A Family of Single-Phase Voltage-Doubler High-Power-Factor SEPIC Rectifiers Operating in DCM
Abstract
This paper extends the voltage-double concept to the single-phase SEPIC rectifier in discontinuous conduction mode (DCM) and, as a consequence, novel rectifiers are proposed. A comparison with the classic SEPIC rectifier shows that the proposed converters can either provide reduced voltage stress on the semiconductors for the same output voltage level or supply double the gain of the output voltage with the same voltage stress. The proposed voltage-doubler SEPIC rectifiers provide a high power factor with no current control and they can be applied in order to improve the static gain of the structure, which can make the SEPIC rectifier suitable for applications that require a high voltage level. In this paper the generic structure based on a three-state switch, four different implementations of the proposed concept (including bridgeless structures), steady state analysis, a dynamic model, system control and experimental results are presented. The proposed rectifiers were verified by experimental results obtained with a prototype built with the following specifications: 1000 W output power; 220 V input voltage; 400 V output voltage; and 50 kHz switching frequency. Peak efficiency of 95.84%, THD of 2% and power factor of 0.9997 were obtained and, most importantly, double the gain of the output voltage was verified.
EXISTING SYSTEM:
Another option for single-phase PFC rectifiers is to use topologies derived from the SEPIC converter, which are single-stage topologies that can operate as step-down / step-up voltage regulators (boost works only as step-up). In general, the SEPIC rectifier is employed in discontinuous conduction mode (DCM), because the input current naturally follows the input voltage. Hence, the converter does not need a current control loop which simplifies its control system. Furthermore, the input current of the SEPIC rectifier in DCM does not present the third harmonic and it does not require additional bulk filters (which are needed in buck, buck-boost or boost rectifiers in DCM). These attributes make the SEPIC rectifier attractive for certain applications and therefore rectifiers of this type have gained interest from researchers in recent years, for instance: (i) classical bridgeless versions with improved efficiency (ii) modified bridgeless versions with zero-voltage transition, resonant operation and extended gain, which can increase the efficiency, enhance the gain, or decrease the voltage stress on semiconductors and (iii) three-phase versions with a high-power-factor
PROPOSED SYSTEM:
The current trend in relation to single-phase rectifiers is the use of converters to process higher power levels (from 1 kW to 15 kW), provide higher output voltage levels (above 400 V), decrease the voltage levels applied to semiconductors and increase the efficiency. In this context, this paper extends the voltage-doubler concept to the SEPIC rectifier, and consequently a novel rectifier is proposed, which has a high power factor, low harmonic distortion rates, lower voltage stress on the semiconductor and, most importantly, extended voltage gain. The detailed analysis and experimental verification of a 1 kW prototype is reported herein. The proposed topology of the single-phase voltage-doubler SEPIC rectifier. The structure integrates two classical SEPIC rectifiers in a single converter. The circuit works as two half-wave rectifiers, one for each half-line cycle and the two output voltages are series-connected (the principle being similar to that of the voltage-doubler boost rectifier). The results obtained show that the proposed converter multiplies the output voltage by two when compared to the classic SEPIC rectifier (hence the term ‘voltage-doubler’). The current flows through the green part at the positive half-line cycle, the blue part at the negative half-line cycle and the black part for the whole line cycle. .
CONCLUSIONS
In this paper a single-phase voltage-doubler SEPIC rectifier in DCM, which is obtained from the integration of two classical SEPIC rectifiers in a single converter, was proposed. It operates as two half-wave rectifiers, one for each half-line cycle, and the two output voltages are series-connected (as a voltage doubler). Therefore, the main contribution of the paper is the proposal of a voltage-doubler concept for the SEPIC rectifier, which improves the static gain of the converter and makes it suitable for applications that require high voltage levels. SEPIC rectifiers in DCM do not employ an input filter (which is used in boost rectifiers in DCM), and can supplylow-level output voltage as in the case of buck rectifiers.Furthermore, in DCM, the SEPIC rectifiers have a resistive load characteristic and thus they do not require the use of a current-loop control. The proposed converter maintained all ofthese characteristics and, in relation to the classic SEPICrectifier, it can either provide reduced voltage stress on the semiconductors for the same output voltage level or supplydouble the gain of the output voltage with the same voltagestress. The proposed rectifier employs a three-state switching cell(rectifier stage and active switch). Four different types oimplementation are suggested: three being bridgeless structures, two of which were verified by experimental results (a three-state switch with two active switches (2S – Fig. 1. (c)and one with one active switch (1S – Fig. 1. (b)). Themaximum efficiencies obtained were 95.84% (2S) and 94.55%(1S) and the efficiencies at rated power (1 kW) were 95.75% lter y fiers.
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