In-situ observations on α/γ phase transformation were made to study the effects of grain boundary microstructures on the formation of a new phase and the migration of α/γ interphase boundary in an iron4. 2%Cr allo...In-situ observations on α/γ phase transformation were made to study the effects of grain boundary microstructures on the formation of a new phase and the migration of α/γ interphase boundary in an iron4. 2%Cr alloy. It was found that triple junctions with more random boundaries could be the primary nucleation sites for a new phase, while triple junctions with low angle or low ∑ coincidence boundaries did not play any role as preferential sites. The migration of α/γ interphase boundary during heating over the transformation temperature range showed the two stage behaviour characterized by a stage with a migration velocity of 0. 33-0. 75 mm/s and secondly by a stage with 3. 7-7. 6 mm/s. It was also found that abnormal grain growth and a high density of ∑3 coincidence boundaries could occur in a phase with bcc structure after cycling of α/γ phase transformation. A new mechanism of nucleation and growth of a new phase in α/γ phase transformation is proposed on the basis of roles of plane-matching interphase boundaries, as previously discussed on the origin of anisotropy of grain growth due to the migration of {110} plane-matching boundaries in Fe-3z%Si alloy. The most recent theoretical work on the distribution of plane-matching boundaries in solids with different crystal structures was found to be useful for the understanding of nucleation and growth during α/γ phase transformation.展开更多
针对弱电网普遍存在的直流偏置、频率变化等问题,提出1种适合单相并网逆变器的改进反Park变换锁相环IPT-PLL(inverse Park transform phase-locked loop)技术。首先,在鉴相环节选用Park变换后的α分量为基准电压,解决电网电压直流偏置问...针对弱电网普遍存在的直流偏置、频率变化等问题,提出1种适合单相并网逆变器的改进反Park变换锁相环IPT-PLL(inverse Park transform phase-locked loop)技术。首先,在鉴相环节选用Park变换后的α分量为基准电压,解决电网电压直流偏置问题,采用1/4基波周期延时的方法构造其正交分量;其次,引入拉格朗日插值多项式逼近分数阶延时,以降低频率变化造成的延时计算误差,并理论分析PI调节器的设计方法;最后,通过实验验证了所提改进IPT-PLL频率适应性强,能明显抑制电网直流偏置干扰,且具有较好的动、静态性能。展开更多
从抑制谐波电流和减小体积质量的目的出发,设计了基于星形连接自耦变压器的24脉波自耦变压整流装置(ATRU),提出了采用4组相间变压器并联整流桥输出的方法来简化电路。介绍了ATRU的工作原理,分析了整流电路的等效容量。对相间变压器的结...从抑制谐波电流和减小体积质量的目的出发,设计了基于星形连接自耦变压器的24脉波自耦变压整流装置(ATRU),提出了采用4组相间变压器并联整流桥输出的方法来简化电路。介绍了ATRU的工作原理,分析了整流电路的等效容量。对相间变压器的结构和工作机理进行了详细分析。在Saber仿真的基础上,研制了一台18 k W ATRU原理样机。实验结果表明改进了相间变压器的24脉波ATRU不仅能够保证各个整流桥独立工作,降低输入电流的总谐波畸变,而且通过降低整流装置的等效容量,有效减小了其体积和质量,简化了电路结构。展开更多
文摘In-situ observations on α/γ phase transformation were made to study the effects of grain boundary microstructures on the formation of a new phase and the migration of α/γ interphase boundary in an iron4. 2%Cr alloy. It was found that triple junctions with more random boundaries could be the primary nucleation sites for a new phase, while triple junctions with low angle or low ∑ coincidence boundaries did not play any role as preferential sites. The migration of α/γ interphase boundary during heating over the transformation temperature range showed the two stage behaviour characterized by a stage with a migration velocity of 0. 33-0. 75 mm/s and secondly by a stage with 3. 7-7. 6 mm/s. It was also found that abnormal grain growth and a high density of ∑3 coincidence boundaries could occur in a phase with bcc structure after cycling of α/γ phase transformation. A new mechanism of nucleation and growth of a new phase in α/γ phase transformation is proposed on the basis of roles of plane-matching interphase boundaries, as previously discussed on the origin of anisotropy of grain growth due to the migration of {110} plane-matching boundaries in Fe-3z%Si alloy. The most recent theoretical work on the distribution of plane-matching boundaries in solids with different crystal structures was found to be useful for the understanding of nucleation and growth during α/γ phase transformation.
文摘针对弱电网普遍存在的直流偏置、频率变化等问题,提出1种适合单相并网逆变器的改进反Park变换锁相环IPT-PLL(inverse Park transform phase-locked loop)技术。首先,在鉴相环节选用Park变换后的α分量为基准电压,解决电网电压直流偏置问题,采用1/4基波周期延时的方法构造其正交分量;其次,引入拉格朗日插值多项式逼近分数阶延时,以降低频率变化造成的延时计算误差,并理论分析PI调节器的设计方法;最后,通过实验验证了所提改进IPT-PLL频率适应性强,能明显抑制电网直流偏置干扰,且具有较好的动、静态性能。
文摘从抑制谐波电流和减小体积质量的目的出发,设计了基于星形连接自耦变压器的24脉波自耦变压整流装置(ATRU),提出了采用4组相间变压器并联整流桥输出的方法来简化电路。介绍了ATRU的工作原理,分析了整流电路的等效容量。对相间变压器的结构和工作机理进行了详细分析。在Saber仿真的基础上,研制了一台18 k W ATRU原理样机。实验结果表明改进了相间变压器的24脉波ATRU不仅能够保证各个整流桥独立工作,降低输入电流的总谐波畸变,而且通过降低整流装置的等效容量,有效减小了其体积和质量,简化了电路结构。
