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.
KEYWORDS:
1.
LLC resonant converters
2.
AC-DC converters
3.
soft switching
4.
PFC
5.
THD
6.
DC bus
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Figure 1. Proposed Three-Level Single Stage Llc Converter.
EXPECTED SIMULATION RESULTS:
Figure 2. Source Voltage And
Current Waveform.
Figure 3. Input Current Waveform
Through Input Inductor.
Figure 4. Flying Capacitor
Voltage Waveform, Vc1.
Figure 5. Dc Bus Voltage
Waveform, Vc1 C Vc2.
CONCLUSION:
This
paper has proposed a three-level flying capacitor based topology for AC/DC LLC
resonant converters. The converter has a bridgeless topology which reduces the
number of con- ducting devices. The controller uses a dual control scheme which
varies duty ratio and frequency to regulate DC bus and output DC voltages
respectively. The converter is designed to operate in discontinuous conduction
mode to obtain a near unity power factor without having any active current
control techniques. Furthermore, the topology provides low voltage stress, ZVS
for all the four switches, and reduces losses. For verification, a 250W, 230V
to 48V AC-DC converter proto- type has been designed and implemented. The DC bus
voltage is held constant at 750V with a peak overshoot of 3.3% even when the
load is reduced by 30% from full load.
REFERENCES:
[1]
A. K. Peter and J. Mathew, ``A three-level half-bridge flying capacitor topology
for single-stage AC-DC LLC resonant converter,'' in Proc. IEEE Int.
Conf. Power Electron., Drives Energy Syst. (PEDES), Dec. 2018,pp. 1_6.
[2] A. Hillers, D. Christen, and J. Biela,
``Design of a highly efficient bidirectional isolated LLC resonant
converter,'' in Proc. 15th Int. Power Electron. Motion Control Conf.
(EPE/PEMC), Sep. 2012, pp. DS2b_13.
[3]
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
ECCE Asia Downunder, Jun. 2013, pp. 6_11.
[4]
Y. Qiu, W. Liu, P. Fang, Y.-F. Liu, and P. C. Sen, ``A mathemati- cal guideline
for designing an AC-DC LLC converter with PFC,'' in Proc. IEEE Appl.
Power Electron. Conf. Expo. (APEC), Mar. 2018, pp. 2001_2008.
[5]
S.-Y. Chen, Z. R. Li, and C.-L. Chen, ``Analysis and design of single-stage AC/DC
LLC resonant converter,'' IEEE Trans. Ind. Electron., vol. 59,
no. 3, pp. 1538_1544, Mar. 2012.
