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Qin Qinghai,Qiu Yalan,Cai Bin 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.4
In this article, the multistage magnetic gearbox for wind turbine (WMGB) which contains two-stage magnetic gears (MGs) is studied. The MG is a coaxial MG and consists of outer rotor, modulator and inner rotor. First, the gear ratios of MGs are optimized based on the maximum gravimetric torque density under the constraint of structural parameters. Second, in view of the importance of the first-stage MG (FSMG), the multi-objective optimization method NSGA-II based on back propagation neural network surrogate model is combined with the single parameter scanning method to achieve higher torque performance of FSMG. The simulation results show that the torque density increases by 13.28%, the torque ripple of the modulator and inner rotor decreases to below 5%, and the maximum magnetic force exerted on the modulator is reduced by 22.73%, which verifies the effectiveness and efficiency of the proposed hierarchical optimization strategy. Finally, aiming at the aerodynamic load, the dynamic characteristics of FSMG are analyzed under different wind speed conditions, which verifies the feasibility of the proposed WMGB applied in MW-scale wind power drive systems.
Throughput of QoS Guaranteed Wireless Systems With/Without Channel State Information
Qin, Meng,Yang, Qinghai,Yang, Jian,Kwak, Kyung Sup,Rao, Ramesh R. IEEE 2017 IEEE Transactions on Vehicular Technology VT Vol.66 No.7
<P>In this paper, we investigate the throughput of wireless systems in the presence of random data arrivals and quality-of-service (QoS) requirements, which are statistically characterized by the queueing-bound violation probability. By combining the concepts of effective capacity and effective bandwidth, we propose a unified analytical framework to investigate the achievable throughput. Employing the proposed unified framework, we further acquire the explicit expressions of the throughput of QoS guaranteed wireless systems with the channel state information (CSI) known/unknown at the transmitter. Specifically, the acquired throughput is characterized by the first-and second-order statistics of the random data arrivals, and it is shown that the QoS requirements affect the throughput by the second-order statistics of the random data arrivals and the random data transmissions. In addition, our theoretical analysis demonstrates that the throughput under QoS constraints is tighter than the conventional stable throughput, and that the first-order statistic of the random data arrivals is sufficient to characterize the throughput when the system can tolerate an arbitrarily long queueing delay. In particular, we prove that the queueing-bound violation probability decays exponentially with the queueing bound. Finally, simulation results corroborate the theoretical analysis.</P>
Energy-aware resource allocation for OFDMA wireless networks with hybrid energy supplies
Qin, Meng,Yang, Qinghai,Yang, Jian,Park, Daeyoung,Kwak, Kyung Sup IET 2017 IET COMMUNICATIONS Vol.11 No.11
<P>In this study, the authors investigate the resource allocation for orthogonal frequency-division multiple access (OFDMA) wireless networks, where the base station is powered by renewable energy and electric grid. To fully exploit the renewable energy, the authors propose an energy-aware resource allocation (EARA) algorithm to maximise the network utility, which captures the tradeoff between the system throughput and the grid energy consumption. Specifically, the EARA algorithm only has to track the current system states (e.g. channel and queueing conditions) without requiring a relevant priori distribution knowledge, making it applicable for practical OFDMA wireless networks with unpredictable channel dynamics, renewable energy arrivals and stochastic traffics. Moreover, the performance achieved by the EARA algorithm is theoretically characterised. Most importantly, the authors develop an implementation architecture to take the EARA algorithm into practice, and also analyse the low implementation costs (e.g. low computational complexity, trivial signalling overhead etc.). Finally, simulation results verify the theoretical analysis and also demonstrate the advantages of the EARA algorithm.</P>