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Standard boost converter layout, swapping diode for GANFET on node from inductor to battery, which is a pretty standard edit.
Timeline
Decision 1: Boost vs Zeta vs Resonance
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Option 1: Boost
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Option 2: Zeta
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Option 3: Resonance
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Overview
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Design already implemented, and tested so kinks are worked out. Only capable of boosting, and has a generally lower efficiency than other two options.
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Capable of boosting or bucking, very standard circuit layout that wouldn’t take too much messing around to make work. Generally higher efficiency and smaller passive components than boost converter.
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Can implement ZVS or “soft switching” which is intended to reduce or eliminate switching losses. Probably most efficient design, but only has this efficiency at relatively small input voltage ranges in basic designs. There are slightly more complex versions that can handle large ranges of voltage inputs and maintain efficiency. Dr. Hanson has a really good paper over this which pretty much tells you how to design one of these.
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Visual
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Pros and Cons
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Simple Design |
| Tip |
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Already made and tested so no changes needed other than flyback concerns |
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Least efficient option |
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| Tip |
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Simple Design |
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Very well known design and component requirements |
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Efficient |
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Can boost and buck |
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Needs to be designed and tested from scratch |
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| Tip |
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Most efficient option |
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Can boost and buck |
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Dr. Hanson has a paper telling us how to make one that works for our purposes, he could be a valuable resource |
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Slightly more complex design |
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More difficult to design and implement |
I am going to design the circuit using the resonance converter for now. The only concern that I have is that resonance converters are known to lose efficiency outside of specific input ranges. However the circuit topology I am choosing to use should be capable of maintaining high efficiency at larger input ranges.
ZVS Converter Spice Simulation
I am using LTSpice to simulate the converter with a python library that interfaces with it.
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Iteration 1
Purpose: Make a viable product that can boost the array voltage to the battery voltage. Less concern about efficiency than final product will have.
Design is a standard asynchronous boost converter with a simple feedback system.
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Used a standard, over-specced silicon MOSFET and diode to ensure robustness. The past design had problems with flyback voltage spikes and MOSFETS exploding. Mine should be very resistant to this since the switches should be very resistant to high voltages, and I implemented a varistor and tvs diode on the output side.
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Because it is asynchronous, the gate driver needs no bootstrapping scheme and is only for the low-side switch.
This boost converter design should be very robust and have a low likelihood of component failure. Assuming this iteration works, the next step in the project will be to make the converter half-bridge to improve efficiency. I don’t think it is a good idea to use GANFETs at this stage of the project. They may be able to improve efficiency marginally, but their tendency to fail under high-voltage conditions makes them difficult to effectively implement in a board as important to the car's function as the MPPT. Reliability > Efficiency
Engineering Diary
Check out Dr. Hanson's paper on a ZVS resonance converter design he made:
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