Hi,
My requirement: To convert 1 phase 115V 50Hz power to 3 Phase 200VRMS, 200-600Hz.
I am using VFD1A6MS11ANSAA for my requirement.
VFD 3phase output connected to a transformer to convert to 15 phase then rectified to generate 270VDC.
VFD1A6MS11ANSAA rated for 1.9A max current , but my transformer inrush is >5A for 2 ms and steady state current is 200mA per phase.
Once i turn on VFD, after few seconds, its stops and shows OCa indication on display.
I would like to know how to make it work with inrush. Do i need to have any
- additional softstart between VFD output to transformer
- OR go for different module
- OR any option to enable in VFD to support inrush
Hello dineshbabu.chandran2, welcome to the TechForum! My initial thought is that it would be easiest to limit the inrush before trying other VFDs through some kind of ICL. However, I am not well versed in selecting these, so I asked my colleagues for some input regarding this. Hopefully I hear back from them soon.
It’s unclear from the information provided what the point of this step is; if the goal is to end up with a DC output, there are more direct ways to achieve such a result.
That said, p.494 of the user manual indicates that the ocA fault message indicates an overcurrent condition during acceleration:
If one’s trying to drive a transformer rather than a motor however, trying to “accelerate” it by starting at a low output frequency is not going to be very beneficial from an inrush standpoint, since a transformer is essentially a short circuit under such conditions. Any filter capacitance that may be present after the mentioned rectification stages would also need to be filled during the startup process, making the problem worse still.
Assuming the unit in question isn’t simply under-specified for the load that you eventually want to drive, configuring the ‘acceleration’ parameters to start at a high output frequency while ramping up the voltage would seem likely to offer you the best chances of success.
Hi,
I appreciate your time. To make it clear on my requirement.
I need a minimum of 12 pulse DC of 270V to drive my 3 refrigerator motors through IGBT
For that i need 12 phase AC with rectifier circuit to generate 12 pulse DC output.
To generate 12 phase i am using a transformer to convert 3 phase to 12 phase.
To generate 3 phase with variable frequency from standard available source 115V/50Hz single phase AC i am using this VFD here. Hope it make sense
I’m afraid I’m still not understanding the intent here; if the goal is to generate a DC output from an AC source, there are lots of items in the AC-DC converter or the test bench supply product families that could do that for you more directly and with less inconvenience.
Hi Rick,
I appreciate your suggestion. Unfortunately i dont have flexibility on modifying circuitry after transformer . it is proven and certified aerospace product in market more than a decade.
Only thing which i can do is changing the 3 phase source.
If i power with standard programmable power supply with 1.9A current limit. i can power my circuitry with out an issue. power supply capable to handle the inrush >5A and after 2ms steady state current approx 300ma on each phase.
But when i power through VFD, it starts with 200V with noise and in few sec it trigger the OCa and output is 0V.
I am trying to understand a limitation of VFD or really Inrush is a issue.
Since it is purchased from digikey. I really appreciate a visit to our Bangalore facility to understand and suggest your recommendation.
What power supply is being used in that case, and why is its continued use not a solution?
If the supply being used allows a current limit to be set as the first statement above suggests, then the supply is limiting any inrush phenomena that may otherwise occur.
The VFD does not limit current by restricting its output as a current-limited supply generally does; it simply shuts down if an overload is detected.
Especially if it is configured to “accelerate” by ramping up output frequency from a low value when a startup command is issued, attempting to drive your transformer using a VFD is likely to result in worse inrush behaviors than if the lead were simply plugged into a low-impedance source such as a utility service.
The manual discusses some relevant settings on or about p.276
Could you please suggest ICL part for my requirement
Products in the inrush current limiter family can be selected by choosing one with a steady-state current rating equal or greater to the steady-state current requirement of the application, and an initial (25°C) resistance sufficient to provide the necessary degree of initial impedance.
I am doubtful that this will solve the problem however, because they are typically used to address phenomena that occur on time scales of a few AC cycles, rather than several seconds as is reported to be the case here.
Please measure and plot the VFD output frequency and voltage during the startup process.
When i powered transformer with standard 3 phase programable power supply with 3A current limit, channel 4 is an inrush across phase 1. Followed by Ch1,2,3 or voltage across U-V, V-W, W-U using differential probe.
Inrush is around >5A for approx < 4ms once powered on
This is to be expected, however it is the output of the VFD that is in question.
no. When i use VFD as source to the transformer
Ch1: VFD input 115V single phase 50Hz
CH2 and CH3: voltage across U-V and V-W using differential probe
CH4: Current on phase U.
Once VFD output On, output flickers for few seconds and turned OFF with error OCa.
The envelope of the output voltage waveforms suggests that the VFD is attempting to generate an output with a frequency of approximately 0.5 Hz.
A transformer designed for ~400Hz operation would appear essentially as a short circuit to such a signal, and an overcurrent error is absolutely to be expected under such conditions.
The issue here does not appear to have anything to do with “inrush,” but rather a VFD configuration that is completely inappropriate for the task.
My advice would be to adjust the VFD settings to more appropriate values in consultation with the user manual, using a resistive dummy load (incandescent light bulbs perhaps) during the process to limit the potential for damaging the VFD.
