The Buck-Boost DC conversion circuit adjusts the duty cycle of the switching tube. The smaller the duty cycle, the smaller the output voltage; the larger the duty cycle, the larger the output voltage. In this way, the output voltage Uo can be higher than the input voltage Us, which not only plays the role of boosting the voltage of the circuit; but also can realize the output voltage Uo lower than the input voltage Us, which not only plays the role of stepping down.
Power circuit: Combining the topological structures of the Buck conversion circuit and the Boost conversion circuit, removing the passive switch in the Buck circuit and the active switch in the Boost, constitutes a new topology of the conversion circuit—the boost Step-down (Buck-Boost) DC conversion circuit. It consists of a voltage source Us, a current converter, and a voltage load, and the middle part contains a first-stage inductive energy storage current converter. Buck-Boost DC conversion circuit is a single-tube non-isolated DC conversion circuit whose output voltage can be higher than or lower than the input voltage; There is a big difference, namely: the polarity of the output voltage Uo and the polarity of the input voltage Us are opposite, the output current and the input current are both pulsating, but due to the existence of the filter capacitor, the load current is continuous.
Control circuit: set the expected output voltage value U_ref, and make a difference between the expected output voltage value U_ref and the actual voltage value U_o to obtain the current control error U_eer. After the lower limit is limited, the current control value Uc is obtained, and Uc is compared with the sawtooth wave Sw to obtain the current PWM pulse. When the input or load of the Buck-Boost converter changes, the current output voltage U_o will change, and the feedback control circuit will automatically generate a new control value U_c. After comparing with the sawtooth wave Sw, a new duty cycle PWM is obtained. Pulse, so as to adjust the main circuit to quickly recover to the desired output voltage value.
Control circuit: set the expected output voltage value U_ref, and make a difference between the expected output voltage value U_ref and the actual voltage value U_o to obtain the current control error U_eer. After the lower limit is limited, the current control value Uc is obtained, and Uc is compared with the sawtooth wave Sw to obtain the current PWM pulse. When the input or load of the Buck-Boost converter changes, the current output voltage U_o will change, and the feedback control circuit will automatically generate a new control value U_c. After comparing with the sawtooth wave Sw, a new duty cycle PWM is obtained. Pulse, so as to adjust the main circuit to quickly recover to the desired output voltage value.
Experimental simulation:
Technical indicators: Design a non-isolated Buck-Boost conversion DC voltage power supply with an input of 20V-60V and an output of 40V , and use a PI controller to build a voltage single-loop feedback conversion circuit .
Build a simulation circuit diagram based on the circuit schematic diagram
see emulator
Experimental results
1. Input DC voltage 20V, output DC voltage 40V (boost function)
2. Input DC voltage 60V, output DC voltage 40V (step-down effect)
The emulator gets:
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