Implementation of three-phase four-leg inverter using SiC MOSFET for UPS applications
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ORIGINAL ARTICLE
Implementation of three‑phase four‑leg inverter using SiC MOSFET for UPS applications Jun‑Hyeok Jegal1 · Minho Kwon1 · Chang‑Yeol Oh1 · Kiryong Kim1 · Jong‑Pil Lee1 Received: 3 September 2020 / Revised: 14 October 2020 / Accepted: 15 October 2020 © The Korean Institute of Power Electronics 2020
Abstract This study implemented a 30 kW, 750 Vdc, silicon-carbide (SiC)-based uninterruptible power supply(UPS) applied it on a three-phase four-leg inverter. For component selection, LC filter and DC-link capacitor were designed based on the PSIM simulation. SiC MOSFET was used to achieve higher efficiency and better reliability than the conventional Si IGBT-based UPS applications. Furthermore, desaturation (DeSat) protection method was applied to protect the overcurrent during the short-circuit condition of SiC MOSFET. Thus, the DeSat protection method was applied to SiC MOSFET, thereby enabling a 1 μs protection by complementally switching and zener diode voltage optimization. Accordingly, the transient time of the DeSat protection can be disregarded, thereby enabling fast protection. Meanwhile, several topologies have been studied for unbalanced loads compensation. The current research used a three-phase four-leg inverter topology for compactness and neutral current control. In addition, voltage compensation became possible even in unbalanced load condition by introducing a dual-loop controller for the three-phase four-leg inverter. A dual-loop controller comprises PR and PI controllers to the stationary αβo and synchronous dqo reference frames, respectively. Thermal and efficiency tests were also performed in the rated power test. Under a 30 kW load condition, the surface epoxy molding compound temperature of SiC MOSFET was approximately 72 °C, and the highest efficiency was approximately 99.1% under 10 kW load condition. Finally, the effectiveness of the implementation was demonstrated through the experiment results. Keywords UPS · SiC MOSFET · Desaturation protection · Three-phase four-leg · Unbalanced loads
1 Introduction Uninterruptible power supply (UPS) applications supply emergency power in case of grid power failures for critical loads such as medical equipment and data centers. These critical loads need high-quality power regardless of voltage variance at the grid side. Hence, UPS should have excellent performance in terms of voltage regulation, power factor correction, and total harmonic distortions. To solve the aforementioned requirements, various control strategies have been reported [1–3]. The UPS system case can be configured as on-line and off-line UPS. The main difference is that on-line UPS must be normally turned-on and off-line UPS must be normally turned-off in the actual field. This study * Jong‑Pil Lee [email protected] 1
Power Conversion System Research Center, Korea Electrotechnology Research Institute (KERI), Changwon, South Korea
selected an off-line UPS for the SiC-based three-phase UPS implementation. Traditionally, silicon (Si) IGBT-based devices have been widely u
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