60->50Hz Frequency Converter with Regenerative Loads

[bill318]

We have an application that requires the use of a frequency converter 480V/60Hz mains, 400V/50Hz loads. The 50Hz side must be a low distortion sine wave so a rotary phase converter is being considered.

(Scenario 1) On the 400V/50Hz load side we will have:
1) A constant 3-phase load of 10KW
2) A 10KW 3-phase device that can regenerate AC.

During regeneration, the power generated will be consumed by the constant 10KW 3-phase load and the loading of the frequency converter drops and all is well.

(Scenario 2) On the 400V/50Hz load side we will have:
1) A constant 3-phase load of 10KW
2) A 10KW single-phase device that can regenerate AC.

During regeneration we will have 10KW flowing back on a single phase pair (10KW/400V = 25A). The 3-phase load will consume 10KW 3-phase = 14.4A per phase leaving 10.6A of current flowing back towards the frequency converter on a single phase pair.

From what I have been able to find so far, most frequency converters do not like current flowing back into them as the voltage may rise causing a shut down. One solution is to load down the single phase pair so that the frequency converter always sees a load even during regeneration. To keep the distortion low a resistive load bank could be used. Burning off the excess power as heat is not desirable in this application.

Questions:
1) Does anyone know of a phase converter that can handle these two scenarios without faulting or going out of control?
2) Since it is only a single phase pair that current would be flowing backwards on, would this current be used by the phase converter to provide a portion of the shaft torque and still remain under control?

Thanks in advance for any thoughts on this.

Bill

 

[waross]

You can use a transformer to mitigate this somewhat.
Delta primary and zig-zag or double delta secondary.
aif the single phase load is connected on C phase, then "C" phase will supply 1/2 of the current and "A" phase and "B" phases, acting as an open delta with a load across the open side will supply 1/2 of the current. The phase angles of the currents will be such that "A" phase will see 2.5 kW and 5 KVA and phase "B" will see 2.5 kW and 5 KVA.
But, if the rotary phase converter is using a delta winding it may do this itself without the aid of a transformer.

Bill
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"Why not the best?"
Jimmy Carter