In this paper, we investigate the problem of downlink precoding for the narrowband massive multi-user multiple-input multiple-output (MU-MIMO) system with low-resolution digital-to-analog converters (DACs). We introduce a low-complexity precoding scheme based on the alternating direction method of multipliers (ADMM) framework in this work. An efficient gradient descent (GD) algorithm with adaptive step-size determination mechanism (ASGD) is proposed to alleviate the computational complexity bottleneck of the inherent matrix inversion. Numerical results demonstrate that the ASGD precoder achieves an attractive trade-off between the performance and computational complexity compared with other counterparts.
Out-of-step oscillation separation devices based on apparent impedance angle trajectory are widely used in the
power grid in China, and their reliability is of great importance. In this paper, the influence mechanism of series
compensation on apparent impedance angle trajectory is analyzed. It reveals that series compensation capacitors
reduce the equivalent impedance angle and consequently the apparent impedance angle cannot pass through all
four zones, resulting in the risk of failure for the separation devices. A revised method of apparent impedance angle
based on compensation principle is discussed, and then an improved out-of-step oscillation detection criterion is
proposed. In view of the fact that the apparent impedance angle at the moment of maximum current is equal to the
equivalent impedance angle during an oscillation process, a practical algorithm based on the compensated apparent
impedance angle is proposed. RTDS tests are conducted to verify the effectiveness of the new criterion, considering
transmission lines with a high series compensation level. 相似文献