The issue at hand is a part of a VFD system that is seldom discussed, called a "pre-charge" circuit. This is absolutely necessary for all VFDs, because the DC bus caps, when FIRST energized, will instantly charge themselves up, and will do so at the AVAILABLE FAULT CURRENT level, even though that might actually damage the caps themselves. So for the first few seconds, the VFD puts a current limiting resistor in series with the caps as they charge, then once charged, a relay (or contactor depending on the size) shorts around that resistor so that it's not in the circuit constantly. Some VFDs however use SCRs instead of Diodes on the rectifier, so they "soft start" the DC rectification to get the same effect. Yet others use an NTC thermistor in series with the DC bus, which has a high resistance when cold and low resistance when hot, so it inherently soft starts the DC into the caps. There is no way of knowing by looking at them how any particular VFD accomplishes this.
The problem with feeding a VFD directly with DC, is just that; you don't know HOW the VFD mfr designed that pre-charge circuit and where it is in the unit. So if you tap your DC into it on the down stream side of the pre-charge, you might blow the caps the instant to energize it the first time (or some future subsequent time if you dodge the first bullet).
So some drives are designed to allow you to do this, some are not, there is no way to tell in advance without asking the VFD mfr if it's possible,
and if they will stand behind the warranty in writing if you do (always a good way to filter out the idiot inside sales people who say yes to everything without really knowing).
One way around this is to build the pre-charge functionality yourself into the DC power source. There are companies that actually MAKE DC power sources specifically for this purpose and offer them WITH the DC pre-charge in their package. One that I have used is
Bonitron, it's a great unit. One issue with using a VFD for single phase input is that you must at LEAST double the size of the VFD with respect to the motor size, because the drive needs more DC bus capacitance to handle the added ripple from rectifying the single phase. At 230V 3HP and below, this is often designed into the VFDs anyway, because the added device cost at that level is negligible. But if your motor is 5HP or more, that's where you must at least double the size of the VFD (
if it has a DC bus choke,
triple the size if not). That's where using a DC input from a unit like the Bonitron pays off. When you double the size of the VFD to get the added capacitance, you are also doubling the size of the transistors and although you don't need that, you are paying for it so it's a waste. Feeding it (correctly) with DC avoids having to over size the VFD, assuming that the DC is already smoothed out (another thing the Bonitron unit does for you).