Uninterruptible power supplies (UPSs) including voltage converters are fundamental parts of many electrical systems such as power supply systems for computers and servers in data centers. UPSs can be used with many typical power systems including single and 3-phase connections, and can be used with low-power systems (e.g., a household computer) and high-power systems (e.g., large data centers or process facilities). High-power systems typically use a 3-phase power connection (e.g., X, Y, and Z phases). A 3-phase UPS voltage converter is typically used to provide 3-phase AC power to a 3-phase load, to convert a 3-phase AC voltage from one level to another, and to provide 3-phase power to a load in the event of a power failure. The input and output connections to a 3-phase UPS voltage converter are typically three- or four-terminal connections, one connection for each phase of the 3-phase power connection and an optional neutral connection. A battery is also typically coupled to the UPS voltage converter and is used to store energy for use in case of a power failure.
Typical high power (e.g., above 100 kW) UPSs are operated using nominal AC input voltages of 3×400 V (in Europe) or 3×480 V (in the U.S.). Transformerless UPSs may operate with an internal DC bus voltage of ±450 V. In such a configuration, components contained in the UPS are preferably rated for at least 1200 V operation due to large voltage overshoots associated with stray inductances of physically large insulated gate bipolar transistor (IGBT) modules. The use of 1200 V components, however, typically leads to increased conduction and switching losses, thus lowering the efficiency.