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571 Posts
It's not a new idea; AFAIK some HEVs use exactly that. It makes sense when you use a boost converter from a lower voltage battery pack anyway to make the boost stage adjustable.
However, I'd suggest the general approach that:
- first define exactly what is the problem you are going to solve
- then make sure it really is a problem.
Your suggestion boils down to these parts:
- There is a PWM "inaccuracy" when stepping down too much
- High voltage pulses are stressful to insulation
- There are more switching losses.
First, I don't get the "inaccuracy" point at all. If you have that kind of problem, you have chosen absolutely wrong tool for the job.
Are the voltage pulses stressful to insulation? The motor needs to withstand the high voltage anyway if you are going to boost the voltage when necessary. Does it make a difference if it runs a little bit lesser time? Your suggestion would necessitate two parts with high insulation requirements, the converter and the motor.
And, any improvement in switching losses is negated in increased conduction losses and extra losses in the first boost/buck stage, I think.
IMO, you just introduce extra complexity with extra parts which need similar ratings to the motor, when you already have the motor that can do the buck converter job just perfectly fine (and need to do it anyway), and it's already there.
However, I'd suggest the general approach that:
- first define exactly what is the problem you are going to solve
- then make sure it really is a problem.
Your suggestion boils down to these parts:
- There is a PWM "inaccuracy" when stepping down too much
- High voltage pulses are stressful to insulation
- There are more switching losses.
First, I don't get the "inaccuracy" point at all. If you have that kind of problem, you have chosen absolutely wrong tool for the job.
Are the voltage pulses stressful to insulation? The motor needs to withstand the high voltage anyway if you are going to boost the voltage when necessary. Does it make a difference if it runs a little bit lesser time? Your suggestion would necessitate two parts with high insulation requirements, the converter and the motor.
And, any improvement in switching losses is negated in increased conduction losses and extra losses in the first boost/buck stage, I think.
IMO, you just introduce extra complexity with extra parts which need similar ratings to the motor, when you already have the motor that can do the buck converter job just perfectly fine (and need to do it anyway), and it's already there.