Mitsubishi UPS

[penman53]

Can someone please explain to me how the chopper circuit works for battery charging in a UPS. How is the voltage and current controlled? I noticed on one particular circuit that two DCCT's were in series with each other. I think one is used to monitor the current (current limit) the batteries during charging. The other one is most likely used to monitor the battery discharge when Utility power is lost and the UPS is operating on batteries. I really need to understand the chopper circuit. Thanks for all your help in advance.

Mark

 

[itsmoked]

Google up how any "switching supply" with "current limiting" works.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[penman53]

Well I googled and googled and never found anything specific about the UPS chopper circuitry used for charging UPS batteries. If you know of a specific site, I would be most appreciative.

 

[itsmoked]

I'm having a little trouble with this as I've never heard of a battery being charged with anything called a 'chopper'. If you are googling "chopper" I can see why.

Furthermore if this is just a semantic point it confuses me as to why you want to "understand" this. If you need to supply power to this thing, or you are trying to understand it for 'fun', or you are going to try to troubleshoot it now that it's dead.?????

Your question is like "why do cars go". Someone could spend a month, 8 hours a day, answering that question, if you see what I mean.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[NewbieButTrying]

Try this...

http://www.st.com/stonline/products/literature/an/1650.pdf

Discusses stepper motor performance and
constant current chopper drive ups

 

[penman53]

Mitsubishi UPS uses a device refered to as a chopper to charge the batteries for the UPS. The chopper is comprised of 1. an IGBT module, 2. two energy return diodes and 3. A fairly large choke.

I was hoping to fine out (because I am developing course materials on the UPS) how a chopper works to voltage control and current control the dc link and also charge the batteries when Utility (or generator) power is availabe. I have had lots of experience with IGBT controlled motor controllers but never a battery charger. I was hoping to find out here how it works to better enable me to write lessons to technicians that will be responsible for maintaining, troubleshooting and repairing the UPS. Mitsubishi is very close mouthed about the technical aspects of any of their products like most vendors they would love to not only sell the equipment but maintain and troubleshoot it as well.

 

[bjenks]

Since you are familiar with IGBT's then explaining should be pretty easy. The chopper cicuit is like a 6 or 12 pulse rectifier, but is usually firing at 8-23khz. The IGBT as you know fires fast and can handle a lot of current. The way it rectifies AC current to DC is the same way a computer power supply works. By varying the firing rate of the IGBT across a coil you can control the voltage (think faradays law or V=L di/dt). The output voltage of the coil then feeds into a large charging capacitor which is now your DC bus.

The firing of the IGBT at such a high rate has two advantages: 1) if it is firing as the 16kHZ or higher then you will have low audible noise compared to SCR. 2) Since the IGBTs are firing so fast and the firing is controlled by a feedback loop you actually get a power factor corrected circuit. Here is the little dirty secret that Toshiba and Mitsubishi won't tell you: That the only reason the IGBT are firing is to keep the DC voltage across the capacitor constant. But, what happens if you are only at 30% load and the capacitor is not being completely drained each cycle? Well the IGBT actually slows down it's firing rate or widens the pulse width. The little secret is that at about 50% load you start to loose the power factor correction. At 25% load the IGBT starts to act like a full bridge diode and you know have a non-linear power supply.

The Chopper Circuit consist of the IGBT and a base drive board and feedback controls. Mitsubishi brags about the base drive board being part of the IGBT and thus more efficient/reliable.

I hope that helps

 

[penman53]

Thank you, now were talking. Sounds like you have been around the block with some of these manufacturers. I appreciate such a straight forward concise answer.

 

[Tyranosaurus]

constant current limiting is straight-forward with "chopper" or switching power supplies. Most CMC (current mode control) PWM ICs have current limiting built in. It simply turns of an active switch when output current hits a threshold, similar to constant current in linear regulator.

 

[Tyranosaurus]

Is there a schematic with UPS? That would clarify everything. I'm designing a new inverter, to be used in UPS too, therefore my vested interest. What are the ratings of that UPS? Model # etc...The mfg may have complete docs on line.