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.

REFERENCES  

[1] C. A. Gallo, F. L. Tofoli, and J. A. C. Pinto, “Two-stage isolated switch-mode power supply with high efficiency and high input power factor,” IEEE Trans. Ind. Electron., vol. 57, no. 11, pp. 3754-3766, Nov. 2010.

[2] K. Y. Lee and Y. S. Lai, “Novel circuit design for two-stage ac/dc converter to meet standby power regulations,” IET Power Electron, vol. 2, no. 6, pp. 625-634, Nov. 2009

[3] H. Wang, S. Dusmez, and A. Khaligh, “Design considerations for a level-2 on-board PEV charger based on interleaved boost PFC and LLC resonant converters,” in Proc. IEEE Transportation Electrification Conference and Expo (ITEC), 2013, pp. 1-8.

[4] J. –H. Kim, M. –Y. Kim, C. –O. Yeon, and G. W. Moon, “Analysis and design of boost-LLC converter for high power density AC-DC adapter,” in Proc. IEEE Energy Conversion Congress and Exposition (ECCE) Asia, 2013, pp. 6-11.

[5] K. Raggl, T. Nussbaumer, G. Doerig, J. Biela, and J. W. Kolar, “Comprehensive design and optimization of a high-power-density single-phase boost PFC,” IEEE Trans. Ind. Electron., vol. 56, no. 7, pp. 2574-2587, Jul. 2009.

[6] I. –O. Lee and G. –W. Moon, “A new asymmetrical half-bridge converter with zero DC-offset current in transformer,” IEEE Trans. Power. Electron., vol. 28, no. 5, pp. 2297-2306 May. 2013.

[7] B. Whitaker, A. Barkley, Z. Cole, B. Passmore, D. Martin, T. R. McNutt, A. B. Lostetter, J. S. Lee, K. Shiozaki, “A high-density, high-efficiency, isolated on-board vehicle battery charger utilizing silicon carbide power device,” IEEE Trans. Power. Electron., vol. 29, no. 5, pp. 2606-2617 May. 2014.

[8] S. Zong, H. Luo, W. Li, X. He, and C. Xia, “Theoretical evaluation of stability improvement brought by resonant current loop for paralleled LLC converters,” IEEE Trans. Ind. Electron., vol. 62, no. 7, pp. 4170-4180, Jul. 2015.

[9] S. –H. Lee, C. –Y. Park, J. –M. Kwon, and B. –H. Kwon, “Hybrid-type full-bridge dc/dc converter with high efficiency,” IEEE Trans. Power. Electron., vol. 30, no. 8, pp. 4156-4164, Aug. 2015.

[10] T. Yan, J. Xu, F. Zhang, J. Sha, and Z. . “Variable-on-time-controlled critical-conduction-mode flyback PFC converter,” IEEE Trans. Ind. Electron., vol. 61, no. 11, pp. 6091-6099, Nov. 2014