Research On Energy Active Recovery Snubber During The Switching Transition In Power Electronics

The device loss of power electronics converters is consisted of switching loss and conduction loss, so the cooling devices are needed in the surroundings of switching devices. Moreover, the switching loss is proportional to the switching frequency of control signal. With the development of switching frequency, the switching loss must be reduced to decrease the size of cooling devices and improve the efficiency of the converter systems. Nowadays, the soft-switching technology is presented as the main method of reducing switching loss. It can be classified as two categories according the auxiliary branches:active soft-switching and passive soft-swicthing. The passive soft-switching isn’t affected by the variance of parameters in the resonant circuits and it doesn’t need the auxiliary switching devices. So it is more and more attractive. Especially with the development of high power applications, passive soft-switching is used in the bridge-leg unit to reduce switching loss. At the same time, an energy recovery snubber unit is used to transfer the switching loss from snubber capacitor to the input voltage source. However, there is loop current exiting in the energy passive recovery circuit presented in the literature, thus the efficiency of entire converter will be reduced. To solve these problems, four types of bridge-leg units with energy active recovery snubber are proposed in this paper, the energy recovery snubber can be any types of isolated DC/DC converter and its control signal is independent with the signal of main switching devices and the modularization can be realized.Firstly, the constructions and working principles of bridge-legs with energy active recovery snubber are analyzed in detail in this paper. Their resonant equations in every mode are given according to the equivalent circuits and the lasting time can be calculated. Secondly, the comparisons of characteristics on passive soft-switching among the four types are analyzed. The advantages of four types can be obtained by calculating the switching loss, additional loss of auxiliary diodes and extra loss in the energy recovery snubber. At last, the prototypes of single and double snubber capacitor, low voltage stress energy active recovery circuit topologies are set up to verify the advantages. The switching waveforms, switching loss and efficiency of power electronics converters are compared with those of energy passive recovery circuit. It is shown that the switching loss of passive soft-switching can be reduced and the efficiency can be improved. To further reduce the turn-off loss of IGBT, a kind of voltage controlled variable capacitor is presented in this paper. When IGBT is turned off, the voltage controlled variable capacitor is equivalent to the characteristics of large capacitor. Thus the rising rate of voltage across collector and emitter is suppressed greatly. When the auxiliary MOSFET of voltage controlled variable capacitor is turned off automatically, the voltage νCE is increased to the input voltage rapidly. So it has no effect on the working state of the converter. The prototype of passive soft-switching with voltage controlled variable capacitor is built in this paper to test the turn-off loss of IGBT. The results show that the turn-off loss of the voltage controlled variable capacitor can be reduced to28%of the turn-off loss of hard-switching, comparing with the constant capacitor. So the size of cooling device can be greatly reduced. At the same time, the realization circuit of voltage controlled variable capacitor is very simple and the cost is low. So it will be widely used in the power electronics applications.