Research On Medium-low Power AC/DC Power Supply Adapter For High Conversion Efficiency

Being one of the cleanest secondary energy in 21st Century, electric energy is not only treated as the base of the human civilization existence but also the guarantee of the worldwide social development. With the popularization of the environmental protection consciousness in the global scale from the 1990's, the sustainable development is going to be a well-known social topic. Many national energy agencies and research centers not only point out the direction of the scientific research, but also stimulate the innovation of the industrial technology. "Green Power" is becoming one of the most important research points of the current social development. Being the main technological means of power control and power conversion, the power electronics technology should play as an important role in the process of the sustainable development of human society and the top runner of the "Green Power" project. With the extension of consumer electronic products market in recent years, the sale quantity of the external AC/DC power supply adapter in the global scale increases rapidly. It not only stimulates the development of marketing economy, but also leads to the series energy environment problem. This dissertation presents the research of the low and medium power level external AC/DC power supply adapter with high conversion efficiency and high power density, which is one of the current research hotspots in the world.Based on the detailed analysis of power conversion stage configuration of the low and medium power level external AC/DC power supply adapter, sectionâ…¡of this dissertation focuses on the research about several DC/DC topologies, which have relatively higher conversion efficiency. For the inherent issues of the conventional PWM phase-shift full-bridge (PSFB) converter, a novel synchronous rectified soft-switched PWM PSFB converter is proposed. It not only achieves the soft switching condition over wide operation range for all the semiconductor switches, but also reduces the voltage stress on the secondary-side rectifiers, and then it has much higher conversion efficiency than what the conventional one has. However, the traditional fixed frequency PWM phase-shift control strategy can not make the step down converter always operate in boundary continuous conduction mode (BCM) over wide operation range, therefore the full-bridge converter has to operate in discontinuous conduction mode (DCM) at high-side input voltage, which means always lower conversion efficiency than operating in BCM. For this issue, a novel variable frequency BCM controlled synchronous rectified soft-switched full-bridge converter is proposed also in sectionâ…¡, which not only can extend the BCM operation range effectively and is suitable for the applications with wide input voltage range, but also helps to simplify the design of front-stage PFC control strategy and bus capacitor. Besides, although LLC resonant DC/DC converter has great advantages in high conversion efficiency and high power density, its complex operation principle analysis and difficult circuit parameters design slows down the rate of practical project progress tremendously, which is going to be the main bottleneck for the development of this converter. With the fundamental harmonic analysis in frequency domain, a general optimal design strategy for LLC resonant DC/DC converter is proposed based on the loss breakdown. For easy use in the practical applications, an improved optimal design strategy is simplified from the general one further and can be a useful reference to speed up the rate of project progress.For most of the practical applications with low output voltage and high output current, the secondary-side rectifier loss always occupies a main part of the total converter loss. Therefore, sectionâ…¢of this dissertation focuses on the research about several secondary-side rectifier topologies and control strategies, which have relatively higher conversion efficiency. With the detailed review about the issues of conventional centre-tapped rectifier with output capacitive filter especially in voltage stress on the rectifiers and output current ripple, a centre-tapped rectifier configuration with effective voltage stress clamping is analyzed first and then an improved symmetrical rectifier configuration with output capacitive filter is proposed, which has obvious advantages in low voltage stress and low output current ripple. It not only can reduce the secondary-side conduction loss by utilizing the rectifiers with much lower break down voltage rate due to the lower voltage stress on them, but also can use the secondary-side winding leakage inductance and the output capacitive filter to compose an L-C filter, which can reduce the output voltage ripple and simplify the design of output filter. Therefore, compared with the conventional centre-tapped rectifier with output capacitive filter, this improved symmetrical rectifier configuration can help to improve the converter conversion efficiency considerably. Current mode driving strategy can make the synchronous rectifier (SR) operation principle equal to a diode rectifier with extreme lower forward voltage and prevent the risk of energy reverse conduction and capacitive turnon of the primary-side MOSFET switches, which could occur when using voltage mode driving strategy for the SRs. However, for the applications of LLC resonant DC/DC converter, the current transformer only can sense the load current signal by putting in series with the SR at the secondary-side. It would increase the conduction loss of the current signal sensing circuit and the complexity of PCB layout because of its considerable size. Therefore, it is hard to improve the converter conversion efficiency further. A novel primary-side current signal sensing strategy is proposed in sectionâ…¢for the applications of LLC resonant DC/DC converter. It can sense the load current signal accurately for the SRs' driving at the primary-side by eliminating the impact of parallel resonant inductor current effectively. And then, the lower conduction loss in the current signal sensing circuit and the simpler secondary-side PCB layout help to improve the converter conversion efficiency and power density effectively.This dissertation also presents the research about several difficulties in the design of 300W external AC/DC power supply adapter with high conversion efficiency and 90W external AC/DC power supply adapter with high power density both.300W external AC/DC power supply adapter employs two-stage configuration, bridgeless hard-switching Boost PFC converter as the primary stage and LLC resonant DC/DC converter as the secondary stage. Both of them have the conversion efficiency higher than 96%, which can make sure that the power supply adapter's conversion efficiency is higher than 92% over the universal input voltage range and meets the high requirement of future consumer electronic market in "Green Power". With the universal input voltage range,90W external AC/DC power supply adapter with high power density achieves the conversion efficiency target of "80Plus" over the output load range from 25%-100% and the full load efficiency is higher than 91%. The power supply adapter's power density is about 1W/cm3 (16.5W/in3), which can meet the high requirement of future consumer electronic market in portability.