https://bourns.com/ UNINTERRUPTABLE POWER SUPPLIES 27 www.power-mag.com Issue 4 2024 Power Electronics Europe failure within the UPS and shields downstream loads. In data center applications where the consequences of power loss are especially harmful, fuses provide extra defense against worst-case transient threat scenarios. Rectifier Power Factor Correction To maximize efficiency and reduce stress on the electrical grid and UPS components, rectifiers in UPS systems integrate power factor correction (PFC). The rectifier is a key sub-circuit in a UPS responsible for converting AC from the electrical grid into a stable DC voltage. This conversion also filters out waveform irregularities and fluctuations from the incoming AC supply. A clean DC output is essential for both charging and discharging the UPS battery and establishes a stable foundation for the subsequent DC-to-AC inversion stage. Without PFC, the rectifier is not in compliance with regulatory standards in high-power installations. PFC is also needed to align the input current with the AC voltage waveform to help minimize total harmonic distortion (THD) and enhance the effective power factor of the UPS. Implementing PFC and rectification requires a suite of high-performance components. A key solution is with Silicon Carbide (SiC) Schottky diodes that enable high frequency switching with low conduction losses to improve efficiency and reduce harmonic content. Also, current sense resistors can be implemented to provide precise real-time current monitoring for control loops, overcurrent detection, and system diagnostics, helping to ensure stable operation under varying loads. Another PFC solution to consider is with power transient voltage su¶ppression (TVS) diodes that protect sensitive rectifier and PFC circuitry from voltage spikes. Together, these components enable UPS rectifiers to deliver reliable DC output, optimize energy efficiency, reduce stress on both the UPS and the electrical grid. Battery Control Protection UPS devices not only protect against electrical grid fluctuations but also safeguard against flickers and temporary power outages. This is typically accomplished with a rechargeable battery. In most UPS designs, the battery is connected in parallel with the power bus, positioned between the AC-DC rectifier and the DC-AC inverter. During normal operation, the power bus charges the battery. In the event of a power interruption, the battery seamlessly discharges to maintain continuous operation for critical systems such as servers. This article has highlighted the complexities of UPS designs that call for a multi-stage protection approach. This also applies for auxiliary control circuits like the Battery Management System (BMS). Each component has an essential role: PTVS diodes and surface-mount multilayer varistors (MLVs) provide compact, highDelivering the benefits of both MOV and GDT technologies, Bourns® IsoMOV™ protectors provide low capacitance, low leakage, and high surge-handling capability, streamlining surge protection while improving reliability. Figure 2 and Figure 3. Examples of AC mains protection using a space-saving Bourns® IsoMOV® protector for a UPS system 3-phase wye and delta input. Figure 2 Figure 3
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