Single-phase single-stage power-factor-corrected converter topologies

Outline

• I. Introduction
• II. Converters Operating with a Low-Frequency Ac Source and Without a Dc-Link Capacitor
• III. Converters Operating with a Low-Frequency Ac Source and with a Dc-Link Capacitor
• IV. Ac–dc Converters Operating with a High-Frequency Ac Source
• V. Conclusion

Conclusions

In this paper, single-stage converters were classified according to the input ac source frequency and the existence or absence of a large bulk capacitor in their dc link. For each of the converter types presented in this paper, the issues associated with each type were discussed, various approaches were examined, and experimental results for particular converters were discussed. The key points of the paper can be summarized as follows. 1) Resonant and PWM ac–dc converters without a large dc-link capacitor can operate with a near-unity input power factor and provide regulated dc voltage. The resonant converters provide higher power levels (up to 3 kW) than the PWM converters (up to 1 kW); however, the resonant converters operate with variable frequency while the PWM converters operate with fixed frequency. The resonant converters are preferred in all the applications except where frequency synchronization is required. The outputs in either type of converters carry a large low frequency current ripple and thus require large filters.

They are, therefore, suitable for online ac UPS systems or in some batteryless offline telecommunication systems to convert ac input voltage to 48-V dc output voltage for downstream converters.

2) Single-stage ac–ac converters that produce a low frequency trapezoidal output voltage can be implemented at power levels up to several kilowatts with very high input power factor. These converters exhibit very high efficiency and are suitable for new hybrid fiber coax networks and existing cable TV applications.

3) Single-stage single-switch-type ac–dc converters with a large dc-link capacitor provide regulated and low-ripple dc output voltages with input power factor and current harmonics that satisfy regulatory agency standards. These converters are practical to implement up to 150-W power levels for universal input voltage range (90–265 V ac), and up to 250 W for restricted input voltage range (90–135 V or 170–265 V ac).

4) Single-stage full-bridge-type ac–dc converters with a large dc-link capacitor provide regulated and low-ripple dc output voltages with input power factor and current harmonics that can satisfy regulatory agency standards. These converters are practical to implement up to 500-W power levels for universal input voltage range (90–265 V ac), and up to 1 kW for restricted input voltage range (90–135 V or 170–265 V ac).

5) AC–AC converters with built-in PFC that produce a high-frequency sinusoidal output voltage are practical to implement up to power levels of 250 W with universal input voltage range (90–265 V ac). These converters are well suited for high-frequency ac architectures in future desktop computers.

6) Single-stage resonant ac–dc converters operating from a high-frequency ac source can achieve near-unity power factor, high efficiency, and regulated dc output with very low ripple. These converters are well suited for high-frequency ac architectures in future desktop computers, servers, and telecommunications, or, in general, for powering the low-voltage semiconductor technology of the future.