.Set the negative terminal of DC bu

.Set the negative terminal of DC bus and the negative terminal of supercapacitor to zero point. It can be clearly seen that if the phase shift angle is 0, Q1Q3 and Q2Q4 are turned on at the same time, then the energy on the DC bus cannot enter the transformer, and there is no energy output on the secondary side. If the phase shift angle is 180, that is, the phase difference is half a cycle, and Q1Q4 and Q2Q3 are conducted uniformly, then the primary side of the transformer (point AB in Figure 2-7) can get a square wave voltage alternating with positive and negative, with the peak-to-peak value of the square wave voltage being twice V1, and the secondary side and the primary side voltage are in a corresponding relationship of variable ratio. If the phase shift angle is between 0 and 90, the voltage obtained after secondary rectification (point E in Figure 2-7) is the direct voltage with a certain duty cycle