HIGH EFFICIENCY SOFT-SWITCHING AC-DC CONVERTER WITH SINGLE-POWER-CONVERSION METHOD
Abstract
This paper presents a high efficiency isolated ac-dc converter topology. The proposed converter consists of a full-bridge diode rectifier, an isolated resonant dc-dc converter, and only one controller. The proposed converter provides the soft-switching technique for all components operating at high frequency, allowing for an improvement in power density without a cost of power-conversion efficiency. Furthermore, by using a novel control algorithm that controls both power factor and output power, the converter performs ac–dc power conversion in only a single power processing step. These characteristics enable the proposed converter to provide high efficiency, high power density, and a high power factor. A 2 kW prototype was implemented, and its performance and validity were evaluated based on experimental results
EXISTING SYSTEM:
Because the converter increases the effective switching frequency using the interleaved technique and employs soft-switching operation of all components in the dc–dc stage, it improves both efficiency and power density. However, conventional two-stage converters, including the converter introduced in, have inherently high circuit owing to their two-stage complexity and low efficiency circuit The single-stage circuit configuration is an alternative that may overcome the drawbacks of the conventional two-stage converters . Single-stage converters have been developed based on various converter topologies involving, e.g., a flyback, a forward converter, and a full-bridge converter. Such converters are simpler and more cost-effective than two-stage ac–dc converters; however, they suffer from huge switching losses owing to their hard-switching operation. Furthermore, the single-stage approach performs ac–dc power conversion depending on the circuit design without any PFC control, which results in a poor power factor and very large harmonics. In, single-stage converters using an additional auxiliary circuit were developed; the use of the additional circuit provides high power factor and power quality, but causes additional power losses and involves a highly complex circuit structure.
PROPOSED SYSTEM:
This paper presents an ac–dc converter with high efficiency and high power density. The proposed converter consists of a full-bridge diode rectifier, an isolated resonant dc–dc converter, and only one controller. To obtain high power density without a cost of power-conversion efficiency, the proposed converter provides soft-switching for all components operating at high frequency. The proposed converter performs both PFC and output power control in only one power-processing step by using a novel control algorithm; thus, the converter provides high power quality, producing a high power factor and low total harmonic distortion (THD) without requiring a PFC circuit. Overall, the proposed converter has the following advantages: 1) Due to its soft-switching technique and single-power- conversion approach, the proposed converter can achieve high efficiency and high power density. 2) Without an additional circuit, the proposed converter can provide a high power factor using its control algorithm, unlike the converters . The dc–dc converter is derived from a current-fed push–pull converter. It employs an active-clamp circuit and a series resonant circuit. The active-clamp circuit is composed of the auxiliary switches S 1a , S 2a and the clamping capacitor C c . The active-clamp circuit increases conversion efficiency by reducing the switching losses on the switches and by recycling energy stored in the leakage inductance L lk . Moreover, this circuit limits voltage stresses across the switches and avoids damage caused by surge voltage. The series resonant circuit consists of the leakage inductance L lk and a voltage doubler rectifier circuit. This resonant circuit alleviates the reverse recovery problem on the rectifier diodes D 1 and D 2 by providing zero-current switching (ZCS) turn-off for the diodes The proposed converter regulates the input current and output power by adjusting the pulse-width-modulation (PWM) signals of the switches. The main switches S 1 and S 2 have the same duty D, and their PWM signals are generated with a 180° phase difference. S 1a (S 2a ) operates complementarily to S 1 ) with a short dead-time.
CONCLUSION
A novel ac–dc converter topology with high efficiency and high power density was introduced and analyzed. The proposed converter employs soft-switching techniques and a single-power-conversion method, which together contribute to improving the power-conversion efficiency and power density. The proposed converter uses a control algorithm that enables it to perform both PFC and output power control without the use of a complex circuit structure or the need for several power-conversion steps. Because of these advantages, the proposed converter is suitable for use in industrial applications that require high efficiency and high density. To validate the proposed converter, a 2 kW prototype was built and tested. The experimental results indicate that the proposed converter achieves a high efficiency of 96.1% over the full range of load conditions and provides a power factor of nearly unity over the entire input voltage range.
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