When it works normally, it is in a stable state, and when the switch tube Qi is closed, the inductor Li corresponding to the bridge arm is charged and the current rises; When the switch Qi is turned off, the inductor Li corresponding to the bridge arm is discharged and the current drops. Volt-second balance, rising and falling current are the same in each opening cycle. The rise and fall of inductor current is reflected on the load as voltage ripple. If it is a resistive load, the voltage ripple and inductor current ripple are in positive correspondence. With three inductors connected in parallel, it can be seen that the output current ripple is 1/3 of the current ripple of a single inductor and the frequency is 3 times of the original one.