CAT BOARD A3-290605 CONTROL AND TRIGGER BOARD FOR 3-PHASE POWER SUPPLIES Dynapower/Rapid Power Corporation 85 Meadowland Drive South Burlington, Vermont 05403 Phone: 802-860-7200 Fax: 802-864-3782 Toll Free : 800-332-1111
The Control and Trigger Board, CAT Board, is designed to the requirements learned from many years of experience with SCR controlled high power equipment. Modern CMOS integrated circuit technology has allowed an extremely compact, unitized design with low power consumption. The following description covers the major features and applications of the design. The CAT board has been designed and adjusted to operate in either 50 Hz or 60 Hz power systems. Spare boards are shipped configured for 60 HZ. For operation in 50 Hz power systems, the User must remove the jumper connected to TB4. CONTROL AMPLIFIER AND TRIGGER SETTINGS AND SPECIFICATIONS
I. Power and Reference Regulator 1. Control power (120 VAC nominal) must be applied to terminals TB1-1 and terminal TB1-2. a) Minimum input voltage: 85 VAC b) Maximum input voltage: 135 VAC 2. Phasing References a) Must be applied to terminals TB1-3, TB1-4, and TB1-5. b) Correct phase rotation and sequence is important to assure proper firing of the SCR s. c) The 3-phase references must be balanced to within ± 5% of each other. The CAT board incorporates phase imbalance detection and in the event of a lost phase or high imbalance the board will inhibit its output until the phase balance has been restored. d) The voltage of the 3-phase reference is not critical; it may be between 60 VAC and 200 VAC. e) The 3-phase reference may be obtained through a resistor divider or through three small control transformers. 3. Control Amplifier Reference a) A stable control reference with a low temperature co-efficient is provided on terminal TB1-7. b) The reference must be preset to 5.00 volts through P1; it can supply approximately 30 ma to the control potentiometers. c) The control potentiometers may be 10K, 2 watts. They are returned to terminals TB1-12 (VREF) and TB1-13 (IREF). The ground return is terminal TB1-6. d) Ample filtering of the input reference inputs (RC = 0.4) is used to obtain maximum noise suppression before the control amplifier.
II. Voltage and Current Feedbacks 1) All feedback signals are applied to the control amplifier through TB3. Through the use of a single external feedback resistor virtually any voltage or current feedback level may be accommodated without the need to modify the board. a) The VFB input (terminals TB3-1 and TB3-3) has an input resistance of 1.5 Kohms and together with feedback resistor Rx a voltage divider is formed. Resistor Rx must be scaled so that approximately 6 ± 15% volts is developed across the VFB input. Any error due to resistor tolerances or non-exact values may be trimmed by Voltage Limit adjustment, P2. b) The feedback inputs may utilize either a negative or positive shunt by proper arrangement of the VFB input. c) The IFB (current feedback) is preset to utilize a standard 50 mv shunt, no calibration is required. The IFB connection to the shunt should be made through a twisted shielded pair of at least 14 AWG gauge wire to minimize voltage drops. d) IFB inputs, other than the standard 50 mv, may be accommodated through the use of an external resistor. For input greater than 50 mv, resistor Ry is scaled so that 50 mv is developed across the 100 ohm input resistance of the IFB input. When input of less than 50 mv are required, IREF (current reference) is lowered by connecting an external resistor across terminal #13 and terminal #14 on TB1. The reference voltage from the control potentiometer is then connected to terminal TB1-14. Supply Voltage Rating Rx K ohm FEEDBACK RANGE RESISTORS IFB < 50 mv RI K ohm IFB > 50 mv 6 0 37 57.6 100 100 9.681 38 56.2 5 Volts 10 k ohm 12 1.62 39 47.5 10 Volts 18.2 k ohm Ry
15 2.15 40 47.5 18 2.74 41 39.2 21 3.94 42 36.5 24 4.75 43 36.5 48 10 44 24.9 60 14.7 45 24.9 75 18.2 46 21.5 100 24.9 47 18.2 150 36 48 14.7 III. Peak Overload The CAT board contains circuitry that the SCR peak current and in the event of an overload will inhibit the gate pulses to the SCR s in less than ½ milliseconds. The gate pulses will remain inhibited for approximately 100 milliseconds after which the phase angle will begin to increase, ramping up the output and reaching current set-point in approximately 200 milliseconds. If a bolted fault exists on the output of the power supply, the peak current may be very high although the average current is low due to the retarded firing angle. The detector will again inhibit the output and this process will continue until the fault is removed. During an overload condition the READY indicator LED1 will turn off, providing a visual indication of a fault. The level at which the peak detector trips is programmable through dipswitch DS2, positions 1 through 4, making available 16 steps from 100% to 400% of the power supply s rated output current. PEAK OVERLOAD SETTINGS DIPSWITCH 2 O/L Trip - mv 1 2 3 4 50 Off Off Off Off 80 On
