4-quadrant DC/DC converter - advantage and disadvantage - Page 1
Forum section: electronics / projects

author: Mehran
author_rank: Contributor
timestamp: May 23, 2020, 04:05:09 pm
content: I have been given a multi-part question to answer. Answered everything but stuck on the last part, which asked for a 4-quadrant DC/DC converter - advantage and disadvantage but can't use complexity andcost as a disadvantage. I cant use the lecture sides since... don't want to say any bad... but not up to standard for an EE course. Google is likeplenty of advantages but not being able to say cost or complexity for a disadvantage has really cut me off at the knees.Any good technical reasons why a 4-quadrant DC/DC converter should not be used over a 2-quadrant? Or a drawback...or anything other than cost or complexity?Any ideas? thanks

author: Siwastaja
author_rank: Super Contributor
timestamp: May 23, 2020, 05:34:40 pm
content: The question seems, IMHO, so strange that just making sure, do you know what 4-quadrant operation means? Let's start there.Obviously, if yourequire4-quadrant operation, then it's indeed an "advantage" being able to do what you need to do. If you don't require it, then there are the obvious disadvantages of complexity and cost you already listed.

author: Benta
author_rank: Super Contributor
timestamp: May 23, 2020, 05:38:16 pm
content: I'm also stumped.OP, could it be that you mean full-bridge vs. half-bridge?

author: Picuino
author_rank: Super Contributor
timestamp: May 23, 2020, 08:10:03 pm
content: 1 quadrant means positive voltage and positive current. You feed a motor only in one direction and only for accelerate, not to slow it down.You can do this with one transistor.2 quadrant means positive voltage and positive or negative current. The motor runs only in one direction but in this case you can accelerate and decelerate it. In this case you need 2 transistors (half bridge) and has one disaventage: the deceleration energy of the motor pushes up the input voltage so, to avoid this, one mechanism is necessary to consume this electric energy.4 quadrant is the same that 2 quadrant with the capacity of moving the motor in both directions. In this case you need 4 transistors (full bridge)

author: Benta
author_rank: Super Contributor
timestamp: May 23, 2020, 08:31:34 pm
content: Quote from: Picuino on May 23, 2020, 08:10:03 pmFrom the Department of the Obvious.There's a heck of a lot of difference between a DC/DC converter and a motor controller.We're still waiting for the OP's reply. I have a feeling it's a language issue.

author: Picuino
author_rank: Super Contributor
timestamp: May 23, 2020, 09:14:51 pm
content: 4 quadrant has the disadvantage of having a higher voltage drop and greater dissipation because the current has to pass through two transistors.The advantage is that you can rotate the motor in two directions.

author: Picuino
author_rank: Super Contributor
timestamp: May 23, 2020, 09:26:01 pm
content: Quote from: Benta on May 23, 2020, 08:31:34 pmSimple question, simple answerQuote from: Benta on May 23, 2020, 08:31:34 pmNo, they are the same thing, and it seemed to me that Mehran was talking about motor controllers.

author: Benta
author_rank: Super Contributor
timestamp: May 23, 2020, 09:29:51 pm
content: It's a trick question.Back when I studied EE, I had a professor who loved doing that as well.The so-called "2-quadrant" controller will only work in one direction. The lower transistor can be used for braking, that's all.The full bridge will let the motor operate in both directions, and will provide braking in both directions as well.

author: Picuino
author_rank: Super Contributor
timestamp: May 23, 2020, 09:44:42 pm
content: "Braking" is performed with both transistors (Low and High side) transferring energy from the motor (acting as dynamo) to input voltage source (like a boost converter).When that input source does not accept to absorb energy, it has to be dissipated in resistors. Is the case of big brake resistors placed at the top of the trains.http://www.resistorguide.com/braking-resistor/The "hard braking" made by short-circuiting the motor with the low side transistor can burn out transistor and/or the motor itself because the large amount of kinetic energy that is converted into heat.

author: Benta
author_rank: Super Contributor
timestamp: May 23, 2020, 09:50:46 pm
content: Quote from: Picuino on May 23, 2020, 09:44:42 pmWho said anything about "hard braking"? PWM is also an option. And now you're talking about "resistors placed on top of trains"?This is no longer normal.The fact is, that the so-called "2-quadrant" stage will only power the motor in one direction.'Nuff said.

author: ch_scr
author_rank: Frequent Contributor
timestamp: May 23, 2020, 10:41:32 pm
content: If you only need one direction, the 4 quadrant has the downside of having more losses, does'nt it?

author: Picuino
author_rank: Super Contributor
timestamp: May 24, 2020, 09:02:39 am
content: Quote from: Benta on May 23, 2020, 09:50:46 pmI need a resistor to dissipate the braking energy. Why do you say the braking resistors are not normal?http://www.resistorguide.com/braking-resistor/Quote from: ch_scr on May 23, 2020, 10:41:32 pmYes, twice as many losses because the current goes through two transistors instead of one.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 24, 2020, 06:09:35 pm
content: Hi,There are other examples;Low voltage UPS.You can have a synchronous buck batter charger, working as a synchronous boost in the back-up mode.This is two quadrant positive voltage, positive and negative current.TEC controllerThis is two quadrant, positive voltage, positive current and negative voltage, negative current.A class D amplifier is four quadrant.A 4 quadrant power supply must be fed by a two quadrant power supply, that is one that can absorb power.In two of the quadrants power is flowing from the load back to the source.Regards,Jay_Diddy_B