The influences of chemical segregation and phase transformation on liquid density variation during solidification of Ni-based supperalloy Inconel 718 were investigated using SEM and EDS. It was found that significant ...The influences of chemical segregation and phase transformation on liquid density variation during solidification of Ni-based supperalloy Inconel 718 were investigated using SEM and EDS. It was found that significant segregation in liquid prompts high Nb phase to precipitate directly from liquid, which results in the redistribution of alloy elements and liquid density in their vicinity. The term "inter-precipitate liquid density" is therefore proposed and this concept should be applied to determine the solidification behavior of superalloy Inconel 718.展开更多
在微源半桥变流器串联结构星型连接微电网(half-bridge converter series Y-connection microgrid,HCSY-MG)系统中,由于环境因素(如风速、光照等)影响,各风、光微源的输出功率存在显著差异,导致系统三相输出功率不一致,进而引发三相并...在微源半桥变流器串联结构星型连接微电网(half-bridge converter series Y-connection microgrid,HCSY-MG)系统中,由于环境因素(如风速、光照等)影响,各风、光微源的输出功率存在显著差异,导致系统三相输出功率不一致,进而引发三相并网电流不对称,严重影响系统的并网运行。为解决该问题,提出了一种正序分量合成零序电压注入和过调制补偿相结合的控制方法。该方法利用与三相电网电压同相位的正序分量合成零序电压,与传统方法相比,简化了计算过程。然而,零序电压注入的功率平衡能力有限,当三相功率不平衡程度较大时,系统容易发生过调制。为此,过调制补偿通过修改零序电压,进一步扩大了系统的相间功率平衡范围,从而确保在相间功率不平衡的情况下,系统仍然能够正常运行,且并网电流能够满足并网要求。最后,通过仿真和实验验证了所提控制策略的正确性与可行性。展开更多
OFDM has been widely adopted in several communication systems. However, OFDM systems are very sensitive to the phase noise, which causes the CPE （common phase error） and ICI （inter-carrier interference）, and thus ...OFDM has been widely adopted in several communication systems. However, OFDM systems are very sensitive to the phase noise, which causes the CPE （common phase error） and ICI （inter-carrier interference）, and thus degrades the system performance significantly. Based on the IEEE 802.11a standard, a simplified iterative phase noise mitigation algorithm is proposed. The proposed algorithm has very low complexity, and requires no additional pilot information. The simulation result shows that good BER performance can be achieved through several few times of iteration.展开更多
匝间短路是无刷直流电机(brushless DC motor,BLDCM)的常见故障之一,因此开展短路下电机在线检测非常关键。目前,关于BLDCM匝间短路在线检测的研究鲜见报道,同时BLDCM的机械结构、驱动方式与其他类型电机差异明显,现有的研究成果无法直...匝间短路是无刷直流电机(brushless DC motor,BLDCM)的常见故障之一,因此开展短路下电机在线检测非常关键。目前,关于BLDCM匝间短路在线检测的研究鲜见报道,同时BLDCM的机械结构、驱动方式与其他类型电机差异明显,现有的研究成果无法直接适用。为此,该文提出基于零序电压特性的无刷直流电机匝间短路在线检测法,构建新的特征参数指标。首先,建立匝间短路下绕组解析模型,理论推导故障下零序电压基频分量的演变特性;其次,联合三相电流与零序电压基频分量,提出全新的故障相定位参数与故障程度评估参数;最后,为了验证所提方法的有效性,联合Simulink仿真模型与实验平台开展研究,结果表明该方法能有效实现匝间短路的故障检测、故障相定位及故障程度评估。另外,该方法对电机瞬时状态具有鲁棒性,能够实现BLDCM匝间短路的实时检测。展开更多
基金supported by the National Natural Science Foundation of China under a grant No. 50974144
文摘The influences of chemical segregation and phase transformation on liquid density variation during solidification of Ni-based supperalloy Inconel 718 were investigated using SEM and EDS. It was found that significant segregation in liquid prompts high Nb phase to precipitate directly from liquid, which results in the redistribution of alloy elements and liquid density in their vicinity. The term "inter-precipitate liquid density" is therefore proposed and this concept should be applied to determine the solidification behavior of superalloy Inconel 718.
文摘在微源半桥变流器串联结构星型连接微电网(half-bridge converter series Y-connection microgrid,HCSY-MG)系统中,由于环境因素(如风速、光照等)影响,各风、光微源的输出功率存在显著差异,导致系统三相输出功率不一致,进而引发三相并网电流不对称,严重影响系统的并网运行。为解决该问题,提出了一种正序分量合成零序电压注入和过调制补偿相结合的控制方法。该方法利用与三相电网电压同相位的正序分量合成零序电压,与传统方法相比,简化了计算过程。然而,零序电压注入的功率平衡能力有限,当三相功率不平衡程度较大时,系统容易发生过调制。为此,过调制补偿通过修改零序电压,进一步扩大了系统的相间功率平衡范围,从而确保在相间功率不平衡的情况下,系统仍然能够正常运行,且并网电流能够满足并网要求。最后,通过仿真和实验验证了所提控制策略的正确性与可行性。
文摘OFDM has been widely adopted in several communication systems. However, OFDM systems are very sensitive to the phase noise, which causes the CPE （common phase error） and ICI （inter-carrier interference）, and thus degrades the system performance significantly. Based on the IEEE 802.11a standard, a simplified iterative phase noise mitigation algorithm is proposed. The proposed algorithm has very low complexity, and requires no additional pilot information. The simulation result shows that good BER performance can be achieved through several few times of iteration.
文摘匝间短路是无刷直流电机(brushless DC motor,BLDCM)的常见故障之一,因此开展短路下电机在线检测非常关键。目前,关于BLDCM匝间短路在线检测的研究鲜见报道,同时BLDCM的机械结构、驱动方式与其他类型电机差异明显,现有的研究成果无法直接适用。为此,该文提出基于零序电压特性的无刷直流电机匝间短路在线检测法,构建新的特征参数指标。首先,建立匝间短路下绕组解析模型,理论推导故障下零序电压基频分量的演变特性;其次,联合三相电流与零序电压基频分量,提出全新的故障相定位参数与故障程度评估参数;最后,为了验证所提方法的有效性,联合Simulink仿真模型与实验平台开展研究,结果表明该方法能有效实现匝间短路的故障检测、故障相定位及故障程度评估。另外,该方法对电机瞬时状态具有鲁棒性,能够实现BLDCM匝间短路的实时检测。
