I am currently researching on the application of the Four Switch Buck Boost Converter on a Fuel Cell Hybrid Vehicle, and I would like to ask about the transition mode of the buck boost converter. I have found 2 methods of implementation for the transition mode.
Figure 1: First implementation of the FSBBC (a) circuit (b) PWM signals
The first implementation uses two different duty cycles. The buck operation is achieved by the application of the buck duty cycle on Q1 (complementary buck duty cycle is applied on Q2) and the boost operation is achieved by the application of the boost duty cycle on Q3 (complementary boost duty cycle is applied on Q4). The buck duty cycle is fixed to 0.8, and the boost duty cycle varies from 0.05 to 0.45, depending on the desired Vout from the applied Vin
Figure 2: Second implementation of the FSBBC
The second implementation uses one duty cycle and has the transistors working in pairs. The A-D pair turns on during the first sub-interval of the duty cycle, and the B-C pair turns on during the second sub-interval of the duty cycle. The duty cycle is around 0.5 depending on the desired Vout from the applied Vin.
- The simulation of each implementation works, but are each implementation possible from a physical implementation standpoint?
- What are the advantages or disadvantages to using the first implementation over the second implementation and vice versa? It seems that the second implementation is more common compared to the first implementation, despite the higher current flowing through the inductor during its operation. I say "common", because most of the papers I've found online use the second implementation.
- Why is the current flowing through the inductor in the second implementation higher (input current + output current) as detailed in this link: https://e2e.ti.com/blogs_/b/powerhouse/archive/2015/03/16/do-not-operate-a-4-switch-buck-boost-converter-in-buck-boost-mode
I have attached the 2 papers I've referenced in the google drive link below for further information: https://drive.google.com/drive/folders/1Z25cREcIzBCCv4K6PO2a87GD-ruKcjmQ?usp=sharing
Please correct me if my understanding is incorrect, or there are gaps in my explanation. I would greatly appreciate any help you can provide. Thank you.