This paper proposes a dual-bridge (DB) LLC resonant converter for wide input applications. The topology is an integration of a half-bridge (HB) LLC circuit and a full-bridge (FB) LLC circuit. The fixed-frequency pulse width-modulated (PWM) control is employed and a range of twice the minimum input voltage can be covered. Compared with the traditional pulse frequency modulation (PFM) controlled HB/FB LLC resonant converter, the voltage gain range is independent of the quality factor, and the magnetizing inductor has little influence on the voltage gain, which can simplify the parameter selection process and benefit the design of magnetic components as well. Over the full load range, zero-voltage switching (ZVS) and zero-current switching (ZCS) can be achieved for primary switches and secondary rectifier diodes, respectively. Detailed analysis on the modulation schedule and operating principle of the proposed converter is presented along with the converter performance. Finally, all theoretical analysis and characteristics are verified by experimental results from a 120-V to 240-V input 24 V/20 A output converter prototype.
- Dual bridge (DB)
- Fixed frequency
- Wide input voltage range
Fig. 1. (a) Proposed DB LLC resonant converter. (b) Equivalent circuit when the proposed DB LLC resonant converter operates in the HB mode. (c) Equivalent circuit when the proposed DB LLC resonant converter operates in the FB mode.
EXPECTED SIMULATION RESULTS:
Fig. 2. Measured steady-state voltage and current waveforms at full load with different input voltages. (a) Vin = 120 V; (b) Vin = 130 V; (c) Vin = 190 V; (d) Vin = 240 V.
Fig. 3. ZVS waveforms of switches Q1 and Q2 with the converter operating at (a) full load with 120 V input, (b) full load with 240 V input, (c) 10% load with 120 V input, and (d) 10% load with 240 V input.
Fig. 4. Experimental results of the DB LLC resonant converter with closed loop control in response to ramp changes in the input voltage Vin. (a) Ramp increase of the input voltage Vin from 130 to 190 V. (b) Ramp decrease of the input voltage Vin from 190 to 130 V.
Fig. 5. Experimental results of the DB LLC resonant converter with closed loop control in response to step changes in the load. (a) Step increase of load from light load to full load. (b) Step increase of load from full load to 10% load.
Fig. 6. Measured power stage efficiency of the converter prototype for different input voltages.
A fixed-frequency-controlled DB LLC resonant converter with a wide input range has been proposed in this paper. In the proposed DBLLC resonant converter, two operating modes (HB and FB modes) are identified and utilized to regulate the output voltage within a wide input voltage range. The modulation strategy, operating principle and characteristics are investigated in depth. Compared with a conventional PFM-controlled LLC converter, the proposed DB LLC resonant converter adopts the fixed-frequency PWM control. The voltage gain range is independent of the quality factor Q and the magnetizing inductance has little impact on the dc voltage gain characteristics. Thus, the process of parameter design can be simplified and also a larger inductor ratio can be chosen to reduce the conduction loss. The structure and control strategy of the DB LLC resonant converter are simpler compared with conventional fixed-frequency TL LLC resonant converters. The performance of the proposed DB LLC resonant converter is experimentally verified on a 120–240 V input 24 V/20 A output converter prototype. All primary-side switches operate with ZVS and secondary-side diodes turn off with ZCS within wide input voltage and full-load ranges. Also, good dynamic performance with respect to input variations and load changes can be achieved under the closed-loop control. Therefore, the DB LLC resonant converter is a good candidate for wide input voltage applications.
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