COTS AC DC Power Supplies

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					                                                                                               2001 Fulling Mill Road
                                                                                               Middletown PA 17057
                                                                               Phone: 717-939-2300 Fax 717-939-7170

                              COTS AC-DC Power Supplies
By Robert Kirker Application Engineer

Advanced Conversion Technology, Inc (ACT) has developed an approach for COTS AC-DC power supplies that takes
advantage of the high power densities of standard DC-DC converters. Using standard DC-DC converters, ACT wraps the
needed customization around these bricks in order to meet the EMI, housekeeping and rugged mechanical requirements of a
military power supply application. These standard brick converters are then combined in a variety of configurations to produce
a wide range of output voltages and currents. Using similar proven topologies and physical configurations new single phase
and three phase AC-DC military power supplies can be quickly developed that incorporate many of the following features.

    •    High Power density.
    •    Very low input current harmonic distortion.
              o <3% harmonic distortion over a wide load range, 20% to 100%.
    •    EMI and low input harmonic distortion requirements are maintained for a wide range of changes in the output
    •    Phase load balancing for three phase power supplies.
    •    Long hold up times during low line input transients, >100msec.
    •    A variety of output voltages and currents available within the same form factor without redesigning the unit.
              o Uses standard DC-DC converter bricks.
    •    Shortened development time.
    •    Fully compliant EMI Filtering for MIL-STD-461 and most other EMI standards.
    •    High transient protection for MILSTD-704, MIL-STD-1399, MIL-STD-1275 & lightening strikes, etc.

                                     Single Phase AC-DC Applications
ACT’s single phase topology is the building block for its AC-DC power supplies and is shown in the following block diagram.
The active PFC module converts the AC input voltage into a 375VDC bus while maintaining very low input current harmonic
distortion and a power factor >99%. The 375VDC bus voltage generated by the PFC module is used to power standard DC-
DC converters.

                                           Single Phase AC-DC Block Diagram
                                                   –2–                                      March 18, 2009

                                    Multi-Kilowatt Single Phase Active PFC Module

This proven technology can be easily adapted to a wide range of input voltages and frequencies with minimum changes.
             • 80 Vrms to 440Vrms
             • 47Hz to 800Hz
             • 100 to 325VDC

Prior to installing standard DC-DC converters into one of its power supplies, ACT wraps the necessary EMI shielding and
housekeeping circuitry around the converters in order to prepare them for operation with other DC-DC converter modules.
These individual DC-DC converters can then be combined in a variety of configurations to produce a wide range of output
voltages and currents. In many cases modules are connected in parallel (often in a N+1 configuration) and load sharing
circuitry is employed to make sure the output load is evenly shared among the paralleled bricks. Additionally the DC-DC
converters provide the required input to output isolation.

                       Standard Quarter Brick 150W DC-DC Converter with Custom Treatment

                                                                              Phone: 717-939-2300 Fax 717-939-7170
                                                   –3–                                       March 18, 2009

                                     Three Phase AC-DC Applications
In three phase power supplies ACT places active PFC circuits in each input phase to achieve low input current harmonic
distortion and high power factors. To achieve optimum system performance it is important that power load balancing among
the phases be implemented. Optimum phase to phase load balancing can be achieved in a number of different methods and
can vary from application to application. One common method is to equally distribute the DC-DC converters among the
phases such that the total output power is equally shared among the phases.

                                           Three Phase AC-DC Block Diagram

In many cases a secondary share buss is often utilized and if phase isolation exists the share buss can be used on the PFC

With the addition of a transformer input module this approach has been successfully used in 440V multi-kilowatt three phase

                Single Phase Active Power Factor Correction (PFC) Front End
ACT’s active PFC front accepts a single phase input voltage and applies this to the Inrush circuit & EMI filter. The filtered
input voltage is then full wave rectified and applied to our boost PFC circuitry. A boost topology charging a large output
capacitor can generate very large inrush currents during turn-on. In order to minimize this high input currents a resistive
element is placed in series with the input which limits the input current during turn-on. After the 375VDC bus voltage is
charged up a low loss FET power element is switched on shorting out the resistor. Overall power losses in the EMI filter and
Inrush circuits are very low and can achieve efficiencies of 98% or greater.

