IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 55, NO. 8, AUGUST 2008 2963 A Novel AC UPS With High Power Factor and Fast Dynamic Response Elias Rodríguez, Nimrod Vázquez, Member, IEEE, Claudia Hernández, Member, IEEE, and Javier Correa Abstract—This paper presents a novel ac uninterruptible- power-system (UPS) scheme with high power factor, which offers excellent characteristics such as sinusoidal input current, sinu- soidal output voltage, fast regulation of the ac mains, galvanic isolation, and fast transient response. The proposed converter includes the offline–online concept, which avoids the continuous charging and discharging of the battery as it occurs in a typical online UPS. Analysis and design considerations, as well as simula- tion and experimental results, are given in this paper. Index Terms—Battery charger, boost inverter, high power factor, uninterruptible power systems (UPSs). I. I NTRODUCTION U NINTERRUPTIBLE power supplies are used to keep high-quality power sourcing for critical loads, such as computer and communication system, against the poor utility system. Recently, the demands of single-phase uninterruptible power system (UPS) are growing very fast in the computer- equipment markets, and different market areas have their own different requirements. A wide selection of UPS single-phase topologies has been proposed in the literature [1]–[12]. Sinusoidal and optimal pulsewidth-modulation (PWM) tech- niques have been used to control the rms value of the UPS output voltage and to suppress the harmonic components. These techniques are simple and have good characteristics under the steady-state condition, but they operate with poor transient response, and the total-harmonic-distortion (THD) factor of the output is high at the condition of nonlinear loads. Therefore, the control technique used is one of the most significant factors that affect the whole performance of the system. Additionally, in conventional UPS systems, high power factor is achieved by employing an additional power-factor-correction stage. Unfor- tunately, this additional stage limits the overall efficiency and reduces the reliability. In this paper, a novel topology is proposed mainly to solve the disadvantages of the conventional UPS systems. It presents the advantages of fast dynamic response to nonlinear load, high power factor, galvanic isolation between line load, as well as Manuscript received February 28, 2007; revised January 14, 2008. First published February 22, 2008; last published July 30, 2008 (projected). This work was supported by FONINV under Project 06-09-A-040. E. Rodríguez, N. Vázquez, and C. Hernández are with the Electronics En- gineering Department, Instituto Tecnológico de Celaya, Celaya 38010, México (e-mail: n.vazquez@ieee.org; elias@itc.mx; chdz@itc.mx). J. Correa is with the Electronics Engineering Department, Instituto Tecnológico de Morelia, Morelia 58120, México. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2008.918484 Fig. 1. Proposed idea without galvanic isolation between the battery and the load. high conversion efficiency for application in a commercial ac online UPS. An experimental 300-W UPS was built to verify the proposed converter. II. PROPOSED SYSTEM The proposed idea consists of three modules, namely, power- factor corrector (PFC), battery charger, and boost inverter; both ideas integrate the offline–online concept to provide a fast dynamic response when a failure occurs in the utility line. The PFC and boost-inverter modules operate with a sliding-mode control (SMC) to provide a sinusoidal output voltage to linear and nonlinear loads. The battery-charger module operates with a traditional PWM control to provide the load current to the battery. Fig. 1 shows the block diagram of the proposed idea. The PFC module provides a dc bus to power the battery-charger and boost-inverter modules; in this case, the PFC module is con- nected directly to the boost inverter. The battery is connected in parallel with the dc bus through a diode. The diode conduction is determined by the dc bus generated by the PFC module. A. Circuit Description The proposed converter is shown in Fig. 2. As it can be seen, the PFC module is composed of a discontinuous conduction mode (DCM) integrated-boost-rectifier (IBR) and a continuous conduction mode (CCM) full-bridge converter sharing power switches. The battery charger is a buck converter operating in CCM to provide the load current, and the boost inverter is an arrangement of two CCM boost converters to provide a sinusoidal output voltage. The C 2 capacitor voltage is used as a voltage source to the boost inverter and the battery charger. The battery is placed in parallel with the capacitor C 2 through the diode D r . The control stages of the PFC module, battery charger, and boost inverter are independent. The controller used for the full-bridge converter is an SMC; this controller allows 0278-0046/$25.00 © 2008 IEEE