Basic Power Electronics Question

[raschemmel]

Given that B is ALWAYS<A

 

[Diver300]

Maybe I'm missing something here but if Dc source A is in series with dc source B and B reverses polarity then instead of A+B=C uou
have A-B=C.
How is that catastrophic ?

It could be catastrophic for the DC source B.

That is why it's common to put diodes in parallel with power supplies when the power supplies are put in series. See my post #10.

 

[Diver300]

What are the odds ?

Any circuit protection happens by turning things off. You have to allow for it to happen.

If you can't turn off either power supply, how do you shut the system down?

 

[raschemmel]

"4) What happens if the inverter short out or otherwise overloads the circuit?
Does the power supply turn off, the battery management system shut down or a fuse blows?"

The P.S. has very good current limiting.
As you probably know , an inverter using IGBTs
is always subject to IGBT failure. The inverter
is still in the R&D phase so part of this question
is about ways to test it. The battery has a BMS
that shuts it down if conditions warrant it and the
power supply model has been in use for probably
longer than you've been alive. (just a guess).

 

[Pommie]

You seem to have all the answers, so just go ahead and do it. It's only 360V at 220A, what could possibly go wrong.

Mike.

 

[raschemmel]

If I were reckless I would have already done it.
For 80kW you can never have too many second opinions.

 

[Pommie]

If I were reckless I would have already done it.
For 80kW you can never have too many second opinions.

But, you ask a question and then argue against all answers. Why did you ask the question?

Mike.

 

[raschemmel]

If you can't turn off either power supply, how do you shut the system down?

We can turn off the power supply but I'm not sure why that would be necessary if
the current limiting works.
The battery has a BMS with shutdown when the battery becomes fully discrarged.
There is an EPO that can disable the contactor.
It's a valid question and certainly a shutdown protocol would have to be created.

 

[raschemmel]

But, you ask a question and then argue against all answers. Why did you ask the question?

I'm waiting for someone to debunk my all of my answers.
For example:
If A<B,
A>0
B>0
A+B=C
If B<0
.'.
C=A-B
How is that wrong ?

 

[raschemmel]

That is why it's common to put diodes in parallel with power supplies when the power supplies are put in series. See my post #10.

Maybe these ?: (if I <150A)
" vs-45lrseries-1769098.pdf (mouser.com) "

 

[raschemmel]

But, you ask a question and then argue against all answers. Why did you ask the question?

If you answer my question and do not agree with my answer, is there any reason you can't
simply state your reason for not agreeing with my answer instead of implying that I must
accept any answer simply because it is given ?

 

[rjenkinsgb]

Because you cannot grasp one of the basic principles and keep arguing it!
The polarity across the PSU will reverse under fault or overload conditions and the current limit provides no protection.

If everything is working OK within safe limits, this is the configuration:

V1 the battery, V2 the PSU and R1 the system load.

However, if anything overloads the PSU or that shuts down, the effective configuration is this:

The PSU becomes part of the load on the battery, in series with the intended load and with its polarity forced to reverse.
That equals destruction.

Current limiting within the PSU simply means its output voltage can collapse / reverse even more easily than if it had none.

 

[JimB]

I'm waiting for someone to debunk my all of my answers.
For example:
If A<B,
A>0
B>0
A+B=C
If B<0
.'.
C=A-B
How is that wrong ?

If A<B,
A>0
B>0
A+B=C
OK, so far so good.

Then you say If B<0
making B a negative quantity
So
C= A+B is still the correct mathematical expression.

Try some numbers let A = 10 and B = 5
C = A + B = 10 + 5 = 15

Now let A = 10 and B = -5
C = A + B = 10 + (-5) = 5

But if C = A - B
C = 10 - (-5) = 15

Basic algebra.

JimB

 

[billybob]

Maybe I'm missing something here but if Dc source A is in series with dc source B and B reverses polarity then instead of A+B=C uou
have A-B=C.
How is that catastrophic ?

because the power source with more voltage is having to force its current through the lesser power source probably producing some heat due to the resistance of the lesser power source? Im not completely sure on the theory, but these guys can explain it better.