                                                                               Phone: 717-939-2300 Fax 717-939-7170
                                                          –4–                                      March 18, 2009

                                               ACTIVE PFC

200VAC                         SINGLE              FULL
          IN-RUSH              PHASE                                                   LOCAL              CURRENT
INPUT       LIMIT               EMI               W AVE               PFC
                                                  BRIDGE                              ENERGY               SHARE
                               FILTER                                                 STORAGE                             380VDC


                                                                CONTROL                 PFC

                                              Single Phase Active PFC Block Diagram

     The active PFC circuit operates in such a manner as to minimize the input current harmonic distortion by providing a resistive
     appearing impedance to the input circuit. The result of this is a sinusoidal input current over a wide range of output load
     conditions. This PFC circuit can maintain input current harmonic distortion of less than 3% over a wide output power range,
     from 20% through 100%. The following table shows some typical input current harmonic distortion performance that ACT
     can achieve.

                                             Typical Input Current Harmonic Content

                                             HARMONIC           % Harmonic Content

                                                    1st                  100%
                                                   3rd                   0.4%
                                                   5th                   1.6%
                                                   7th                   1.2%
                                                   9th                   0.0%
                                                   11th                  0.6%
                                                   13th                  0.5%
                                                   15th                  0.1%
                                                   17th                  0.1%
                                                   19th                  0.1%
                                                   21st                  0.1%

                                                                                    Phone: 717-939-2300 Fax 717-939-7170
                                                   –5–                                      March 18, 2009

The amount of power that ACT’s PFC circuit can provide is directly related to the size of the boost storage inductor and low
line input conditions. For a given size boost inductor ACT’s PFC’s can provide more output power with higher input voltages.
Optimizing the boost inductor for size and performance is a key design issue. ACT has developed PFC designs with output
power from hundreds of watts to >2kwatts and achieved efficiencies of greater than 94%. Therefore, from the AC input to
the 375VDC output bus this approach can achieve efficiencies >91%. If the DC-DC converters have an 85% efficiency than
the overall efficiency of the power supply can be >78%.

The 375VDC bus voltage provides an excellent place to add storage capacitance if the design requires hold time for input
voltage transients. Additionally the DC-DC converters typically operate at input voltage levels of <250VDC providing another
level of hold up capability during input transients.

      Multi-kilowatt VME AC-DC Power Supply per MIL-STD-1399 Section 300A
In this example we discuss an AC-DC power supply that accepts 115Vrms, 3 phase delta input voltage at 60Hz and provides
four DC output voltages and 1,278 watts of output power;

             •   +5.1V @ 180A;              uses 6 half bricks
             •   +12V @ 8A;                 uses 3 quarter bricks
             •   -12V @ 4A;                 uses 2 quarter bricks
             •   +24VDC @ 9A                uses 3 quarter bricks

Based on an overall power supply efficiency of 65%, each of the single phase PFC modules are capable of providing 700watts
of power for a total power of 2,100watts of power available to the DC-DC converters. These modules are shown in the
picture below.

                                           Three 700watt Active PFC Modules

These PFC modules contain enough energy storage to hold up the output voltages under full load conditions for 70msec
during loss of input voltage.

                                                                              Phone: 717-939-2300 Fax 717-939-7170
                                                –6–                                   March 18, 2009

The 375VDC power produced by these three active PFC modules are presented to 14 standard DC-DC converters, six half
bricks and eight quarter bricks, as shown below.

                                       Fourteen Standard DC-DC Converters

Using this existing form factor and staying within the power capabilities of the PFC modules ACT can quickly develop
different versions of this COTS AC-DC power supplies.

                                                                         Phone: 717-939-2300 Fax 717-939-7170