Paralleling Outputs

January 7, 2009
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Vicor’s Maxi, Mini and Micro modules support paralleling of identical converters to expand the output power. A PR signal is communicated to all modules within the parallel array to synchronize switching frequency. Current sharing is inherent due to the matched power trains of the converters, even under conditions of dynamic loading. In a parallel array, the PR pin function allows only one module to be the Driver; all other modules will automatically become Boosters. Care should be taken by choosing a proper PR-connection. The following application note discusses different ways to connect the PR interface.

For a group of four converters or more in parallel and for fault tolerant redundant arrays, Vicor’s PR transformer is required. Connecting the SC pin to –SENSE will configure a module as a Booster. This can be helpful where arrays are being variably trimmed as only the Driver module needs to be adjusted.

When constructing arrays all SENSE pins must be connected to a common point. The Micro modules do not incorporate remote sense functionality. Please contact Vicor’s applications engineers before using Micros in redundant or parallel arrays. Make sure that the output pins never become open circuit from the output bus as damage to the module may occur.

Figure 1 – N+1 module array output connections (Maxi and Mini)
  • The +Out and -Out power buses should be designed to minimise and balance parasitic impedance from each module output to the load
  • The +Sense pins should be tied to the same point on the +Out power bus; the -Sense pins should be tied to the same point on the -Out power bus.
  • At the discretion of the power system designer, a subset of all modules within an may be configured as Boosters by shorting SC to ­S.
  • OR’ing diodes may be inserted in series with the +OUT pins of each module to provide module output fault tolerance.

Figure 2 – ORing diodes connections (Maxi and Mini)

 

 

 

 

 

 

Figure 3– Parallel module array output connections (Micro)
  • The +Out and -Out power buses should be designed to minimise and balance parasitic impedance from each module output to the load
  • At the discretion of the power system designer, a subset of all modules within an array may be configured as Boosters by shorting SC to -Out
  • Do not use output OR’ing diodes with parallel arrays of MicroMods

 

 

 

 

For our VI-200 and MI-200 converter family, booster modules are available to increase output power. The way the modules synchronize differs from the way explained above. The daisy chaining of VI/MI200 modules is explained here.

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