Uninterruptible Power Supplies

Uninterruptible Power Supplies (UPS) provide continuity of power in the event of an outage. The alternate power source of UPS systems is batteries that are connected to the main alternating current (AC) source via a set of rectifiers and inverters. The rectifier and inverter systems charge the batteries during normal operations and provide continuity of power in the event of an outage. Like any other equipment, the UPS systems have to be sized correctly for the loads that they are serving. This means that the full-output kilowatt (kW) and kilovoltampere (kVA) rating of the UPS have to match the demand of the load. However, the effects of the ambient environment in which the UPS systems are operating and the effect of the type of load that the UPS systems are serving could affect the maximum rated power of the UPS. Therefore, maximum power of the UPS systems has to be de-rated based on the following factors:


  • Ambient temperature
  • Altitude (ambient pressure)
  • Load power factor

UPS systems are designed to primarily serve computer loads. In this context, the computer loads are the input power source of the computer systems which are mainly switched-mode power supplies. Switched-mode power supplies are generally designed with current waveform controls to reduce harmonics. The power factor for this type of UPS load changes based on how heavily the power supplies are loaded. These power supplies can draw leading power factors when lightly loaded which could create some issues for the UPS systems and emergency diesel generators.

Exponent engineers have leveraged their knowledge of the UPS design and industrial power systems as well as switched-mode power supply systems to tackle problems such as:


  • UPS load studies and de-rating
  • UPS system failure investigations
  • Battery systems failure investigations
  • Battery systems design review and testing
  • Emergency power transfer systems

Additionally, we are well versed in power electronics and datacenter electric power installations that utilize large scale UPS systems. Exponent is consistently in the forefront of providing research, development, and engineering services in the area of power electronics to a wide range of clients. Support to clients for design and construction of power electronic electrical equipment is an important part of those services. We also are routinely performing failure modes and effects analyses (FMEAs) of power supplies for all kinds of lower power applications as well as safety and performance evaluations of such power supplies.

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