High frequency link topology based double conversion UPS system

This paper presents an high frequency link topology based three phase double conversion uninterruptible power supply (UPS) system. A three winding high frequency transformer is designed as the central power exchange node between the input, output and battery. The different voltage levels of the grid, load and battery are interfaced through a compact and inexpensive isolation transformer and the presence of bulky DC link capacitor is completely eliminated by the proposed scheme. The closed loop control of the load side (outer voltage loop with inner current loop) and the front end side (DC battery voltage control with unity power factor grid current regulation) are carried out in synchronously rotating coordinate system. The construction details of the high frequency transformer, closed loop structures and experimental verifications are presented.