Is Recharge Required for Inverter Module?

Again the note regarding slowly pre-charging capacitors of inverters (variable speed drives, etc) if they have been sitting off for 6 months or more is common.

Electrolytic capacitors by their very nature 'break down' (the insulation between plates that is) over time and when power is applied to them they reform, the problem is that the reforming (leakage) current can stress the drives capacitor charging circuitry causing current limiting devices to operate (or in some cases the capacitor to rupture or vent). I have seen this in a number of cases.

Technically for all large electrolytic capacitors (the larger the more applicable) left discharged for long periods you should pre-charge them with a slowly increasing voltage (or voltage steps) to limit the inrush current and the potential stress and damage this can cause.

What happens in the real world is most people don't bother, and in some cases the drive capacitors (or drive electronics) fail prematurely. The note is in the manufacturer documentation as a "we told you so" both for their protection and for the users.

Your thread title said "Recharge", you later said "precharged". They are different things.

I think because of that thread title, this is being confused with STORAGE of a VFD. As I interpret the question using "pre-charge" I see a different issue; you are being told by ABB not to have the VFD in a Run state when you initially close the feeder, is that right?

This can theoretically be true of all brands of VFDs. The reason is that when you first energize a VFD from the line source, the DC bus capacitors have to charge for a few cycles before they get to full voltage and smooth out the ripple from the rectifier. To facilitate this they use what is called a "pre-charge resistor" that limits the current flow while the caps are charging and so that the transistors are not exposed to the ripple, which can make them falsely trigger. Without it, the drive transistors can fire on their own at the wrong times and die in short order. But the resistor is only in the circuit for a brief moment when the drive is initially powered, then it is shorted out. If the VFD is in a Run state when all this is happening, the transistors start seeing the raw rippled low voltage power right off the rectifier and that alone can damage them. In addition, pulling power off of the DC bus before the caps are fully charged can damage pre-charge resistor bypass and when it goes, the resistor doesn't get shorted out of the circuit, then it over heats and opens. Shortly thereafter the transistors die.

There are drives where this pre-charge resistor is not the problem, because they use a front-end rectifier that has SCRs instead of diodes. SCRs are used to slowly ramp the voltage into the capacitors. But that means you must have an SCR firing circuit for them, which adds complexity and a new point of failure. Lastly, some drives have "Line Regenerative" front ends, where essentially they have a 2nd inverse VFD so that they can re-fire excess energy from braking back into the line. Still though, you don't want the VFD in a Run state when being initially powered, because again, the capacitors will not be fully charged yet and you will have low DC rippled voltage on the bus.

All that this means is that you must have your control command system designed so that you wait a second or two before giving the drive a Run command when it is re-powered. Some drives power the control circuit FROM the DC bus, which inherently accomplishes this, others have a separate control power supply and it comes to life earlier than the DC bus. You need this configuration if you are using the SCR ramped rectifier, because you need to have the ramp generator powered BEFORE the DC bus is energized. This is where the danger lies and based on that comment I'd guess this is how the ACS800 is configured. That has become much more common now because of the power requirements of the VFD microprocessors.

If your supplier states that the VFD needs precharging before the feeder, this may imply either:

1. There is no charging circuit in this design so you must provide it according to their advice / recommendations OR

2. As other posts have interpreted, the main DC caps need reforming before you apply the VFD to use.

Can you clarify your question, please?

Some more specialised designs indeed do not include the charging circuit as I recently looked over such a design on a regenerative front end for a lift application, for example.

Or do you have an expanded DC link capacity for a longer mains ride through function?

Or is it just before using drives which have been in storage for some time?