100 On 117 On On 130 On 143 On On 150 On On 158 On On On 165 On 170 On On 174 On On 178 On On On 182 On On 185 On On On 188 On On On 190 On On On On
IV. Control Amplifier The control amplifier provides highly accurate regulation of both voltage and current in closes loop applications. Its response time may be tailored to match any load requirements and is programmable through dipswitch DS2 positions #5 through #8. Sixteen steps are available; all switches OFF set the slowest response time. Other features include automatic crossover of the voltage and current regulators and soft-start ramp capability. The soft-start ramp is fixed at 200 milliseconds and is initiated after power-up, peak overload detection, phase imbalance detection, and when the external INHIBIT has been released. The control amplifier also provides visual indication of an out-of-regulation condition through LED2; this condition will occur if the input voltage to the power supply drops too low or if feedback to the regulator is lost and closed loop operation cannot be maintained. In closed loop operation the control amplifier provides a 0-5 volt control signal to TB1-8. The phase delay (firing angle) is then a linear representation of the voltage applied, with 5 volts being equal to a 0º delay and 0 volts being equal to a 180º delay. CAT Board Response The response time of the CAT board may be programmed through dipswitch DS2 positions #5 through #8. Sixteen steps are available, giving a response time range from 5 milliseconds to 65 milliseconds. This response time applies only to the CAT board and how it responds to a step change on its voltage or current feedback inputs in closed loop operation. The output of the CAT board will stabilize to 90% of its final value within the time programmed by the dipswitch. The actual system response time is dependent on other external factors such as buss-bar and load inductance and (or) load capacitance. If the power supply has any ripple filtering, the major time constant will be that of the filter.
Most power supplies are set up with switches #5 and #6 ON (30 millisecond response), which through experience has been found to give the best results in most applications. The main concern is to have the fastest response time with little or no overshoot. Decreasing the CAT board response time excessively may lead to overshoot and possibly system instability. The response time may be optimized by connecting a storage scope to the load and making a step load change. By gradually decreasing the response time, note should be made of any overshoot, ringing, or instability. It is not recommended to have response times of less than 14 milliseconds; these faster times are used only on very small power supplies or 12-pulse power supplies that can tolerate these settings.
CAT Board Response DS2 Switch Setting 8 7 6 5 Response Time (milli-seconds) Off Off Off Off 65 Off Off Off On 42 Off Off On Off 36 Off Off On On 30 Off On Off Off 25 Off On Off On 20 Off On On Off 16 Off On On On 14 On Off Off Off 12 On Off Off On 11 On Off On Off 10 On Off On On 9 On On Off Off 8 On On Off On 7 On On On Off 6 On On On On 5
V. Trigger Section The timing logic of the Trigger Section implements a phase locked loop as originally described by Ainsworth and developed for high power DC converters. This approach gives the best possible triggering balance, as well as immunity to triggering instability due to power line distortion. Proper phase synchronization is obtained from the three phase line voltages and is connected to the CAT board through a resistive divider or through phasing transformers. a) Phase reference section is programmable through Dip Switch DS1, positions 1-6. Setting switches 1, 2, and 3 in the ON position and 4, 5, and 6 OFF will produce trigger pulses leading the line voltage by 30 degrees, as is needed by primary SCR and bridge circuit configurations. b) Setting switches 4, 5, and 6 ON and 1, 2, and 3 in the OFF position will produce trigger pulses in phase with the line voltage, as needed by the six phase star configuration. DS1 PHASE REFERENCE SWITCH SETTINGS 1 2 3 4 5 6 Power Supply Circuit ON ON ON OFF OFF OFF 3-Phase bridge. ON ON ON OFF OFF OFF Primary SCR s OFF OFF OFF ON ON ON 6-Phase Star The Trigger Section also incorporates phase imbalance detection, which, in the event of a lost input phase or high phase imbalance, will inhibit SCR triggering until phase balance is regained. In closed loop operation, the Control Amplifier provides a zero (0) to five (5) volt command signal and is connected internally to the Trigger Section through Dip Switch #1, position #8. The Trigger Section may be manually controlled by switching OFF position #8, then applying an external zero (0) to five (5) volt command signal to TB1-8. The phase delay is then a linear representation of the voltage applied with zero (0) volts producing a 180º phase delay and five (5) volts producing a 0º phase delay.
