A NEW DUAL-BRIDGE SERIES RESONANT DC-DC CONVERTER WITH DUAL-TANK
Abstract:
Compared to the dual active bridge (DAB)converter, the dual-bridge series resonant converter(DBSRC) can widen soft-switching range. To furtherwiden the soft-switching range and improve the circuitperformance, a new dual-bridge series resonantconverter with dual-tank based on DBSRC is proposedin this paper. This new converter features two resonanttanks and a tapped-transformer, and it can performbetter than the DBSRC by optimized tap-coefficient x ofthe tapped-transformer. Its operation principle, voltagegain, the soft-switching characteristics and output powerare analyzed in detail, and compared with the DBSRC.Results show that the proposed dual-tank topology haspresented higher voltage gain, wider soft-switchingregion, and larger output power than the traditionalDBSRC when the tap-coefficient x is selected reasonably.At last, a 1kW prototype is built; experimental resultsverify the feasibility and advantages of the proposeddual-tank converter
PROPOSED SYSTEM:
The major contribution of this paper is to propose adual-tank DBSRC by modifying the topology of thetraditional DBSRC. The tapped-transformer of the proposeddual-tank DBSRC has asymmetric structure in the primaryside, and this proposed converter presents samecharacteristics with the traditional one when thetap-coefficient x of the tapped-transformer is 0.5. However,if x is larger than 0.5, the proposed circuit presents highervoltage gain, wider soft-switching region and larger outputpower than the traditional DBSRC.Based on DBSRC, many novel bidirectional resonantconverters are proposed. A bidirectional topology ofcomposed of a full-bridge series resonant converter and athree-level converter is introduced in. The controlstrategy adopted by the circuit consists of frequency controland EPS modulation. It is mentioned that all switches of thisconverter can realize ZVS without auxiliary circuit, but theZVS soft-switching situation is not discussed at all. In ,a bidirectional converter combining DAB and LLC resonanttank is proposed, and frequency control is used to regulateoutput voltage in the forward mode. The switches in inverterside can achieve ZVS, while the switches in rectifier sidecan achieve ZCS. The converter in the reverse operation isequivalent to an SRC; therefore, ZVS can only be obtainedwith larger load, and ZCS features are lost. The efficiency ofreverse work is low. In , an asymmetric CLLC resonanttank is added to the DAB, and frequency control is adoptedboth in the two power flow directions. In a wide voltage gainrange, ZVS is achieved in the inverter side switches, andZCS is achieved in the rectifier side switches. In [32], asymmetrical CLLC resonant tank is introduced on the DAB,and the frequency modulation is adopted. ZVS is realized bythe inverter side switches, and the rectifier side switchesachieved the soft commutation. Furthermore, due to thesymmetry of the resonant tank, the power transmissionefficiency in the two directions is identical. Although each circuit aforementioned has its ownadvantages, LLC-type and CLLC-type topologies both havetwo different resonant frequencies. For achievingsoft-switching, their operating frequencies are always variedbetween the lower and higher frequency; however, DBSRChas only one resonant frequency, and ZVS can be achievedeasily as long as the switching frequency is higher than theresonant frequency. Obviously, the control difficulty ofLLC-type and CLLC-type resonant converters is increasedthan DBSRC. In this paper, a dual-bridge series resonantconverter with dual-tank is proposed based on the traditionalDBSRC, and its operation principle is similar to DBSRC,while its circuit performance is increased remarkably.
EXSITNG SYSTEM:
In, the comparison of DAB and DBSRC in super-resonant mode shows that the resonant capacitor hasnegative effect on the circuit characteristics such as transformer power level and resonant tank volume, but the resonant capacitor can effectively filter the DC component of the transformer, and reduces the eddy current losses of thetransformer winding. In [8], DAB, DBSRC, and theirtwo-stage topologies are compared. The study shows that theefficiency of single-stage DAB topology is the lowest, andthe efficiencies of the two-stage DBSRC and single-stageDBSRC are respectively highest and the second. It isobvious that whether it is a single-stage or dual-stagetopology, DBSRC can achieve higher efficiency than DABconverter. In [9], based on the application background of a1MW, 12kV-1.2kV bi-directional converter in the renewableenergy power generation system, the performance of DABand DBSRC were compared, and the result tells that DBSRCis more efficient than DAB. Frequency control can be used to regulate the outputvoltage of DBSRC. In the AC equivalent model ofDBSRC based on frequency control is analyzed fromforward and reverse directions, and the frequency range ofrealizing ZVS and ZCS for primary-side bridge is obtained.The discontinuous operating mode of DBSRC underfrequency control is emphatically analyzed and someguidance is provided for controller design in .Phase-shift modulations have been widely used by DAB andare also being applied to DBSRC. Phase-shift modulationscover traditional single-phase-shift modulation (SPS) ,dual-phase-shift modulation (DPS) ,extended-phase-shift modulation (EPS) , andtriple-phase-shift modulation (TPS), athree-port converter composed of DBSRC is proposed, andSPS modulation between bridges is used for energy transfer.
CONCLUSION
This paper proposed a new dual-bridge series resonantconverter with dual-tank, which features asymmetricaltapped-transformer. Through comparison with DBSRC, theproposed dual-tank topology has larger soft-switching range,higher voltage gain, and higher output power. Furthermore,research shows that the asymmetrical structure of thetapped-transformer can improve the circuit performance. Atlast, the experimental and simulation results validate the theoretical analysis. But the drawbacks of the proposedconverter is that unbalanced currents is brought to the primary-side legs, so the corresponding control strategy needto be studied in further.
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