Greetings all,
I am working on a somewhat strange project in which I am planning to use the rectified output of a three phase engine-driven generator to charge a large bank of ultracapacitors (20.8 F total, full potential of 389 V, total ESR ~100 mΩ). I will be using a series delta-wound generator capable of producing 266 VAC at 3600 rpm (375 V DC when rectified).
The challenge is to make sure that the DC charging voltage is kept below 50 A at all times in order to avoid overloading the generator (a real problem when the capacitors are at a low charge state).
I had first considered using phase-angle fired SCR to limit the AC current before rectifying, although this approach is expensive:
**broken link removed**
I am now wondering about direct control of the alternator field windings by with proportional feedback control. Basically, this involves controlling the current to the exciter stator. Excitation at zero load is 300 mA, full load excitation is about 1 A. The exciter stator resistance is 16Ω, so I could apply a variable DC voltage to the exciter between 4.8 and 16 V, by referencing the drop across a shunt resistor:
**broken link removed**
So, if I had a 1 mΩ shunt and wanted to maintain 50 DC amps, I would want the DC controller to increase exciter current for measured shunt voltage drops of less than 50 mV, and would decrease it if it was greater than 50 mV.
I already have the shunt and bridge rectifier in hand, but I have no idea if there is a device to control the power in this way. I have looked at programmable DC supplies without much luck in finding the flexibility in application that I'd need. I would hope to find as inexpensive a solution as possible.
This is a bit outside my normal field so I apologize for any silly mistakes, and I appreciate any advice. Thanks!
I am working on a somewhat strange project in which I am planning to use the rectified output of a three phase engine-driven generator to charge a large bank of ultracapacitors (20.8 F total, full potential of 389 V, total ESR ~100 mΩ). I will be using a series delta-wound generator capable of producing 266 VAC at 3600 rpm (375 V DC when rectified).
The challenge is to make sure that the DC charging voltage is kept below 50 A at all times in order to avoid overloading the generator (a real problem when the capacitors are at a low charge state).
I had first considered using phase-angle fired SCR to limit the AC current before rectifying, although this approach is expensive:
**broken link removed**
I am now wondering about direct control of the alternator field windings by with proportional feedback control. Basically, this involves controlling the current to the exciter stator. Excitation at zero load is 300 mA, full load excitation is about 1 A. The exciter stator resistance is 16Ω, so I could apply a variable DC voltage to the exciter between 4.8 and 16 V, by referencing the drop across a shunt resistor:
**broken link removed**
So, if I had a 1 mΩ shunt and wanted to maintain 50 DC amps, I would want the DC controller to increase exciter current for measured shunt voltage drops of less than 50 mV, and would decrease it if it was greater than 50 mV.
I already have the shunt and bridge rectifier in hand, but I have no idea if there is a device to control the power in this way. I have looked at programmable DC supplies without much luck in finding the flexibility in application that I'd need. I would hope to find as inexpensive a solution as possible.
This is a bit outside my normal field so I apologize for any silly mistakes, and I appreciate any advice. Thanks!