A Unity Power Factor Single-Phase Three-Level Rectifier Associated with A Passive Nondissipative Snubber Fernando L. Tofoli, Carlos A. Gallo, Marcos T. Galelli, Ernane A. A. Coelho, João Carlos de Oliveira, Luiz Carlos de Freitas, Valdeir J. Farias, João Batista Vieira Jr. * Power Electronics Research Group Federal University of Uberlândia Uberlândia-MG – Brazil E-mail: batista@ufu.br * Abstract—This paper proposes a single-phase Boost-type three- level rectifier employing a passive nondissipative snubber. The converter is supposed to present high input power factor, low current harmonics, low total harmonic distortion and simple control scheme. A theoretical analysis, design procedure, as well as analytical results regarding a 1.2kW prototype are presented to validate the proposal. Keywords  power factor correction, soft switching, three-level rectifiers. I. INTRODUCTION The single-phase Full Bridge diode rectifier associated with the conventional Boost converter is the former choice for power factor correction, employing the average current control technique for input current waveshaping [1]. Numerous soft switching schemes have been proposed so far, allowing the operation at high switching frequency [2] [3] and also implying reduced volume and high efficiency, although complexity is increased. Conduction losses are significant because the current flows through three elements simultaneously during the converter operation. An interesting alternative to reduce them was proposed in [4], where the current flows simultaneously through two elements instead, in any operating stage. Additionally, soft switching techniques can be applied to the converter, minimizing switching losses and increasing overall efficiency [5]. For three-phase applications, several PWM Boost rectifiers are available in literature [6]. Such topologies are supposed to overcome common limitations imposed by high current stresses through the switches, appreciable losses and reverse recovery of diodes. Desirable features are the reduced number of components and input current with low harmonic content, resulting in low cost and increased robustness. The Full Bridge rectifier shown in Figure 1 allows bidirectional power flow, although current stresses are quite high and very high switching frequencies are necessary to reduce the filters size. This converter presents high cost and low efficiency if compared to similar topologies. The proposal developed in [7] presents low cost and inherent simplicity, but it operates in discontinuous conduction mode, causing high EMI levels. Another alternative lies in the converter represented in Figure 2, where a three-phase Full Bridge rectifier is associated with a wye-connected six-switch bridge. It presents low cost, reduced losses and high reliability, but the unidirectional power flow is a limitation. By connecting the switching elements of each phase with the capacitive center point of the output voltage, one can obtain the three-phase three-level rectifier shown in Figure 3 [8]. According to [9], it can operate with half of the losses verified in the topology illustrated in Figure 2. For low power applications, the concept of three-level rectifiers can be extended to a single-phase structure, shown in Figure 4. Figure 1. Three-phase Full Bridge rectifier. Figure 2. PWM Boost rectifier associated with a wye-connected six-switch bridge. 0-7803-8975-1/05/$20.00 ©2005 IEEE. 1730