P-164000476 9395P 500kVA / 600 kVA 65Revision 002 User’s and Installation Guide6.2.4 Variable Module Management SystemNOTEVMMS and ESS modes are mutually exclusive. If VMMS mode is enabled, ESS mode isdisabled.In VMMS mode, the UPS operates as a traditional double-conversion UPS. However, the UPS willselectively shift the load to fewer UPMs based on the required load in order to force the remainingUPMs to carry a higher load. The efficiency rating for each UPM is highest when loads are greater than50% of the UPM rating. Therefore, with multiple UPMs, a UPS can achieve higher efficiencies forlighter loads.When a UPM is inactivated by VMMS mode, the UPM will stop gating the inverter and rectifier andkeep the output contactor closed in order to maintain voltage match and phase lock to the critical bus.In this mode the UPS actively monitors the critical bus, keeping the UPM input contactor closed inorder to keep the DC link primed (through the rectifier diodes) and also to allow the UPM toimmediately return to active mode in the event of a disturbance or load step on the critical bus.VMMS limits the maximum power available from a UPM when in VMMS mode. The default setting is80% of the UPM full power rating. If the limit is exceeded, additional UPMs are activated to take on theincreased load. The VMMS redundancy setting sets the number of redundant UPMs that the customerrequires. Both the VMMS UPM load limit and UPM redundancy are user-configurable.In High Alert mode, the UPS defaults to double-conversion Online mode and all UPMs go active for onehour (user-configurable). At the end of the hour, the UPS defaults back to VMMS mode. If the HighAlert mode is reactivated during the one hour, the one hour timer will be restarted.6.2.5 Energy Saver System (ESS)NOTEVMMS and ESS modes are mutually exclusive. If ESS mode is enabled, VMMS mode isdisabled.When the UPS is operating in Energy Saver System, the bypass source supplies the commercial ACpower to the load directly through the static switch. Some power line filtering and transient protectionis provided to the load but no active power conditioning or battery support is available. All powerconverters are off and are in the ready state (in case a forward transfer is needed). During this mode,the output contactor is closed and the link is maintained through the diode bridge. Figure 6-4 showsthe path of electrical power through the UPS system when operating in Energy Saver System.
