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SixPac™ Series
CAP-AC1 Configuration
Features Include:
• 200-800 Amp Load Capability |
(configuration guidelines)|
Description: The APS SixPac™ Series of power controllers are built on a rugged, compact, all-inclusive, economical base. They have a great deal of flexibility to provide a fully functional set of power stages. They have been designed for long life in heavy-duty industrial applications. The SixPac™ CAP-AC1 includes three dual isolated SCR modules that can are configured for a three-phase AC Controller (AC in, phase-controlled AC out). These converters are ideal for any power application that needs phase controlled AC including solid-state motor starters, soft-start/soft-stop, variable speed drives, windmill alternator converters and regulated power supplies to name a few. The isolated SCR modules are mounted on a high efficiency heatsink with optional fusing, forced air cooling, snubbers and freewheeling diode. The snubber for the SCRs is suggested if dv/dt limiting is required. The compact design measures 11.75 x 8.70 x 8.16” including the cooling fan. The SixPac™ is available with operate with inputs from 10VAC to 700VAC, and is optimized for 220 / 480 / 575 VAC input ranges and 50/60Hz or 400Hz Input frequencies without tuning (this means that input from variable frequency alternators is acceptable as long as the frequency is within limits). AC Controller output currents range from 50ARMS to over 200ARMS. For higher current levels see the CAP-AC2 models capable of 200~800ARMS. All units are integrated with our our industry proven three-phase SCR controller. Utilizing advanced FPGA control logic to increase reliability, circuit flexibility and reduce circuit component count, our controller board is designed to keep the programmed phase delay angle constant over a wide input frequency range (40Hz to 80Hz). This universal input feature does not require tuning in applications where the input mains frequency may vary, as in motor generator sets, windmill power generating equipment, and all field generating systems. The three-phase mains input is filtered by a unique signaling processing circuit that is not sensitive to harmonic distortion, input voltage amplitude fluctuations, frequency variations or phase sequence. Signal Conditioning of Input Reference Controlling SCRs requires varying the phase angle at which they turn on in order to control the portion of the input voltage that is conducted to the output. The converter phase locks to the input source in order to create the references required to control the conduction angle of SCRs in any topology. The signals used to create the references are filtered in order to remove unwanted harmonics that will affect the precision with which the delay angle is controlled. The phase rotation of the three-phase input is sensed and the SCR gating is automatically adjusted to account for either ABC or ACB rotation. Therefore, the three-phase input source cannot be connected with an incorrect phase rotation. SCR Gating Phase Locked to the Utility Input In order for the delay angles to control the conduction angle of the SCRs, the delay angle must be phase locked and then phase shifted from the utility input by an amount determined by the delay angle control. The controller circuit uses a phase locked loop circuit to keep the SCR gating signals in phase with the three-phase input. An additional control loop has been added that will force the delay angle to remain constant as the input frequency varies. Delay Angle Control The magnitude of the delay angle determines the point on the input waveform an SCR will be switched on. This controls the output voltage of the AC Controller (AC in, phase-controlled AC out). The controller circuit will accept a voltage or a current that allows the user to control the delay angle. The default scaling for the Delay Angle Control input is:
• 0V corresponds to maximum delay angle (minimum conduction angle) or zero output The control input can be modified to accept a current input or a different scaling of the input voltage. In order to provide a controlled and orderly start up sequence, the delay angle commanded by the user is not instantly applied to the SCRs at turn-on. At start up, the delay angle is forced to the maximum value. When the SCR control signals are phase locked to the input references, with no errors present, the delay angle will ramp down from the maximum value to the programmed value in approximately 400mS. While in operation, the SCR gate firing can be turned off using either the soft stop function (shorting TB1-5 to TB1-6) or the fast turn off feature (open the contact closure between TB1-4 and TB1-6). When the soft stop is used, the delay angle will ramp up to its maximum value in approximately 100mS. If the board is forced into a fast turn off condition, all SCR gate signals will be turned off within 1mS. Logic Implementation All of the logic required to perform the delay angle control is contained on a single FPGA (Field Programmable Gate Array). Since it is programmable, it can be modified to adapt to customer needs in certain applications (please consult factory). DC Gate Drive The controller circuit comes equipped with DC gate drives, rather than picket fence drives, which offers improved performance in circuits with discontinuous load currents. If an SCR loses its holding current when being driven with a picket fence, the SCR will turn off and may not turn on again until it is turned on with the higher current leading edge pulse of the next turn on transition. The DC drive keeps current flowing into the gate so that the SCR will continue to be commanded on for the entire time that the SCR can be in conduction. The current waveform sourced to each SCR gate is an initial 2 Amp peak pulse (rising at a rate of approximately 1A/μS) approximately 10μS wide, followed by 500mA of DC current for the remainder of the turn-on signal. The open circuit voltage applied to the gate is 24 volts, which enables the controller circuit to drive large area devices under high dI/dt conditions.
