Flexible Mode Bridgeless Boost PFC Rectifier with High Efficiency over a Wide Range of Input Voltage
Abstract
For the conventional PFC rectifiers, the high efficiency cannot be achieved over a wide input range, and the efficiency will be greatly decreased at low input voltages. In order to overcome the efficiency bottleneck under low line input, a flexible mode bridgeless boost power factor correction (PFC) rectifier is proposed in this paper. According to the input voltage, the proposed rectifier can be flexibly adapted to the suitable operating mode to obtain the maximum efficiency. Meanwhile, the circuit components can be reused by different operating modes, so the extra cost is low. In the proposed rectifier, a back-to-back bridgeless boost PFC topology is adopted at high line conditions and a three-level bridgeless boost PFC topology is rebuilt to reduce the switching losses at low line conditions. Compared with the traditional bridgeless boost PFC rectifier, an extra low-voltage bidirectional switch (usually composed of two switches) is added, so the increased cost is low. In addition, the low common mode noise can be achieved at both high and low line conditions due to the direct connection between the input mains and the output electrolytic capacitor. The detailed principle analysis about the proposed rectifier is presented in this paper. Finally, an experimental prototype is built to verify the feasibility and the effectiveness of the proposed topology.
EXISTING SYSTEM
It seems to be much difficult to further reduce the conduction losses for the bridgeless PFC rectifiers; so many bridgeless PFC rectifiers have been modified to improve the efficiency via soft switching techniques. According to the ways of realizing soft switching, these modified PFC rectifiers can be divided into several groups. The first group adopts the discontinuous current mode (DCM) or critical current mode (CRM) instead of continuous current mode (CCM). The rectifiers working in DCM or CRM mode are only suitable for low power applications (< 300 W) due to the restriction of switch current stress. Additionally, a large input filter must be employed to suppress the high frequency components of the pulsating input current, which increases the overall volume and cost of the rectifier. The second group involves adding some auxiliary components (including the capacitors, inductors and active switches) to the traditional bridgeless PFC rectifiers, which usually makes the circuit more complex and decreases the reliability of system. Besides, the voltage or current stress of the power devices is also significantly increased due to the resonance between the capacitors and inductors. That is, the higher-rated or, usually, more expensive components are needed.
PROPOSED SYSTEM:
Another common solution to improve the efficiency is to adopt multilevel converters which have the advantages of small inductor size, low switching losses, low device stress, etc. Based on the full-bridge PFC converter, a traditional three-level boost converter is proposed, which suffers from high conduction losses due to the diode bridge. So an improved three-level PFC rectifier shown in Fig. 4 is developed to reduce the conduction losses, and the high efficiency can be achieved. Recently, several new three-level single -phase bridgeless PFC rectifiers are presented, which have lower conduction losses than. However, many extra power devices and high-side drivers are needed for those complicated circuits proposed. On the other hand, the advantage of low CM noise in the previous two-level bridgeless PFC rectifiers is lost for all of the three-level rectifiers mentioned above since the voltage potential of the output bus in regard to the ground is pulsating. A new concept of flexible converter is proposed. There are two or more topologies or operating modes involved in a flexible converter, where different topologies are formed for different applications. In order to solve the problem of low efficiency at low input for the rectifier, a flexible mode bridge- less boost PFC (FMBL PFC) converter is proposed based on the flexible converter concept. The basic design principle can be concluded as follows. According to the input voltage, the rectifier can be flexibly adapted to the suitable topology and mode for obtaining the maximum efficiency. Meanwhile, in order to reduce the extra cost, the circuit components should be reused as much as possible in different topologies and modes. Based on this idea, a novel flexible mode bridgeless PFC rectifier (FMBL PFC) is proposed, in which the high efficiency over a wide input range can be achieved. In the proposed rectifier, a BTBBL PFC rectifier is adopted at high line voltages and a three-level bridgeless boost PFC rectifier (TLBL PFC) is formed to achieve high efficiency at low line voltages. Compared with the traditional bridgeless boost PFC rectifier, an extra low-voltage bidirectional switch (usually composed of two switches) is added; therefore the increased cost is low. At both high and low line conditions; low CM noise can be achieved due to the direct connection between the input power grid and the output electrolytic capacitor during half line cycle. The detailed principle analysis about the proposed FMBL PFC rectifier is presented. Finally, an experimental prototype is built to verify the feasibility and the effectiveness of the proposed topology.
CONCLUSION
In this paper, a novel FMBL PFC rectifier is proposed, in which the high efficiency over a wide input range can be achieved. In the proposed rectifier, a BTBBL PFC rectifier is adopted at high line voltages and a TLBL PFC rectifier is formed to achieve high efficiency at low line voltages. Compared with the traditional bridgeless boost PFC rectifier, an extra low-voltage bidirectional switch (usually composed of two switches) is added, therefore the increased cost is low. At both high and low line conditions, low CM noise can be achieved due to the direct connection between the input power grid and the output electrolytic capacitor during half line cycle. The detailed principle analysis about the proposed FMBL PFC rectifier is presented. Finally, an experimental prototype is built to verify the feasibility and the effectiveness of the proposed topology.
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