The ground current of a high-voltage direct current (HVDC) transmission system can cause DC bias in transformers near the grounding electrode during monopole operations, which affects the alternating current (AC) power system operation. Owing to multiple bias current flow paths, a capacitance blocking device installed at the neutral point of a transformer may increase the DC bias in adjacent transformers, while suppressing the DC current in that transformer. This paper introduces the use of an effective bias current indicator to describe the effect of the grounding current on transformers in a network, considering the wiring characteristics of the autotransformers and the power system topology. Additionally, a combination optimization method for the capacitance and resistance is applied in order to determine the minimum number of installed devices that restrict the maximum effective bias current throughout the network to a permissible range. A genetic algorithm based on an improved roulette selection method is adopted to solve the optimal configuration problem. The method is validated by using a test case based on the Xizhe HVDC transmission receiving-end grid near the Jinsi grounding electrode. The configuration of the capacitance and resistance was optimized by the improved genetic algorithm. This method can achieve the desired level of DC bias management with fewer devices than the conventional method, which verifies the feasibility and superiority of the proposed optimization method.

SINCE quadrature amplitude modulation (QAM) was discovered in the early 1960s, more and more research (e.g. [1,2,3,4,5]) has been done on extracting more bandwidth and power efficiencies with QAM. Coded modulation, which combines modulation and coding, has been accepted as a more efficient transmission scheme in [2]. Multilevel coding (MLC), a coded modulation scheme proposed by ImailHirakawa in 1977, together with multistage decoding (MSD) has been known to be optimum in the sense of channel capacity over the A WGN channel model (see [1, 7, 8]). However, over Rayleigh fading channels Bit-Interleaved Coded Modulation (BICM), which was originally proposed by Zehavi.[4], gains much better performance [9, 10].One of the critical and costly components in digital cellular communication systems is the RF power amplifier.Theoretically, one of the main concerns in an RF power amplifier design is the nonlinear effect of the amplifier.Quantitatively, so far, no explicit relationship or expression currently exists between the out-of-band emission level and the nonlinearity description related to the third-order intercept point (IP3). Further, in experiments and analysis, it was discovered that, in some situations, using IP3 only is not accurate enough to describe the spectrum regrowth, especially when the fifth-order intercept point (IPS) is relatively significant compared to the third-order intermodulation. In this article, we analyze the nonlinear effect of an RF power amplifier in the MIRS M-16-QAM system, give an expression of the estimation of the out-of-band emission levels for an MIRS signal power spectrum in terms of the IP3 and the IPS, as well as the power level of the signal. This result will be useful in the design of RF power amplifier for the MIRS M-16-QAM system and other wireless communication systems.In this paper, we present a hybrid mixed cost-function adaptive initialization algorithm for the time domain equalizer in a discrete multitone (DMT)-based asymmetric digital subscriber loop. Using our approach, a higher convergence rate than that of the commonly used least-mean square algorithm is obtained, whilst attaining bit rates close to the optimum maximum shortening SNR and the upper bound SNR. Moreover, our proposed method outperforms the minimum mean-squared error design for a range of TEQ filter lengths. 0-7803-7402-9/02/$17.00 @2002 IEEE IV -4183