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Fault Detection and Shut Down Sequence The delay angle is controlled directly by the delay angle control voltage supplied by the user at TB1-8 or by adjusting a pot installed in the J10 location. It can be turned off fast by removing the contact closure between TB1-4 and TB1-6 or ramped down slowly by shorting TB1-5 to TB1-6. Either of these conditions will turn on the INHIBIT LED. If one or all of the input phases are lost, the PHASE LOSS LED is illuminated and a fast turn off is initiated which inhibits all gate signals within 1mS. When the lost phase is restored, the unit will ramp up to the programmed delay angle in 400mS. If the optional temperature sensing circuit is used, the OVERTEMP LED will be illuminated and the gate signals are inhibited 1mS after the over temperature threshold is exceeded. The default value for the over temperature threshold is 90ºC. The gate signals will ramp up to the programmed value after the heatsink temperature drops to 85C. This value of thermal hysteresis can be modified to suit the customer’s requirements. Overtemperature Inhibit SCR gating is instantaneously inhibited in an over temperature condition. Phase Reference Options The default method of deriving references is to sense the cathodes of the three SCRs on J5 that are connected to the input voltage. This is a convenient point to obtain the utility inputs, which are then attenuated and filtered so they can be phase locked to the delayed gate commands. Current Limit Control The value of current at which the power supply will fold back can be adjusted with a remote pot connected to J8 or on-board pot installed in the J8 location. A 10 kΩ pot should be used in this application. The controller circuit allows the user to incorporate this feature in open loop or closed loop modes. Current feedback provided at J11 by an open loop Hall Effect sensor and a current limit controlling pot installed locally or remotely at J8 is all that is required. Rotating J8 to the fully CW position, will result in maximum output current, determined by the size of the Hall Effect Sensor and resistor scaling on the controller circuit. Rotating the pot in the CCW will reduce the amount of currentoutput from the SCRs. This feature allows the BAP1950A to operate as a current source in open or closed loop mode. Remote Voltage Control The output voltage of the power supply can be controlled by a potentiometer connection at J10 (the minimum pot used in this application should be a 1K) or a 0 to 5V signal. The 5V reference at J10-1 has a limited source capability of 10 mA. Therefore, it should not be used for any circuitry other than the pot. Current Feedback The controller circuit provides a connectorized interface to an open loop current transducer for current feedback to be used for an inner current loop and/or current limiting. The inner current loop enhances system performance by improving stability and allowing the user to set or vary a current limit. The 4 pin header on the board interfaces directly with the HAS and HAX open loop hall effect sensors from LEM, providing an inexpensive means for obtaining accurate current feedback.
The LEM current transducer can be placed on either side of the load. All diagrams show the current transducer on the positive load side, with the appropriate the current flow (arrow). If the current transducer is required on the negative side of the load, to eliminate floating the current transducer in high voltage supplies, for example, the current flow is reversed (arrow points away from the load). An on board low pass filter is used to greatly reduce the harmonic content of the mains input used to generate the reference signals. The low pass filter attenuates the fifth harmonics above 60Hz, reducing delay angle errors from input line distortion. Additional circuitry actively forces the programmed delay angle to remain invariant over a mains input frequency from 40Hz to 80Hz. Therefore, operation of the SixPac™ in applications where frequency fluctuations occur regularly, i.e. when running from an alternator input powered by a diesel, gasoline or turbine engine; or when running from a system with an un-stabilized frequency is permissible. The programmed delay angle will remain constant over the frequency range from 40Hz to 80Hz with an accuracy of ±0.25º. Closed Loop Voltage Regulation The SixPac™, when supplied as a DC Converter, is equipped with circuitry to provide a regulated DC output, with adjustable voltage and current limits. The output is determined by a voltage reference that can be obtained from either an off board reference, the on board pot or an off board pot. The voltage reference is compared via an error amplifier to output voltage feedback that is processed through an isolation amplifier. Current feedback is brought back to the board via a connector (J11) that interfaces with an industry standard Hall Effect current transducer. An example of such an application is shown in Figure 1. Consult factory for output voltage scaling and error amplifier compensation networks to obtain the desired transient response and stability. Soft-Start /Stop This circuit overrides the gate delay angle command. It is enabled by the power-on-reset feature or by contact closure inputs. SCR gating begins at the maximum delay angle limit and ramps down to the commanded delay angle at a rate determined by the soft-start time constant. The Soft-Stop feature, when activated by a contact closure, causes the SCR gate delay angle to ramp up from the command angle to the maximum delay angle limit before SCR gating is inhibited. Fast Turn-off SCR gating is quickly enabled or inhibited (~20μSec) on contact closure input. |
