Abstract
Single stage LLC resonant converters with inherent power factor correction are getting popularity in AC-DC converters due to its reduced size and weight. However, single stage topologies are usually less efficient in regulating the dc bus capacitor voltage pertaining to line and load transients. This paper proposes a multi-level flying capacitor based single stage AC-DC LLC topology to address the issue of voltage balancing of dc-bus capacitor and to reduce the voltage stress of the switching devices. The proposed three-level inverter topology guarantees zero voltage switching, less circulating currents, reduced switching stress and losses. The converter uses bridgeless rectification scheme for better efficiency and the power factor is made nearly unity by operating the source-side inductor in discontinuous current conduction. Variable switching frequency control is used to regulate the output voltage of the converter and pulse width modulation is used to control the dc-bus voltage. This dual control scheme is very effective to keep the dc-bus voltage nearly constant over a wide range of line and load variations. The proposed topology and control scheme have been validated by hardware results on a 250W resistive load.
Highlights
Soft switching of switching devices, inherent short circuit and open circuit protection, and high efficiency are some of the benefits of LLC resonant converters [2]–[4]
COMPARISON WITH CONVENTIONAL SINGLE STAGE AC-DC LLC RESONANT CONVERTERS The proposed topology has all advantages of conventional topologies [5]–[9] such as natural power factor correction, single-stage operation and zero voltage switching
Transient response of the DC bus voltage when the load is reduced by 30% from full load at instant A as shown in Fig. 24, where the capacitor voltage rises by 3% and settles to the reference bus voltage in 4.5 seconds
Summary
Soft switching of switching devices, inherent short circuit and open circuit protection, and high efficiency are some of the benefits of LLC resonant converters [2]–[4]. The average output power of the converter may not be equal to that of the PFC stage during load variations and transients This power imbalance causes the DC bus capacitor voltage to vary until energy balance is achieved [5]. In [7]–[9], a burst mode control scheme is used where the controller pauses the switching action for a certain time intervals based on the bus capacitor voltage and output DC voltage when the switching frequency increases to extreme high levels. Different types of single stage bridgeless PFC topologies have been presented in literature [19]–[23] They suffer from shortcomings such as poor DC bus voltage regulation, High switching frequency at light loads, requirement of more switching devices and high voltage stress.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
