Made by Lichuang eda-bidirectional DCDC automatic voltage stabilizing system with 9v output

Engineering principles:
(1) Derivation of the BUCK converter voltage gain formula:
Assume the input voltage is Ud, the output voltage is Uo, the duty cycle of the switch tube is D, and one cycle time is Ts.
In the continuous mode, the inductor voltage in the switching converter must repeat periodically, and the storage energy of the inductor in each switching cycle is 0, then there is (Ud-U0)*D*Ts-Ud*(1-D)*Ts=0 , the solution is Uo/Ud=D, that is, the voltage gain of the buck circuit in continuous mode is D.
In intermittent mode, assuming the diode freewheeling duty cycle is D1. Then there is (Ud-Uo)*D*Ts-Uo*D1*Ts+0=0, and the solution is Uo/Ud=D/(D+D1 ). And the voltage across the inductor UL=L*diL/dt, integrate both sides to get L*ILmax=(Ud-Uo)*D*Ts, and the solution is Io=(D+D1)*Ts*ILmax/(2* Ts), you can get the value of D+D1. Substitute it into the voltage gain formula in discontinuous mode to get M=D^2*L*fs/(Ud8(1-M)*D).
 
Define Ib=Ud/L*fs (base value), Io*=Io/Ib (ratio). The voltage gain formula of the buck circuit is derived as follows: In continuous mode, M=D, in intermittent mode, M=D^2/(2*Io*+D^2)
 
 
(2) Derivation of the voltage gain formula of BOOST converter:
Assume the input voltage is Ud, the output voltage is Uo, the duty cycle of the switch tube is D, and the cycle time is Ts.
In continuous mode, the current change of the inductor in each cycle is 0, UL=L*diL/dt, integrating both sides,
the BOOST voltage gain in continuous mode is 1/(1-D).
 
In discontinuous mode:
for the output Current, in one cycle, the total output current is equal to the total current flowing through the inductor. According to the current-time graph flowing through the inductor, the area of ​​the rectangle is the product of the output current and time, and the area of ​​the triangle is the product of the current flowing through the inductor and time.
 
 
(3) Derivation of the voltage gain formula of the bidirectional DCDC converter:
 
In pure buck and pure boost modes, the voltage gain is consistent with the buck converter and boost converter respectively.
In the buck-boost interactive mode:
Therefore, it can be concluded comprehensively that assuming the turn-on duty cycle of tube 1 is D1, the turn-on duty cycle of tube 2 is D2, D1+D2=1, then the voltage gain of the bidirectional DCDC converter is D1 or 1 -D2
 
Engineering Explanation:
                Based on the above analysis, the purpose of this circuit is to automatically reduce the voltage of 9v-50v (up to 600v, 50v is only limited by the withstand voltage of the electrolytic capacitor) to 9v for output. It is realized by outputting PWM wave from the microcontroller. For example, input 18v, output 9v, the duty cycle of the PWM wave is 50%; input 12v, output 9v, the duty cycle of the PWM wave is 75%, and so on. Then the output logic setting of the pwm wave is relatively simple and can be achieved using a simple pid algorithm (see mian.c of the engineering code file).
Physical demonstration:
                See the video attachment (voltmeter on the left), it can be seen that the input voltage is between 13v and 24v When changing between them, the output can be stable at around 9v.