speed end of the gearbox to obtain the constant speed output at varying wind speeds for the generator. The frequency converter can then be neglected. However, shafts of the CVT suffer the external disturbances caused by grid faults. The speed tracking accuracy of the CVT can be affected seriously. So, this paper presents the adaptive robust speed control (ARSC) for the CVT, which regulates the speed output through the permanent magnet synchronous motor (PMSM). Model uncertainties of the PMSM, such as the inertia load, friction force, and external disturbances, are considered in the control scheme. The designed controller guarantees high performance and speed tracking accuracy at different wind speeds and simulated grid faults. The experimental results demonstrate the proposed CVT controller at varying wind speeds simulated via the software of FAST and the simulation of grid faults, such as one phase short-circuit and sudden load fluctuation, at a built testbed, which is used to emulate the wind turbine with the CVT. For the comparison, the PID controller for the CVT is then applied in the testbed. The results show that the ARSC method owns better performance and speed tracking accuracy than the PID method. In order to verify the utility scale for the ARSC based CVT, we build a Simulink program for a 1.5 MW wind turbine with the CVT. Simulation results show that the ARSC based CVT still owns high speed tracking accuracy in the large scale wind turbine.

The increased cross section of overhead conductors can obviously improve the power transmission capacity. Whereas its large plastic-creep elongation may make the design works be more difficult. In this paper, time hardening model was proposed to analyze the creep properties of the large cross section conductor. To perform such analysis, the creep test results of the typical large cross section conductor JL1/G2A-1250/100-84/19 under different temperature conditions were adopted. Then the time hardening model excluding and including temperature coefficient were deduced respectively and the field observation was carried out. The results showed that the calculation results based on the time hardening model were well agreed with the test results, and the accuracy of the time hardening model in this paper is higher than the fitting model. Finally, on considering the loading time and tension as well as the temperature of each part of the conductor during the nonsynchronous stringing process is different, the section integration model was discussed based on the fitting and time hardening model so as to provide a new method for calculating the creep value of large cross section conductors.

The structure stability of the diameter-expanded conductor with fewer inner wires is the principal limitation in its large-scale use at present. As the traditional design method cannot be adopted to solve this problem, the instability properties of the diameter-expanded conductors were studied in this paper. To perform this analysis, different typical diameter-expanded conductors with fewer inner wires were chosen for the sheave tests under different working conditions at first. Then the simulation model as well as the instability criterion was established to analyze the influence factors of the structure stability. Finally, the synchronous stringing tests were carried out to assess the correctness of the model proposed. The results showed that the weakened support of the inner layer(s) and the local buckling of the external wires are the main causes of the wire jumping phenomenon. Therefore, a reasonable increase in the outmost wire's gap and decrease in the inner wire's gap are feasible to improve the load-carrying ability of the diameter-expanded conductor.