High Precision Power Supply SCE Model 450
This family of high precision power supplies was custom developed for Brookhaven National Laboratory to power superconducting Corrector and Control Magnets for the Relativistic Heavy Ion Collider (RHIC). Six hundred and fifty units are located around the two mile ring.
These power supplies are actually controlled current sources which are remotely programmed to deliver specified currents through the superconducting magnet coils. Time and temperature stability specs are very tight -.05% repeatability and stability over 12 hours and 20 ppm temperature stability at full current. Output noise is also exceptionally low 5 mvpp. Additionally, during beam formation and shutdown, magnet current is ramped up and down. However, because of the very low resistance associated with these magnets - it is only the lead-in cable resistance during ramp down, the voltage across the magnet reverses polarity and the magnet actually delivers power to the supply. Thus the supply must be capable of 4 quadrant operation, while keeping current under very tight control at all times.
The SCE model 450, the first unit delivered, consists of a full bridge resonant phase controlled converter whose variable output feeds a bridge output circuit that performs polarity switching and fine-grain control. A new current sensor was developed based on flux gate magnetometer techniques that features much better stability and less noise than traditional current shunts - these power supplies can be set to within milliamps of commanded current at the 50 Amp level.
The unit features full protection, error detection and reporting, start-up sequencing, etc., all under microprocessor control. In addition, a special over-voltage circuit called 'Quench Protection' (necessary only with superconductiong magnets) is incorporated.
Major Specifications
Model 450
Output:
| Voltage | -20 to +20 VDC |
| Current | -50 to +50 Amps |
| Control | Analog: 5 Amps/Volt |
| Linearity/Repeatability | .05% control voltage to output current |
| Absolute Accuracy | .5%, .1% typical |
| Stability | 20ppm/ºC, 50 ppm/12 hours |
| Output Noise, Common Mode | 10MVPP/1MHz BW |
| Output Noise, Normal Mode | 5 MVPP/1MHz BW |
| 2nd and 4th Quadrant Operation | 2V Max, internally settable |
| Switching Frequency | 100KHz ±10%, front panel adjustable |
Input Power:
| Voltage | 208VAC ± 15%, 60 HZ, 3 |
| Maximum | 1400W |
| Input Power Factor | >85% at 700 watts or more! Better than 90% at full load |
Remote Inputs:
| Standby | TTL Levels |
| Off | TTL Levels |
| Operate | TTL Levels |
| Contactor Enable | TTL Levels |
Analog Outputs:
| Output Voltage (Chassis Reference) | 1V/2V ± .2% |
| Current (Chassis Reference) | 1V/5 Amp ± .1% |
| Setpoint (Chassis Reference) | 1V/1V ± .1% |
| Error: | 1V=10 mV error |
Operating Modes:
| Current Mode | 1Volt = 5 Amps |
| Voltage Mode | 1Volt = 2 Amps |
Front Panel Adjustments & Testpoints:
| Overcurrent | 30% - 100%, full output |
| Overvoltage (quench) | 1V to 20V |
| Quench Delay | V/sec |
| Heatsink Temperature | 10 mV/°C |
The model 450 performed so well that the family was expanded to include the 150 Amp (Model 440) and 300 Amp (Model 470).
The circuitry for the 440 and 470 is very similar to the 450, except control circuitry for the large supplies is modularized and relocated to removable VME cards.
The Model 440 (150 Amp) consists of a single off-line converter coupled with a larger (compared to the 450) bridge output section.
The Model 470 consists of two Model 440 power sections (converter and bridge output modules) stacked on the control electronics card cage. The technique is readily expandable to higher power levels.