On the basis of second-order perturbation approximate and modal expansion approach,we investigate the enhancement effect of cumulative second-harmonic generation(SHG)of circumferential guided waves(CGWs)in a circular ...On the basis of second-order perturbation approximate and modal expansion approach,we investigate the enhancement effect of cumulative second-harmonic generation(SHG)of circumferential guided waves(CGWs)in a circular tube,which is inherently induced by the closed propagation feature of CGWs.An appropriate mode pair of primary-and double-frequency CGWs satisfying the phase velocity matching and nonzero energy flux is selected to ensure that the second harmonic generated by primary CGW propagation can accumulate along the circumference.Using a coherent superposition of multi-waves,a model of unidirectional CGW propagation is established for analyzing the enhancement effect of cumulative SHG of primary CGW mode selected.The theoretical analyses and numerical simulations performed directly demonstrate that the second harmonic generated does have a cumulative effect along the circumferential direction and the closed propagation feature of CGWs does enhance the magnitude of cumulative second harmonic generated.Potential applications of the enhancement effect of cumulative SHG of CGWs are considered and discussed.The theoretical analysis and numerical simulation perspective presented here yield an insight previously unavailable into the physical mechanism of the enhancement effect of cumulative SHG by closed propagation feature of CGWs in a circular tube.展开更多
兼顾二次谐波电流抑制和动态性能改善是两级式逆变器中前级直流变换器的基本控制目标。该文从阻抗的观点出发,指出使前级直流变换器的闭环输出阻抗在二倍输出电压频率处呈现高阻抗,而在非二倍输出电压频率处呈现低阻抗是实现此控制目标...兼顾二次谐波电流抑制和动态性能改善是两级式逆变器中前级直流变换器的基本控制目标。该文从阻抗的观点出发,指出使前级直流变换器的闭环输出阻抗在二倍输出电压频率处呈现高阻抗,而在非二倍输出电压频率处呈现低阻抗是实现此控制目标的基本方法。采用与前级直流变换器的输出阻抗串联虚拟阻抗,并同时与中间母线电容并联虚拟阻抗的方法,实现了所提出的基本方法,并以Buck类的前级直流变换器为例,给出实现虚拟串联阻抗和虚拟并联阻抗的控制框图。通过对该控制框图进行等效变换,可推导得到现有文献中已提出的二次谐波电流抑制方法。最后,研制一台1 k VA原理样机,并通过理论分析和实验验证对这些不同控制方法的二次谐波电流抑制效果及对系统动态性能的改善作用进行对比。实验结果证明了理论分析的正确性。展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11834008,11704410,11632004,11474361,and U1930202).
文摘On the basis of second-order perturbation approximate and modal expansion approach,we investigate the enhancement effect of cumulative second-harmonic generation(SHG)of circumferential guided waves(CGWs)in a circular tube,which is inherently induced by the closed propagation feature of CGWs.An appropriate mode pair of primary-and double-frequency CGWs satisfying the phase velocity matching and nonzero energy flux is selected to ensure that the second harmonic generated by primary CGW propagation can accumulate along the circumference.Using a coherent superposition of multi-waves,a model of unidirectional CGW propagation is established for analyzing the enhancement effect of cumulative SHG of primary CGW mode selected.The theoretical analyses and numerical simulations performed directly demonstrate that the second harmonic generated does have a cumulative effect along the circumferential direction and the closed propagation feature of CGWs does enhance the magnitude of cumulative second harmonic generated.Potential applications of the enhancement effect of cumulative SHG of CGWs are considered and discussed.The theoretical analysis and numerical simulation perspective presented here yield an insight previously unavailable into the physical mechanism of the enhancement effect of cumulative SHG by closed propagation feature of CGWs in a circular tube.
文摘兼顾二次谐波电流抑制和动态性能改善是两级式逆变器中前级直流变换器的基本控制目标。该文从阻抗的观点出发,指出使前级直流变换器的闭环输出阻抗在二倍输出电压频率处呈现高阻抗,而在非二倍输出电压频率处呈现低阻抗是实现此控制目标的基本方法。采用与前级直流变换器的输出阻抗串联虚拟阻抗,并同时与中间母线电容并联虚拟阻抗的方法,实现了所提出的基本方法,并以Buck类的前级直流变换器为例,给出实现虚拟串联阻抗和虚拟并联阻抗的控制框图。通过对该控制框图进行等效变换,可推导得到现有文献中已提出的二次谐波电流抑制方法。最后,研制一台1 k VA原理样机,并通过理论分析和实验验证对这些不同控制方法的二次谐波电流抑制效果及对系统动态性能的改善作用进行对比。实验结果证明了理论分析的正确性。
