This Letter has proposed a synchronous control strategy of dual five-level converters based on the improved space vector pulse-width modulation (SVPWM). Firstly, the main topology of the neutral point clamped (NPC) five-level converter was introduced and its operational principle was analysed. Then, the space voltage vector diagram was offered. Considering the reduction of switching loss, the optimisation of the synthesis method of target voltage vectors and the addition of the neutralpoint potential balancing algorithm can lead to an improved SVPWM strategy for the five-level converter. The analysis of the switching rules proves that the improved SVPWM has an advantage over the traditional three-segment SVPWM due to its fewer times of switching. On the basis of the improved SVPWM, a synchronous control method of dual single-phase five-level converters is proposed to carry out a real-time control of the dual five-level converters through the combinational-encoding transmission of output pulses. Thus, the synchronous control method can, to a great extent, solve the problems caused by the traditional dual five-level independent control method, such as high hardware cost, the complexity of control, and poor synchronous performance. Simulations and experiments show that the proposed synchronous control method is feasible and effective.
An excellent electrical contact state is necessary to ensure safe and stable operation of the system. Therein, contact resistance and arc ablation are essential indexes for estimating the contact state. In view of the characteristics of brush-rail device with transient large current for AC electromagnetic propulsion, a contact resistance model and the concept of arc ablative trigger boundary are proposed in this paper. Firstly, an equivalent circuit model is developed based on structural properties of brush-rail device. Then, the corresponding contact resistance model is established considering the contact pressure, amplitude and frequency of current, sliding velocity and consecutive run times. In addition, the main affecting factors of arc ablation are analyzed and the p-v parameters of arc ablation boundary are determined. Finally, the contact resistance and arc ablative trigger boundary of the brush-rail device are tested on a rotating transient large current experimental platform, which proves the correctness of the proposed method.
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