Quasi Z-source converter is a single stage soft switched power converter derived from Z-source converter topology, employing an impedance network coupling the source with the converter. The quasi Z-source source conve...Quasi Z-source converter is a single stage soft switched power converter derived from Z-source converter topology, employing an impedance network coupling the source with the converter. The quasi Z-source source converter can buck or boost the voltage and current flow is bidirectional. The duty cycle of the switch can be adjusted to maintain constant voltage during load change. To obtain constant output voltage, proper controller design is a must. This paper presents closed loop control of quasi Z-source converter using PI controller where controller parameters are estimated using the small signal model of the entire system. The transfer function of the system with AC sweep is used to obtain appropriate proportional and integral gain constants to reduce transient dynamics and to reduce steady state error.展开更多
The advance in the wide-area measurement system(WAMS)is driving the power system to the trend of wide-area monitoring and control.The Prony method is usually used for low frequency oscillation online identification.Ho...The advance in the wide-area measurement system(WAMS)is driving the power system to the trend of wide-area monitoring and control.The Prony method is usually used for low frequency oscillation online identification.However,the identified amplitude and phase information is not sufficiently used.In this paper,the amplitude is adopted to detect the occurrence of the oscillation and to obtain the mode observability of the sites.The phase is adopted to identify the oscillation generator grouping and to obtain the mode shapes.The time varying characteristics of low frequency oscillations are studied.The behaviors and the characters of low frequency oscillations are displayed by dynamic visual techniques.Demonstrations on the"11.9"low frequency oscillation of the Guizhou Power Grid substantiate the feasibility and the validation of the proposed methods.展开更多
Insulating liquid plays an important role for the life span of the transformer.Petroleum-based mineral oil has become dominant insulating liquid of transformer for more than a century for its excellent dielectric and ...Insulating liquid plays an important role for the life span of the transformer.Petroleum-based mineral oil has become dominant insulating liquid of transformer for more than a century for its excellent dielectric and cooling properties.However,the usage of petroleum-based mineral oil,derived from a nonrenewable energy source,has affected the environment for its nonbiodegradability property.Therefore,researchers direct their attention to renewable and biodegradable alternatives.Palm fatty acid ester,coconut oil,sunflower oil,etc.are considered as alternatives to replace mineral oil as transformer insulation liquid.This paper gives an extensive review of different liquid insulating materials used in a transformer.Characterization of different liquids as an insulating material has been discussed.An attempt has been made to classify different insulating liquids-based on different properties.展开更多
文摘Quasi Z-source converter is a single stage soft switched power converter derived from Z-source converter topology, employing an impedance network coupling the source with the converter. The quasi Z-source source converter can buck or boost the voltage and current flow is bidirectional. The duty cycle of the switch can be adjusted to maintain constant voltage during load change. To obtain constant output voltage, proper controller design is a must. This paper presents closed loop control of quasi Z-source converter using PI controller where controller parameters are estimated using the small signal model of the entire system. The transfer function of the system with AC sweep is used to obtain appropriate proportional and integral gain constants to reduce transient dynamics and to reduce steady state error.
基金supported by the National Natural Science Foundation of China(Grant No.50595413)
文摘The advance in the wide-area measurement system(WAMS)is driving the power system to the trend of wide-area monitoring and control.The Prony method is usually used for low frequency oscillation online identification.However,the identified amplitude and phase information is not sufficiently used.In this paper,the amplitude is adopted to detect the occurrence of the oscillation and to obtain the mode observability of the sites.The phase is adopted to identify the oscillation generator grouping and to obtain the mode shapes.The time varying characteristics of low frequency oscillations are studied.The behaviors and the characters of low frequency oscillations are displayed by dynamic visual techniques.Demonstrations on the"11.9"low frequency oscillation of the Guizhou Power Grid substantiate the feasibility and the validation of the proposed methods.
文摘Insulating liquid plays an important role for the life span of the transformer.Petroleum-based mineral oil has become dominant insulating liquid of transformer for more than a century for its excellent dielectric and cooling properties.However,the usage of petroleum-based mineral oil,derived from a nonrenewable energy source,has affected the environment for its nonbiodegradability property.Therefore,researchers direct their attention to renewable and biodegradable alternatives.Palm fatty acid ester,coconut oil,sunflower oil,etc.are considered as alternatives to replace mineral oil as transformer insulation liquid.This paper gives an extensive review of different liquid insulating materials used in a transformer.Characterization of different liquids as an insulating material has been discussed.An attempt has been made to classify different insulating liquids-based on different properties.
