An Uninterruptible power supply (UPS) is used to protect electrical devices such as computers from power failures, when the main power fails. Using a model where both the physical behavior and the reliability is modeled, conclusions can be drawn about both the switching behavior and the system reliability.
An offline UPS turns on backup power from a battery when the incoming voltage from the wall power falls below a certain threshold.
A consumer-market uninterruptible power supply.
Top: Traditional operation when the utility power is stable.
Bottom: Battery powered mode when utility power is down.
Simulating the model, we can see that after 5 seconds of operation the power switches from wall power to the battery. After 17 minutes, the battery cannot power the inverter anymore and the equipment turns off.
The UPS switching from external power to battery.
The UPS turns off when battery voltage goes under a certain threshold.
Annotating the system with lifetime distributions for the different components, we can compare how long the expected mean time to failure (MTTF) is for a traditional consumer-oriented product with one that has a more expensive battery.
Switching to the professional grade battery improves the mean time to failure from 27,400 hours to 38,380 hours, or with 40%.