对双主动全桥DAB(dual active bridge)双向DC/DC变换器的调制方案进行了研究,DAB变换器的主要优势在于具有对称结构、双向潮流能力、宽软开关区域和灵活的控制能力等特点。控制这种拓扑结构最简单的方法是通过控制变换器原副边全桥之间...对双主动全桥DAB(dual active bridge)双向DC/DC变换器的调制方案进行了研究,DAB变换器的主要优势在于具有对称结构、双向潮流能力、宽软开关区域和灵活的控制能力等特点。控制这种拓扑结构最简单的方法是通过控制变换器原副边全桥之间的移相角来控制功率传输的方向和大小。然而在轻载条件下,当变换器的输入或输出电压变化较大时,会产生大量的无功功率,同时部分开关管的零电压开关ZVS(zero voltage switching)操作会丢失而直接导致转换效率变低。因此,为了提高DAB变换器的效率,提出了一种混合单移相调制PSM(phase shift modulation)方案,在保持控制简单的基础上,通过减小电感电流有效值,扩大软开关的范围,提高了变换器的效率。首先,通过让拓展移相EPS(extended phase shift)、双移相DPS(dual phase shift)以及三移相TPS(triple phase shift)调制方案中的可控变量相等,从而形成了4种不同的PSM方案。接着,对这些调制方案进行了稳态特征的比较分析,包括传输功率容量、电感电流水平以及软开关性能等。在此基础上,提出了一种混合PSM方案。最后,通过搭建实验平台验证了所提出调制方案的有效性和正确性。展开更多
Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life.But the variable which can represent the health of machine is hardly measure...Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life.But the variable which can represent the health of machine is hardly measured on line.To a degree,the difficulty of on-line application restricts the scope of application of Paris law.The relationship between characteristic values of vibration signals and the variable in the Paris equation which can describe the health of machine is investigated by taking ball bearings as investigative objects.Based on 6205 deep groove ball bearings as a living example,historical lives and vibration signals are analyzed.The feasibility of describing that variable in the Paris equation by the characteristic value of vibration signals is inspected.After that vibration signals decomposed by empirical mode decomposition（EMD）,root mean square（RMS） of intrinsic mode function（IMF） involving fault characteristic frequency has a consistent trend with the diameter of flaws.Based on the trend,two improved Paris models are proposed and the scope of application of them is inspected.These two Paris Models are validated by fatigue residual life data from tests of rolling element bearings and vibration signals monitored in the process of operation of rolling element bearings.It shows that the first improved Paris Model is simple and plain and it can be easily applied in actual conditions.The trend of the fatigue residual life predicted by the second improved Paris model is close to the actual conditions and the result of the prediction is slightly greater than the truth.In conclusion,after the appearance of detectable faults,these improved models based on RMS can predict residual fatigue life on line and a new approach to predict residual fatigue life of ball bearings on line without disturbing the machine running is provided.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50705096)National Science and Technology Major Project of China(Grant No. 2009zx04014-014)
文摘Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life.But the variable which can represent the health of machine is hardly measured on line.To a degree,the difficulty of on-line application restricts the scope of application of Paris law.The relationship between characteristic values of vibration signals and the variable in the Paris equation which can describe the health of machine is investigated by taking ball bearings as investigative objects.Based on 6205 deep groove ball bearings as a living example,historical lives and vibration signals are analyzed.The feasibility of describing that variable in the Paris equation by the characteristic value of vibration signals is inspected.After that vibration signals decomposed by empirical mode decomposition（EMD）,root mean square（RMS） of intrinsic mode function（IMF） involving fault characteristic frequency has a consistent trend with the diameter of flaws.Based on the trend,two improved Paris models are proposed and the scope of application of them is inspected.These two Paris Models are validated by fatigue residual life data from tests of rolling element bearings and vibration signals monitored in the process of operation of rolling element bearings.It shows that the first improved Paris Model is simple and plain and it can be easily applied in actual conditions.The trend of the fatigue residual life predicted by the second improved Paris model is close to the actual conditions and the result of the prediction is slightly greater than the truth.In conclusion,after the appearance of detectable faults,these improved models based on RMS can predict residual fatigue life on line and a new approach to predict residual fatigue life of ball bearings on line without disturbing the machine running is provided.
