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24 | THE DATA CENTER JOURNAL www.datacenterjournal.com To make electrons leave the silicon valence band and travel to the conduction band, we will use a component in the IGBT called the P-N junction. is component is where all the action takes place (see Figure 6). To make the valence band electrons more controllable, we "dope" the silicon material by adding other materials at the P-N junction. Doping facilitates the movement of electrons across the depletion region (bandgap). e "P" side (or valence band) con- tains a collection of positive particles called electron holes. e "N" side (or conduction band) contains a collection of negatively charged electrons. By applying a voltage (forward bias), the deple- tion region shrinks and we create current flow. When the voltage is removed, the depletion region returns and the flow of electrons stops. Using the P-N junction, the IGBT produces a conditioned output current for the UPS. e IGBTs are turned on and off in a controlled manner to support the critical load. With respect to uninterruptible power supplies, the term double conversion refers to the conversion of the incoming AC voltage to DC voltage and then back to a pure AC sine wave. is process has the effect of eliminating any power fluctuations and enables the UPS to deliver a clean, steady signal to the load, providing the highest quality of continuous conditioned power. e UPS thereby isolates equipment from raw utility power and protects equipment that may suffer adverse effects from power sags and surges. Double conversion of the utility power remains the best and most reliable method of providing uninterruptable power to critical loads. Wide-Bandgap materials Over the last 25 years, researchers have discovered that the use of wide-bandgap materials, such as silicon carbide, allow semiconductor components to be smaller, faster, more reliable and more efficient than the existing silicon technology. 1 In solid-state physics, a bandgap is an energy range in a solid material where no electron states can exist. e term generally refers to the energy difference (in electron volts, or eV) between the top of the valence band and the bottom of the conduction band (see Table 1). e term wide bandgap here refers to higher-energy elec- tronic bandgaps, usually larger than one electron volt (eV)—typi- cally at least two or three eV, which is much greater than that of silicon (1.1 eV). WBG semiconductors permit devices to operate at much higher temperatures, voltages and frequencies, making the power electronic modules using these materials much more powerful and energy efficient than those made from conventional semiconductor materials. 3 Table 1: Bandgap energy levels. 2 Material Bandgap Energy Application Germanium (Ge) 0.67 eV First-generation electronics, fiber optics, transistors Gallium arsenide (GaAs) 1.4 eV Microwave circuits, thin-film solar cells Silicon (Si) 1.11 eV Lasers, LEDs, integrated circuits, photovoltaic cells, power electronics Silicon carbide (SiC) 3.25 eV LEDs, power electronics, new emerging technologies introdUcing the game changer e use of SiC components in double-conversion UPS technology allows the user to operate in the double-conversion mode and maintain higher efficiencies. A 100% SiC set of power- switching modules produces a 70% reduction of power losses (see Figure 7). Figure 7: SiC reduces semiconductor power losses by 70%. e 70% reduction in power losses of the SiC-based UPS directly leads to an increase in the double-conversion efficiency to 98.6% (see Figure 8). is high efficiency not only occurs at high- load situations but also extends to smaller loads (see Table 2). e need for eco-mode (utility power instead of inverter power) is gone. e UPS can now provide the same energy savings as eco-mode while also providing the critical load with conditioned, more reliable, high-quality power. Figure 6: Model of a P-N semiconductor junction.