Research On Soft Switch Of Asymmetrical Half Bridge

Soft switching technology have been one of hot point of power electronic technologies for smaller and lighter and modularization converter .Soft switching is zero voltage switching and zero current switching , which the voltage (or current ) of the switch varies by law of sine or quasi sine , so the switch is on when the voltage of switch drop to zero(the switch is off when the current of switch is zero) during the resonance. It makes switch loss is zero, so it can increase the switch on-off frequency ,raise the power density, minimize the size of the transformer and introductory. However it makes the circuit complex ,which means the increase of cost, and affect the competitiveness of commercial product . A topology of asymmetrical half bridge which is researched in this thesis can performance the Zero voltage switch (ZVS) by the resonating between the leakage introduction of power transformer and the parasitic capacitor to achieve higher efficiency without increase the cost of converter.The following items are studied in this thesis:(1) The topology of asymmetrical half bridge is introduced , including the principle of circuit ,relationship between the duty cycle ,input voltage and output voltage ,and the deflection of magnetism.(2) each state of the whole switch on-off cycle has been studied in detail. The voltage of block capacitor and the current of the original turns of transformer of each state have been discussed, then deduce the condition of Zero voltage switch(ZVS),which give the theory guidance for setting the reasonable dead time. Finally, the possibility of zero voltage switching is proved by the simulation of Saber software.(3) Modeling the asymmetrical half bridge converter In this thesis ,a small average circuit half bridge converter power stage is established by method of state space averaging. In term of the method referred, a system model of total converter is founded. The characteristic of stabilization and dynamic is analysed and the compensator is designed basing on it. At last ,the simulation performed by Matlab software confirm the stabilization of system.(4) The experiment of asymmetrical half bridge and the result Based on the analysis above, a two-class AC/DC converter ,consist of power factor circuit and asymmetrical half bridge circuit is designed to prove that the asymmetrical half bridge can achieved zero voltage switching .Then the thesis gives a method for the asymmetrical voltage of output rectified diodes ,which is to change the turns of second side of transformer and prove the idea by the experiment result.