VI. CAT BOARD CALIBRATION Verify that the switch settings on the CAT board match those listed below: CAT Board DS1 Switches Closed (ON) DS2 Switches Closed (ON) A3-290605 4, 5, 6 = 6Ǿ* 8 = Closed Loop 1, 2 = 117% Peak Overload 5, 6 = 30 ms response 1. Calibration Current The following procedure should be performed on the CAT board in the rectifier to calibrate the output current. a) Connect a load resistance to give full current at less than full voltage. b) Energize the main contactor and enable DC power on the rectifier to be calibrated. c) Set the Voltage Ref. to 100%. d) Set the Current Ref. to 100%. e) Verify that the voltage between TB1-12 (VREF) and TB1-6 (neg) on the CAT board is 5 ±.005 VDC. If it is not, adjust the Voltage Ref. pot until 5 ±.005 VDC is present. f) Verify that the voltage between TB1-13 (IREF) and TB1-6 (neg) on the CAT board is 5 ±.005 VDC. If it is not, adjust the Current Ref. pot until 5 ±.005 VDC is present. g) Verify that the voltage between TB3-6 and TB3-7 (neg) on the CAT board is 50 mv ±.05 mvdc. h) If necessary, adjust gain pot (P6) to give 50 mv ±.05 mv on terminals TB3-6 and TB3-7 i) Set the Current Ref. to 5%. j) Verify that the voltage between TB1-12 and TB1-6 (neg) on the CAT board is 5 ±.005 VDC. If it is not, adjust the Voltage Ref. pot until 5 ±.005 VDC is present. k) Verify that the voltage between TB1-13 and TB1-6 (neg) on the CAT board is.250 ±.005 VDC. If it is not, adjust the Current Ref. pot until.250 ±.005 VDC is present.
l) If necessary, adjust offset pot (P7) to give 2.50 mv +/-.05 mv on terminals TB3-6 and TB3-7 m) Verify gain trim (steps c through h). If gain is changed, also do offset (steps i through l). 2. Calibration Voltage The following procedure should be performed on the CAT Board in the rectifier to calibrate the output voltage. a) Connect a load resistance to give full voltage at less than full current b) Energize the main contactor, and enable DC power on the rectifier to be calibrated. c) Set the Voltage Ref. to 100%. d) Set the Current Ref. to 100%. e) Verify that the voltage between TB1-12 (VREF) and TB1-6 (neg) on the CAT board is 5 ±.005 VDC. If it is not, adjust the Voltage Ref. pot until 5 ±.005 VDC is present. f) Verify that the voltage between TB1-13 (IREF) and TB1-6 (neg) on the CAT board is 5 ±.005 VDC. If it is not, adjust the Current Ref. pot until 5 ±.005 VDC is present. g) Verify that the voltage between TB3-3 and TB3-1 (neg) on the CAT board is 6 ±.005 VDC. h) If necessary, adjust gain pot (P3) to give 6 ±.005 VDC on terminals TB3-3 and TB3-1. i) Set the Voltage Ref. to 5%. j) Verify that the voltage between TB1-12 (VREF) and TB1-6 (neg) on the CAT board is.250 ±.005 VDC. If it is not, adjust the Voltage Ref. pot until.250 ±.005 VDC is present. k) Verify that the voltage between TB1-13 (IREF) and TB1-6 (neg) on the CAT board is 5 ±.005 VDC. If it is not, adjust the Current Ref. pot until 5 ±.005 VDC is present. l) If necessary, adjust offset pot (P4) to give.3 ±.005 VDC on terminals TB3-3 and TB3-1. m) Verify gain trim (steps c through h). If gain is changed, also do offset (steps I through l).