Proposal of Three-Phase High-Frequency Transformer Isolation UPS Topologies for Distributed Generation Applications

Abstract

A family of double conversion three-phase uninterruptible power systems with power factor correction and high-frequency transformer (HFT) isolation topologies, are presented in this work. This might be a suitable alternative compared to large conventional UPS systems that are based upon bulky transformers that operate at the grid frequency. This system is commonly used to supply critical loads, but nowadays, due to the increasing interest in renewable energy integration and distributed generation (DG), it can be also be a suitable solution for energy storage in microgrids or renewable power conditioning interface applications. The three-phase HFT UPS used for further analysis is composed of single-phase chopper modules, one -three-phase boost module, and one three-phase inverter. The relevant features are soft commutation of the controlled switches in the chopper stage, simple control strategy that can be implemented with well-known integrated circuits (IC), and the use of a few batteries in series due to the same reference of the step-up stages. Principle of operation of the chosen system for experimental validation, implemented control strategy and experimental results obtained for a 15kVA prototype are presented.Index Terms-high-frequency transformer isolation, power factor correction (PFC), three-phase uninterruptible power supply, distributed generation (DG).

Analysis, Design, and Experimental Verification of a Synchronous Reference Frame Voltage Control for Single-Phase Inverters

“…3 illustrates the structure of a first-order APF. The input-tooutput transfer function describing the dynamics of APF is shown in (2), where w f is the fundamental angular frequency.…”

Investigation on Common-Mode Voltage Suppression in Smart Transformer-Fed Distributed Hybrid Grids

“…Generally, the CM component suppression strategies are based on the converter architecture [10]- [12], modulation strategy [13], [14], and CM filter [15], [16] [19], the wye connection point of the AC side filter capacitors [13], and connection of the DC-link capacitor midpoint and wye point of AC filter capacitors [20], [21], were proposed to be used as neutral line for three-leg converter. The neutral line can also be supplied by an additional leg [13], [22].…”

“…Since the bypass CM filter can avoid the aforementioned drawback, it is used for CM suppression in the hybrid grids in this paper. However, as the bypass filter is mainly used in single-phase [26] and three-phase three-wire system [21] [24] so far, the impacts from the unbalanced AC loads on the filter performances have not been studied. The mechanism and attenuation of the fundamental CM voltage caused by unbalanced AC loads are never considered.…”

A High-Frequency Isolated Online Uninterruptible Power Supply (UPS) System with Small Battery Bank for Low Power Applications

“…[1]. Typically, the UPS provides unity power factor, high efficiency, high reliability, low cost, and continuous power supply, irrespective of the grid conditions [2][3][4].…”