28 UNINTERRUPTIBLE POWER SUPPLIES https://bourns.com/ Issue 4 2024 Power Electronics Europe www.power-mag.com density overvoltage protection for DC busses against transient voltage spikes, and positive thermal coefficient (PTC) resettable fuses that help prevent overcurrent events by temporarily increasing resistance during fault conditions. In addition, precision current sense resistors and integrated current sense modules deliver needed reliable real-time measurement, enabling the BMS to regulate charging, detect faults, and optimize battery utilization. Also beneficial are transient blocking units (TBUs) that supply high-speed protection against rapid voltage transients for critical communication lines, ensuring system integrity under abnormal operating conditions. Uninterrupted Inverter Safeguards The DC-AC inverter is the second stage in an online double-conversion UPS. It is responsible for transforming the stable DC voltage from the rectifier and battery stages back into a high-quality AC waveform. This stage ensures that the output voltage and frequency match the characteristics of the input grid while providing complete isolation from disturbances such as sags, surges, or momentary outages. Therefore, it is a vital element for maintaining uninterrupted, clean power to sensitive loads, including servers, networking equipment, and medical or industrial systems. Inverters operate by rapidly switching the DC voltage through power transistors to reconstruct an AC waveform. The precision of this switching directly impacts the fidelity of the output waveform where any imbalance or timing error can lead to harmonics, voltage distortion, or even system failure. In order to meet the demanding UPS performance and reliability requirements, high-quality switching devices are necessary. Insulated Gate Bipolar Transistors (IGBTs) offer an effective switching choice for inverter applications. IGBTs deliver the features that enable high energy operation, reduce thermal losses, and maintain consistent performance under heavy loads. In addition to IGBTs, other supporting components such as precision trimming potentiometers and resistors, TVS diodes, and current sense shunts that enhance inverter protection, should also be included in any switching control design to further optimize overall UPS reliability. The Necessity for Broadline Protection Support The ability of a UPS to maintain clean, continuous energy hinges on sophisticated circuit design, high-quality components, and comprehensive protection strategies. From the rectifier and PFC stages to battery management and DC-AC inversion, every sub-circuit needs to perform with precision and resilience to safeguard sensitive loads. So, given all the sub-circuits in a UPS that require some sort of protection, it is advised to evaluate component suppliers that offer a broad line of circuit protection products. This way, designers have multiple component options that allow them to select the optimal solutions to safeguard the myriad of sensitive components from voltage and current anomalies. As the demand for greater uptime and energy efficiency from modern power infrastructures and data center topologies continues, so does sourcing high-quality components that meet UPS extended battery life, higher voltage and reduced operational risk goals. Trusted broadline suppliers such as Bourns have built their protection portfolios to deliver the advanced capabilities complex doubleconversion architecture UPS sub-circuits require to withstand voltage transients, overcurrent conditions, and grid anomalies while maintaining optimal performance. Figure 4. Example rectifier and PFC topology for 3 phase systems — Termed a “Vienna Rectifier” To receive your own copy of Power Electronics Europe subscribe today at: www.power-mag.com
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