Repurposing a VFD for a fixed frequency specialty single phase motor?
Repurposing a VFD for a fixed frequency specialty single phase motor?
(OP)
I'm working for a company that is making Stirling engine cryocoolers. We have a single phase, permanent magnet linear motor that reciprocates at 60Hz. You vary the amount of cooling by modulating the voltage applied the the windings. More voltage equals more linear motion, which displaces a higher volume of the working fluid, which in turn extracts more heat from the heat exchangers. Se we need a 10kW, 0-270VAC variable source of 60Hz power. It seems like a sufficiently over-sized off-the-shelf VFD has all the necessary hardware to perform the power conversion that is required to go from 3-phase 480V on the input side, to single phase variable AC voltage on the motor side, at a constant 60Hz. The problem as I see it is the embedded firmware in the VFD. Does anyone know of a VFD that has enough flexibility which would allow us to operate in a fixed frequency, variable voltage manner? Or one that allows extensive reprogramming of the internal operation of the drive? I've contacted a few VFD manufacturers, and so far the message is that they don't support something like this.
Thoughts?
Thoughts?





RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Just curious, have you considered a lamp dimmer? 10kw modules are available.
iceworm
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Output:
Single phase
Sine wave
Fixed 60hz
variable voltage 0V - 270V
Nope - No help. I don't have any good ideas at all.
Motorized 10kva variacs are available. But that won't meet your input even loading spec. And one would have to gin up a 4-20 (or what ever control signal you are using) to control the variac motor.
As for theratrical dimmers, the few I've seen are triacs (or parallel SCRs) The control inputs are available, but you would need an output filter, input transformer, and it still would not meet the 3ph input even loading
I'm pretty sure you have already considered all these things.
ice
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
From experience Schaefer's C-Series is fairly versatile and very good reliability. They have a 'specials' group who can take on custom work based on their standard blocks. This link is something which I haven't seen before from them - looks like a good match to your requirements.
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Curt Wilson
Delta Tau Data Systems
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Connect the secondaries in zig-zag, such as is used to convert three phase generators to single phase generators.
At unity power factor the KVA loading will be equal on all three phases.
The power factor on one phase will be unity, on one phase the power factor will be leading and on the other phase the power factor will be lagging.
The sum of the transformer KVAs will be 150% of the load KVA.
Because of the power factor issues, one leg will supply 50% of the KW loading and the other two phases will each supply 25% of the KW loading.
Now you have 240 Volts AC with the KVA load balanced across three phases.
Add a 240 Volt to 280 Volt Variac and you are done.
Bill
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"Why not the best?"
Jimmy Carter
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
ice
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Bill
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"Why not the best?"
Jimmy Carter
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Truthfully, I would not have a clue how to calculate ground fault currents with a grounded Wye primary and a grounded zig-zag secondary. Of course , maybe it doesn't matter - it's only 10kva.
In any event, the idea of using a 3ph primary and a 120/240 zig-zag secondary to partialy balance a single phase load across 3 phase is good.
ice
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
The zig-zag connection that I was referring to is the connection used to convert a three phase generator to true single phase output. No relation to a zig-zag grounding transformer.
Bill
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"Why not the best?"
Jimmy Carter
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
Possibily I knew that too. About the same as I figured you knew that when you said
I don't know what brought up z-z grounding transformers.
ice
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?
http://www.deltatau.com/DT_IndexPage/index.aspx
RE: Repurposing a VFD for a fixed frequency specialty single phase motor?