Power Module Based Solutions for UPS
The power quality and power security are crucial measures for today's industry. Uninterruptible Power Supply (UPS) devices are the key players to sustain power quality and power security. UPS is defined as a device which provides power conditioning and backup power when utility power fails, either long enough for critical equipment to shut down gracefully so that no data is lost, or long enough to keep required loads operational until a secondary AC source, like a generator, comes online.
3-level inverter topologies
Two different 3-level topologies are competing for the output inverter spot in UPS applications:
The NPC topology is able to operate exclusively with 650-V components, so higher switching frequencies are easily achieved. The MNPC topology is superior when comes to static losses, overvoltage and fault-handling. Whereas NPC circuits require a turn-off sequence to protect components against overvoltage in the event of a (fault) shutdown, this is not necessary for MNPC circuits. The crossover (efficiency vs. PWM frequency) between the two topologies depends largely on the components used. With the new IGBT generation, NPC shows the best performance already above 8 kHz if Si components are used. For same current rating NPC costs are 10% lower than MNPC.
3-level PFC Topologies
Power factor correction has long been a staple of UPS (uninterruptible power supply), SMPS (switched-mode power supply) and embedded drive devices. In recent years, a number of newly designed PFC topologies have hit the market. Now engineers are spoiled for choice: With so many more options, it is getting harder to pick the right topologies and components. Three-level, boost type PFC is an enticing solution for high power density and high efficiency.
The three-level topology's great advantage is that it reduces voltage stress on the semiconductor, which enables engineers to cut the losses and costs of power semiconductors and move toward higher switching frequencies. It is common practice to combine three single-phase modules in an AC system, thereby achieving the required output power level with three-phase PFC.
The graph below is the topologies' efficiency from 4 kHz to 50 kHz for comparison. To this end, the semiconductors' efficiency was calculated to benchmark the various types of power modules and see how the different designs measure up.
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